The most critical part and barrier of phase change material (PCM) applications are the accuracy of simulations and the control of the process. The state of the PCM and the momentarily stored energy cannot be estimated easily unless numerous temperature sensors are used. There are a lot of models used by researchers, but most of them focus solely on the full charging or discharging of the PCM thermal energy storage. In a real working environment, the phase change is often interrupted so this phenomenon should also be modelled with high accuracy. The aim of this paper is to present the newly developed diagonal model validated by differential scanning calorimetry measurements, which can model what occurs inside the hysteresis of the solid-liquid two-phase state. The model was created and validated by using paraffin wax (P53) and was further tested with coconut oil (C.oil20), which has a very wide hysteresis. The modelling accuracy of the different models was compared with each other, and the evaluations were carried out. Keywords Phase change materials (PCM) Á Differential scanning calorimetry (DSC) Á Enthalpy-temperature curves Á Phase transition Á Interrupted melting/solidification List of symbols c Specific heat capacity (kJ kg -1 K -1 ) c app Apparent heat capacity of the PCM during melting (kJ kg -1 K -1 ) f Liquid fraction of PCM (1) H Enthalpy (kJ kg -1 ) L f Latent heat of fusion (kJ kg -1 ) T Temperature (°C)
In this paper phase change materials are presented, as effective thermal energy storage due to their great latent heat storing possibility. The main substance used for thermal energy storage purposes is water. Storing the energy with water is not that effective as with phase change materials, because the temperature of water has to change, and it worsen the heat exchange intensity. On the other hand, with phase change materials the temperature of the material does not have to change due to the latent heat storage possibilities. A buffer tank with two pipe coils filled with phase change materials is investigated with the aim to reduce the storage volume. An own thermodynamic model, a CFD simulation and an experimental system are presented. The models could be validated and the process of phase change could be examined with a life-size thermal energy storage system in the laboratory of the department. The performance of heat absorption and release of the phase change material could be calculated in the function of inlet water temperature and mass flow.
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