Compensation of Three-Dimensional Heat Conduction Inside Wall in Heat Transfer Measurement of Dimpled Surface by Using Transient Technique(Thermal Engineering)

Abstract

The transient technique using infrared-thermography or liquid-crystal has widely been used for measuring the distribution of local heat transfer coefficients. In this technique, wall surface temperature is measured, and the heat transfer coefficient is calculated so as to accord the measured temperature with the theoretical solution of one-dimensional heat conduction problem. In actual cases of complicated surface geometry, however, three-dimensional heat conduction, caused by the three-dimensionality of the wall surface and the distribution of heat transfer coefficient, occurs in the wall. In this study, the heat transfer coefficient on the hemispherically dimpled surface was measured with an infrared camera, while the three-dimensional heat conduction in the wall was numerically calculated. In the compensation process, modification of the heat transfer coefficient was repeated till the numerical result agreed with the measured surface temperature. The present results showed that the heat transfer coefficient near the dimple edge was overrated, while that within the cavity was underrated. The maximum error induced by the three-dimensional heat conduction was 60% on the leading edge of the dimple, and the error in the other area was about 20% at most. At the dimple edge, the convex geometry increased the surface area where the heat flew into the wall, and consequently temperature rise became larger than the flat part. On the other hand, within the dimple, the concave geometry formed the radially-expanding heat conduction area, and the temperature became lower. The principal factor contributing to the error of the measurement is the three-dimensionality of the surface.