Study on the energy charging process of a plate-type latent heat thermal energy storage unit and optimization using Taguchi method

•The combination influence of HTF temperature, velocity and inclination angle was studied.•The energy charging rate was improved by 23% after the Taguchi optimization.•The enhancement in melting process was realized via PCM natural convection.•Actual melting temperature range and time should be identified for the melting process. To understand the energy charging process of a plate-type thermal energy storage unit using phase change materials (PCMs) under various conditions, an experimental system was fabricated to identify the impact of heat transfer fluid (HTF) temperature, HTF velocity and plate inclination. The energy charging cycles were studied using liquid fraction and accumulated energy storage density with detailed temperature profiles. After the Taguchi optimization, a maximum energy charging rate of 759 W with a 23% increment was obtained with the HTF temperature of 55 °C, the HTF velocity of 5 m/s and the plate inclination of 75°. The melting process was influenced the most by the HTF temperature, followed by the HTF velocity and the plate inclination based on the standardized melting time. However, the influence of inclination angle was larger than the HTF velocity according to the actual melting time. Optimizing inclination angle was an effective way to improve the melting process without consuming additional materials and energy. Because of the PCM natural convection, the melting temperature range varied under different conditions. It was critical to identify the actual melting temperature range to predict the melting performance accurately.