Heat Transfer Enhancement On An Impingement Surface Of Impinging Jet Array By Mounting Air-induced Duct

Jet impingement has been studied by many researchers especially focusing on heat enhancement with passive method.The mounting expansion pipe or air-induced duct at nozzle exit is a method which has been investigated in previous work,but it has been performed as a single jet.Therefore,the purpose of this research is to investigate experimentally and numerically the effect of air-induced duct on heat transfer and flow characteristics of impinging jet array with mounting air-induced duct.Jets discharging from pipe nozzle with fully developed flow impinged upon the target surface.Nozzle arrangement were distributed in 5 rows×5 columns with an in-line configuration,and air-induce ducts were mounted at the end of each nozzles.An infrared camera is used to measure the temperature distribution on the impingement surface at opposite side.The length of air-induced duct(L)and the inner diameter of air-induced duct(D)were varied at L/d=2,4,6,and D/d=2,4,6.The jet-to-plate distance(H)was varied at H/d=2,4,6 and 8,while the jet-to-jet distance(S)was varied at S/d=4,6 and 8.Reynolds number of the jets were varied from 10,000 to40,000.The conventional impinging jets were also performed with the same mass flow rate for the comparison.Flow characteristics were simulated using computational fluid dynamics(CFD)with v~2-f turbulence model.Results showed that the ambient air was induced into the air-induced duct.An entrainment of induced air became greater at air-induced duct inlet when the ducts length was elongated,and the main jets were more distributed before impinging on the surface when the ducts diameter were expanded.This influenced was more markedly on enhancement of average Nusselt number for narrow jet-to-jet distance and high jet-to-plate distance.The correlation equations for array of jet mounting air-induced duct were also constructed.