Natural convection heat transfer between concentric rectangularparallelpipeds was studied numerically for low Rayleigh numbersRa(<=3500_ with aspect ratios of the inner parallelepiped of 2.0,4.0,and, and 8.0. It has been found that the flow patterns for the higherRayleigh numbers in the space over the inner parallelpied are ring orrectangular rolls. The number of rolls increases with the aspectratio. The flow pattern in the side space is an oblong circulation,which extends into the bottom space.
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