Free Convection
The experiments to determine heat transfer coefficient for natural heat transfer consists of heating a flat plate or a cylinder to a particular temperature and then cooling in air. In some experiments the orientation of plate or cylinder with reference to air cooling is also varied; the plate/cylinder is kept horizontal or vertical. In all these experiments heat transfer coefficient is shown to be a function of Prandtl  number and Grashof number  Heat transfer coefficient is related to Nusselt number  .
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(6) |
 is a characteristic linear dimension, Cp specific heat, is density, and  is acceleration due to gravity. The following relation is proposed to calculate heat transfer coefficient for natural convection
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(7) |
The numeral value of alpha depends on the orientation of the plate/cylinder with reference to the cooling air. This will be illustrated in the exercises.
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