An analytical solution has been obtained for the longitudinal fully developed laminar flow between cylinders arranged in triangular or square array. Numerical results for the pressure drop and the friction factor are given over a wide range of spacing-to-diameter ratios. For large spacings the results can be represented by a single expression independent of the type of array. Plots are also given of velocity distributions and of the variation of the local shear stress around the periphery of a cylinder.

Consideration is given to the fully developed heat-transfer characteristics for longitudinal laminar flow between cylinders arranged in an equilateral triangular array. The analysis is carried out for the condition of uniform heat transfer per unit length. Solutions are obtained for the temperature distribution, and from these, Nusselt numbers are derived for a wide range of spacing-to-diameter ratios. It is found that as the spacing ratio increases, so also does the wall-to-bulk temperature difference for a fixed heat transfer per unit length. Corresponding to a uniform surface temperature around the circumference of a cylinder, the circumferential variation of the local heat flux is computed. For spacing ratios of 1.5 ∼ 2.0 and greater, uniform peripheral wall temperature and uniform peripheral heat flux are simultaneously achieved. A simplified analysis which neglects circumferential variations is also carried out, and the results are compared with those from the more exact formulation.

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