Natural Convection Heat Transfer in Moderate Aspect Ratio Enclosures

Abstract

Local and average heat transfer coefficients for natural convection between parallel plates separated by slats to create enclosures of moderate aspect ratio have been experimentally determined using an interferometric technique. The effects of Rayleigh number, tilt and slat angle, and aspect ratio on the Nusselt number have been determined. The Rayleigh number range tested was up to 7 × 104, and the aspect ratio (ratio of enclosure length to plate spacing) varied between 0.25 and 4. The angles of tilt of the enclosure with respect to the horizontal were 45, 60 and 90 deg. Slat angles of 45, 60, 90 and 135 deg were studied. The results obtained in a previous investigation [1] for aspect ratios of 9 to 36 are included to show continuity. The results indicate that the convective heat transfer is a strong function of the aspect ratio for aspect ratios less than 4. For aspect ratios in the range of 0.5 to 4, spacers between the plates increase, rather than decrease, natural convection heat transfer compared to that for long enclosures. Slat angles less than 90 deg (i.e., oriented downward) reduce convective heat transfer.