Performance of heat pipes as capillary pumps: modelling and comparison with experimental results (original) (raw)
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Performance of heat pipes as capillary pumps: experiments
International Journal of Low-Carbon Technologies, 2007
This paper describes the development of an experimental setup to investigate the performance of heat pipes as capillary pumps. The experimental setup and the research that was performed by LFME was part of an EU funded research project called TRI-GEN EGD that aims in the overall development of a novel Tri-generation Electrogasdynamic converter system. The capillary pump will be used to pump the working fluid of the system using external waste heat. Furthermore, since the capillary pump has no moving parts it will provide the system with greater reliability. The experimental setup designed and constructed by LFME is a Capillary Pumped Loop (CPL). A CPL is a closed loop system that pumps liquid by passive means, based on the operating principles of heat pipes. Specifically capillary forces are generated on a porous structure that exists in the evaporation section and is responsible for pushing the working fluid from a high temperature source to a low temperature sink. In this paper, a brief description of the experimental setup that was constructed and a description of the experimental procedure that was followed will be given together with some results that were obtained for various configurations.
Investigation of the performance of heat pipes used as capillary pumps
International Journal of …, 2006
This paper describes the investigation being performed by the Laboratory of Fluid Mechanics and Energy (LFME) in order to test the performance of heat pipes as capillary pumps. This investigation is part of the EU funded research project TRI-GEN EGD that aims in the development of a novel Tri-generation Electrogasdynamic converter system. The capillary pump will be used to pump the working fluid of the system using external waste heat. Furthermore, since the capillary pump has no moving parts it will provide the system with greater reliability. To this end, a Capillary Pumped Loop (CPL) experimental setup was designed and constructed by LFME. A CPL is a closed loop system that pumps liquid by passive means, based on the operating principles of heat pipes. Specifically capillary forces are generated on a porous structure that exists in the evaporation section and is responsible for pushing the working fluid from a high temperature source to a low temperature sink. In this paper the experimental setup constructed as well as the experimental procedure followed are described and preliminary results are presented.
2016
This paper describes the development of an experimental setup to investigate the performance of heat pipes as capillary pumps. The experimental setup and the research that was performed by LFME was part of an EU funded research project called TRI-GEN EGD that aims in the overall development of a novel Tri-generation Electrogasdynamic converter system. The capillary pump will be used to pump the working fluid of the system using external waste heat. Furthermore, since the capillary pump has no moving parts it will provide the system with greater reliability. The experimental setup designed and constructed by LFME is a Capillary Pumped Loop (CPL). A CPL is a closed loop system that pumps liquid by passive means, based on the operating principles of heat pipes. Specifically capillary forces are generated on a porous structure that exists in the evaporation section and is responsible for pushing the working fluid from a high temperature source to a low temperature sink. In this paper, a...
Modelling of the flow behaviour in a capillary pumped loop
The objective of this paper is to present a theoretical investigation of the operational characteristics on a small-scale Capillary Pump Loop (CPL). A typical design of a CPL is composed of a capillary evaporator, a condenser, a two-phase reservoir, liquid and vapour lines. The capillary evaporator generates the required pressure pumping for moving the working fluid from the condenser to the evaporator section. The fundamental principles of the proposed modelling are: The overall pressure drop in the loop must be less than the maximum capillary pressure in order to ensure that the system will operate continuously. The major components of the CPL pressure drop are related to the flow in the wick structure, condenser, vapour and liquid lines. The wick structure present in the evaporator causes flow restriction that affects the CPL performance, which is dependent on the wick permeability, a property of the porous material that describes its ability to transport the liquid under an applied pressure gradient. An experimental lab-scale installation is used for the validation of the theoretical analysis. The results showed that the proposed CPL modelling is able to describe very well the CPL performance.
Effect of the working liquid to the capillary pumped loop performance
The purpose of this paper is to present a theoretical analysis of the capillary pumped loop (CPL) performance using different working liquids. CPL is a passive heat transfer device, using no mechanical pump to circulate the working liquid, usually composed of a liquid tank, an evaporator, a condenser, a liquid and a vapor line. Heat load is applied on the external surface of the evaporator, partially transferred to the wick inside. Because of this heat load capillary forces are developed inside the porous structure, due to meniscus formation between liquid and vapor surface of the liquid, causing a pressure oscillation capable to pump the flow out of the evaporator. In this paper CPL performance is evaluated using different working liquids, such as water, ammonia, acetone and freon-134. These have different thermophysical properties such as latent heat, viscosity and density, causing different behavior when used as working liquid. Water was found more stable for higher temperature differences, due to higher latent heat of vaporization, while ammonia could take advantage of its viscosity for small temperature differences.
Applied Thermal Engineering, 2016
Heat and mass transfer with phase change in an evaporator unit cell is analysed using a mixed pore network model. Two different kind of wick are investigated: a monoporous capillary structure characterised by a monomodal pore size distribution and a bidispersed capillary structure characterised by a bimodal pore size distribution. The evaporator thermal performance, i.e. the conductance, and the overheating of the casing are compared at different heat loads with experimental results and show a good agreement. For a large range of flux, the bidispersed wick has higher thermal performance than the monoporous wick. A bidispersed wick prevents the overheating of the casing which is the most encountered limit in LHP application. The liquid-vapour phase distribution, as well as the vapour saturation and the vapour mass flow rate are investigated to explain these behaviours.
Numerical Simulation of Capillary Pump Evaporator Using Water for Different Inclination Angles
A Capillary Pump Loop (CPL) is a two-phase heat transfer device considered a useful solution for thermal control applications in spacecrafts, satellites and electronic components. Purpose of this paper is to study aspects of the working state of the Capillary Pump Loop. A two dimensions computational model was designed to analyze heat transfer and liquid saturation inside the wick. Different cases were studied by changing the saturation temperature of the working fluid, water in our case, the heat load applied to the evaporator external wall, the wick heated length and the inclination angle to the horizontal level. Temperature flow results, inside the wick and at the evaporator exit, are presented, giving a better understanding of the function under several circumstances which enables more efficient evaporator design, capable to transfer bigger amounts of heat.
Investigation of the influence of capillary effect on operation of the loop heat pipe
Archives of Thermodynamics, 2014
In the paper presented are studies on the investigation of the capillary forces effect induced in the porous structure of a loop heat pipe using water and ethanol ad test fluids. The potential application of such effect is for example in the evaporator of the domestic micro-CHP unit, where the reduction of pumping power could be obtained. Preliminary analysis of the results indicates water as having the best potential for developing the capillary effect.