Photo-thermal Conversion And Heat Storage Characteristics Of Magnetic Latent Functionally Thermal Fluid

In recent years,people's awareness of exploring renewable energy has been on the rise due to the increasing energy shortage and environmental pollution.Solar energy,as the most abundant renewable energy in the world,can effectively alleviate the increasing energy and environmental problems.At present,as a typical solar energy utilization technology,solar energy photo-thermal utilization can efficiently convert solar energy into heat energy and store it.For the direct absorption solar energy collecting system,the combination of nanofluids prepared by photo-thermal conversion materials and latent heat energy storage technology can further improve the photo-thermal conversion performance and heat storage capacity of the collector.In this paper,two kinds of magnetic latent functionally thermal fluids with photo-thermal conversion characteristic were developed and then applied in direct absorption solar energy collecting system to investigate the photo-thermal conversion and heat storage characteristics.Among them,the carbon-based nanomaterials served as photo-thermal conversion material,and magnetic phase change microcapsules served as phase change energy storage materials.At first,magnetic phase change microcapsules were prepared by in situ polymerization,which realized the permanent solid-state of phase change materials.The synthesized magnetic phase change microcapsules were spherical in shape and had a compact core-shell structure,showing excellent magnetic response and phase change energy storage properties.The peak phase change temperature and latent heat of microcapsules was about 29? and 145.01 J g^-1,respectively.In addition,the microencapsulation technology can effectively improve the thermal stability of octadecane and avoid the leakage problem during utilizing.Then,the latent functionally thermal fluids were prepared by dispersing magnetic phase change microcapsules into multi-walled carbon nanotubes/water nanofluids.The experimental results showed that the latent functionally thermal fluids exhibited outstanding photo-thermal conversion performance and heat storage capacity when they are applied in the direct absorption solar collector.Specifically,as the concentrations of multi-wall carbon nanotubes and magnetic phase change microcapsules were 0.01 wt.%and 15 wt.%,respectively,the thermal fluid had the highest stored heat,which was about twice as that of deionized water.Furthermore,graphene oxide was selected to modify the previously synthesized magnetic phase change microcapsules,and the reduced graphene oxide modified magnetic phase change microcapsules were prepared by UV-assisted reduction method.In particular,the functional microcapsules realized the integration of photo-thermal conversion,phase change energy storage and magnetic controllability.Also,they had excellent magnetic response,light absorption and thermal properties.Additionally,the introduction of photo-thermal conversion materials had no obvious effects on the phase change characteristics of microcapsules.The latent functionally thermal fluid was prepared by dispersing reduced graphene oxide modified magnetic phase change microcapsules into deionized water.The photo-thermal conversion and heat storage characteristics of it were systematically studied as well.The experimental results showed that this kind of latent functionally thermal fluid has excellent photo-thermal conversion performance and heat storage capacity.Meanwhile,the thermal resistance between photo-thermal conversion materials and phase change materials was effectively reduced in this system.When the illumination intensity was500 W m^-2 and illumination time was 800 s,the stored heat of latent functionally thermal fluid was increased from 215.65 J,which was stored by deionized water,to391.95 J.In conclusion,the two kinds of magnetic latent functionally thermal fluids developed in this paper had shown excellent photo-thermal conversion performance and heat storage capacity,and have promising prospects in the field of solar energy utilization.There are 24 figures,9 tables and 117 references in this paper.