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This paper investigates ellipsoid-shaped macro-encapsulated phase change material (PCM) on a component scale. The selected PCM is a paraffin-based commercial material, namely ATP60; differential scanning calorimetry and transient plane source method are used to measure ATP60's thermo-physical properties. A 0.382 m3 latent heat thermal energy storage (LHTES) component has been built and experimentally characterized. The temperature measurement results indicate that a thermocline was retained in the packed bed region during charging/discharging processes. The experimental characterization shows that increasing the temperature difference between the heat transfer fluid (HTF) inlet temperature and phase-change temperature by 20 K can shorten the completion time of discharge by 65%, and increasing HTF inlet flowrate from 0.15 m3/h (Re = 77) to 0.5 m3/h (Re = 256) can shorten the completion time of charge by 51%. Furthermore, a one-dimensional packed bed model using source-based enthalpy method was developed and validated by comparison to experimental results, showing discrepancies in the accumulated storage capacity within 6.6% between simulation and experiment when the Reynolds number of the HTF inlet flow ranges between 90 and 922. Compared with a conventional capsule shaped in 69-mm-diameter and 750-mm-long cylinders, the ellipsoidal capsule shows 60% less completion time of discharge but 23% lower storage capacity. Overall, this work demonstrates a combined experimental and numerical characterization approach for applying novel macro-encapsulated PCM geometries for heating-oriented LHTES. • Investigation of a novel PCM in ellipsoidal macro-encapsulation. • Characterization of thermo-physical properties of an organic PCM. • Prototyping of a 15 kWh storage and charge/discharge thermal performance testing. • Validation of a one-dimensional numerical model within 6.6% uncertainty. • Comparison of thermal performance of ellipsoidal and cylindrical encapsulations. [ABSTRACT FROM AUTHOR]

Latent heat thermal energy storage has been receiving increasing interests in residential heating applications. In this paper, a numerical heat transfer model was built with finite element method for a cylindrically encapsulated latent heat storage prototype and used for investigating its thermal performance optimization measures. The model was validated against four sets of experimental results for both charge and discharge, as the difference in accumulated storage capacity between simulation and experiment is less than 4%. Transient storage inlet boundary conditions were set in simulation for discharge considering the thermal output from the coupled radiators. The results of the optimization analyses show that: 1) reducing the capsule diameter from 69 mm to 15 mm shortens the completion time of charge and discharge by up to 70%, however, at the expense of 23% decrease in total storage capacity; 2) using parabolic or linear time-increasing heat transfer fluid flowrate profiles than a time-constant one extends around twofold the useful discharge timespan; 3) increasing the storage vessel diameter from 0.6 m to 0.7 m and to 0.8 m prolongs the useful discharge timespan from 2 hrs to the recommended 3 hrs, though the further enlargement to 0.8 m results in a lower state of charge after 3 hrs due to increase in unexploited storage capacity. From the numerical optimization study, we proposed a storage design adjustment of using 15 mm-diameter phase change material capsules in a 0.7 m-diameter cylindrical storage vessel, coupled with a parabolic flow strategy, to improve the storage on-peak discharging performance. [ABSTRACT FROM AUTHOR]

• A commercial sodium acetate trihydrate-based PCM is tested with two methods. • T-history tests are conducted for determining PCM thermal properties. • A storage prototype is developed to investigate PCM's full-scale thermal performance. • PCM thermal behavior is different between the two test methods. Latent heat thermal energy storage (LHTES) has been receiving increasing attention from researchers and engineers. A practical LHTES installation requires a deep understanding of phase change material's (PCM's) thermal behavior under thermal property testing and realistic operating conditions. To enrich this understanding, an experimental study on a commercial sodium acetate trihydrate-based PCM (Climsel C58) is presented in this article. C58 was characterized with two test methods: T-history tests and full-scale LHTES tests. The results are presented and discussed to exhibit the thermal behavior of C58 with these two test methods and the variations between them. With T-history tests, the thermal properties of C58 such as melting/solidification temperature range (57–61 °C/55–50 °C) and latent heat of fusion (216 kJ/kg) were determined. In full-scale LHTES tests, a parametric study was conducted to investigate the effects of heat transfer fluid flowrate and operating temperature range on the thermal performance of a 0.38 m3 storage prototype containing cylindrically macro-encapsulated C58. Moreover, longitudinal and radial PCM temperature distributions in full-scale tests were analyzed, suggesting the presence of phase separation. In general, C58 behaved differently between the two test methods regarding phase separation (negligible in T-history tests), supercooling effects (within 3 K in full-scale but up to 10 K in T-history tests), and thermal energy storage capacity (10% lower in full-scale tests). When using C58 or other salt hydrate-based PCMs for large-scale heat storage, these thermal behavior differences between the property-measurement and the application-oriented environments should be properly addressed in the design stage to ensure performance. [ABSTRACT FROM AUTHOR]