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Heat Transfer Handbook part 52

Heat Transfer Handbook part 52. The Heat Transfer Handbook provides succinct hard data, formulas, and specifications for the critical aspects of heat transfer, offering a reliable, hands-on resource for solving day-to-day issues across a variety of applications. | 502 FORCED CONVECTION EXTERNAL FLOWS The impinging jet may be circular U round o or planar rectangular or slot based on its crorr section. It may be submerged fluid discharged in the same ambient medium or free surface a liquid discharged into ambient gas . The flows in each of these cases may be unconfined or partially confined. Moreover in the case of multiple jets interaction effects arise. 6.7.2 Submerged Jets A schematic of a single submerged circutus or planarte se men in Fig. 6.29. Typh Uy the jet is turbulent at the nozzle exit and can be characterized by a nearly uniform axial velocity profile. With increasing distance from the nozzle exit the potential core region within which the uniform velocity profile persists shrinks as the jet interacts with the ambient. iarther downstream in the free jet region the velocity profile is nonuniform across the entire jet cross section. The centerline velocity decreases with distance from the nozzle exit in this region. The effect of the impingement surface is not felt in this region. The impingement surface influences the flow in Stagnation point Figure 6.29 Transport regimes in a submerged circular unconfined jet impinging on a surface. TURBULENT JETS 503 the stagnation or impingement zone. Within this region the flow accelerates in the transverse direction r or x and decelerates in the z direction. Farther away in the transverse direction in the wall jet region the flow starts to decelerate due to entrainment of the ambient fluid. Average Nusselt Number for Single Jets Martin 1977 provides an extensive review of heat tannsfer data Oor impinning gas jets. For sinele nozzles the average Nusselt number is oS the form Martin 1977 Incropera and DeWitt 1996 Nu f Re Pr - H 6.188a Dh Dh J or NU f Re Pr X H 6.188b Dh Dh where h Nu k 6.189a Dh and Re YD 6.189b V where Ve is the uniform exit velocity at the jet nozzle Dh D for a round nozzle and Dh 2W for a slot nozzle. Figure 6.29 defines the geometric parameters. For a single