| The efficient utilization of solar energy is an important means to alleviate energy shortage and environmental pollution and take the road to sustainable development.Due to the intermittency and volatility of solar energy,energy storage technology plays a crucial role in the field of solar heat utilization.Among them,phase change energy storage has the advantages of high energy storage density,stable operating temperature and high safety,and has broad application prospects.However,the low thermal conductivity of phase change materials restricts the development of phase change energy storage technology,so it is necessary to take effective measures to strengthen heat transfer to improve energy storage efficiency.In order to further study the energy transport characteristics of solar energy storage system and improve energy efficiency,a fan-shaped fin structure has been proposed as a means to enhance heat transfer.The experimental platform of solar energy phase change heat storage has been built with the fan-finned shell and tube phase change heat storage unit as the basic structure and paraffin wax as the heat storage material.Meanwhile,the heat transfer characteristics in the fan-finned shell and tube phase change heat storage device have been studied by numerical simulation.Firstly,the effects of fin height,angle and number on the heat transfer performance of the system have been analyzed based on structural parameters of fan-shaped fins.Then,the influence of inlet conditions of heat transfer fluid on heat transfer process has been explored and the fin structure has been further optimized under the best inlet conditions.Finally,combined with the characteristics of periodic variation of solar radiation intensity,the influence rule of the fluctuation characteristics of periodic unsteady heat source on the heat storage process has been explored,so as to clarify the difference between the unsteady heat source and the steady-state heat source.The results show that the experimental results are in good agreement with the numerical simulation.When the fin height increases to more than 51.30 mm,the influence on the heat storage process is not obvious.When the fin angle is 30° and the fin is uniformly arranged,the strengthening effect is the best.However,when the fin number is increased,the filling amount of phase change material should be taken into account.Increasing the inlet temperature of heat transfer fluid can effectively improve the thermal performance of the system,and the inlet flow rate of 5 L/min is the most suitable within the study range.When the amplitude is 10 K,the effect of small period(P=2,4,8 min)on the melting process is small,while the effect of large period(P=60,90,150 min)is obviously improved,and the melting time can be shortened by 15.3%.The effect of vibration amplitude on the heat storage process is stronger than that of the fluctuation period.When the amplitude increases from 5 to 25 K,the melting time can be shortened by up to 42.7%.This study can provide reference value for optimization design and performance enhancement of solar finned tube phase change heat storage system. |
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