Experimental and Numerical Analysis of Heat Transfer Characteristics of an Impinging Round Jet with Vortex Generators

Abstract

Jet impingement is an active heat transfer enhancement technique that has been used in many engineering applications marked by high heat transfer rates. In this study, heat transfer from a confined single round air jet impinging orthogonally on a flat plate using rectangular winglet type vortex generator pairs (VGPs) has been investigated numerically and experimentally. The jet Reynolds number is maintained at 24000 and the ratio of distance between jet plate and heating plate to jet diameter (H/D) is fixed as 2. The effect of angle of attack of the VGP (?), spacing between the VGP (l) and diameter of VGP arrangement (d) are considered as the variables of the study. Numerical studies were performed using RANS simulation coupled with SST k-? turbulence model and the predictions were in good agreement with the experimental measurements. Employment of the rectangular winglet type longitudinal VGPs in a confined single jet impingement resulted in heat transfer enhancement of 16.74% to 68.36% corresponding to variations in parameters such as ?, l/d ratio and d/D ratio at the expense of jet pressure drop from 2.67% to 34.67%. The maximum enhancement in heat transfer rate is obtained when the VGPs are arranged at an angle of attack of 45⁰, l/d ratio of 0.5 and d/D ratio of 4 whereas the heat transfer rate is found to decrease by 1.15% when VGPs are arranged at an angle of attack of 15⁰, l/d ratio of 1.5 and d/D ratio of 6. The average surface heat transfer rates are seen to increase monotonically with increase in the angle of attack of the VGPs from 15⁰ to 45⁰and a decrease in l/d ratio from 1.5 to 0.5. Heat transfer rates are found to increase with increase in d/D ratio from 2 to 4. Further increase of d/D ratio resulted in decrease in heat transfer rates. Thermal enhancement factor is found to be greater than one for all sets of VGP configurations except one particular case when VGPs are kept at an angle of attack of 15⁰, l/d ratio of 1.5 and d/D ratio of 6, which may be due to vortex interactions and dissipation.