a b s t r a c tThis work describes the effect of steady-state laminar forced convection on multiscale rotating cylinders in cross-flow. The objective was to numerically maximise the heat-transfer-rate-density from the multiscale cylinder assembly under a prescribed pressure drop. Two main configurations were studied, the first was with two different-sized cylinders aligned along the same centreline, and the second configuration was that in which the axis of rotation of the two cylinders was not on the same centreline but the leading edges of the cylinders were on the same line. In both configurations, the cylinders were subjected to two types of rotations, counter-rotation and co-rotation. Numerical solutions for stationary and rotational cylinders were solved to determine the optimum cylinder diameter, spacing and the corresponding maximum heat transfer rate density. The effects of different centres of rotation and the dimensionless pressure drop on the cylinder-to-cylinder spacing, optimal diameter of the cylinder and the maximum heat transfer rate density were reported. Results show that the optimal smaller cylinder diameter was robust with respect to the dimensionless pressure drop number, for both configurations. Results further showed that rotation was only beneficial for cylinders with the same axis of rotation and the effect was minimal when the axis of rotation is different.

A steady-state two dimensional numerical simulation was carried out to optimize the heat transfer rate density from cylinders under different conditions. The geometric design of the cylinders was varied in two ways. In the first case the cylinders are located on a plane where their leading edges are aligned, and in the second case the cylinders are aligned on a plane which passes through their respective centre-lines. The rotation of the cylinders is within the range of 0 ≤ ω˜ ≤ 1, and the dimensionless pressure drop number, Be, which drives the flow is in the range of 10 ≤ Be ≤ 104. The continuity, momentum and energy equations describing the flow of the coolant, across the cylinders in the computational domain are performed using a computational fluid dynamics code, the results obtained were validated by comparing it with past results in the open literature for stationary cylinders. The effects of the various parameters (dimensionless pressure drop number, rotation) on the maximum heat transfer rate density from the cylinders in terms of augmentation and the suppression were analysed and reported.