Research Project A06

The project starts as a new research project in the second funding period of SFB 1313.

In the realm of advanced cooling concepts, transpiration cooling (TC) is considered an effective thermal protection technique for high-temperature components, as required for gas turbine applications or combustion chambers in rocket engines. In this project, we consider an extension of this methodology: the self-pumping transpiration cooling (SPTC) concept. Such systems are able to automatically adapt the coolant mass flow to different free-flow conditions without employing any pump or control unit. Moreover, thanks to the combined effect of high heat capacities of liquids and heat absorption during evaporation, they can attain much higher heat fluxes compared to gaseous coolants as used in conventional TC devices.

Despite progress, many open questions remain both at the fundamental and operational level. Fundamental research questions pertain to the formulation of coupling conditions between the free-flow/porous media region to describe the interfacial exchange of mass, momentum and energy for two-phase flows under evaporative conditions. Moreover, it is not fully understood how capillary forces are affected by changes in pore size and morphology (e.g. due to clogging) or non-isothermal conditions within the porous region. All these effects influence not only the interfacial coupling conditions, but also hamper the functionality of SPTC systems that use capillary forces to drive the liquid coolant (e.g. water) from the tank to the heated porous surface.

To answer these questions, we will first perform a systematic study of the turbulent interfacial flow at representative conditions for SPTC applications, by measuring fluid and surface temperatures, time- resolved velocity and concentration fields within the respective laminar sub-layers. These investigations will enable us to identify the relevant driving processes and to formulate new coupling conditions for energy, momentum and mass transfer at the interface under turbulent, non-isothermal and evaporative conditions. Second, we will investigate how the interface exchange processes (mass, momentum and energy) are affected by systematic variations of thermal loads, cross-flow turbulent conditions, porous media topology and pore size morphology due to clogging.