Investigation On Transpiration Cooling Within Sintered Porous Material

With the development of aero-space technology, near space aero-craft system, long-endurance navigation, hypersonic vehicles are becoming the focuses of current research. However this development of aero-vehicles has to face huge challenges of thermal environment, especially for the hypersonic vehicles. When the vehicles pass through the near space, they have to protect their thermal structures from the high temperature of the combustion in propulsion system, extremely high aerodynamic heating in the front of the vehicles. In these situations, transpiration cooling technique, as the most effective approach of active thermal protections, is widely studied.In this dissertation, several transpiration cooling experimental investigations carried out by stainless steel and metal-ceramic sintering porous specimens are presented. At first, clean air was used as cooling medium, and infrared thermal imaging technique was adopted to measure the surface temperature distribution exposed in high temperature mainstream. The generation and development performances of cooling air boundary layer in the high temperature surface are measured and analyzed. In the experiments, clean air was used as cooling medium, the specimen was made of the metal-ceramic powder sintered material, and the influence factors on the cooling effectiveness, such as mainstream temperature and velocity, cooling injection rate and temperature, were analyzed and discussed.In order to investigate the penetration performances of fluid flow passing through heterogeneous porous media, a sintered porous alloy plate was used as specimen in this dissertation. The relationships of the mass flow rate of different fluids with the corresponding driving force were measured in the experiment. Single phase alcohol, pure water and clean air were used as penetrating fluids. Through this experiment, three non-Darcy phenomena, the transient pressure of liquid flow penetrating porous media, pre-force to open all pores and viscosity interaction between fluid and solid, were discovered and discussed. Based the discussions, a relatively perfect Darcy’s equation, in which the transient pressure, pre-force to open all pores and viscosity interaction between fluid and solid wall are considered, was suggested.Liquid coolant has the advantages for the aero-space vehicles, for example, high latent heat of vaporization, smaller storage space and lower transportation cost. Therefore it is important to carry out the basic experimental investigations on the transpiration cooling with liquid-coolant phase change. In the experiments, the injection mass flow rate of liquid water was adjusted to keep the phase change position inside sintered porous structure at different mainstream temperatures and velocities. The transpiration cooling characteristics of high-temperature mainstream across the sintered porous plate are studied, the mechanical properties of the transpiration cooling with liquid phase change are analyzed, and the interaction of the driving pressure drop of the coolant with the capillary force is discovered. To analyze the influence rules of heat flux on the cooling efficiency with liquid phase change, a minimal coolant mass injection rate was introduced as evaluation criterion.On the basis of the experimental investigations on the phase change transpiration cooling, this dissertation presents a feasibility test using the sintered porous media and liquid water. To create a relatively real condition of supersonic aircraft, the stainless sintered porous specimen was put in an electric arc heating wind tunnel, and the experiments were conducted at a mainstream Mach number of2.19, a total pressure of0.14Mpa and a heat flux of1.4MW/m2. With heat transfer deterioration phenomena appeared in the process of transpiration cooling, the interaction mechanism of the liquid water temperature with the cavity pressure drop and temperature of the specimen was discussed. Under the conditions of extremely high heat flux, the relationship of the coolant cavity pressure drop, the diving force of coolant and capillary force is discussed.