Heated thin film gauge arrangements to reduce uncertainty in transient heat transfer measurements

Abstract

This paper describes the development of heated double-sided thin film gauge configurations for transient heat transfer measurements. By heating the substrate it is possible to measure the heat flux over a range of surface temperatures and deduce the adiabatic wall temperature and the external heat transfer coefficient. The accuracy of the measurement depends on the stability of the regression of heat flux against wall temperature and can be improved by extending the range of wall temperature over which the regression is performed. In this paper we compare two methods of local heating: double-sided gauges with an underside thin film heater and self-heating double-sided gauges. Both arrangements have been used in the Oxford Turbine Research Facility to measure the heat transfer on the uncooled turbine shroud of the MT1 high-pressure turbine stage at engine-representative conditions. These measurements yield improved regressions compared to conventional techniques to determine the adiabatic wall temperature and the heat transfer coefficient.

Investigation of a High-Pressure Turbine Stage in a High-Speed Rotating Transient Test Facility for Rotor Tip Study and a Parametric Study for Improved Heat Transfer Calculation

“…Given the good agreement between the 1D analytical solution and 3D thermal model over the short test window, the three-dimensional diffusion effects of heat can therefore be neglected. Usandizaga [14] also reported that lateral conduction is negligible if the test time t is sufficiently short such that αt << l 2 where l is the lateral length over which significant temperature variations could occur.…”

“…A thin, high resistivity and high length-width ratio thin-film gauge is desirable for good voltage-temperature sensitivity. The design and dimensions of the thin-film gauges have been optimised through numerous studies carried out at Oxford [11,12,14]. Serpentine gauges developed by Collins [12] were found to give erroneous measurements due to strain effects coupled with temperature effects.…”

“…Double-sided thin-film gauges developed by Usandizaga [14] feature a second thin-film several microns below the surface thin-film. This provides an additional temperature boundary condition that can be used to solve the 1D heat conduction equation without the semi-infinite assumption.…”