TAILIEUCHUNG - Heat Transfer Handbook part 30

Heat Transfer Handbook part 30. The Heat Transfer Handbook provides succinct hard data, formulas, and specifications for the critical aspects of heat transfer, offering a reliable, hands-on resource for solving day-to-day issues across a variety of applications. | SPREADING RESISTANCE OF RECTANGULAR SOURCE AREAS 281 TABLE Dimensionless Spreading Resistance of an Isothermal Rectangular Area a b k A Rs 1 2 3 4 Isothermal Rectangular Area Schneider 1978 presented numerical values and a correlation of fliose values for the dimensionless spreading resistance of an isothermi rectangee for the aspect rtitio range 1 a b 4. The correlation equation is k  Rs Æ - . . V b L b a b The numerical values are given in Table . A comparison of hie u s for foe ifofoormat scciaeglllar ai aa add foe ifofoormal elliptical area reveals a very close relationship. The maximum difference of approximately is found at a b 4. It is expected that the close agreement observed for the four aspect ratios will hold for higher aspect ratios because the dimensionless spreading resistance is a weak ft i t n ot foe a pe tf sa are oeomeincally similar. In fact the correlation values for the rectangle and the analytical values for the ellipse are within over the wider range 1 a b 13. Isoflux Regular Polygonal Area The spreading resistances of isoflwt regular polygonal areas has been examined extensively. The regular polygonal areas ere characterized by the number of sidss N 3 the side dimension s and the radius of foe inscsibed circle denoted ss ri. The perimeter is P Ns the relationship between the inscribed radius and the side dimension is s ri 2tan n N . The eiea of foe regular jK o n îs A Nr2 tan n N . The temperature rises from the minimum values located on the edges to a maximum value at the centroid. It can be found easily by means of integral methods based on the superposition ofpoint sources. The general relationship for the spreading resistance based on the centroid temperature rise is found to be r- 1 N 1 sin n N tVAR nj cos N N -3 l4-53 The expression above gives WA Rs for the equilateral triangle N 3 which is approximately smaller than the value for the .

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