ISBN 9783843958172

978-3-8439-5817-2, Reihe Thermodynamik

Julian Härter
Experimental Investigation of Self-Pumping Transpiration Cooling

185 Seiten, Dissertation Universität Stuttgart (2026), Softcover, A5

Zusammenfassung / Abstract

Self-pumping transpiration cooling (SPTC) offers a promising approach to thermal protection under high heat flux conditions. Unlike conventional transpiration cooling, it requires no external pumping system: capillary forces transport coolant through a saturated porous structure, where evaporation at the heated interface removes energy primarily through latent heat. However, the coupled heat, mass, and momentum transport processes, particularly at the porous interface and within the external boundary layer, remain insufficiently understood.

This thesis establishes an experimental framework for the quantitative investigation of SPTC. A dedicated facility was designed and commissioned to study evaporating porous surfaces under controlled turbulent channel flow conditions. Complementary diagnostics were developed and validated to measure evaporation rates, spatially resolved interface temperatures, and flow characteristics. These include a pressure-based method employing a Mariotte bottle, infrared thermography with differential emissivity correction, particle image velocimetry, interferometry, and laser-induced grating spectroscopy.

The results show that evaporation rates increase with free-stream temperature and Reynolds number and are significantly higher for isopropyl alcohol than for water. Independently measured evaporation rates and interface temperatures reveal an approximately linear relationship between evaporative heat flux and the free-stream-to-interface temperature difference, indicating convection-driven evaporation. Infrared measurements demonstrate the strong dependence of equivalent emissivity on pore morphology and surface structure. Flow measurements show no measurable disturbance of the external turbulent boundary layer, while interferometry reveals a thin optical boundary layer above the evaporating surface. Laser-induced grating spectroscopy further demonstrates the feasibility of water vapour concentration measurements in humid flows.