Simulation Of Dynamic Processes In The Thermocline Of A Rectangular Energy Storage Tank

With the rapid development of China’s economy,people’s standard of living has improved,and the proportion of heating ventilation air conditioning(HVAC)systems’ energy consumption in the total building energy consumption continues to rise.As the divergence between peak and valley power loads continues to expand,the demand for load-side peak shaving is progressively augmenting.As water storage air conditioning systems utilize the difference in peak and valley electricity prices through the summer storage of cold and winter storage of heat,It meets the maximum load-side peak shaving demand and fill the peak of the electric load to fill the valley.While significantly diminishing operating costs,it has immense potential for development.Rectangular energy storage tanks are typically arranged underground and can be utilized in conjunction with firefighting tanks.The dynamic characteristics of the thermocline of a rectangular tank have a critical role in its energy storage performance.Therefore,It is of great theoretical and practical value to simulate the dynamic process of thermocline of rectangular tank.In this study,a combination of theoretical analysis and numerical simulation was employed to investigate the dynamic processes of the thermocline of a naturally stratified water storage tank.To investigate the influence of the water distribution design parameters on the dynamic characteristics of the thermocline,a simplified model with various water distribution forms was constructed to analyze the dynamic growth law of the thermocline during the storage process of the tank.The temperature distribution in the tank and the growth process of the thermocline and its trend can be investigated under different flow rates,temperature differences between imports and exports,numbers of water distribution holes,and hole diameters.The response surface method is innovatively applied to the study of the dynamic performance of the natural stratified water tank thermocline,and the dynamic performance of the thermocline under the influence of multiple parameters such as flow rate,number of water distribution holes,and pore diameter is investigated.The optimal design conditions for the initial thermocline thickness of the energy storage process are determined to guide engineering practice.The main research conclusions are presented as follows:Through theoretical analysis and numerical simulation,the influence of the design parameters of the water distributor on the dynamic characteristics of the thermocline was studied.The results indicated that the initial thermocline thickness augmented with the increase of the design flow rate,and and the change rate of the thermocline thickness decreases.When the flow rate is excessive,the change rate of the thickness of the thermocline is negative.The thickness of the initial thermocline diminishes as the temperature difference between the inlet and outlet increases.As the number of holes increases,the thickness of the initial thermocline decreases.When the flow rate and the number of holes are constant,the initial thermocline thickness decreases with increasing hole diameter.Under conditions of high flow rate,there is a significant reduction in the thickness of the initial thermocline with an increase in both the number of holes and diameter of the water distributor.When the flow rate is constant,the rate of variation in the thickness of the thermocline is higher for a water distributor with a larger aperture.The Box-Behnken design approach of response surface methodology was employed to explore the dynamic performance of a naturally stratified water storage tank.This methodology minimizes the number of simulations required while providing a comprehensive analysis of design parameters within a relatively short time.Statistical analysis of the model was conducted through ANOVA evaluation,which indicated that the model is a good fitting degree for simulations and exhibits a strong correlation between predicted and observed values.The simulated process is significantly influenced by the flow rate,number of holes,and hole size,with the interaction between hole diameter,flow rate,and number of holes exhibiting a significant effect.Through the optimization of design conditions,the optimal parameters for the initial thermocline thickness in the energy storage process were identified while considering multiple factors such as flow rate,number of water distributor holes,and hole diameter.The optimal design conditions were determined as a flow rate of 0.36 kg/s,a total of 36 holes,and a hole diameter of 12.5 mm.Through a simulation study of energy storage processes in rectangular and cylindrical reservoirs,it was determined that the thickness of the thermocline in a rectangular tank and a cylindrical tank with identical height is equal,given a specific storage volume,temperature differential at the inlet and outlet,and flow rate.Under the condition of a fixed height for the rectangular tank,the thickness of the maximum thermocline is thinner within an aspect ratio range of 1 to 3.Beyond this range,the thickness of the maximum thermocline steadily increases with increasing aspect ratio.In a tank with a square bottom surface,the thickness of the maximum thermocline steadily increases with a greater ratio of height to side length.However,when the tank volume is fixed,the volume of the thermocline decreases as the longitudinal height increases and the bottom area of the tank decreases.In other words,the volume of the thermocline area steadily decreases with an increasing ratio of height to side length.