Controlled Preparation Of Paraffin Phase Change Microcapsules And Their Solid-Liquid Phase Variation Properties

The rapid heat charging and heat release ability of instruments and equipment has become more and more the demand of People’s Daily life with the fast development of society.Phase change energy storage technology is considered to be a kind of energy saving technology to coordinate the space-time mismatch of energy supply and demand,which can improve the utilization ratio of renewable energy and the comprehensive utilization efficiency of energy.The phase change material is encapsulated to form micron scale phase change microcapsule particles,which can not only prevent the leakage of phase change material,but also facilitate the use and transportation.It can also increase the specific heat of the latent heat type functional suspension,increase the heat transfer area between PCM and base liquid,and improve the charging and releasing rate.As far as phase change microcapsule particles are concerned,the charging and releasing rates are related to the size of the capsule particles,the thickness of the shell and the thermal conductivity of the shell materials.In previous studies,the phase change microcapsule particle sizes,the heat storage and heat release rate not normalized,the result of the function caused by latent heat type suspension as the working medium of heat transfer and heat storage equipment is difficult to precise design,the capsule is not fully melting and solidification of the phenomenon,some scholars in the heat transfer is simulated joined the melting parameters(solidification)degree.But these parameters cannot be predicted in advance,which is not conducive to industrial applications.In order to reveal the influence of microcapsule particle size and shell material on the charging and releasing heat rate,this study used microfluidic method to prepare phase change microcapsules with regular structure and uniform and controllable particle size,and investigated the effects of particle size,shell material and thickness of microdroplets on the solid-liquid phase variable properties.The main research contents are as follows:(1)The influencing factors of solid-liquid phase change properties of phase change microdroplets at micron scale were investigated.The phase change microdrops with regular morphology,stable structure and uniform and controllable particle size were prepared bymicrofluidic method.The droplet size was adjustable from 217μm to 818μm.On this basis,the solidification and melting processes of the phase change microdrops were observed by using a high-speed camera and an optical microscope.The results show that the solidification and melting modes of the phase change microdroplet are not affected by droplet size and control temperature.The solidification and melting of the phase change microdroplet both start from the surface of the droplet and end in the center of the droplet in the form of ring evolution.The solidification and melting rates of the phase change microdroplets are affected by the control temperature.The solidification rate increases with the decrease of cooling temperature,and the melting rate increases with the increase of heating temperature.The solidification and melting rates of phase change microdroplet are also affected by droplet size.The solidification and melting rates of the phase change droplets decrease with the increase of particle size.(2)The effects of different shell materials on the solid-liquid phase transformation characteristics of microcapsules were investigated,and a kind of phase change microcapsules with low undercooling and good charging and releasing performance were prepared.Three kinds of paraffin phase change microcapsules(TMPTA,HDDA and ETPTA)were prepared by using coaxial flow microfluidic chip and double emulsification and photocurable method.They were characterized by regular morphology,uniform particle size,stable shell/core structure and strong monodispersibility(PDI < 3%).The surface characteristics and thermal conductivity of three kinds of microcapsules were analyzed with contact Angle measuring instrument and thermal conductivity measuring instrument.The effects of TMPTA,HDDA and ETPTA wall materials on the solid-liquid phase change characteristics of paraffin phase change microcapsules were studied in detail.Results show that compared with HDDA,ETPTA,TMPTA with minimum contact Angle and the largest coefficient of thermal conductivity,therefore TMTPA as cystic wall of paraffin phase change microcapsule heterogeneous nucleation of stronger,paraffin phase change microcapsule can effectively eliminate the supercooling phenomenon,and has the largest solidification and melting phase transformation rate,can effectively realize the heat for quick delivery.(3)The scale effect of shell thickness on the solid-liquid properties of TMPTA phase change microcapsules at micron size was studied.The results show that the solidification rate and melting rate of phase change microcapsules(PDI < 3%)decrease with the increase of the shell thickness of phase change microcapsules.Compared with the results of the monodisperse system,the influence of the particle size of the phase change microcapsule on the solid-liquid phase variation characteristics is more random and chaotic in the multi-disperse system.When PDI is 5% < PDI≤10%,the phase transformation rate of the microcapsule particles is higher than that of the monodisperse system.The difference between the maximum solidification rate and the minimum solidification rate is 0.13J/g·s,and the melting rate is 0.12J/g·s.When PDI is 10% < PDI≤15%,the phase transformation rate of the microcapsule particles is lower than that of the monodisperse system.The difference between the maximum solidification rate and the minimum solidification rate is0.05J/g · s,and the melting rate is 0.04J/g·s.When PDI is 15% < PDI ≤ 20%,the solidification rate of the microcapsules is much lower than that of the monodisperse system.The difference between the maximum solidification rate and the minimum solidification rate is 0.08J/g·s,and the melting rate is 0.09J/g·s.The polydispersity of particle size plays an important role in the solid-liquid phase variation of phase change microcapsules.Therefore,it can be seen that strict control of the polydispersity of particle size of phase change microcapsules can regulate the solid-liquid phase variation properties of phase change microcapsules.