11/03/2023
By Danielle Fretwell

The Francis College of Engineering, Department of Plastics Engineering, invites you to attend a Doctoral Dissertation defense by Jay Thakkar entiutled "Optimizing design of salt hydrate phase change materials (PCM) for building and cold chain applications."

Candidate Name: Jay Thakkar
Degree: Doctoral
Defense Date: Friday, Nov. 17, 2023
Time: 10 a.m. to noon
Location: Perry 415

Committee

  • Advisor: Margaret Sobkowicz Kline, Dandeneau Endowed Professor, Plastics Engineering Department, UMass Lowell
  • Co-Advisor: Jan Kosny, Research Professor, Mechanical Engineering Department, UMass Lowell
  • Amir Ameli, Assistant Professor, Plastics Engineering Department, UMass Lowell
  • Juan Pablo Trelles, Professor, Department of Mechanical and Industrial Engineering, UMass Lowell

Brief Abstract:
Depletion of fossil resources and the climate crisis increase the urgency of work towards sustainable energy sources. Thermal energy storage (TES) systems are of interest for energy efficiency applications because of increasing energy demands, which escalate use of fossil fuels and put pressure on electrical systems. Phase change materials (PCM) can be a critical part of a TES system because they passively absorb and release energy during heating and cooling. This research concerns the salt hydrate class of PCM suitable for building efficiency and cold chain applications. The overall goal of this work is to achieve stable PCM formulations with targeted transition temperatures that can be used for commercial applications. In addition, different grades of chemicals and water were used to study the effect of purity on congruency in melting and crystallization process. Salt hydrate PCM formulations with phase transition temperatures in range of 4-15°C were investigated for cold chain, and in the range of 20-65°C for building applications. Calcium chloride hexahydrate, sodium sulfate decahydrate and sodium acetate trihydrate were the three base salt hydrates studied, and their properties and transition temperatures were optimized with additives. PCM preparation methods that result in the desired hydrates were explored. Nucleating agents and stabilizers/thickening agents were utilized to suppress supercooling and phase separation, and analyses including differential scanning calorimetry (DSC), temperature-history method, X-ray diffraction (XRD), rheometer and dynamic heat flow meter (DHFM) were used to determine the impact of composition on the PCM performance and stability. In one study, the primary goal was to prevent the separation of phases (specifically the formation of a lower hydrate, CaCl2.4H2O) and to reduce the occurrence of supercooling in CaCl2.6H2O, a phase change material. It was achieved this by optimizing the choice of a nucleating agent (SrCl2.6H2O) and the addition of stabilizers (NaCl/KCl). The result was a stabilized phase change material with the same latent heat capacity as the unmodified material, and supercooling was effectively minimized. In another work, a eutectic phase change material was developed for applications in the cold chain. This involved using Na2SO4.10H2O (commonly known as Glauber's salt) as the base phase change material. NH4Cl and KCl were introduced to lower the melting temperature, and borax, as well as CMC or SPA, were used as nucleating and thickening agents. The primary objective was to stabilize a phase change material within the temperature range of 4-15°C while maximizing its latent heat capacity and minimizing the occurrence of supercooling. Different molecular weights of CMC were examined to assess their impact on the stability and viscosity of the phase change material. Lowest molecular weight CMC turned out to be best for stability of PCM. For applications requiring higher temperatures (58-60°C), sodium acetate trihydrate (SAT) which has incongruent melting and significant supercooling issues upon thermal cycling. In this case, a nucleating agent (Na2HPO4.12H2O) was optimized to reduce supercooling, and SPA was utilized to prevent phase separation, thereby preserving the material's latent heat during thermal cycling. Work was done on different grades of chemicals (ACS, lab and technical grade) and grades of water (DI, distilled and tap) to study the impact on crystallization and phase change with and without impurities.