Abstract
This paper presents a theoretically modelled and experimentally validated laminated woven copper wire mesh used to enhance heat transfer area of regenerative and compact Stirling Engine (SE) heat exchangers (HEs). SE HEs consist with three key components, namely, the heater, cooler and regenerator. A lumped parameter model was used to describe the thermo-fluid characteristics and dynamic behaviour of these HEs. In order to validate the theoretical results, a mathematical model was developed first to compute the mesh porosity and metal fraction of the heater, cooler and regenerator that use woven copper wire mesh inserts as their heat transfer medium. Thereafter, a uni-directional flow experimental investigation was performed. The regenerator performance described in terms of the change in temperature with position through its woven wire matrix is reported considering the regenerator dual function in the regenerative HE assembly. The theoretical model was adjusted so that it simulates the experimentally determined HE thermo-fluid characteristics. This was done by identifying the flow and geometrical variables influencing the HEs theoretical results. It was found that in regenerative and compact HEs using woven wire mesh as heat transfer areas, all geometrical variables influencing the theoretical results are captured in the porosity, while the flow variables are captured in the Reynolds number. Both the Reynolds number and porosity are then captured in the thermal resistance. Porosity is defined as a measure of the void (empty) spaces in a material and is the fraction of the volume of voids to the total volume of the control volume containing the wire mesh; therefore its use allows the volume of the wire mesh to be corrected and, by extension the number of laminating screens in the HE, and therefore, the flow resistance. It was found that the woven wire mesh screens laminating process and configuration must be carefully controlled to insure that a target porosity, specific surface area and effective thermal conductivity are achieved. Effective thermal conductivities are found to be much improved in the heater and cooler as they use water as a coolant than in the regenerator where the working fluid (air) plays also the role of a coolant. Finally it was noticed that the obtained heater, cooler and regenerator mesh friction factor and Stanton number are comparable to those achieved with other exchanger surface technologies. The HE performance comparison shows that in regenerative and compact HEs using laminated woven wire mesh as fins, a high performance may be achieved.
Published Version
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