Performance assessment of K-type, E-type and J-type coaxial thermocouples on the solar light beam for short duration transient measurements

Abstract

The estimation of transient surface heat flux from transient temperatures background using fast response thermal sensors is one of the most prevalent technique used for short duration measurements where the heat transfer rate changes rapidly such as in the applications of internal combustion engine, gas turbine engine, high-speed flight test, aerodynamics re-entry vehicle, etc. The coaxial thermocouples are quite beneficial in these engineering applications due to having a very quick response time in the order of a millisecond or less (~0.1 ms). Moreover, these coaxial thermocouples are more cost-effective because they can be contrived in-house. As they have coaxial geometry, it can be directly executed in any type of surface geometry. This work deals with the fabrication of K-type, E-type and J-type coaxial thermocouples and a unique type of calibration technique has experimented in the laboratory. These fabricated coaxial thermocouples are calibrated statically using oil-bath based technique for performance analysis and calculate the thermal coefficient resistance (TCR) & sensitivity (S). A new type of experimental arrangement is devised by applying a known value of step heat load on the junction of the coaxial thermocouple. The concentrated sunlight beam has been focused on the junction of the coaxial thermocouple and the variation in transient temperature has been recorded. Subsequently, their transient heat flux has been estimated using one-dimensional heat conduction modeling for the semi-infinite body. The numerical analysis carried out using commercial software Ansys 15.0 and analytical evaluation is found to be a reasonable covenant between experimental results. This analysis states that these handmade coaxial thermocouples are suitable to measure the surface heat flux in the sunlight based application for short duration transient measurements.