Influence of the shape of the orifice on the local heat transfer distribution between smooth flat surface and impinging incompressible air jet

An experimental investigation is performed to study the influence of the shape of the orifice (circular, square, triangular and elliptical), jet to plate distances and Reynolds number on the local heat transfer distribution to normally impinging submerged air jet on smooth and flat surface. The Reynolds numbers were varied from 5000 to 30,000 in the steps of 5000 and the jet to plate distances used were 0.5, 1, 2, 4, 6 and 8. The equivalent diameter (ratio of area to the perimeter) of all the orifices were maintained nearly constant (5.7 mm). The local heat transfer characteristics are estimated using thermal images obtained by infrared thermal imaging technique. For all the shapes, the area averaged Nusselt number increases with increase in Reynolds number. The area averaged Nusselt number at all Reynolds number is observed to be highest at a z/d of 4. Axis switching is observed for all the shapes except circular orifice. The square, triangular and elliptical orifice respectively undergoes a 45°, 180° and 90° axis switch. Pressure loss coefficients of various orifices are reported.