Heat transfer and fluid flow of natural convection adjacent to upward-facing horizontal plates

Abstract

Natural convective flows over upward-facing horizontal plates were investigated experimentally. The main concerns were the fluid flow and local heat transfer characteristics over a wide range of modified Rayleigh numbers from 10 6 to 10 15. Test plates 20–1500 mm wide were utilized to attain such Rayleigh numbers and they were heated with uniform heat fluxes. The test fluid was water. The fluid flows over the plates and the surface temperatures of the plates were visualized with dye and by liquid crystal thermometry respectively. Extensive measurements of the local heat transfer coefficients were also carried out. The result from the wide plates showed that the following four regions appear over the plates at a streamwise distance x from the leading edge: (1) a laminar boundary layer region, (2) a streaky, transitional flow region, (3) a turbulent region and (4) a collision region. In particular, the second region covers a considerable portion of the total surface, and the local heat transfer coefficients there decrease proportionately with x. Thus, it was found that the width of the plates exerts a serious influence on the average heat transfer coefficients even at the highest Rayleigh numbers of the present experiments.