Structural Optimization Of Heat Accumulator Filled With Paraffin Phase Change Materials Based On Field Synergy Principle

Renewable energy is a vital part of the energy system,promoting the coupling of energy storage system and renewable energy can realize the flexible regulation of renewable energy and improve its utilization efficiency,which is of great significance to the practice of energy conservation and emission reduction.In this paper,combined with the solar phase change heat storage system,the model of tubular phase change heat accumulator is established.In order to optimize the structure of heat accumulator,the melting and solidification process of 1.5% graphene/paraffin composite phase change materials outside the special-shaped tubes will be analyzed by numerical simulation,and the mechanism of heat transfer enhancement of special-shaped tubes is studied by using the principle of field synergy.Through the eccentric arrangement of special-shaped tube and the addition of fins,the structure of the heat accumulator is further optimized,which provides a theoretical basis for the application of the heat accumulator filled with paraffin phase change materials in the solar phase change heat storage system in the future.The special-shaped tubes are used to optimize the structure of tubular phase change heat accumulator,the melting and solidification of phase change materials outside elliptical and drop tubes are numerically analyzed,and compared with the traditional circular tube,the results show that: the special-shaped tubes can enhance the heat storage and release performance of the phase change heat accumulator,and the effect of heat transfer enhancement by drop tube is the best.The melting rate of phase change materials outside drop tube is 62% higher than that of circular tube,53% higher than that of elliptical tube,and the solidification rate of phase change materials is 9.8% higher than that of circular tube,6.7% higher than that of elliptical tube.Based on the principle of field synergy,this paper studies the essence of heat transfer of phase change materials strengthened by special-shaped tubes.The synergy angle of phase change materials outside circular tube,elliptical tube and drop tube in the melting process is simulated and calculated.It is found that the synergy of velocity field and temperature field of phase change materials outside special-shaped tubes is better than that of circular tube,the phase change materials outside the drop tube has the best field synergy and the best convective heat transfer effect.The tubular phase change heat accumulator with built-in elliptical tube is the research object,the structure of heat accumulator is optimized by setting an eccentric inner tub,the melting and solidification process of phase change materials outside the elliptical inner tube with different eccentricities and ratios of long and short axes were studied.The results show that compared with the concentric tubular model,the melting efficiency of phase change materials in the models with inner tube eccentricity of 20 mm,30mm and 40 mm is increased by 26%,34% and 35%,and the solidification efficiency is increased by 11%,7% and-2%;The ratio of long and short axes of the elliptical inner tube has little effect on the melting and solidification process of the phase change materials.Among the three kinds of elliptical inner tubes with long short axis ratio of 1.5,2 and 2.5,the elliptical inner tube with long short axis ratio of 1.5 is more conducive to the melting and solidification of phase change materials;The synergy of velocity field and temperature field of phase change materials in eccentric tubular model is not as good as that in concentric tubular model;The eccentric tube structure can increase the thermal convection region of the phase change materials,reduce its heat conduction region,improve the melting rate of the phase change materials as a whole,and shorten the heat storage time of the heat accumulator.The tubular phase change heat accumulator with built-in drop tube is the research object,the structure of heat accumulator is optimized by adding fins.The effects of the angle,height and width of the fins and the fork structure of fins on the melting and solidification process of phase change materials were studied.It is found that the addition of fins improves the floating of liquid phase change materials and the precipitation of solid phase change materials,and makes the phase change process more uniform;Compared with the model without fin,in the T-shaped fins model with an angle of 45°,a height of 45 mm and a width of 2mm,the complete melting time of phase change materiasls is shortened by 66% and the complete solidification time is shortened by 63%.The synergy of temperature field and velocity field of phase change materials near the fins is poor,but the existence of fins will strengthen the thermal convection of other parts of phase change materials.