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The two-phase flow modeling is done using the level set method to identify the interface of vapor and liquid. The modifications to the incompressible Navier-Stokes equations to consider surface tension, viscosity, gravity and phase change are discussed in detail. The governing equations are solved using finite difference method. In the present work, investigations on the effect of thermal conductivity and latent heat of vaporization of liquid on heat transfer in a 44 µm thick liquid film containing vapor bubble with droplet impact is investigated. The importance of thermal conductivity and latent heat of vaporization of liquid on heat transfer is identified. The variation of heat flux with thermal conductivity and latent heat is plotted. The computed liquid and vapor interface, velocity vector and temperature distributions at different time instants are also visualized for better understanding of the heat removal.

A closed loop spray cooling test setup is established for the cooling of high heat flux heat sources. Eight miniature nozzles (in a multi-nozzle plate) are used to generate a spray array targeting at a 1×2 cm2 cooling surface. FC-87, FC-72, methanol and water are used as the working fluids. Thermal performance data for the multi-nozzle spray cooling in the confined and closed system are obtained at various operating temperatures, nozzle pressure drops (from 0.69 bar to 3.10 bar) and heat fluxes. It is exhibited that the spray cooler can reach the critical heat fluxes of 90 W/cm2 with fluorocarbon fluids and 490 W/cm2 with methanol. For water, the critical heat flux is higher than 500 W/cm2. The air purposely introduced in the spray cooling system with FC-72 fluid has a significant influence on heat transfer characteristics of the spray over the cooling surface.

The rotating heat pipe (RHP) technology is revisited in the context of finding a suitable thermal management solution for the advanced electrical machines such as switched reluctance and permanent magnet types. These machines, with potential applications involving direct mounting to gas turbine main shaft, have very high operating speeds and rotor thermal loads requiring new research studies on the use of RHP technology. The RHP literature data of the 1970's and 1980's are mostly limited to low speeds and off-axis mode tests. In this paper, results of a stainless steel - water on-axis RHP are presented. Also, potential application areas are identified.

Rotating Heat Pipe (RHP) technolog y is being developed for high speed (>20 krpm) regimes of electric motor/generator cooling. The motivation for this research is the potential application of the high speed RHPs for the thermal management of advanced rotating electrical machines. The passive nature and relatively simple features of this device are attractive for the removal of waste heat from the rotors of electric machines. Interesting air-cooling experimental results of two high speed RHPs designed, fabricated and tested at AFRL are presented here. Emphasis is made on external heat removal concepts useful for cooling the RHP condenser in order to be successful in promoting this technology to real world problems.