Effect of a Parallel Adiabatic Covering Surface on the Natural Convective Heat Transfer from Horizontal Upward Facing Heated Surfaces

Abstract

In this chapter, attention is given to natural convective heat transfer from a horizontal upward-facing-heated surface that is imbedded in a surrounding adiabatic surface, the heated and adiabatic surfaces being in the same horizontal plane for the case where there is an adiabatic parallel plane covering the surface (a shroud) above and relatively near to the heated surface. In such an arrangement, the presence of the covering surface can have a significant influence on the rate of heat transfer from the heated surface. Attention in this chapter has been given to heated surfaces having a circular, a square, and a rectangular shape. For the square-and circular-shaped surfaces, the effect of the presence of the covering surface on the Nusselt number variation with Rayleigh number for the various dimensionless gap values is approximately the same. For the rectangular surface case, the aspect ratio of the surface has a very significant influence on the form of the variation of Nusselt number with Rayleigh number and on the effect the dimensionless-heated surface gap value on the Nusselt number variation.