02/03/2026
By Danielle Fretwell

The Francis College of Engineering, Department of Energy Engineering - Renewable, invites you to attend a Doctoral Dissertation Proposal defense by Sai Bhargav Annavajjala on: "Thermofluid and Phase-Change Performance of High-Energy Density, CO2 Hydrate Based Materials for Advanced Cooling and Thermal Storage Applications."

Candidate Name: Sai Bhargav Annavajjala
Degree: Doctoral
Defense Date: Thursday, Feb. 5, 2026
Time: 10 a.m. - Noon
Location: Southwick 240

Committee:

  • Advisor: Noah Van Dam, Associate Professor, Mechanical and Industrial Engineering, University of Massachusetts Lowell
  • Co-Advisor: Jan Kosny, Research Professor, Mechanical and Industrial Engineering, University of Massachusetts Lowell
  • Jasmina Burek, Assistant Professor, Mechanical and Industrial Engineering, University of Massachusetts Lowell
  • Devinder Mahajan, Professor, Materials Science and Chemical Engineering, Stony Brook University

Abstract:
The increasing cooling demand in buildings, data centers, and industrial facilities is driving the need for cold thermal energy storage systems that can reduce peak electrical load and improve refrigeration efficiency. Ice storage is an established cold thermal energy storage approach, and its performance depends on achievable charge/discharge rates, heat transfer area, and practical operating strategies. CO₂ clathrate hydrates offer an alternative phase-change storage pathway with high latent cooling capacity and the potential to operate near standard refrigeration temperatures under moderate pressure. Major research challenges include variability in induction time, sensitivity to operating conditions, and limited system-level thermal performance datasets.

This dissertation investigates the thermodynamic, kinetic, and thermofluid behavior of CO₂ hydrate systems for advanced cooling applications. The work develops pressure-temperature equilibrium points for the CO₂-H₂O system under laboratory conditions, quantifies induction time trends under controlled pressure and temperature settings, and evaluates the impact of selected promoters on formation reliability. Experiments are conducted using an existing 2 L high-pressure reactor to establish repeatable procedures and generate baseline datasets on pressure drop behavior, temperature response, and hydrate growth characteristics. A custom-designed 11 L reactor is included for exploratory evaluation of scale-related thermal behavior, thermal gradients, and instrumentation feasibility under larger working volumes. Measured formation and dissociation conditions are compared with reported equilibrium data to assess consistency and identify sources of deviation linked to kinetics and experimental constraints.

To translate laboratory results into system-relevant performance metrics, this study integrates experimental observations with heat transfer modeling to interpret thermal resistance effects and temperature gradients during charging and discharging. The outcomes provide experimental guidance for improving CO₂ hydrate formation consistency by defining operational parameters/conditions for reliable nucleation, and assessing the feasibility of hydrate-based cold thermal energy storage relative to conventional ice and PCM systems.