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  • 1.
    Abuasbeh, Mohammad
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Palm, Björn (Editor)
    KTH, Superseded Departments (pre-2005), Energy Technology. KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Aquifer Thermal Energy Storage Insight into the future2018Report (Refereed)
    Abstract [en]

    Underground Thermal Energy Storage (UTES) systems, such as Aquifer thermal energy storage(ATES) are used in several countries. The regulation and research on the potential impacts of ATESon groundwater resources and the subsurface environment often lag behind the technologicaldevelopment of an ever-growing demand for this renewable energy source. The lack of a clear andscientifically supported risk management strategy implies that potentially unwanted risks might betaken at vulnerable locations such as near well fields used for drinking water production. At othersites, on the other side, the application of ATES systems is avoided without proper reasons. Thisresults in limiting the utilization of the ATES technology in many occasions, affecting the possibilityto increase the share of renewable energy use. Therefore, further studies to characterizegroundwater resources, performance monitoring and identification of environmental impacts areneeded to understand the advantages and limitations of ATES systems.

    The environmental impact and technical performance of a Low Temperature ATES (LT-ATES)system in operation since 2016 is presented. The system is called Rosenborg and is owned byVasakronan. It is located in the northern part of Stockholm, on a glaciofluvial deposit called theStockholm esker. The ATES system is used to heat and cool two commercial buildings with a totalarea of around 30,000 m2. The ATES consists of 3 warm and 2 cold pumping wells that are able topump up to 50 liters per second.

    Analysis of groundwater sampling included a period of 9 months prior to ATES operation as well asthe first full season of heating and cooling operation. The sampling was conducted in a group ofwells in the vicinity of the installation and within the system. Means of evaluation constituted astatistical approach that included Kruskal-Wallis test by ranks, to compare the wells before and afterthe ATES was used. Then principal component analysis (PCA) and clustering analysis were used tostudy the ground water conditions change before and after the ATES. Aquifer Variation Ratio(AVR) was suggested as mean to evaluate the overall conditions of the aquifer pre- and post- ATES.

    The results showed some variations in redox potential, particularly at the cold wells which likely wasdue to the mixing of groundwater considering the different depths of groundwater beingabstracted/injected from different redox zones. Arsenic, which has shown to be sensitive to hightemperatures in other research showed a decrease in concentration. A lower specific conductivityand total hardness at the ATES well compared to their vicinity was found. That indicates that theyare less subject to salinization and that no accumulation has occurred to date. It is evident that theenvironmental impact from ATES is governed by the pre-conditions in soil- and groundwater. ThePCA and clustering analysis showed very little change in the overall conditions in the aquifer whencomparing the ATES before and after operation. Temperature change showed negligible impact.This can be mainly attributed to the relatively small temperature change (+6 and – 5 degrees) fromthe undisturbed Aquifer temperature which is 10.5°C.

    Performance of Aquifer Thermal Energy Storage (ATES) systems for seasonal thermal storagedepends on the temperature of the extracted/injected groundwater, water pumping rates and thehydrogeological conditions of the aquifer. ATES systems are therefore often designed to work witha temperature difference between the warm side and cold side of the aquifer without riskinghydraulic and thermal intrusion between them, and avoiding thermal leakage to surrounding area, i.e. optimize hydraulic and thermal recovery. The hydraulic and thermal recovery values of the first yearof operation in Rosenorg weres 1.37 and 0.33, respectively, indicating that more storage volume(50500m3) was recovered during the cooling season than injected (36900m3) in the previous heatingseason.

    Monitoring the operation of pumping and observation wells is crucial for the validation of ATESgroundwater models utilized for their design, and measured data provides valuable information forresearchers and practitioners working in the field. After months of planning and installation work,selected measurements recorded in an ATES monitoring project in Sweden during the first threeseasons of operation are reported in this report.

    The monitoring system consists of temperature sensors and flow meters placed at the pumpingwells, a distributed temperature-sensing rig employing fiber optic cables as linear sensor andmeasuring temperature every 0.25 m along the depth of all pumping and several observation wells,yielding temporal and spatial variation data of the temperature in the aquifer. The heat injection andextraction to and from the ground is measured using power meters at the main line connecting thepumping wells to the system. The total heat and cold extracted from the aquifer during the firstheating and cooling season is 190MWh and 237MWh, respectively. A total of 143 MWh of heatwere extracted during the second heating season. The hydraulic and thermal recovery values of thefirst year of operation was 1.37 and 0.33, respectively, indicating that more storage volume(50500m3) was recovered during the cooling season than injected (36900m3) in the previous heatingseason. The DTS data showed traces of the thermal front from the warm storage reaching the coldone. Only 33% of the thermal energy was recovered. These losses are likely due to ambientgroundwater flow as well as conduction losses at the boundaries of the storage volume. Additionally,the net energy balance over the first year corresponds to 0.12 which indicates a total net heating ofthe ATES over the first year. It is recommended to increase the storage volume and achieve morehydraulic and thermal balance in the ATES system. This can enhance the thermal recovery andoverall performance. Continuous monitoring of the ATES is and will be ongoing for at least 3 moreyears. The work presented in this report is an initial evaluation of the system aiming to optimize theATES performance.

    Furthermore, data management and processing tool has been established for the ATES system in Rosenborg. Additionally, a conceptual model of the ATES area has been established. Current andfuture work is focussed on completing a full scale numerical model in FEFLOW and validated themodel (both hydraulically and thermally) with the available monitoring data. Furthermore,establishing recommendations for optimum design and operation of ATES system.

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  • 2.
    Abuasbeh, Mohammad
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Acuña, José
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Lazzarotto, Alberto
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Long term performance monitoring and KPIs' evaluation of Aquifer Thermal Energy Storage system in Esker formation: Case study in Stockholm2021In: Geothermics, ISSN 0375-6505, E-ISSN 1879-3576, Vol. 96, article id 102166Article in journal (Refereed)
    Abstract [en]

    The majority of Aquifer Thermal Energy Storage (ATES) systems studies have been conducted in aquifer systems located in large sand aquifers. Esker formation present a more challenging geometrical complexity compared to typical sand aquifers. This study aims to conduct comprehensive and long term performance evaluation of doublet type ATES system in esker geological formation in Stockholm, Sweden. The total heating and cooling used from the ATES are 673 MWh and 743 MWh respectively during the first 3 annual storage cycles of operation. The licensed total amount of water extraction and injection is 50 liters per second with undisturbed groundwater temperature of 9.5 degrees C. Over the first three storage cycles, the average injection and extraction temperatures for the warm side are 13.3 degrees C and 12.1 degrees C, and for the cold side 7.6 degrees C and 10.5 degrees C. The average temperature differences across the main heat exchanger from the ATES side are 4.5 K during winter and 2.8 K during summer which is 4-5 degrees lower than the optimum value. The average thermal recovery efficiency over the first 3 storage cycles were 47 % and 60 % for warm and cold storages respectively. The data analysis indicated annual energy and hydraulic imbalances which results into undesirable thermal breakthrough between the warm and cold side of the aquifer. This was mainly due to suboptimal operation of the building energy system which led to insufficient heat recovery from the warm side, and subsequently insufficient cold injection in the cold wells, despite the building heating demand and the available suitable temperatures in the ATES. The cause of the suboptimal operation is the oversizing of the heat pumps which were designed to be coupled to larger thermal loads as compared to the ones in the final system implementation. As a result, the heat pumps could not be operated during small-medium loads. Additionally, the paper discusses the limitations of currently used energy and thermal key performance indicators (KPI) for ATES and propose an additional thermal KPI named heat exchanger efficiency balance (beta HEX) that connects and evaluate the optimum operational point of temperature differences from both the building and ATES prospective. In addition to ATES energy and hydraulic KPIs, beta HEX can contribute in providing more complete picture on the ATES-building interaction performance as well as highlights if the losses in energy recovery from ATES are due to the subsurface processes or building energy system operation which has been proven to be critical for the optimum ATES performance.

  • 3.
    Acuna, José
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Fossa, Marco
    University of Genova.
    Monzó, Patricia
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Numerically generated g-functions for ground coupled heat pump applications2012In: Proceedings of the COMSOL Conference in Milan, 2012Conference paper (Refereed)
    Abstract [en]

    In most ground-coupled heat pump systems, Borehole Heat Exchangers (BHE) represent the typical engineering solution for utilizing renewable energy from the ground. The design of a complex BHE field is a challenging task, due the inherent transient nature of the thermal interaction between the heat exchangers and the surrounding soil. A computation effective method for solving the 3D transient conduction equation describing the ground response to a variable heat load profile is the temporal superposition of pre-calculated temperature response factors or g-functions. In this study Comsol heat conduction models have been developed to calculate g-function values for a borehole field with 64 boreholes. The aim of the investigation is to get an insight on the numerical generation of temperature transfer functions and to some extent provide new information on the Finite Line Source method for analytically generated g-functions as well as on those existing behind existing design software such as EED. The results generally showed a good agreement in lower time ranges. Further in time, the Comsol model revealed to be influenced either by the domain dimensions or the simulation end time.

  • 4.
    Acuña, José
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Mogensen, Palne
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Distributed Thermal Response Tests on a Multi-pipe Coaxial Borehole Heat Exchanger2011In: HVAC & R RESEARCH, ISSN 1078-9669, E-ISSN 1938-5587, Vol. 17, no 6, p. 1012-1029Article in journal (Refereed)
    Abstract [en]

    In a distributed thermal response test, distributed temperature measurements are taken along a borehole heat exchanger during thermal response tests, allowing the determination of local ground thermal conductivities and borehole thermal resistances. In this article, the first results from six heat injection distributed thermal response tests carried out on a new, thermally insulated leg type, multi-pipe coaxial borehole heat exchanger are presented. The borehole heat exchanger consists of 1 insulated central and 12 peripheral pipes. Temperature measurements are carried out using fiber-optic cables placed inside the borehole heat exchanger pipes. Unique temperature and thermal power profiles along the borehole depth as a function of the flow rate and the total thermal power injected into the borehole are presented. A line source model is used for simulating the borehole heat exchanger thermal response and determining local variations of the ground thermal conductivity and borehole thermal resistance. The flow regime in the peripheral pipes is laminar during all distributed thermal response tests and average thermal resistances remain relatively constant, independently of the volumetric flow rate, being lower than those corresponding to U-pipe borehole heat exchangers. The thermal insulation of the central pipe significantly reduces the thermal shunt to the peripheral pipes even at low volumetric flow rates.

  • 5.
    Acuña, José
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Mogensen, Palne
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Evaluation of a coaxial borehole heat exchanger prototype2010In: Proceedings of the 14th ASME International Heat Transfer Conference, ASME Press, 2010Conference paper (Refereed)
    Abstract [en]

    Different borehole heat exchanger designs have been discussed for many years. However, the U-pipe design has dominated the market, and the introduction of new designs has been practically lacking. The interest for innovation within this field is rapidly increasing and other designs are being introduced on the market. This paper presents a general state of the art summary of the borehole heat exchanger research in the last years. A first study of a prototype coaxial borehole heat exchanger consisting of one central pipe and five external channels is also presented. The particular geometry of the heat exchanger is analyzed thermally in 2-D with a FEM software. An experimental evaluation consisting of two in situ thermal response tests and measurements of the pressure drop at different flow rates is also presented. The latter tests are carried out at two different flow directions with an extra temperature measurement point at the borehole bottom that shows the different heat flow distribution along the heat exchanger for the two flow cases. The borehole thermal resistance of the coaxial design is calculated both based on experimental data and theoretically.

  • 6.
    Acuña, José
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Mogensen, Preben
    Palne Mogensen AB.
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Distributed Thermal Response Test on a U-Pipe Borehole Heat Exchanger2009In: Proc. Effstock 2009, 11th International Conference on Thermal Energy Storage, Stockholm, Sweden: Academic Conferences Publishing, 2009Conference paper (Refereed)
    Abstract [en]

    In a Distributed Thermal Response Test (DTRT) the ground thermal conductivity and boreholethermal resistance are determined at many instances along the borehole. Here, such a testis carried out at a 260 m deep water filled energy well, equipped with a U-pipe borehole heatexchanger, containing an aqueous solution of ethanol as working fluid. Distributed temperaturemeasurements are carried out using fiber optic cables placed inside the U-pipe, duringfour test phases: undisturbed ground conditions, fluid pre-circulation, constant heat injection,and borehole recovery. A line source model is used for simulating the borehole thermal response.Fluid temperature profiles during the test are presented. The results show local variationsof the ground thermal conductivity and borehole thermal resistance along the boreholedepth, as well as a deviation of the latter as compared to the one resulting from a standardthermal response test.

  • 7.
    Acuña, José
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    A novel coaxial BHE: Description and first Distributed Thermal Response Test Measurements2010In: Proceedings World Geothermal Congress 2010, 2010, p. paper 2953-Conference paper (Refereed)
    Abstract [en]

    The thermal performance of a Borehole Heat Exchanger plays a significant role when defining the quality of heat exchange with the ground in Ground Source Heat Pumps. Different designs have been discussed and increased interest on innovation within this field has taken place during the last years. This paper presents the first measurement results from a 189 meters deep novel coaxial Borehole Heat Exchanger, consisting of an inner central pipe and an annular channel in direct contact with the surrounding bedrock. The measurements were taken during a distributed thermal response test using fiber optic cables installed in the energy well. Fluid temperature every ten meters along the borehole depth are presented and compared with similar measurements from a common U-pipe heat exchanger. A unique measurement of the borehole wall temperature in the coaxial collector illustrates how effective the heat transfer performance is through the annular channel.

  • 8.
    Acuña, José
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Comprehensive Summary of Borehole Heat Exchanger Research at KTH2010In: IIR/Eurotherm Sustainable Refrigeration and Heat Pump Technology Conference, Stockholm: KTH Royal Institute of Technology, 2010, p. 69-Conference paper (Refereed)
    Abstract [en]

    A research project that aims at presenting recommendations for improving the COP of ground source heat pump systems by 10-20% through better design of Borehole Heat Exchangers (BHE) is described in this paper. Experiments are carried out with temperature measurements taken in different BHE types during heat pump operation conditions as well as during the thermal response tests. It is also expected to point out methods for having natural fluid circulation in the BHE, i.e. demonstrating that the heat carrier fluid can naturally circulate thanks to temperature induced density differences along the borehole depth, and thereby avoiding the use of electricity consuming pumps. A brief background presenting the most relevant work regarding BHE research around the world is first presented, followed by a comprehensive description of the current research at KTH. Some new measurements and obtained results are presented as an estimation of to what extent the project results have been achieved is discussed. An analysis on how the project results could allow reducing the borehole depth keeping today’s Coefficient of Performance is presented.

  • 9.
    Acuña, José
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Distributed Temperature Measurements on a Multi-pipe Coaxial Borehole Heat Exchanger2011In: IEA Heat Pump Conference, International Energy Agency , 2011, p. 4.19-Conference paper (Refereed)
    Abstract [en]

    The first experiences with a multi-pipe borehole heat exchanger prototype consisting of an insulated central pipe and twelve parallel peripheral pipes are described. Secondary fluid distributed temperature measurements along the borehole depth, being the only ones of its kind in this type of heat exchanger, are presented and discussed. The measurements are carried out with fiber optic cables during heat injection into the ground, giving a detailed visualization of what happens both along the central and peripheral flow channels. The heat exchange with the ground mainly occurs along the peripheral channels and an indication of almost no thermal short circuiting, even while having large temperature differences between the down and upwards channels, is observed.

  • 10.
    Acuña, José
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Distributed thermal response tests on pipe-in-pipe borehole heat exchangers2013In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 109, no SI, p. 312-320Article in journal (Refereed)
    Abstract [en]

    Borehole Thermal Energy Storage systems typically use U-pipe Borehole Heat Exchangers (BHE) having borehole thermal resistances of at least 0.06 K m/W. Obviously, there is room for improvement in the U-pipe design to decrease these values. Additionally, there is a need for methods of getting more detailed knowledge about the performance of BHEs. Performing Distributed Thermal Response Tests (DTRT) on new proposed designs helps to fill this gap, as the ground thermal conductivity and thermal resistances in a BHE can be determined at many instances in the borehole thanks to distributed temperature measurements along the depth. In this paper, results from three heat injection DTRTs carried out on two coaxial pipe-in-pipe BHEs at different flow rates are presented for the first time. The tested pipe-in-pipe geometry consists of a central tube inserted into a larger external flexible pipe, forming an annular space between them. The external pipe is pressed to the borehole wall by applying a slight overpressure at the inside, resulting in good thermal contact and at the same time opening up for a novel method for measuring the borehole wall temperature in situ, by squeezing a fiber optic cable between the external pipe and the borehole wall. A reflection about how to calculate borehole thermal resistance in pipe-in-pipe BHEs is presented. Detailed fluid and borehole wall temperatures along the depth during the whole duration of the DTRTs allowed to calculate local and effective borehole thermal resistances and ground thermal conductivities. Local thermal resistances were found to be almost negligible as compared to U-pipe BHEs, and the effective borehole resistance equal to about 0.03 K m/W. The injected power was found to be almost evenly distributed along the depth.

  • 11.
    Acuña, José
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Experimental Comparison of Four Borehole Heat Exchangers2008In: Refrigeration Science and Technology Proceedings, Copenhagen: International Institute of Refrigeration, 2008, p. SEC09-W1-09Conference paper (Refereed)
    Abstract [en]

    The most common way to exchange heat with the bedrock in ground source heat pump applications is circulating a secondary fluid through a closed U-pipe loop in a vertical borehole. This fluid transports the heat from the rock to the ground source heat pump evaporator. The quality of the heat exchange with the ground and the necessary pumping power to generate the fluid circulation are dependent on the type of fluid and its flow conditions along the pipe. Four different borehole heat exchangers are tested using ethyl alcohol with 20% volume concentration. The fluid temperatures are logged at the borehole inlet, bottom, and outlet. The collectors are compared based on their borehole thermal resistance and pressure drop at different flow rates. The results indicate that the pipe dimensions play an important roll, spacers might not contribute to better heat transfer, and inner micro fins in the pipes improve the performance of the collectors.

  • 12.
    Acuña, José
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    First Experiences with Coaxial Borehole Heat Exchangers2011In: Proceedings of the IIR Conference on Sources/Sinks alternative to the outside Air for HPs and AC techniques, International Institute of Refrigeration, 2011Conference paper (Refereed)
    Abstract [en]

    Some experiences with coaxial borehole heat exchanger prototypes are discussed here. Four different designs are described as they have been part of a research project at KTH: two pipe-inpipe annular designs, one multi-pipe and one multi-chamber design. A special focus is given to two of the prototypes, a pipe-in-pipe design with the external flow channel consisting of an annular cross section and partly insulated central pipe, and a multi-pipe design with twelve parallel peripheral pipes and an insulated central channel. The secondary fluid temperature profiles at low volumetric flow rates are presented for these two prototypes, measured with fiber optic cables during thermal response tests and allowing a detailed visualization of what happens along the heat exchanger depth. It is the first time this is carried out in these types of borehole heat exchangers. The measurements indicate good thermal performance and point at potential uses for these heat exchangers in different ground coupled applications.

  • 13.
    Acuña, José
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Hill, Peter
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Characterization of Boreholes: Results from a U-pipe Borehole Heat Exchanger Installation2008In: Proceedings 9th IEA Heat Pump Conference 2008: Conference Proceedings, Zurich, Switzerland: International Energy Agency , 2008, p. 4-19Conference paper (Refereed)
    Abstract [en]

    Heat exchange with the bedrock for ground source heat pumps is commonly done with the help of U-pipe energy collectors in vertical boreholes. At the moment, there exist many uncertainties about how efficient the heat transfer between the rock and the collector is. For a complete performance analysis of these systems, a 260 m deep water filled borehole is characterized, by measuring the borehole deviation, the ground water flow and the undisturbed ground temperature. Significant attention is devoted to detailed temperature measurements along the borehole depth during operation providing a complete description of the temperature variations in time both for the secondary working fluid and for the ground water. The results show a deviated borehole from the vertical direction without any relevant ground water flow. The undisturbed ground temperature gradient varies from negative to positive at approximately half of the borehole depth. The transient response of the borehole during the heat pump start up is illustrated and it is observed that there does not exist any thermal short circuiting between the down and up-going pipes when the system is in operation.

  • 14.
    Acuña, José
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Khodabandeh, Rahmat
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Weber, Kenneth
    Distributed Temperature Measurements on a U-pipe Thermosyphon Borehole Heat Exchanger With CO22010In: Refrigeration Science and Technology Proceedings, Sydney, Australia: International Institute of Refrigeration, 2010Conference paper (Refereed)
    Abstract [en]

    In thermosyphon Borehole Heat Exchangers, a heat carrier fluid circulates while exchanging heat with the ground without the need of a circulation pump, representing an attractive alternative when compared to other more conventional systems. Normally, the fluid is at liquid-vapor saturation conditions and circulation is maintained by density differences between the two phases as the fluid absorbs energy from the ground. This paper presents some experimental experiences from a 65 meter deep thermosyphon borehole heat exchanger loop using Carbon Dioxide as heat carrier fluid, instrumented with a fiber optic cable for distributed temperature measurements along the borehole depth. The heat exchanger consists of an insulated copper tube through which the liquid CO2 flows downwards, and a copper tube acting as a riser. The results show temperatures every two meters along the riser, illustrating the heat transfer process in the loop during several heat pump cycles.

  • 15.
    Ali, Rashid
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Palm, Björn E.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Dryout Characteristics During Flow Boiling of R134a in Vertical Circular Minichannels2011In: International Journal of Heat and Mass Transfer, ISSN 0017-9310, E-ISSN 1879-2189, Vol. 54, no 11-12, p. 2434-2445Article in journal (Refereed)
    Abstract [en]

    In this paper, the experimental results of dryout during flow boiling in minichannels are reported and analysed. Experiments were carried out in vertical circular minichannels with internal diameters of 1.22 mm and 1.70 mm and a fixed heated length of 220 mm. R134a was used as working fluid. Mass flux was varied from 50 kg/m(2) s to 600 kg/m(2) s and experiments were performed at two different system pressures corresponding to saturation temperatures of 27 degrees C and 32 degrees C. Experimental results show that the dryout heat flux increases with mass flux and decreases with tube diameter while system pressure has no clear effect for the range of experimental conditions covered. Finally, the prediction capabilities of the well known critical heat flux (CHF) correlations are also tested.

  • 16.
    Ali, Rashid
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Palm, Björn E.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Claudi, Martin-Callizo
    Maqbool, Mohammad H.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Flow Patterns and Flow Pattern Maps for Microchannels2010In: 2010 3rd International Conference on Thermal Issues in Emerging Technologies, Theory and Applications - Proceedings, ThETA3 2010, 2010, p. 33-42Conference paper (Refereed)
    Abstract [en]

    Dense packaging of electronic components generates very high heat fluxes and therefore results in challenges for proper thermal management of such components. Microchannel based evaporators with phase changing liquids are regarded as a promising solution for such high heat flux cooling applications. Due to confinement of flow and differences in the relative importance of governing phenomena, the two-phase flow and heat transfer characteristics of microchannels have been shown to be different from those of conventional sized channels. The fact that microchannel is an attractive cooling option but at the same time there is a clear lack of understanding of related hydrodynamic and thermal transport phenomena which provides an impetus for microchannel research. This paper presents the flow patterns and flow pattern maps obtained for an experimental study of R134a during flow boiling in a horizontal microchannel. The microchannel was a fused silica tube, the outer surface of which was coated with thin, transparent and electrically conductive layer of Indium-Tin-Oxide (ITO). The microchannel was 781 m in internal diameter and 191 mm in heated length. Operating parameters during the experiments were: mass flux 100-400 kg/m2 s, heat flux 5-45 kW/m2, saturation temperature 25 and 30 °C. A High speed camera was used with a close up lens to capture the flow patterns evolved along the channel. Flow pattern maps are presented in terms of superficial gas and liquid velocity and in terms of Reynolds number and vapor quality plots. The results are compared with some flow pattern maps for conventional and micro scale channels available in literature.

  • 17.
    Ali, Rashid
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Palm, Björn E.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Maqbool, Mohammad H.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    A Visualization Study During Flow Boiling of R134a In A Horizontal Microchannel2010In: ASME 2010 8th International Conference on Nanochannels, Microchannels, and Minichannels Collocated with 3rd Joint US-European Fluids Engineering Summer Meeting, ICNMM2010, 2010, p. 85-94Conference paper (Refereed)
    Abstract [en]

    In this paper, the experimental flow boiling visualization results of a microchannel are presented and discussed. A series of visualization experiments have been conducted in a horizontal, circular, uniformly heated microchannel, to record the two-phase flow patterns evolved during the boiling process and to study the ebullition process. A high speed camera (REDLAKE HG50LE) with a maximum of 100000 fps together with tungsten lights was used to capture the images along the test section. Microchannel was made of circular fused silica tube having an internal diameter of 0.781 mm and a uniformly heated length of 191 mm. Outside of the test tube was coated with a thin, electrically conductive layer of Indium Tin Oxide (ITO) for direct heating of the test section. Refrigerant R134a was used as working fluid and experiments were performed at two different system pressures corresponding to saturation temperatures of 25 degrees C and 30 degrees C. Mass flux was varied from 100 kg/m(2)s to 400 kg/m(2)s and heat flux ranged from 5 kW/m(2) to 45 kW/m(2). Visualization results show that the bubble growth is restricted by the tube diameter which results in very short existence of isolated bubbly flow regime except essentially restricted to a very short length of test tube. Flow patterns observed along the length were: Isolated bubble, elongated bubble, slug flow, semi annular and annular flow. Rigorous boiling and increased coalescence rates were observed with increase in heat flux. Bubble frequency was observed to increase with both heat and mass flux. A comparison with our previous flow boiling visualization studies, carried out for a test tube of 1.33 mm internal diameter, shows that the number of active nucleation sites is less while the bubble frequency is higher for the current study. Mean bubble length and bubble velocity during elongated bubble flow pattern have also been calculated from the images obtained during the tests.

  • 18.
    Ali, Rashid
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Palm, Björn E.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Maqbool, Mohammad H.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Experimental Investigation of Two-phase Pressure Drop in a Microchannel2011In: Heat Transfer Engineering, ISSN 0145-7632, E-ISSN 1521-0537, Vol. 32, no 13/14, p. 1126-1138Article in journal (Refereed)
    Abstract [en]

    Experimental results of two-phase pressure drop in a horizontal circular microchannel are reported in this paper. A test tube was made of fused silica having an internal diameter of 781 mu m with a total length of 261 mm and a heated length of 191 mm. The outer surface of the test tube was coated with an electrically conductive thin layer of ITO (indium tin oxide) for direct heating of the test section. Refrigerants R134a and R245fa were used as the working fluids, and mass flux during the experiments was varied between 100 and 650 kg/m(2)-s. Experiments were performed at two different system pressures corresponding to saturation temperatures of 25 degrees C and 30 degrees C for R134a and at three different system pressures corresponding to saturation temperatures of 30 degrees C, 35 degrees C, and 40 degrees C for R245fa. Two-phase frictional pressure drop characteristics with variation of mass flux, vapor fraction, saturation temperature, and heat flux were explored in detail. Finally, the prediction capability of some well-known correlations available in the literature, some developed for macrochannels and others especially developed for microchannels, was assessed.

  • 19.
    Ali, Rashid
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Palm, Björn E.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Maqbool, Mohammad H.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Flow Boiling Heat Transfer Characteristics of a Minichannel up to Dryout Condition2011In: Journal of heat transfer, ISSN 0022-1481, E-ISSN 1528-8943, Vol. 133, no 8, p. 081501-Article in journal (Refereed)
    Abstract [en]

    In this paper, the experimental flow boiling heat transfer results of a minichannel are presented. A series of experiments was conducted to measure the heat transfer coefficients in a minichannel made of stainless steel (AISI 316) having an internal diameter of 1.70 mm and a uniformly heated length of 220 mm. R134a was used as a working fluid, and experiments were performed at two different system pressures corresponding to saturation temperatures of 27 degrees C and 32 degrees C. Mass flux was varied from 50 kg/m(2) s to 600 kg/m(2) s, and heat flux ranged from 2 kW/m(2) to 156 kW/m(2). The test section was heated directly using a dc power supply. The direct heating of the channel ensured uniform heating, which was continued until dryout was reached. The experimental results show that the heat transfer coefficient increases with imposed wall heat flux, while mass flux and vapor quality have no considerable effect. Increasing the system pressure slightly enhances the heat transfer coefficient. The heat transfer coefficient is reduced as dryout is reached. It is observed that the dryout phenomenon is accompanied with fluctuations and a larger standard deviation in outer wall temperatures.

  • 20.
    Ali, Rashid
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Palm, Björn E.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Maqbool, Mohammad H.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Flow Boiling Heat Transfer Characteristics of a Minichannel up to Dryout Condition2010In: MNHMT2009, VOL 2, New York: AMER SOC MECHANICAL ENGINEERS , 2010, p. 25-34Conference paper (Refereed)
    Abstract [en]

    In this paper the experimental flow boiling heat transfer results of a minichannel are presented. A series of experiments was conducted to measure the heat transfer coefficients in a minichannel made of stainless steel (AISI 316) having an internal diameter of 1.7mm and a uniformly heated length of 220mm. R134a was used as working fluid and experiments were performed at two different system pressures corresponding to saturation temperatures of 27 degrees C and 32 degrees C. Mass flux was varied from 50 kg/m(2) s to 600 kg/m(2) s and heat flux ranged from 2kW/m(2) to 156 kW/m(2). The test section was heated directly using a DC power supply. The direct heating of the channel ensured uniform heating and heating was continued until dry out was reached. The experimental results show that the heat transfer coefficient increases with imposed wall heat flux while mass flux and vapour quality have no considerable effect. Increasing the system pressure slightly enhances the heat transfer coefficient. The heat transfer coefficient is reduced as dryout is reached. It is observed that dryout phenomenon is accompanied with fluctuations and a larger standard deviation in outer wall temperatures.

  • 21.
    Ali, Rashid
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Palm, Björn E.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Maqbool, Mohammad H.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Flow Boiling Heat Transfer Of Refrigerants R134a And R245fa In A Horizontal Micro-Channel2012In: Experimental heat transfer, ISSN 0891-6152, E-ISSN 1521-0480, Vol. 25, no 3, p. 181-196Article in journal (Refereed)
    Abstract [en]

    Micro-channel-based evaporators are a promising option for high heat flux cooling applications. Micro-channels offer several advantages, including a smaller coolant inventory, superior heat transfer performance, compactness, lightness of weigh. Despite being attractive, the governing phenomena in micro-channels, especially during phase change, are less understood. This article reports the experimental flow boiling heat transfer results of refrigerants R134a and R245fa in a horizontal micro-channel. A series of experiments was conducted to measure the heat transfer coefficients in a circular micro-channel made of fused silica having an internal diameter of 781 mu m and a uniformly heated length of 191 mm. The outer surface of the test tube was coated with a thin, electrically conductive layer of indium-tin-oxide. The surface coating with the electrically conductive layer of indium-tin-oxide made it possible to visualize the flow boiling process simultaneously with uniform heating of the test section. R134a and R245fa were used as working fluids and experiments were performed at a system pressure of 7.7 bar for R134a and at 1.8 bar for R245fa, corresponding to saturation temperature of 30 degrees C. Mass flux was varied from 175 kg/m(2)s to 500 kg/m(2)s, and heat flux ranged from 5 kW/m(2) to 60 kW/m(2). A high-speed camera was used to capture the images in the case of flow boiling of R134a. The experimental results indicated that the heat transfer coefficient increased with heat flux while the mass flux proved to have a negligible effect on heat transfer coefficient.

  • 22.
    Ali, Rashid
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Palm, Björn E.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Maqbool, Mohammad H.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Flow Boiling Heat Transfer of Refrigerants R134a and R245fa in a Horizontal Microchannel2010In: Proceedings of 2nd European Conference on Microfluidics, 2010Conference paper (Refereed)
  • 23.
    Ali, Rashid
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Maqbool, Mohammad H.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Experimental investigation of two phase pressure drop in a microchannel2009In: Proceedings of 2nd Micro & Nano flows Conference, Academic Conferences Publishing, 2009Conference paper (Refereed)
  • 24.
    Ali, Rashid
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Martin-Callizo, C.
    Maqbool, Muhammad Hamayun
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Study of flow boiling characteristics of a microchannel using high speed visualization2013In: Journal of heat transfer, ISSN 0022-1481, E-ISSN 1528-8943, Vol. 135, no 8, p. 081501-Article in journal (Refereed)
    Abstract [en]

    This paper presents the visualization results obtained for an experimental study of R134a during flow boiling in a horizontal microchannel. The microchannel used was a fused silica tube having an internal diameter of 781 lm, a heated length of 191mm, and was coated with a thin, transparent, and electrically conductive layer of indium-tin-oxide (ITO) on the outer surface. The operating parameters during the experiments were: mass flux 100-400 kg/m2 s, heat flux 5-45 kW/m2, saturation temperatures 25 and 30 °C, corresponding to saturation pressures of 6.65 bar and 7.70 bar and reduced pressures of 0.163 and 0.189, respectively. A high speed camera with a close up lens was used to capture the flow patterns that evolved along the channel. Flow pattern maps are presented in terms of the superficial gas and liquid velocity and in terms of the Reynolds number and vapor quality plots. The results are compared with some flow pattern maps for conventional and micro scale channels available in the literature. Rigorous boiling and increased coalescence rates were observed with an increase in the heat flux.

  • 25. Andersson, K.
    et al.
    Granryd, Eric
    KTH.
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Water to water heat pump with minimum charge of propane2018In: Refrigeration Science and Technology, International Institute of Refrigeration, 2018, p. 725-732Conference paper (Refereed)
    Abstract [en]

    This paper describes the technology for an environmentally friendly ground source heat pump for a single family home, characterized by using pure water as coolant and propane as refrigerant. The objective was to build a test system, operating under realistic conditions, using less than 150 g of propane, providing at least 5 kW heating capacity with reasonable efficiency and without freezing the coolant water. The borehole heat exchanger was of coaxial type, providing about half the thermal resistance compared to a standard U-tube collector (Acuña 2010). The evaporator and condenser where asymmetrical plate heat exchangers with small channel height (< 1 mm) on the refrigerant side. They were developed and manufactured exclusively for this project with a new type of press pattern, including a special, small volume sub-cooling section at the end of the condenser. A DC-motor scroll compressor for AC in electric vehicles was used, characterized by small internal volumes, small oil charge and wide capacity range (800-9000 rpm). A PAG-type oil was used, which however seemed to cause some problems with heat transfer and pressure drop in the evaporator. The system also included a specially built mini channel liquid/suction line heat exchanger and a standard thermostatic expansion valve. The paper presents test results for a heating capacity range of 2-10 kW. The performance was reasonable in this range with a charge of 100 g of propane (-1<T2<5°C, 30<T1<55°C). The charge that is required is determined at the lowest capacities, at low compressor speed and high evaporating pressures. A lower charge is beneficial at higher capacities.

  • 26.
    Anton, Raul
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Jonsson, Hans
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Modeling of Air Conditioning Systems for Cooling of Data Centers2002In: Proc. 8th  InterSociety Conf. on Thermal and Thermomechanical Phenomena in Electronic Systems (ITherm 2002), San Diego, CA, USA, IEEE Press, 2002, p. 552-558Conference paper (Refereed)
    Abstract [en]

    Cooling of data centers has emerged as an area of increasing importance in the field of electronics thermal management. As the packaging and power densities are steadily increasing, so will the need for efficient and reliable cooling systems.

    In this paper, a model of an air conditioning unit is described. The model offers considerable flexibility in terms of the ability to choose between different designs of heat exchangers (evaporators and condensers), and working media, and hence the model offers the possibility to optimize the design.

    The model is developed using EES (Engineering Equation Solver), a programming environment that provides the thermo-physical properties for the working media used. The heat transfer and pressure drop in the components are modeled using an integral approach, i.e. the overall behavior of each component is modeled. This approach has been proven to give adequate accuracy.

  • 27. Anwar, Z.
    et al.
    Palm, Björn E.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Khodabandeh, Rahmatollah
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Dryout characteristics of natural and synthetic refrigerants in single vertical mini-channels2015In: Experimental Thermal and Fluid Science, ISSN 0894-1777, E-ISSN 1879-2286, Vol. 68, p. 257-267Article in journal (Refereed)
    Abstract [en]

    Experimental results on dryout of seven refrigerants (R134a, R1234yf, R152a, R22, R245fa, R290 and R600a) in small, single vertical tubes under upward flow conditions are reported in this study. The experiments were conducted under a wide range of operating conditions in stainless steel tubes (0.64-1.70. mm and 213-245. mm heated length). The effects of operating parameters like mass flux, vapor quality, saturation pressure and channel size are discussed in detail. In general, dryout heat flux increased with increasing mass flux, and with increasing tube diameter. No effect of varying saturation temperature was observed. The experimental findings were compared with well-known macro and micro-scale correlations from the literature and it was found that Wu's correlation (in modified form) quite satisfactorily predicted the whole database. A new correlation for prediction of heat flux at dryout conditions is also proposed.

  • 28. Anwar, Z.
    et al.
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Khodabandeh, Rahmatollah
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Flow boiling heat transfer and dryout characteristics of R152a in a vertical mini-channel2014In: Experimental Thermal and Fluid Science, ISSN 0894-1777, E-ISSN 1879-2286, Vol. 53, p. 207-217Article in journal (Refereed)
    Abstract [en]

    This article reports on flow boiling heat transfer and dryout characteristics of R152a in a vertical mini-channel. The experiments were carried out with a resistively heated stainless steel tube (1.60mm in diameter and 245mm heated length) at 27 and 32°C saturation temperature. Five mass fluxes in the range 100-500kg/m2s with heat fluxes from 5 to 245kW/m2 were tested. Under similar operating conditions experiments were repeated with R134a in the same setup to compare thermal performance of R152a. The results showed that the heat transfer was strongly influenced by the applied heat flux with insignificant convective contributions. The dryout heat flux increased with increasing mass flux but no effect of varying operating pressure was noticed. The experimental results for heat transfer and dryout heat flux were compared with well-known macro and micro-scale correlations from the literature.

  • 29.
    Anwar, Zahid
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration. Department of Mechanical, Mechatronics and Manufacturing Engineering (KSK-Campus), University of Engineering and Technology, Lahore, Pakistan .
    Palm, Björn E.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Khodabandeh, Rahmatollah
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Flow boiling heat transfer, pressure drop and dryout characteristics of R1234yf: Experimental results and predictions2015In: Experimental Thermal and Fluid Science, ISSN 0894-1777, E-ISSN 1879-2286, Vol. 66, p. 137-149Article in journal (Refereed)
    Abstract [en]

    Flow boiling heat transfer, pressure drop and dryout characteristics of R1234yf in a vertical stainless steel test section (1.60mm inside diameter and 245mm heated length) under upward flow conditions are reported in this article. The experiments were carried out at 27 and 32°C saturation temperatures with five mass fluxes in the range of 100-500kg/m2s while the applied heat flux was in the range of 5-130kW/m2. The experiments were carried out with gradual increase of the applied heat flux til completion of dryout. Under similar conditions, tests were repeated with R134a in the same test setup to compare thermal performance of these two refrigerants. The results showed that boiling heat transfer was strongly controlled by the applied heat flux and operating pressure with insignificant dependence on mass flux and vapor quality. The frictional pressure drop increased with mass flux and vapor quality and decreased with increasing saturation temperature as expected. Signs of dryout first appeared at vapor qualities of 85%, with the values generally increasing with increasing mass flux. The effect of varying system pressure was insignificant. The experimental results (boiling heat transfer, pressure drop and dryout heat flux) were compared with the predictions from well-known correlations (for macro and micro-scale channels) from the literature.

  • 30.
    Anwar, Zahid
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Khodabandeh, Rahmatollah
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Dryout characteristics of natural and synthetic refrigerants in vertical mini-channelsManuscript (preprint) (Other academic)
  • 31.
    Anwar, Zahid
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Khodabandeh, Rahmatollah
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Dryout characteristics of R1234yf in a vertical mini-channel2013In: Eurotherm seminar on convective heat transfer, 2013Conference paper (Refereed)
    Abstract [en]

    This article reports dryout characteristics of R1234yf in a single, uniformly heated vertical stainless steel channel (d=1.6mm, Lh=245mm). Tests were conducted at 27 and 32 oC saturation temperature with 100-500 kg/m2s. Results of various operating parameters (mass flux, vapor quality, saturation temperature) were discussed in detail. Comparison with R134a revealed lower (about 18%) critical heat flux values with R1234yf.  Experimental findings were compared with various macro & micro scale correlations from the literature. Katto- Ohno and Wu’s correlations [7,8] accurately predicted the data from macro and micro scale models respectively.

  • 32. Anwar, Zahid
    et al.
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Khodabandeh, Rahmatollah
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Flow Boiling Heat Transfer and Dryout Characteristics of R600a in a Vertical Minichannel2015In: Heat Transfer Engineering, ISSN 0145-7632, E-ISSN 1521-0537, Vol. 36, no 14-15, p. 1230-1240Article in journal (Refereed)
    Abstract [en]

    Refrigerant-related environmental concerns forced legislative bodies to phase out some types of refrigerants, namely, chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) and in the near future European legislation will be affecting hydrofluorocarbons (HFCs) as well. Natural refrigerants such as hydrocarbons can thus be expected to be more common as refrigerants in the future. Experimental findings on flow boiling heat transfer and dryout characteristics of isobutane (R600a) in a uniformly heated, vertical, stainless-steel test section (1.60mm inside diameter and 245mm heated length) are reported in this article. The experiments were conducted at two saturation pressures corresponding to the temperatures of 27 and 32 degrees C, with five mass fluxes in the range 50-350kg/m(2)-s and at outlet vapor qualities up to dryout conditions. Analysis showed that heat transfer was primarily controlled by the applied heat flux with insignificant effect of mass flux and vapor quality. The dryout heat flux increased with increasing mass flux; however, no significant effect of varying saturation temperature was observed. The experimental results (for heat transfer and dryout) were compared with different macro and microscale correlations from the literature.

  • 33.
    Anwar, Zahid
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Khodabandeh, Rahmatollah
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Flow boiling heat transfer of R600a in a uniformly heated smooth vertical minichannel2013In: Proceedings of the 13th UK Heat Transfer Conference Sept. 2-3, 2013, UKHTC2013, 2013Conference paper (Refereed)
    Abstract [en]

    Refrigerant related environmental concerns forced legislative bodies to phase out some types of refrigerants namely CFC’s and HCFC’s and in the near future European legislation will be affecting HFCs as well. Natural refrigerants such as hydrocarbons can thus be expected to be more common as refrigerants in the future. Experimental studies with these fluids are important in understanding their performance and potential. Experimental findings on flow boiling of Isobutane in a uniformly heated, vertical, stainless steel test section (1.6 mm inside diameter and 245mm heated length) are reported in this article. Experiments were conducted at two saturation pressures corresponding to the temperature of 27 and 32 oC, with five mass fluxes in the range 50-350 kg/m2s and at outlet vapour qualities up till dryout conditions. Analysis showed that heat transfer was primarily controlled by the applied heat flux with insignificant effect of mass flux and vapor quality. The experimental results were compared with different macro and micro-scale correlations from the literature, and Owhaib, Liu & Winterton and Mikielewicz correlations quite accurately predicted the heat transfer data.

  • 34.
    Anwar, Zahid
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Khodabandeh, Rahmatollah
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Flow boiling of R1234yf in a uniform smooth vertical minichannel2013In: Science et Technique du Froid. Comptes Rendus/Refrigeration Science and Technology. Proceedings, 2013, Vol. 3, Institut International du Froid , 2013, p. 1-11Conference paper (Refereed)
    Abstract [en]

    This study describes experimental findings on flow boiling heat transfer with R1234yf in a smooth, vertical stainless steel tube of 1.6 mm inner diameter and 245 mm heated length. Tests were conducted at two saturation pressures corresponding to saturation temperatures of 27 and 32 °C. Other operating parameters were: mass flux 100-500 kg/m²s with heat flux 3-65 kW/m² while quality change was up to 60%. The heat transfer coefficient appeared to be a strong function of the applied heat flux and insignificant effect of mass flux and quality was observed. Increase in saturation temperature/pressure increased the heat transfer performance. Experiments were repeated with R134a in the same test section to compare the two fluids, almost similar results were duplicated with R134a. Experimental results were compared with different correlations, Tran et al. (1996), Gungor and Winterton (1986) and Martín-Callizo et al. (2007) correlations accurately predicted the data.

  • 35.
    Anwar, Zahid
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Khodabandeh, Rahmatollah
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Flow boilingheat transfer and dryout characteristics of R600a in a vertical mini-channelManuscript (preprint) (Other academic)
  • 36.
    Anwar, Zahid
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Rahmatollah, Khodabandeh
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Dryout characteristics of R1234yf in a uniformly heated vertical mini-channel2013In: UK Heat Transfer Conference, 2013Conference paper (Refereed)
    Abstract [en]

    Two phase heat transfer in small channels has many practical applications like, miniature heatexchangers, high powered electronics, miniature refrigeration system. Flow boiling in these compactchannels offers many potential advantages like, cope with high heat flux, less fluid inventory,compactness in size. It is well known that two phase heat transfer is drastically reduced when theheater surface becomes partially dry, for any reason. Moving beyond the point where this happensresults in a sharp increase in the temperature of the heated surface and eventually leads towardsburnout. So the upper operational limit (from safety and efficiency point of view) is extremelyimportant to be able to predict.Experimental findings on dryout of Isobutane in a uniformly heated, vertical, stainless steel testsection (1.6 mm inside diameter and 245mm heated length) are reported in this article. Experimentswere conducted at two saturation pressures corresponding to temperatures of 27 and 32 oC, with fivemass fluxes in the range 50-350 kg/m2s and with vapor fractions at the outlet up till dryout conditions.Analysis showed that the dryout heat flux increased with increasing mass flux, while no effect ofvarying the operating pressure was observed. Experimental results were compared with differentcorrelations from the literature, Wu [5], Mikielewicz [6], Callizo [3] and Katto-Ohno [4] correlationsquite satisfactorily predicted the data.

  • 37.
    Baina, Fabiola
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology. Universidad Mayor de San Siḿona, Bolivia .
    Malmquist, Anders
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Alejo, Lucio
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Fransson, Torsten H.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Analysis of a high-temperature heat exchanger for an externally-fired micro gas turbine2015In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 75, p. 410-420Article in journal (Refereed)
    Abstract [en]

    The externally-fired gas turbine (EFGT) can convert fuels such as coal, biomass, biomass gasification gas and solar energy into electricity and heat. The combination of this technology with biomass gasification gas represents an interesting option for gasification, for which it has been difficult to find a conversion technology. In this system, the heat exchanger deals with the contaminants of biomass derived gas instead of the turbine itself. However, these contaminants can build a deposit layer in the heat exchanger that can affect its performance. The heat exchanger is important in externally fired gas turbines since the turbine inlet temperature is directly dependent on its performance. Several studies on heat exchangers for externally fired gas turbines have been carried out. However, very few detailed studies were found comparing the performance of heat exchangers for externally fired gas turbines considering the effect of deposit materials on the surfaces. In this regard, this work compares the performance of a corrugated plate heat exchanger and a two-tube-passes shell and tube heat exchanger considering the effect of thickness of deposit material with different thermal conductivities on pressure drop and effectiveness. The results show that the effectiveness of the corrugated plate heat exchanger is more influenced at larger thicknesses of deposit materials than the two-tube-passes shell and tube heat exchanger. There is an exponential increase in the pressure drop of the plate heat exchanger while a monotonic increase of pressure drop is seen for the shell and tube heat exchanger. The increase in the thickness of the deposit material has two effects. On one hand, it increases the resistance to heat transfer and on the other hand, it reduces the through flow area increasing the velocity and hence the heat transfer coefficient. Additionally, the effectiveness of the heat exchangers had a stronger influence on the power output than the pressure drop.

  • 38. Behi, M.
    et al.
    Mirmohammadi, S. A.
    Suma, A. B.
    Palm, Björn E.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Optimized energy recovery in line with balancing of an ATES2014In: American Society of Mechanical Engineers, Power Division (Publication) POWER, 2014, Vol. 2Conference paper (Refereed)
    Abstract [en]

    The present study explores the potential imbalance problem of the Aquifer Thermal Energy Storage (ATES) system at the Eindhoven University of Technology (TU/e) campus, Eindhoven. This ATES is one of the largest European aquifer thermal energy storage systems, and has a seasonal imbalance problem. Reasons for this issue may be the high cooling demand from laboratories, office buildings and the direct ATES cooling system. Annually, cooling towers use on average 250 MWh electricity for the removal of about 5 GWh of excess heat from the ATES to the surroundings. In addition, the TU/e uses a large amount of natural gas for heating purposes and especially for peak supplies. Recovering the surplus heat of the ATES, a CO2 Trans-critical Heat Pump (HP) system to cover particularly peak demands and total heating demand is proposed, modeled and optimized. The model is validated using data from International Energy Agency. Based on simulation results, 708294 nm3 of natural gas are saved where two different scenarios were considered for the ATES efficiency, cost saving and green house gas reduction. In scenario I, the COP of the ATES increased up to 50% by which K€ 303.3 energy cost and 1288.5 ton CO2 are saved annually. On the other hand, it will be shown that the ATES COP in Scenario II will improve up to 20%. In addition, the proposed energy recovery system results in a 606 ton CO2 -reduction and K€152.7 energy cost saving for the university each year.

  • 39.
    Behi, Mohammadreza
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology. Univ Sydney, Sch Chem & Biomol Engn, Sydney, NSW 2006, Australia..
    Mirmohammadi, Seyed Aliakbar
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology. Univ Sydney, Sch Civil Engn, Sydney, NSW 2006, Australia..
    Ghanbarpour, Morteza
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Behi, Hamidreza
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Evaluation of a novel solar driven sorption cooling/heating system integrated with PCM storage compartment2018In: Energy, ISSN 0360-5442, E-ISSN 1873-6785, Vol. 164, p. 449-464Article in journal (Refereed)
    Abstract [en]

    Recently the interest in solar thermal cooling has been growing for Air Conditioning (AC) applications. This paper presents an applied experimental and numerical evaluation of a novel triple-state sorption solar cooling module. The performance of a LiCl-H2O based sorption module (SM) for cooling/heating system with integration of an external energy storage has been evaluated. The dynamic behavior of the SM, which can be driven by solar energy, is presented. Two PCM assisted configurations of the SM have been studied herein; (i) PCM assisted sorption module for cooling applications (ii) PCM assisted sorption module for heating applications. Initially, an experimental investigation was carried out to evaluate the charging/discharging process of the SM without external energy storage. Secondly, the initial experimental configuration was modeled with a PCM integrated storage compartment. The PCM storage compartment was connected to the Condenser/Evaporator (C/E) of the SM. The temporal history of the sorption module's C/E and PCM storage, the cyclic and average performance in terms of cooling/heating capacity, cooling/heating COP, and the total efficiency were experimentally and numerically investigated. Furthermore, PCM charging/discharging power rate and solidification/melting process of the PCM in the integrated storage compartment to the SM were predicted by the model.

  • 40. Beier, R. A.
    et al.
    Acuña, José
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Mogensen, P.
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Borehole resistance and vertical temperature profiles in coaxial borehole heat exchangers2013In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 102, p. 665-675Article in journal (Refereed)
    Abstract [en]

    Ground source heat pump systems are often coupled to the ground by circulating a fluid through vertical Borehole Heat Exchangers (BHEs). The design of a system requires estimates of the ground thermal conductivity and the borehole thermal resistance, which are usually determined by an in situ thermal response test on a completed borehole. The usual test interpretation methods average the inlet and outlet fluid temperatures and use this mean temperature as the average temperature along the borehole length. This assumption is convenient but does not strictly apply. For a coaxial heat exchanger this paper develops an analytical model for the vertical temperature profiles, which can be used instead of the mean temperature approximation to estimate borehole resistance. The model is verified with measured temperatures on a BHE, where an optical technique allows continuous measurements along a coaxial borehole during a distributed thermal response test. A sensitivity study shows that the proposed method corrects errors in the mean temperature approximation, which overestimates the borehole resistance in a coaxial borehole.

  • 41. Beier, R. A.
    et al.
    Acuña, José
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Mogensen, P.
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Vertical temperature profiles and borehole resistance in a U-tube borehole heat exchanger2012In: Geothermics, ISSN 0375-6505, E-ISSN 1879-3576, Vol. 44, p. 23-32Article in journal (Refereed)
    Abstract [en]

    The design of ground source heat pump systems requires values for the ground thermal conductivity and the borehole thermal resistance. In situ thermal response tests (TRT) are often performed on vertical boreholes to determine these parameters. Most TRT analysis methods apply the mean of the inlet and outlet temperatures of the circulating fluid along the entire borehole length. This assumption is convenient but not rigorous. To provide a more general approach, this paper develops an analytical model of the vertical temperature profile in the borehole during the late-time period of the in situ test. The model also includes the vertical temperature profile of the undisturbed ground. The model is verified with distributed temperature measurements along a vertical borehole using fiber optic cables inside a U-tube for the circulating fluid. The borehole thermal resistance is calculated without the need for the mean temperature approximation. In the studied borehole, the mean temperature approximation overestimates the borehole resistance by more than 20%.

  • 42. Beier, Richard A.
    et al.
    Acuña, José
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Mogensen, Paine
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Transient heat transfer in a coaxial borehole heat exchanger2014In: Geothermics, ISSN 0375-6505, E-ISSN 1879-3576, Vol. 51, p. 470-482Article in journal (Refereed)
    Abstract [en]

    Ground-source heat pumps often use vertical boreholes to exchange heat with the ground. A transient heat transfer model has been developed for a thermal response test on a pipe-in-pipe coaxial borehole heat exchanger. The analytical model calculates the vertical temperature profiles in the fluid flowing through the pipes, which are coupled to the surrounding grout and ground. The model is verified against measured vertical temperature profiles in the circulating fluid during a distributed thermal response test. The comparison with measured data indicates that the proposed model gives a more accurate estimate of the borehole thermal resistance than the conventional analytical model that uses a mean temperature approximation. The model demonstrates how strongly the shapes of the temperature profiles are dependent on the thermal resistance of the internal pipe wall and the flow direction.

  • 43.
    Bekele, Getachew
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Feasibility study for a standalone solar–wind-based hybrid energy system for application in Ethiopia2010In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 87, no 2, p. 487-495Article in journal (Refereed)
    Abstract [en]

    The aim of this paper is to investigate the possibility of supplying electricity from a solar-wind hybrid system to a remotely located model community detached from the main electricity grid in Ethiopia. The wind energy potential of four typical locations has been assessed in a previous article. The solar potential has also been investigated and the results are presented in detail in an accompanying article awaiting publication. For one of the sites, Addis Ababa, the results of the investigation are given here in detail. For the other sites, the results are given as sensitivity diagrams only. Based on the findings of the studies into energy potential, a feasibility study has been carried out on how to supply electricity to a model community of 200 families, which comprises 1000 people in total. The community is equipped with a community school and a health post. The electric load consists of both primary and deferrable types and comprises lighting, water pumps, radio receivers, and some clinical equipment. A software tool, Hybrid Optimization Model for Electric Renewables (HOMER) is used for the analysis. The result of the analysis is a list of feasible power supply systems, sorted according to their net present cost. Furthermore, sensitivity diagrams, showing the influence of wind speeds, PV costs, and diesel prices on the optimum solutions are also provided.

  • 44.
    Bekele, Getachew
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Solar energy potential assessment at four typical locations in EthiopiaIn: Energy for Sustainable Development, ISSN 0973-0826, E-ISSN 2352-4669Article in journal (Other academic)
    Abstract [en]

    As a continuation of the study into wind energy potential previously completed, solar energy potential at the same four locations in Ethiopia has been investigated. These are Addis Ababa, 09” 02’N, 38” 42’E, 2408 m (AMSL); Mekele, 13” 33’N, 39” 30’E, 2130 m; Nazret 08:32N, 39:22E, 1690 m; and Debrezeit, 08”44’N, 39” 02’E 1850 m. As in the case of the wind data no radiation data has been properly recorded to evaluate the sola renergy potential of the country, except for in one single location, Addis Ababa. However, sunshine duration data has been collected over a relatively long period of time. Therefore, this study is based on sunshine duration data collected over more than 10 years at the specified locations and also on software and satellite interpolated data obtained from sources outside the country. A thorough literature survey has been carried out and different models by different authors have been investigated. After analyzing the data using well known equations taken from standard text books, the results obtained are given in the form of solar radiation plots for all locations. This study is the second stage in the assessment of the feasibility of a hybrid standalone electricity supply system to remotely located communities detached from the main grid.

  • 45.
    Bekele, Getachew
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Solar-wind-based village electrification in Ethiopia: a comparision of technologiesIn: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682Article in journal (Refereed)
    Abstract [en]

    The aim of this paper is to investigate the possibility of supplying electriclight and potable water from a solar-wind based hybrid system. The main target is a remotely resettled community in Ethiopia out of reach of the electric grid. The wind energy potential of the location has been assessed in a previous article. The solar potential has also been investigated in an accompanying article awaiting publication. Based on the findings of the potential, a feasibility study has been carried out on how to supply electricity to the community, modeled as having 200 families, comprising of approximately 1000 to 1200 people in total. A community school and a health post is also considered for the community. The electric load considered is of both primary and deferrable types consisting of lighting ,water pumps, radio receivers, and some clinical equipment. In theattempt of finding the most economical solution, a system with less energy efficient, and less expensive components have been compared to a more expensive system with the latest, most energy efficient ,technology on both the supply and load sides.

    A system solution on individual basis (solution per house hold) has also been considered and the net present cost (NPC) is compared against the aggregate solution. A software tool, Hybrid Optimization Model for Electric Renewables (HOMER) is used for the analysis. The result of the analysis is a list of feasible power supply systems, sorted according to their net present cost. Furthermore, sensitivity diagrams, showing the influence of wind speeds, PV costs, and diesel prices on the optimum solutions are also provided.

  • 46.
    Bekele, Getachew
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Wind energy potential assessment at four typical locations in Ethiopia2009In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 86, no 3, p. 388-396Article in journal (Refereed)
    Abstract [en]

    The wind energy potential at four different sites in Ethiopia - Addis Ababa (09:02N, 38:42E), Mekele (13:33N, 39:30E), Nazret (08:32N, 39:22E), and Debrezeit (8:44N, 39:02E) - has been investigated by compiling data from different sources and analyzing it using a software tool. The results relating to wind energy potential are given in terms of the monthly average wind speed, wind speed probability density function (PDF), wind speed cumulative density function (CDF), and wind speed duration curve (DC) for all four selected sites. in brief, for measurements taken at a height of 10 m, the results show that for three of the four locations the wind energy potential is reasonable, with average wind speeds of approximately 4 m/s. For the fourth site. the mean wind speed is less than 3 m/s. This study is the first stage in a longer project and will be followed by an analysis of solar energy potential and finally the design of a hybrid standalone electric energy supply system that includes a wind turbine, PV, diesel generator and battery.

  • 47.
    Bitaraf Haghighi, Ehsan
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Nikkam, Nader
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Saleemi, Mohsin
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Behi, Mohammadreza
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Mirmohammadi, Seyed Aliakbar
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Poth, H.
    Khodabandeh, Rahmatollah
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Muhammed, Mamoun
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Shelf stability of nanofluids and its effect on thermal conductivity and viscosity2013In: Measurement science and technology, ISSN 0957-0233, E-ISSN 1361-6501, Vol. 24, no 10, p. 105301-Article in journal (Refereed)
    Abstract [en]

    This study proposes a method and apparatus to estimate shelf stability of nanofluids. Nanofluids are fabricated by dispersion of solid nanoparticles in base fluids, and shelf stability is a key issue for many practical applications of these fluids. In this study, shelf stability is evaluated by measuring the weight of settled solid particles on a suspended tray in a colloid versus time and correlated with the performance change of some nanofluid systems. The effects of solid particle concentration and bath sonication time were investigated for selected nanofluids. The results show the applicability of this simple method and the apparatus to evaluate nanofluid shelf stability. Furthermore, it shows that Stokes' law is not valid for determining the settling time of the tested nanoparticles probably due to their complicated shape and presence of surface modifiers. The effect of shelf stability on thermal conductivity and viscosity was illustrated for some nanofluids. Experimental results show that water-based Al2O3 nanofluids have quite good shelf stability and can be good candidates for industrial applications.

  • 48.
    Bitaraf Haghighi, Ehsan
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Saleemi, Mohsin
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Nikkam, Nader
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Anwar, Zahid
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Lumbreras, Itziar
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Behi, Mohammadreza
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Mirmohammadi, Seyed A.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Poth, Heiko
    Khodabandeh, Rahmatollah
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Muhammed, Mamoun
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Cooling performance of nanofluids in a small diameter tube2013In: Experimental Thermal and Fluid Science, ISSN 0894-1777, E-ISSN 1879-2286, Vol. 49, p. 114-122Article in journal (Refereed)
    Abstract [en]

    This article reports convective single-phase heat transfer performance in laminar flow for some selected nanofluids (NFs) in an open small diameter test section. A 0.50 mm inner diameter, 30 cm long stainless steel test section was used for screening single phase laminar convective heat transfer with water and five different water based NFs. Tested NFs were; Al2O3 (two types), TiO2 (two types) and CeO2 (one type), all 9 wt.% particle concentration. The effective thermal conductivity of the NFs were measured with Transient Plane Source (TPS) method and viscosity were measured with a rotating coaxial cylindrical viscometer. The obtained experimental results for thermal conductivity were in good agreement with the predicted values from Maxwell equation. The local Shah correlation, which is conventionally used for predicting convective heat transfer in laminar flow in Newtonian fluids with constant heat flux boundary condition, was shown to be valid for NFs. Moreover, the Darcy correlation was used to predict the friction factor for the NFs as well as for water. Enhancement in heat transfer for NFs was observed, when compared at equal Reynolds number, as a result of higher velocity or mass flow rate of the NFs at any given Reynolds number due to higher viscosity for NFs. However, when compared at equal pumping power no or only minor enhancement was observed.

  • 49.
    Bitaraf Haghighi, Ehsan
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Saleemi, Mohsin
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Nikkam, Nader
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Ghadamgahi, Mersedeh
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Khodabandeh, Rahmatollah
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Palm, Björn E.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Toprak, Muhammet
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Muhammed, Mamoun
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Measurement of temperature–dependent viscosity of nanofluids and its effect on pumping power in cooling systems2013Conference paper (Refereed)
    Abstract [en]

    Nanofluids are engineered colloids of nanoparticlesdispersed homogenously in a base fluid, which theirthermophysical properties are changed by adding solidnanoparticles. Among the characteristic parameters,viscosity is one of the most important, as it directly affectsthe pumping power in cooling systems. In this study, theviscosity of water based Al2O3, ZrO2, and TiO2 (with 9wt%for all) nanofluids was measured and its impact on pressuredrop in a simple tubular pipe was estimated for bothlaminar and turbulent flow by classical correlations. Theeffect of temperature on the viscosity of these nanofluidswas also studied in the temperature range of 5˚C - 30˚C. Toassess the applicability of the classical correlations, pressuredrops across an open 30cm long, 0.50mm diameterstainless steel test section was measured for water andnanofluids by a differential pressure transducer. Theaverage viscosity increments compared to water in thetemperature range of 5˚C - 30˚C are 105%, 98% and 31% forAl2O3, ZrO2, and TiO2 nanofluids respectively. Moreover, theresults show that the viscosity of nanofluids decreases withthe increase of temperature; however the relative viscosity,which is defined as the viscosity ratio between a nanofluidand its base fluid is constant in 5˚C - 30˚C temperaturerange.

  • 50.
    Bitaraf Haghighi, Ehsan
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Utomo, Adi T.
    Ghanbarpour, Morteza
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Zavareh, Ashkan I. T.
    Nowak, Emilia
    Khodabandeh, Rahmatollah
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Pacek, Andrzej
    Palm, Björn E.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Combined effect of physical properties and convective heat transfer coefficient of nanofluids on their cooling efficiency2015In: International Communications in Heat and Mass Transfer, ISSN 0735-1933, E-ISSN 1879-0178, Vol. 68, p. 32-42Article in journal (Refereed)
    Abstract [en]

    The advantages of using Al2O3, TiO2, SiO2 and CeO2 nanofluids as coolants have been investigated by analysing the combined effect of nanoparticles on thermophysical properties and heat transfer coefficient. The thermal conductivity and viscosity of these nanofluids were measured at two leading European universities to ensure the accuracy of the results. The thermal conductivity of nanofluids agreed with the prediction of the Maxwell model within +/- 10% even at elevated temperature of 50 oC indicating that the Brownian motion of nanoparticles does not affect thermal conductivity of nanofluids. The viscosity of nanofluids is well correlated by modified Krieger-Dougherty model providing that the effect of nanoparticles aggregation is taken into account. It was found that at the same Reynolds number the advantage of using a nanofluid increases with increasing nanofluid viscosity which is counterintuitive. At the same pumping power nanofluids do not offer any advantage in terms of cooling efficiency over base fluids since the increase in viscosity outweighs the enhancement of thermal conductivity.

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