Numerical investigation on heat transfer of supercritical carbon dioxide in Zig-Zag PCHE channel

Near the pseudo-critical point, the properties of supercritical carbon dioxide (CO₂) vary dramatically with temperature, which makes its heat transfer in channels very complex. Moreover, the complicated geometry significantly perturbs the supercritical CO₂ flow in the Zig-Zag printed circuit heat exchanger (PCHE) channel. In this study, the Large eddy simulation (LES) has been performed to investigate the heat transfer of supercritical carbon dioxide in the Zig-Zag PCHE channel under cooling conditions. An implicit, second order accurate finite volume scheme is applied to solve the flow and heat transfer equations, while the WALE model is used to account for the subgrid-scale effects. The size of mesh is set in the inertial subrange to capture the large eddy structure. The simulation results shows that the instantaneous velocity has significant influence on the large-scale time-averaged properties of supercritical CO₂. The instantaneous turbulent flow result in the fluctuation and irregular distribution the temperature fields and heat transfer in the channel. In the cross section of channel, the CO₂ with high-density, low heat capacity and high thermal conductivity contacts with the wall to ensure a better heat transfer capability, which result in the large temperature gradient near wall. Furthermore, due to the Zig-Zag channel, the mean wall shear stress on one side of pitch is higher than that of other side of pitch, which lead to that the higher heat transfer coefficient occurs the side with higher wall shear stress. (author)