No abstract

No abstract

Supercritical-pressure heat transfer of a hydrocarbon fuel has practical importance in fuel precooling technology in hypersonic air-breathing propulsion systems. Heat transfer of n-decane in helical tubes is numerically studied at a supercritical pressure of 5 MPa, with consideration of endothermic fuel pyrolysis and surface carbon deposition. The effects of helical curvature on temperature variations, pyrolytic chemical reactions, and surface coking are analyzed. Results indicate that, owing to the centrifugal force and secondary flows, the averaged wall temperature in a helical tube is significantly reduced in the inlet region (x/D < 50). The fluid temperature is higher on the inner side of the helical tube, and as a result, the pyrolytic chemical reactions and heat absorption rates become correspondingly higher. With around 50% n-decane thermally decomposed at the tube exit, the bulk fluid temperature can be decreased up to 120 K. The coking precursors produced from fuel pyrolysis cause surface carbon deposition, and the coking amount on the inner side of the tube wall, with stronger fuel pyrolysis, is around twice that on the outer side. An empirical heat transfer correlation is found to work well for predicting supercritical-pressure heat transfer of n-decane in helical tubes, with or without fuel pyrolysis.