<p>Phase change material heat exchangers (PCMHX) can play an important role in accelerating the widespread adoption of renewable energy systems. Phase change material heat exchangers offer high storage density at various temperatures of interest and can be used for shifting grid load and reduce peak power demand. The cylindrical phase change material heat exchangers are one of the most used technologies due to their simplicity. To solve the issue of low thermal conductivity of phase change materials, the use of fins in this type of heat exchanger is also common. Numerical models enable engineers to estimate the performance of such phase change material heat exchangers for different design parameters and operating conditions without having to test them all. Modeling phase change phenomena are challenging due to the complex time-dependent process and the accuracy is highly sensitive to phase change material thermo-physical properties. One of the major difficulties to the modeling of phase change material heat exchangers is the lack of information regarding some thermophysical properties of phase change materials. The thermal expansion coefficient and viscosity of a phase change material are two such important properties, especially when natural convection is not negligible. In phase change material heat exchangers modeling, improper use of those parameters can have significant impacts on the simulation outcomes. The existing literature lacks proper phase change material properties referencing and discussions thereof. This paper presents a brief review of the literature and a numerical study investigating the model sensitivity to thermal expansion coefficient and viscosity for a straight tube phase change material heat exchanger, with and without annular fins. Commercially available computational fluid dynamics (CFD) code is used to evaluate the charging (melting) and discharging (solidification) phenomena. The study measures the impact of these parameters on the melting/solidification rate, temperature, and velocity profiles within the phase change material domain. Additionally, both constant wall temperature and convective boundary conditions are considered along with ambient heat loss. The results show that thermal expansion coefficient and viscosity have a significant effect on the melting rate and development of the melting front. For certain phase change materials, the literature provides thermal expansion coefficient and viscosity values that differ by 70% and 1000% respectively. When these different values are used, the melting time changes by 10% for thermal expansion coefficient and 30% for viscosity. The effect of these parameters is also found to be more pronounced in the without fins configuration compared to the finned one.</p>

Effect of Thermal Expansion Coefficient, Viscosity and Melting Range in Simulation of PCM Embedded Heat Exchangers With and Without Fins

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

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