HIGH-FREQUENCY HEAT-FLUX SENSOR CALIBRATION AND MODELING

A new method of in-situ heat flux gage calibration is evaluated for us e in convective facilities with high heat transfer and fast time respo nse. A Heat Flux Microsensor (HFM) was used in a shock tunnel to simul taneously measure time-resolved surface heat flux and temperature from two sensors fabricated on the same substrate. A method is demonstrate d for estimating gage sensitivity and frequency response from the data generated during normal transient test runs. To verify heat flux sens itivity, shock tunnel data are processed according to a one-dimensiona l semi-infinite conduction model based on measured thermal properties for the gage substrate. Heat flux signals are converted to temperature , and vice versa. Comparing measured and calculated temperatures allow s an independent calibration of sensitivity for each data set. The res ults match gage calibrations performed in convection at the stagnation point of a free jet and done by the manufacturer using radiation. In addition, a finite-difference model of the transient behavior of the h eat flux sensor is presented to demonstrate the first-order response t o a step input in heat flux. Results are compared with shock passing d ata from the shock tunnel. The Heat Flux Microsensor recorded the heat flux response with an estimated time constant of 6 mu s, which demons trates a frequency response covering DC to above 100 kHz.