Heat transfer in inclined and direct impinging synthetic jets

The study was undertaken to determine the effect of inclination of impinging synthetic jet on the heat transfer from a uniformly heated flat plate. The average heat transfer coefficient was determined as a function of inclination angle of synthetic jet relative to the plate, for various jet to heated surface spacing (z/d = 3-15) and Reynolds number (Re = 5865). The maximum heat transfer coefficient occurs for normal or direct impingement (theta = 90 degrees) for all spacings. A non-monotonic reduction in the average heat transfer coefficient is observed as the angle of jet impingent is decreased. It is found that the flow is predominantly direct impingement at large impingement angles which changes to cross flow for theta < 40 degrees. The synthetic jets can be used at the optimum angle of impingement and spacing without serious reduction in average heat transfer coefficient. At an optimal angle of around 60 degrees the average heat transfer coefficient is slightly higher as compared to other angles of impingement. Existence of an optimal angle for such a configuration has not been previously reported for impinging flows. These results are significant for design of cooling solution in space-constrained applications.