| World's traditional energy is facing a crisis today,and renewable energy has gradually become an important direction for human development because of its characteristics such as pollution-free,clean and large quantity.However,due to the discontinuity of renewable energy such as solar energy,energy storage is particularly important.Among them,the soil heat storage system plays an important role in the long-term storage of solar energy.The soil heat storage system is large,and its experimental engineering quantity and implementation are difficult.The accurate simulation calculation amount is also huge.In order to reduce the system from the perspective of space and time,reducing the simulation and experimental workload of soil heat storage,based on the similarity theory,this paper derives the similar function relationship of soil heat storage system,and then established the traditional CFD model and similar model.Then,referring to the similarity research method of step-by-step approximation,the results of the traditional model and the similar model are compared from single tube to multi-tube,from simple working condition to complex working condition,which reflects the efficiency and accuracy of the similar model: Under long-term heat storage conditions,the calculation time of similar models can be shortened by more than 10 times;the error of soil temperature rise obtained by the two models is very small,within 2?.In addition,in the CFD modeling process,the work of grid independence verification and step independence verification was also carried out.After the modeling was completed,the actual size CFD model was verified by the data of an experimental system in Tianjin.The relative error of the tube heat exchange amount is within 5%.According to the similar model of soil heat storage,the corresponding experimental system is established,and the experimental results of long-term heat storage in soil are compared with the calculation results of CFD similar model: the relative error of inlet and outlet temperature difference is within 10%,and the error of soil temperature rise is also Below 1 °C.At the same time,the experimental results of different working conditions can be concluded that the near-surface soil heat flow of 0.1m and shallower is greatly affected by the temperature,resulting in a lower temperature of 0.2m of the surface in the regenerator.The temperature of the intermediate position at 0.5m of the soil is largest.The heat flow is very small at the side of the pipe group 0.1m away from the pipe.Compared with the measuring point at a distance of 0.05 m,the heat flow changes in a consistent trend with delay.Based on the design conditions of this paper,the 40°C-inlet water temperature is better than 30 °C and 50 °C,and the temperature rise obtained when the inlet flow rate is 610 L·h-1 is much higher than that of 814 L·h-1 and 407 L·h-1.Finally,the similar model is applied to the long-term storage of solar energy in the hot summer and cold winter zone in China.It can be obtained that the heat impact radius of 1 month is less than 2m,the heat storage is carried out until the end of September,the center temperature is increased by 17 °C,and the temperature at the heat storage boundary is increased by 6.5 °C;when the temperature changes from low temperature to high temperature,The shallow soil affected by low temperature will produce some low temperature layer due to the delay of response;the monthly internal energy change will gradually decrease,and the average soil temperature will eventually increase by 11.37 °C;the surface heat dissipation is most affected by temperature,and the side heat dissipation is the main part.This paper proposes different control strategies and compares the efficiency changes of the three heat storage strategies.The results show that the first scheme(interval heating)will have some effect in the early stage of heat storage,but its efficiency in long-term heat storage for more than 3 months will decrease,and the advantages of Option 2(doubling time)also decrease.This paper also uses the CFD similar model to compare the effects of different starting months in the heat storage period on long-term heat storage efficiency.It is found that the later the starting month of the heat storage period,the higher the average heat storage efficiency.If July is the starting month,then The average heat storage efficiency during the entire heat storage period can reach 63.02%.In summary,the traditional simulation model and similar model experimental system have been used to verify the CFD similar model,which shows that the model can efficiently and accurately complete the long-term heat storage simulation of the soil.It is applied to the long-term heat storage of solar energy in hot summer and cold winter regions and has reached a guiding conclusion. |
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