Research On Heat Transfer Enhancement Of Hydrocarbon Fuel Under Supercritical Pressure Conditions In Mini-channel

Regenerative cooling process is very important for thermal protective system of hydrocarbon fueled scramjet engine.In order to weaken the thermal stratification and heat transfer deterioration inside the cooling channel,numerical investigations of the flow and heat transfer characteristics of supercritical hydrocarbon fuel in rectangular mini cooling channels with micro-ribs are applied.Firstly,a 3-d fluid-solid-thermal couple model with rans turbulence model of a micro-ribbed cooling channel for scramjet regenerative cooling systems.The flow and heat transfer charateristics of the smooth channel and micro-ribbed channel are co MPared.It has been found that the micro-ribs could decrease the wall temperature.And the micro-ribbs alliviate the thermal stratification and delay the heat tranfer deterioration.In addition,the “shock effect” occurs in front of micro-ribs caused by dramatic properties change of supercritical fuel and the heat conduction of channel side walls is improved,both of which promot the mixing of fluid in the radial direction of the channel and effectively enhance the convective heat transfer inside the channel.Then,PPD model was adopted to explore the thermal cracking and heat transfer inside the micro-ribbed cooling channel.The results show that the effects of micro-ribs on the channel center region and near wall region are different.The complex second flows and strong shear effect coused by micro-ribs enhcane the heat transfer in the near walkl region,thus,the wall temperature decreases and thermal cracking slows down.Besides,the micro-ribs enhance the mixing of fluid in the radial direction of the channel and extend the residual time of fuel,which promotes the thermal cracking.Meranwhile,smaller activation energy and bigger pre-exponential factor will accelarate the thermal cracking,so the heat transfer inside the channel is enhanced.And higher heat flux will aggravate the thermal stratificationand higher pressure reduces fluid velocity,which all decrease the heat transfer.And higher micro-ribs will increase the turbulence intensity in the radial direction of the channel,which all promotes the thermal cracking and heat transfer.