Preparation, Application And Numerical Simulation Of Graphene Modified Phase Change Microcapsules

With the increasing of atmospheric pollution,the use of high pollution energy based on oil and coal has been limited.The phase change energy storage technology gains rapid development in this context.Phase change materials(Phase change material,PCM)is a kind of material,which happens phase state change and absorb or release a large number of latent heat when the temperature changes to a certain extent.The discontinuous and unstable heat can fully utilied due to the reservoir characteristics of phase change materials.Phase change microcapsules containing phase change material by the microcapsule technology can be overcome the problem of easy to leak,poor compatibility and corrosion resistance in the process of phase change materials used in single.Composite phase change microcapsules and other materials,through the phase transition behavior of microcapsule core materials to adjust the temperature of the composite material surroundings,can effectively increases the energy utilization rate.First,in order to overcome the problem of easy to leak,poor compatibility and corrosion resistance in the process of phase change materials used in single,phase change microcapsules containing n-hexadecane as the core material and melamine-urea-formaldehyde resin as the wall material were prepared by in-situ polymerization.The mass ratio of core material and wall material,mass fraction of melamine and compound emulsifier ratio and dosage,and the influences of emulsifying speed and other factors for microcapsules morphology,microcapsule thermal performance and coating efficiency were studied by using optical microscope(OM),Fourier transform infrared spectrometer(FT-IR),differential scanning calorimetry(DSC)and thermogravimetric analyzer(TG)analysis method.Through the Design-Expert 8.0 software software,the multiple regression model of the melamine mass fraction,core-wall ratio,composite emulsifier mass fraction was established with phase change latent heat of microcapsule as response value.Best preparation conditions of n-Hexadecane microcapsule:the mass fraction of melamine was 4.8 wt%,the mass ratio of core material and wall material was 1.6:1,and the mass fraction of composite emulsifier was 1.6 wt%.The microcapsule prepared in the condition was round and had a good dispersion,The latent heat of the phase change microcapsules was 171.8 J/g,and encapsulation rate reached 86.6%.The coefficient of thermal conductivity and thermal diffusivity of phase change microcapsules were only 0.053 W/mK and 0.238 m2/s,which limited the phase change microcapsule effect in practical application.Second,in order to increase the heat conduction function of phase change microcapsules and improve the supercooling phenomenon,graphene modified phase change microcapsules,graphene as modifying agent,were prepared with ideal heat conduction performance,higher phase change latent heat.The influences of additive polyvinyl alcohol(PVA)quality fraction and graphene quality fraction for microcapsules morphology,microcapsule thermal storage performance,heat-resisting performance,crystal form,coefficient of thermal conductivity and permeability resistance were studied by using emission scanning electron microscope(FE-SEM)and Fourier transform infrared spectrometer(FT-IR),differential scanning calorimetry(DSC),X-ray diffraction(XRD),and thermogravimetric analyzer(TG)analysis methods.The results show that the microcapsules were generally spherical and the particle size distribution was uniform and dispersive.Graphene had been successfully coated in the phase change microcapsule,and microcapsules had the high crystallization degree and the ideal crystal type.As the amount of graphene increased,the characteristic diffraction peak of graphene gradually increased.Polyvinyl alcohol(PVA)can introduce linear macromolecule chain on the molecular chain of microcapsule wall material to improve the flexibility of wall material.The optimal dosage of PVA was 3?4 wt%.The thermal conductivity and thermal diffusion coefficient of the phase change microcapsule were 0.154 W/mK and 0.56 m2/s respectively as the 0.1 wt%amount of graphene added,with a year-on-year increase of 190.5%and 135.3%.In addition,the addition of a small amount of graphene can reduce the self-polymerization effect of MUF prepolymer in the reaction solution,making the wall of the microcapsule more smooth and solid.Third,graphene modified microcapsules were coated to the surface of fabric by the intumescent coating,and thermo-regulated compound fabric was obtained.The influences of microcapsule dosage,the dosage of polyacrylic ester(PAE),speed,air inflow,and baking temperature and time influencing factors for heat storage performance,breathable performance,mechanical properties and wash resistance of compound fabric were studied.Through the Design-Expert 8.0 software software,the multiple regression model of the phase change microcapsule mass fraction,speed,air inflow was established with phase change latent heat of microcapsule as response value.The response value and the optimal level of influencing factors were obtained.Best preparation conditions of phase change microcapsule compound fabric:the quality score of microcapsules was 19.5 wt%,the speed was 6.2 m/min,and the air inflow was 10.5 L/min.When the baking temperature was too low and the time was too short,the degree of crosslinking between the finishing liquid and the fabric is poor,and the microcapsule was easy to fall off.When the baking temperature was too high and the time was too long.the cotton fabric was prone to yellowing,and the energy consumption was increased.The best baking process was 160 ? × 2 min.Under the optimum preparation process,the phase change latent heat of the phase change microcapsule composite fabric was about 76.5 J/g,which had the ideal heat storage performance.Finally,the thermal process and heat transfer characteristics of graphene modified microcapsules were simulated numerically by the Fluent finite element software.Model Of graphene modified phase change microcapsules was reasonably simplified.Two-dimensional plane geometry model of the graphene modified phase change microcapsules was established using Fluent software Gambit module and mesh generation,and after setting parameters for numerical simulation.The simulation results showed that the temperature field and the solid-liquid phase distribution of the graphene modified phase change microcapsule model in the liquefaction process were presented.When the liquefaction range of core material into graphene area,graphene can quickly heat conduction to the surrounding solid phase in the core material and the liquefaction rate of core material accelerated because of its extremely strong thermal conductivity.The influences of thermal conductivity of the modifier and the addition of modifier on the storage process of phase change microcapsule core material were investigated.The resulted show that the thermal conductivity of the modifier and the addition amount significantly affected the liquefaction rate of the core material.When the thermal conductivity of the modifier was set at 3500 W/mK,the time required for the complete liquefaction of the core material was 7400 ms.which was 60.2%less than that of the core material without modifier.When the volume fraction of graphene modifier was set to 12%,the time for core material completely liquefied for 6200 ms,compared with the core material without modifier,which shortened by 66.7%.This confirmed the graphene modifier had a promoting effect on the thermal storage process of core material.In addition,the regression models between modifier thermal conductivity coefficient and dosage and the completely liquefied time of core material were established respectively,offering reference for the modified materials selection and dosage of phase change microcapsules and providing the theoretical support for the store thermal performance prediction of the modification phase change microcapsules.