Conical coaxial impinging air jets: angle effect on the heat transfer performance

Abstract

Herein, an experimental attempt is conducted to research thermal and flow behaviors of an impinging jet exiting from a coaxial type nozzle with a conical outer and a circular inner outlets. the experiments include four different values of the cone angle (phi = 0 degrees, 10 degrees, 20 degrees and 30 degrees) and several values of the separation distance between the nozzle outlet and the target surface (0.5 <= H / D <= 6). Tests are performed for a single value of total flowrate (1.33 x 10(-3) m(3) s(-1)). It is revealed that the local Nusselt numbers on the target surface increase with decreasing separation distance. Especially, in the close-range impingement conditions (H / D <= 2), the cone angle of 20(o)performs the optimum thermal performance. Both the rate and spatial uniformity of convective heat transfer strongly depend on the coupling of the nozzle-to-plate distance and angle. From the flow dynamics aspect, wall pressure distributions are measured, and positive and negative (subatmospheric) peaks are observed depending on the combined influence of angle and distance.