The Natural Convection Heat Transfer Of Small Objects

The characteristics of natural convection heat transfer of small objects are studied in this dissertation. A special Laser speckle photography system, by which the heat flux distribution of small objects along their width and height can be measured simultaneously has been developed. The dimensionless correlation of heat transfer of the vertical strip is deduced for the first time by means of the dimensional analysis of the governing equations,based on taking the width of the strip as characteristic length, where the coefficients are determined by experimental data. That the heat transfer correlation for vertical strip is approximately applicable to the block objects has been tested. The natural convection heat transfer of small objects is enhanced remarkably, due to the side edge effect and leading edege effect. As long as the strip is narrow enough, the variation of heat flux along strip height becomes much less, and the heat flux can be even regarded approximately as constant, except for the region of the leading edge. Consequently, heat transfer of small objects posseses some simplicity. The effect of conduction of the substrate on the natural convection is also investigated. The conduction of substrate in the direction of strip height can obviously increase the total heat flux from the board to the gas, while the conduction of substrate in the direction of strip width is of few effect on the total heat flux.