Study On The Growth Process And Suppression Method Of The Thermocline In Stratified Chilled Water Storage Tank

With the continuous improvement of social economy,the consumption of electricity is also increasing.Rapid growth of electricity peak load,unbalanced load of network and increasing peak val ey load difference are the new characteristics of electricity load.Based on the new characteristics of power load,energy storage technology is an effective way for power demand side management.H-type slotted pipe diffuser is suitable for rectangular cold storage tank,but there are some problems,such as the number of pipes and fittings consumed,the existence of dead zones during discharging and hydraulic imbalance.In this paper,the growth process of the thermocline and the improvement of water diffuser used in rectangular cold storage tank are studied in order to improve the efficiency of cold storage tank.A test system was designed and constructed to collect the temperature data in the vertical direction of the tank under different flow rates during charging and discharging.Flow visualization tests were performed in a transparent tank to investigate the performance of square water diffuser,then the square water diffuser was optimized and the square water diffuser with shutter and circular hole was made.The cold storage and cold releasing experiments were carried out using H-type slotted pipe diffuser,square water diffuser and square water diffuser with shutter and circular hole.According to the temperature distributions during charging and discharging,the performance of three kinds of water diffuser is evaluated From the following five aspects: the thickness of thermocline,the growth rate of thermocline,the initial thickness of thermocline,temperature fluctuation,and the figure of merit of tank during charging or discharging(FOM1/2).The numerical simulation was used to study the flow characteristics of the square water diffuser with shutter and circular hole,and the numerical simulation results were compared with the experimental results to determine the accuracy of numerical simulation.The position of the shutter and the flow channel structure of the square water diffuser with shutter and circular were adjusted,and the effect was evaluated by the numerical simulation.According to the experimental results,it can be found that water mixing of the cold storage process is stronger than that of the cold releasing process,and the temperature distribution of the thermocline is in accordance with the distribution function of skewed function.The thickness of the thermocline decreases first and then increases.When the flow rate is smal,the initial thermocline is thin and the thermocline thickness will increase gradually.When the flow rate is large,the water mixing makes the initial thermocline thicker,and when the thermocline is stable,the thickness of the thermocline gradually increased.The square water diffuser with shutter and circular hole can effectively reduce the water mixing during charging at different flow rates.When the flow rate is 920/h,the maximum FOM1/2.charge is 91% using the square water diffuser with shutter and circular holes,and H-type slotted pipe diffuser and square water diffuser in the flow rate of 720L/h to a maximum of 87%,the optimal storage efficiency and flow rate have been improved.In the process of cold releasing,the H-type slotted pipe diffuser has the best performance,and the square water diffuser with shutter and circular holes is not suitable for the situation that the flow rate is more than 920L/h,and the square water diffuser can be used instead of the square water diffuser with shutter and circular holes during discharging.According to the results of numerical simulation,adjust the position of the shutter and optimize the flow channel structure can effectively reduce the water flow mixing,improve the stability of the thermocline,so as to improve the efficiency of storage tank.