Electronic Thesis and Dissertation Repository

Thesis Format

Monograph

Degree

Master of Engineering Science

Program

Mechanical and Materials Engineering

Supervisor

Straatman, Anthony G.

Abstract

This thesis evaluates the effectiveness of the enthalpy-porosity approach in simulating melting and solidification of phase change materials within latent heat thermal energy storage systems. It systematically investigates the sensitivity of the computational model to four adjustable parameters: mushy zone coefficient, thermal expansion coefficient, solidus/liquidus temperatures, and latent heat. The study includes individual and combined analyses of these factors in simulations of the melting process by comparing outcomes with extensive experimental data, resulting in a calibrated melting model. The calibrated model is validated across various heating conditions in the cylindrical cavity, and then in a rectangular cavity, confirming its reliability in predicting the main features of PCM melting behavior. When applied to solidification, significant discrepancies arise in terms of overall freezing time and in the temporal evolution of the interface separating the solid and liquid regions of the domain. It is thought that a key factor influencing this discrepancy is the lack of supercooling considerations in the enthalpy-porosity model that was utilized, indicating a need for improved freezing process modeling.

Summary for Lay Audience

Given the increasing global demand for energy and the expected continued reliance on fossil fuels in the near future, discussions concerning the role of renewable energy in supporting energy security have gained prominence. A challenge currently faced by renewable energy sources is their limited capacity to generate power during specific times of the day. This obstacle can be mitigated through the implementation of energy storage systems, which can store excess energy for later use. One effective approach is to store this energy in the form of heat, using thermal storage systems. These systems are advantageous due to their affordability, long lifespan, and ease of scalability.

Phase change materials (PCMs) are unique substances capable of transitioning between a liquid and solid state at specific temperatures. This transformation is linked to the absorption or release of a significant amount of heat called latent heat. This special feature makes PCMs valuable for practical applications where effective thermal energy storage is necessary, like in solar thermal systems to provide space heating and domestic hot water. One key advantage is that during the phase change, the material remains at a nearly constant temperature, allowing for the efficient storage of a substantial amount of energy. As a result, gaining insights into how PCMs behave during the process of melting and solidifying is of utmost importance.

This research involved the application of computational models to accurately simulate the melting and solidification of PCMs. Among the various numerical methods available in this field, the enthalpy-porosity method was chosen due to its ability to simulate complex phase transitions. This study introduced and investigated four different adjustable factors inherent in this method that affect the simulation, aiming to derive a calibrated model through comparison with available experimental data. The resulting calibrated model demonstrated the capability to predict the melting process in various conditions and structures with higher accuracy than other available simulations. The research results are valuable as they can be used to develop effective energy management solutions, leading to a decrease in environmental emissions.

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