Study On The Preparation And Performance Test Of A New Phase Change Microcapsule Nanofluid

Microcapsule technology refers to the technology of coating film-forming materials on the surface of solid or liquid to form micro particles with core-shell structure.These particles have a polymer shell,mostly spherical shape,particle size between one micron and one millimeter.At present,the technology of microcapsule has been extensive researched.Most scholars combined it with phase change materials to prepare microcapsule phase change materials.The special core-shell structure of the microencapsulated phase change material helps to reduce the leakage of the liquid phase change material and the external influence on the core material,and the micron or even nanometer particles greatly increase the heat transfer area,so that the phase change material with low thermal conductivity has higher thermal conductivity.When the phase change microcapsules are prepared into the slurry,the low thermal conductivity and the phase stratification,supercooling,volatilization and other phenomena of the phase change slurry can be effectively solved.In the early stage of research,our group proposed to combine the phase-change materials with nano materials to improve the performance of phase-change slurry.However,it is found that the phase-change slurry with nanoparticles is unstable and volatile.In order to solve this problem,our group also proposed to encapsulate the phase-change materials,and to solve the volatile problem by preparing the phase-change materials into phase-change microcapsules.The microcapsule phase change material has a clear core-shell structure,in which the phase change material with higher latent heat value is used as the core material,while the external wall material which can prevent the core material from leaking and maintain the spherical structure is used to coat the surface of the internal core material to obtain the phase change microcapsule.Microencapsulation can transform the phase change material into powder solid.It not only increases the specific surface area of the phase change material,but also improves the heat transfer efficiency,so it has a wide application value in heat transfer,energy storage and temperature control.Based on amount of literature research,we selected the appropriate phase change materials and shell materials,prepared some groups of phase change microcapsules with docosane as the core and titanium dioxide as the shell material.According to changing the single variable conditions of the experiment,we determined the best preparation ratio of the microcapsules.On this basis,the micro morphology of phase change microcapsules was screened and their thermophysical properties were tested.Then,the phase-change microcapsules with the best performance were prepared into phase change slurry.The stability and thermal properties of the phase change slurry added with phase change microcapsules were tested,and the nano phase change slurry with the best performance was determined,which laid the foundation for the subsequent practical application of the thermal slurry in PV / T solar energy collection system.The main conclusions of this paper are as follows:(1)Scanning electron microscopy was used to observe the micro morphology of the phase-change microcapsules.The phase-change microcapsules prepared in this paper are spherical in shape,complete in structure,uniform and smooth in surface,no damaged or large agglomerated particles are found,and the particles have good dispersion,and the particle size of the microcapsules is between 2-5μm.(2)According to the thermophysical property test,by changing a single experimental variable,the phasechange microcapsules prepared under different experimental conditions were compared and analyzed.Finally,when SDS was selected as emulsifier,the ultrasonic time was 10 min,pH value was 3.5,emulsifier mass fraction was 0.45 g,and core-shell ratio was 1:1,the performance of the phase-change microcapsules was the best.(3)Among the five dispersants,CTAB(cetyltrimethylammonium bromide)is the best one,and all the indexes of the phase change microcapsule slurry are in accordance with the characteristics of thermal fluid required by PV/T solar energy system.The research results of this project provide a favorable theoretical basis and data support for the practical application of phase change microcapsule slurry in solar energy collector system in the future.