On Thin-Film Heat-Transfer Measurements in Shock Tubes and Shock Tunnels

Abstract

In the measurement of aerodynamic heat transfer in shock tubes and tunnels utilizing thin-film resistance thermometers, it is assumed that the thermal properties of the gauge (film and substrate) are constant. Since surface temperatures of bodies in hypersonic flow often reach temperatures of several hundred degrees, the validity of this assumption should be tested. A technique is described for measuring the temperature dependence of the product of the density, thermal conductivity, and heat capacity of various substrates for thin-film resistance thermometers. The results for Pyrex, quartz, and plate glass, which have been used as backing materials for thin-film resistance thermometers, indicate that sizable errors may be encountered in inferring heat-transfer rates from measured surface-temperature histories if the thermal properties are assumed constant. The corrections which must be applied to account for the temperature dependence of the thermal conductivity and the specific heat have been established through an approximate theoretical solution of the nonlinear one-dimensional heat-conduction equation. The magnitude of the correction depends on the material of the substrate and the surface temperature. For Pyrex at 150°C it is about 45% and for fused quartz and glass about 15%.