Electronic Thesis and Dissertation Repository

Thesis Format



Master of Engineering Science


Mechanical and Materials Engineering


Straatman, Anthony G.

2nd Supervisor

Siddiqui, Kamran.



A novel computationally efficient method for modelling melting and solidification processes in packed beds of PCM encapsulated spheres is introduced. The proposed method involves the full discretization of only one centrally located sphere to fully simulate the phase change process, while treating all other spheres in the packed bed as voids with boundary conditions derived from the simulated sphere. At each time step, the computed heat transfer parameters on the exterior surface of the simulated sphere undergoing the phase change process are extracted, and imposed as boundary conditions on surrounding spheres. The proposed method results in a significant reduction in computational resources that otherwise are required to simulate phase change in all spheres in the packed bed, while accurately simulating the thermal exchange between the packed bed elements and heat transfer fluid. Sample results are presented to demonstrate the proposed method.

Summary for Lay Audience

This research work involves using computer software to simulate the melting and solidification processes of materials. The purpose of the work is to support the development of energy storage systems which rely on storing energy as heat. This type of energy storage is called thermal energy storage. Because materials absorb thermal energy as they undergo melting, they can effectively store thermal energy during their transition from a solid to a liquid. Storing thermal energy in this way can be advantageous, because the material stays at approximately the same temperature as it melts, and a significant amount of energy can be stored before the material is fully melted.

Specific materials which are used for the purpose of storing thermal energy through a change of state are considered in the study. These materials, which are called phase change materials, have certain favorable properties which make them good candidates for thermal energy storage.

It can be quite challenging to model the melting and solidification processes of phase change materials accurately. Describing the phase change process using mathematical models and computer software is difficult, and depends on the specific materials being used, and the geometry of the containers in which they are contained. This research focuses on modelling the melting and solidification of a specific phase change material in a spherical container.

The goal is to produce a computational model which is capable of accurately modelling the melting and solidification process within a single sphere, before extending the model to a larger thermal energy storage system containing many spheres.

The ultimate goal of the research is to support the development of more efficient thermal energy storage systems by providing a practical approach which can be used to test the design of different concepts. As it stands the currently established methods for testing conceptual designs are either relatively inaccurate, or require such unrealistic computational processing requirements that they are impractical to use.