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

CBET-1233106PI：Schaefer热管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类流动的性质，我们将使用一种称为格子Boltzmann方法的技术来模拟这些流动。虽然这种方法在分析复杂流动时非常有用，但在包含热效应方面仍存在不足。因此，我们建议发展先进的、更高阶(更精确)的基于格子Boltzmann的数值模拟，以加深我们对热管中微观热流体现象的了解。拟议工作的智力价值既来自开发更严格、更现实和更多功能的计算工具，也来自于对复杂流动的更深入理解，从而可以获得。所有格子Boltzmann模型的基本基础是描述流体元素的密度和动量(有时还包括温度)的粒子分布函数。为了发展高阶热格子Boltzmann模型，我们将平衡粒子分布函数展开到四阶。为了对多相进行建模，我们将使用对有效质量的更好描述来考虑流体颗粒相互作用。结合这些方法意味着作用在粒子上的力将需要在大量的速度上离散，这在数值上是复杂的。然而，虽然这是相当具有挑战性的，但它可能会导致对格子Boltzmann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更多洞察，从而扩大格子Boltzmann方法的适用性。该模型将使用文献中提供的大量实验数据进行验证。所得到的模型将能够探索几何、流体性质等变化对热管效率的影响，并将导致更好地理解驱动热管系统的微流体现象的基本物理。更准确地模拟多相、多组分、热流，特别是在小范围和/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(典型的数据中心将三分之一的能源消耗用于冷却)。同样的道理也适用于发电和暖通空调及空调行业中的许多其他更传统的热交换器；通过将微制造工艺与对这些通道和表面中发生的相变的准确模拟相结合，可以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节约。研究热管也有教育上的好处。这些装置将被用作本科生课程的示范单位，以推动对相变和热传递现象的讨论。高水平本科生的设计团队还将帮助将热管的概念(及其基本原理)转化为高中和中学水平，方法是设计和建造研究不同材料、工质和配置的示范单元，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。

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.