Experimental Analysis of Cascaded Micro Heat Exchanger

Abstract

Heat exchangers are used for transfer of thermal energy between fluids and channels. The main goal in the design of heat exchangers is to maximize the heat transfer with minimum cost in terms of energy and material. Micro heat exchangers provide a promising solution in terms of thermal performance and reduced cost for devices generating high heat fluxes. They are categorized among other heat exchangers based upon hydraulic diameter having less than 1mm. The design variables determining the thermal and hydraulic performance of micro heat exchangers include width, height, length, total heated surface area, lateral and axial channel profile and inlet- outlet plenum geometry. The best performance is achieved by finding the optimal values of design variables keeping the cost as minimum as possible. In this study, we analyzed the thermo-hydraulic performance of bent rectangular channel micro heat exchangers in cascaded configuration. The design variables selected were width and height of the channel while keeping others constant. Four different microchannel heat exchangers with widths of 200µm and 300 µm, heights of 35 µm and 70 µm were used for analysis. Single phase open loop experimental configuration was used with water as the working fluid. Water was forced to flow through microchannel using syringe pump and varying flow rates ranging from 20-100 ml/hr with constant inlet temperature of 5°C. Infrared camera was used to take the thermal images of the microchannel for temperature measurements using image processing software. The measured temperatures and pressures were analyzed to assess the performance of microchannel heat exchangers. Keeping the height constant and increasing the width from 200µm to 300 µm, the average relative increase in Nu and decrease in pressure was 12% and 46% respectively. Similarly, keeping the width constant and increasing the height, the relative decrease in Nu and pressure drop was 8% and 150% respectively. Microchannel with width 300µm and height 70µm gives relatively best overall performance in terms of heat transfer and pressure drop.