Experimental Performance of a Heat Flux Microsensor

Abstract

The performance characteristics of a heat flux microsensor have been measured and analyzed. This is a new heat flux gage system that is made using microfabrication techniques. The gages are small, have high frequency response, can measure very high heat flux, and output a voltage directly proportional to the heat flux. Each gage consists of a thin thermal resistance layer sandwiched between many thermocouple pairs forming a differential thermopile. Because the gage is made directly on the measurement surface and the total thickness is less than 2 μm, the presence of the gage contributes negligible flow and thermal disruption. The active surface area of the gage is 3 mm by 4 mm, with the leads attached outside this area to relay the surface heat flux and temperature signals. Gages were made and tested on glass and silicon substrates. The steady and unsteady response was measured experimentally and compared with analytical predictions. The analysis was performed using a one-dimensional, transient, finite-difference model of the six layers comprising the gage plus the substrate. Steady-state calibrations were done on a convection heat transfer apparatus and the transient response was measured to step changes of the imposed radiative flux. As an example of the potential capabilities, the time-resolved heat flux was measured at a stagnation point with imposed free-stream turbulence. A hot-film probe placed outside the boundary layer was used to provide a simultaneous signal showing the corresponding turbulent velocity fluctuations.

High Pressure Turbine Vane Annular Cascade Heat Flux and Aerodynamic Measurements With Comparisons to Predictions

“…The gauges are fabricated on 50-micron polyirnide Upilex sheets using conventional photolithography techniques, Cue (1994), Guo et al (1995) and Jones (1995). Similar heat flux microsensors have also been developed by Vatell Corp. (Hager et al 1991). The Upilex and glue layers have similar uniform thermal properties, requiring only a single calibration for temperature coefficient of resistance.…”

Comparison of Thin Film Heat Flux Gauge Technologies Emphasizing Continuous-Duration Operation

“…Since then, this technology has enabled the study of unsteady heat flux for turbine components in both the stationary [5,14,15] and rotating [15][16][17] reference frame of airfoils, in the tip region [18][19][20], and more, benefitting from a minimally intrusive design. Different types have been used [21][22][23][24], but all operate by solving the unsteady conduction equation through a substrate or substrates given a set of boundary conditions.…”

Review of Heat Flux Measurements for High Enthalpy Flows

“…HFM are known since the 1990s and are commercially available. 23 The size of these sensors is very small and this results in fast response times (≈ 5 µs). 24 The temperature measurement is realized as thin films forming a thermopile on both sides of the resistance element.…”