A Deeper Understanding of Small-Scale Phenomena in Heat Pipes through a Higher Order Lattice Boltzmann Method

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CBET-1233106PI: SchaeferHeat pipes are compact, reliable devices used for transporting heat, but there is a lack of understanding of their microscale fluid flow behavior. In order to gain deeper insights into the nature of these types of flows, which also often occur in complicated geometries, we will model the flows using a technique known as the lattice Boltzmann method. While that method is very useful in analyzing complicated flows, it still suffers from inadequate development on the inclusion of thermal effects. Therefore, we propose the development of advanced, higher order (more accurate) lattice Boltzmann-based numerical simulations that can further our knowledge of micro thermal-fluid phenomena in heat pipes. The intellectual merit of the proposed work comes both from developing a more rigorous, realistic, and versatile computational tool, and from the deeper understanding of complex flows that can be gained as a result. The fundamental underpinning of all lattice Boltzmann models are particle distribution functions that describe the density and momentum (and sometimes temperature) of the fluid elements. To develop a higher-order thermal lattice Boltzmann model, we will expand the equilibrium particle distribution function to the fourth order. In order to model multiple phases, we will incorporate fluid particle interactions using a better description of the effective mass. Combining these approaches means that the forces acting on the particles will need to be discretized over a large number of velocities, which is numerically complicated. However, while this is quite challenging, it will likely lead to additional insights into the contribution of the various aspects of the lattice Boltzmann formulation to instabilities and inaccuracies in the numerical simulations, thereby expanding the applicability of the lattice Boltzmann method. The model will be validated using the vast range of experimental data available in the literature. The resulting model will then be able to explore the effect of variations in geometry, fluid properties, etc., on heat pipe efficiency, and will lead to a better understanding of the underlying physics of the micro fluid phenomena that drive heat pipe systems.More accurate simulations of multiphase, multicomponent, thermal flows, particularly in small-scale and/or complicated geometries have many applications. Improving heat pipe performance can lead to increases in the overall energy efficiency of computer cooling systems, which currently consume huge amounts of power (a typical data center uses 1/3 of its energy consumption for cooling). The same is true for many other more conventional heat exchangers in the power generating and HVAC&R industries; it may be possible to design more efficient condensers, evaporators, generators, etc., by combining micromanufacturing processes with accurate simulations of the phase transitions that occur in those channels and surfaces. Improving the energy efficiency can directly lead to both economic and environmental savings. There are also educational benefits from the study of heat pipes. The devices will be used as demonstration units for undergraduate classes, in order to provide an impetus for discussion of phase change and heat transfer phenomena. Design teams of upper-level undergraduates will also help to translate heat pipe concepts (and their underlying principles) to the high-school and middle-school level, through designing and building demonstration units that examine different materials, working fluids, and configurations, as well as applications for heat pipes, such as cooling devices for overclocking processors and the creation of heat pipe boats.