Numerical study on enhanced heat transfer and flow characteristics of supercritical methane in a square mini-channel with dimple array

Developing a high thermal performance heat exchanger is of great importance to the storage and usage of liquid natural gas (LNG). In this paper, the heat transfer and flow characteristics of supercritical methane in a square mini-channel with dimple array were studied numerically to enhance the thermal performance of LNG in the mini-channel heat exchanger made by 3D printing technology. The Reynolds number and average temperature of fluid are ranged from 10000 to 85000 and 125K to 265K respectively which covers the pseudo critical temperature of supercritical methane. By preliminary optimal design, the basic sizes of dimple array were determined. Then, the present study focused on the effects of Reynolds number or the mass flow rate, the average fluid temperature or inlet temperature, and the pressure on the heat transfer coefficient, Nusselt number, flow friction factor and PEC (performance evaluation criteria) by comparing the dimple channel to the smooth channel. Moreover, the local flow pattern and thermal performance are analyzed to discover the enhancement mechanism of heat transfer. The results show that the heat transfer of supercritical methane in the dimple channel has a great increase compared to the smooth channel. While the flow friction factor in the dimple channel has an only weak increase. In addition, the thermal enhancement mechanism of the dimple channel is that the dimple structure results in the vortex and the increase of turbulent kinetic energy. (C) 2020 Elsevier Ltd. All rights reserved.