Experimental Investigation of Local Heat Transfer of Carbon Dioxide at Super-Critical Pressures in a Vertical Tube and Multi-Port Mini-Channels Under Cooling Conditions

A method to obtain the local heat transfer coefficients of carbon dioxide at supercritical pressures in vertical multi-port mini-channels and in a vertical small tube under cooling conditions was presented through the combination of experiments and numerical simulation in this paper. The CFD code FLUENT 6.1 was used to simulate the convection heat transfer of cooling water to determine the local heat flux on the outside wall of the multi-port mini-channels and the small tube for the experimental conditions. The effects of pressure, mass flow rate of CO2, inlet temperature, and mass flow rate of cooling water on heat transfer were investigated. The experimental results showed that the sharply variable thermophysical properties of carbon dioxide have a significant effect on the local heat transfer coefficient which varies significantly along the vertical mini-channels and small tube when the CO2 bulk temperatures werewithin the near-critical region.