Experimental and Numerical Analysis of Heat Transfer Enhancement in Latent Thermal Energy Storage Systems

Latent thermal energy storage (LTES) systems using phase change materials (PCMs) offer high energy density and nearly isothermal operation, making them promising candidates for thermal management and renewable energy applications. However, their adoption is limited by the low thermal conductivity of PCMs, which slows charging and discharging times, and the lack of robust design guidelines. The mean temperature difference (LMTD) and NTU-effectiveness methods cannot be directly applied due to the transient and nonlinear nature of the moving boundary in phase change of PCM. This thesis addresses these challenges through an integrated experimental and numerical study, focusing on geometry optimization, PCM selection, and detailed phase change front tracking. First, bar-and-plate LTES units with finned and finless configurations were fabricated and tested using paraffin wax RT42 as the PCM and water as the heat transfer fluid. Under ΔT = 3 °C and 200 kg h-1, the finless unit required 34775 s (~9.6 h) to complete melting (phase transition), while the finned unit reduced this to 5705 s (~1.6 h), corresponding to an 84% reduction in charging time. At ΔT = 9 °C and 200 kg h-1, the melting time further decreased to 2695 s (~0.75 h), representing a 53% reduction compared to ΔT = 3 °C at the same flow for the finned unit. Doubling the flow rate from 100 to 200 kg h-1 at ΔT = 6 °C reduced melting time by up to 36% (from 5445 to 3590 s). A resistance–capacitance numerical model, validated against experiments with <6% deviation on melting time, was developed and applied for geometry optimization. Parametric analysis revealed significant trade-offs: larger fin heights and moderate fin pitches increase stored energy but prolong melting times, whereas designs with smaller fin pitches and reduced fin heights accelerate melting but reduce energy storage. Second, the thermal performance of three PCMs, lauric acid, RT42, and RT60, was systematically compared in a prototype finned bar-and-plate heat exchanger. Lauric acid, being one with the highest latent heat, showed a slower melting/solidification time to latent heat ratio (γ) in both charging and discharging because of its lower thermal conductivity. RT42 showed the fastest γ at low ΔT. RT60 delivered the highest overall storage capacity, reaching ~500 kJ kg-1 acid in the tested unit, while showing slower γ than RT42. The LTES unit achieved an overall efficiency of approximately 84%. These results establish that PCM choice must be tailored to operating conditions: RT42 for rapid response at low-to-moderate ΔT, Lauric Acid for high ΔT/high flow rate systems, and RT60 for long-duration, high-temperature storage. Finally, an application of infrared thermography enabled the detailed visualization of phase change front dynamics in an RT42-based LTES unit incorporating an additively manufactured fin-and-tube heat exchanger, providing unprecedented insights into the thermal behavior within this innovative test section. Infrared (IR) thermography captured the detailed movement of the phase change front during charging and discharging processes. Optical imaging confirmed the morphology of the advancing interface. Tracking methods were benchmarked: the average temperature approach quantified both liquid fraction and front position, while the threshold temperature method, which offered simpler but less precise binary tracking. By integrating geometry, materials, and advanced visualization, this thesis advances both the scientific understanding and the practical design of PCM-based LTES, supporting their deployment in renewable energy integration, building energy systems, and industrial heat recovery.