The parametric investigation of heat transfer characteristics of annular and synthetic impinging jet on a flat surface

In this study, heat transfer performance from a turbulent annular jet impingement on a constant heat flux heated flat surface was investigated experimentally and numerically. Annular impinging jets enhance the heat transfer and spread the flow more uniformly over the impingement surface compared to the round impinging jet, and have one noteworthy characteristic of forming a reverse stagnation flow. In the investigations, the distance between the target surface and the jet exit (H/D), the jet Reynolds number (Rej), the amplitude (Ao) and frequency (Wo) of the synthetic jet were changed, while the Prandtl number (Pr) and geometric parameters were kept constant, and the effects of these parameters on heat transfer were analyzed. Experiments were carried out for three different impact distances, four different amplitudes and six different frequencies at the determined Reynolds number. The synthetic jet is used as an active heat transfer enhancement method, temperature measurements were made in detail on the experimental setup and Nusselt numbers were calculated with the based on measured temperatures. Numerical modeling was carried out in accordance with the experimental parameters, and detailed evaluations were made about the flow structure. The obtained results are expressed as a function of dimensionless numbers, and the results are compared with the heat transfer results of continuous (circular) jet impingement. Experimental results showed that the annular synthetic jet has a significant effect on heat transfer enhancement. It was observed that the annular synthetic jet significantly increased the heat transfer compared to the continuous jets.