The influence of coking on heat transfer in turbulent reacting flow of supercritical hydrocarbon fuels

Abstract

Significant influence from coking (aggregation and formation of a non-desirable carbonaceous porous layer on a solid metal surface) on the heat transfer in a cooling system of hypersonic aircraft with hydrocarbon fuel as the coolant is observed. In the present work, an explanation was proposed to understand the influence mechanism of coking on the heat transfer in cooling channel. In addition, a numerical model was further established to verify the explanation by comparing the heat transfer in cooling channel with different thicknesses of coke layer. The results indicated that critical thicknesses of coke layer with respect to effective thermal conductivity (δcl,λc) and heat transfer (δcl,hc) existed. More specifically, the heat transfer was noticeably enhanced when δcl <δcl,hc, while the heat transfer is deteriorated as δcl > δcl,hc. A transition thickness with length of (δcl,hc–δcl,λc) existed between δcl,λc and δcl,hc under the combined influences of convection of core flow and coke layer. By comparing the heat transfer in cooling channel after coke deposit at different inlet Reynolds number, it was further found that δcl,λc and δcl,hc decrease with increasing the turbulent intensity. This implied that the influence of inlet Reynolds number on the coke deposition rate and turbulent heat transfer were dissimilar. This study is expected to provide further insight into the optimization of cooling channel for the purpose of reducing the heat transfer deterioration caused by coke.