Viscous drag

On the other hand, when a liquid is sheared between two planes, and there is bonding with the planes, the bonds transfer momentum from the faster plane to the slower one. This is the liquid-like mode. In this case, the viscosity coefficient decreases with increasing temperature. 

In pure metals at low stresses and temperatures, the gas-like mode is important, and the momentum carriers are electrons and phonons. For pure, simple metals there is essentially no shear bonding at the cores of dislocations, so the 

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Dissipative particle dynamics (DPD) is a technique for simulating the motion of mesoscale beads. The technique is superficially similar to a Brownian dynamics simulation in that it incorporates equations of motion, a dissipative (random) force, and a viscous drag between moving beads. However, the simulation uses a modified velocity Verlet algorithm to ensure that total momentum and force symmetries are conserved. This results in a simulation that obeys the Navier-Stokes equations and can thus predict flow. In order to set up these equations, there must be parameters to describe the interaction between beads, dissipative force, and drag. 

The friction coefficient determines the strength of the viscous drag felt by atoms as they move through the medium its magnitude is related to the diffusion coefficient, D, through the relation Y= kgT/mD. Because the value of y is related to the rate of decay of velocity correlations in the medium, its numerical value determines the relative importance of the systematic dynamic and stochastic elements of the Langevin equation. At low values of the friction coefficient, the dynamical aspects dominate and Newtonian mechanics is recovered as y —> 0. At high values of y, the random collisions dominate and the motion is diffusion-like. 

Viscotester Viscotron Viscous drag Viscous flow Viscous liquids VI. See Viscosity index. 

Equation 36 must be corrected for changes in the drop shape and for the effects of the inertia of Hquid flowing through the orifice, viscous drag, etc (64). As the orifice or aperture diameter is increased, d has less effect on the drop diameter and the mean drop si2e then tends to become a function only of the system properties ... 

La.mina.r Flow Elements. Each of the previously discussed differential-pressure meters exhibits a square root relationship between differential pressure and flow there is one type that does not. Laminar flow meters use a series of capillary tubes, roUed metal, or sintered elements to divide the flow conduit into innumerable small passages. These passages are made small enough that the Reynolds number in each is kept below 2000 for all operating conditions. Under these conditions, the pressure drop is a measure of the viscous drag and is linear with flow rate as shown by the PoiseuiHe equation for capilary flow ... 

Several wick stmctures are in common use. First is a fine-pore (0.14—0.25 mm (100-60 mesh) wire spacing) woven screen which is roUed into an annular stmcture consisting of one or more wraps inserted into the heat pipe bore. The mesh wick is a satisfactory compromise, in many cases, between cost and performance. Where high heat transfer in a given diameter is of paramount importance, a fine-pore screen is placed over longitudinal slots in the vessel wall. Such a composite stmcture provides low viscous drag for Hquid flow in the channels and a small pore size in the screen for maximum pumping pressure. 

The cross-sectional area of the wick is deterrnined by the required Hquid flow rate and the specific properties of capillary pressure and viscous drag. The mass flow rate is equal to the desired heat-transfer rate divided by the latent heat of vaporization of the fluid. Thus the transfer of 2260 W requires a Hquid (H2O) flow of 1 cm /s at 100°C. Because of porous character, wicks are relatively poor thermal conductors. Radial heat flow through the wick is often the dominant source of temperature loss in a heat pipe therefore, the wick thickness tends to be constrained and rarely exceeds 3 mm. 

Viscous Drag. The velocity, v, with which a particle can move through a Hquid in response to an external force is limited by the viscosity, Tj, of the Hquid. At low velocity or creeping flow (77 < 1), the viscous drag force is /drag — SirTf- Dv. The Reynolds number (R ) is deterrnined from... 

Based on such analyses, the Reynolds and Weber numbers are considered the most important dimensionless groups describing the spray characteristics. The Reynolds number. Re, represents the ratio of inertial forces to viscous drag forces. 

The concentration boundary layer forms because of the convective transport of solutes toward the membrane due to the viscous drag exerted by the flux. A diffusive back-transport is produced by the concentration gradient between the membranes surface and the bulk. At equiUbrium the two transport mechanisms are equal to each other. Solving the equations leads to an expression of the flux ... 

The sequence, flocculation — coalescence — separation, is compHcated by the fact that creaming or sedimentation occurs and that this process is determined by the droplet size. The sedimentation velocity is monitored by the oppositely directed forces which form the buoyancy and the viscous drag of the continuous phase on the droplet ... 

Viscous Drag Jet (Ejector-boosted) Gas Lift Hydraulic Ram Electromagnetic Screw Centrifugal Rotating Casing (Pitot)... 

Nucleation due to crystal-to-ciystal contact is greater for equal striking energies than ciystal-to-metal contact. However, the viscous drag of the liquid on particle sizes normaUy encountered hmits the velocity of impact to extremely low values. The assumption that only the largest crystal sizes contribute significantly to the nucleation rate by ciystal-to-crystal contact permits a simple computation of the rate ... 

When a spherical particle of diameter d settles in a viscous liquid under earth gravity g, the terminal velocity V, is determined by the weight of the particle-balancing buoyancy and the viscous drag on the... 

Transition from Thermal Activation to Viscous Drag... 

Dislocation motion in the clear region between obstacles is determined by the viscous drag coefficient B [2]. The relationship between the applied shear stress and dislocation velocity is... 

Combination of effects of thermal activation and viscous drag then gives for an average dislocation velocity... 

Transition from thermal activation to viscous drag occurs when... 

J.N. Johnson and D.L. Tonks, Dynamic Plasticity in Transition from Thermal Activation to Viscous Drag, in Shock Compression of Condensed Matter— 1991 (edited by S.C. Schmidt, R.D. Dick, J.W. Forbes, and D.G. Tasker), Elsevier Science, Amsterdam, 1992, pp. 371-378. 

A. Kumar, F.E. Hauser, and J.E. Dorn, Viscous Drag on Dislocations in Aluminum at High Strain Rates, Acta Metall 16, 1189-1197 (1968). 

Surface area of torpedo = nDL Viscous drag force = nDLx... 

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