Experimental and numerical investigations were carried out onair-filled cavities containing heated inner cylinders.The effect of varying the position of radial spacers on asingle cylinder was studied. It was concluded that for centralpositioning of the cylinder within the cavity. the rate ofheat-transfer was minimised at a radial spacer angle of 480(measured from the vertically downwards radius vector). Whenthe cylinder was positioned at displacement ratio of 0.7, therate of heat-transfer was minimised at a corresponding spacerangle of 520. The corresponding reductions in the total rateof heat-transfer were found to be 25% and 31% less than thatobtained for the system with no spacers at a cylinderdisplacement ratio of zero.Following this research investigation, the behaviour of atwo-pipe arrangement, consisting of a hot supply and coolerreturn pipe within a rectangular sectioned cavity, wasstudied. Eccentric positioning of both supply and return pipesshowed that minimum rates of heat-transfer occur at supply andreturn pipe displacement ratios of 0.45 and -0.33respectively. This value of heat-transfer is approximately 20%less than that obtained for a system where supply and returnpipe displacement ratios are 0.7 and zero respectively.As experimental testing has proved to be excessively timeconsuming (e. g. due to having to wait until a steady-stateensued before measurments were taken) and laborious, afinite-element numerical model was developed and used topredict the heat-transfer between a heated inner cylinder and acooled outer square duct.This study investigated eccentricity effects on the rate ofheat-transfer for different ratios of duct height to cylinderradius. Solutions were obtained for Rayleigh numbers 1 to 300and optimal pipe eccentricity for minimum heat-transfer waspredicted. These predictions were in good agreement withprevious experimental results.
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