Experimental Study on Heat Tranfer of Supercritical Kerosene in a Vertical Upward Tube
|Keywords||Supercritical pressure vertical upward tube heat transfer coefficient Kerosene enhanced heat transfer|
A major challenge scramjet engines currently faced is the high aerodynamic heat load. The wall temperature of combustion chamber without cooling can reach 3000K, which exceeds the limit of the general material used. Active regenerative cooling method which uses fuel to cool the wall is a significant innovation. As a new type of aviation fuel, Endothermic hydrocarbon fuel can not only take advantage of their own physical heat sink to absorb heat, but also occur high temperature cracking reactions to absorb a large amount of heat under the supercritical state, which cool the engine combustion chamber wall and improve the fuel efficiency.Three works have been done in this paper. At first, a literature review of heat transfer on supercritical fluids was completed. Secondly, a experimental facility for heat transfer of supercritical fluid on the 3rd kerosene was designed and built. Finally the experimental studies on the three main factors (the mass flow, heat flux, supercritical pressure) were carried out, which could affect heat transfer in supercritical fluids.From the experimental results, the increase of the mass flow can effectively decrease the wall temperature and improve the average heat transfer coefficient in supercritical state. At low mass flow, the wall temperature will rise when increased the heat flux. Because the viscosity and density would decrease when the fluid was heated continuously, the thermal boundary layer would be enhanced and the local heat transfer coefficient will increase gradually. However, the average heat transfer coefficient will increase as the heat flux decreases, when the fluid bulk temperature are same. Heat transfer Enhancement mainly occurs when the fluid bulk temperature reaches 300℃, while the corresponding wall temperature exceeded 400℃. This indicates the enhancement of heat transfer occurs when the fluid bulk temperature below the pseudo-critical temperature, while the wall temperature is higher than the pseudo-critical temperature, which has the same behaviors with the phenomenon in supercritical water and supercritical carbon dioxide. The increasing of supercritical pressure will weaken the heat transfer to some extent, which is mainly because the fluid specific heat will decrease as the increasing of the pressure. In addition, the cracking and coking of kerosene in high temperature also have an impact on heat transfer.