Dynamic coking simulation of supercritical n-decane in circular tubes

Abstract

Carbon deposition is an inevitable phenomenon in regenerative cooling systems using endothermic hydrocarbon fuels (EHFs), which seriously affects heat transfer performance and even clogs cooling channels. In this study, a framework of 2D dynamic coking study is established by coupling simultaneously a detailed pyrolysis model with the MC-II coking model. Two types of coke, i.e., catalytic coke and pyrolytic coke, are considered, and the coking process is simulated via dynamic mesh techniques. The flow and heat transfer characteristics, and heat sink before and after the carbon deposition under typical working conditions are compared and discussed in detail. The results reveal that the secondary cracking reactions promote the concentration of the coking precursors, and the coking simulation results agree well with the experiment. The maximum fluid flow velocity and maximum solid temperature are increased after the coking formation due to the reduction of the cross section area and the poor thermal conductivity of the deposited coke. As the coke deposits, the total heat sink per temperature rise and pressure drop both deteriorate. However, the maximum conversion of n-decane is almost unchanged, which can be well explained by the local DamkÖhler (Da) number.