Measurement of Time-Averaged Turbulent Free Convection in a Tall Enclosure Using Interferometry

Abstract

Laser interferometry is combined with high-speed digital cinematography to measure time-averaged transient and turbulent convective heat transfer rates. The method is applied to study free convection in a tall vertical air-filled enclosure. Measurements are made at three wall spacings in the turbulent flow regime (5.2×104≤RaW≤2.8×105). An automated image processing algorithm is used to calculate the instantaneous local heat flux from a sequence of interferograms that is captured by a high-speed camera. The local Nusselt number distributions on the hot and cold walls are obtained by time-averaging the fluctuations in local heat flux. The effects of key experimental parameters, such as the camera frame rate and the total image capture time, are investigated. For the current problem, it is shown that a total capture interval of about 10 s is required to accurately measure the time-average local Nusselt number. Within the measurement uncertainty, the average Nusselt number results are in agreement with a widely used empirical correlation from the literature.