An experimental investigation on transpiration cooling performances using solid hydrogel as coolant

Abstract

This paper presents an experimental investigation on a new conception of thermal protection techniques for hypersonic vehicles, namely, transpiration cooling using solidified water as coolant. In the work, a commercial superabsorbent polymer, SAP-50, was used to make swollen hydrogel, and then a thermogravimetric analysis test of the home-made hydrogel was conducted. To enhance the heat transfer inside the solid hydrogel, a copper foam was embedded. The transpiration cooling experiments were carried out with a porous flat plate specimen in a hot wind tunnel, and the cooling characteristics captured by an infrared thermal imaging system are exhibited and compared between the hydrogel and water, with and without the copper foam. The original thermal images and the comparisons reveal the following novel and valuable phenomena: (1) Solid hydrogel and liquid water can provide approximate transpiration cooling effect. (2) Different from liquid water cooling, the hydrogel coolant can provide a longer acting time, and get a more homogenous cooling effectiveness distribution. (3) In the transpiration cooling systems without coolant injection force, the copper foam installed in the coolant chamber can provide a better cooling performance and longer effective time.