Measurements of Time-Space Distribution of Convective Heat Transferto Air Using a Thin Conductive Film

Abstract

A measurement technique of time-space characteristics of heat transfer to air has been developed using a thin conductive film and infrared thermography. In this work, a titanium foil of 2μm thick and an infrared thermograph of 120Hz were employed for measurements. The accuracy of the measurements was confirmed by comparing the heat transfer coefficient of a laminar boundary layer to the numerical analysis. Also, the dynamic response of the temperature against a stepwise change was confirmed to agree well to the numerical analysis. In order to verify the applicability of this measurement technique to practical measurements, unsteady heat transfer on the wall of a turbulent boundary layer was examined. It was possible to restore the time-space distribution of the heat transfer coefficient up to0.033 sec in time and 4.5mm in space for the conditions of a low heat transfer coefficient of h=10-20W/ (m²·K), by solving the heat conduction equations inside the wall.Consequently, the time-space behaviour of the heat transfer, which was reflected by streaks formed in the near-wall region of the turbulent boundary layer, was revealed, showing that this technique is promising to study the heat transfer to air caused by flow turbulence.