An experimental study for the enhancement of stratification in heat-storage tank by equalizer and PCM module. (February 2020) - Wang, Zilong
Highlights: A thermal storage tank containing a novel equalizer coupling with the sodium acetate trihydrate is developed. The performances of thermal stratification in water tanks are compared. The impact of the position of PCMs on the thermal stratification with various flow rates have been analysed. The Fill efficiency is used as a measurement index to judge the performance of a thermal storage tank. Abstract: The heat storage technology can improve the performance of a solar collector system effectively. A novel equalizer was proposed in this paper, in addition, different positions of phase-change material balls and flow rates were investigated. Their influence on the temperature of the heat-storage water tank was measured with respect to dimensionless time. The Richardson number, Fill Efficiency, and MIX number were used to extensively analyse the thermal characteristics of heat-storage water tanks with different inlet structure as the variation in flow rates. The results indicate that the water inlet structure with the equalizer can not only enhance the thermal stratification effectively in the heat-storage water tank, but also stabilize the heat output characteristics. Based on the same position of the phase-change material balls and inlet flow, the Richardson number and the Fill Efficiency of the heat-storage water tank with equalizer are both bigger than those of the water tank with a typical inlet structure; however, the MIX number is smaller in comparison. The thermal stratification of the heat-storage water tank is decreased as the flow rates and the position of the phase-change material balls increased. For the heat-storage tank contained PCM with equalizer, when the inlet flow rate is 9 L/min, the FE increases by 1.3% as the position of PCMs dropped from PCM1 to PCM4; and for PCM4, the FE decreases by 8.6% as the inlet flow rate increasing from 1 L/min to 9 L/min. The effect on thermal stratification of water tank by equalizer is stronger than that of the PCM balls, and the equalizer could effectively relieve the cold-hot water mixing in the heat-storage water tanks that caused by the increasing of flow rate and improve the thermal stratification of the heat-storage water tanks.