Development of fast response heat transfer measurement technique with thin-film thermocouples

A transition boiling on a high temperature solid beyond the Leidenfrost temperature is characterized by a strong unstable heat transfer. This unstable one brings a rapid temperature change beneath the surface in the solid and causes a repetition in time as well as a space of wet and dry on the surface. Therefore, the development of a fast temperature measurement technique is indispensable to understand this transition phenomenon. The developed temperature sensor has a junction of the end face of chromel fine wire of phi 0.32 mm diameter, whose position is 3 mu m away from the surface of nickel disk of 5 mm thickness and can follow a rapid temperature change within 100 kHz. The heat transfer can be calculated from the measured temperature by using an inverse problem analysis for one-dimensional unsteady heat conduction. Besides, the calculated heat flux is also confirmed to be sufficient to capture the characteristics of unsteady boiling heat transfer in the experiment that a sessile ethanol droplet impacts onto the hot surface. (C) 2020 Elsevier Ltd. All rights reserved.