Study On Phase-change Heat Transfer Of Nanofluids

With the increasingly prominent energy problem,the research of phase changeenergy storage materials gradually enters the horizon.The main purpose of this paper is to improve the paraffin phase change energy storage properties of materials,by adding the high thermal conductivity of carbon nanotubes and nanoparticles of alumina,the preparation of nanofluid as emulsion and paraffin base composite material,develop a new type of phase change energy storage material,studies its coefficient of thermal conductivity and the changes of characteristic of the phase change energy storage.In the experiment,the paraffin wax/water emulsion was prepared by using agent in oil,and the paraffin emulsion with good stability and dispersibility was obtained.The quality scores were prepared by two steps of paraffin emulsion:0.05%wt%,0.1wt%,0.2wt%,0.4wt%,0.6wt%,0.8wt%,0.8wt%and 1.00wt%of Al₂O₃/emulsion,MWCNTs/emulsion nanofluids.The sedimentation method is used to find that the prepared nanofluid has good dispersion stability.Through Hot Disk Hot constant analyzer measurement emulsion,Al₂O₃/emulsion and MWCNTs/emulsion coefficient of thermal conductivity of nanofluids,found that the types of nanoparticles,mass fraction are factors influencing the emulsion nano fluid thermal conductivity.When the mass fraction of nanoparticles is larger,the coefficient of thermal conductivity of nanofluids as nanoparticles is gradually increasing with the increase of mass fraction,and MWCNTs/emulsion change rate coefficient of thermal conductivity of nanofluids is Al₂O₃/emulsion nanofluids is fast.Through to set up the test rig,measuring nano fluid phase change cooling curve of the process,the experimental results show that the emulsion of heat time is far less than deionized water,and the phase change of the nanofluids time associated with the mass fraction of nanoparticles,in the process of cold storage,the supercooling degree of nano fluid decreases gradually with the increase of the mass fraction of nanoparticles,and the starting time of phase-change nanofluids are greater than the emulsion of heat starting time,when the mass fraction of nanoparticles is bigger,its heat time gradually decreased with the increase of mass fraction;In the process of heat storage,carbon nanotubes and alumina nanoparticles have an influence on the phase transition process of nanofluids,but the influence of carbon nanotubes is more significant.Two-step method is also used in the experiment,by adding Span60 as the surfactant,the preparation of the mass fraction of 0.05 wt%,0.1 wt%and 0.2 wt%,0.5 wt%and 1.0 wt%,2.0 wt%and 3.0 wt%of paraffin base carbon nanotubes and paraffin base alumina composite material,and to measure the composite phase change thermal storage and cold storage process.The experimental results show that the cold curve of the paraffin base composite is affected by the quality fraction of the nanoparticles,the inner diameter of the heat exchange container,the content of the composites and the types of nanoparticles.