Study On The Rheologicalproperties Of Viscoelastic Fluid Based Nanofluid

The viscoelastic fluid such as aqueous solution of surfactant may cause a dramaticfrictional drag reduction in turbulent flow state, but a very serious heat transferdeterioration always occurs simultaneous. Nanofluid fluid can enhance the heat transferperformance of a heat transfer systems, however the extra flow resistance will beintroduced caused by the suspended soild particles. The combination of these two kindsof fluid named viscoelastic fluid based nanofluid brings the advantages of fluidresistance reduction and heat transfer enhancement, which is meaningful in practicalengineering application. The rheological properties of these fluid which are basicphysical properties for theory research and practical application need to study deeply.Firstly, the related knowledge and basic method of rheology and the experimentsystem are introduced. The detailed preparation method of nanofluid is as follows: theaqueous solution of cetyltrimethylammonium chloride (CTAC) and sodium salicylate(NaSal) with1:1in mass ratio is used as viscoelastic base fluid and several differentkinds of nanoparticles are tested, such as Cu, Ag, et al. Subsequently, the suspensionstability of prepared viscoelastic fluid based nanofluid is analysed, the time-dependedbehavior and thixotropy are carried out.The shear viscosity varied with shear rate with different volume of nanoparticles,different concentration of base fluid, different temperature is measured when the shearrate ranged from0.01s-1to100s-1. The relaxtion time of test fluid is got by a recoverytest and frequrcy sweep test. The rheology results show that the viscoelastic behaviourof fluid depends on the concentration of based fluid and the materials of nanoparticles.By the detailed analysis on the rheology results of nanofluid with Cu nanoparticlessuspended, the results show that the nanoparticles can increase the zero shear viscosity,accelerate the shear-thinning effect and enhance the viscoelasticity. Meanwhile, thetemperature can deaden the viscoelastic of nanofluid.Through the comparative analysis of viscoelastic constitutive models such as theO-B model，the FENE-P model，and the Giesekus model with experimental shearviscosity of test fluid, the Giesekus model is selected as the best viscoelasticconstitutive model to describe the viscoelasticity of test fluid. The experimentalviscosity correlation which based on Giesekus model and related to the concentration ofnanoparticals and based fluid is got by large amount of experiment data. And theexperimental viscosity correlation is also validated. From the N1curves got by theexperimental viscosity correlation, the nanoparticals can be proved to enhance theviscoelasticity of the nanofluid again.Finnaly, a dynamic thermal conductivity measurement experiment is carried out.The results show that the shear-rate-depended thermal conductivity and viscosity behave similar variation trend.