Investigation on flow and heat transfer of fluid in self-driven circulation system for transpiration cooling

Transpiration cooling has attracted extensive attention from industry as an efficient thermal protection strategy to cope with the extreme thermal environment during hypersonic vehicle flight. Unfortunately, the investigation on transpiration cooling in combination with internal coolant piping layout is inadequate. Here, we propose a self-driven natural circulation system as the internal coolant channel in the lower layer of the transpiration cooling structure, aiming to achieve comprehensive thermal management. Meanwhile, a time-resolved Quantitative Light Sheet technique is applied in experimental research on the natural circulation system. Through investigating the flow, heat transfer and phase transition characteristics of the fluid in the system, it is concluded that this system utilizes the heat flux difference loaded on the pipe wall to drive the coolant to circulate in the loop, and the maximum wall heat flux reaches about 15.4 kW/m², realizing internal self-adaptive cooling. Additionally, this proposed system ensures that the phase transition occurs in the lower pipes of the transpiration structure to avoid heat transfer deterioration. Besides, the system releases 57,600 cm³ steam within 100 s under the 500 W/m² heat flux difference of pipes acting as coolant for transpiration cooling. Thus, this work provides an innovative reference for combined application of transpiration cooling and self-driven natural circulation system.