Investigations Of Heat And Mass Transfer In Boundary Layer Shear Flow Of Complex Fluids

The complex fluids always exhibit the anomalous heat and mass transfer behaviors.People desire to explore novel theoretical and experimental approaches to study all these behaviors which should be described by complex non-linear constitutive models rather than traditional simple linear models.In this work,we mainly focus on the heat and mass transfer in boundary layer shear flow of the complex fluids,such as power law non-Newtonian fluids,the dispersed micro/nano-particles suspensions.The generalized power law diffusion(N-diffusion)theories are employed to characterize the non-linear rheology and heat-conduction constitutive relations of the power law non-Newtonian fluids,and the convection heat transfer in such fluids with various boundary conditions,for instance the inclined plate,the moving plate,suction/injection,nonuniformly heated plate,has been solved and analyzed in detail.The typical non-Newtonian behaviors considered as intrinsic properties are controlled by power law index n as an important empirical parameter,whereas other boundary conditions generate the analogous effects on the different power law fluids.Moreover,the N-diffusion model is also found to describe availably the shear-thinning behavior due to the collective micro-rotation effects of particles in a micropolar fluid,consequently the non-linear rheology and heat-conduction constitutive models are derived for a micropolar fluid firstly.It is the first time to achieve the integrated measurement of rheology and heat-conduction of the non-Newtonian fluids with shear flow by designing independently "integrated test system for rheology and heat conduction of complex fluids".The experiment results by testing a typical shear-thinning fluid support well the evidence that the effective thermal conduction of a pseudoplastic non-Newtonian fluid depends on shear rate obviously and the N-diffusion model mentioned earlier can be used to model such dependency relationships exactly.We also study the anomalous heat and mass transfer in the viscoelastic Maxwell fluid base micro-particles suspension by utilizing the Cattaneo-Christov constitutive model involving relaxation diffusion item.As a result,a framework of viscoelastic relaxation parameters has been constructed uniquely in characterizing the anomalous transport process.Besides,the investigations of heat conduction enhancement in static nanofluids display that the nano-particle interfacial ordered layer(IOL)plays an important role on it,in particular a multilevel equivalent aggregation(MEA)model based on IOL theory is proposed originally to modify classical Maxwell thermal conductivity model.The predictions by modified model are not only highly in agreement with the popular experiments data,but all the parameters,such as particulate aggregation ratio and interfacial layer thickness,are proved in the acceptable ranges.Furthermore,we report the critical role of time-dependent fractal aggregation kinetic on the unsteady thermal convection of the nanofluids,which presents the variable effective viscosity and thermal conductivity due to non-equilibrium particulate aggregation.Interestingly,a characteristic time ratio tp/tm(tp is the aggregate time,and tm is the mean convection time)is introduced to connect non-equilibrium aggregation and unsteady thermal convection processes closely.A detail discussion about the effects of time,fractal dimension and initial particles volume fraction on the flow and heat transfer of nanofluids.Particularly,two kinds of empirical fractal formulas are presented to predict the momentum and enthalpy boundary layers’ thickness for different initial particles volume fraction.In this work,we employ some applicable similarity transformations for original physics problems,and the highly nonlinear difficulties caused by the complex constitutive models are overcome by incorporating approximate analytical techniques and numerical methods together,which are convenient to probe the effects of all the parameters we concerned on the anomalous transport processes of the complex fluids.