Transient Response Characteristics and Performance Assessment of a Calorimetric Surface Junction Probe Under Impulsive Thermal Loading

Abstract

The measurement of surface temperatures in highly unsteady flow environments is a challenging task pertaining to the need for high-frequency sensors. This paper contains the sequential activities related to a fast response thermal probe (coaxial surface junction probe—CSJP). This probe is prepared in the laboratory, and its salient features are explored for short-duration (∼20 ms) experiments. The surface junction morphology and inside texture of the probe are examined under field emission scanning electron microscope (FESEM). The study confirms the plastic deformation of thermo-elements with an average junction thickness of 21 μm. The static calibration of the probe using a glycerin bath shows a linear trend between voltage and temperature from which the sensitivity value is calculated as 59 μV/°C. The “thermal product” of the probe is also measured experimentally through the “water droplet technique,” and its value is found to be 8677 J/m2 s0.5 K. The concept of one-dimensional heat flux modeling is followed to infer surface heat flux from transient temperatures. For assuring prediction of heat flux, the probe is calibrated experimentally by exposing to a laser source of known wattage (2 W and 3 W). These findings are also supported by numerical simulation of the probe with accuracy in prediction for surface temperature and heat flux as ± 2% and ±3%, respectively. The performance capability of the probe is demonstrated through shock-tube flow experiments to measure instantaneous heat flux. The comparison of the transient response behavior (9500 K/s) with pressure transducer justifies the utility of the probe under hostile flow environment.