High-Temperature Calibration of Direct Write Heat Flux Sensors From 25 °C to 860 °C Using the In-Cavity Radiation Method

Abstract

Heat flux sensors fabricated using Direct Write Thermal Spray are thin, surface-based devices that can operate at high temperatures. In this paper, Direct Write heat flux sensors are calibrated over a temperature range of 25°C-860°C. A substitution-based quartz lamp configuration is used to measure the steady-state sensitivity and transient response of Direct Write sensors at ambient temperatures, with repeatability confirmed over a 10-month period and after thermal aging. A matched heat flow approach is used to characterize the sensors at operating temperatures up to 860°C. The sensitivity is found to increase by a factor of two from 25°C to 650°C, after which it plateaus up to the maximum tested temperature of 860°C. A cubic polynomial calibration function captures the temperature dependence of the sensitivity and provides a good agreement for the measured data.Index Terms-Heat flux, heat flux sensor, high temperature, thermal sensor, heat flow sensor, thermopile.

Development of thin film heat flux sensor based on transparent conductive oxide thermopile with antireflective coating

“…Polynomial calibration curves can be used to describe nonlinear behavior exhibited by thermocouple sensors (Trelewicz, 2015). Furthermore, as we can see from Figure 9(d), there was a third-order polynomial to describe relation between temperature and sensitivity factor from ambient to 794°C in Figure 9(d).…”

“…The large heat flux was provided by laser radiation (Trelewicz, 2015). The standard sensor measured the load heat flux provided by laser beam whose energy was nearly homogeneous, then the output characteristics of thin film HFS was calibrated.…”

Heat Flux Measurements in a Scramjet Combustor Using Embedded Direct-Write Sensors

“…The Seebeck coefficient is temperature-dependent, and the selected value is an appropriate estimate for direct-write deposited type N alloys operating over the range of 75-150°C (167-302°F), which captures the range of sensor temperatures during operation in the conduction experimental apparatus. These values yield a sensitivity β ≈ 3.0 mV∕W · cm −2 , which is roughly an order of magnitude greater than the estimated sensitivity for similar sensors in [19]. This enhanced sensitivity can be attributed to having twice the number of thermocouple junctions and a thicker thermal resistance layer with an inherently lower thermal conductivity (YSZ).…”

“…For use over larger temperature ranges, standard thermocouple polynomials for S AB and literature values for the temperature dependence of k [18] can be used. Alternatively, the heat flux sensor can be calibrated directly over the temperature range of interest [19].…”

“…The preliminary calibrations shown in Table 1 indicate a variation of up to 13% compared to the value of 3.0 mV∕W · cm −2 used for the reported results later. Temperature changes in the sensor will also likely augment the sensitivity [35] but were not characterized for the specific sensors investigated in this work. In light of these contributions to the measurement uncertainty, the heat flux values are estimated to have an overall uncertainty of 20% of the indicated reading.…”