Study On Solidification Heat Transfer Of Paraffin Containing Metal Skeleto

The development of energy storage technology has been promoted by the goal of double carbon,among which the phase change energy storage technology has gained wide attention with the advantages of high energy storage density and easy control,etc.Phase change energy storage stores thermal energy through phase change materials and releases it when needed.Most phase change materials have low thermal conductivity.However,there is a lack of in-depth research on the heat transfer mechanism of phase change materials containing skeletons,especially on the characteristics of the solidification process of phase change materials.In this thesis,we use a combination of experimental and numerical simulations to study and analyze the heat transfer characteristics of the solidification process of pure paraffin wax and paraffin wax with metal skeleton to provide a theoretical basis for the relevant engineering applications.In this thesis,a solid-liquid phase change solidification experimental system was set up to observe the solidification process of pure paraffin wax and paraffin wax with metal skeleton by infrared thermography,in order to analyze their phase change interface migration law and temperature distribution law.The temperature inside the embedded metal skeleton paraffin wax was precisely measured by arranging T-type thermocouples to obtain the temperature change law inside the composite phase change material,focusing on the local thermal non-equilibrium effect.It is shown that(1)Compared to pure paraffin wax,the phase change cavities embedded with different structures of metal skeletons can accelerate the solidification process of paraffin wax,with the shortest solidification time for paraffin waxes containing X-positive gradient skeletons.Comparing the solidification rates of the cold source temperature of 5℃,10℃ and15℃ respectively,the lower the cold source temperature,the faster the solidification rate of the composite phase change material.During solidification,the paraffin wax with the metal skeleton dominates in terms of thermal conductivity.The addition of the metal skeleton affects the migration of the solid-liquid phase change interface and inhibits the natural convection of the paraffin wax,where the weaker the natural convection the less the bottom of the solid-liquid phase change interface tilts to the right.(2)The temperature change within the metal skeleton paraffin is divided into three main stages,namely the liquid phase rapid cooling stage,the solidliquid coexistence stage and the solid phase cooling stage,the duration of the solid-liquid coexistence phase shortens as the cold source temperature decreases,there is a small temperature rise in the solid-liquid coexistence stage,the lower the cold source temperature the weaker the solidification temperature rise phenomenon.The structure of the metal skeleton affects the temperature distribution of the composite phase change material.The temperature difference between the upper and lower part of the uniformly estimated skeleton and paraffin wax containing X-positive gradient skeleton is small,while the temperature difference between the upper and lower part of paraffin wax containing Z-positive gradient skeleton is large,and the smaller the porosity,the lower the temperature.The different structure of the skeleton affects the cooling rate of the composite phase change material,in which the cooling rate of X-positive gradient skeleton is faster in the early stage of solidification,the cold source temperature is different,there are differences in the solidification temperature rise phenomenon.(3)There is a complex and significant local thermal non-equilibrium effect in the solidification process of paraffin containing metal skeleton.There are two peaks and two valleys of the local thermal non-equilibrium effect with time at each point,which is mainly due to the significant difference between the thermal conductivity of paraffin and metal skeleton and the difference between the thermal conductivity in the skeleton and the natural convective heat transfer in the paraffin during the phase change phase of solid-liquid coexistence.The peak and trough values of the local thermal non-equilibrium effect at each location in the horizontal direction show concave fluctuations,while the local thermal non-equilibrium effect at each location in the vertical direction has a similar pattern of variation and similar values.The peaks and troughs of the thermal non-equilibrium effect of paraffin containing metal skeletons with different structures differ,with the peaks and troughs of gradient skeletons appearing earlier than those of uniform skeletons.Changes in the temperature of the cold source have a direct effect on the local thermal nonequilibrium effect.The lower the temperature of the cold source,the more significant the local thermal nonequilibrium effect of the solidification process.(4)Numerical simulations and experimental studies were mutually verified to be in good agreement,where the maximum temperature measurement error was 4.4%.The different structures of the metal skeleton affect the rate of paraffin solidification and the uniformity of the internal temperature.Five different working conditions were analyzed and compared,with the X-positive directional gradient skeleton performing optimally.