| Phase change heat storage technology is a new energy saving technology which uses heat absorbed or released by substance in the process of phase change to realize energy storage and utilization.Its advantages include high energy density,small temperature variation range during phase transition and required device is simple and so on.In recent years,it has been widely used in the direction of power peak clipping and valley filling,building energy saving and green energy development.In this paper,the horizontal shell and tube phase change heat storage device is taken as the research object.Fluent is used for numerical simulation to study the phase change heat transfer process of composite phase change materials.The main research contents and conclusions of this paper are as follows:(1)The larger the content of EG in paraffin/EG composite phase change material,the shorter the time of complete transformation.Compared with pure paraffin,the melting time of PCM with EG mass fraction of 20% is reduced by 60%.During solidification,the complete solidification time was shortened by 37.9%.(2)The effect of changing the temperature and flow velocity of the heat transfer fluid on the phase transition process is simulated.The increase of the temperature of the heat transfer fluid leads to the increase of the heat transfer rate during the phase change process.However,as the temperature of the heat transfer fluid continues to rise,the efficiency of improving the phase change heat transfer gradually decreases.The change of flow velocity has obvious effect on the outlet temperature of the phase change heat storage device.In the melting process,the heat transfer fluid with a lower flow velocity can fully heat transfer with the PCM,so the lower flow velocity leads to a lower outlet temperature.In the solidification process,the lower the flow velocity,the heat transfer fluid can fully absorb the heat of the PCM.At a flow velocity of0.05m/s,the heat transfer fluid can be increased from 283 K to 296.3K.(3)Under the condition of constant filling amount of PCM,the complete melting time of the PCM heat storage device with the length of 900 mm is shortened by 5.6%compared with that with the length of 600 mm.The increase of the length of the heat exchange tube can accelerate the melting of PCM,but the effect is not obvious.Considering the pipe consumption and heat storage efficiency,according to the situation in this paper,the phase change heat storage device with the length of 800 mm is the best.(4)Set the eccentric distance of the heat exchange pipe along the negative direction of the Y axis.The results show that the eccentric distance promotes the melting process.The total melting time of the device with-20 mm eccentricity is 23%shorter than that of the concentric structure.In the solidification process,the eccentricity distance inhibits the solidification of PCM,and the complete solidification time increases by 17.9% compared with the concentric structure.(5)The heat transfer enhancement effect of adding ribs is simulated.When the number of ribs is 2,the time of complete melting and solidification is shortened by22.3% and 15.9% compared with that without fins.When the number of fins is 2,different angles have influence on the phase transformation process.The ribs with 0°arrangement have the best heat transfer performance during melting and solidification.The phase transition process with different rib height and number was analyzed,and the change of phase interface distribution and liquid phase ratio with time was analyzed.Combined with the melting and solidification process,the optimal rib number in this paper is 6,and the optimal fin height is 10 mm.In this paper,the structural optimization of phase change heat storage unit is analyzed by numerical simulation.It is hoped to provide useful reference for the application of composite phase change materials in shell and tube type phase change heat storage device. |
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