Study On The Radiation And Heat Conduction Properties Of Thiol-modified Copper Nanofluid

Nanofluid refers to a uniform fluid prepared by adding metal or non-metal powder(with a particle size of 1-100 nm)to the traditional heat exchange,and using a certain method to stably disperse the particles.Existing research conclusions confirm that nanofluids have better heat transfer capabilities than pure liquids,and have been widely used in new energy,chemical engineering,rapid cooling,aerospace,medical,electronics,and other fields.The direct absorption solar heat collection system is a new and efficient way to use solar energy.The fluid medium in the heat collector can absorb solar radiation energy and convert the solar energy into heat energy that can be used by people.Therefore,the working efficiency of the heat collection system depends on The light and heat characteristics of the heat collection medium,nanofluid has unique light and heat characteristics,theoretically suitable for application in direct absorption solar systems.In this paper,toluene and n-decane are used as the base fluids,and copper nanoparticles modified with dodecyl mercaptan as the solid phase,a stable and dispersed copper nanofluid is prepared,and the stability and radiation characteristics of the copper nanofluid are studied through experiments.And thermal conductivity,provides a theoretical basis for copper nanofluid into production and life applications.In this paper,a "two-step method" is used to prepare copper nanofluids.In order to improve the oil solubility and stability of copper nanoparticles,dodecyl mercaptan is used to modify the surface of copper nanoparticles.It is evenly dispersed in the base fluid.After the static sedimentation experiment and the spectrophotometric experiment,it is found that the copper nanofluid prepared in this paper can be dispersed for more than one week in a stable environment.The four factors of nanofluid temperature,ultrasonic dispersion time,nanofluid concentration,and surface modification have a greater impact on the stability of nanofluids.As the temperature and concentration increase,the stability of nanofluids deteriorates;the stability of nanofluids when ultrasonic oscillation is 3h The best,too short or too long ultrasonic dispersion time will lead to deterioration of fluid stability;copper nanoparticles without surface modification are difficult to disperse in non-polar liquids,and re-aggregate and settle within24 h after ultrasonic dispersion.After surface modification,the stability of the copper nanofluid is improved considerably.Test the transmittance and absorbance of copper-toluene nanofluid and copper-n-decane nanofluid in the visible-near infrared wavelength range through experiments,and study the three factors of volume fraction,particle size,and optical path on the radiation characteristics of the nanofluid Impact.Experimental results show that the radiation absorption capacity of nanofluids increases with the increase of volume fraction.The transmittance of copper nanofluids with a volume fraction of 0.30% is close to zero;the larger the nanoparticle size,the stronger the scattering effect and the smaller the nanofluid transmittance;The longer the test optical path,the longer the movement distance of the incident light in the nanofluid,the weaker the intensity of radiation passing through the nanofluid,and the smaller the transmittance.On the whole,the radiation absorption capacity of toluene and n-decane is greatly enhanced after copper nanoparticles are added.Copper nanofluids have better radiation characteristics in the visible and near-infrared,and are theoretically suitable for direct absorption as a heat collection medium.In the solar heat collection system.In this paper,the transient hot-wire probe method is used to measure the thermal conductivity of copper nanofluids under different experimental conditions,and the factors affecting the thermal conductivity of nanofluids are analyzed.The experimental results show that the thermal conductivity of the fluid is significantly increased after copper nanoparticles are added,this is because copper nanoparticles have a thermal conductivity value much higher than that of the base fluid;and the fluid temperature and concentration Two factors have a great influence on the thermal conductivity of nanofluids,but too high temperature and concentration will increase the agglomeration rate of nanoparticles and deteriorate the stability of nanofluids.The smaller the particle size,the larger the heat transfer area under the same volume fraction,the faster the Brownian motion of the particles,and the increase in thermal conductivity.However,the volume fraction of the copper nanofluid studied in this article is low(0.05%-0.30%),and the particle size has little effect on the thermal conductivity of the nanofluid.Surface modification of nanoparticles can improve the stability of copper nanofluids at higher temperatures(above 50°C).Therefore,copper nanofluids modified with dodecyl mercaptan have higher thermal conductivity at higher temperatures.Copper nanofluid without surface modification.The Maxwell model,Y&C model,Kumar model,and Prasher model were used to calculate the thermal conductivity of copper nanofluids with different volume fractions,and compared with the experimental data.It was found that the difference between the calculation results of the Prasher model and the experimental values was small,it is proved that factors such as nanoparticle size,shape,concentration and fluid microconvection have a certain influence on the thermal conductivity of nanofluids,but the mechanism of enhanced heat transfer of nanofluids still needs more in-depth study.