Simulation And Experimental Study On Water Storage Device For Geothermal Heating

In the context of "double carbon",the huge challenge facing our country is energy substitution and transformation.With the rapid popularization of geothermal heating technology,it provides a solid energy guarantee for China to realize clean heating.However,with the rapid development of economy and the improvement of power demand,the matching problem between geothermal heating technology and shortage of power resources needs to be solved urgently.The coupling technology of geothermal heating and energy storage can solve the contradiction between the supply and demand of heat energy and realize the "peak shifting and valley filling",and the energy storage device plays an important role in this process.In this paper,a new type of horizontal multi-tank water energy storage device is proposed in the geothermal heating energy storage coupled system.Firstly,this paper studies the temperature stratification theory and evaluation method of water energy storage device,gives the classification of existing heat storage technology,the basic principle,influencing factors and evaluation indexes of temperature stratification performance,at the same time gives the corresponding definition and application conditions.On the basis of theoretical research,a horizontal multi-tank water energy storage device with an equalizing plate was designed and a geometric model was established.Using Fluent software,the outlet temperature changes of the new water energy storage device with three different flow equalizing plate structures,including uniform shunt,side shunt and middle shunt,are simulated and studied under the conditions of different heat storage flow and initial temperature.The results show that: the larger the heat storage flow rate,the earlier the temperature rise time of the outlet temperature and the initial temperature has no effect on the variation law of the outlet temperature.When the heat storage flow is <1.2 m3/h,the flow equalizing plate of side shunt structure can make the stratification effect of the device the best.When the heat storage flow is≥1.2 m3/h,the flow equalizing plate of uniform shunt structure can make the stratification effect of the device the best.Referring to the results of simulation study,an experimental system for temperature stratification characteristics of water energy storage device is designed and a test rig is built.The features of thermocline thickness of water energy storage device with three different flow equalizing plate structures under different flow rates and the heat storage/release performance of water energy storage device at three initial temperatures of 30℃,35℃ and 40℃ are studied.The results show that: Under the same working condition,the thickness of thermocline in the water storage tank with flow equalizing plate is significantly lower than that without flow equalizing plate.And when the heat storage flow rate is <1.2 m3/h,the thickness of the thermocline for the water storage tank with the side shunt equalizing plate structure is the smallest,only18.8 cm;When the heat storage flow rate is ≥1.2 m3/h,the uniform shunt equalizing plate structure has the smallest thickness of the thermocline,which is only 16.2 cm,and the temperature stratification performance is the best,which is consistent with the results of the simulation study.At the same time,it can be obtained that with the increase of the initial temperature in the water energy storage device,the total heat storage and heat release of the device decrease,and the heat release/storage ratio of the device corresponding to the initial temperature of 30℃,35℃ and 40℃ are 95.11%,93.07% and 92.04% respectively.Finally,in order to further verify the performance of the new water energy storage device,the heat storage/release performance of the water energy storage device is tested by using the geothermal public heating system in Xianxian County,Hebei Province.The results are as follows: The heat release/storage ratio of the heating system coupled with the water energy storage device under three loads of low,medium and high loads are: 86.72%,93.18%,91.29%,and energy storage rate are: 100%,66.67%,50%,respectively.So the performance of the heat storage/release is better.