Experimental and numerical investigation of natural convection effects on confined impinging jet heat transfer

The influence of natural convection on the local and average heat transfer at increasing temperature differences between the jet and the target plate from confined impinging jets has been experimentally and numerically investigated. Local Nusselt numbers were obtained numerically for jet Reynolds numbers in the range of 250–1000, and jet to target spacings of 2, 4, 8, 12 jet diameters at various modified Grashof numbers, to determine the effect of buoyancy induced natural convection. To determine the overall effect of natural convection on the average heat transfer, experiments have been conducted for Re numbers in the range 250–5000 and dimensionless jet to target spacing 2, 4, 6, 8, and 12 at increasing modified Grashof numbers. It has been determined that buoyancy induced natural convection might have opposing or assisting influence on local heat transfer at different locations of the target plate. It has also been shown that especially at low jet inlet velocities the average heat transfer coefficient at the highest modified Grashof number, where the natural convection is effective, is higher than the value corresponding to the lowest Grashof number at which buoyancy effects are negligible, by as much as 37%.