An Interferometric Study of Free Convection at a Window Glazing with a Heated Venetian Blind

Abstract

The free convective heat transfer rate from a vertical isothermal plate adjacent to a heated aluminum venetian blind has been measured using a Mach-Zehnder interferometer. The blind was heated electrically to simulate solar heating, and the plate was heated above the room temperature to simulate an indoor window glazing. Local and average heat transfer data were obtained for three blind heat flux levels, two blind-to-plate spacings, and four slat angles in the laminar flow regime. For most cases, data were obtained up to a plate Rayleigh number of Ra _L = 2.8 × 10⁶ based on the distance from the leading edge. Infinite fringe interferograms were taken for temperature field visualization. The results show that blind heat flux has a strong influence on local and average heat transfer coefficients on the plate. It was also found that the spacing between the inner tips of the slats and the plate had a substantial impact on the convection. For close spacings, the heated slats were found to produce a strong periodic variation in the local heat transfer distribution on the plate. For all cases studied, as the blind heat flux increased, the convective heat transfer rate from the plate decreased dramatically. In addition, as the blind heat flux increased, the average convection coefficient became more dependent on both the blind-to-plate spacing and slat angle.