Effect of Nozzle Orifice Diameter and Position of Hydraulic Jump on Stagnation Point Heat Transfer During Liquid Jet Impingement Cooling

Liquid jets have excellent potential to dissipate high thermal loads while maintaining surface temperatures well below the specified reliability limit of electronic devices. The present study investigates orthogonal liquid jet impingement from a single nozzle over a heated substrate while examining the simultaneous effect of nozzle orifice diameter and the appearance of a hydraulic jump on the stagnation point heat transfer rates. Characteristics of single-phase convective heat transfer are explored for five different nozzle orifice diameters ranging from 0.4 mm to 3 mm and coolant flow rates of 50-350 ml/min (Reynolds number ∼ 1,000-12,000). Using high-speed imaging, liquid jet impingement over the target surface is recorded to estimate the location of the hydraulic jump. The heat transfer coefficient (HTC) is found to be a strong function of the coolant flow rate, nozzle orifice diameter, and the position of the hydraulic jump. The stagnation point heat transfer rate degrades in the presence of hydraulic jump despite always being covered with a thin liquid film. It is enhanced by increasing the jet's Reynolds number at a fixed orifice diameter or by decreasing its diameter while maintaining a constant Reynolds number. In addition, a parametric study of the stagnation point's Nusselt number as a function of the flow variables, including the hydraulic jump, is carried out, and a new correlation is proposed. The Nusselt number correlation for the stagnation point agrees well with the present experimental data within a ± 15% error band, allowing a rational design of a single nozzle liquid jet for various thermal management applications.