Preparation And Physical Properties Of Silver Nanofluids With Different Morphologies

The nanofluids were prepared by adding metal or metal oxide nanoparticles into the liquid,they have good heat transport properties and excellent spectral absorption performance,which are used in the direct absorption type solar collector as the working fluid,which can effectively improve the thermal utilization efficiency.In this paper,the preparation of Ag-EG nanofluids with different morphology was studied,and the thermal properties of nanofluids such as thermal conductivity,viscosity,wettability and thermal characteristics were analyzed also.The main work is as follows:(1)The cubic shape and different size linear Ag-EG nanofluids were prepared by polyol method;The silver nanorods were prepared by seed method,then dispersed into glycal to prepare.rod-shaped Ag-EG nanofluids.(2)Using KD2 Pro thermal physical analyzer measuring the thermal conductivity of Ag-EG nanofluid,then study the influence of the temperature,the mass fraction,particle size and morphology of silver nanoparticles on the thermal conductivity.The results showed that,With the increase of temperature,the thermal conductivity of Ag-EG nanofluids increases,When the temperature increases from 25? to 65?,the maximum thermal conductivity increases by 48.60%;With the increase of mass fraction,the thermal conductivity increases,and the cubic Ag-EG nanofluid increases by 57.99%;In addition,particle size and morphology are two factors affecting thermal conductivity.The cubic Ag-EG nanofluid has the highest thermal conductivity,followed by rod like and linear Ag-EG nanofluids;By analyzing the thermal conductivity of linear Ag-EG nanofluids with different particle sizes,it is found that the smaller the particle size is,the better the thermal conductivity is.Finally,the experimental values are compared with the calculated values of the theoretical model.It is found that the experimental values consistent with the theoretical values calculated by the H-C model,and the minimum error is 0.18%.(3)Using DV2 T viscometer measuring the viscosity of Ag-EG nanofluid,then study the influence of the temperature,the mass fraction,particle size and morphology of silver nanoparticles on viscosity.The results showed that,with the increase of temperature,the viscosity of Ag-EG nanofluid decreases,and when the temperature increases from 25? to 65?,the viscosity reduction rate is above 50%;The viscosity of Ag-EG nanofluids were increased with the increase of the mass fraction of silver nanoparticles;By comparing and analyzing the viscosity of linear nanoparticles with different particle sizes,it is found that the viscosity of nanofluids increases with the decrease of particle size;The viscosity of cubic Ag-EG nanofluids is lower than that of rodlike and linear Ag-EG nanofluids.Under the condition of 65?,when the mass fraction is 0.020 wt.%,the viscosity of cubic Ag-EG nanofluid is 6.83 mPa s,which is 9.80% higher than that of base liquid EG.Based on this,this paper compared experimental value with the calculated value of theoretical model,found that the experimental values consistent with the theoretical value of Godson model.(4)The wettability of Ag-EG nanofluid has carried on the experiment analysis,through the two aspects of surface tension and contact Angle.Then study the influence of the temperature,the mass fraction,particle size and morphology of silver nanoparticles on surface tension and contact Angle,the results found that Ag-EG nanofluids is less than the base fluid EG on both surface tension and contact Angle,the wettability of nanofluids are better than EG.The cubic-shaped Ag-EG nanofluid has the minimum surface tension and contact Angle,under the condition of 65?,when the mass fraction is 0.020 wt %,the surface tension is 45.042 mN/m,under the condition of 25?,the contact Angle is 27.5°.(5)Using UV/Vis spectrophotometer test the transmittance of Ag-EG nanofluids,and the device of photo thermal experiment used in the experiment was assembled by self,by which the photo thermal of Ag-EG nanofluid was measured.Then study the influence of the temperature,the mass fraction,particle size and morphology of silver nanoparticles on solar-thermal conversion characteristics thermal transfer characteristics.The experimental results show that the thermal conversion characteristics of nanofluid is better than EG,and when the mass fraction of nanofluid increased from 0.005 wt.% to 0.015 wt.% can aheieve the highest balance temperature,in the same time,the temperature rise rate were increased,when continue to add nanoparticles to the mass fraction of 0.020 wt.%,the solar-thermal conversion characteristics of nanofluids was decreased.The thermal properties of cubic-shaped nanofluids are best,the temperature difference is 12?,relative to EG,the increase rate of the highest equilibrium temperature increased by 26.64%.