Collaborative Research: Supercritical Fluids and Heat Transfer - Delineation of Anomalous Region, Ultra-long Distance Gas Transport without Recompression, and Thermal Management

超临界(SC)条件下的流体，即不再存在不同的液体和气相，在自然界和技术系统中都可以找到，这些系统可以利用在临界温度和压力附近发生的极端变化。SC流体的传热增加、流体摩擦减少和高溶解度在天然气管道运输、作为碳捕获和储存过程一部分的二氧化碳输送、热电厂和核电站的工质、太阳能和地热能转换系统以及电子设备和数据中心的强化冷却方面具有当前和潜在的应用。尽管超临界流体具有独特的性质所带来的优势，但由于对其异常行为的认识不足，限制了其广泛应用，其特征是临界区域内热物性的大范围变化，导致热和流动振荡等有害现象。此外，特定于每种物质的临界温度和压力范围可能不适合特定的技术需求。这项研究将解决一组重要的SC流体的异常行为知识空白，这将为高容量、高能效和对环境负责的流体流动和热管理系统打开新技术的大门。例如，SC条件下的天然气(SNG)可以通过陆上、地下和海底管道运输，距离超过2,000公里。SNG运输是高能效的，可以减少或完全取消途中再压缩站的数量，实现目前不可能的新的跨洋航线，服务于美国的国家利益，并为世界其他地方提供能源安全。与液化天然气(LNG)相比，SNG运输成本更低，对环境的影响更小，更安全。研究近海气体输送所产生的知识将有助于确定二氧化碳从海岸线输送到海底进行封存时的热力学状态。同样，输送SC氧气、氮气和其他重要工业/医疗气体的方法的开发也将从这项工作中受益。这项研究的更广泛影响包括在SC传输现象方面的教育机会，以及使用广泛的当前和潜在的SC技术来激发对热力学的兴趣的未被充分代表的群体。先前的研究表明，临界点附近的异常流体传输行为始于三相点以上的亚临界状态，并持续到SC状态的深处。在这个研究计划中，将建立一个基于吉布斯自由能的热力学模型来描述反常状态的温度-压力边界，并表征高阶相变。它将应用于一系列自然/工业上重要的SC流体，包括水、二氧化碳、甲烷、Ar和氮气。这一分析将导致确定SC流体，包括超临界天然气(SNG)，可以在不再压缩的情况下长距离运输的安全条件。SNG输送的全部潜力将通过建立SC热输送的一维计算模型来量化，该模型考虑了输送性质的变化和可压缩性、环境热条件、焦耳-汤姆逊现象以及管道的热阻。将开发一个三维模型，以研究进出口区域的流动和热行为，以及周围环境温度变化的影响。热力学模型还将用于设计定制的SC流体混合物，以实现有效的热管理。拟议的研究包括计划制造一种用于SC流体流动和热分析的实验设备，以生成与SC流体属性相关的数据，检查模型验证的参数效应，并探索增强热传递的方法。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Fluids under supercritical (SC) conditions, where distinct liquid and gas phases no longer exist, are found in nature and technological systems that can take advantage of the extreme changes that take place near the critical temperature and pressure. The increases in heat transfer, reductions in fluid friction, and high solubility of SC fluids have current and potential applications in pipeline transport of natural gas, delivery of carbon dioxide as part of carbon capture and storage processes, working fluids for thermal and nuclear power plants, solar and geothermal energy conversion systems, and enhanced cooling of electronic devices and data centers. Despite the advantages offered by the unique properties of SC fluids, their wide-spread use has been curtailed because of inadequate understanding of anomalous behaviors, characterized by large-scale variations in thermophysical properties in the critical region, resulting in thermal and flow oscillations and other detrimental phenomena. Additionally, the critical temperature and pressure range, specific to each substance, may not fit a particular technological need. This research will address the anomalous behavior knowledge gaps of an important set of SC fluids, which will open the door to new technologies for high-capacity, energy-efficient, and environmentally responsible fluid flow and thermal management systems. For example, natural gas under SC conditions (SNG) can be transported via overland, underground, and undersea pipelines for distances greater than 2,000 km. SNG transport is power-efficient and can reduce the number of enroute recompression stations or eliminate them altogether, enabling new trans-oceanic routes that are currently impossible, serving the US national interest as well as providing energy security elsewhere in the world. In comparison with liquified natural gas (LNG), SNG transport can be less expensive, have reduced environmental impact, and be more secure and safe. Knowledge generated in the study of SNG transport will be useful in determining the thermodynamic states of carbon dioxide when it is transported from shorelines to the ocean floor for sequestration. Likewise, development of methods to transport SC oxygen, nitrogen, and other important industrial/medical gases will benefit from this work. The broader impacts of this research include educational opportunities in SC transport phenomena and outreach to underrepresented groups using the wide range of current and potential SC technologies to motivate interest in thermodynamics.Previous research has shown that anomalous fluid transport behavior near the critical point starts in the subcritical state above the triple point and continues deep into the SC state. In this research program, a thermodynamic model based on Gibbs free energy will be developed to delineate the temperature-pressure boundaries of the anomalous states and characterize the higher-order phase transitions. It will be applied to a set of naturally/industrially important SC fluids including water, carbon dioxide, methane, argon, and nitrogen. This analysis will lead to the identification of safe conditions at which SC fluids, including supercritical natural gas (SNG), can be transported over long distances without recompression. The full potential for SNG transport will be quantified by developing a one-dimensional computational model for SC thermal transport, accounting for transport property variations and compressibility, environmental thermal conditions, Joule-Thomson phenomena, and thermal resistance of the pipeline. A three-dimensional model will be developed to examine the flow and thermal behavior in the inlet and outlet regions as well as the impact of temperature variations in the surrounding environment. The thermodynamic models also will be employed to design customized mixtures of SC fluids for effective thermal management. The proposed research includes plans to fabricate an experimental apparatus for SC fluid flow and thermal analysis to generate data relevant to SC fluid properties, examine parametric effects for model validation, and explore methods to enhance heat transfer.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.