Comparative Study of Straight and Venturi Channel Cross Sections of Microchannel Heat Exchangers

Abstract

This study provides extensive research on fluid flow and heat transfer for four-layered ceramic-compact counterflow microchannel heat exchangers (CFMCHE) using CFD-ACE®, a computational fluid dynamics (CFD) package. The goal is to build and expand upon previous studies in this area to identify a more efficient channel shape or cross section for better performance of the microchannel through numerical analysis under the same operating conditions. To develop the methodology for numerical analysis, a three-dimensional (3D) computational model of the CFMCHE was developed and validated with published and experimentally tested results with a percentage difference in outlet temperatures of 3–5% for hot fluids and 6–12% for cold fluids across the entire design of experiments (DoEs). Microchannel heat exchangers (MCHEs) exhibit high heat-transfer rates and area-to-volume ratios, making them suitable for industrial applications. In this study, various design options for channel cross sections in a venturi shape were assessed numerically using a validated methodology in a segmented venturi CFMCHE to enhance performance. The steady-state performance of the Venturi CFMCHE was compared to that of the straight CFMCHE baseline design under the same bucket volume, area, and operating conditions. It was found that the venturi CFMCHE showed a ∼4–9% improvement as compared to the straight CFMCHE, but same time the pumping power was also 15–40% under the same operating conditions. Making the right choice regarding feasibility often involves weighing the pros and cons. The high-power requirements are manageable in terms of the cost of high thermal performance for ground applications, such as power plants, industrial refrigeration, and air-conditioning. However, for aviation, space, and automobiles, weight/power requirements are given more weight than thermal performance. Therefore, the Venturi CFMCHE can be used for ground applications, whereas the straight CFMCHE can be used for aviation, space, and automobile applications. When the Goodness factor is plotted for all configurations for all operating conditions, it is also concluded that an improvement of ∼7.5% is observed in the two design configurations with the Venturi channel (20pc_TOP_BTM_Step and 40pc_BTM_Step) with respect to the straight channel. This implies that these two best designs can be used for all applications over the straight-channel CFMCHE.