Viscosity

About: Viscosity is a research topic. Over the lifetime, 53600 publications have been published within this topic receiving 1061193 citations.

Viscosity, Plasticity, and Diffusion as Examples of Absolute Reaction Rates

Abstract: Since to form a hole the size of a molecule in a liquid requires almost the same increase in free energy as to vaporize a molecule, the concentration of vapor above the liquid is a measure of such ``molecular'' holes in the liquid. This provides an explanation of the law of rectilinear diameters of Cailletet and Mathias. The theory of reaction rates yields an equation for absolute viscosity applicable to cases involving activation energies where the usual theory of energy transfer does not apply. This equation reduces to a number of the successful empirical equations under the appropriate limiting conditions. The increase of viscosity with shearing stress is explained. The same theory yields an equation for the diffusion coefficient which when combined with the viscosity and applied to the results of Orr and Butler for the diffusion of heavy into light water gives a satisfactory and suggestive interpretation. The usual theories for diffusion coefficients and absolute electrical conductance should be replaced by those developed here when ion and solvent molecule are of about the same size.

The Penetration of a Fluid into a Porous Medium or Hele-Shaw Cell Containing a More Viscous Liquid

Abstract: When a viscous fluid filling the voids in a porous medium is driven forwards by the pressure of another driving fluid, the interface between them is liable to be unstable if the driving fluid is the less viscous of the two. This condition occurs in oil fields. To describe the normal modes of small disturbances from a plane interface and their rate of growth, it is necessary to know, or to assume one knows, the conditions which must be satisfied at the interface. The simplest assumption, that the fluids remain completely separated along a definite interface, leads to formulae which are analogous to known expressions developed by scientists working in the oil industry, and also analogous to expressions representing the instability of accelerated interfaces between fluids of different densities. In the latter case the instability develops into round-ended fingers of less dense fluid penetrating into the more dense one. Experiments in which a viscous fluid confined between closely spaced parallel sheets of glass, a Hele-Shaw cell, is driven out by a less viscous one reveal a similar state. The motion in a Hele-Shaw cell is mathematically analogous to two-dimensional flow in a porous medium. Analysis which assumes continuity of pressure through the interface shows that a flow is possible in which equally spaced fingers advance steadily. The ratio λ = (width of finger)/(spacing of fingers) appears as the parameter in a singly infinite set of such motions, all of which appear equally possible. Experiments in which various fluids were forced into a narrow Hele-Shaw cell showed that single fingers can be produced, and that unless the flow is very slow λ = (width of finger)/(width of channel) is close to , so that behind the tips of the advancing fingers the widths of the two columns of fluid are equal. When λ = 1/2 the calculated form of the fingers is very close to that which is registered photographically in the Hele-Shaw cell, but at very slow speeds where the measured value of λ increased from 1/2 to the limit 1.0 as the speed decreased to zero, there were considerable differences. Assuming that these might be due to surface tension, experiments were made in which a fluid of small viscosity, air or water, displaced a much more viscous oil. It is to be expected in that case that λ would be a function of μU/T only, where μ is the viscosity, U the speed of advance and T the interfacial tension. This was verified using air as the less viscous fluid penetrating two oils of viscosities 0.30 and 4.5 poises.

An Introduction To Rheology

Abstract: 1) What is rheology? historical perspective the importance of non-linearity solids and liquids rheology is a difficult subject components of rheological research. 2) Viscosity practical ranges of variables which affect viscosity the shear-dependent viscosity of non-Newtonian liquids viscometers for measuring shear viscosity. 3) Linear viscoelasticity the meaning and consequences of linearity the Kelvin and Maxwell models the relaxation spectrum oscillatory shear relationships between functions of linear viscoelasticity methods of measurement. 4) Normal stresses the nature and origin of normal stresses typical behaviour of N 1 and N 2 observable consequences of N 1 and N 2 methods of measuring N 1 and N 2 relationships between viscometric functions and linear viscoelastic functions. 5) extensional viscosity importance of extensional flow theoretical considerations experimental methods experimental results some demonstrations of high extensional viscosity behaviour. 6) Rheology of polymeric liquids general behaviour effect of temperature on polymer rheology effect of molecular weight on polymer rheology effect of concentration on the rheology of polymer solutions polymer gels liquid crystal polymers. molecular theories the method of reduced variables empirical relations between rheological functions practical applications. 7) Rheology of suspensions the viscosity of suspensions of solid particles in Newtonian liquids the colloidal contribution to viscosity viscoelastic properties of suspensions suspensions of deformable particles the interaction of suspended particles with polymer molecules also present in the continuous phase computer simulation studies of suspension rheology. 8. Theoretical rheology basic principles of continuum mechanics successful applications of the formulation principles some general constitutive equations constitutive equations for restricted classes of flows simple constitutive equations of the Oldroyd/Maxwell type solution of flow problems.