Preparation And Characterization Of Direct Photothermal Conversion Paraffin Pickering Emulsion

Direct solar thermal conversion is an important way to utilize solar energy comprehensively.In direct absorption solar collector(DASC),the properties of collector medium are considered the most significant factor influencing collector efficiency.At present,nanofluids are widely studied as heat collecting media;However,the energy storage mode of nanofluids is sensible heat storage,and energy storage are finite,which limit the development and utilization of DASC is greatly.So,this paper is dedicated to developing a new type of heat collection medium with good light-to-heat conversion performance and characterizing its light-heat characteristics.The main research contents and results are as follows:(1)In the present work,O/W type paraffin Pickering emulsion was prepared via high mechanical shear,using magnesium-aluminum double-layer metal hydroxide(Mg-Al LDHs)instead of chemical surfactant.The microscale morphology,particle size distribution,viscosity,stability,and thermal properties of the as-prepared paraffin Pickering emulsion were characterized by using scanning electron microscope,laser diffraction particle size analyzer,rheometer,multiple light scatter meter and differential scanning calorimeter,respectively.The results show that,with the increase of Mg-Al LDHs content from 1 wt.%and 5 wt.%,the mean particle size of paraffin Pickering emulsion decreased,while the viscosity increased significantly,resulting in better longterm stability of the emulsion.The subcooling of paraffin Pickering emulsion was suppressed completely via heterogeneous nucleation of paraffin,which was induced by Mg-Al LDHs nanoparticles absorbed at the water-paraffin interface.(2)A new paraffin Pickering emulsion was prepared by adding graphene oxide(GO),which integrated the functions of photothermal conversion,heat transfer and heat storage.The electrostatic interaction between Mg-Al LDHs and GO increased the viscosity of paraffin Pickering emulsion significantly,resulting in a better long-term stability.The photo-thermal conversion efficiency of paraffin Pickering emulsion improved dramatically with the increase of GO content up to 0.08 wt.%,while the latent heat remained unchanged.