Single-phase and boiling cooling of small pin fin arrays by multiple slot nozzle suction and impingement

Experimental measurements of forced convection single-phase and boiling heat transfer from pin fin arrays were made using fluorocarbon liquid FC-72. Liquid flow was directed to and from the pin fin arrays by multiple slot nozzles, alternately providing suction and impingement flow. Rectangular pin fin arrays having equal width and spacing of 0.1 and 0.2 mm and aspect ratios of 1, 2.25 and 5 were machined from 1 cm square copper blocks, providing total surface areas of 200 to 600 mm². The multiple slot nozzles featured alternating inlet and outlet channels 1 mm wide on a 2 mm pitch, providing inlet and outlet cross-sectional areas of 25 mm². Flow rates of 1.25 to 10 cm ³/s (0.075 to 0.6 l/min) were tested, resulting in inlet and outlet velocities of 0.05 to 0.4 m/s and pin fin array velocities from 0.05 to 4.0 m/s. The range of flow rates and pin fin geometries provided single-phase heat transfer coefficients (based on planform area) from 5.2 to 38.5 kW/m²K and critical heat flux from 89 to 369 W/cm ² at an inlet temperature of 16°C, corresponding to 40°C subcooling. At a fixed pin fin aspect ratio and liquid flow rate, reducing pin fin width from 0.2 mm to 0.1 mm increased single-phase heat transfer by an average of 7%, while critical heat flux remained constant. Correlations of the single-phase heat transfer coefficient and critical heat flux as functions of liquid flow rate, pin fin aspect ratio and width are provided