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

CBET-1233106 PI：SchaeferHeat pipes是用于传输热量的紧凑，可靠的设备，但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性质，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格子玻尔兹曼方法的技术来模拟流动。虽然该方法在分析复杂流动时非常有用，但它在包含热效应方面的发展仍然不足。因此，我们建议发展先进的，更高阶（更准确）的格子玻尔兹曼为基础的数值模拟，可以进一步我们的知识，在热管中的微观热流体现象。所提出的工作的智力价值来自开发一个更严格的，现实的，和多功能的计算工具，并从复杂的流动，可以获得更深入的理解。所有格子玻尔兹曼模型的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。为了发展一个高阶的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。为了模拟多个阶段，我们将纳入流体粒子的相互作用，使用更好的描述的有效质量。结合这些方法意味着作用在颗粒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，它可能会导致额外的见解的格子玻尔兹曼公式的各个方面的贡献，在数值模拟中的不稳定性和不准确性，从而扩大格子玻尔兹曼方法的适用性。该模型将使用文献中的大量实验数据进行验证。然后，所得到的模型将能够探索几何形状、流体性质等变化的影响，更精确地模拟多相、多组分的热流，特别是在小尺度和/或复杂的几何形状中，具有许多应用。提高热管性能可以提高计算机冷却系统的整体能效，目前计算机冷却系统消耗大量电力（典型的数据中心将其能耗的1/3用于冷却）。对于发电和HVAC R行业中的许多其他更传统的热交换器也是如此;可以设计更有效的冷凝器、蒸发器、发电机等，通过将微制造过程与发生在这些通道和表面中的相变的精确模拟相结合。提高能源效率可以直接导致经济和环境节约。热管的研究也有教育上的好处。这些设备将被用作本科课程的演示单元，以便为相变和传热现象的讨论提供动力。高年级本科生的设计团队还将帮助将热管概念（及其基本原理）转化为高中和初中水平，通过设计和建造演示单元来检查不同的材料，工作流体和配置，以及热管的应用，例如超频处理器的冷却设备和热管船的创建。

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.