Effect of Nozzle Exit to Surface Spacing on the Cooling of Electrically Heated Surface with Jet Impingement

The transient surface cooling of a hot stainless steel surface is obtained by a water jet impingement cooling method. The surface is electrically heated up to the initial temperature of 800 C. Water flow rate is kept constant so that jet Reynolds number remains at Re=24000. Nozzle exit to surface spacing has been changed in a range of z/d = 4-16. For larger surface temperature drop change in nozzle exit to surface spacing does not affect the surface cooling time significantly. However, for lesser surface temperature drop particularly at higher range of surface temperature, surface cooling time is approximately 15 % higher with z/d =4.