The use of cooled axial conduction guarded probe for the measurement of transient heat flux by calibrating the unit step response

A novel water-cooled device with inserted thermocouple beneath the sensing surface is designed for long-duration heat flux measurement in harsh environments. The unit step response (USR) of the device, which is temperature-independent, is calibrated using a diode laser system. The heat flux is determined from the calibrated USR and measured temperature by solving an inverse heat conduction problem (IHCP). By calibration, the device achieves a high accuracy in measuring heat fluxes up to 800 kW/m² The proposed procedure inherently accounts for all system parameters, including the thermocouple dynamics and the surface emissivity, which can decrease the experimental uncertainty. A detailed uncertainty analysis reveals the uncertainty of reconstructed heat flux can be significantly decreased with well-designed calibration tests and a prudent choice of the regularization parameter. Two examples for laser heat flux measurement are tested to validate the feasibility of the proposed method by comparing with the measurements from a reference sensor. The experimental results illustrate that the estimations are stable and accurate.