Abstract
Natural convection heat transfer from three isothermally heated horizontal cylinders submerged in water in a triangular arrangement is investigated. Two configurations, named here as one over two and two over one, are characterised for three cylinder spacings (S = 2, 3 and 4 cylinder diameters) and Rayleigh number conditions (Ra = 2×106, 4 × 106 and 6 × 106). Combined local heat flux measurements and flow velocity measurements using particle image velocimetry are employed to examine the governing heat transfer mechanisms. For many cases of the one over two configuration, substantial differences from the single cylinder case are noted. The buoyant plumes generated from the two lower cylinders interact with the flow field and heat transfer around the upper cylinder, altering the local fluid velocities and temperature fields. This effect is dependent on both the inter-cylinder spacing and the Rayleigh number condition. For the two over one setup, both upper cylinders for all cases, except S=4D and Ra = 6 × 106, behave in the same manner as a single cylinder. This is due to the competing effects of the buoyant plume rising from the lower cylinder and the restriction of flow through the gap between the two upper cylinders.
Highlights
Convective heat transfer from cylinder arrays occurs in many industrial and domestic applications
These changes in behaviour are due to the interactions between the buoyant plumes that are generated by each cylinder, which may impinge on downstream cylinders
As a baseline for the triangular array testing, the local heat transfer results from a single cylinder are presented. These results are shown in Fig. 5. 0◦ is the bottom of the cylinder and 180◦ is the top in a clockwise direction
Summary
Convective heat transfer from cylinder arrays occurs in many industrial and domestic applications. Eckert and Soehngen [23] investigated the interaction of the developing thermal plumes and thermal boundary layers of two vertically aligned cylinders They showed that the plume generated from the lower cylinder could either enhance or diminish the heat transfer performance of the upper cylinder depending on the applied spacing (S). Other researchers [26,27,28,29,30,31,32,33,34] have investigated natural convection heat transfer from two vertically aligned cylinders over a range of working fluids, Rayleigh numbers, confinement conditions, and spacings. Lieberman and Gebhart [43] studied the temperature distributions around a flat array of long horizontal wires They noted a peak average Nusselt number for the different angle-spacings at a tilt angle of 60◦. Particle image velocimetry (PIV) is used to investigate the local fluid flow field around the isothermal cylinders to gain a deeper understanding of their heat transfer mechanisms
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