Measurement of Time-Averaged Turbulent Free Convection Using Laser Interferometry

Laser interferometry has been combined with high-speed digital cinematography to measure time-averaged turbulent convective heat transfer rates. The method has been demonstrated for turbulent free convection in a tall vertical enclosure filled with air. Sample results have been obtained for a Rayleigh number (based on the enclosure width) of 2.8×10⁵ and an enclosure aspect ratio of 17.1. An automated digital image processing algorithm has been used to calculate the instantaneous local heat flux from the sequence of interferograms captured by a high-speed camera. The effects of key experimental parameters, such as the camera frame rate and the total image capture time, have been investigated. The average Nusselt number for the entire enclosure was found to compare well with a widely used empirical correlation from the literature.