Experimental And Numerical Study Of Thermally Stratified Storage In Heat And Ice Storage Tank

Along with the advancement of electric heating reform project,valley electricity utilized heat and ice storage air conditioning(HISAS)have a rapid development.HISAS uses icestorage method for cooling in the summer,combined heating by heat water storage in the winter.In the process of ice storage,the glycol solution flows inside the ice-storage coils,namely walltype heat exchange;in the process of heat water storage,hot water charge directly in the energy storage tank,namely mixing heat exchange.Thermal stratification is a kind of proven technique in fluid mixing heat exchange systems.The hot water boiled by heater charge from the inlet.The water's density changes with the temperature.Due to buoyancy,the fluid of different temperature separate and develop into thermal stratification which promote the efficiency of system and has economic benefits.The heat storage in winter conditions of heat and ice storage air conditioning is different from the normal thermally stratified storage water tank.Due to sharing the same equipment in winter and summer conditions,the ice storage coil with which fixed inside the tank will have influence on thermal stratification,which have been verified that will directly affect the efficiency of whole system.It is necessary to furtherly study the special thermal stratification.By summarizing the current studies about the thermally stratified technology from the perspective of theory,experiment and numerical simulation,it is found that the failure of evaluation indexes utilized in thermal stratification model and the blank fields on internal obstacles.Firstly,based on thermodynamics laws,the evaluation indexes of thermal stratification model in existing researches are reviewed and classified.Through analyzing the applicability of indexes,it is found that the indexes based on the first law of thermodynamics occur to failure when estimating the effect on thermal stratification from the internal obstacle,and that the assessment system which is short of the supplement and modified considering the internal obstacle based on the second law of thermodynamics is imperfect.Based on exergy analysis,thus,the internal obstacle exergy loss ratio-a modification index of exergy efficiency is put forward to assessing the influence on thermal stratification.Secondly,the heat storage test bed is designed and built,on which the insulation experiment and thermal stratification experiment were operated.The transient temperature field and heat flux in insulation layers were measured.In the thermal stratification experiment,a controlled experiment with internal obstacle and a blank experiment were designed.It is resulted that the temperature tendency with time of these two experiments are different.The type 1 indexes are failure to evaluating the thermal stratification heat storage,and the type 2 indexes are opposed to be adopt.Thirdly,the reliability of numerical model established by mathematical model and experimental data is verified comparing the experiment.The temperature and velocity fields were qualitatively analyzed using the numerical model.The effects on 3D transient flow field and thermal stratification by internal obstacle was illustrated.The differences between heat and ice storage tank and the normal heat storage tank were demonstrated and it is indicated that the existing indexes can't evaluate the thermal stratification in heat and ice storage.The solving method of the internal obstacle exergy loss ratio was built.The negative influence on thermal stratification was verified after adding the internal obstacle.Finally,four numerical models with different inlet conditions were established.The effects of the inlet position and the spatial structure,which is of important meaning on designing and engineering,on the internal obstacle exergy loss ratio of heat and ice storage tank has were primarily investigated.