Hydrodynamics flow behavior

The viewpoint sketched above has been so far developed and applied mainly in the context of mechanics and thermodynamics of complex fluids (Grmela, 2009 and references cited therein, also Section 3.1.6 of this review). The coupling between macroscopic (hydrodynamic) flow behavior and the behavior of a microstructure (e.g., macromolecules in polymeric fluids or suspended particles or membranes in various types in suspensions) is naturally expressed in the multiscale setting. In this review we shall include in illustrations also... 

Dispersion of a soHd or Hquid in a Hquid affects the viscosity. In many cases Newtonian flow behavior is transformed into non-Newtonian flow behavior. Shear thinning results from the abiHty of the soHd particles or Hquid droplets to come together to form network stmctures when at rest or under low shear. With increasing shear the interlinked stmcture gradually breaks down, and the resistance to flow decreases. The viscosity of a dispersed system depends on hydrodynamic interactions between particles or droplets and the Hquid, particle—particle interactions (bumping), and interparticle attractions that promote the formation of aggregates, floes, and networks. 

In this chapter the regimes of mechanical response nonlinear elastic compression stress tensors the Hugoniot elastic limit elastic-plastic deformation hydrodynamic flow phase transformation release waves other mechanical aspects of shock propagation first-order and second-order behaviors. 

The preceding sections have demonstrated that dendrimers of lower generation are akin to branched polymeric structures. It is therefore to be expected that their flow behavior in dilute solution may be described in terms of the well-known concepts of dilute polymer solutions [14, 15]. Hence, dissolved dendrimers should behave like non-draining spheres. From an experimental comparison of and the immobilization of solvent inside the den-drimer can be compared directly since in this case the dendrimer may be approximated by a homogeneous sphere. Therefore R = 3/5 Rl where Ry, denotes the hydrodynamic radius of the dendrimer. This has been found experimentally [19]. 

Hydrodynamic Flow Models. The discouraging result with the previous approaches lead us reluctantly to the conclusion that we must know more about what goes on in the bed if we hope to develop a reasonable predictive flow model. In particular we must learn more about the behavior of rising gas bubbles, since they probably cause much of the difficulty. 

Small bubbles and flow uniformity are important for gas-liquid and gas-liquid-solid multiphase reactors. A reactor internal was designed and installed in an external-loop airlift reactor (EL-ALR) to enhance bubble breakup and flow redistribution and improve reactor performance. Hydrodynamic parameters, including local gas holdup, bubble rise velocity, bubble Sauter diameter and liquid velocity were measured. A radial maldistribution index was introduced to describe radial non-uniformity in the hydrodynamic parameters. The influence of the internal on this index was studied. Experimental results show that The effect of the internal is to make the radial profiles of the gas holdup, bubble rise velocity and liquid velocity radially uniform. The bubble Sauter diameter decreases and the bubble size distribution is narrower. With increasing distance away from the internal, the radial profiles change back to be similar to those before contact with it. The internal improves the flow behavior up to a distance of 1.4 m. 

Finally, a challenging problem is to discuss the influence of hydrodynamic flow fields on the phase behavior of polymer blends. This is of fundamental interest and of technological importance as well since stresses and corresponding deformations are encountered during processing of blends. Extension of studies to blend systems under external flow is necessary for the better understanding of structure formation in polymer blends outside equilibrium. 

Polymers can be confined one-dimensionally by an impenetrable surface besides the more familiar confinements of higher dimensions. Introduction of a planar surface to a bulk polymer breaks the translational symmetry and produces a pol-ymer/wall interface. Interfacial chain behavior of polymer solutions has been extensively studied both experimentally and theoretically [1-6]. In contrast, polymer melt/solid interfaces are one of the least understood subjects in polymer science. Many recent interfacial studies have begun to investigate effects of surface confinement on chain mobility and glass transition [7], Melt adsorption on and desorption off a solid surface pertain to dispersion and preparation of filled polymers containing a great deal of particle/matrix interfaces [8], The state of chain adsorption also determine the hydrodynamic boundary condition (HBC) at the interface between an extruded melt and wall of an extrusion die, where the HBC can directly influence the flow behavior in polymer processing. 

Koelman and Hoogerbrugge (1993) have developed a particle-based method that combines features from molecular dynamics (MD) and lattice-gas automata (LGA) to simulate the dynamics of hard sphere suspensions. A similar approach has been followed by Ge and Li (1996) who used a pseudo-particle approach to study the hydrodynamics of gas-solid two-phase flow. In both studies, instead of the Navier-Stokes equations, fictitious gas particles were used to represent and model the flow behavior of the interstial fluid while collisional particle-particle interactions were also accounted for. The power of these approaches is given by the fact that both particle-particle interactions (i.e., collisions) and hydrodynamic interactions in the particle assembly are taken into account. Moreover, these modeling approaches do not require the specification of closure laws for the interphase momentum transfer between the particles and the interstitial fluid. Although these types of models cannot yet be applied to macroscopic systems of interest to the chemical engineer they can provide detailed information which can subsequently be used in (continuum) models which are suited for simulation of macroscopic systems. In this context improved rheological models and boundary condition descriptions can be mentioned as examples. 

Many flow control methods based on liquid flow behaviors in micrometer-scale channels have been reported and demonstrated [3]. Hydrodynamic flow control methods using two-dimensional (2D) or 3D microstructures have been developed... 

Sood and Jackson (1970) have measured the collection efficiency for various aerosols by falling ice particles with nominal diameters in the range 1-10 mm. The general behavior of the capture efficiency with the size of aerosol particles was found to be similar to that for water drops. Quantitative differences arise from the different shape of the ice crystals and the corresponding changes in hydrodynamic flow patterns. 

This chapter describes the basic hydrodynamic characteristics and the general modes and mechanisms of heat transfer over a wide range of fluid-solid flow regimes. Since the flow behavior in the bed varies with the geometric configuration, different arrangements of the... 

The heat transfer characteristics in multiphase systems depend strongly on the hydrodynamics, which vary significantly with particle properties. The particle size, size distribution, and shape affect the particle and fluid flow behavior through particle-fluid and particle-particle interactions. A discussion of the hydrodynamic characteristics of packed and fluidized beds follows. 

The hydrodynamic study at a mesoscopic scale requires the understanding of instantaneous local solids flow structure. The time-variant flow behavior is complex. Analyses of the instantaneous flow structure require recognizing the following factors. 

The hydrodynamic component of the net force hr is obtained, as shown in Fig. 8.4.IB, by considering a second flow in which the particle is held stationary. In this local flow the fluid velocity vanishes on the collector surface and on the particle, while far from the particle the velocity approaches the stagnation flow behavior characterized by Eq. (8.4.1). From dimensional considerations... 

In contrast to the low-molecular liquids the high-molecular ones, namely polymeric solutions and melts, are called by viscoelastic . This means that the measured or effective viscosity of the polymeric solutions should has the frictional component, caused by the forces of friction between the layers of liquid, which are moving under the action of gradient rate of the hydrodynamic flow with different rates, and the elastic component, caused by the property of conformation of polymeric chain to do the resistance to the shear strain. Such fact, that a so-called anomalous behavior of the polymeric solutions, that is the dependence of their effective viscosity on gradient rate of the hydrodynamic flow is not properly for the low-molecular... 

Perhaps the most significant feature of hydrodynamic cavitation is that as the flow changes from nonturbulent to turbulent, bubble behavior changes from oscillatory to transient, and the latter resembles acoustic cavitation. Thus features similar to those of acoustic cavitation can be replicated in hydrodynamic flow by manipulating the level of turbulence. 

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