NSF Award
2327572
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.<br/><br/>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.<br/><br/>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.
