Numerical Study on Natural Circulation System under Various Cooling Mediums

Aiming at the global design issue of transpiration cooling thermal protection system, a self-driven circulation loop is proposed as the internal coolant flow passage for the transpiration cooling structure to achieve adaptive cooling. To enhance the universality of this internal cooling pipe design and facilitate its application, numerical studies are conducted on this system with four commonly used cooling mediums as coolant. Firstly, the accuracy of the numerical method is verified through an established experimental platform. Then, transient numerical simulations are performed on the flow states of different cooling mediums in the new self-circulation system. Based on the numerical result, the flow, phase change, and heat transfer characteristics of different cooling mediums are analyzed. Differences in fluid velocity and latent heat of phase change result in significant variation in heat exchange capacity among different cooling mediums, with the maximum difference reaching up to 3 times. Besides, faster circulation speed leads to greater heat transfer capacity, with a maximum of 7600 W/m². Consequently, the operating mechanism and cooling laws of the natural circulation system is further investigated, providing a reference for the practical application of this system.