Enclosures, natural convection horizontal

Free convection in inclined enclosures is discussed by Dropkin and Somerscales [12], Evans and Stefany [9] have shown that transient natural-convection heating or cooling in closed vertical or horizontal cylindrical enclosures may be calculated with... 

Mass How Rate ttirougn ttie Space beLV, een Plates 519 9-5 Natural Convection Inside Enclosures 521 effective Thermal Conductivity 522 Horizontal Rectangular Enclosures 523 Inclined Rectangular Enclosures 523 Vertical Rectangular Enclosures 524 Concentric Cylinders 524 Concentric Spheres 525 Combined Natural Convection and Radiation 525... 

The characteristics of heat transfer through a horizontal enclosure depend ou whether the hotter plate is at the top or at the bottom, as shown in Fig. 9-22. When the hotter plate is at the top, no convection currents develop in the enclosure, since Ihe lighter fluid is always on top of the heavier fluid. Heat transfer in tlris case is by pure conduction, and we have Nu - 1. When the hotter plate is at the bottom, the heavier fluid will be on top of the lighter fluid, and there will be a tendency for Ihe lighter fluid to topple the heavier fluid and rise to the top, where it comes in contact with the cooler plate and cools down. Until that happens, however, heat transfer is still by pure couduc-tion and Nu — I. When Ra > 1708, the buoyant force overcomes the fluid resistance and initiates natural convection currents, which are observed to be in the form of hexagonal cells called BSnard cells. For Ra > 3 X 10, the cells break down and the fluid motion becomes turbulent. 

When both bottom and top surfaces are maintained at constant temperatures and there is internal generation, there is a superposition of the horizontal layer problem discussed in the section on natural convection within enclosures and the internal generation problem previously described. These are characterized by the external Rayleigh number defined in the section on natural convection within enclosures and the internal Rayleigh number defined in Fig. 4.40a. The dependence of the layer stability on these parameters has been discussed by Ning et al. [208]. The heat transfer at the top and bottom surfaces has been estimated for these conditions by Baker et al. [13], Suo-Anttila and Catton [276], and Cheung [51],... 

Hideo, I. Yanlai, Z. Akihiko, H. Naoto, H. Numerical simulation of natural convection of latent heat phase-change-material microcapsulate slurry packed in a horizontal rectangular enclosure heated from below and cooled from above. Heat Mass Transfer 43 (2007) 459-470. 

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