Experimental validation of an air-PCM storage unit comparing the effective heat capacity and enthalpy methods through CFD simulations

Two computational fluid dynamics (CFD) models were developed for the simulation of an air- thermal energy storage (TES) unit. The TES unit was experimentally tested with air flowing over horizontal metallic panels filled with phase change material (PCM). The commercial PCM was characterised by differential scanning calorimetry (DSC), namely: phase change temperature range, specific heat and enthalpy values. These properties were coupled to the CFD models in order to setup the two most common methods for phase change problems: enthalpy and the effective heat capacity methods. Both models predicted the PCM temperature and air outlet temperature and were compared with the experimental results. The PCM temperature presented the major differences. The enthalpy method shows the phase change stage by a quasi-horizontal curve, appropriate for pure PCMs. However, most of the commercial PCMs are composed by different compounds and hence this is not linear during the phase change as presented by the experimental results. The smooth increase over the phase change was accurately predicted by the effective heat capacity method. For the air outlet temperature, both methods present good agreements with the experimental results. Hence, for analysis requiring particular attention on the PCM behaviour the effective heat capacity method is recommended.