Björn Palm | KTH Royal Institute of Technology (original) (raw)
Papers by Björn Palm
The use of natural refrigerants has become of increasing concern in recent years due to the high ... more The use of natural refrigerants has become of increasing concern in recent years due to the high GWP and ODP of commonly used CFCs, HCFCs and HFCs. The use of hydrocarbons can be considered as pote ...
The number of magnetic refrigeration prototypes with high cooling capacity and large temperature ... more 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 prototy ...
ASME 2009 Second International Conference on Micro/Nanoscale Heat and Mass Transfer, Volume 2, 2009
In this paper the experimental flow boiling heat transfer results of a minichannel are presented.... more In this paper the experimental flow boiling heat transfer results of a minichannel are presented. A series of experiments was conducted to measure the heat transfer coefficients in a minichannel made of stainless steel (AISI 316) having an internal diameter of 1.7mm and a uniformly heated length of 220mm. R134a was used as working fluid and experiments were performed at two different system pressures corresponding to saturation temperatures of 27 °C and 32 °C. Mass flux was varied from 50 kg/m2 s to 600 kg/m2 s and heat flux ranged from 2kW/m2 to 156kW/m2. The test section was heated directly using a DC power supply. The direct heating of the channel ensured uniform heating and heating was continued until dry out was reached. The experimental results show that the heat transfer coefficient increases with imposed wall heat flux while mass flux and vapour quality have no considerable effect. Increasing the system pressure slightly enhances the heat transfer coefficient. The heat transfer coefficient is reduced as dryout is reached. It is observed that dryout phenomenon is accompanied with fluctuations and a larger standard deviation in outer wall temperatures.
International Journal of Refrigeration-revue Internationale Du Froid, Dec 1, 2018
ABSTRACT The selection of an available natural alternative to replace harmful artificial refriger... more ABSTRACT 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.
Heat exchangers with mini- and micro-channel components are capable of high energy exchange due t... more Heat exchangers with mini- and micro-channel components are capable of high energy exchange due to their incumbent large surface area to volume ratio. Concurrently, recent advances in additive manufacturing simplify the creation of metallic minichannels that incorporate turbulators for heat transfer enhancement. As part of the development of a minichannel heat exchanger with turbulators, this study analyzes the three-dimensional conjugate heat transfer and laminar flow in a minichannel heat exchanger equipped with rectangular winglet vortex generators (VGs) through numerical simulation. The minichannels have a hydraulic diameter of 2.86 mm and are assumed to be made from aluminum alloy AlSi10Mg. This material is one of the popular alloys in the additive manufacturing industry (three-dimensional (3D) printing) because of its light weight and beneficial mechanical and thermal properties. The working fluid is distilled water with temperature-dependent thermal properties. The minichannel is heated by a constant heat flux of 5 W cm−2 and the Reynolds number is varied from 230 to 950. The simulations are performed using the COMSOL® platform, which solves the governing mass, momentum, and energy equations based on the finite element method. The effect of the VG design parameters, which include VG angle of attack, height, length, thickness, longitudinal pitch, and distance from the sidewalls, is investigated. It is found that the generation of three-dimensional vortices caused by the presence of the vortex generators can notably boost the convective heat transfer, at the cost of increased pressure drop, potentially reducing the heat exchanger size for a given heat duty. A sensitivity analysis indicates that the angle of attack, VG height, VG length, and longitudinal pitch have the most significant effects on the heat transfer and flow friction characteristics. In contrast, the VG thickness and distance from the sidewalls only had minor influences on the heat exchanger performance over the studied range of design parameters.
The most common way to exchange heat with the bedrock in ground source heat pump applications is ... more The most common way to exchange heat with the bedrock in ground source heat pump applications is circulating a secondary fluid through a closed U-pipe loop in a vertical borehole. This fluid transports the heat from the rock to the ground source heat pump evaporator. The quality of the heat exchange with the ground and the necessary pumping power to generate the fluid circulation are dependent on the type of fluid and its flow conditions along the pipe. Four different borehole heat exchangers are tested using ethyl alcohol with 20% volume concentration. The fluid temperatures are logged at the borehole inlet, bottom, and outlet. The collectors are compared based on their borehole thermal resistance and pressure drop at different flow rates. The results indicate that the pipe dimensions play an important roll, spacers might not contribute to better heat transfer, and inner micro fins in the pipes improve the performance of the collectors. The ground is an attractive energy source for heating and cooling applications. It has near constant temperature along the year regardless of the ambient temperature variations, which allows having a reliable and long lasting resource which permits delivering a constant amount of heat with stable temperatures over the years. Profit from the ground energy is normally obtained by means of a Borehole Heat Exchanger (BHE) installed in vertical boreholes. The most popular BHE consists of a closed U-pipe, through which a secondary fluid travels down and then up while collecting the heat from the bedrock. The collected energy is subsequently delivered to a so called ground source heat pump (GSHP). The heat transfer between the secondary fluid and the surrounding ground depends on the arrangement of the BHE flow channels, the convective heat transfer in the ducts, and the thermal properties of the BHEs as well as the filling material (groundwater in this case). The thermal resistances associated with these different parts are normally added together and called borehole thermal resistance Rb, normally determined between the secondary fluid and the borehole wall. An increase of one degree Celsius of the out coming fluid from the borehole can give a COP increase in the heat pump of approximately 3%. Therefore, it is of great importance to use the most appropriate BHE in order to efficiently extract heat from the ground. This paper presents a comparison of four different Borehole Heat Exchangers which are tested at the same heat pump installation. Considering the borehole as a cylindrical heat exchanger with two inner tubes inserted into a shell (the borehole wall), an energy balance could be made by equalizing the absorbed heat by the fluid with the Newton's law of cooling, as presented in equation 1. Since the fluid is heated as it travels through the BHE channels (in the heating mode, which is the case for the actual study), the temperature arises between different points when the fluid travels down and upwards.
21st IIR International Congress of Refrigeration: Serving the Needs of Mankind., Aug 17, 2003
In this study, we investigate the influence of the pressure and temperature drops in the suction ... more 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 en ...
Heat Transfer Engineering, Apr 6, 2015
Heat Transfer Engineering, Oct 1, 2007
ABSTRACT
International Journal of Refrigeration-revue Internationale Du Froid, Sep 1, 2015
... maqbool@kth.se, bpalm@energy.kth.se, rahmat@energy.kth.se, rashid.ali@energy.kth.se 1Applied ... more ... maqbool@kth.se, bpalm@energy.kth.se, rahmat@energy.kth.se, rashid.ali@energy.kth.se 1Applied Thermodynamics and Refrigeration, Royal Institute of Technology, KTH, Brinellvägen 68, SE-100 44, Stockholm, Sweden ... 2000 , Lockhart-Martinelli [11] Φ , Φ 1 with C given by: ...
ASME 2008 6th International Conference on Nanochannels, Microchannels, and Minichannels, 2008
ABSTRACT
The use of natural refrigerants has become of increasing concern in recent years due to the high ... more The use of natural refrigerants has become of increasing concern in recent years due to the high GWP and ODP of commonly used CFCs, HCFCs and HFCs. The use of hydrocarbons can be considered as pote ...
The number of magnetic refrigeration prototypes with high cooling capacity and large temperature ... more 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 prototy ...
ASME 2009 Second International Conference on Micro/Nanoscale Heat and Mass Transfer, Volume 2, 2009
In this paper the experimental flow boiling heat transfer results of a minichannel are presented.... more In this paper the experimental flow boiling heat transfer results of a minichannel are presented. A series of experiments was conducted to measure the heat transfer coefficients in a minichannel made of stainless steel (AISI 316) having an internal diameter of 1.7mm and a uniformly heated length of 220mm. R134a was used as working fluid and experiments were performed at two different system pressures corresponding to saturation temperatures of 27 °C and 32 °C. Mass flux was varied from 50 kg/m2 s to 600 kg/m2 s and heat flux ranged from 2kW/m2 to 156kW/m2. The test section was heated directly using a DC power supply. The direct heating of the channel ensured uniform heating and heating was continued until dry out was reached. The experimental results show that the heat transfer coefficient increases with imposed wall heat flux while mass flux and vapour quality have no considerable effect. Increasing the system pressure slightly enhances the heat transfer coefficient. The heat transfer coefficient is reduced as dryout is reached. It is observed that dryout phenomenon is accompanied with fluctuations and a larger standard deviation in outer wall temperatures.
International Journal of Refrigeration-revue Internationale Du Froid, Dec 1, 2018
ABSTRACT The selection of an available natural alternative to replace harmful artificial refriger... more ABSTRACT 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.
Heat exchangers with mini- and micro-channel components are capable of high energy exchange due t... more Heat exchangers with mini- and micro-channel components are capable of high energy exchange due to their incumbent large surface area to volume ratio. Concurrently, recent advances in additive manufacturing simplify the creation of metallic minichannels that incorporate turbulators for heat transfer enhancement. As part of the development of a minichannel heat exchanger with turbulators, this study analyzes the three-dimensional conjugate heat transfer and laminar flow in a minichannel heat exchanger equipped with rectangular winglet vortex generators (VGs) through numerical simulation. The minichannels have a hydraulic diameter of 2.86 mm and are assumed to be made from aluminum alloy AlSi10Mg. This material is one of the popular alloys in the additive manufacturing industry (three-dimensional (3D) printing) because of its light weight and beneficial mechanical and thermal properties. The working fluid is distilled water with temperature-dependent thermal properties. The minichannel is heated by a constant heat flux of 5 W cm−2 and the Reynolds number is varied from 230 to 950. The simulations are performed using the COMSOL® platform, which solves the governing mass, momentum, and energy equations based on the finite element method. The effect of the VG design parameters, which include VG angle of attack, height, length, thickness, longitudinal pitch, and distance from the sidewalls, is investigated. It is found that the generation of three-dimensional vortices caused by the presence of the vortex generators can notably boost the convective heat transfer, at the cost of increased pressure drop, potentially reducing the heat exchanger size for a given heat duty. A sensitivity analysis indicates that the angle of attack, VG height, VG length, and longitudinal pitch have the most significant effects on the heat transfer and flow friction characteristics. In contrast, the VG thickness and distance from the sidewalls only had minor influences on the heat exchanger performance over the studied range of design parameters.
The most common way to exchange heat with the bedrock in ground source heat pump applications is ... more The most common way to exchange heat with the bedrock in ground source heat pump applications is circulating a secondary fluid through a closed U-pipe loop in a vertical borehole. This fluid transports the heat from the rock to the ground source heat pump evaporator. The quality of the heat exchange with the ground and the necessary pumping power to generate the fluid circulation are dependent on the type of fluid and its flow conditions along the pipe. Four different borehole heat exchangers are tested using ethyl alcohol with 20% volume concentration. The fluid temperatures are logged at the borehole inlet, bottom, and outlet. The collectors are compared based on their borehole thermal resistance and pressure drop at different flow rates. The results indicate that the pipe dimensions play an important roll, spacers might not contribute to better heat transfer, and inner micro fins in the pipes improve the performance of the collectors. The ground is an attractive energy source for heating and cooling applications. It has near constant temperature along the year regardless of the ambient temperature variations, which allows having a reliable and long lasting resource which permits delivering a constant amount of heat with stable temperatures over the years. Profit from the ground energy is normally obtained by means of a Borehole Heat Exchanger (BHE) installed in vertical boreholes. The most popular BHE consists of a closed U-pipe, through which a secondary fluid travels down and then up while collecting the heat from the bedrock. The collected energy is subsequently delivered to a so called ground source heat pump (GSHP). The heat transfer between the secondary fluid and the surrounding ground depends on the arrangement of the BHE flow channels, the convective heat transfer in the ducts, and the thermal properties of the BHEs as well as the filling material (groundwater in this case). The thermal resistances associated with these different parts are normally added together and called borehole thermal resistance Rb, normally determined between the secondary fluid and the borehole wall. An increase of one degree Celsius of the out coming fluid from the borehole can give a COP increase in the heat pump of approximately 3%. Therefore, it is of great importance to use the most appropriate BHE in order to efficiently extract heat from the ground. This paper presents a comparison of four different Borehole Heat Exchangers which are tested at the same heat pump installation. Considering the borehole as a cylindrical heat exchanger with two inner tubes inserted into a shell (the borehole wall), an energy balance could be made by equalizing the absorbed heat by the fluid with the Newton's law of cooling, as presented in equation 1. Since the fluid is heated as it travels through the BHE channels (in the heating mode, which is the case for the actual study), the temperature arises between different points when the fluid travels down and upwards.
21st IIR International Congress of Refrigeration: Serving the Needs of Mankind., Aug 17, 2003
In this study, we investigate the influence of the pressure and temperature drops in the suction ... more 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 en ...
Heat Transfer Engineering, Apr 6, 2015
Heat Transfer Engineering, Oct 1, 2007
ABSTRACT
International Journal of Refrigeration-revue Internationale Du Froid, Sep 1, 2015
... maqbool@kth.se, bpalm@energy.kth.se, rahmat@energy.kth.se, rashid.ali@energy.kth.se 1Applied ... more ... maqbool@kth.se, bpalm@energy.kth.se, rahmat@energy.kth.se, rashid.ali@energy.kth.se 1Applied Thermodynamics and Refrigeration, Royal Institute of Technology, KTH, Brinellvägen 68, SE-100 44, Stockholm, Sweden ... 2000 , Lockhart-Martinelli [11] Φ , Φ 1 with C given by: ...
ASME 2008 6th International Conference on Nanochannels, Microchannels, and Minichannels, 2008
ABSTRACT