Experimental characterisation of a plume above rectangular thermal sources. Effect of aspect ratio

An experimental study of the thermal plume emerging above a number of plane rectangular heat sources of finite dimensions was performed with the aim of verifying the corresponding point source or linear source models and the evolutions of the dynamic and thermal fields in relation to the aspect ratio. The heat sources were assembled from four rectangular units 1.5 m in length and 0.25 m in width. Four different configurations with aspect ratios between 1.5 and 6 were tested. Surface temperatures were chosen to maintain approximately the same convected power from the sources, for all the situations. A battery of sixteen anemometric probes and sixty four thermometric probes simultaneously recorded plume velocity and temperature distribution. These measurements allowed to determine the actual energy entrained by the plume above the source. Velocity measurements also allowed the plume flow rate to be evaluated. The evolution of ΔTc, the temperature difference between the maximum temperature and the ambient temperature for a given horizontal plane, yielded an approximation of the virtual origin that is in close agreement with the plume thermal and dynamic radii above the source. The values found for the flow rate and ΔTc are compared with those predicted by linear or point source formulae in order to determine an aspect ratio limit.