Experimental investigation of thermal and flow characteristics of a prototype minichannel heat exchanger

Abstract

The paper presents an experimental investigation of the thermo-hydraulic performance of a prototype single-plate minichannel heat exchanger. The symmetric heat exchanger plate made of aluminum alloy consists of square cross section channels with a hydraulic diameter of 1000 µm and a length of 100 mm and rectangular inlet and outlet plenums. The heat exchanger operates in a counterflow configuration and the working fluids are hot and cold deionized water, respectively. The flow in minichannels is considered laminar due to its maximum Reynolds number limited to approximate value of 2200. Experimental measurements were carried out for various combinations of hot and cold side Reynolds numbers for the purpose of seeking optimal thermo-hydraulic performance. The minichannel geometry and operating conditions were chosen to operate in the laminar thermal entry length in order to achieve higher average Nusselt number along the minichannel length compared to the Nusselt number in the fully developed laminar flow. The general analytical model for prediction of the heat transfer performance of these types of heat exchangers is presented and includes the heat transfer process in the inlet plenum, the parallel configuration of the minichannels, and the outlet plenum. A comparison of the overall heat transfer coefficient resulting from the experiment and the analytical model is presented. The thermo-hydraulic performance of the investigated minichannel heat exchanger and exemplary microchannel heat exchangers is also presented. The main advantage of the presented minichannel heat exchanger is a very high overall heat transfer coefficient up to 3000 W/(m²K) and relatively low pressure drop on the one side of the heat exchanger up to 6.5 kPa, while still maintaining the high compactness and ease of manufacturing compared to microchannel heat exchangers. The comparison of minichannel heat exchanger considered in this paper and exemplary microchannel heat exchangers reflected slight decrease of the overall heat transfer coefficient, while still being approximately of the same order, together with incomparably lower pressure drop, on average of two orders of magnitude.