Parametric analysis on the thermal behavior of cracking hydrocarbon fuel flow inside asymmetry heated cooling channels with micro-ribs

Abstract

Micro-rib is an efficient heat transfer enhancement method for supercritical fuel in the regenerative cooling channel of advanced aero-engines. The endothermic hydrocarbon fuel would crack into smaller molecules at high temperatures and significantly change fluid properties, giving more complexity for flow and heat transfer in the micro-ribbed cooling channel. In this paper, a three-dimensional simulation model, embedded with a skeletal 22-step cracking mechanism, was established to conduct parametric analysis on thermal behaviors of cracking n-Decane at supercritical pressures in asymmetry heated channels with micro-ribs. The results reveal that thermal cracking would thicken the velocity boundary layer in the channel. Under this circumstance, regular size micro-ribs (h/H ≈ 10%) might abnormally weaken heat transfer of cracking hydrocarbon fuel and higher micro-ribs are required for effective heat transfer enhancement in the channel. Due to the low-density zone caused by cracking products near the heated wall, heat transfer enhancement brought by micro-ribs becomes less sensitive to the increase of micro-rib height. Besides, thermal cracking shortens the range of recirculation zones behind micro-ribs, thus much smaller micro-rib pitch is required for effective heat transfer enhancement. Furthermore, micro-ribs have better heat transfer enhancement performance in higher fuel conversion region, where the density gradient is smaller.