Experimental investigation on thermal cracking and convective heat transfer characteristics of aviation kerosene RP-3 in a vertical tube under supercritical pressures

Abstract

This study experimentally investigated the pyrolysis and heat transfer characteristics of a specific EHF (aviation kerosene RP-3) flowing in a vertical upward tube under supercritical pressures (2.5–5.5 MPa). Three wall heat flux conditions, i.e. 700, 950, and 1240 kW/m2 are designed to represent the condition with no significant cracked, mildly cracked, and deeply cracked of fuel, respectively. The results show that the elevated pressure could impact on the reaction pathway of alkanes and alkenes, resulting in a smaller alkene/alkane ratio and less endothermicity. A promoting effect of the elevated pressure and heat flux on the conversion and gas yield is confirmed in this work. Then heat transfer characteristics are analyzed in detail based on the wall temperature and the local (apparent)/average HTC distributions. The buoyancy effect causes the deterioration of heat transfer under high heat flux. The elevated pressure decreases the maximum wall temperature whereas enlarges the range of heat transfer deterioration region. A conclusion could be obtained that the increase of pressure has little effect on alleviating of heat transfer deterioration under rather large heat flux conditions. The average HTCs in the cracked region is twice larger than that in the non-cracked region, indicating that the pyrolysis improves the heat transfer of fuel. Besides, it is found that the influence of pressure on heat transfer characteristic is dominated by the isobaric specific heat capacity and density in the non-cracked region and the cracked region, respectively. Furthermore, the effect of pyrolysis on heat transfer deterioration is investigated. It is found that the strong pyrolysis reaction near the wall is beneficial to lower the wall temperature in the HTD region, and the buoyancy effect is not significantly increased by the further decrease in fluid density caused by pyrolysis.