Dynamic viscosity, definition

Note 2 See Definition 5.2, note 6 rj = M" co may be used for evaluating the dynamic viscosity. The same expression is often used to evaluate the shear viscosity. The latter use of this expression is not recommended. 

POISE (P). A unit of dynamic viscosity. The unit is expressed in dyne second per square centimeter The centipoise (cP) is more commonly used The formal definition of viscosity arises from the concept put forward by Newton that under conditions of parallel flow, the shearing stress is proportional to the velocity giadieut. If lire force acting on each of two planes of aiea A parallel to each oilier, moving parallel lo each other with a relative velocity V, and separated by a perpendicular distance X, be denoted by F. the shearing stress is F/A and the velocity gradient, which will be linear for a true liquid, is V/X. Thus, Ft A = q V/X, where the constant if is the viscosity coefficient or dynamic viscosity of the liquid. The poise is the CGS unit of dynamic viscosity. 

Relations (10.22) are quite similar to the definitions of dynamic viscosity r)(u>) and dynamic modulus G(u>), so that relations (10.23) are similar to the relations between the components of dynamic modulus and dynamic viscosity (equations (6.10)). 

In the definition of the Nu -number, the characteristic length is chosen to be a function of the dynamic viscosity til gravitational acceleration g, because the... 

The presence of this property in the system allows one to compose with the dynamic viscosity ri a path linking the concentration of momentum to the local pressure P (shear stress), which constitutes a definition for the operator ambiguously named kinematic viscosity... 

Particles moving relative to the surrounding air are subjected to a resisting force by collision with air molecules. This force is the same whether the particle moves through the air or the airflows past the particle. For small airborne aerosol particles the resisting force, or drag force (Fd), is described by Stokes law Fd = S.jr.q.U.D, to which several correction factors may be applied (as for the shape factor see definition). In this equation q is the dynamic viscosity of the air, U is the particle velocity (relative to the air) and D is the particle diameter. 

Indeed, by definition, the dynamic viscosity is q (m). j, = —, so that data points... 

In Eq. 59, t) is also called the dynamic viscosity. In Eq. 55, 7o is the instantaneous compliance (sometimes called the glassy compliance and denoted by 7g) and is associated with solid-like elastic behavior while 1 /cor] is associated with liquidlike viscous behavior, which leaves 7 and 7" as the terms that are thus associated with viscoelastic behavior. Again, the reader should note that some authors introduce the dynamic creep components differently, by burying these terms into the definitions of 7 and 7". If one goes along with the latter definitions, Eq. 55 becomes... 

It was made clear in Chapter II that the surface tension is a definite and accurately measurable property of the interface between two liquid phases. Moreover, its value is very rapidly established in pure substances of ordinary viscosity dynamic methods indicate that a normal surface tension is established within a millisecond and probably sooner [1], In this chapter it is thus appropriate to discuss the thermodynamic basis for surface tension and to develop equations for the surface tension of single- and multiple-component systems. We begin with thermodynamics and structure of single-component interfaces and expand our discussion to solutions in Sections III-4 and III-5. 

The dynamic response of a particle in gas-solid flows may be characterized by the settling or terminal velocity at which the drag force balances the gravitational force. The dynamic diameter is thus defined as the diameter of a sphere having the same density and the same terminal velocity as the particle in a fluid of the same density and viscosity. This definition leads to a mathematical expression of the dynamic diameter of a particle in a Newtonian fluid as... 

Moreover, for comparison the values of the effective diameter a, obtained from the expression for the dynamic shear viscosity for a system of soft spheres, are also presented in Table. More definitely, the formula... 

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