11/05/2026
By Thomas Dugan

The Francis College of Engineering's Department of Mechanical and Industrial Engineering invites you to attend a doctoral dissertation defense by Sai Bhargav Annvajjala, titled “Thermofluid and Phase Change Performance of High Density, CO2 Hydrate Based Materials for Advanced Cooling and Thermal Storage Applications.”

Details

  • Date: November 18, 2026
  • Time: 9:30 a.m.
  • Location: ETIC 345

Committee members

  • Noah Van Dam, Associate Professor, Department of Mechanical and Industrial Engineering
  • Jan Kosny, Research Professor, Department of Mechanical and Industrial Engineering
  • Jasmina Burek, Assistant Professor, Department of Mechanical and Industrial Engineering
  • Devinder Mahajan, Professor, Department of Materials Sciences and Chemical Engineering at Stony Brook University

Abstract

Rising cooling demands from artificial intelligence data centers, advanced semiconductor manufacturing, and electrified buildings are placing increasing pressure on electrical grids. Cold thermal energy storage can shift refrigeration demand away from peak operating hours, but conventional ice storage requires sub-zero refrigeration. Carbon dioxide (CO₂) clathrate hydrates present a promising alternative as high-energy-density, non-flammable phase-change materials that operate near the freezing point of water under pressure. Their practical application remains challenging because nucleation is unpredictable, induction times vary, and growing hydrate crystals require a continuous supply of dissolved CO₂ and effective removal of crystallization heat. Understanding how these thermodynamic and transport limitations affect hydrate formation is necessary before such materials can be used reliably in advanced cooling and high-heat-flux applications.

This dissertation examines these challenges by connecting hydrate thermodynamics with the physical conditions under which crystallization occurs. Experiments in a multi-point instrumented 2 L stirred reactor investigate how measured pressure and temperature conditions relate to published hydrate equilibrium boundaries and influence the calculated driving force for formation. Building on this thermodynamic assessment, repeated formation-dissociation experiments investigate the memory effect, showing how water history changes induction time and gas uptake without consistently improving both. The research also investigates whether crystallization behavior can be influenced through simple, natural, and non-toxic approaches, including ice-assisted formation and pre-gassed water, rather than conventional chemical promoters. These experiments identify differences between the initial nucleation response and subsequent hydrate growth with a focus on gas-liquid mass transfer and heat removal. High-pressure differential scanning calorimetry is used to evaluate the associated phase transitions and measured enthalpy. The design and fabrication of a larger 11 L reactor address the need for improved internal cooling and mixing at increased scale. By linking equilibrium conditions, nucleation behavior, phase-change characteristics, and reactor design, this work provides an experimental basis for developing more reliable CO₂ hydrate-based cold thermal energy storage systems.