Convective heat transfer of supercritical CO2 flowing a mini circular tube under high heat flux and low mass flux conditions

To obtain the heat transfer law of supercritical CO2 under high heat flow and low flow rate, the experimental study on convective heat transfer of supercritical CO2 in a small circular tube with an inner diameter of 2 mm was carried out, and the effects of variable properties, buoyancy and thermal acceleration were discussed. The operating parameters were as follows: system pressure p = 7.6-8.4 MPa, mass flux G = 400-500 kg/(m2∙s), heat flux q = 0-200 kW/m2, fluid temperature Tb = 20-62℃, and Reynolds number Re = 1.23×104-4.3×104. The dimensionless parameters of Gr/Re2 and Kv were adopted to represent the buoyancy effect and thermal acceleration, respectively. The results show that the buoyancy effect is significant (Gr/Re2 > 10-3) under high heat flux and low mass flux conditions, and the heat transfer coefficients at top wall are always lower than those at bottom wall for a certain section. The buoyancy effect is the main factor that cause heat transfer deteriorate, while the thermal acceleration criterion is insignificant (Kv < 8.5×10-7) and thus can be neglected. The experimental data were compared with typical heat transfer empirical correlations, in which the Liao-Zhao correlation fit well with the experimental data. © All Right Reserved.