Collaborative Research: Thermal Transport in Elastic Turbulence

合作研究：弹性湍流中的热传输

• 批准号: 1501587
• 负责人: Phillip Ligrani
• 金额: $ 16.53万
• 依托单位: University of Alabama in Huntsville
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2014
• 资助国家: 美国
• 起止时间: 2014-10-01 至 2019-09-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1501587&HistoricalAwards=false
• 关键词: Collaborative; Research; Thermal; Transport; Elastic

CBET 1336085PI: P. Ligrani (SLU), R. Handler (TAMU)Polymer additives, such as polyacrylamide, have unique characteristics in liquids, including highly non-linear, non-Newtonian behavior. To augment transport, the polymers are stretched in constriction by flow strain, which is induced by, for example, streamline curvature. The extensibility of the polymer and resulting polymer deformation, leads to a sharp growth in the local elastic stress, a sequence of events referred to as the Weissenberg instability, which occurs when the Weissenberg number is greater than approximately ½ or 0.5. Overall consequences include increased polymer viscosity, in some cases, by up to 3 orders of magnitude. Such changes also lead to increases in effective polymer thermal conductivity, and augmentation of thermal transport. However, such increases in thermal transport from elastic turbulence have never before been investigated, and thus, to develop innovative methods to enhance mixing and thermal transport in small-scale environments at low Reynolds numbers, experiments and simulations will be coordinated and conducted on thermal transport in elastic turbulence. One principal aim is to determine the efficacy of using elastic turbulence to augment thermal transport, by characterizing the phenomena both experimentally and numerically. Numerical modeling and prediction of the physical trends of both measured and non-measured quantities will be performed with three-dimensional Direct Numerical Simulations (DNS). As such, another overall intent is enhancement of fundamental understanding of the associated physical processes associated with elastic turbulence, as it is induced in liquids by polymers subject to stretching and constriction by flow strain. A resulting product will be new numerical and analytic models to describe and represent the related elastic turbulence physical phenomena, especially thermal transport. Generally, milliscale (or millimeter-scale) devices and flow environments will be employed to produce flows in the rotating-Couette and Dean flow geometries. These flows each provide shear and streamline curvature (centrifugal effects) and thus are ideally suited to producing elastic turbulence in dilute polymer solutions. As part of this research, a new Prandtl number model and a new effective conductivity model for elastic turbulence will also be developed. This will be facilitated by measurements of flow characteristics (time-varying and time-averaged) and heat transfer coefficients, and fully three-dimensional direct numerical simulations (DNS) with non-linear elastic models, such the FENE-P, to elucidate polymer solution characteristics. The present study follows several important recent, related fluid mechanics investigations, and as such, will address important gaps in knowledge regarding the effects and influences of polymer additives on thermal transport in milliscale and microscale liquid flows. As such, the present study is highly transformational and relevant because of the new physical understanding which will be provided, and because of the variety of applications. In recent years, much attention has been devoted to technological advances related to miniaturization, with particular attention to technologies at the micro-scale and nano-scale, but also to milli-scale devices. For example, improvements in manufacturing technology and micro-fabrication have led to the miniaturization of a variety of different types of devices and sensors. The ability to predict the fluid motion in and around these devices is essential for their design and optimization. As the length scales of these devices decrease for liquid flows, effects become significant which are not present in larger-scale devices. Because of the small dimensions and very low speeds which are involved, the flows within these components are generally laminar, with relatively low magnitudes of mixing and thermal transport. Such laminar flows are thus a consequence of the limitations imposed by the small sizes of the miniature devices. Such flows, and the devices associated with them, are vital and important for a range of applications in areas such as pharmaceutics, medicine, heat transfer, biomedical engineering, and electronics cooling. In every case, the devices associated with these application areas would generally benefit by increased mixing and augmented transport from elastic turbulence. Such mixing is important for a variety of situations within the mentioned application areas, including the use of liquids to cool electronic components, mixing of different chemical components to manufacture pharmaceuticals, lab-on-a-chip devices which involve the interaction and mixing of different fluid streams, and miniature heat exchangers for use in devices ranging from automobiles, to appliances, to components within space systems, including satellites.

CBET 1336085PI：P.Lgrani(SLU)，R.Handler(TAMU)聚合物添加剂，如聚丙烯酰胺，在液体中具有独特的特征，包括高度非线性、非牛顿行为。为了增加传输，聚合物被流动应变拉伸，流动应变是由例如流线曲率引起的。聚合物的延伸性和由此产生的聚合物变形导致局部弹性应力急剧增长，这一系列事件称为魏森伯格不稳定性，当魏森伯格数大于约1/2或0.5时发生。总体后果包括聚合物粘度增加，在某些情况下，高达3个数量级。这样的变化还会导致聚合物有效导热系数的增加，以及热传输的增强。然而，这种由弹性湍流引起的热输运的增加以前从未被研究过，因此，为了开发新的方法来加强小规模环境中低雷诺数下的混合和热输运，将对弹性湍流中的热输运进行实验和模拟。一个主要的目的是通过实验和数值分析来确定使用弹性湍流来增强热传输的有效性。将使用三维直接数值模拟(DNS)对已测量和未测量的量的物理趋势进行数值建模和预测。因此，另一个总体意图是加强对与弹性湍流相关的相关物理过程的基本理解，因为弹性湍流是由聚合物在液体中诱导的，聚合物受到流动应变的拉伸和收缩。由此产生的产品将是新的数值和解析模型，用于描述和表示相关的弹性湍流物理现象，特别是热传输。通常，将采用毫级(或毫米级)装置和流动环境来产生旋转Couette和Dean流几何形状的流动。这些流动中的每一个都提供了剪切和流线曲率(离心力效应)，因此非常适合在稀溶液中产生弹性湍流。作为这项研究的一部分，还将发展一种新的普朗特数模型和一种新的弹性湍流有效导电率模型。这将通过测量流动特性(时变的和时间平均的)和传热系数，以及使用非线性弹性模型(如Fene-P)的全三维直接数值模拟(DNS)来阐明聚合物溶液的特性，从而促进这一过程。这项研究是在最近几项重要的相关流体力学研究之后进行的，因此，将解决有关聚合物添加剂对毫秒级和微米级液体流动中热传输的影响和作用的重要知识空白。因此，本研究具有高度的变革性和相关性，因为将提供新的物理理解，并因为应用的多样性。近年来，与小型化相关的技术进步引起了人们的极大关注，特别是微米和纳米级的技术，以及毫米级的设备。例如，制造技术和微制造的改进导致了各种不同类型的设备和传感器的小型化。预测这些设备内部和周围的流体运动的能力对于它们的设计和优化至关重要。随着这些设备的长度尺度对液体流动的减小，影响变得显著，这在更大规模的设备中是不存在的。由于所涉及的尺寸小且速度非常低，这些部件内的流动通常是层流，混合和热传输的程度相对较低。因此，这种层流是微型设备的小尺寸所施加的限制的结果。这种流动及其相关设备对于制药、医药、热传递、生物医学工程和电子冷却等领域的一系列应用是至关重要和重要的。在每一种情况下，与这些应用领域相关的设备通常都将受益于弹性湍流增加的混合和增强的传输。这种混合对于上述应用领域内的各种情况都很重要，包括使用液体冷却电子元件、混合不同的化学成分来制造药物、涉及不同流体相互作用和混合的芯片实验室设备以及用于从汽车到家用电器到包括卫星在内的空间系统内的各种设备的微型热交换器。