Experimental and numerical investigation of air entrainment into an infrared suppression device

Experiments on a laboratory scale Infra-Red Suppression (IRS) device as well as its numerical computation have been carried out to investigate mass entrainment into it. The nozzle Reynolds number (Re) and its distance from the bottom funnel (Hnz/Dnz) have been varied over the range of 3525 ≤ Re ≤ 8000 and0 ≤ Hnz/Dnz ≤ 6.4, respectively. The funneloverlap height as well as the fluid temperature are also varied in the range of −4 ≤ Hoverlap/Dnz ≤ 4 and1 ≤ Tnz/T∞ ≤ 1.1, respectively. Conservation equations for mass, momentum and energy are solved in a two dimensional axi-symmetric domain by employing eddy viscosity based two equation k–ε turbulence model, using log law wall functions. It has been observed that the computed and the measured the mass suction rate agree fairly well with each other, and also depends on nozzle Reynolds numbers. The entrainment rate increases, as the nozzle moves towards the bottom funnel. With further movement of the nozzle into the funnel, the mass entrainment is found to decrease. Therefore, an optimum nozzle protruding height (Hp/Dnz = 1.6) as well as an optimum funnel overlap height (Hov/Dnz = 0) is found out for maximum mass entrainment. Experiments with hot nozzle fluid are conducted to establish the fact that hotter fluid will always entrain more surrounding air compared to the cold nozzle fluid.