Plenum Pressure Behavior in Transiently Heat Loaded Transpiration Cooling System

Abstract

In this paper, the behavior of the plenum pressure behind a transpiration-cooled porous material sample after an incident surface heat flux to the sample is analyzed in experiment and theory. Two porous materials, zirconium diboride and carbon/carbon, were characterized using the pressure-based noninteger system identification method. The resulting impulse responses are analyzed based on two numerical models. One model calculates a plenum pressure impulse response by modeling the porous sample’s heat conduction. A second model considers an additional plenum behind the sample and allows a changing mass flow rate through the sample. The experimentally obtained impulse responses show a stronger response for increasing coolant mass flow rates. Both models cover this trend, essentially depending on the volumetric heat transfer coefficient. However, only the second model allows the entire rebuilding of the experimental data. The plenum pressure impulse response for a transpiration-cooled system depends not only on the material parameters of the porous sample, but also on the volume of the plenum. The reason is that the flow rate changes through the porous sample although the mass flow rate at the controller always stays constant.