Numerical and experimental investigation of a wire-net compact heat exchanger performance for high-temperature applications

Abstract

The objective of this paper is to have a detailed numerical investigation of the microchannel performance of a complex wire-net compact heat exchanger and investigate its collector performance experimentally for a micro combined heat and power system. Localised turbulence can enhance heat exchanger performance. Besides, this will increase the pressure losses also. In microchannels, shifting the Reynolds critical to smaller Reynolds number using perturbators will control the pressure losses and enhance the microchannel thermal efficiency. In this paper, we consider microchannels with wire-net perturbators. The wire-net micro heat exchanger is assembled as a stack of counterflow flow passages with optimised thickness separated by thin foils. A metallic wire-net mesh is inserted in the flow passages to provide the required stiffness and enhance the microchannel efficiency.A parametric study was conducted on various heat exchanger parameters to optimise the heat exchanger size, thermal effectiveness and pressure losses for a micro-CHP system. Besides, a detailed investigation of the wire-net flow physics was made using a higher order Reynolds stress turbulence model to obtain the full velocity gradient tensor. This could detail the effect of anisotropic flow physics in the isotropic wire-net microchannels. Lambda 2 criterion was implemented to investigate the flow mixing of the centrally convected non-disturbed mass flow. Furthermore, the analysis of the turbulence production terms provided a deeper insight into flow attachment and detachment near the wire-net intersections. The heat exchanger was experimentally tested, and it was found that the collector pressure losses are not sufficiently low as compared to the microchannel pressure losses. The microchannel conjugate heat transfer thermal effectiveness is in good agreement with the overall experimental efficiency.