Button gages have been extensively used to measureconvective heat transfer coefficients in a number of short durationexperiments. A button gage consists of a small insert made from an insulatormaterial, typically Pyrex, with a thin film of Platinum active element paintedon its surface. In a typical short duration experiment, gages are initially at thesame temperature as the test article. As the flow is established, convectiveheat flux results in the surface temperature of the gage to rise much morerapidly than the surrounding metal walls. The influence of this non-isothermal wall condition on the local thermal boundary layer and hence themeasured data is the focus of the present program.A detailed experimental study of the influence of local non-isothermalconditions on the inferred heat flux from button heat-flux gages is performed.An existing wind tunnel capable of generating subsonic through transonicflow conditions has been modified to include an isothermal flat plate testsection with a row of surface flush-mounted button heat-flux gages. Inaddition to the button gages, a uniform sheet of two-layered Kapton heat-flux gages, operating under isothermal conditions, are also applied to the flatplate surface. A detailed study of the uncertainties of experimental results isperformed. As part of this study, flow Mach number and Reynolds numberare varied and their relative significance upon the deviation in the responseof the gages is quantified. The measured heat flux did show a deviation fromthe isothermal measured values. It is further shown that a correction termbased on classical heat transfer theory will adjust the measured heat flux onthe flat plate to match isothermal values for a range of Reynolds numbersand temperature ratios.
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