Experimental Study on Convection Heat Transfer of CO ₂ in C/SiC Composite Porous Material at Subcritical, Transcritical, and Supercritical States

Using C/SiC as the structure for transpiration cooling is prospective for new hypersonic vehicles, based on clarification of heat transfer process in porous media. But there are still gaps due to the complexity of pore structure of C/SiC, together with the effects of capillary force and strong variation of thermophysical properties for subcritical and supercritical flow. In this study, heat transfer analysis for C/SiC with CO2 as the coolant is presented by experiments. Heat transfer characteristics in typical C/SiC sample under various mass flow rates (0.003–0.018 kg/s), inlet fluid temperatures (20–40 °C) and pressures (5.9–10 MPa) are analyzed. Heat transfer and pressure drop correlations have been developed. The results show heat transfer coefficient at supercritical state behaves non-monotonic under varying flow rates caused by the combined effect of sharp increase of specific heat and the change of flow rate. The effect of pressure on heat transfer can be neglected compared to that of flow rate, while for Reynolds number (Re) >100, the pressure drop of supercritical cases are smaller than that of phase-change cases under similar Re, due to the effect of capillary force in C/SiC. This study can provide basic support for further study of transpiration cooling using C/SiC and CO2.