Abstract
Phase change offers a highly effective mechanism for heat and mass transfer in a wide variety of applications. These diverse applications, in additions to international regulations on working fluids pertaining to global climate change, require operation across a wide parameter space: hydraulic diameters (100 µm < Dh < 15 mm), operating pressures (100 kPa < P < 20 MPa), and mass fluxes (25 < G < 1000 kg m-2 s-1). These conditions necessitate an understanding of phase change in pure fluids (e.g., synthetic refrigerants, CO2, ammonia, propane, pentane) as well as mixtures (e.g., refrigerant and hydrocarbon mixtures, ammonia-water) with widely varying thermodynamic and transport properties. Techniques for accurately measuring the high condensing heat transfer coefficients at small Dh will be presented. Flow regime maps and dimensionless transition criteria for a range of fluids with operating pressures up to the critical pressure will be discussed. Self-consistent models for phase change across this parameter space based on flow morphology and momentum, heat and mass transfer will be presented. Rigorous non-equilibrium models to address challenges due to temperature and concentration gradients and coupled heat and mass transfer resistances in the liquid and vapor phases of zeotropic mixtures, and their use in the design of absorbers, desorbers, and distillation columns will be discussed. Recent developments in applying AI/ML techniques to develop reduced-order models for this wide parameter space will be presented. Practical issues that govern component design such as flow maldistribution and techniques to mitigate them will be addressed. Also, emerging techniques such as the use of surfactants and tunable acoustic enhancement for phase change will be briefly mentioned. Opportunities to exploit AI/ML and additive manufacturing techniques for the development of compact phase-change devices will be presented. The role of phase change in enabling a variety of applications from Watts to Megawatts such as thermally driven sorption heat pumps, thermochemical energy storage, data center thermal management, food preservation, water purification, metals processing, small modular reactors, and carbon capture will be highlighted.
About the Speaker
Dr. Srinivas Garimella is the Hightower Chair in Engineering and Director of the Sustainable Thermal Systems Laboratory at Georgia Institute of Technology. He is a Fellow of the ASME and of ASHRAE. He is Editor of the Int. J. Air-conditioning and Refrigeration, and past Associate Editor of the ASME J. Heat Transfer and ASME J. Energy Resources Technology, and of the ASHRAE SBTE Journal. He is Past Chair of the Advanced Energy Systems Division of ASME and was on the ASHRAE Research Administration Committee. He has mentored over 75 students pursuing their M.S. and Ph.D. degrees, postdoctoral researchers, and research engineers, with his research resulting in over 400 archival journal and conference publications, a textbook on Heat Transfer and Fluid Flow in Minichannels and Microchannels (2nd Ed., Elsevier 2014), and books on Condensation Heat Transfer (World Scientific Publishing, 2015) and Adsorption Heat Pumps (Springer Nature, 2021.) He is the recipient of the NSF CAREER Award (1999), the ASHRAE New Investigator Award (1998), the SAE Ralph E. Teetor Educational Award for Engineering Educators (1998). He received the ASME Heat Transfer Memorial Award (2024) and the Georg Alefeld award (2024) for outstanding and lifelong contributions to the field of sorption chillers and heat pumps. He also received the ASME Award for Outstanding Research Contributions in the Field of Two-Phase Flow and Condensation in Microchannels (2012) and the Prominent Researcher Award at the Micro Flow and Interfacial Phenomena Conference 2022 for sustained and outstanding contributions to the fundamentals of phase change heat transfer at mini‐ and micro‐scales and coupled heat and mass transfer in binary fluids. He was recognized with the Thomas French Distinguished Educator Achievement Award (2008) from The Ohio State University, and the Zeigler Outstanding Educator Award (2012) and the Sigma Xi Sustained Research Award (2023) from Georgia Tech.
Host: Professor Nenad Miljkovic