Polymer nozzles, made with a 3D printer using stereolithography, were used to impinge water jets on a high heat-flux surface. The nozzles had nine staggered orifices from which water emerged, flowed through an internal cavity over the heated surface, and then returned through a slot. Multiple nozzles were made with varying cavity heights (0.25 mm to 2 mm), while the jet diameter (0.75 mm) and spacing between jets (1mm) were kept constant. Experiments were done to measure convective heat transfer from a copper surface with a surface area of 0.143 cm 2 emitting heat fluxes of 50 to 900 W/cm 2 while varying the water flow rate from 0.1 to 1.0 L/min. An energy balance was used to estimate the heat transfer from the copper surface to the coolant. Heat transfer increased with the water flow rate. It was possible to remove the highest heat flux while avoiding boiling. Reducing the cavity height while keeping the water flow rate constant increased the flow velocity and enhanced convection, but also raised the pressure drop across the nozzle. Heat transfer coefficients as high as 120,000 W/m 2 °C were measured during impingement cooling.

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