The development of a new direct-heat-flux gauge for heat-transfer facilities

A new type of direct-heat-flux gauge (DHFG) comprising an insulating layer mounted on a metal substrate has been developed. The gauge measures the heat flux across the insulating layer by measuring the top surface temperature employing a sputtered thin-film gauge (TFG) and the metal temperature using a thermocouple. The TFGs are platinum temperature sensors with physical thickness less than 0.1 µm. They are instrumented on the insulating layer. The thermal properties and the ratio of the thickness over the thermal conductivity of the insulating layer have been calibrated. A detailed method of analysis for calculating the surface heat flux from DHFG temperature traces is presented. The advantages of the DHFG include its high accuracy, its wide range of frequency response (from dc to 100 kHz) and, most significantly, that there is no requirement for knowledge of the structure of the metal substrate. Since the metal substrate is of high conductivity, few thermocouples are required to monitor the small spatial variation of the metal temperature, whereas multiple thin-film gauges may be employed. The DHFGs have been applied to a gas turbine nozzle guide vane and tested in the Oxford Cold Heat Transfer Tunnel successfully.