Thermal Cracking and Heat Transfer of Hydrocarbon Fuels at Supercritical Pressures in Vertical Tubes

Regenerative cooling is being used to meet the high cooling requirements of advanced hypersonic flight vehicles using the fuel at supercritical pressures as the coolant. The heat transfer and thermal cracking characteristics vary with the pressure, mass flow rate and heat flux. This work presents an experimental investigation of the thermal cracking and the heat transfer characteristics of supercritical pressure hydrocarbon fuels and their interactions. A proportional production distribution chemical model was developed for the thermal cracking with the pre-exponential factor and activation energy to describe the reactions. Numerical results show good agreement with experimental data at low conversions (<25%). The heat transfer for supercritical pressure fuels with thermal cracking is very different from that without thermal cracking. Thermal cracking near the wall enhances the heat transfer by adding an extra heat sink, while coking and a bubble layer add thermal resistances to reduce the convective heat transfer.