The design of a supercooled latent heat store

Mullen, Paul Andrew (2017) The design of a supercooled latent heat store. PhD thesis, University of Glasgow.

Abstract

Thermal energy accounts for 49% of the National annual energy budget of the United Kingdom. In a typical household, the consumption of thermal energy makes up to 77% of its annual energy consumption, made of space heating and hot water production. Intermittent renewable energy sources are often used to reduce the domestic energy expenditure of national energy systems such as the electric grid or the natural gas network. Energy storage, and increasingly heat storage, is often described as one way to overcome the unpredicatable nature of many renewable energy systems.
This thesis investigates the use of a latent heat storage system, which uses the enthalpy of transition between two physical states, as a means to store thermal energy at a low thermal loss. To achieve this, a phase change material (PCM), a material with a high enthalpy of transition, is allowed to supercool and enter a metastable state. A novel trigger mechanism is presented and refined to initiate nucleation in the supercooled PCM, beginning the phase transition and releasing the enthalpy of transition. From over 150 PCMs which are described in the literature, four are investigated in detail for their suitability in this application. A particular PCM, CaCl2.6H2O is investigated further and its issue of incongruent melting is successfully suppressed.
The trigger mechanism presented uses a Peltier heat pump to locally cool a small amount of PCM, contained within a latent heat store. The supercooled PCM was cooled to a critical point, its autonucleation temperature, where a stable nucleus is spontaneously formed through heterogeneous nucleation. The trigger mechanism was demonstrated to work on multiple PCMs.
The trigger mechanism was then implemented into a latent heat storage system, reffered to as a heat battery. The heat battery was filled with a characterised eutectic PCM mixture, CaCl2.6H2O + 5% KCl (w.t.). The trigger mechanism was demonstrated to initiate nucleation within the heat battery.
The work demonstrates the ability for a heat battery to operate using a supercooled PCM and activation mechanism, and then highlights the limitations of such an approach. Future work is identified, which must first be tackled in order to construct a fully technically viable system.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Additional Information: Due to copyright restrictions the full text of this thesis cannot be made available online. Access to the printed version is available once any embargo periods have expired.
• Keywords: Phase Change Materials, supercooling, heat storage, latent heat storage, peltier cooler, nucleation.
• Subjects: Q Science > QD Chemistry; T Technology > TA Engineering (General). Civil engineering (General); T Technology > TK Electrical engineering. Electronics Nuclear engineering
• Colleges/Schools: College of Science and Engineering > School of Engineering > Electronics and Nanoscale Engineering
• Supervisor's Name: Knox, Professor Andrew R.
• Date of Award: 2017
• Embargo Date: 11 July 2021
• Depositing User: Paul A. Mullen
• Unique ID: glathesis:2017-8297
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 12 Jul 2017 13:43
• Last Modified: 11 Aug 2022 15:54
• Thesis DOI: 10.5525/gla.thesis.8297
• URI: https://theses.gla.ac.uk/id/eprint/8297