Characterization of melting and solidification in a real scale PCM-air heat exchanger: Numerical model and experimental validation

This paper describes the models developed to simulate the performance of a thermal energy storage (TES) unit in a real scale PCM-air heat exchanger, analyzing the heat transfer between the air and a commercially available and slab macroencapsulated phase change material (PCM). The models are based on one-dimensional conduction analysis, utilizing finite differences method, and implicit formulation, using the thermo-physical data of the PCM measured in the laboratory: enthalpy and thermal conductivity as functions of temperature. The models can take into account the hysteresis of the enthalpy curve and the convection inside the PCM, using effective conductivity when necessary. Two main paths are followed to accomplish the modeling: the thermal analysis of a single plate, and the thermal behavior of the entire TES unit. Comparisons between measurements and simulations are undertaken to evaluate the models. Average errors of less than 12% on thermal power are obtained for the entire cycle. Once the model is validated, a series of parameters and variables is studied to verify their influence on the behavior and design of the TES unit.

Research highlights
► A mathematical model of a PCM-air heat exchanger is developed and validated.
► Validation range is 0.7–2.1 m/s for airflow and 8–45 °C for air inlet temperature.
► Better λPCM lead to minor improvement as the main resistance is mostly on air side.
► 1 °C mismatch in the PCM h-T curve could lead to errors of up to 20% in power.
► The accuracy of material properties’ data used as inputs in the model is stressed.