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  • 1.
    Alanne, Kari
    et al.
    Department of Energy Technology, Aalto University.
    Saari, Kari
    Department of Energy Technology, Aalto University.
    Jokisalo, Juha
    Department of Energy Technology, Aalto University.
    Martin, Andrew R.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Thermo-economic analysis of a micro-cogeneration system based on a rotary steam engine (RSE)2012In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 44, p. 11-20Article in journal (Refereed)
    Abstract [en]

    A rotary steam engine (RSE) is a simple, small, quiet and lubricant-free option for micro-cogeneration. It is capable of exploiting versatile thermal sources and steam temperatures of 150 to 180 ºC, which allow operational pressures less than 10 bar for electrical power ranges of 1 to 20 kWe. An RSE can be easily integrated in commercially available biomass-fired household boilers. In this paper, we characterize the boiler-integrated RSE micro-cogeneration system and specify a two-control-volume thermodynamic model to conduct performance analyses in residential applications. Our computational analysis suggests that an RSE integrated with a 17 kWth pellet-fuelled boiler can obtain an electrical output of 1.925 kWe, in the design temperature of 150 ºC, the electrical efficiency being 9% (LHV) and the thermal efficiency 77% (LHV). In a single-family house inFinland, the above system would operate up to 1274 h/a, meeting 31% of the house’s electrical demand. The amount of electricity delivered into the grid is 989 kWh/a. An economic analysis suggests that incremental costs not exceeding € 1,500 are justifiable at payback periods less than five years, when compared to standard boilers.

  • 2. Amos, I. G.
    et al.
    Jablonowski, T.
    Rossi, E.
    Vogt, Damian M.
    KTH, Superseded Departments, Energy Technology.
    Boncinelli, P.
    Design and off-design optimisation of highly loaded industrial gas turbine stages2004In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 24, no 12-nov, p. 1735-1744Article in journal (Refereed)
    Abstract [en]

    A European collaborative project to investigate the design of advanced industrial gas turbine stages (DAIGTS) has now completed 30 months of a 36-month programme of work. The objectives of the project were to investigate advanced aerodynamic analysis of industrial gas turbine stages, off-design performance characteristics, prediction of aero-mechanical behaviour.This paper gives an overview of the technical progress made and includes a description of the rigs used in the study. Key results include the development of advanced CFD models to include cooling and real engine geometric features, off-design performance mapping of transonic industrial turbine stages and the development of a unique oscillating cascade rig.

  • 3.
    Araoz, Joseph Adhemar
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology. Universidad Mayor de San Simon (UMSS), Bolivia.
    Salomon, Marianne
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Alejo, Lucio
    Universidad Mayor de San Simon (UMSS), Bolivia.
    Fransson, Torsten
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Non-ideal Stirling engine thermodynamic model suitable for the integration into overall energy systems2014In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, ISSN 1359-4311, Vol. 73, no 1, p. 203-219Article in journal (Refereed)
    Abstract [en]

    The reliability of modelling and simulation of energy systems strongly depends on the prediction accuracy of each system component. This is the case of Stirling engine-based systems, where an accurate modelling of the engine performance is very important to understand the overall system behaviour. In this sense, many Stirling engine analyses with different approaches have been already developed. However, there is a lack of Stirling engine models suitable for the integration into overall system simulations. In this context, this paper aims to develop a rigorous Stirling engine model that could be easily integrated into combined heat and power schemes for the overall techno-economic analysis of these systems. The model developed considers a Stirling engine with adiabatic working spaces, isothermal heat exchangers, dead volumes, and imperfect regeneration. Additionally, it considers mechanical pumping losses due to friction, limited heat transfer and thermal losses on the heat exchangers. The predicted efficiency and power output were compared with the numerical model and the experimental work reported by the NASA Lewis Research Centre for the GPU-3 Stirling engine. This showed average absolute errors around ±4% for the brake power, and ±5% for the brake efficiency at different frequencies. However, the model also showed large errors (±15%) for these calculations at higher frequencies and low pressures. Additional results include the calculation of the cyclic expansion and compression work; the pressure drop and heat flow through the heat exchangers; the conductive, shuttle effect and regenerator thermal losses; the temperature and mass flow distribution along the system; and the power output and efficiency of the engine.

  • 4.
    Araoz Ramos, Joseph Adhemar
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology. Universidad Mayor de San Simon (UMSS), Bolivia.
    Cardozo, Evelyn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology. Universidad Mayor de San Simon (UMSS), Bolivia.
    Salomon, Marianne
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Alejo, Lucio
    Universidad Mayor de San Simon (UMSS), Bolivia.
    Fransson, Torsten
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Development and validation of a thermodynamic model for the performance analysis of a gamma Stirling engine prototype2015In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 83, p. 16-30, article id 6439Article in journal (Refereed)
    Abstract [en]

    This work presents the development and validation of a numerical model that represents the performance of a gamma Stirling engine prototype. The model follows a modular approach considering ideal adiabatic working spaces; limited internal and external heat transfer through the heat exchangers; and mechanical and thermal losses during the cycle. In addition, it includes the calculation of the mechanical efficiency taking into account the crank mechanism effectiveness and the forced work during the cycle. Consequently, the model aims to predict the work that can be effectively taken from the shaft. The model was compared with experimental data obtained in an experimental rig built for the engine prototype. The results showed an acceptable degree of accuracy when comparing with the experimental data, with errors ranging from +/- 1% to +/- 8% for the temperature in the heater side, less than +/- 1% error for the cooler temperatures, and +/- 1 to +/- 8% for the brake power calculations. Therefore, the model was probed adequate for study of the prototype performance. In addition, the results of the simulation reflected the limited performance obtained during the prototype experiments, and a first analysis of the results attributed this to the forced work during the cycle. The implemented model is the basis for a subsequent parametric analysis that will complement the results presented.

  • 5.
    Baina, Fabiola
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology. Universidad Mayor de San Simón (UMSS), Bolivia .
    Malmquist, Anders
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Alejo, Lucio
    Fransson, Torsten H.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Effect of the fuel type on the performance of an externally fired micro gas turbine cycle2015In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 87, p. 150-160Article in journal (Refereed)
    Abstract [en]

    Externally fired gas turbines open the possibility of using fuels of lower quality than conventional gas turbines and internal combustion engines. This is because in externally fired gas turbines, the flue gases heat the compressed air in a high temperature heat exchanger. This heat exchanger can more easily deal with contaminants present in the flue gases. In this regard, the configuration of externally fired gas turbines represents an interesting option for biomass gasification gas. The contaminants and low heating value (LHV) of this fuel have made it difficult to find a conversion technology for heat and power generation. For this reason, it is important to study the influence of biomass derived gas as fuel on the performance of this system and consider the effects of the contaminants in the high temperature heat exchanger. This is studied in this work through simulations using Aspen Plus and Matlab. The test data of an externally fired micro gas turbine prototype was used to validate the simulation. The fuel considered was biomass gasification gas with varying concentrations of benzene 100, 10 and 1 g/Nm3 (hereafter named m100, m10, and m1 respectively). Additionally, mixtures of biomass derived gas and methane were studied for 10 and 50% of the thermal power of the combustor. The fuel inlet temperature to the combustor varied from 150 °C to 750 °C in order to represent the fuel gas after removal of particles by a cyclone and a filter. The results showed that the electrical power output increases when high fuel inlet temperatures to the combustor are used. Additionally, although it would be expected that fuels with higher LHV (lower heating value) show higher temperatures and higher output power, this does not always occur because of the composition of the fuels and their respective flue gas temperatures. The addition of methane does not have a large effect on the electrical power output. For a fixed temperature limit in the heat exchanger, the composition of the fuels does not play an important role. However, high fuel inlet temperatures to the combustor show slightly higher efficiencies. Additionally, the effect on the electrical power output of increasing the pressure drop as a result of increased thickness of deposit materials in the heat exchanger was analyzed.

  • 6.
    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.

  • 7.
    Behi, Hamidreza
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Ghanbarpour, Morteza
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Behi, Mohammadreza
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Investigation of PCM-assisted heat pipe for electronic cooling2017In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 127, p. 1132-1142Article in journal (Refereed)
    Abstract [en]

    Today, higher-power computer chips are available, but they generate too much heat that irreparably damages inside components. In this paper, a horizontal phase change material (PCM)-assisted heat pipe system for electronic cooling was introduced as a potential solution to this problem. A computational fluid dynamic model was developed and validated to assist the investigation. A surface temperature profile along the heat pipe was used to validate the CFD model. The liquid fraction and temperature distribution of PCM were reported during the charging process at different input powers. It was found that the PCM-assisted heat pipe provided up to 86.7% of the required cooling load in the working power range of 50-80 W. Contribution of PCM was calculated to be 11.7% of the provided cooling load and preventing heat dissipation.

  • 8. Belman-Flores, J. M.
    et al.
    Mota-Babiloni, A.
    Ledesma, S.
    Makhnatch, Pavel
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Using ANNs to approach to the energy performance for a small refrigeration system working with R134a and two alternative lower GWP mixtures2017In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 127, p. 996-1004Article in journal (Refereed)
    Abstract [en]

    In this paper, an artificial neural network application to model a small refrigeration system is presented. The main objective of this study is an energy comparison of three refrigerants: R134a, R450A and R513A. The application of the artificial neural network was designed to model individually three typical energy parameters: the cooling capacity, the power consumption and the coefficient of performance, as a function of the evaporating temperature and the condensing temperature. Each model was validated using a technique called cross-validation, producing minimum relative errors of 0.15 for the cooling capacity and the coefficient of performance, while 0.05 for the power consumption. Based on the appropriate validation results, computer simulations were performed to build 3D color surfaces. After inspecting these 3D color surfaces, it was concluded that R450A presented a slightly lower cooling capacity than R134a, actually a 10% reduction in the cooling capacity was estimated. Similar results were observed for the power consumption, that is, R450A had about 10% less power consumption than the other two refrigerants. On the other hand, it was observed that R134a and R513A presented very similar energy behaviors. With respect the COP, it was concluded that all three refrigerants showed a very similar behavior. After the analysis performed with the artificial neural networks and the use of 3D surface color, it was concluded that R450A and R513A are appropriate refrigerants to replace R134a in the short term in applications at medium evaporating temperature.

  • 9.
    Björk, Erik
    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.
    Nordenberg, Johan
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    A thermographic study of the on-off behavior of an all-refrigerator2010In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 30, no 14-15, p. 1974-1984Article in journal (Refereed)
    Abstract [en]

    In this work a thermographic camera is used to observe the temperature distribution of a household refrigerator cooling system operating at on off cycling conditions. This technique offers an alternative method to analyze the cooling system compared to conventional thermocouples. In particular it is interesting to view the overall picture of how the refrigerant charge is distributed over the cooling system at transient conditions. In addition, four sources of energy losses were identified and discussed. Out of these losses, two would have been difficult to find using conventional thermocouple temperature measurements. (C) 2010 Elsevier Ltd. All rights reserved.

  • 10.
    Björk, Erik T.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    A simple technique for refrigerant mass measurement2005In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 25, no 8-9, p. 1115-1125Article in journal (Refereed)
    Abstract [en]

    A simple technique for refrigerant mass measurement is described and evaluated. First, quick-closing valves trap the refrigerant in the section under consideration. Then, the refrigerant is expanded into a tank, thus reaching a superheated state. Finally the mass is calculated by p-nu-T relationship. The technique was implemented on a domestic refrigerator and was computer automated (no need for manual intervention). Preliminary (1) data are reported of the charge distribution during an on-off cycle.

  • 11.
    Björk, Erik T.
    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.
    Refrigerant mass charge distribution in a domestic refrigerator. Part I: Transient conditions2006In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 26, no 8-9, p. 829-837Article in journal (Refereed)
    Abstract [en]

    Experimental results are presented of the refrigerant mass charge distribution in a steadily cycling domestic refrigerator. In detail it is shown how the charge is displaced at compressor start-up and shut-down. At start-Lip it was found that the charge was temporarily displaced towards the condenser before returning to a steady state distribution in the latter part of the on-period. As a result, initially the evaporator was starved with a lowered evaporation temperature and a peak 10 degrees C superheat. The superheat disappeared within 3 min as the evaporator was gradually refilled with refrigerant. At shut-down the pressure equalised within 3 min as refrigerant was pushed into the evaporator from the condenser. The losses due to charge displacements were estimated to 11% (capacity) and 9% (efficiency). Possible ways to reduce the losses are discussed.

  • 12.
    Björk, Erik T.
    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.
    Refrigerant mass charge distribution in a domestic refrigerator. Part II: Steady state conditions2006In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 26, no 8-9, p. 866-871Article in journal (Refereed)
    Abstract [en]

    Experimental results are presented of the refrigerant mass charge distribution in a steady state operating domestic refrigerator at varied thermal loads. It was found that the charge decreased in the evaporator and increased in the condenser and compressor upon increased thermal load. No subcooling or superheat was observed over the range of capacities tested (74-145 W). The combination of a low side accumulator and an expansion device with high capacity (short capillary tube) explained this. The study suggests that a capillary tube throttled cooling system, with a floating condensation temperature, can handle large load variations without becoming destabilised (superheat or subcooling) just like a more sophisticated thermostatic expansion device control system.

  • 13.
    Cardozo, Evelyn
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology. Universidad Mayor de San Simón, Bolivia .
    Erlich, Catharina
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Malmquist, Anders
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Alejo, Lucio
    Integration of a wood pellet burner and a Stirling engine to produce residential heat and power2014In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 73, no 1, p. 669-678Article in journal (Refereed)
    Abstract [en]

    The integration a Stirling engine with a pellet burner is a promising alternative to produce heat and power for residential use. In this context, this study is focused on the experimental evaluation of the integration of a 20 kWth wood pellet burner and a 1 kWe Stirling engine. The thermal power not absorbed by the engine is used to produce hot water. The evaluation highlights the effects of pellet type, combustion chamber length and cycling operation on the Stirling engine temperatures and thermal power absorbed. The results show that the position of the Stirling engine is highly relevant in order to utilize as much as possible of the radiative heat from the burner. Within this study, only a 5 cm distance change between the Stirling engine and the pellet burner could result in an increase of almost 100 °C in the hot side of the engine. However, at a larger distance, the temperature of the hot side is almost unchanged suggesting dominating convective heat transfer from the hot flue gas. Ash accumulation decreases the temperature of the hot side of the engine after some cycles of operation when a commercial pellet burner is integrated. The temperature ratio, which is the relation between the minimum and maximum temperatures of the engine, decreases when using Ø8 mm wood pellets in comparison to Ø6 mm pellets due to higher measured temperatures on the hot side of the engine. Therefore, the amount of heat supplied to the engine is increased for Ø8 mm wood pellets. The effectiveness of the engine regenerator is increased at higher pressures. The relation between temperature of the hot side end and thermal power absorbed by the Stirling engine is nearly linear between 500 °C and 660 °C. Higher pressure inside the Stirling engine has a positive effect on the thermal power output. Both the chemical and thermal losses increase somewhat when integrating a Stirling engine in comparison to a stand-alone boiler for only heat production. The overall efficiency of the pellets fired Stirling engine system reached 72%.

  • 14.
    Cardozo, Evelyn
    et al.
    Univ Mayor San Simon, Fac Ciencias & Tecnol, Cochabamba, Bolivia.
    Malmquist, Anders
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Performance comparison between the use of wood and sugarcane bagasse pellets in a Stirling engine micro-CHP system2019In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 159, article id 113945Article in journal (Refereed)
    Abstract [en]

    The use of locally available agricultural residues is an interesting alternative for residential heat and power generation based on the Stirling engine technology. However, some biomass with high ash content (agricultural residues) may cause operational problems and impact on the performance of the Stirling engine and the overall CHP system. This work is focused on the evaluation of useful parameters of a CHP system based on a 20 kW(th) pellet burner, a 1 kW(e) Stirling engine and a 20 kW(th) residential boiler using wood and sugar cane bagasse pellets. Similar temperatures in the Stirling hot end were found when using both fuels under steady-state and transient conditions. CO emission levels when using bagasse were lower than for wood pellets but slightly higher levels of NOx and higher accumulated ash were found. A fouling factor of the Stirling heat exchanger was found to be around 1.1 m(2) degrees C/kW after two cycles (6 h) and 3.2 m(2) degrees C/kW after three cycles (9 h) of operation when using wood pellets. A linear relation between the Stirling power output and the accumulated ash was assessed which was used to predict a longer operation time using bagasse pellets. This shows that after three cycles of operation with bagasse pellets, without removing accumulated ash, the CHP efficiency is still kept over 83% and for wood pellets, the CHP efficiency was kept over 90%.

  • 15.
    Chen, Jianyong
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Havtun, 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.
    Investigation of ejectors in refrigeration system: Optimum performance evaluation and ejector area ratios perspectives2014In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 64, no 1-2, p. 182-191Article in journal (Refereed)
    Abstract [en]

    This paper presents an ejector model to determine the optimum performance as well as obtaining the design area ratio of an ejector in a refrigeration system. Working fluid properties and auxiliary dynamic equations are used to model the processes in the ejector. The normal compression shock in the mixing chamber is considered. Experimental data from literature are used to validate the model, and the agreement with the model at optimum operating conditions is very good. The deviation between the model and the experimental data at non-optimum conditions is slightly larger. A study of working conditions for refrigerants R123 and R141b indicates that the condenser temperature has more influence than the generator and evaporator temperatures on the area ratio and the entrainment ratio in the ejector. Furthermore, area ratios need to keep up the pace with the variation of entrainment ratio as operating conditions are changed. A variable-geometry ejector seems a very promising alternative to ensure that the ejector refrigeration system operates at its optimum conditions. Ejector efficiencies play a very important role in the present model, and the influence of the efficiencies on the ejector performance is investigated. This ejector model may be used for parametric analysis and optimum performance evaluation as well as ejector design.

  • 16.
    Chen, Jianyong
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Havtun, 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.
    Parametric analysis of ejector working characteristics in the refrigeration system2014In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 69, no 1-2, p. 130-142Article in journal (Refereed)
    Abstract [en]

    A detailed investigation of ejector working characteristics in terms of refrigeration efficiency, ejector entrainment ratio, and irreversibilities in each ejector component (nozzle, mixing chamber and diffuser) is carried out by using R141b, R245fa and R600a as the working fluids. The aim of this paper is to generalize the interactions and relationships of various ejector parameters to get better understanding of the ejector working characteristics in the refrigeration system. External and internal ejector parameters are studied separately. The operating conditions and ejector component efficiencies have significant influence on the ejector behavior, and different refrigerants perform distinctively different in the ejector refrigeration system. However, effects of superheat of the three working fluids are negligible. The irreversibility related to the shock process dominates in the diffuser and plays an important role in the ejector performance. Further attention is paid on an analysis of quantifying the ejector component efficiencies based on published test data. Correlations are established to estimate the ejector efficiency and to show how ejector parameters interact.

  • 17.
    Chen, Yang
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Lundqvist, Per Gunnar
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Johansson, Anders
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Platell, P
    A comparative study of the carbon dioxide transcritical power cycle compared with an organic rankine cycle with R123 as working fluid in waste heat recovery2006In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 26, no 17-18, p. 2142-2147Article in journal (Refereed)
    Abstract [en]

    The organic rankine cycle (ORC) as a bottoming cycle1The expression "bottoming cycle" refers to the power cycle that uses waste industrial heat for power generation by supplementing heat from any fossil fuel.1 to convert low-grade waste heat into useful work has been widely investigated for many years. The CO2 transcritical power cycle, on the other hand, is scarcely treated in the open literature. A CO2 transcritical power cycle (CO2 TPC) shows a higher potential than an ORC when taking the behavior of the heat source and the heat transfer between heat source and working fluid in the main heat exchanger into account. This is mainly due to better temperature glide matching between heat source and working fluid. The CO2 cycle also shows no pinch limitation in the heat exchanger. This study treats the performance of the CO2 transcritical power cycle utilizing energy from low-grade waste heat to produce useful work in comparison to an ORC using R123 as working fluid. Due to the temperature gradients for the heat source and heat sink the thermodynamic mean temperature has been used as a reference temperature when comparing both cycles. The thermodynamic models have been developed in EES2EES - Engineering equation solver. The thermodynamic properties for carbon dioxide in EES are calculated by the fundamental equation of state developed by R. Span and W. Wagner, A new equation of state for carbon dioxide covering the fluid region form the triple-point temperature to 1100 K at pressures up to 800 MPa, J. Phys. Chem. Ref. Data, Vol. 25, No. 6, 1996. http://www.fchart.com/ees/ees.shtml.2 The relative efficiencies have been calculated for both cycles. The results obtained show that when utilizing the low-grade waste heat with the same thermodynamic mean heat rejection temperature, a transcritical carbon dioxide power system gives a slightly higher power output than the organic rankine cycle.

  • 18.
    Chen, Yang
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Lundqvist, Per Gunnar
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Platell, P.
    Theoretical research of carbon dioxide power cycle application in automobile industry to reduce vehicle's fuel consumption2005In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 25, no 14-15, p. 2041-2053Article in journal (Refereed)
    Abstract [en]

    The current work discusses means to utilize low-grade small-scale energy in vehicle exhaust gases, to reduce the vehicle's fuel consumption and to make it run more environmental friendly. To utilize the energy in the exhaust gas, a CO2 bottoming system in the vehicle's engine system is proposed. Several basic cycles-according to the different design concepts-are presented, and the efficiencies are calculated using Engineering Equation Solver (EES).1 Several thermodynamic models in EES show that after system optimization, in CO2 Transcritical power cycle with a gas heater pressure of 130 bars and 200 °C expansion inlet temperature, about 20% of energy in the exhaust gas can be converted into useful work. Increasing the pressure in the gas heater to 300 bars and with same expansion inlet temperature, about 12% of exhaust gas energy can be converted. When raising the pressure both in the gas cooler and in the gas heater, the cycle runs completely above the critical point, and the efficiency is about 19%. Besides, in the CO2 combined cycle, the system COP is 2.322 and about 5% of exhaust gas energy can be converted.

  • 19.
    Furberg, Richard
    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.
    Boiling heat transfer on a dendritic and micro-porous surface in R134a and FC-722011In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 31, no 16, p. 3595-3603Article in journal (Refereed)
    Abstract [en]

    A visualization study was conducted with the aim of deepening the understanding of the boiling mechanism in a dendritic and micro-porous copper structure for enhanced boiling heat transfer. The unique structure has earlier been shown to enhance heat transfer in pool boiling applications as well as in convective boiling in both small and large channels. Pool boiling tests were conducted in R134a and in the dielectric fluid FC-72 and were visualized with a high speed imaging system. Data on bubble size, bubble frequency density, heat transfer coefficient and the latent and sensible heat flux contributions were collected and calculated at heat flux varying between 2 and 15 W/cm(2). The enhanced surface produces smaller bubbles and sustains a high bubble frequency density in both fluids, even at low heat flux. An enhanced latent heat transfer mechanism of up to 10 times, compared to that of a plain reference surface, is the main reason for the improved boiling heat transfer performance on the enhanced surface. The data also suggests that the high nucleation bubble frequency density leads to increased bubble pumping action and thus enhancing single-phase convection of up to 6 times. The results in this study highlight the importance of both two and single-phase heat transfer within the porous structure.

  • 20.
    Ghadamgahi, Mersedeh
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Ovako AB, Stockholm, Sweden..
    Olund, Patrik
    Ovako AB, Stockholm, Sweden..
    Ekman, Tomas
    AGA AB, Linde Grp, Lidingo, Sweden..
    Andersson, Nils
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Jönsson, Pär
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Numerical and experimental study on flameless oxy-fuel combustion in a pilot-scale and a real-size industrial furnace2018In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 141, p. 788-797Article in journal (Refereed)
    Abstract [en]

    Previously validated CFD model was used to simulate the flameless oxy-fuel combustion in a pilot-scale furnace and a full-scale soaking pit furnace. The CFD predictions for temperature were compared with experimental data measured by shielded S-type thermocouples for both furnaces. The results indicate the validity of using shielded S-type thermocouples for temperature measurement, although use of the suction pyrometers renders more accurate results. Afterwards, the validation of previously proposed CFD model for simulating the flamaless oxy-fuel combustion is investigated in a full-scale soaking pit furnace in the production route of steel bars. The validation has been done by comparing the predicted temperatures with experimental data obtained by using S-type thermocouples. For both pilot-scale and full-scale furnaces a three dimensional CFD model with realizable k-epsilon, Probability Density Function (PDF) with Steady Laminar Flamelet Model (SLFM) and Discrete Ordinates Model (DOM) with Sum of The Weighted Gray Gases Model (SGGWM) for simulating turbulence, combustion and radiation was performed. The predicted temperature results show a good agreement with measured data from shielded S-type thermocouples for pilot-scale and full-scale furnace. More specifically the maximum deviation was 3.3% and 9.95% respectively. Afterwards, the simulation results on the full-scale furnace have been used to investigate the non-uniformity of temperature distribution inside the chamber. 

  • 21.
    Ghaem Sigarchian, Sara
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Orosz, Matthew S.
    Hemond, Harry F.
    Malmquist, Anders
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Optimum design of a hybrid PV-CSP-LPG microgrid with Particle Swarm Optimization technique2016In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 109, p. 1031-1036Article in journal (Refereed)
    Abstract [en]

    Designing an energy system using multiple energy sources including renewables and providing multiple energy services (e.g. electricity, heating) can enhance the reliability and efficiency of the system while mitigating the environmental footprint. However, interaction among various components, variation of the energy demand profile, and local ambient conditions make design optimization a complex task, and suggesting that efficient simulation tools and optimization techniques can help designers to determine the best solutions within a reasonable timeframe and budget. Previous work on a dynamic microgrid simulation tool called "u-Grid" used an exhaustive search technique to find optimum configurations. However, the high computational cost of the exhaustive search was a motivation to explore alternative optimization methods to improve the optimization process and also to enhance search speed. In this paper Particle Swarm Optimization (PSO) has been presented as a global optimizer and incorporated within the problem context. Results from the exhaustive search have been used as a benchmark for testing and validation of the newly introduced optimization technique. The result shows that the PSO method is an efficient technique which has the ability to determine a high quality design solution for an optimized microgrid with a relatively low computational cost. Applying this PSO-based algorithm to the case study has reduced the total computation time a factor of about 6 in a significantly smaller computational platform.

  • 22.
    Ghanbarpour, Morteza
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Nikkam, N.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    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.
    Improvement of heat transfer characteristics of cylindrical heat pipe by using SiC nanofluids2015In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 90, p. 127-135Article in journal (Refereed)
    Abstract [en]

    An experimental study was performed to investigate the thermal performance of heat pipes using SiC/water nanofluid as the working fluid. Four cylindrical copper heat pipes containing two layers of screen mesh were fabricated and tested with water and water based SiC nanofluids with nanoparticle mass concentrations of 0.35%, 0.7% and 1.0% as working fluids. SiC nanofluids properties and characteristics are evaluated and its effects on thermal performance improvement of screen mesh heat pipes at different concentrations and inclination angles are investigated. Experimental results show that nanofluid improves the performance of the heat pipes and the thermal resistance of the heat pipe with SiC nanofluid decreases with increasing nanoparticle concentration. Thermal resistance reduction of heat pipes by 11%, 21% and 30% was observed with SiC nanofluids containing 0.35 wt.%, 0.7 wt.% and 1.0 wt.% SiC nanoparticles as compared with water. In addition, it is revealed that the inclination angle has remarkable influence on the thermal performance of the heat pipes and the lowest thermal resistance belongs to the inclination angle of 60 in all concentrations. The present investigation indicates that the maximum heat removal capacity of the heat pipe increases by 29% with SiC nanofluids at nanoparticle mass concentration of 1.0 wt.%.

  • 23.
    Gong, Shengjie
    et al.
    KTH, School of Engineering Sciences (SCI), Physics.
    Ma, Weimin
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Power Safety.
    Dinh, Truc-Nam
    KTH, School of Engineering Sciences (SCI), Physics.
    Simulation and validation of the dynamics of liquid films evaporating on horizontal heater surfaces2012In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 48, p. 486-494Article in journal (Refereed)
    Abstract [en]

    In this study a non-linear governing equation based on lubrication theory is employed to model the thinning process of an evaporating liquid film and ultimately predict the critical thickness of the film rupture under impacts of various forces resulting from mass loss, surface tension, gravity, vapor recoil and thermo-capillary. It is found that the thinning process in the experiment is well reproduced by the simulation. The film rupture is caught by the simulation as well, but it underestimates the measured critical thickness at the film rupture. The reason may be that the water wettability of the heater surfaces is not taken into account in the model. Thus, the minimum free energy criterion is used to obtain a correlation which combines the contact angle (reflection of wettability) with the critical thickness from the simulation. The critical thicknesses predicted by the correlation have a good agreement with the experimental data (the maximum deviation is less than 10%).

  • 24.
    Gong, Shengjie
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Power Safety.
    Ma, Weimin
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Power Safety.
    Li, Liangxing
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Power Safety.
    An experimental study on the effect of liquid film thickness on bubble dynamics2013In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 51, no 1-2, p. 459-467Article in journal (Refereed)
    Abstract [en]

    Experiments were conducted to investigate the boiling phenomenon in various liquid layers on a silicon heater surface with an artificial cavity. Deionized water is employed as working liquid. The emphasis is placed on how the liquid layer thickness affects bubble behaviour and liquid layer integrity for nucleate boiling under the isolated bubble regime. The experimental results show that for boiling in a liquid layer of ∼7.5 mm, the bubble dynamics reproduce the typical pool boiling characteristics with the averaged maximum diameter of 3.2 mm for the isolated bubbles growing on the cavity. As the water layer thickness decreases to the level comparable with the bubble departure diameter, the bubble is found to remain on the heater surface for an extended period, with a dry spot forming under the bubble but rewetted after the bubble rupture occurs. Further reducing the liquid layer thickness, an irreversible dry spot appears, suggesting a minimum rewettable thickness ranging from 1.2 mm to 1.9 mm corresponding to heat flux of 26 kW/m2 to 52 kW/m2. The void measured in the cavity confirms that it is dry inside the artificial cavity at high heat flux.

  • 25.
    Khodabandeh, Rahmatollah
    KTH, Superseded Departments, Energy Technology.
    Thermal performance of a closed advanced two-phase thermosyphon loop for cooling of radio base stations at different operating conditions2004In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 24, no 17-18, p. 2643-2655Article in journal (Refereed)
    Abstract [en]

    ln this investigation an advanced thermosyphon loop with extended evaporator and condenser surfaces has been tested at high heat fluxes. The thermosyphon investigated is designed for the cooling of three parallel high heat flux electronic components. The tested evaporators were made from small blocks of copper in which five vertical channels with a diameter of 1.5 mm and length of 14.6 mm were drilled. The riser and downcomer connected the evaporators to the condenser, which is an air-cooled roll-bond type with a total surface area of 1.5 m(2) on the airside. Tests were done with Isobutane (R600a) at heat loads in the range of 10-90 W/cm(2) to each of the components with forced convection condenser cooling and with natural convection with heat loads of 10-70 W.

  • 26.
    Khodabandeh, Rahmatollah
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Furberg, Richard
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Instability, heat transfer and flow regime in a two-phase flow thermosyphon loop at different diameter evaporator channel2010In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 30, no 10, p. 1107-1114Article in journal (Refereed)
    Abstract [en]

    In this study, the influence of different channel geometries on heat transfer, flow regime and instability of a two-phase thermosyphon loop, is investigated. Instabilities in flow regime and heat transfer, at low and high heat fluxes, are observed. Bubbly flow with nucleate boiling heat transfer mechanism, confined bubbly/slug flow with backflow for small channel height (H) and finally slug/churn flow at high heat fluxes are observed. This study shows that flow and thermal instability increases as channel height (H) decreases and also heat transfer coefficient increases with increasing channel height and heat flux. Bubbly flow characterizes the flow regime at high heat transfer coefficients while confined bubbles, backflow and intermittent boiling are more significant for low channel heights with lower heat transfer coefficient and critical heat flux. (C) 2010 Elsevier Ltd. All rights reserved.

  • 27. Laukkanen, Timo
    et al.
    Tveit, Tor-Martin
    Ojalehto, Vesa
    Miettinen, Kaisa
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Fogelholm, Carl-Johan
    Bilevel heat exchanger network synthesis with an interactive multi-objective optimization method2012In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 48, p. 301-316Article in journal (Refereed)
    Abstract [en]

    Heat exchanger network synthesis (HENS) has been an active research area for more than 40 years because well-designed heat exchanger networks enable heat recovery in process industries in an energy-and cost-efficient manner. Due to ever increasing global competition and need to decrease the harmful effects done on the environment, there still is a continuous need to improve the heat exchanger networks and their synthesizing methods. In this work we present a HENS method that combines an interactive multi-objective optimization method with a simultaneous bilevel HENS method, where the bilevel part of the method is based on grouping of process streams and building aggregate streams from the grouped streams. This is done in order to solve medium-sized industrial HENS problems efficiently with good final solutions. The combined method provides an opportunity to solve HENS problems efficiently also regarding computing effort and at the same time optimizing all the objectives of HENS simultaneously and in a genuine multi-objective manner without using weighting factors. This enables the designer or decision maker to be in charge of the design procedure and guide the search into areas that the decision maker is most interested in. Two examples are solved with the proposed method. The purpose of the first example is to help in illustrating the steps in the overall method. The second example is obtained from the literature.

  • 28.
    Liu, Qingming
    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.
    Numerical study of bubbles rising and merging during convective boiling in micro-channels2016In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 99, p. 1141-1151Article in journal (Refereed)
    Abstract [en]

    A three dimensional numerical study on bubble growth and merger in a micro-channel with diameter of 0.64 mm has been conducted. The working fluid is R134a and the wall material is steel. The inlet Reynolds number is set at 549 in order to keep the flow in laminar regime. Two different heat fluxes () are supplied to the wall to heat up the fluid. The coupled level set and volume of fluid (CLSVOF) method is used to capture the distorted two-phase interface. An evaporation model is also implemented through UDF (User defined function). The combination of these two methods has successfully eliminated spurious velocities which is a common problem in two phase flow simulation. The boiling and merger processes are well-predicted by the simulation. It is found that the whole process can be divided into three sub-stages: sliding, merger, and post-merger. The dynamics and heat transfer are found to be different in these stages. The evaporation rate is much higher in the first two stages due to the thermal boundary layer effects.

  • 29.
    Liu, Qingming
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Wang, Wujun
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    A numerical study of the transition from slug to annular flow in micro-channel convective boiling2017In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 112, p. 73-81Article in journal (Refereed)
    Abstract [en]

    A numerical study on the transition from slug flow (or elongated flow) to annular flow of convective boiling under high heat flux in a micro-channel with diameter of 0.4 mm is conducted. A constant velocity inlet boundary with mass flux 400 kg/m2 s, and heated wall with a constant heat flux (160, 80 kW/m2) are applied. A novel initialization method is proposed. Growth rate of the bubble and transition of the flow regime are well predicted by comparing with an experimental visualization. Effects of the transition are studied and findings are that this process disturbs thermal boundary layer which further enhances bubble evaporation.

  • 30.
    Mader, Gunda
    et al.
    Danfoss A/S, Thermodynamics and Product Concepts, Nordborgvej 81, 6430 Nordborg, Denmark .
    Thybo, Claus
    Danfoss A/S, Thermodynamics and Product Concepts, Nordborgvej 81, 6430 Nordborg, Denmark .
    A new method of defrosting evaporator coils2012In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 39, p. 78-85Article in journal (Refereed)
    Abstract [en]

    A new method is presented to defrost evaporator coils of heat pumps using air as a heat source. At low outdoor temperatures the evaporation temperature can drop below the freezing point of water, the water vapor in the air then freezes on the outer surface of the coil. This increases air side pressure drop and reduces the heat transfer capability of the evaporator coil, leading to a decrease in system efficiency. Long frost build-up times would lead to a partly or totally blocked evaporator coil, rendering the system inoperable. To maintain the functionality of the system it is therefore necessary to remove the frost regularly. For a reversible air conditioning system this is typically done by reversing the flow of the system. In the reversed mode the outdoor coil serves as a condenser, hereby melting the frost on the coil surface. Each of these defrost cycles however further reduces the system efficiency substantially. The new method uses an actively distributing valve which is able to feed parallel evaporator passes individually. With this valve single evaporator circuits are regularly shut off. While no refrigerant is evaporated in a closed circuit, the coil surface temperature increases and the flow of the ambient air is sufficient to defrost this part of the evaporator as long as the air temperature is above 0 °C. Experimental results show that under standard frost conditions the evaporator can be kept frost-free and even under severe conditions most of the highly inefficient system reversals can be avoided. Thereby system efficiency is increased significantly.

  • 31.
    Martin, Andrew R.
    et al.
    KTH, Superseded Departments, Energy Technology.
    Drotz, M.
    Talja, R.
    Kaijaluoto, S.
    Puumalainen, T.
    Energy analysis of impulse technology: research-scale experimental papermaking trials and simulations of industrial applications2004In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 24, no 16, p. 2411-2425Article in journal (Refereed)
    Abstract [en]

    The impact of impulse technology on a system-wide level has been investigated in this study for non-integrated fine paper and linerboard mills. Impulse unit data were obtained from STFI's EuroFEX research paper machine and correlations were developed in order to predict performance (dewatering, electricity consumption) under commercial operating conditions. Mill analyses were conducted for different configurations (i.e. one or two impulse units with and without web preheating) operating with roll temperatures of 200-320 degreesC. Results show that the ingoing dryness to the dryer section can be increased within a wide span, from 7 to 27 percentage points depending upon the grade and operating parameters. Even though electricity consumption rises dramatically from the inductively heated rolls, overall fuel savings of up to 20% can be achieved with either one or two impulse units operating at 200 degreesC (external power plant efficiency assumed to be 45%). Impulse technology appears to be neutral in terms of production costs since increases in energy costs are expected to be counterbalanced by savings in feedstock materials and enhanced product quality. Estimates show that this technology can lead to substantial reductions in dryer section sizes for new installations or alternatively enhance productivity in existing paper machines.

  • 32.
    Mellin, Pelle
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Energy and Furnace Technology.
    Zhang, Qinglin
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Energy and Furnace Technology.
    Kantarelis, Efthymios
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Energy and Furnace Technology.
    Yang, Weihong
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Energy and Furnace Technology.
    An Euler–Euler approach to modeling biomass fast pyrolysis in fluidized-bed reactors – Focusing on the gas phase2013In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 58, no 1-2, p. 344-353Article in journal (Refereed)
    Abstract [en]

    A developed 3D Euler–Euler CFD model, with an integrated pyrolysis model, is proposed as a way of predicting vapor phase dynamics and product distributions in the fluidized bed process for biomass fast pyrolysis. The main interest in this work is the gases resulting from the pyrolysis mixed with the fluidizing gas. We propose therefore a simple rendering of the solid material while directing attention to the vapor phase. At the same time the required computational resources for reaching stabilized conditions in the reactor are reduced. Temperature profile, velocity profile and pyrolysis products are predicted and globally verified by a series of parallel cases, which are compared to experimental measurements and known trends of liquid, solid and gas yields. The comparison of experimental measurements and model predictions satisfy the accuracy of the model and on a quantitative basis, the product yields agree with commonly known trends of bio oil versus temperature and residence time.

  • 33.
    Nikkam, Nader
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Ghanbarpour, Morteza
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Saleemi, Mohsin
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Haghighi, Ehsan Bitaraf
    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.
    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.
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Experimental investigation on thermo-physical properties of copper/diethylene glycol nanofluids fabricated via microwave-assisted route2014In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 65, no 1-2, p. 158-165Article in journal (Refereed)
    Abstract [en]

    This study investigates the fabrication, thermal conductivity and rheological characteristics evaluation of nanofluids consisting of copper nanoparticles in diethylene glycol base liquid. The fabricated Cu nanofluids displayed enhanced thermal conductivity over the base liquid. Copper nanoparticles were directly formed in diethylene glycol using microwave-assisted heating, which provides uniform heating of reagents and solvent, accelerating the nucleation of metal clusters, resulting in monodispersed nanostructures. Copper nanoparticles displayed an average primary particle size of 75 ± 25 nm from SEM micrographs, yet aggregated to form large spherical particles of about 300 nm. The physicochemical properties including thermal conductivity and viscosity of nanofluids were measured for the nanofluids with nanoparticle concentration between 0.4 wt% and 1.6 in the temperature range of 20-50 C. Proper theoretical correlations/models were applied to compare the experimental results with the estimated values for thermal conductivity and viscosity of nanofluids. For all cases, thermal conductivity enhancement was higher than the increase in viscosity showing the potential of nanofluids to be utilized as coolant in heat transfer applications. A thermal conductivity enhancement of ∼7.2% was obtained for nanofluids with 1.6 wt% nanoparticles while maximum increase in viscosity of ∼5.2% was observed for the same nanofluid.

  • 34.
    Nourozi, Behrouz
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Fluid and Climate Technology.
    Wang, Qian
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Fluid and Climate Technology. Uponor AB, Hackstavägen 1, S-72132 Västerås, Sweden..
    Ploskic, Adnan
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Fluid and Climate Technology. Bravida Holding AB, Mikrofonvägen 28, S-12637 Hägersten, Sweden..
    Energy and defrosting contributions of preheating cold supply air in buildings with balanced ventilation2019In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 146, p. 180-189Article in journal (Refereed)
    Abstract [en]

    Residential wastewater is a constant and available source for saving energy. This paper mainly investigated the possibility of utilizing wastewater heat to reduce ventilation heat load. Swedish residential buildings are to a significant extent served by mechanical ventilation with heat recovery (MVHR) systems. MVHR in airtight buildings has greatly reduced ventilation heat loads, especially in cold climate countries such as Sweden. However, cold outdoor air might lead to frost formation in heat recovery exchangers which increases the energy use. Therefore, this study focused on reducing the defrosting need by preheating the incoming cold outdoor air to MVHR during the coldest days. The effects of preheating the incoming air to MVHR on ventilation heat load and annual ventilation heating demand were also studied. It was found that the heat recovery efficiency of MVHR is the most decisive factor in rating the performance of the combined system with an air preheater. Contributions of the studied air preheater to annual energy savings were negligible. On the other hand, the reduction of the initial defrosting need was significant. The obtained results showed that the defrosting need in a building located in central Sweden in two cases of an MVHR system equipped with a rotary heat exchanger/plate heat exchanger was eliminated/reduced to one-third. The defrosting need was reduced by 50% in northern Sweden for both cases.

  • 35.
    Oró, Eduard
    et al.
    GREA UdL.
    Chiu, NingWei Justin
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Martin, Viktoria
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Cabeza, Luisa
    GREA UdL.
    Comparative study of different numerical models of packed bed thermal energy storage systems2013In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 50, no 1, p. 384-392Article in journal (Refereed)
    Abstract [en]

    This paper presents, compares and validates two different mathematical models of packed bed storage with PCM, more specifically the heat transfer during charge of the PCM. The first numerical model is a continuous model based on the Brinkman equation and the second numerical model treats the PCM capsules as individual particles (energy equation model). Using the Brinkman model the flow field inside the porous media and the heat transfer mechanisms present in the packed bed systems can be described. On the other hand, using the energy equation model the temperature gradient inside the PCM capsules can be analysed. Both models are validated with experimental data generated by the authors. The experimental set up consists mainly of a cylindrical storage tank with a capacity of 3.73 L full of spherically encapsulated PCM. The PCM used has a storage capacity of 175 kJ/kg between −2–13 °C. The results from the energy equation model show a basic understanding of cold charging. Moreover, three different Nu correlations found in the literature were analysed and compared. All of them showed the same temperature profile of the PCM capsules; hence any of them could be used in future models. The comparison between both mathematical models indicated that free convection is not as important as forced convection in the studied case.

  • 36.
    Owhaib, Wahib Suleiman
    et al.
    KTH, Superseded Departments, Energy Technology.
    Martín-Callizo, Claudi
    KTH, Superseded Departments, Energy Technology.
    Palm, Björn
    KTH, Superseded Departments, Energy Technology.
    Evaporative heat transfer in vertical circular microchannels2004In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 24, no 8-9, p. 1241-1253Article in journal (Refereed)
    Abstract [en]

    This paper presents new experimental results on saturated flow boiling in microchannels. Heat transfer coefficients were measured for saturated boiling of R134a in vertical circular tubes with internal diameters of 1.7, 1.224 and 0.826 mm, and a uniformly heated length of 220 mm. Heat transfer coefficients were obtained for a heat flux range of 3-34 kW/m(2), a mass flux range of 50-400 kg/m(2) s, and vapour qualities up to 0.6. Experiments were conducted at two different pressures, 8.626 and 6.458 bars. Heat transfer coefficients were found to be a strong function of the wall heat flux and system pressure, while being fairly independent upon mass flux and vapour quality. This suggests that the heat transfer mechanism is strongly related to that in nucleate boiling.

  • 37.
    Owhaib, Wahib Suleiman
    et al.
    KTH, Superseded Departments, Energy Technology.
    Palm, Björn
    KTH, Superseded Departments, Energy Technology.
    Martín-Callizo, Claudi
    KTH, Superseded Departments, Energy Technology.
    Experimental investigation of single-phase pressure drop in circular minichannelIn: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606Article in journal (Refereed)
  • 38.
    Palm, Björn E.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Refrigeration systems with minimum charge of refrigerant2007In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 27, no 10, p. 1693-1701Article in journal (Refereed)
    Abstract [en]

    Concern for the environmental effects of HFC-refrigerants as well as the use of flammable refrigerants has resulted in a need of decreasing the refrigerant charge in refrigeration and heat pump systems. This paper discusses the possibility of such reductions, both at the systems- and the component level. It is shown that a move towards indirect systems, using secondary refrigerants, on both the cold and the hot side of the system may result in considerable reduction of charge. However, this reduction may come at the cost of slightly reduced system performance, which in itself is detrimental from an environmental point of view. At the component level, it may be shown that the main contents of refrigerant is usually contained in the heat exchangers. By selecting compact designs the charge may be reduced to extremely low levels. Specifically, mini-channel heat exchangers can be used for reaching low charge. With proper selection of heat exchangers, the system performance should not be influenced by the reduction of charge. For indirect systems, the amount of refrigerant solved in the compressor oil may be comparable to the amount in the (compact) heat exchangers. A possible solution to reduce this amount is to use compressors with less oil. With components selected for minimum charge, the system design may be different than what is usual. Instead of a high pressure receiver and a thermostatic expansion valve, a capillary tube may be used in combination with a minimal low pressure receiver, similar to the system design used in household refrigerators.

  • 39. Paulino, T. D. F.
    et al.
    de Oliveira, R. N.
    Maia, A. A. T.
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Machado, L.
    Modeling and experimental analysis of the solar radiation in a CO2 direct-expansion solar-assisted heat pump2019In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, p. 160-172Article in journal (Refereed)
    Abstract [en]

    In the present work is presented the dynamic model of an evaporator of a Direct Expansion Solar Assisted Heat Pump (DX-SAHP), charged with CO2. This dynamic model was used to analyze the evaporator response to sudden variations in the solar radiation. Two strategies are used to make the system reach the steady state after the heat pump start-up. The first one is the usual balances of mass, energy and momentum. The second strategy consisted in impose an equal refrigerant mass flow rate at the evaporator inlet and outlet. Both strategies were able to conduct the system to a steady state, however, the second one required less computational effort. The mathematical model was validated using experimental data and employed to perform several simulations. The results obtained with the mathematical model revealed that a small variation of the solar radiation leads to a significant variation in the superheat, therefore requiring an immediate action of the expansion device. It was concluded that an Electronic Expansion Valve (EEV) would be better suited to meet the needs of rapid interventions on the mass flow rate at the evaporator inlet, and also because the DX-SAHP could operate in a continuous transient condition in some seasons.

  • 40.
    Persson, Tomas
    Högskolan i Dalarna.
    Dishwasher and washing machine heated by a hot water circulation loop2007In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 27, no 1, p. 120-128Article in journal (Refereed)
    Abstract [en]

    Electric energy (70-90%) used by electrically heated dishwashers and washing machines is used for heating the water, the crockery, the laundry and the machine and could as well be replaced by heat from other sources than electricity. This article evaluates prototypes of a dishwasher and a washing machine, where the machines are heated by a hot water circulation loop and the heat is transferred to the machines via a heat exchanger. The machine therefore uses water from the cold water pipe. Measurements and simulations have been performed showing that all energy for heating can be replaced if the supply water temperature is 65-70 degrees C. An alternative and common way to save electricity is to connect the machines to the domestic hot water pipe, but the electrical savings with this measure are much smaller, especially for the dishwasher. Computer modelling has been performed and the model has proved to have a high agreement with measured data. However comparison with manufacturers' data indicates that the computer models overestimate the energy demand by about 10%.

  • 41.
    Persson, Tomas
    et al.
    Högskolan i Dalarna.
    Rönnelid, Mats
    Högskolan i Dalarna.
    Increasing solar gains by using hot water to heat dishwashers and washing machines2007In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 27, p. 646-657Article in journal (Refereed)
    Abstract [en]

    Seventy to ninety percent of the electric energy used by dishwashers and washing machines heats the water, the crockery, the laundry and the machine and could just as well be replaced by heating energy from solar collectors, district heating or a boiler. A dishwasher and a washing machine equipped with a heat exchanger and heated by a hot water circulation circuit instead of electricity (heat-fed machines) have been simulated together with solar heating systems for single-family houses in two different climates (Stockholm, Sweden and Miami, USA). The simulations show that a major part of the increased heat load due to heat-fed machines can be covered by solar heat both in hot and cold climates if the collector area is compensated for the larger heat load to give the same marginal contribution. Using ordinary machines connected to the hot water pipe (hot water-fed machines) and using only cold water for the rinses in the washing machine gives almost the same solar contribution; however considerably lower electrical energy savings are achieved. The simulations also indicate that improvements in the system design of a combisystem (increased stratification in the store) are more advantageous if heat-fed machines are connected to the store. Thus, using heat-fed machines also encourages the use of more advanced solar combisystems

  • 42.
    Ploskic, Adnan
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Fluid and Climate Technology.
    Wang, Qian
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Fluid and Climate Technology.
    Evaluating the potential of reducing peak heating load of a multi-family house using novel heat recovery system2018In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 130, p. 1182-1190Article in journal (Refereed)
    Abstract [en]

    The current study evaluated the potential of reducing ventilation heat load by using heat from waste water in mechanical ventilation with heat recovery (MVHR) served Swedish residential buildings. A typical Swedish low-energy, multi-family house locating at the northern part of Sweden was selected to present the analysis. The building was locating at the northern part of Sweden and was served by mechanical ventilation with heat recovery (MVHR). The data from on-site measurements and analytical model were applied to evaluate the reduction potential of the suggested heat recovery system. The study focused on the evaluation of benefit of using an air preheater in front of the existing MVHR system. Two different sizes of an air preheater design: Small air preheater with the size of 0.4 m x 0.4 m x 0.4 m (AP(0.4mx0.4 mx0.4 m)), feed with waste water flow of 0.15 kg/s (from storage tank to air preheater); and a large air preheater with the size of 0.8 m x 0.8 m x 0.4 m (AP(0.8 mx0.8 mx0.4 m)), feed with waste water flow of 0.2 kg/s. It was found that the heat recovery efficiency of MVHR is the core to determine the selection of air preheaters. In comparison to the MVHR without air preheater, maximum air supply temperature improvements of 25% and 41% were found from AP(0.4mx0.4 mx0.4 m) and AP(0.8 mx0.8 mx0.4 m), respectively. The studied system reached its highest contributions when the heat recovery efficiency of MVHR was between 80% and 85%. On average, AP(0.4mx0.4 mx0.4 m) can reduced the peak heat load up to 27%. AP(0.8 mx0.8 mx0.4 m) can reduce the peak heat load up to 40% in the studied climate.

  • 43.
    Ploskic, Adnan
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Fluid and Climate Technology.
    Wang, Qian
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Fluid and Climate Technology.
    Reducing the defrosting needs of air-handling units by using heat from wastewater in apartment buildings in cold climates2019In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 157, article id 113647Article in journal (Refereed)
    Abstract [en]

    This paper is the second part of a two-part series that investigates the energy-saving potentials of a novel wastewater heat recovery system connected to mechanical ventilation with heat recovery (MVHR). The main idea is to use the heat from stored wastewater to preheat the incoming cold outdoor airflow to the MVHR and thereby reduce the defrosting needs of the MVHR. The study evaluated the potential of two air preheaters, AP 0.4 m x 0.4 m x 0.4 m and AP 0.8 m x 0.8 m x 0.4 m , placed in front of the existing MVHR. Dynamic simulations in this study have shown that the smaller air preheater could lower the frost threshold temperature by 5 °C and the larger one could reduce it by 11 °C. Without an air preheater, the defrosting was needed during nearly two-thirds of January in the studied climate. By contrast, with the evaluated air preheaters in front of the MVHR, the defrosting was needed during 45% and 20% of the evaluation period, respectively. The results also showed that frost growth inside the heat exchanger could be reduced by 38% with AP 0.4 m x 0.4 m x 0.4 m and by 62% with AP 0.8 m x 0.8 m x 0.4 m during the peak load. The main conclusion is that the suggested heat recovery system has good potential for improving the overall performance of MVHR systems in cold climates. © 2019 Elsevier Ltd

  • 44.
    Ploskić, Adnan
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Fluid and Climate Technology.
    Holmberg, Sture
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Fluid and Climate Technology.
    Performance evaluation of radiant baseboards (skirtings) for room heating - An analytical and experimental approach2014In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 62, no 2, p. 382-389Article in journal (Refereed)
    Abstract [en]

    The aim of this study was to investigate the thermal performance of the hydronic radiant baseboards currently used for space heating in built environments. The presently available equations for determination of heat outputs from these room heaters are valid for a certain height at a specific temperature range. This limitation needed to be addressed as radiant baseboards may be both energy and cost efficient option for space heating in the future. The main goal of this study was therefore to design an equation valid for all baseboard heights (100-200 mm) and excess temperatures (9-60 C) usually used in built environments. The proposed equation was created by curve fitting using the standard method of least squares together with data from previous laboratory measurements. It was shown that the predictions by the proposed equation were in close agreement with reported experimental data. Besides, it was also revealed that the mean heat transfer coefficient of the investigated radiant baseboards was about 50% higher than the mean heat transfer coefficient of five conventional panel radiators of different types. The proposed equation can easily be used or programed in energy simulation codes. Hopefully this will help engineers to quantify more accurately the energy consumption for space heating in buildings served by radiant baseboards.

  • 45.
    Rafidi, Nabil
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Energy and Furnace Technology.
    Blasiak, Wlodzimierz
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Energy and Furnace Technology.
    Heat transfer characteristics of HiTAC heating furnace using regenerative burners2006In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 26, no 16, p. 2027-2034Article in journal (Refereed)
    Abstract [en]

    The aim is to experimentally study the various modes of heat transfer and to investigate the effect of the HiTAC flame characteristics on the heat transfer intensity and uniformity inside a setni-industrial test furnace using various industrial regenerative burners and various flame configurations namely; single-flame, twin-flame counter. twin-flame parallel and twin-flame stagger. Measurements of local instantaneous and average temperatures, heat fluxes and gas composition at several locations inside the furnace were carried out. It was observed that the HiTAC flame with highly reduced temperature fluctuations. turbulent intensity and combustion intensity have a larger reaction zone than a conventional flame. This large flame emits more thermal radiation in spite of its uniform and reduced temperature. Furthermore, the convective heat transfer was found to be uniform and as high as 30% of the total heat transfer to an object surface in the furnace. On the other hand, the very high reduction of NOx emission is a consequence of the low temperature and temperature fluctuation levels of the HiTAC flames. The above findings are valid to a similar extent in all burners and configurations but to less extent in the twin-flame counter configuration.

  • 46.
    Rafidi, Nabil
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Energy and Furnace Technology.
    Blasiak, Wlodzimierz
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Energy and Furnace Technology.
    Thermal performance analysis on a two composite material honeycomb heat regenerators used for HiTAC burners2005In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 25, no 17-18, p. 2966-2982Article in journal (Refereed)
    Abstract [en]

    Honeycomb heat regenerators do not only reduce the fuel consumption in a high temperature air combustion (HiTAC) burning system but also provide the necessary high temperature of combustion air. A two-dimensional simulation model was developed to numerically determine the dynamic temperature and velocity profiles of gases and solid heat-storing materials in a composite material honeycomb regenerator. Consequently, the energy storage and the pressure drop are calculated and the thermal performance of honeycomb heat regenerator is evaluated at different switching times and loading. The model takes into account the thermal conductivity parallel and perpendicular to flow direction of solid and flowing gases. It considers the variation of all thermal properties of solid material and gases with temperature, Moreover, the radiation from combustion flue gases to the storage materials was considered in the analysis, The results are presented in a non-dimensional form in order to be a design tool as well, These analyses were applied on a regenerator made of two layers of ceramic materials, one is pure alumina and other is cordierite. This regenerator is contained in a. 100 kW twin-type regenerative-burning system used for HiTAC. The effectiveness and the energy recovery rate were 88% and 72% respectively at nominal operating range of the regenerator and the pressure drop across the twin regenerator system wits 1.16 kPa. The periodic steady state condition is reached after about 11 min and it takes only 2 min of operation until the temperature of combustion air remains above the self-ignition temperature that is required for HiTAC. Furthermore. these mathematical analyses show good agreement with experiments made on the same regenerator. In the experiments, the dynamic behavior of the heat regenerator operation was considered in order to compensate measurement readings for this effect.

  • 47.
    Ruiz-Calvo, Félix
    et al.
    Universitat Politècnica de València.
    De Rosa, Mattia
    Queen’s University Belfast.
    Monzó, Patricia
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Montagud, Carla
    Universitat Politècnica de València.
    Corberán, José Miguel
    Universitat Politècnica de València.
    Coupling short-term (B2G model) and long-term (g-function) models for ground source heat exchanger simulation in TRNSYS. Application in a real installation2016In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 105, p. 720-732Article in journal (Refereed)
    Abstract [en]

    Ground-source heat pump (GSHP) systems represent one of the most promising techniques for heating and cooling in buildings. These systems use the ground as a heat source/sink, allowing a better efficiency thanks to the low variations of the ground temperature along the seasons. The ground-source heat exchanger (GSHE) then becomes a key component for optimizing the overall performance of the system. Moreover, the short-term response related to the dynamic behaviour of the GSHE is a crucial aspect, especially from a regulation criteria perspective in on/off controlled GSHP systems. In this context, a novel numerical GSHE model has been developed at the Instituto de Ingeniería Energética, Universitat Politècnica de València. Based on the decoupling of the short-term and the long-term response of the GSHE, the novel model allows the use of faster and more precise models on both sides. In particular, the short-term model considered is the B2G model, developed and validated in previous research works conducted at the Instituto de Ingeniería Energética. For the long-term, the g-function model was selected, since it is a previously validated and widely used model, and presents some interesting features that are useful for its combination with the B2G model. The aim of the present paper is to describe the procedure of combining these two models in order to obtain a unique complete GSHE model for both short- and long-term simulation. The resulting model is then validated against experimental data from a real GSHP installation.

  • 48.
    Sakowitz, Alexander
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Mihaescu, Mihai
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Fuchs, Laszlo
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Flow decomposition methods applied to the flow in an IC engine manifold2014In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 65, no 1-2, p. 57-65Article in journal (Refereed)
    Abstract [en]

    Large Eddy Simulation (LES) of the flow and mixing in an engine manifold of a six cylinder Diesel engine is carried out. Proper Orthogonal Decomposition (POD) and Dynamical Mode Decomposition (DMD) are applied to sets of LES data from these computations. The engine manifold under consideration includes a pipe-junction used for Exhaust Gas Recirculation (EGR). The methods of analysis, POD and DMD, are applied to the velocity field and the exhaust concentration field. It is found that POD facilitates the analysis of the pulsating, complex and turbulent flow field as compared to instantaneous fields. The flow field is dominated by the EGR pulses and their interaction with other pulses originating from the cylinder valves. The maldistribution of EGR concentration among the first cylinder ports can clearly be linked to the EGR pulsations. DMD is able to extract flow structures at certain frequencies. Using these properties of DMD, the motion of the EGR pulses can be extracted and visualized. The combination of LES and flow decomposition is found to give a rational for the interpretation of the flow phenomena, which might facilitate the optimization of engine manifolds in terms of EGR non-uniformity.

  • 49.
    Sawalha, Samer
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Karampour, Mazyar
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Rogstam, Jörgen
    Field measurements of supermarket refrigeration systems: Part I: Analysis of CO2 trans-critical refrigeration systems2015In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 87, p. 633-647Article in journal (Refereed)
    Abstract [en]

    This study investigates the refrigeration performance of three CO2 trans-critical solutions based on field measurements. The measurements are carried out in five supermarkets in Sweden. Using the field measurements, low and medium temperature level cooling capacities and COP's are calculated for ten-minute intervals, filtered and averaged to monthly values. The results indicate that the systems using trans-critical booster system with gas removal from the intermediate vessel have relatively the highest total COP. The reasons are higher evaporation temperatures, lower internal and external superheat and higher total efficiency of booster compressors. Another important factor is gas removal from the intermediate vessel which leads to higher COP of low temperature level. Comparing the older and newer installed systems, a trend in energy efficiency improvement has been seen. The study shows this improvement originates from both changes in the system design (e.g. two stage expansion) and components efficiency improvement (e.g. higher total efficiency of compressors - lower internal superheat and higher evaporation temperatures of cabinets).

  • 50.
    Sawalha, Samer
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Piscopiello, Salvatore
    KTH.
    Karampour, Mazyar
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Manickam, Louis
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Power Safety.
    Rogstam, Jörgen
    KTH.
    Field measurements of supermarket refrigeration systems. Part II: Analysis of HFC refrigeration systems and comparison to CO2 trans-critical2017In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 111, no 1, p. 170-182Article in journal (Refereed)
    Abstract [en]

    This part of the study investigates the performance of HFC refrigeration systems for supermarkets and compares the performance with alternative CO2 trans-critical solutions. The investigated HFC system solutions are typical in supermarkets in Sweden. The analysis in this study is based on field measurements which were carried out in three supermarkets in Sweden. The results are compared to the findings from Part I of this study where five CO2 trans-critical systems were analyzed. Using the field measurements, low and medium temperature level cooling demands and COP’s are calculated for five-minute intervals, filtered and averaged to monthly values. The different refrigeration systems are made comparable by looking at the different COP’s versus condensing temperatures. The field measurement analysis is combined with theoretical modelling where the annual energy use of the HFC and CO2 trans-critical refrigeration systems is calculated. Comparing the field measurement and modelling results of COP’s for HFC and CO2 systems, the new CO2 systems have higher total COP than HFC systems for outdoor temperatures lower than about 24 C. The modelling is used to calculate the annual energy use of HFC and new CO2 system in an average size supermarket in Stockholm, new CO2 systems use about 20% less energy than a typical HFC system. The detailed analysis done in this study (Part I and Part II) proves that new CO2 trans-critical refrigeration systems are more energy efficient solutions for supermarkets than typical HFC systems in Sweden.

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