Quasi-viscous flow

A comparison of the experimental values of the characteristic times t of the viscous flow and the calculated ones shows, that the preexponential multiplier is determined by not only the frequency of the oscillating movement of the particles into the quasi-lattice of the liquid but also by the entropy factor. This leads to the conclusion that the activation entropy at the viscous flow of the liquid can be found via the same expression, as in a case of the entropy at the phase transition by the first kind. Obtained expression for the activation entropy AS = AH /1 permits to explain the low values of XQ 2h/kT for the associated liquids and the observed slope opposition for the dependence between and the activation eneigy of the viscous flow. 

Table I provides a guide to the diverse quasi-equilibrium methods used to detect Tn as reported in ref. 1 and cited later in this report. Dielectric loss, which involves only microscopic viscosity, is discussed with Fig. 30 of ref. 1. Dynamic mechanical loss, when measured in tension or bending, does not appear to involve viscous flow as discussed in Table VI and Fig. 31 of ref 1.

More recent experiments [62] concerning the viscous sublayer have shown a three-dimensional structure for turbulence near the wall. In a plane normal to the mean flow, counterrotating eddy pairs are involved (Fig. 6c), whereas in the direction of the mean flow, the motion is quasi-periodic (as described earlier). Since the wavelength along the mean flow is much larger than along the perimeter of the tube, a simplified bidimensional model may account only... 

Example 6.14 Squeezing Flow between Two Parallel Disks This flow characterizes compression molding it is used in certain hydrodynamic lubricating systems and in rheological testing of asphalt, rubber, and other very viscous liquids.14 We solve the flow problem for a Power Law model fluid as suggested by Scott (48) and presented by Leider and Bird (49). We assume a quasi-steady-state slow flow15 and invoke the lubrication approximation. We use a cylindrical coordinate system placed at the center and midway between the plates as shown in Fig. E6.14a. 

Table 6.1 gives the most widespread rheological models of nonlinearly viscous fluids. Most of these models do not describe all aspects of the actual behavior of nonlinear viscous fluids in the entire range of the shear rate. Instead, they explain only some specific characteristic features of the flow. Table 6.1 contains quasi-Newtonian relations of two types, namely,... 

Here S(x) is the film thickness with x measured vertically upward from the pool level primes denote differentiation with respect to x. Because of the quasi-one-dimensional character of the flow in the lubrication-film region, we have taken 1. It follows that the Navier-Stokes equation can be written as a balance between viscous and surface tension forces ... 

Electroconvection in nematics is certainly a prominent paradigm for nonequilibrium pattern-forming instabilities in anisotropic systems. As mentioned in the introduction, the viscous torques induced by a flow field are decisive. The flow field is caused by an induced charge density p i when the director varies in space. The electric properties of nematics with their quite low electric conductivity 10 (fl m) ] are well described within the electric quasi-static approximation, i.e. by charge conservation and Pois-... 

It is evident that for a description of such flows the viscosity of the fluid has to be introduced. This has been done by LIM, CHONG PERRY (1980) who showed that there exists a linearised solution of the Navier-Stokes equations which they called a viscous tornado or a complex eigenvalue critical point flow. This solution permits a vortex line to be quasi attached to the wall under non-slip conditions in the sense that a versatil spiral flow around a separation streamline arrises. The concept be scetched as follows The flow near a separation point at the wall can be classified by the form... 

Darcy s law adequately models typical RTM applications in which the Reynolds number (the ratio of inertial force over viscous force on the liquid resin) is small. This allows one to ignore the inertial forces and assume a quasi-steady resin flow. ... 

Details of the kinematics within the mold, which would be required for the computation of stress distributions, require solution of the full (quasi-static) momentum equation with an appropriate stress constitutive equation. This can be done routinely for purely viscous fluids for flows with two velocity components... 

---