Flow And Heat Transfer Characteristics Of Kerosene Flowing Inside The Regenerative Cooling Channels Of Scramjet

The flow and heat transfer characteristics of RP3 kerosene flowing inside the cooling channels of scramjet have been studied in this paper. Research focuses on the flow patterns under different pressures while absorbing heat, the heat transfer characteristics of kerosene under sub-critical and supercritical pressures and the flow instability near the critical point.Flow pattern observation indicates that, conventional two-phase flow patterns, such as bubble flow, slug flow, churn flow, annular flow and so on would appear under sub-critical pressures; the opalescence phenomenon occurs when kerosene is heated to its critical temperature under critical pressure; it looks like single-phase flow under supercritical pressures; when the cracking reactions occur, the cracked gas products and coke would be dissolved in the supercritical uncracked kerosene, and the flow looks like single-phase flow too. Flow directions(vertical, horizontal, inclined) have little effects on the type of flow patterns, but will affect the distribution of the phases. The flow patterns under sub-critical pressures are divided into three types according to their effects on heat transfer, namely, bubble flow, gas core flow and dry out flow. Empirical formulas to predict the transitions between the flow patterns were put forward.The heat transfer characteristics of n-decane(suggoate of kerosene) under sub-critical and supercritical pressures were investigated. Under sub-critical pressures, the heat transfer characteristics could be divided into three regimes, namely, the liquid heat transfer, the two-phase heat transfer and the gas heat transfer. In the liquid heat transfer regime, mini-boiling happerns under a high heat flux(0.3MW/m2, i.e.)and the wall temperature keeps constant at the value of boiling point while the fluid temperature gradually increases. However, if the heat flux is low(0.08MW/m2, i.e.), it is single-phase heat transfer and the wall temperature would be below the boiling point and increase. Heat transfer coefficient increases with bulk temperature in liquid heat transfer regime. In the two-phase heat transfer regime, nucleate boiling and film boiling happern. The wall temperature keeps constant at the value of boiling point and the heat transfer coefficient is extremly high when nucleate boiling happerns. When film boiling occurs, the wall temperature increases sharply and the heat transfer coefficient decreases. In the gas heat transfer regime, it is single-phase heat transfer. Both wall temperature and fluid temperature increase. And the heat transfer coefficient nearly keeps constant. Furthermore, effects of heat flux, velocity and pressure on the heat transfer characteristics of n-decane under sub-critical pressures were investigated. Heat transfer characteristics of n-decane under supercritical pressures were also investigated and the results indicate that the heat transfer coefficient under supercritical pressure is lower than that under sub-critical pressure.The heat transfer characteristics of kerosene under supercritical pressures were investigated. It was found that when the inlet temperature of kerosene is low, there is a relatively deteriorated heat transfer region at the tube inlet because of the effects of laminar boundary layer. The heat transfer characteristics of kerosene under supercritical pressures could be divided into three regimes, namely, the common heat transfer regime, the enhanced heat transfer regime and the deteriorated heat transfer regime. The variations of properties and laminar flow are supposed to be responsible for the common heat transfer while turbulence is the main reason of enhanced heat transfer. In the deteriorated heat transfer regime, chemical reactions(combination of small molecules to big molecules) are attributed to the heat transfer deterioration. Furthermore, effects of heat flux, velocity and pressure on the heat transfer characteristics of kerosene under supercritical pressures were investigated.Comparison between the heat transfer data of kerosene under supercritical pressures and correlations were made. By taking the effects of property gradients into consideration, a new correlation was put forward, and the accuracy is improved a lot, with 90% of the data in the ±30% error band.Flow instability of kerosene near the critical point was investigated. It was found that this instability has a low frequency. Instability is more likely to happern under higher heat flux, smaller pressure, smaller velocity, smaller inlet temperature and smaller tube diameter conditions. According to the analysis of mass flow rate, differential pressure and wall temperature variations, this instability is supposed to be density wave instability. It starts when kerosene temperature approaches the pseudo-critical temperature and density decreases sharply, and would sustain if the density variation, mass flow rate and differential pressure match.