EFFECT OF MULTIPLE FACTORS ON FLOW AND HEAT TRANSFER OF SUPERCRITICAL METHANE IN A MINICHANNEL WITH DIMPLED STRUCTURE

It is a novel and feasible treatment to use spherical and teardrop dimple structure for enhancing the methane thermal performance in printed circuit heat exchanger under supercritical pressure. This paper numerically investigated the flow and heat transfer characteristics of supercritical methane in minichannels under multiple factors, including the fluid temperature, mass flux, wall heat flux, dimple depth, dimple radius, and dimple spacing. The Reynolds numbers are ranged from 15,000 to 70,000. The heat transfer coefficient and friction factor were applied to evaluate the overall characteristics, and local flow and heat transfer were also analyzed to explain the mechanism of dimples influence under supercritical pressure. It is found that the heat transfer coefficient of supercritical methane is enhanced by increasing mass flux (from 400 to 1200 kg/m(2) s), and the Nusselt number enhancement rate with dimple is up to 1.4 times. Besides, the heat transfer coefficient increases firstly and then decreases with the increases of temperature (from 165 to 245 K), which reaches the maximum near the pseudocritical temperature. The dimple structure can attenuate the heat transfer deterioration caused by the increase of heat flux to some extent (from 20 to 80 kW/m(2)). Moreover, a spherical dimple has better heat transfer performance than a teardrop dimple according to performance evaluation criteria and total entropy, and heat transfer performance can be improved by increasing the dimple depth (from 0.05 to 0.11 mm) or decreasing the spacing (from 0.8 to 0.2 mm), and the largest PECs are 1.26 and 1.34, respectively. On the other hand, the intersection of mainstream and near-wall fluid is significantly enhanced by vortex generation from the streamline distribution, thereby the local heat transfer is also enhanced.