Increases in microprocessor power density along with an accompanying spatial variation in power density has been well documented in recent years. These combined factors pose a severe challenge for the provisioning of cooling resources at the microprocessor level. The use of thermal inkjet technology to precisely supply coolant onto the surface of a microprocessor has the potential to address this problem in a chip-scale form factor. By providing coolant when and where it is needed on the surface of a chip or package, very high critical heat fluxes can be obtained in an energy efficient manner in a minimum of physical space. In this paper, the unique heat transfer characteristics of inkjet assisted spray cooling of a heated surface are investigated. Sprays of water are used to cool heated surfaces ranging from 281mm2 to 35mm2. Several experiments are conducted at different nozzle-to-surface distances to measure critical heat flux (CHF) at different flow rates and firing frequencies. The impact of volumetric flux variation on CHF is studied. CHF data, measured over broad range of operating conditions is correlated to volumetric flux and liquid properties. Flow visualization studies are also conducted to understand the vapor-liquid interaction at the heater surface and the intermediate region. Jet breakup length studies are carried out to understand the propagation of Rayleigh instabilities in the spray jets and, subsequent, formation of liquid drops. CHF data combined with fluid flow studies have been used to optimize the nozzle-to-surface clearance. Results obtained from these experiments are invaluable for the design of micro scale spray cooling devices for chips.

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