Novel Sensor for Fast Heat-Flux Measurements

摘要

The Atomic Layer Thermopile is a novel fast-response sensor for transient heat-flux measurements. The sensor's very fast frequency response allows for highly-time-resolved heat-flux measurements up to the 1 MHz range. Its working principle is based on the transverse Seebeck effect. The output signal is directly proportional to heat-flux density and has a linear characteristic from the mW/cm~2 to the kW/cm range. Its steady and unsteady responses have been determined experimentally by a step change of imposed radiative flux. The results correlate well with theoretical values obtained from analytical solutions. Furthermore, the dynamic properties of the Atomic Layer Thermopile have also been evaluated by a passing shock wave. The Atomic Layer Thermopile gauge recorded a steplike change in heat flux less than 1 μs after the shock had passed. After the peak heat flux, a laminar boundary-layer state could be detected for a unit Reynolds number of 11.31 × 10~6/m. In addition, in particular, the temporal resolution and the spatial resolution of the Atomic Layer Thermopile were demonstrated in instability studies performed in a hypersonic conical boundary layer at M = 6. In addition to second-mode instability in the 220-370 kHz frequency range, a second peak in the spectra revealed a first harmonic of this instability at 430-730 kHz.