Theory and Applications of Non-Equilibrium Thermodynamics

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The applicant's main research concerns development of accurate models for simulation and understanding of processes in microscale systems, where the degree of nonequilibrium is strong and the well-established laws of fluid dynamics and heat transfer cease to be valid. These powerful simulation tools provide important process details that are not accessible to measurements, and minimize costs of prototyping and physical testing. The applicant had excellent success and recognition in developing and applying advanced flow models from the microscopic description, which refine the equations of fluid dynamics, and extend the validity towards microflows. The refined equations give useful approximations of the microscopic physics, and describe all interesting transport regimes. Advanced cooling systems rely on evaporative cooling on the microscale, hence an accurate description of evaporation and condensation phenomena must be included in the models. While evaporation and condensation are everyday phenomena, their behavior on the microscale is difficult to ascertain. For instance, the reported values for the evaporation coefficient of water scatter over several orders of magnitude. Molecular simulations reveal that what appears to the naked eye as a sharp interface between liquid and vapor, is in fact a small region in which mass density and other properties change continuously over the distance of few atomic diameters-the change is steep, but not sharp. In collaboration with co-workers and students, the applicant has recently embarked on the development and testing of a refined set of fluid dynamics equations which describe liquid and vapor phases as well as resolved phase interfaces with surface tension and interface resistivities. In comparison to molecular simulations, the new equations can be solved with significantly higher efficiency. Preliminary results do not show stochastic noise, and exhibit all the salient features of nonequilibrium interfaces: marked deviation from saturation pressures; strong variations of temperature across the interface, corresponding to temperature jumps; offset of temperature and density variation; Knudsen transition layers that extend some mean free paths into the vapor; and strong variations of velocity across the interface, corresponding to slip. The proposed research program will focus on the further development of the model, and its use to gain a comprehensive understanding of the factors that affect the behavior of nonequilibrium phase interfaces. The applicant's research team will continue to build on the success of the previous NSERC Discovery Grant funded program and exploit the speed and efficiency offered by the new equations to explore a wide range of interface processes, from near equilibrium to strong nonequilibrium. The applicant will also continue and extend previous work in nonequilibrium thermodynamics, e.g., on alignment of theories, and wider applications to energy systems.