Numerical investigation on heat transfer and pressure drop characteristics of coupling transcritical flow and two-phase flow in a printed circuit heat exchanger

摘要

Printed Circuit Heat Exchanger (PCHE) has attracted researchers a lot those years due to its advantages of sturdy structure, compact volume and high thermal efficiency. Transcritical flow and condensation flow can be coupled as cold fluid and hot fluid respectively to exchange heat. However, large variation of thermophysical properties of transcritical process as well as large energy density of phase-change process bring unknown thermo-hydraulic characteristics when the two-process coupled with each other. In this study, double bank channel unit PCHE model was established to simulate the real case transcritical-condensation heat transfer. The effects of buoyancy and flow acceleration were calculated for transcritical process. Local information of heat transfer and flow characteristics for both hot side (condensation flow) and cold side (transcritical flow) were obtained and analyzed. The effect of mass flux on the two-side was then presented. At last, comparisons were conducted between the heat transfer and pressure drop characteristics of the double bank channel unit and that of the single bank channel unit with constant heat flux boundary conditions. Exergy analysis was also present to evaluate the irreversibility of coupled transcritical-condensation flow. The results showed that the effect of buoyancy and flow acceleration can be neglected under the present working conditions. As for the effect of mass flux, the variation of condensation flow mass flux would bring larger effect on heat transfer. Besides, the heat transfer performance of transcritical flow would be deteriorated when coupled with condensation flow due to a large heat flux segment caused by condensation, implying that the real thermal boundary was mainly constructed by condensation process. Besides, larger irreversible loss can be obtained when transcritical flow coupled with condensation flow compared to couple with single phase flow. The results would give a valuable reference for the study on conjugate heat transfer and the design on PCHE.