Steady-State and Frequency Response of a Thin-Film Heat Flux Gauge

Abstract

Anew and simpler design of thin- lm heat ux gaugehas been developed for use in high-heat- ux environments. Heat ux gauges of the same design were fabricated on three different substrates and tested. The heat ux gauge comprises a thermopile and a thermocouple junction, which measures the surface temperature. The thermopile has 40 pairs of S-type thermocouples and is covered by two thermal resistance layers. Calibration and testing of these gaugeswere rst carried out in an arc-lamp calibrationfacility. Sensitivityof the gaugewasdiscussed in terms of the relative conductivity and surface temperature. The heat ux calculated from the gauge output was in good agreement with the precalibrated standard sensor. The steady-state and the transient response characteristics of the heat ux gauge were also investigated using a carbon dioxide pulse laser as a heat source. The dynamic frequency response was evaluated in terms of the nondimensional amplitude ratio with respect to the frequency spectrum of a chopped laser beam. The frequency response of the gauge was determined to be about 3 kHz. The temperature pro les in the thin- lm heat ux gauge were obtained numerically in steady-state conditions using FLUENT and compared with the experimental results. Nomenclature d = thickness of thermal resistance layer, m Es = thermopile voltage output, mV K = thermal conductivity,W/m C K = relative conductivity,W/m C N = number of thermocouple pairs in the thermopile Q = heat ux, W/m2 S T = absolute thermoelectric power at temperature T, mV / C T = temperature, C t = time, s = absorptivity d = thickness difference in thermal resistance layers between 1 and