Conjugate heat transfer, endothermic fuel pyrolysis and surface coking of aviation kerosene in ribbed tube at supercritical pressure

Supercritical-pressure heat transfer of hydrocarbon fuel plays an important role in regenerative engine cooling in propulsion systems. Conjugate heat transfer, fuel pyrolysis, and surface coking of the aviation kerosene RP-3 in ribbed tubes are numerically studied at a supercritical pressure of 5 MPa, with consideration of detailed pyrolytic chemical reactions. The rib effects on heat transfer, pressure loss, endothermic fuel pyrolysis, and surface coking are comprehensively examined. Results indicate that a ribbed tube is very effective in enhancing heat transfer of a hydrocarbon fuel at supercritical pressure, particularly in the inlet region, in which the tube wall temperature can be reduced by around 300 K. A ribbed tube surface makes significant impacts on fluid temperature distribution and thus fuel pyrolysis. The enhanced heat transfer leads to higher fluid temperature inside a ribbed tube in the downstream section, in which strong fuel pyrolysis occurs not only in the near-wall region, as in a smooth tube, but also inside the tube. Therefore, the pyrolytic chemical reaction rate of RP-3 increases in the downstream section in a ribbed tube. Owing to the decreased tube wall temperature and decreased species molar concentrations of coking precursors in the near-wall region, pyrolytic surface coking is weakened in a ribbed tube. The thermal performance factor is used to quantify the combined effects of different rib heights on both heat transfer and pressure loss for supercritical-pressure heat transfer of RP-3 in ribbed tubes.