| The improvement of the thermal insulation performance of the building envelope structure,and the effective use of renewable energy sources,industrial waste heat,waste heat,and geothermal energy can effectively reduce energy consumption.Phase change heat storage accumulates external heat in the material through the physical properties of the material.When external conditions change,the energy is released to the outside world and used.It is of great significance to study the mechanism of the solid-liquid phase transition process,especially the evolutionary morphology of the solid-liquid interface mushy zone,for the popularization and application of phase change materials.In this paper,pure paraffin wax is used as the research medium.The combination of experimental research and simulation calculations is used to deeply study the characteristics and development mechanism of phase transition process.Firstly,a phase change observation experiment bench was set up to experimentally study the paraffin wax surface migration process and its characteristics.The surface process was observed by CCD high speed camera technology,focusing on the observation of the migration and change morphology of the solid-liquid interface,and then setting up a phase change test station for nuclear magnetic resonance technology.The internal imaging observation of the paraffin wax melting process was performed by NMR,and the microscopic morphology and solid particle distribution characteristics of the mushy zone at the solid-liquid interface were further explored.The experimental results show that: changing the heating temperature has a significant effect on the melting speed of paraffin.Increasing the heating temperature can accelerate the paraffin wax heat transfer process,so that paraffin absorbs more heat per unit time,accelerates natural convection and increases the whole energy transfer rate;nuclearmagnetic resonance The technology can image the phase change melting process and can effectively distinguish paraffin solid liquids,and clearly demonstrate the microscopic morphology of the solid-liquid interface mushy zone and the characteristics of solid-liquid particles;the thickness of the mushy zone at the solid-liquid interface in different melting regions is Differently,the overall appearance of the upper mushy zone is relatively thin,and the lower mushy zone is thicker;the NMR hydrogen spectrum can be used to collect signals from the liquid paraffin region.The paramagnetic signal attenuation of the paraffin-embedded solid paraffin can cause serious signal loss.In this paper,a numerical simulation model is established and compared with the experiment.The paraffin wax phase change heat storage principle is further explored.The influence of different heating temperatures on the melting of wax is studied,and the temperature change in the mushy zone is further analyzed.The results show that natural heat convection of paraffin liquid results in higher heat transfer in the upper part,which results in faster melting than in the lower part.The upper part of the mushy area is thin.The lower part of paraffin wax only depends on heat conduction,so the mushy area is obviously thicker than the upper part;the same exists in the mushy area.Paraffin solids and liquids,heat transfer is accompanied by melting of paraffin wax in this area.Since the solid-liquid phase will absorb heat,the temperature will be stabilized at the paraffin phase transition temperature;increasing the heating temperature can promote the phase transition process and shorten the melting time..Comparing the numerical simulation with the experimental results,the two are completely consistent.NMR as an advanced non-contact measurement research method was applied to the paraffin melting experiment.A new method was developed and the feasibility of the experiment was verified.The existence of a mushy zone was objectively verified,and the paraffin phase was further studied for the next step.Change the laws and principles to lay the foundation. |
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