This work presents a 3-D-printed polymer nozzle designed for cooling gallium nitride (GaN) power devices using direct water-jet impingement. The nozzle employs nine jet orifices with 0.75-mm diameter and can withstand temperatures up to 200 ◦C. In static tests, it is capable of removing heat fluxes of up to 900 W/cm2 from a 0.143-cm2 surface (simulating a GaN power device), while keeping its temperature below 100 ◦C. Tests over a wide range of parameter values demonstrate performance trade-offs under different design choices and operating conditions. The nozzle achieves a heat transfer coefficient of up to 100 kW/m2K under forced-convection conditions. A superstructure containing four nozzles is used to cool four topside-cooled (TSC) GaN power devices operating as the power stage of a dc-ac power-electronic converter. A boron nitride (BN) coating and an Al2O3-based paint are evaluated as the electrical insulation between the devices and the coolant. The structure can maintain device temperatures below 100 ◦C with dynamic converter operation, removing up to 21 W of heat from the devices at a heat flux of 37 W/cm2 and coolant flow rate of 1 L/min. Corrosion is observed on the GaN power devices with the BN coating under converter operation, demonstrating the necessity for testing under representative conditions.

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