Effect of thermal pyrolysis on heat transfer and upward flow characteristics in a rectangular channel using endothermic hydrocarbon fuel

Supercritical heat transfer deterioration can be found in active regenerative cooling processes. Thermal pyrolysis occurs once the temperature of the hydrocarbon fuel exceeds a certain value. To investigate the influence of thermal pyrolysis on the heat transfer behavior and flow-upward characteristics in a rectangular channel, the wall temperature distribution, thermal acceleration, mass fraction of n-decane, streamline characteristics and vortex structure are analyzed based on a 26-step chemical reaction including 16 species. It is found that the wall temperature increases when the velocity in the viscous sublayer is similar to that in the buffer layer under the influence of thermal pyrolysis. This is because the shear stress and turbulence kinetic energy are diminished. Still affected by thermal pyrolysis, the velocities in the boundary layer become large so that the wall temperature is greatly decreased. This is because the n-decane near the wall is highly cracked and the density of the product is greatly decreased compared to cases without thermal pyrolysis. This indicates that thermal acceleration is beneficial to heat transfer. Besides, many vortices are created under the influence of thermal pyrolysis and this fact can be observed in terms of the distribution of the vortex structures. Vortices are also beneficial to heat transfer. This work is meaningful and significant to the practical design of active regenerative cooling systems.