Experimental Study On Melting Heat Transfer Characteristics Of Paraffin Wax Containing Metal Framework

The solid-liquid phase change material achieves the purpose of storing and releasing energy through the endothermic and exothermic effects accompanying the phase transition process.Since it has the advantages of strong stability,large heat storage density,easy packaging,and easy control of strong stability have become the focus of research.In the field of construction,phase change materials are mainly used in the outer protective structure of buildings and in cold and hot storage devices,which can achieve the purposes of reducing energy consumption,reducing indoor temperature fluctuations,and improving human comfort.Therefore,the research on the heat transfer characteristics of solid-liquid phase change becomes the most important research.In this paper,the experimental research and numerical simulation are used to carry out in-depth research on the phase transition characteristics and heat transfer mechanism of paraffin containing metal framework during melting.The solid-liquid phase change experiment platform of paraffin and pure paraffin containing metal framework was built.The influence of the metal framework on the heat transfer process of paraffin melting is analyzed.First,the high-definition camera and infrared camera were used to visually observe and analyze the migration and development of the phase interface and the temperature distribution in each region during the paraffin melting process.The melting process of paraffin containing metal framework was compared with pure paraffin to investigate the influence of the addition of metal framework on its melting and heat transfer.Secondly,by arranging miniature thermocouples at the nodes of the metal framework,the temperature changes of the framework and the paraffin near them are measured to verify the existence of local thermal non-equilibrium effect.The results show that the visual interface shows that the phase interface continuously migrates to the right during the melting process of pure paraffin and presents a smooth arc shape that curves to the right.There is a heat-intensive area on the upper left side of the square cavity.During the melting process of the metal-containing framework,the phase interface presents a right-inclined linear shape during the migration to the right.The phenomenon of using the framework as the melting center at the local position of the phase interface causes vortices to appear in the temperature field.The heat in the heat dense area on the upper left side of the square cavity is quickly transferred to the low temperature area on the right side.It can be seen from the comparison of pure paraffin and metal-containing framework wax that the addition of metal framework accelerates the melting and heat transfer speed of paraffin,reduces the curvature of the phase change interface,the melting morphology and temperature distribution are affected by the framework distribution,and the temperature unevenness is improved.By analyzing the measurement results of the temperature change of the framework and its adjacent paraffin at different temperature measurement points by thermocouples,it can be seen that the temperature rises faster at the temperature measurement point closer to the hot wall surface,and the temperature rises faster at higher altitudes.There is a temperature difference during the temperature rise of paraffin and framework at the same temperature measurement point,proving the existence of local thermal non-equilibrium effect.The temperature difference gradually increases and reaches when a phase change occurs at the temperature measurement pointThe maximum peak is at this time,the thermal non-equilibrium is most significant,and then the temperature difference gradually decreases to zero,and the thermal non-equilibrium effect weakens.The temperature difference between the framework and the paraffin tends to thermal equilibrium and there will still be a small rise in fluctuation.The closer the temperature measurement point in the horizontal direction to the hot wall surface,the earlier the temperature rise and temperature difference appear,the maximum peaks of the first three measurement points from left to right gradually decrease,the last one suddenly increases,and the closer to the hot wall surface,the greater the peak of fluctuation;The higher the temperature of the temperature measurement point in the height direction,the higher the temperature rise and the earlier the temperature difference occurs,and the larger the maximum peak value.In order to further study the influence of the metal framework on the heat transfer characteristics and flow of the paraffin melting process,based on experimental research,a three-dimensional mathematical model was established to carry out numerical simulation calculations on the paraffin and pure paraffin containing the metal framework.The experimental results were mutually verified,and the results were in good agreement.The numerical simulation results show that the paraffin phase interface becomes thicker after theframework is added,the melting rate is always higher than that of pure paraffin,and the difference gradually increases.The dense area of pure paraffin isotherms is mainly concentrated near the hot wall and the upper left side and the solid-liquid junction.The metal framework makes the distribution of isotherms more uniform.The overall temperature rise rate of the paraffin-cutting temperature of the metal-containing framework is faster than that of pure paraffin.During the melting process,the temperature distribution of the interception line is uneven due to the temperature difference between the framework and the paraffin.The natural convection speed of paraffin with metal framework is lower than that of pure paraffin,and the velocity distribution range is faster than that of pure paraffin.