Preparation Of Silver/Carbon Nanocomposite Materials And Study On Its Nanofluid Properties

As a new type of heat transfer medium,nanofluid has broad application prospects in industrial production,microelectronic equipment,energy applications and other fields.However,it is difficult for nanofluids to have both high thermal conductivity and high stability in actual production applications,which severely limits the application of nanofluids.New types of carbon nanomaterials,especially graphene and carbon nanotubes,have been widely studied and applied in the field of nanofluids due to their unique structure,high specific surface area,high thermal conductivity,and strong mechanical properties.Especially,carbon-based composite nanomaterials synthesized from carbon nanomaterials and other nanoparticles have become a research hotspot in the preparation of high thermal conductivity and high stability nanofluids in recent years.However,graphene nanosheets are easy to stack and carbon nanotubes are prone to entanglement and aggregation,which reduce their stability in the base fluid and make it difficult to achieve theoretical performance in practical applications,which greatly limits their practical large-scale application in production.To solve this problem,this paper designed two carbon nanocomposite materials:One is a three-dimensional graphene-like porous carbon and silver nanoparticle composite material with a unique self-supporting structure;the other is a silver nanoparticle/carbon nanotube composite material.The preparation processes of the two composite materials were studied in detail,and the synthetic carbon-based nanocomposites were prepared into nanofluids,and their stability,thermal conductivity and rheological properties were systematically studied.The main findings of this article are as follows:(1)Using water-soluble polyvinyl alcohol(PVA)as a carbon source,nickel acetate as a catalyst,and potassium hydroxide as an activation pore former,research and adjust different experimental parameters to control the pore structure of three-dimensional graphene-like porous carbon(3D GPC).By adding silver salt during the preparation process,without adding any reducing agent,a three-dimensional graphene-like composite material(Ag/3D GPC)loaded with silver nanoparticles was synthesized,and the best preparation process was determined.The prepared 3D GPC has a high degree of graphitization and crystallinity,and its specific surface area is as high as 1592.7 m~2/g.It has a hierarchical porous structure of micropores,mesopores and macropores.The Ag nanoparticles have a particle size of about 10nm and are evenly distributed in 3D GPC inner surface.(2)Water and Ethylene glycol(EG)based nanofluids were prepared using the above-mentioned 3D GPC and Ag/3D GPC,and their properties were studied in detail.The results show that the nanofluid has excellent stability,thermal conductivity,and rheological properties.Without adding any surfactants,after 22 days of standing,the maximum sedimentation rate of0.08 wt%nanofluid is 80%and 31%,respectively.The nanofluid with low concentration(<0.1wt%)can be stably dispersed in the base liquid for six months.The thermal conductivity enhancement for the nanofluids with 0.1 wt%can reach 95.5%at 65℃compared with pure,which is as high as 1.253 W/(m.K).The viscosity of Ag/3D GPC water-based and glycol-based nanofluids obeys the Arrhenius model,which decreases with the increase of temperature and increases with the increase of mass concentration.(3)The combination of ultrasonic-assisted impregnation and chemical reduction is used to realize the controllable growth of silver nanoparticles on the surface(Ag/CNT-O)and inside(Ag/CNT-I)of carbon nanotubes.Due to the different positions where silver nanoparticles are loaded with carbon nanotubes,the size of the grown particles and the properties of the formed nanofluid are different.The Ag nanoparticles filled inside are around 5-10 nm,and those grown on the outside are around 10-15 nm.The stability and thermal conductivity of nanofluids are significantly improved.(4)Ag/CNT nanofluids were prepared without adding any dispersants,and the performance of Ag/CNT-O and Ag/CNT-I nanofluids was compared and studied.Ag/CNT nanofluid has good stability,thermal conductivity,and rheological properties.Under the same conditions,the stability of Ag/CNT-I nanofluid is higher than that of Ag/CNT-O nanofluids.The thermal conductivity of Ag/CNT water-based and glycol-based nanofluids increases with the increase of temperature and mass concentration.Under the same conditions,the thermal conductivity of f-CNT,Ag/CNT-I and Ag/CNT-O nanofluids all obey the law of Ag/CNT-I>Ag/CNT-O>f-CNT.The viscosity of Ag/CNT water-based and glycol-based nanofluids obeys the Arrhenius model.It decreases with increasing temperature and increases with increasing mass concentration.Moreover,under the same conditions,the viscosity of the two nanofluids is less than that of carbon nanotubes.