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

热管是一种紧凑、可靠的用于传热的设备，但人们对其微尺度流体流动行为缺乏了解。为了更深入地了解这些类型的流动的本质，这些流动也经常发生在复杂的几何形状中，我们将使用一种称为晶格玻尔兹曼方法的技术对流动进行建模。虽然该方法在分析复杂流动时非常有用，但在包含热效应方面的发展仍然不足。因此，我们提出发展先进的、高阶的（更精确的）基于晶格玻尔兹曼的数值模拟，以进一步了解热管中的微热流体现象。所建议的工作的智力价值来自于开发更严格、更现实、更通用的计算工具，以及由此获得的对复杂流程的更深入的理解。所有晶格玻尔兹曼模型的基本基础是描述流体元素的密度和动量（有时还有温度）的粒子分布函数。为了建立一个高阶热晶格玻尔兹曼模型，我们将平衡粒子分布函数扩展到四阶。为了模拟多相，我们将结合流体粒子的相互作用，使用更好的有效质量描述。结合这些方法意味着作用在粒子上的力需要在大量的速度上离散化，这在数值上是复杂的。然而，虽然这是相当具有挑战性的，但它可能会导致对晶格玻尔兹曼公式的各个方面对数值模拟中的不稳定性和不准确性的贡献的额外见解，从而扩大晶格玻尔兹曼方法的适用性。该模型将使用文献中大量可用的实验数据进行验证。由此产生的模型将能够探索几何形状、流体性质等变化对热管效率的影响，并将更好地理解驱动热管系统的微流体现象的潜在物理。更精确的多相、多组分、热流模拟，特别是在小尺度和/或复杂几何中有许多应用。改进热管性能可以提高计算机冷却系统的整体能源效率，目前冷却系统消耗大量电力（一个典型的数据中心将其能源消耗的1/3用于冷却）。对于发电和暖通空调行业的许多其他更传统的热交换器也是如此；通过将微制造工艺与发生在这些通道和表面的相变的精确模拟相结合，有可能设计出更高效的冷凝器、蒸发器、发电机等。提高能源效率可以直接带来经济和环境的节约。研究热管也有教育上的好处。这些装置将作为本科课堂的演示单元，以推动相变和传热现象的讨论。高年级本科生的设计团队也将通过设计和建造测试不同材料、工作流体和配置的演示单元，以及热管的应用，如超频处理器的冷却装置和热管船的创建，帮助将热管概念（及其基本原理）转化为高中和初中水平。

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.