Effects of Interactions Between Adjoining Rows of Circular, Free-Surface Jets on Local Heat Transfer From the Impingement Surface

Abstract

Experiments have been conducted to obtain single-phase local heat transfer coefficient distributions associated with impingement of one or two rows of circular, free-surface water jets on a constant heat flux surface. The nozzle diameter, the centerline-to-centerline distance between nozzles in a row, and the nozzle-to-heater separation distance were fixed at 4.9, 6.3, and 89.7 mm, respectively. Two row-to-row separations (81 and 51 mm) were considered, and nozzle discharge Reynolds numbers were varied over the range from 16,800 to 30,400. The interaction zone created by opposing wall jets from adjacent rows is characterized by an upwelling of spent flow (an interaction fountain) for which local coefficients can approach those of the impingement zones. Interactions between wall jets associated with nozzles in one row can create sprays that impact the adjoining row with sufficient momentum to induce a dominant/subordinate row behavior. In this case the interaction zone is juxtaposed with the subordinate row, and local coefficients in the impingement and wall jet regions of the affected row may be significantly enhanced. This result contrasts with the deleterious effects of crossflow reported for submerged jets throughout the literature. Spray-induced enhancements, as well as interaction zone maxima, increase with decreasing row-to-row pitch and with increasing Reynolds number.