均流结构蓄热水箱热特性的模拟与实验研究

CFD SIMULATION AND EXEPERIMENT RESEARCH ON THERMAL STRATIFICATION OF HOT WATER STORAGE TANK WITH EAUALIZER

蓄热技术是太阳能光热利用的重要组成部分,而以水作为蓄热介质的中低温蓄热技术是太阳能热利用系统中的关键技术之一。本文提出并设计一种用于提高蓄热水箱热分层特性的新型均流器,在初始水温70℃、进水温度10℃的工况下,测试得到了水箱的热力学特性,并基于ANSYS软件建立该水箱的数学模型,研究结果表明随着进口流量的增大,水箱中斜温层的厚度和混合数(MIX number)先减小后变大,填充效率先变大后减小,而理查森数(Ri)减小,当流量为3 L/min时,水箱的热分层效果最好,效率最高。实验和理论计算表明,该文所设计的均流器对进入水箱的水流具有抑流作用,能有效降低进水速度,减弱了水箱中冷热水的混合程度,使得水箱的斜温度层厚度减小,进而使得水箱的分层效率提高。

Heat storage is an important part in solar thermal energy utilization,in particular when using water as the thermal storage material in medium and low temperature zone,it is one of key technologies.In order to improve the thermal stratification of a heat storage water tank,a novel equalizer was designed in this paper.When the operating condition is that the initial water temperature and the inlet temperature is 70℃and 10℃,respectively,the influence factors of thermodynamic stratification in hot water storage tank were tested.And based on the ANSYS software,the mathematical model of the water tank was established.The performance parameters,such as the Richardson number the MIX number and exergy,were involved in the evaluation.This study was further extended to explore the filling efficiency as the performance parameters of thermal stratification within a storage tank.The numerical model was validated with the experimental data.The results demonstrate that with the increase of flow rate,the Richardson number decreases,but the thickness of thermocline and the MIX number decrease first and then increase.When the flow rate is 3 L/min,the equalizer performs best,and the storage tank has the best thermal stratification.The RMS error increases firstly and subsequently decreases with the increase of the flow rate.Furthermore,the MIX number touch the bottom at the dimensionless time of 0.5 in the numerical results,whereas it is 0.4 in the experimental results.It is also observed that the equalizer has the influence on the flow-suppressing which decreases input flow rate and mixing process between the hot and cold water in the tank,so as to improve the thermal stratification.