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J. W. Yang
Department of Applied Science Brookhaven National Laboratory, Upton, New York 11973


Laminar combined natural and forced convection through vertical rod arrays has been studied for two basic arrangements: the equilateral triangular and square arrays. Rod surface heat flux is considered uniform in the flow direction and surface temperature is uniform in the circumferential direction. The governing momentum and energy equations were transformed to a single equation by defining a complex function ψ. The real and imaginary parts of the complex function denote the fluid velocity and temperature, respectively. A solution by the point-matching method in terms of a series containing trigonometric, Bessel and Kelven functions has been obtained. Nusselt numbers, pressure loss, and local heat flux have been investigated for a large range of pitch-to-diameter ratios. Numerical results indicate that the superimposed natural convection plays an important role in arrays with large pitch-to-diameter ratio. Both the Nusselt number and the pressure loss are increased with the increase of Gr/Re ratio. The circumferential variation of heat flux is reduced under the conditions of combined convection. Implications of the results to the nuclear reactor are discussed.

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