Nanostructure Boiling Enhancement and Spray Cooling

Phase-change heat transfer is characterized by high heat transfer coefficients of 2,500 to 100,000 W/(m^2*K). Thus, for low temperature differences between the heated surface and the cooling liquid, high heat fluxes are possible. Means for high heat flux cooling are necessary for continued advancements in microelectronics development, nuclear power generation, metallurgical processing, and other applications where thermal management is important.

Two high heat flux cooling methods we are investigating involve boiling and spray cooling. Investigation of these methods of heat dissipation is important because they are often integral processes to many thermal management systems. The boiling investigation focuses on the effects of nanostructured surface features on nucleate boiling. During nucleate boiling, bubbles initiate in cavities on the heater surface (nucleation sites). By changing the nucleation site geometry and distribution, the heat flux can be increased or decreased. Using nanostructured layers, deposited on the heater surface, nucleation site characteristics can be modified to maximize heat flux in the nucleate boiling regime.

Spray cooling can also be used to produce high heat fluxes at low superheat temperatures. Spray cooling of an inverted, heated surface is being investigated to determine heat fluxes for various spray and surface conditions. Unlike conventional spray cooling experiments in which droplets are directed downward onto a heated surface, in this investigation, the spray is directed upwards to cool a heated surface that faces downward. Thus, in this configuration, vapor that is created by droplet evaporation does not freely move away from the heated surface. Objectives of this investigation are identification of the underlying physical mechanisms affecting heat transfer, determination of heat transfer regimes, and development of correlations to estimate heat fluxes.

Sponsor: Department

Principal Investigator: Frank Pyrtle, III

Collaborators: N/A