A closed two-phase loop system was developed that combined with a multi-nozzle spray cooling unit for the cooling of high heat flux power sources. The fluid circulation was sustained by a magnetic gear pump operating with an ejector pump unit. The motive flow of the ejector shared the pumping liquid flow with the multi-nozzle spray. The use of the ejector stabilized the circulation of the two-phase flow. A multi-nozzle plate with 48 miniature nozzles was designed to generate an array of 4×12 sprays. A closed loop spray cooling experimental setup with a cooling area of 19.3 cm 2 was built. The spray nozzle to target distance was 10 mm. Water and FC-72 were used as the working fluids. Spray cooling experiments were performed in three orientations of the spray target surface, namely (a) horizontal facing upward, (b) vertical, and (c) horizontal facing downward. The thermal performance of the horizontal facing downward surface was the best. A comparison with the thermal performance data for a smaller cooling surface area of 2.0 cm 2 was made.

Spray cooling has been studied thoroughly over the years in an effort to understand its unique heat transfer potential. Spray cooling is characterized by its ability to dissipate high heat transfer rates while maintaining relatively uniform surface temperatures. Despite of all the recent developments, liquid-surface properties such as contact angle and surface tension have been shown to limit the ability of spray cooling to dissipate high heat flux. Recent high-speed images of multiple droplet impingent events have revealed that liquid film thickness, impact crown morphology, and tangential velocity gradients tend to dominate the overall heat transfer process. All these aspects are intrinsically linked to surface morphology. Therefore, enhancement of heat transfer should be preceded by the design, fabrication and use of surfaces that reduce film thickness, promote constructive impact crown morphology, and facilitate greater tangential velocity gradients. Recently, a new type of nanostructured surface has been designed, fabricated, and tested that reduces film thickness and contact angle by at least 30%. The nanostructured surface consists of nanopillars of 100 nm in height and 200 nm in diameter. The combination of spacing and nanopillar size has resulted in a thinner liquid film. The nanostructured surface was fabricated using the Step and Flash Imprinting Lithography (S-FIL) technique. Current work also includes the study of the relationship between the effective thermal diameter and heat flux when using nanostructured and bare surfaces.