Effect of nozzle shape on jet impingement heat transfer from a circular cylinder

Experimental and numerical investigations were carried out to study the effect of nozzle shape on unconfined jet impingement heat transfer from a heated circular cylinder. Air was considered as the working fluid. The heated cylinder surface was maintained at a constant heat flux. In this work, circular, square and rectangular nozzles of equal hydraulic diameters were selected for a comparative study. The Reynolds number, Re-hyd defined based on the hydraulic diameter of the nozzle was varied from 10,000 to 25,000. The ratio of hydraulic diameter of the nozzle to the diameter of heated cylinder, d(hyd)/D was maintained at 0.2 for the parametric study. The non-dimensional distance between the nozzle exit and the cylinder, h/d(hyd) was varied from 4 to 16. For a fixed jet Reynolds number, the mass flow rates through different nozzles are different. Hence, a parametric study was also carried out to know the effect of nozzle shape for various fixed mass flow rates. For this, a modified Reynolds number (Re) over bar (hyd) was kept constant for all nozzle shapes. For a fixed jet Reynolds number, heat transfer from the cylinder was higher for the case of rectangular nozzle. On the other hand, for a fixed modified Reynolds number (Re) over bar (hyd), heat transfer rate from the cylinder was found to be higher when the circular nozzle was used. For the same geometry, numerical simulations were also carried out using three different two-equation turbulence models. Using the experimental data, two correlations for stagnation Nusselt number Nu(stag). have also been provided. (C) 2015 Elsevier Masson SAS. All rights reserved.