Analysis of the flow and heat transfer performance of nonlinear variable cross-section microchannels based on analytical method

In this paper, a continuous microchannel with nonlinear cross section (M-NCS) applied to parallel plate heat exchangers is designed, and the M-NCS is quantitatively analyzed using an analytical calculation method. By comparing the M-NCS with the microchannel with a fixed cross section (M-FCS), it is deduced that under the same internal volume of the pipe and the same average flow velocity at the inlet, the internal flow rate of M-NCS is greater than that of M-FCS, with a local maximum increase of 43%, which can improve heat exchange efficiency. The Darcy friction factor of the internal fluid of M-NCS is smaller than that of M-FCS. The internal fluid pressure drop of the M-NCS is more significant, which requires a higher external pump energy required. It is also deduced that the average temperature change of the fluid inside M-NCS is larger than that inside M-FCS. In addition, the Nusselt number and convective heat transfer coefficient of the fluid inside M-NCS are larger than those of inside M-FCS. Moreover, the local maximum value of M-NCS is 18.5% higher than that of M-FCS. In summary, the obtained results show that, compared with M-FCS, M-NCS can improve the heat exchange degree and heat diffusion capacity of the fluid inside the microchannel pipe under the same inlet mass flow rate, allowing to enhance the heat transfer. This paper also studies the impact of the microchannel local structural changes on the heat transfer and fluid performance, which provides a theoretical support for the optimization of the microchannel design of heat exchangers.