Flow and impingement cooling heat transfer along triangular rib-roughened walls

Experiments are performed to study slot air jet impingement cooling flow an d the heat transfer along triangular rib-roughened walls. Both flow visuali zation and local heat transfer measurements along the ribbed wall are made. The effect of different rib protrusions (heights) on the impinging flow an d heat transfer along the wall is studied, which is achieved by using diffe rent sizes of nozzles. Two different ribbed walls with different rib pitche s are selected which have a rib pitch-to-height ratio of 2 and 4, respectiv ely. The widely opened cavity between neighboring ribs make more intense tr ansport of momentum between the wall jet and cavity flow so that recirculat ion cell in the cavity is hardly observed. This leads to a higher heat tran sfer around the cavity wall than in the case with rectangular ribs. However , in the region of laminar wall jet, a number of air bubbles enclosing the cavities are formed which prevent penetration of the wall jet into the cavi ties. This leads to a significant reduction in the heat transfer. The geome tric shape of the triangular ribs is more effective in rebounding the wall jet away from the wall than in the case with rectangular ribs. The rebound of the jet away from the wall causes a significant reduction in the heat tr ansfer. A comparison and correlations of the stagnating point Nusselt numbe r under different conditions are presented and discussed. During the experi ments, the Reynolds number varies from 2500 to 11,000, the slot width-to-ri b height ratio from 1.17 to 6.67, and nozzle-to-plate spacing from 2 to 16. (C) 2000 Elsevier Science Ltd. All rights reserved.