超临界航空煤油在不同管径内的换热特性

Supercritical fluids are widely used in aeronautic, astronautic and nuclear engineering. Active cooling is necessary for scramjet engines to survive the extreme heat generated in hypersonic flight. Regenerative cooling system, where engine fuel works as coolants and travels through the cooling tubes along the chamber wall, carrying away heat from the wall via heat convection and endothermic chemical reactions, is developed as an effective thermal management technique. In this paper, experimental results of convective heat transfer performances of aviation kerosene at supercritical pressures were presented. Stainless steel circular tubes having inner diameters of 1and 1.8 mm were investigated for pressures ranging from 3 to 4 MPa, mass flow rates from 1.87 to 2.41 g/s and heat fluxes from 285 to 365 kW/m2. It was found that the heat transfer coefficient increases with mass flow rate at the former part of the tube. However, as the Reynolds increases significantly at the latter part of the tube at relatively low mass flow rate, the heat transfer coefficient increases dramatically at the latter part of the tube at relatively low mass flow rate. The effect of heat flux on heat transfer is complicated, while the effect of pressure on heat transfer is insignificant. The experimental results also indicated that the heat transfer coefficient decreases with the reduction in tube diameter. The heat transfer behaviors in relation to changes in tube sizes might be caused by the buoyancy effect.