Numerical investigation of heat transfer by rows of rectangular impinging jets

Abstract

The velocity field and heat transfer in rows of rectangular impinging jets have been analyzed from the numerical solution of unsteady Navier-Stokes and energy equations. Jets emanating axially and radially from rectangular slot nozzles (feed tubes) have been considered. For the radial jets, the jet exit angle has also been varied. Steady flows have been obtained for Reynolds numbers smaller than a critical value above which periodic flows appear. At a higher Reynolds number than the critical value, the flow becomes unsteady and nonperiodic. For the laminar axial jets, an optimum relative nozzle area for maximum heat transfer, as experimentally observed for turbulent jets, is also obtained. For the radial jets, heat transfer monotonically increases with relative nozzle area. For the densely spaced jets, i.e.,for a large relative nozzle area, average heat transfer for the radial jets can be larger than that for the axial jets. Heat transfer can also be substantially increased by vectoring the radial jets toward the impingement surface. Densely packed and vectored radial jets can give 20%-30% more heat transfer than the axial jets, for the same mass flow ate.