Study on the three-dimensional heat flow field of supercritical nitrogen in a micro-channel plate heat exchanger

Micro-channel plate heat exchanger (MCPHE) has been recognized as a new high-efficiency heat transfer device and widely utilized in the energy field due to its compactness and high heat exchange rate. In this paper, the three-dimensional heat flow field of supercritical nitrogen (SCN2) in a simplified MCPHE is numerically simu-lated using computational fluid dynamics (CFD) simulation technology. The numerical approach predicts the thermo-hydraulic performance of SCN2 with a relatively good accuracy, by comparing with the published experimental data. Furthermore, the effects of pressure (3.6 -7 MPa) and mass flux (800 -1200 kg/(m2.s)) on the convective heat transfer characteristics of SCN2 are thoroughly examined, especially the heat flow field of SCN2 in different circumferential directions of the micro-channel is revealed. The obtained results show that under the condition of low pressure and high mass flux, the maximum circumferential inner wall temperature appears at 90 of the micro-channel at the same axial position. With an increased mass flux, the maximum inner wall temperature and minimum heat transfer coefficient gradually shifts from 180 to 90. When the buoyancy coefficient Gr*/Re2 > 1, the buoyancy force is conducive to enhance the fluid heat transfer capacity gathered at the bottom of the micro-channel. Meanwhile, the buoyancy force could make the distribution of thermo-physical properties of SCN2 uneven at the same time. Finally, in view of the obtained data, a new dimensionless corre-lation is proposed to predict the convective heat transfer process of SCN2 inside MCPHE, and the prediction error is less than 20%. The research outcomes could provide a reference for the optimal design and safe operation of MCPHE.