Analysis Of Unsteady Stagnation-Point Flow,Heat And Mass Transfer Of Non-Newtonian Fluid

The stagnation-point flow of non-Newtonian fluids has an extensive background of applications,such as industry,agriculture and manufacturing,and it has drawn the attentions of many researchers.In this paper,the Maxwell fluid,Oldroyd-B fluid and Oldroyd-B-power-law fluid in non-Newtonian fluids are taken as the research objects,and unsteady stagnation-point flow,heat and mass transfer over the stretching sheet or the wedge are analyzed.In the first part,the unsteady stagnation-point flow of upper-convected Maxwell nanofluid past a wedge is discussed.The wedge is embedded in a porous medium.Baesd on Cattaneo-Christov double diffusion model,heat and mass transfer processes are simulated.Meanwhile,the effects of thermophoresis,Brownian motion and convective boundary conditions are considered.Ordinary differential equations after similar transformations are manipulated by the Homotopy Analysis Method（HAM）.In addition,the entropy generation of the fluid during stagnation-point flow,heat and mass transfer is scrutinized,and the variation trend of entropy generation is accounted by altering the values of associated parameters.The results show that when the stagnation-point parameter increases,the flow velocity accelerates.The progressing value of Reynolds number brings about more friction force of the fluid,thus enlarging the amount of entropy generation.In the second part,three nanofluids with volume fraction of 5%are prepared with 2g/L xanthan gum solution as the base fluid,copper oxide（Cu O）,aluminum oxide（Al₂O₃）and silver（Ag）as nanoparticles.The thermal conductivity of the base solution and nanofluids are measured by a thermal conductivity meter.Then,the unsteady stagnation-point flow of Oldroyd-B-power-law nanofluid with the characteristics of viscoelasticity and shear thinning simultaneously is addressed.Relaxation-retardation heat flux model is applied to describe behaviors of thermal relaxation and thermal retardation in heat transfer process.Different from the viscous dissipation of Newtonian fluid,based on the constitutive relation of Oldroyd-B-power-law fluid,the effect of relaxation-retardation viscous dissipation is scrutinized.The solutions of the equations are yielded by employing the double-parameter transformation expansion method with the base function method.The results show that as the Eckert number hikes,the temperature of the fluid is lowered and the thermal boundary thickness becomes thinner.Compared with Cu O-xanthan gum nanofluid and Al₂O₃-xanthan gum nanofluid,Ag-xanthan gum nanofluid has the strongest heat transfer ability.The third part mainly discusses the unsteady slip flow of the upper-convected Oldroyd-B fluid over the wedge.The process of heat transfer and the effect of thermal retardation time on heat transfer are simulated by the relaxation-retardation heat flux model.It also considers the influencing factors such as buoyancy,thermal radiation and convective heat boundary condition.The HAM is used to solve the ordinary differential equations.It is found that the velocity of the fluid boosts with the increase of slip parameter.For larger thermal radiation parameter,fluid temperature rises and the thickness of the thermal boundary layer becomes thicker.