Study of Conjugate solid-liquid phase change heat transfer in heatsink filled with phase change material-metal foam

نوع: Type: Thesis

مقطع: Segment: PHD

عنوان: Title: Study of Conjugate solid-liquid phase change heat transfer in heatsink filled with phase change material-metal foam

ارائه دهنده: Provider: Razie Hasan Zahraei

اساتید راهنما: Supervisors: Dr. Habib Olah Sayehvandِ

اساتید مشاور: Advisory Professors:

اساتید ممتحن یا داور: Examining professors or referees: Dr. Ramin Kouhikamali and Dr. Ebrahim Afshari

زمان و تاریخ ارائه: Time and date of presentation: 2026

مکان ارائه: Place of presentation: آمفی تئاتر

چکیده: Abstract: The integration and increasing compactness of components in electronic systems intensify heat generation, significantly raise operating temperatures, and consequently degrade their performance. Phase change material (PCM)-based heatsinks effectively control temperature rise in such systems by absorbing and storing heat during the phase-change process. Thermal and chemical stability, a low melting temperature, and corrosion resistance are among the important factors contributing to the broader application of PCMs in energy management and storage. In many electronic devices and batteries, variations in power, current, and loading conditions result in transient and pulsed heat fluxes. In batteries, PCM acts as a thermal buffer by absorbing the heat generated by heat-flux peaks, thereby limiting battery temperature rise and improving its performance, safety, and service life. During this process, the PCM melts by storing heat during the heat-flux pulse and subsequently solidifies as the heat flux decreases and heat is transferred to the surroundings. Despite the high thermal energy storage capacity of PCMs, their low thermal conductivity limits the rate of heat transfer and prevents the heatsink from responding rapidly to transient thermal loads. Therefore, thermal conductivity enhancers are required to improve heat transfer and prevent excessive temperature rise. These enhancers can generally be classified into two groups: dispersed conductive particles and embedded solid components, such as fins, metal plates, meshes, microchannels, and metal foams. In this dissertation, the performance of an annular heatsink filled with PCM and surrounding a battery is comprehensively and systematically investigated under pulsed thermal loading using metal foam, different fin arrangements, and combined foam–fin structures. The performance improvement achieved through the incorporation of these thermal conductivity enhancers is analyzed and compared among the resulting configurations. The modeled configurations include a pure-PCM heatsink as the baseline case and enhanced configurations with metal foam, metal fins arranged in three different layouts, namely internal, external, and combined (internal and external) arrangements, and combined foam–fin structures with the aforementioned fin arrangements. Within this framework, the capability of the heatsink to control the initial rise in battery surface temperature following the application of each thermal pulse, as well as the increase in battery surface temperature throughout the pulse and the resulting maximum temperature at the end of the pulse, is examined. In addition, the transient behavior of the PCM during successive melting and solidification processes is analyzed, and the contributions of thermal conduction and natural convection to heat transfer in the molten region are investigated to assess the effect of natural convection on the performance of different configurations. To numerically simulate fluid flow and heat transfer accompanied by phase change, the continuity, momentum, and energy equations were solved simultaneously using COMSOL Multiphysics, with the effects of natural convection taken into account. The phase-change process was modeled using the enthalpy–porosity approach on a fixed computational mesh, with the PCM phase state varying continuously. The porous metal-foam region was modeled using an extended Darcy–Brinkman formulation. Following mesh generation for each heatsink configuration, mesh-size and time-step independence were assessed. In addition, multiple comparisons with experimental and numerical data reported in previous studies were conducted to validate the numerical methodology and ensure the accuracy of the results, with very good agreement obtained in all cases. The thermal and hydrodynamic behavior of the PCM during melting and solidification was examined using temperature, melt fraction, and streamline contours. For comparative analysis, heatsink performance metrics, including the temporal variations in the average battery surface temperature, melt volume fraction, and heatsink efficiency, were presented graphically. To quantitatively evaluate and compare the performance of the enhanced heatsinks, the key and critical values of the performance metrics and their corresponding time intervals were presented in tables. Analysis of the heat-transfer mechanisms showed that the metal foam provides multiple conductive pathways, resulting in a more uniform temperature distribution within the molten region. Internal fins increase the heat-transfer area, enabling more effective utilization of the latent heat capacity of the PCM to control battery surface temperature, whereas external fins enhance heat rejection to the surroundings, thereby reducing the extent of PCM phase change and the duration of the solidification process. Natural convection in the molten PCM is governed by the competition between buoyancy forces induced by heat from the battery surface and viscous and shear resistance forces, with Darcy resistance additionally acting in the porous medium. The results showed that when natural convection becomes dominant over thermal conduction, heat transfer in the heatsink reaches a quasi-steady state, and the battery surface temperature remains approximately constant after reaching its maximum value until the end of the pulse. This behavior was observed in both the pure-PCM and PCM–metal-foam heatsinks; however, the stabilized maximum temperature in the PCM–metal-foam heatsink was 9.7 K lower and persisted for 160 s less. The battery surface temperature in the metal-foam heatsink and combined-fin heatsink exhibited similar variations for more than half of the pulse duration. Thereafter, the more rapid enhancement of natural convection in the combined-fin heatsink, due to the absence of the flow restrictions imposed by the porous structure, reduced the rate of temperature rise, resulting in a maximum temperature of 351.8 K at the end of the pulse. In contrast, the battery surface temperature in the metal-foam heatsink increased by an additional 2.3 K and, unlike that in the combined-fin heatsink, remained constant at this temperature for 190 s before the end of the pulse. Comparison of the two heatsinks with internal and combined fins showed that, despite the stronger natural convection in the combined-fin heatsink, the maximum battery surface temperature was 5.1 K lower in the internal-fin heatsink. This finding indicates that increasing the number of internal fins is more effective in reducing battery surface temperature than enhancing natural convection. In the pure-PCM and PCM–external-fin heatsinks, despite the development of natural convection in the molten PCM, the absence of effective conductive pathways, such as metal foam or internal fins, limited rapid heat transfer from the battery surface during the initial moments of the pulse, before natural convection became sufficiently developed. Consequently, heat accumulation led to rapid PCM melting and a temperature peak exceeding 366 K at the beginning of the pulse. External fins could prevent this initial temperature peak only when combined with metal foam. In this configuration, the increased contribution of direct heat transfer from the battery surface to the surroundings minimized the maximum melt volume fraction of the PCM. In combined foam–fin structures, natural convection plays only a minor role in heat transfer because thermal conduction is dominant. The final evaluation showed that, among the heatsinks equipped with a single thermal conductivity enhancer, the heatsink with internal fins provided the most effective control of battery temperature during the application of the thermal pulse, limiting the maximum battery surface temperature to 346.7 K, although 2380 s was required for the PCM to return to the solid phase. The fastest solidification was achieved by the metal-foam heatsink, with a solidification time of 1320 s. In this configuration, the battery surface temperature remained constant for 190 s at a temperature 7.4 K higher than the maximum temperature reached by the heatsink with internal fins. The short solidification time and the cessation of battery surface temperature rise before the end of the pulse make this configuration suitable for longer discharge and shorter charging processes. Among the heatsinks equipped with two thermal conductivity enhancers, the combined metal-foam and internal-fin heatsink substantially reduced the maximum battery surface temperature to 336.2 K while also markedly shortening the PCM solidification time to 500 s. Investigation of the effect of fin length in this configuration indicated that increasing fin length generally improves system performance; however, this improvement is not necessarily linear or proportional to the increase in fin length.

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