Effect of nozzle geometry on local convective heat transfer to a confined impinging air jet

This article reports results on the effects of hyperbolic nozzle geometry on the local heat-transfer coefficients for confined impinging air jets. A thermochromatic liquid-crystal technique is used to visualize and record isotherms on a uniformly heated impingement surface. Experiments are conducted at low nozzle-to-plate spacings (0.25 < H/D < 6.0) and Reynolds numbers in the range of 10,000 to 50,000 for two different confined, hyperbolic nozzles. As a reference, results have also been obtained for a confined orifice and are compared with those for the hyperbolic nozzles. The effects of Reynolds number, nozzle-to-plate spacing, and nozzle geometry on the local heat-transfer coefficients are reported and compared with similar experiments for unconfined jets. It is concluded that the local heat-transfer coefficients for confined jets are more sensitive to Reynolds number and nozzle-to-plate spacing than those for unconfined jets.