Change search
Refine search result
12345 151 - 200 of 207
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
  • 151.
    Monfared, Behzad
    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.
    New magnetic refrigeration prototype with application in household and professional refrigerators2016In: Refrigeration Science and Technology Proceedings, 2016Conference paper (Refereed)
    Abstract [en]

    The number of magnetic refrigeration prototypes with high cooling capacity and large temperature span islimited and there is ample room for new designs and improvements. In this paper a new prototype, designedand built, aiming at 200 W cooling capacity and about 40 K temperature span is presented. Such a unit issuitable for applications in household and professional refrigerators. In the current work, design of theprototype is described, practical issues solved to make the prototype running are explained, and preliminarytest results are presented.

  • 152.
    Monfared, Behzad
    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.
    Optimization of layered regenerator of a magnetic refrigeration device2015In: International journal of refrigeration, ISSN 0140-7007, E-ISSN 1879-2081, Vol. 57, p. 103-111Article in journal (Refereed)
    Abstract [en]

    Magnetic refrigeration, as an alternative to vapor-compression technology, has been the subject of many recent investigations. A technique to enhance the performance of magnetic refrigerators is using layers of different materials in the regenerator of such devices. In this study the choice of magnetocaloric materials in a multi-layered packed bed regenerator is investigated in order to optimize the performance. A numerical model has been developed to simulate the packed bed in this study. Optimized packed bed designs to get maximum temperature span or maximum efficiency are different. The results indicate that maximum temperature span can be achieved by choosing the materials with the highest magnetocaloric effect in the working temperature range, while maximum Carnot efficiency is achieved by choosing materials with Curie temperatures above the average layer temperature.

  • 153.
    Monfared, Behzad
    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.
    Small Ammonia Heat Pump with Variable Speed Compressor2012Conference paper (Refereed)
    Abstract [en]

    Ammonia is a natural refrigerant which has been used continuously for more than 100 years. From almost any technical perspective, it is an attractive refrigerant, having good cycle efficiency, good heat transfer properties and low pressure drop compared to most other refrigerants. The volumetric refrigerating effect is also higher than for other fluids of the same vapor pressure. Applications are nowadays restricted almost exclusively to large industrial or commercial systems.

    We have previously demonstrated that ammonia is also a viable refrigerant for small systems (Palm 2008, Monfared and Palm 2011). In this paper we report on additional tests with a small capacity (7.2 kW) water to water heat pump for sanitary hot water production and space heating. Particularly, the losses in the compressor, electric motor and variable speed drive are investigated under full and part load conditions. New data for the general performance of the heat pump in terms of heat delivered at 60 °C for sanitary hot water production and at 40 °C for space heating, energy efficiency, etc. will also be reported.

  • 154.
    Monzó, Patrcia
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Acuna, Jose
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Fossa, Marco
    University of Genova.
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Numerical generation of the temperature response factors for  a borehole heat exchanger field2013In: Numerical generation of the temperature response factors for  a borehole heat exchanger field, 2013Conference paper (Refereed)
    Abstract [en]

    Ground Coupled Heat Pump (GCHP) systems connected to a set of vertical ground heat exchangers require short and long term dynamic analysis of the surrounding ground for an optimal operation. The thermal response of the ground for a multiple Borehole Heat Exchanger (BHE) field can be described by proper temperature response factors or “g-functions”. This concept was firstly introduced by Eskilson (1987). The g-functions are a family of solutions of the transient heat conduction equation and each of them refer to a given borehole field geometry. Furthermore the g-functions are the core of many algorithms for simulating the ground response to a GCHP system, including the well-known commercial software EED.

    Analytical approaches based on the Finite Line Source (FLS) model have been developed by Eskilson (1987), Zeng et al. (2002) and later by Lamarche (2007). Such solutions can be in principle applied together with space superposition to infer the thermal response for any BHE configuration.

    This study is a continuation of the previous work presented in Acuña et al. (2012), and a further investigation is devoted to optimize a numerical model of a squared configuration of 64 boreholes using the commercial software Comsol Multiphysics©. Symmetry conditions and different Fourier numbers have been applied and explored together with the effects related to the dimensions of the calculation domain with respect to the BHE depth and BHE field width. Furthermore, a parametric analysis is addressed to boundary conditions, which points out possible limits on the calculation domain extension. The results of the proposed numerical model are compared with the g-functions embedded within the EED software as well as those calculated by FLS method through the spatial superposition. In a closer approximation to reality, the numerical model is also studied accounting for an adiabatic part at the top of the BHE.

  • 155.
    Monzó, Patrcia
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Acuna, Jose
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Mogensen, Palne
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    A study of the thermal response of a borehole field in winter and summer2013In: : ICAE2013-524, 2013Conference paper (Refereed)
    Abstract [en]

    A Ground Source Heat Pump system is a well-known technology used to provide space heating and cooling in residential and commercial buildings. For large energy demands, a number of boreholes, which can vary between tens and hundreds, may be required. The boreholes can be arranged in linear, square, rectangular, or any other configuration not necessarily symmetric. The heat exchangers in the boreholes are typically connected in parallel. Recently, the idea of a more flexible configuration of multiple Borehole Heat Exchangers (BHEs) has been introduced in commercial applications, enabling the system to operate in a more versatile manner, dividing the ground into different thermal zones. In this new arrangement, the BHEs are connected into thermal sub-groups allowing them to operate separately as sub-systems, depending on the building energy needs and the seasonal periods.

     

    In this project, the temperature response of a multiple BHE configuration is obtained from simulations in a numerical model using FEM software, Comsol Multiphysics© under different operational conditions. First, the loads are imposed under the usual conditions so that all boreholes are operated to provide heating in winter and cooling in summer. The results of this study show that our numerical model presents a good agreement with the ones generated from EED when the system is balanced. Moreover, some hypothetical scenarios with respect to the BHEs arrangement and the operational mode are performed thanks to the flexibility of our numerical model. The hypothetical scenarios provide a first approach about the thermal behavior of the boreholes and their interactions within the field with respect to its wall temperature, previous operation and thermal storage. Further work will be devoted to study more realistic scenarios.

  • 156.
    Monzó, Patricia
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Acuña, José
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Analysis of the influence of the heat power rate variations in different phases of a Distributed Thermal Response Test2012Conference paper (Refereed)
  • 157.
    Mälhammar, Åke
    et al.
    KTH, Superseded Departments, Energy Technology.
    Palm, Björn
    KTH, Superseded Departments, Energy Technology.
    Kylsystem för Elektronik1995Patent (Other (popular science, discussion, etc.))
    Abstract [en]

    The present invention relates to a cooling system, especially for electronic components, comprising a hermetically closed pipe conduit including evaporator and condenser and utilizing thermosiphon circulation of the refrigerant used in the pipe conduit, the evaporator being in heat conducting contact with a heat emitting component to be cooled and absorbs heat therefrom, the heat being transported through the pipe conduit by the refrigerant to the condenser and dissipated therein. According to the invention the pipe conduit (3) includes a plurality of evaporators (1a, 1b, 1c) in series, each being in heat conducting contact with a heat emitting component, and the condenser (2) is placed so that the liquid level of the condensed refrigerant is below the uppermost situated evaporator (1c) in the pipe conduit (3). This is rendered possible by the increased pumping action achieved by the evaporators (1a, 1b, 1c) connected together in series in the circulation direction after the evaporators partly evaporated refrigerant used in the pipe conduit (3).

  • 158.
    Nikkam, Nader
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Bitaraf Haghigh, Ehsan
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Saleemi, Mohsin
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Behi, Mohammadreza
    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 study on preparation and base liquid effect on thermo-physical and heat transport characteristics of α-SiC nanofluids2014In: International Communications in Heat and Mass Transfer, ISSN 0735-1933, E-ISSN 1879-0178, Vol. 55, p. 38-44Article in journal (Refereed)
    Abstract [en]

    Nanostructured solid particles dispersed in a base liquid are a new class of nano-engineeredcolloidal solutions, defined with a coined name of nanofluids (NFs). These fluids have shownpotential to enhance heat transfer characteristics of conventional base liquids utilized in heattransfer application. We recently reported on the fabrication and thermo-physical propertyevaluation of SiC NFs systems, containing SiC particles with different crystal structure. In thisstudy, our aim is to investigate the heat transfer characteristics of a particular α-SiC NF withrespect to the effect of α-SiC particle concentration and different base liquids on the thermophysicalproperties of NFs. For this purpose, a series of NFs with various α-SiC NPsconcentration of 3, 6 and 9wt% were prepared in different base liquids of distilled water (DW)and distilled water/ethylene glycol mixture (DW/EG). Their thermal conductivity (TC) andviscosity were evaluated at 20 oC. NF with DW/EG base liquid and 9wt% SiC NPs loadingexhibited the best combination of thermo-physical properties, which was therefore selected forheat transfer coefficient (HTC) evaluation. Finally, HTC tests were performed and compared indifferent criteria, including equal Reynolds number, equal mass flow rate and equal pumpingpower for a laminar flow regime. The results showed HTC enhancement of NF over the baseliquid for all evaluation criteria; 13% at equal Reynolds number, 8.5% at equal volume flow and5.5% at equal pumping power. Our findings are among the few studies in the literature where theheat transfer enhancement for the NFs over its base liquid is noticeable and based on a realistic situation.

  • 159.
    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.

  • 160.
    Nikkam, Nader
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Saleemi, Mohsin
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Bitaraf Haghighi, Ehsan
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Ghanbarpour, Morteza
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Toprak, Muhammet
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    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.
    Design and Fabrication of Efficient Nanofluids Based on SiC Nanoparticles for Heat Exchange Applications2013Conference paper (Other academic)
  • 161.
    Nikkam, Nader
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Saleemi, Mohsin
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Haghighi, Ehsan Bitaraf
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Ghanbarpour, Morteza
    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.
    Fabrication, Characterization and Thermo-physical Property Evaluation of SiCNanofluids for Heat Transfer Applications2014In: Nano-Micro Letters, ISSN 2150-5551, Vol. 6, no 2, p. 178-189Article in journal (Refereed)
    Abstract [en]

    Nanofluids (NFs) are nanotechnology-based colloidal suspensions fabricated by suspending nanoparticles (NPs) in a base liquid. These fluids have shown potential to improve the heat transfer properties of conventional heat transfer fluids. In this study we report in detail on the fabrication, characterization and thermo-physical property evaluation of SiC NFs, prepared using SiC NPs with different crystal structure, for heat transfer applications.  For this purpose, a series of SiC NFs containing SiC NPs with different crystal structure (α-SiC and β-SiC) were fabricated in a water (W)/ethylene glycol (EG) mixture (50/50 wt % ratio). Physicochemical properties of NPs/NFs were characterized by using various techniques such as powder X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Fourier Transform Infrared Spectroscopy (FTIR), Dynamic Light Scattering (DLS) and Zeta Potential Analysis were performed. Thermo-physical properties including thermal conductivity (TC) and viscosity for NFs containing SiC particles (α- and β- phase) were measured. The results showed among all suspensions, NF fabricated with α-SiC particles have more favorable thermo-physical properties compared to the NFs fabricated with β-SiC; the observed difference was attributed to combination of several factors, including crystal structure (β- vs. α-), sample purity, and residual chemicals exhibited on SiC nanoparticles. A TC enhancement of ~20% while 14% increased viscosity were obtained for a NF containing 9wt% of particular type of α-SiC NPs indicating promising capability of these kind of NFs for further heat transfer characteristics investigations. 

  • 162.
    Nikkam, Nader
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Saleemi, Mohsin
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Li, S
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Toprak, Muhammet
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Muhammed, Mamoun
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Bitaraf Haghighi, Ehsan
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Khodabandeh, Rahmatollah
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Palm, Björn E
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Novel Nanofluids Based on Mesoporous Silica for Enhanced Heat Transfer2011In: Journal of nanoparticle research, ISSN 1388-0764, E-ISSN 1572-896X, Vol. 13, no 11, p. 6201-6206Article in journal (Refereed)
    Abstract [en]

    Nanofluids, which are liquids with engineered nanometer-sized particles suspensions, have drawn remarkable attraction from the researchers because of their enormous potential to enhance the efficiency in heat-transfer fluids. In the present study, water-based calcined mesoporous silica nanofluids were prepared and characterized. The commercial mesoporous silica (MPSiO2) nanoparticles were dispersed in deionized water by means of pH adjustment and ultrasonic agitation. MPSiO2 nanoparticles were observed to have an average particle size of 350 ± 100 nm by SEM analysis. The concentration of MPSiO2 was varied between 1 and 6 wt%. The physicochemical properties of nanofluids were characterized using various techniques, such as particle size analyzer, zeta-potential meter, TEM, and FT-IR. The thermal conductivity was measured by Transient Plane Source (TPS) method, and nanofluids showed a higher thermal conductivity than the base liquid for all the tested concentrations.

  • 163.
    Nikkam, Nader
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Saleemi, Mohsin
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Toprak, Muhammet
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Muhammed, Mamoun
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Bitaraf Haghighi, Ehsan
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Khodabandeh, Rahmatollah
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Microwave-assisted Synthesis of Copper Nanofluids for Heat Transfer Applications2011Conference paper (Refereed)
  • 164.
    Nikkam, Nader
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Saleemi, Mohsin
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Toprak, Muhammet
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Muhammed, Mamoun
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Haghighi, E.B.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Khodabandeh, R.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Palm, B,
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Rheological Properties of Copper Nanofluids Synthesised by Using Microwave-Assisted Method2012In: Proceedings of the 4th International Conference on Nanostructures (ICNS4), 2012, p. 1555-1557Conference paper (Refereed)
  • 165.
    Owhaib, Wahib
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Martín-Callizo, ClaudiKTH, 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.
    Flow Boiling Visualization and Heat Transfer in a Single Vertical Microchannel2005Conference proceedings (editor) (Refereed)
  • 166.
    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.

  • 167.
    Owhaib, Wahib Suleiman
    et al.
    SWEP International AB, Landskrona.
    Martín-Callizo, Claudi
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Two-phase flow pressure drop of R-134a in a vertical circular mini/micro channel2008In: Proceedings of the 6th International Conference on Nanochannels, Microchannels, and Minichannels, ICNMM2008, 2008, p. 343-353Conference paper (Refereed)
    Abstract [en]

    This paper presents new experimental results on saturated flow boiling pressure drop in microchannels. The two-phase pressure drops were measured for vertical saturated boiling of R-134a in circular tubes with internal diameters of 1.700, 1.224, and 0.826 mm, and a uniformly heated length of 220 mm, the total flow length is 580 mm. The total pressure drops were obtained for a heat flux range of 10-30 kW/m(2), a mass flux range of 100-400 kg/(m(2)s), and outlet vapor qualities up to 0.6. Experiments were conducted at the average saturation pressure of 8.62 bar. The experimental data was compared to predictions by correlations available in the literature both for microchannels and larger diameter tubes.

  • 168.
    Owhaib, Wahib Suleiman
    et al.
    KTH, Superseded Departments, Energy Technology.
    Palm, Björn
    KTH, Superseded Departments, Energy Technology.
    Experimental investigation of single-phase convective heat transfer in circular microchannels2004In: Experimental Thermal and Fluid Science, ISSN 0894-1777, E-ISSN 1879-2286, Vol. 28, no 2-3, p. 105-110Article in journal (Refereed)
    Abstract [en]

    In this study, the heat transfer characteristics of single-phase forced convection of R134a through single circular micro-channels with 1.7, 1.2, and 0.8 mm. as inner diameters were investigated experimentally. The results were compared both to correlations for the heat transfer in macroscale channels and to correlations suggested for microscale geometries. The results show good agreement between the classical correlations and the experimentally measured data in the turbulent region. Contrary, none of the suggested correlations for microchannels, agreed with the test data. In the laminar regime, the heat transfer coefficients were almost identical for all three diameters.

  • 169.
    Owhaib, Wahib Suleiman
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology. KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Martín-Callizo, Claudi
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    A visualization study of bubble behavior in saturated flow boiling through a vertical mini-tube2007In: Heat Transfer Engineering, ISSN 0145-7632, E-ISSN 1521-0537, Vol. 28, no 10, p. 852-860Article in journal (Refereed)
    Abstract [en]

    Forced convection saturated R-134a boiling experiments were conducted in a vertical mini-quartz tube coated with a transparent heater; the inner diameter of the tube was 1.33 mm and the heated length 235.5 mm. The dynamics of the saturated boiling process, bubble characteristics, and behavior were studied using a high-speed CCD camera at different mass fluxes in up-flow at 6.425 bar. The heat fluxes were 5 and 20 kW/m(2). The flow visualization results show that the bubble departure frequency generally inc

  • 170.
    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)
  • 171.
    Owhaib, Wahib Suleiman
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Martín-Callizo, Claudi
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Flow boiling visualization in a vertical circular minichannel at high vapor quality2006In: Experimental Thermal and Fluid Science, ISSN 0894-1777, E-ISSN 1879-2286, Vol. 30, no 8, p. 755-763Article in journal (Refereed)
    Abstract [en]

    This paper reports on an experimental study of saturated flow boiling of R134a inside a circular vertical quartz tube coated with a transparent heater. The inner diameter of the tube was 1.33 mm and the heated length 235.5 mm. The flow pattern at high vapor qualities and the dryout of the liquid film were studied using a high speed CCD camera at the mass fluxes 47.4 and 124.4 kg/m(2) s in up flow at 6.425 bar. The heat fluxes ranged from 5 to 13.6 kW/m(2) for the lower mass flux and from 20 to 32.4 kW/m(2) for the higher mass flux.

    The behavior of the flow close to dryout was found to be different at low and high mass flux. At low mass flux the location of the liquid front fluctuated with waves passing high up in the tube. In between the waves, a thin film was formed, slowly evaporating without breaking up.

    At high mass flux the location of the liquid front was more stable. In this case the liquid film was seen to break up into liquid streams and dry zones on the tube wall.

  • 172.
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Charge minimizaton in a 30 kW air to water heat pump2014In: 11th IIR Gustav Lorentzen Conference on Natural Refrigerants: Natural Refrigerants and Environmental Protection, GL 2014, 2014, p. 987-994Conference paper (Refereed)
    Abstract [en]

    Modern manufacturing technology allows production of tubes and channels with small hydraulic diameters. Heat pumps and refrigeration equipment designed using such tubes may have considerably lower charge than conventional systems while having just as good thermal performance. In this paper, the possibilities of charge reduction are investigated, using a 30 kW propane air to water heat pump as an example. It is shown that changing the tubing in the evaporator and condenser is a vital first step, but that considerable additional charge reduction can be reached by careful consideration in the selection and designs of other parts of the system as well. In particular it is important to avoid headers where liquid may be trapped and oversized receivers. Additionally, in a well-designed system a substantial part of the refrigerant may be absorbed in the compressor oil. Reducing the amount of refrigerant in this component requires novel thinking concerning the compressor design.

  • 173.
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Hydrocarbons as refrigerants in small heat pump and refrigeration systems - A review2008In: International journal of refrigeration, ISSN 0140-7007, E-ISSN 1879-2081, Vol. 31, no 4, p. 552-563Article, review/survey (Refereed)
    Abstract [en]

    Due to the concern for the effects of the release of HFC refrigerants on the global environment caused by the high global warming potential of these substances, there is a large interest in Europe and elsewhere for the use of hydrocarbons as refrigerants. This article presents a comparison of the properties and performance of hydrocarbons as refrigerants in small-size heat pump and refrigeration systems (< 20 kW cooling). A listing of several commercially available systems is also presented. The designs, safety precautions and performances of some of these systems are described. As a general conclusion, it is shown that using hydrocarbons will result in COPS equal to, or higher than, those of similar HFC systems. It is also shown that components suitable for hydrocarbon systems are available on the market, even though the number of large-size hermetic compressors is limited. A major concern, which should not be taken lightly, is the safety issue. Reduced charge through indirect systems and compact heat exchangers, outdoor placing of the unit, hydrocarbon sensors and alarms and forced ventilation are all steps which may be applied to reduce the risks under normal operation.

  • 174.
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Refrigerants of the future2011In: Proc 10thIEA Heat Pump Conference 2011, 2011Conference paper (Other academic)
    Abstract [en]

    The high global warming potential of most HFC fluids is forcing a change to fluids with less environmental impact. The search for the ideal refrigerant is not new, but has been ongoing for one hundred years, even though the reason for the search has changed.

    The paper gives a background to the present search for new refrigerants, discusses the criteria for the selection and gives some information on the status concerning introduction of new fluids.

    In conclusion, there is only one new refrigerant close to be put on the market, HFO1234yf. Other closely related fluids, such as HFO1234ze may be alternatives in the future. Beside these new fluids, it is believed that natural refrigerants like hydrocarbons, ammonia and carbon dioxide, as well as the low GWP, but flammable, HFC152a, will all find a place in future refrigeration and heat pump systems.

  • 175.
    Palm, Björn
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Claesson, Joachim
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration. KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Sustainable Building Systems.
    Effektiva plattvärmeväxlare som förångare i värmepumpar: Vidare studier. Slutrapport2005Report (Other academic)
  • 176.
    Palm, Björn E.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Ammonia as refrigerant in small-capacity systems2008In: IEA Heat Pump Centre Newsletter, ISSN 2002-018X, Vol. 26, no 4Article in journal (Refereed)
    Abstract [en]

    Ammonia is widely used in large systems because of its excellent thermodynamic and transport properties, resulting in energy-efficient systems with little environmental impact. Nevertheless, despite its favourable properties, ammonia has not been used in small systems. The present paper reports on work on small ammonia systems being performed as part of the EU SHERHPA project, aimed at developing heat pumps with natural refrigerants. First, the availability, and lack, of components for small ammonia systems is considered. Second, potentials and problems specific to small ammonia systems are discussed. Finally, the paper describes the design of a 9 kW water-to-water heat pump that contains as little as 100 g of ammonia, producing domestic hot water at close to 60 ° C while having a condensing temperature of below 50 °C. The text is partly identical to that in previously published reports to the Commission.

  • 177.
    Palm, Björn E.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Ammonia in low capacity refrigeration and heat pump systems2008In: International journal of refrigeration, ISSN 0140-7007, E-ISSN 1879-2081, Vol. 31, no 4, p. 709-715Article in journal (Refereed)
    Abstract [en]

    Ammonia has been used as refrigerant in large vapour compression systems continuously since the beginning of the era of refrigeration. In small systems, it has hardly been used at all since the introduction of the halogenated hydrocarbons around 1930. Lately, with the search for alternatives with less influence on global warming, the use of ammonia in small systems has come into focus again. In the present paper, the work done at the Royal Institute of Technology (KTH) with the aim of developing a prototype of a domestic water to water heat pump with a heating capacity of 9 kW is presented. it has been shown that such a system can be designed to operate with about 100 g of ammonia. Crucial problems in the development of the direct expansion system were to arrange for oil return, and to achieve good heat transfer in the evaporator. These problems were solved by use of an oil which is soluble in ammonia. The main obstacle for introducing this technology commercially is the limited supply of components. Particularly, there are no hermetic or semi-hermetic compressors for ammonia available in this size range.

  • 178.
    Palm, Björn E.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Ammonia in Small Capacity Heat Pump and Refrigeration Systems2005In: Proc. IIR Conf. Ammonia Refrigeration Systems, Renewal and Improvements, Ohrid, Macedonia, May 2005., Ohrid, Macedonia: Academic Conferences Publishing, 2005Conference paper (Refereed)
  • 179.
    Palm, Björn E.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Ammonia in Small Capacity Refrigeration and Heat Pump Systems2007In: Proceedings of IIR Conference: Ammonia Refrigeration Technology for Today and Tomorrow, Academic Conferences Publishing, 2007Conference paper (Refereed)
  • 180.
    Palm, Björn E.
    KTH, Superseded Departments, Energy Technology.
    Heat transfer in microchannels2001In: Microscale thermophysical engineering (Print), ISSN 1089-3954, E-ISSN 1091-7640, Vol. 5, no 3, p. 155-175Article, review/survey (Refereed)
    Abstract [en]

    In this article an attempt has been made to review the literature regarding heat transfer and pressure drop in one- and two phase flow in microchannels. The emphasis has been on reports presented during the last few years. For single phase flow, channels with hydraulic diameters less than 1 min have been considered. For two phase flow, very little information is available for such small channels. Also, for two phase flow, deviations from large-tube behavior start at diameters of a few millimeters. For these reasons a slightly larger diameter range has been considered in this case. As a conclusion, it can be stated that the understanding of flow, in microchannels is increasing steadily, but that there are still many questions to be answered concerning the reasons for deviations from classical theory developed for larger channels.

  • 181.
    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.

  • 182.
    Palm, Björn E.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Summarizing a Decade of Experience on Charge Reduction for Small Hydrocarbon, Ammonia and HFC Systems2009In: RCR 2009, Proc. 1st IIR Workshop on Refrigerant Charge Reduction in Refrigerating Systems, Academic Conferences Publishing, 2009Conference paper (Refereed)
  • 183.
    Palm, Björn E.
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Andersson, Klas
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Lundqvist, Per
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Samoteeva, Oxana
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Designing a Heat Pump for Minimum Charge2005In: IEA HPC newsletter, Vol. 232, p. 17-1§Article in journal (Refereed)
  • 184.
    Palm, Björn E.
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Claesson, Joachim
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Plate heat exchangers, calculation methods for single- and two-phase flow2005In: ICMM 2005, Proceedings of the 3rd International Conference on Microchannels and Minichannels, Pt A, 2005, p. 103-113Conference paper (Refereed)
    Abstract [en]

    Plate heat exchangers were first developed about 100 years ago, but have won increasing interest during the last two decades, primarily because of the development of methods of manufacturing brazed plate heat exchangers. This type of heat exchanger offers very good heat transfer performance in single-phase flow as well as in evaporation and condensation. Part of the reason is the small hydraulic diameters, typically being less than 5 mm. Other advantages of plate heat exchangers are the extremely compact design and the efficient use of the construction material. In spite of their long use, the calculation methods for predicting heat transfer and pressure drop are not widely known. It is the purpose of this article to present such calculation methods for singe phase flow and for flow boiling and to discuss some of the specifics of this type of heat exchangers.

  • 185.
    Palm, Björn E.
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Claesson, Joachim
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Plate heat exchangers: Calculation methods for single-and two-phase flow2006In: Heat Transfer Engineering, ISSN 0145-7632, E-ISSN 1521-0537, Vol. 27, no 4, p. 88-98Article in journal (Refereed)
    Abstract [en]

    Plate heat exchangers were first developed about 100 years ago but have won increasing interest during the last two decades, primarily due to the development of methods of manufacturing brazed plate heat exchangers. This type of heat exchanger offers very good heat transfer performance in single-phase flow as well as in evaporation and condensation. Part of the reason is the small hydraulic diameters, typically being less than 5 mm. Other advantages of plate heat exchangers are the extremely compact design and the efficient use of the construction material. In spite of their long use, the calculation methods for predicting heat transfer and pressure drop are not widely known. It is the purpose of this article to present such calculation methods for single-phase flow and for flow boiling and to discuss some of the specifics of this type of heat exchangers.

  • 186.
    Palm, Björn E.
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Fernando, Primal
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Andersson, Klas
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Lundqvist, Per
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Samoteeva, Oxana
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Designing a Heat Pump for Minimum Charge of Refrigerant2005In: Proc. IEA Heat Pump Conference, Las Vegas, USA, June 2005, Academic Conferences Publishing, 2005Conference paper (Refereed)
  • 187.
    Palm, Björn E.
    et al.
    KTH, Superseded Departments, Energy Technology.
    Khodabandeh, Rahmatollah
    KTH, Superseded Departments, Energy Technology.
    Choosing working fluid for two-phase thermosyphon systems for cooling of electronics2003In: Journal of Electronic Packaging, ISSN 1043-7398, E-ISSN 1528-9044, Vol. 125, no 2, p. 276-281Article in journal (Refereed)
    Abstract [en]

    The heat fluxes from electronic components are steadily increasing and have now, in some applications, reached levels where air-cooling is no longer sufficient. One alternative solution, which has received much attention during the last decade, is to use heat pipes or thermosyphons for transferring or spreading the dissipated heat. In this paper two-phase thermosyphon loops are discussed. Especially, the choice of fluid and its influence on the design and performance is treated. The discussion is supported by results from simulations concerning heat transfer and pressure drop. In general it is found that high-pressure fluids will give better performance and more compact designs as high-pressure results in higher boiling heat transfer coefficients and smaller necessary tube diameter.

  • 188. 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.

  • 189.
    Pelletier, Olivier
    et al.
    KTH, Superseded Departments, Energy Technology.
    Palm, Björn E.
    KTH, Superseded Departments, Energy Technology.
    Two-Phase Flow Pattern between an expansion valve and an evaporator2004Conference paper (Refereed)
  • 190.
    Saleemi, Mohsin
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics (Closed 20120101), Functional Materials, FNM (Closed 20120101).
    Toprak, Muhammet
    KTH, School of Information and Communication Technology (ICT), Material Physics (Closed 20120101), Functional Materials, FNM (Closed 20120101).
    Li, Shanghua
    KTH, School of Information and Communication Technology (ICT), Material Physics (Closed 20120101), Functional Materials, FNM (Closed 20120101).
    Ma, Ying
    KTH, School of Information and Communication Technology (ICT), Material Physics (Closed 20120101), Functional Materials, FNM (Closed 20120101).
    Wang, Xiaodi
    KTH, School of Information and Communication Technology (ICT), Material Physics (Closed 20120101), Functional Materials, FNM (Closed 20120101).
    Nikkam, Nader
    KTH, School of Information and Communication Technology (ICT), Material Physics (Closed 20120101), Functional Materials, FNM (Closed 20120101).
    Muhammed, Mamoun
    KTH, School of Information and Communication Technology (ICT), Material Physics (Closed 20120101), Functional Materials, FNM (Closed 20120101).
    Haghighi, Ehsan Bitaraf
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Khodabandeh, Rahmatollah
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Ceria Nanofluids for Efficient Heat Management2010Conference paper (Refereed)
  • 191.
    Samoteeva, Oxana
    et al.
    KTH, Superseded Departments, Energy Technology.
    Granryd, Erik
    KTH, Superseded Departments, Energy Technology.
    Palm, Björn
    KTH, Superseded Departments, Energy Technology.
    Fernando, Primal
    KTH, Superseded Departments, Energy Technology.
    Modelling of the amount of refrigerant and pressure drop in a rectangular copper microchannel evaporator2002In: Proceedings of Zero leakage-Minimum Charge IIR/IIF conference, Stockholm, August 2002, Stockholm, 2002Conference paper (Other academic)
    Abstract [en]

    The present study covers modelling of the amount of refrigerant and of the pressure drop in a rectangular copper microchannels evaporator. The evaporator has been tested in a test rig simulating a small-capacity heat pump and all the modelled parameters are compared to the measured ones. All the calculations are performed using EES software program [4].

    The void fraction was calculated in order to predict the amount of refrigerant in the evaporator. The choice of the model for the calculation of the void fraction has a big influence on the prediction of the amount. The void fraction was predicted, using several available correlations, out of which the Hughmark, UI ACRC[1]and CISE models seem to give the best approximation. The mass of refrigerant was calculated out of these data and compared to the experimental results. The pressure drop was determined, using the Friedel, Pierre and Granryd’s adjustment ofPierre[2]models. Afterwards results were compared to the experimentally measured pressure drop. Granryd’s model seems to give the closest approximation. 

    Comparisons of the predicted results with the measured ones are presented in figures and analysed. Conclusions regarding the models tested for determination of the void fraction and pressure drop in the present application and probably other applications with rectangular microchannels are drawn. 

  • 192.
    Samoteeva, Oxana
    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.
    Boiling heat transfer and pressure drop in single rectangular microchannel2006In: Proceedings of the 13th International Heat Transfer Conference 13-18 August 2006, Sidney, Australia, 2006Conference paper (Refereed)
    Abstract [en]

    One of the goals of this paper is to investigate the two-phase flow characteristics of the refrigerant changing phase in a high aspect ratio (1:30) rectangular vertically placed microchannel. The hydraulic diameter of the channel is 0,39 mm. The experimental data were collected for the refrigerant R134a for mass fluxes varying from 200 to 970 kg/m2s and a heat flux range of 0,6-28 kW/m2. The results of the heat transfer investigation have shown that the heat transfer coefficient is not influenced by the mass flux or vapour quality but only by heat flux, thus indicating the dominance of nucleate boiling or a related mechanism. In comparison to several conventional correlations from the literature, it was shown that the correlations by Lazarek and Black, 1982 predict the heat transfer coefficient best, the data scattering up to 35%. Measurements have shown that the pressure drop increases approximately linearly with the mass flux.

  • 193.
    Sawalha, Samer
    et al.
    KTH, Superseded Departments, Energy Technology.
    Palm, Björn
    KTH, Superseded Departments, Energy Technology.
    Energy Consumption Evaluation of Indirect Systems with CO2 as Secondary Refrigerant in Supermarket Refrigeration2003Conference paper (Refereed)
    Abstract [en]

    In this study, we investigate the influence of the pressure and temperature drops in the suction and return lines on the energy consumption of a supermarket refrigeration plant. We calculate the energy consumption of CO2indirect systems with R404A, ammonia or propane as the primary refrigerant and compare it to conventional direct expansion (DX) system with R404A or R502. CO2pressure drop and the corresponding saturation temperature drop in the indirect circuit is calculated and compared to that of R404A. The energy consumption of R404A/CO2indirect systems was found to be very close to R404A-DX system using the same pipe size in the return and suction lines. Replacing R404A by ammonia or propane in the indirect system reduced the energy consumption. This study indicates that it is more economical to use CO2indirect system with proper primary refrigerant rather than using the conventional DX systems.

  • 194.
    Sawalha, Samer
    et al.
    KTH, Superseded Departments, Energy Technology.
    Palm, Björn
    KTH, Superseded Departments, Energy Technology.
    Safety Analysis of CO2 as a Refrigerant in Supermarket Refrigeration2002Conference paper (Refereed)
    Abstract [en]

    In this study we analyse some safety aspects related to the usage of CO2 in supermarket refrigeration. The concentration levels in the supermarket’s shopping area and machine room that result from different accident scenarios are calculated for a selected practical example. The ventilation requirements in the supermarket under normal conditions and during a leakage accident are taken into consideration.

    For the selected case, the analysis of the calculations’ results showed that CO2 does not enclose a heath hazard for the customers and workers within the shopping area, whereas safety requirements expressed by efficient ventilation and proper alarm system must be installed in the machine room

  • 195.
    Sawalha, Samer
    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.
    Securité d’utilisation du CO2 dans un supermarché2004In: Revue General du Froid, ISSN 0755-7868, no 1042, p. 39-43Article, book review (Other academic)
  • 196.
    Sawalha, Samer
    et al.
    KTH.
    Palm, Björn
    KTH.
    Rolfsman, Lennart
    CO2 as Secondary Refrigerant in Sweden2000Conference paper (Other academic)
    Abstract [en]

    The selection of an available natural alternative to replace harmful artificial refrigerants depends on the application, which defines the system boundaries and the operation range. In the last ten years, CO2 was introduced as a semi ideal refrigerant due to its environmentally friendly and good performance characteristics. In some applications the unique thermophysical and performance properties of CO2 match the boundary conditions of the system and make it very close to be the ideal working fluid for that specific application.

    Since the rediscovery of CO2 as a refrigerant [Lorentzen, 1990], the studies focussed on finding the possible applications of CO2 according to its properties. Commercial refrigeration accounts for almost 17% of worldwide refrigerants consumption, 11% is the percentage in cold storage applications, 28% in total (135576 tons/year) [DOE/AFEAS, 1991]. CO2 as a phase changing secondary refrigerant was studied and applied successfully in Sweden in the applications of supermarkets and cold stores. By the year 2000, 40 plants are running with capacities ranging from 10 to 280 kW; the refrigerants used in the machine room are NH3, R404, and Care50 (ethane/propane). Two and single-stage plants are used for chilling and freezing needs within the supermarkets.

    This study present the basics of technologies applied in these specific applications and the main results obtained compared to the old systems with artificial refrigerants.

    Installation and running costs, of the systems and the technical problems appearing during the installation of the CO2 systems are discussed. Another important issue discussed in this study is the possibility of converting the old plants to CO2 secondary systems.

    The operation and the analysis of the existing plants proved that CO2 could be successfully used as an alternative for the artificial refrigerants within the application of refrigeration in supermarkets. In addition to the obvious environmental advantages by using such systems, an extra economical achievement was observed during the installation and running of the plants.

  • 197.
    Sommerfeldt, Nelson
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Muyingo, Henry
    KTH, School of Architecture and the Built Environment (ABE), Real Estate and Construction Management.
    af Klintberg, Tord
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
    Björk, Folke (Commentator for written text)
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
    Madani, Hatef (Contributor)
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Photovoltaic Systems for Swedish Prosumers: A technical and economic analysis focused on cooperative multi-family housing2016Report (Other academic)
    Abstract [en]

    This report is designed to be a comprehensive information resource for Swedish prosumers considering an investment in solar PV systems. The target audience are multi-family cooperative houses, however much of the information is applicable to other building owners and solar energy more broadly. The primary question to be answered; is a rooftop PV investment profitable in Sweden? Naturally there are many variables that can affect the answer; therefore a Monte Carlo methodology is used to convert the uncertainties into risks, where the results can be presented as probabilities rather than a vast collection of sensitivity analyses. Several policy scenarios are tested, where the relative impact of each current program on profitability can be seen.

  • 198.
    Su, Chang
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Madani, Hatef
    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.
    Heating solutions for residential buildings in China: Current status and future outlook2018In: Energy Conversion and Management, ISSN 0196-8904, E-ISSN 1879-2227, Vol. 177, p. 493-510Article in journal (Refereed)
    Abstract [en]

    With continuing of urbanization, improving of life quality as well as combating against air pollution, China is facing comprehensive challenges to supply modem clean heating to a majority of its citizens. For space heating solutions, currently in urban areas of north China, coal based district heating is prevalent. In urban areas of south China, distributed heating solutions are used. In rural areas, de-centralized coal stoves and biomass stoves are still commonly used. As renewable building heating solution, ground source heat pumps are installed for large scale applications. Building floor areas heated by ground source heat pumps increased tremendously during past ten years. Air source heat pump is being promoted in north Chinese rural areas as part of coal to clean heating project. Solar water heater and electric water heater for domestic hot water supply is widely used in north China and gas water boiler is widely used in south China. A series of policies have encouraged clean fossil fuel district heating in north China. National development plans are also supporting and subsidizing renewable heating technology such as heat pumps. Different building heating technologies have their own advantages and disadvantages from techno-economic and environmental perspectives. The choice of building heating solutions for different geolocations of China is strongly affected by spatial parameters such as local climate condition, population distribution, natural resource availability etc. Therefore, a spatial data analysis method is essential to help stakeholders decide proper building heating solutions in different parts of China by key performance indicators reflecting lower primary energy use, economic affordability and lower environmental impact.

  • 199.
    Su, Chang
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Madani Larijani, Hatef
    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.
    Building heating solutions in China: A spatial techno-economic and environmental analysis2019In: Energy Conversion and Management, ISSN 0196-8904, E-ISSN 1879-2227, Vol. 179, p. 201-218Article in journal (Refereed)
    Abstract [en]

    Fast urbanization process and promotion of life standard in China requires a great amount of energy input in building heating sector. North China now faces challenges of upgrading existing fossil fuel based high emission district heating systems into more environmental friendly heating systems. South China is discussing to choose proper building heating solutions for new and existing buildings which lack proper heating facilities. Renewable heating technologies such as ground source heat pump and air source heat pump are candidates to upgrade traditional heating solutions such as fossil fuel boilers and electric heaters. In order to find the most feasible building heating solution for different geolocations of China, this paper proposes a spatial data based techno-economic and environmental analysis methodology to fulfill such research gap. Case studies are carried out in two selected cities by using proposed methodology. Evaluation model shows that, heat pumps is quite competitive in south China compared with electric heaters, whereas in north China heat pumps have to reach several preconditions to be competitive with coal boiler district heating system under current techno-economic and environmental situations. In north China, a heat pump should reach a minimum seasonal coefficient of performance of 2.5-3.7 (for ground source heat pump) or 2.7-3.0 (for air source heat pump) to become CO2 and PM2.5 emission neutral as well as economically competitive compared with coal boiler district heating system. The advantage of proposed methodology is its simplicity in execution and could be repeated to other areas as the data required are available.

  • 200.
    Su, Chang
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Madani Larijani, Hatef
    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.
    Spatial Data Assisted Ground Source Heat Pump Potential Analysis in China, a Case of Qingdao City2019In: INNOVATIVE SOLUTIONS FOR ENERGY TRANSITIONS / [ed] Yan, J Yang, HX Li, H Chen, X, ELSEVIER SCIENCE BV , 2019, p. 6099-6104Conference paper (Refereed)
    Abstract [en]

    Nowadays, China faces challenges of further implementing heat pump technology for meeting building heating and cooling demand. The utilization of heat pumps, especially ground source heat pump (GSHP) is associated with a number of geological, hydrological as well as meteorological criteria. Thus it is essential to systematically address the feasibility of ground source heat pumps application using quantitative evaluation. Spatial data analysis is a method widely used in energy field to investigate renewable energy potential. Therefore, this study strives to provide an estimation of electricity driven GSHP's potential in north China using spatial data assisted tools. Followed by a case study using the methodology recommended, a spatial data assisted GSHP potential evaluation model is built for Qingdao city in north China. The evaluation model is constructed and analyzed through spatial data processing software visualized by ground source heat pump potential maps. The result maps show that, places with most potential of GSHP application locate in south Qingdao close to the sea. Such places have a higher ground extractable heat and relatively low drilling cost.

12345 151 - 200 of 207
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf