Coupling of pyrolysis and heat transfer of supercritical hydrocarbon fuel in rectangular minichannels

Abstract The coupling of pyrolysis and heat transfer of endothermic hydrocarbon fuels (EHFs) plays an important role in the design of cooling channels for advanced aircrafts. In this work, the convective heat transfer of EHFs with pyrolysis was experimentally investigated in horizontal rectangular channels under supercritical conditions (3.5 MPa, 700 °C) with different aspect ratios (λ = 1 ~ 5) by electrically heated tube test. CFD simulations with an updated kinetics were conducted and extensively validated to get detailed information of local flow, pyrolysis and heat transfer. The heat transfer is non-uniform in the cross-section with obvious temperature difference due to non-uniformity of boundary layer. Increasing λ is beneficial for heat transfer at topwall because of a relative lower heat flux and higher chemical heat absorption in bulk fluid. In addition, significant distribution of boundary layer along topwall and sidewall results in M-shape velocity distribution and subsequent high-degreed pyrolysis near sidewall region. This leads to dramatical variations of thermophysical properties and considerable decrease of chemical heat absorption, thus increasing the near-wall thermal resistances. Therefore, the local heat transfer is deteriorated at sidewall and corner, ascribed to a thicker boundary layer at the corner for increased fluid viscosity with secondary reactions, as well as the increased thermal resistances attributed to huge property gradient for pyrolysis distribution near sidewall.