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Isobaric Heat Capacity of Supercritical Fluids

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Isobaric Heat Capacity of Supercritical Fluids ISOBARIC HEAT CAPACITY OF SUPERCRITICAL FLUIDS: EXPERIMENTAL MEASUREMENTS AND MODELING A Dissertation Presented to the Faculty of the Graduate School of Cornell University in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy by Mitchell Price Ishmael May 2017 © 2017 Mitchell Price Ishmael ALL RIGHTS RESERVED ISOBARIC HEAT CAPACITY OF SUPERCRITICAL FLUIDS: EXPERIMENTAL MEASUREMENTS AND MODELING Mitchell Price Ishmael, Ph. D. Cornell University 2017 Fluids at high temperature and pressure are commonplace across engineering applications. These fluids are sometimes the product of a harsh environment, as in subsurface operations such as oil and gas development or geothermal energy production, or at other times, exploited for their desirable transport and thermodynamic properties in, for example, chemical extractions and material synthesis. At these elevated conditions, many single and multi-component fluids exist in a supercritical state, where small changes in temperature and pressure cause significant property variations without induction of a phase change. A fluid’s isobaric heat capacity (Cp), a property important to most thermal processes, fluctuates strongly in the supercritical region, ranging from a few times the ideal gas state Cp to infinity exactly at the critical point for pure fluids. Accurately capturing the thermophysical behavior of supercritical pure fluids and mixtures is necessary for optimal design and efficient operation of numerous engineering processes that utilize these substances. The main goal of this research was to increase understanding of isobaric heat capacity property changes in supercritical fluids. The first step in a threefold approach was to design and construct a calorimeter for precise and accurate measurements of Cp in the supercritical region. Second was to carry out experimental Cp measurements for pure fluids and representative fluid mixtures in pressure-temperature-composition regions with only limited available data. Systems studied included: CO2-methanol, common in supercritical fluid extraction and chemical processing; CO2-decane, relevant to tertiary recovery in oil and gas applications; and R1234yf, a low-global-warming-potential drop-in replacement refrigerant for R134a which is currently used in heat pumps and power cycles. And finally, the third step was to use equations of state and molecular simulations to extend Cp data and predict behavior in the supercritical region. A flow calorimeter was built to operate over a wide range of temperatures (20-150 °C), pressures (1-300 bar), and densities (1-1000 kg/m3). By precisely placing both the measurement devices and the heating element in direct contact with the fluid, and by limiting experimental heat losses through vacuum insulation and immersion of the entire apparatus in a fluidized thermal bath, the calorimeter achieved ±1% accurate measurements of Cp. To further our ability to model mixtures at supercritical conditions, measurements of CO2- methanol were compared to Monte Carlo molecular simulation predictions of Cp. The average absolute deviation, when compared to experiment, of the simulation results is comparable with the current state-of-the-art equation of state (4% versus 3%, respectively). However, the molecular simulations were significantly less correct predicting Cp in the near critical region where Cp was most sensitive to small changes in temperature and pressure. This region of greatest sensitivity, called the “heat capacity ridge,” was mapped onto temperature-pressure- composition coordinates for CO2-methanol and CO2-decane using experimental measurements. For single component fluids and binary mixtures, the subtle difference in the relationship between a fluid’s heat capacity ridge and its critical point was demonstrated. BIOGRAPHICAL SKETCH Mitchell Ishmael graduated from Rose-Hulman Institute of Technology in Terre Haute, IN, in 2011 with a bachelor’s degree in Chemical Engineering and a minor in Economics. As an undergraduate, Mitchell took interest in the field of thermodynamics, especially with respect to energy utilization, storage, and conversion. His interest in these topics brought him to Cornell University in Ithaca, NY, for graduate studies in Materials Science and Engineering. Working under the supervision of Prof. Jefferson Tester, Mitchell has pursued his dream to study the intricacies of classical thermodynamics, described in this thesis, as well as gained exposure to a wide array of sustainable energy topics, both through course work and participation in the Earth-Energy IGERT program. Entrepreneurship also holds Mitchell’s interest; he acted as vice president for Technology Entrepreneurship at Cornell for two and half years. In the final year of his studies, he joined the College of Engineering’s inaugural class of PhD Commercialization Fellows and learned-by-doing, following lean startup principles to evaluate the commercial potential of an energy storage technology he developed. iv ACKNOWLEDGMENTS Thank you to my primary adviser, Dr. Jefferson Tester. He cares professionally and personally for each of his students, and I still find myself in disbelief sometimes, amazed our paths crossed and happy to work under his tutelage. His interest and enthusiasm crosses the spectrum of sustainable technology and invaluably broadens each of his student’s perspectives. Thank you to my thesis committee members, Dr. Michael Thompson and Dr. Emmanuel Giannelis. Dr. Thompson, my first semester at Cornell, supremely reinforced my background in thermodynamics and has remained a valuable mentor ever since. Dr. Giannelis not only provided access to his lab and student’s experimental expertise, but also helped mentor me through the PhD Commercialization Fellowship. Thank you to Tom Schryver, Ken Rother, Brad Treat, Steve Gal, and Brian Bauer for their mentorship and coaching during the PhD Commercialization Fellowship. And thank you to Doug Buerkle, Jason Salfi, and Devin Sandon for helping me continue my commercialization work through the NEXUS-NY program. Thank you to Polly Marion. I haven’t found a problem, whether it is Cornell’s bureaucracy or an issue with a supplier, that Polly can’t solve. Her attention to our needs as researchers is second to none, and I am so glad to have worked with her. Thank you to Will (Billy) Gregg and He (Richard) Wan, both undergraduate researchers who worked for me. Billy contributed to many pieces of many projects; I appreciate his patience with me as I developed my managerial skills. Richard aided in my research on encapsulated phase change materials; I appreciate his continued effort on a very frustrating project. Thank you to the Tester Research Group. A special thank you to Maciek Lukawski, who worked with me on a number of these projects; he is a thoughtful and hard-working partner. I am very v lucky to have worked with him and hope we will collaborate in the future. And Lauren Stutzman for all of her work on molecular simulations and coauthoring "Heat capacities of supercritical fluid mixtures: Comparing experimental measurements with Monte Carlo molecular simulations for carbon dioxide-methanol mixtures," (The Journal of Supercritical Fluids 123 (2017): 40-49.) with me. Thank you to Glenn Swan for all the early calorimeter part fabrication, then encouraging me to learn to machine on my own. With each part I’ve made, I appreciate more his skill and the friendly way in which he does his work (whenever I want a creative, simple solution, I go to Glenn). He is an invaluable asset to the College of Engineering. Thank you to Nate Ellis. Not only for teaching me to machine high quality parts, a skill I’ll keep with me throughout my life, but also for all the conversations and council. The accumulated frustration he has seen throughout the years, it’s made him at least as good a mentor to students as a machinist. Hope to see you him in TN one day. A sincere thank you for the financial support that made this work possible, provided by the College of Engineering, Cornell Energy Institute, Atkinson Center for a Sustainable Future, ARPA-E, and The US Department of Energy. To Mom, Dad, Marsh and Syd, let brevity reflect sincerity: thank you for your love and support. And finally, to my wife, Betsy Ellis, anybody would want it to be so flat. vi TABLE OF CONTENTS 1. Introduction and motivation ...............................................................................................1 1.1. Introduction to supercritical fluid phenomena ....................................................1 1.2. Industrial applications of supercritical fluids ......................................................2 1.3. Availability of supercritical fluid thermophysical property data ........................4 1.4. Estimating the thermophysical properties of supercritical fluids .......................5 1.5. References ...........................................................................................................7 2. Dissertation objectives and approach.................................................................................10 2.1. Dissertation objectives ........................................................................................10 2.2. Dissertation content ............................................................................................11 2.3. Author’s note ......................................................................................................14 2.4. References ...........................................................................................................15
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