Research On The Flow And Heat Transfer Characteristics Of Complex Fluid And The Motion Behavior Of Suspended Particles

As research on fluid mechanics steps further,the complexity of the research content is getting higher and higher.Complex fluids have sparked a flurry of research activity in academic field and industrial sectors.Complex fluid refers to a substance with a complex constitutive relationship between ideal solid and fluid,including non-newtonian fluids,nanofluids,granular flow system and other categories.Complex fluids exist widely in nature and industry.All kinds of body fluids,the oil——"blood" of modern industry,the polymer commonly in chemical industry,nanofluids-noval heat tranfer medium,electromagnetic rheological fluids in modern intelligent equipment and the haze recently focused by the public media are all complex fluids.The study of complex fluids is of great significance for industrial transportation,energy power,cryogenic refrigeration,biological medicine,atmospheric control,and communication technology.Based on the linear stability theory,fiber suspension flow theory,and nanoparticle dynamics theory,this paper has focused on two kinds of complex fluids——nanofluid and non-newtonian fluid,analyzed and summarized flow and heat transfer characteristics of the complex fluids and the dynamic behaviors of suspended particles.For nanofluids,the instability of spherical nanoparticle suspensions in shear flow is numerically studied,and the laminar and turbulent flow and heat transfer characteristics of nanofiber suspensions in pipe are explored.Hydrodynamic instability equations of nanofluids in a 2D channel flow and 3D jet flow are deduced for the first time and discreted via finite difference method.The effects of particle mass loading,Stokes number,Knudsen number,jet parameters,Reynolds number and axisymmetric azimuthal mode on hydrodynamic instability of nanoluids are evaluated.It is fould that flow instability of nanofluid gets facilitated normally as Knudsen number increases.Some exceptions are shown in this paper as well.Then this paper numerically studies the flow and heat transfer characteristics ot 3D laminar and turbulent pipe flow containing rod-like particles with the wall temperature holding constantly.The impacts of nanofiber volume fraction,nanofiber aspect ratio on the flow friction and heat transfer characteristics in different flow state are evaluated.The affecting mechanism is analysed.The expressions of friction factor and Nusselt number as a function of particle volume concentration,particle aspect ratio,and Reynolds number are derived based on the numerical data.For turbulent flows,the effccts of nanofiber volume fraction and aspect ratio on energy performance evaluation criterion(PEC)are also studied,and the mathematical model of PEC varing with nanofiber volume fraction and aspect ratio is derived.For non-newtonian fluids,the lattice boltzmann method is adopted to study the dynamic behavior of center-pinned particle and mobile particle pair in channel filled with power law fluid.This paper analyzes the different rotational behavior of the center-pinned particle in channel flow and its influencing factors.The phenomenon of "anomalous rotation" of the center-pinned particles suspended in the confined non-newtonian flow is found.The"anomalous rotation" of the particles is mainly contribututed by flow inertia.Through the analysis of the shear stress exerted on the static particle surfaces and the pressure near the vicinity of the static particle,the mechanism of "anomalous rotation" of the center-pinned particle is explained.At last,the particle pair's motion in power-law fluid flow confined in a channel is numerically investigated via direct numerical simulation.The motion trendency that two particles seperate rapidly at first,then keep a stable distance and reach a stable repeling state finally,is fould in this paper.An excption that two particles would approach finally in shear-thinning fluid flow at a small initial distance is discovered as well.