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

Anewand simplerdesign ofthin-e lm heate ux gaugehasbeendeveloped forusein high-heat-e ux environments. Heat e ux gauges of the same design were fabricated on three different substrates and tested. The heat e 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 thesegaugesweree rst carriedoutin an arc-lamp calibrationfacility.Sensitivityofthegaugewasdiscussed in terms of the relative conductivity and surface temperature. The heat e 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 e 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 proe les in the thin-e lm heat e 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 e ux, W/m 2 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 2 Subscripts 1, 2 = thermal resistance layers 1 and 2, respectively