Heat transfer correlation of impinging jet array from pipe nozzle under fully developed flow

Highlights: • The heat transfer correlation of jet impingement using pipe nozzle is formulated. • At jet-to-plate distance, heat transfer peak is contrast to the using orifice case. • The correlation is formulated based on the location of heat transfer peak. -- Abstract: The objective of this research is to investigate the heat transfer of an impinging jet array under a fully developed flow. 5 × 5 jets discharged from pipe nozzles with a diameter of d = 17.2 mm and a length of 300 mm were evenly spaced in an in-line arrangement. The effects of the jet-to-jet spacing (S) and the jet-to-plate distance (H) were varied at S/d = 4, 6, 8 and H/d = 2, 4, 6, 8. The jet Reynolds numbers were varied at Re = 10,000, 20,000, 30,000 and 40,000. The temperature distributions on the impingement surface were measured using an infrared camera and were then calculated to evaluate the Nusselt numbers. The results showed that the highest average Nusselt number was found at H/d = 4 for all jet-to-jet spacings (S/d). A heat transfer correlation was performed based on the peak of the average Nusselt number occurring at H/d = 4. This was in contrast to the case of impinging jet array discharged from orifice nozzles, in which the average heat transfer decreased monotonically with jet-to-plate distance (H).