Experimental and numerical study of a latent heat storage using sodium acetate trihydrate for short and long term applications

A flexible thermal energy storage with 137.8 kg PCM and 75 L water was introduced. The heat storage combined short-term and long-term heat storage functions by utilizing sodium acetate trihydrate as heat storage material. The thermal performance and flow characteristics of the heat storage were investigated by experiments and by CFD simulations. The result show that after a full charge to 92 degrees C, the heat storage can flexibly release heat in two steps: In the first step, 13.7 kWh sensible heat can be released for short-term use; in the second step, 7.8 kWh latent heat can be released for long-term use. When releasing heat, there is laminar flow of water and a high degree of thermal stratification in the tank. During discharge of the sensible heat, the heat storage can provide 294 L hot water with an average temperature of 68.2 degrees C. During discharge of the latent heat, 334 L hot water with an average temperature of 46.7 degrees C were drawn from the heat storage. In the charging process, a fluid short circuit existed inside the water region. Part of hot water flows out of the tank before sufficiently heated. There was no obvious thermocline inside the tank during charging. The flow rate has a big influence on the thermal characteristics of the heat storage during the charge and discharge periods. By increasing the flow rate from 4 L/min to 14 L/min, the charging time was shortened by 67% from 276 min to 92 min while the discharging time was shortened by 65% and 83% respectively in releasing sensible heat and latent heat.

Automated summary

A flexible thermal energy storage system with both short-term and long-term heat storage functions was investigated. Experimental and CFD simulation results showed that the system can release both sensible heat and latent heat flexibly, with different flow characteristics and thermal stratification in the tank. The study also found that the flow rate significantly affects the thermal characteristics during charging and discharging periods.