Effect of nozzle—surface separation distance on impingement heat transfer for a jet in a crossflow

Measurements were made of the local heat transfer coefficients resulting from the impingement of a turbulent jet which interacts with a crossflow. The experiments were performed for separation distances between the exit of the jet nozzle and the impingement surface ranging from 3 to 12 times the jet exit diameter. The ratio of jet to crossflow mass velocity was varied from 4 to 12. To evaluate the heat transfer coefficients, local recovery temperatures were also measured. The results for the larger mass velocity ratios indicated that as the separation distance is varied, the impingement point heat transfer coefficient attains a maximum when the separation distance is 5-6 times the jet diameter. On the other hand, at a smaller mass velocity ratio such as 4, the maximum is attained at a substantially smaller separation distance. Experiments were also performed to examine how the transfer coefficients are affected by the presence or absence of a simulated duct wall at the exit of the jet nozzle. The differences between the results for the two configurations were confined to dimensionless separation distances greater than 4, with the largest effects at low mass velocity ratios.