Shear Flows of Paper-Pulp of Varying Concentrations

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UDС

676.024

DOI:

10.17238/issn0536-1036.2015.2.133

Abstract

Shear flows of paper-pulp occur in various devices in paper industry machines, for example, between the rotor and sieve pulpers, grading machines, in eddy flows of centricleaners, in converging ducts of flow boxes, in sensing elements of concentration meter. Thus, in a wid-er technological mass concentration range of 0.5 ? 5 %, the degree of mass dispersion (the level of flocculation) is of importance, which should be comparable to the sieve holes of 10 ? 0.1 mm or to a required size of flocculation of the papermachine. Rheology and paper - pulp deflocculation is covered in many studies, in which, however, it is difficult to trace the patterns of change of the rheological parameters and degree of mass dispersion depending on its concentration. Adverse flows in the known viscometers used to measure the rheological properties of multicomponent non-Newtonian ambient, such as pa-per - pulp, makes it difficult to identify these patterns. In this paper, in an experimental vis-cometer a homogeneous shear flow of paper – pulp of variable consistency was created in the gap between the rings. One ring was rotating at a variable speed, and the other was fixed, which allowed defining the experimental dependence of the stresses of the average velocity gradient in laminar, transient and turbulent flow cycles, to construct a characteristic curve of viscosity of variable mass concentration on the velocity gradient and get their ana-lytical description. On its based and two-layer turbulence model, a dimensionless velocity distribution was defined, as well as the boundary layer thickness in different modes of shear flow, which is an important characteristic of the flow between the rotor and the sieve of the sorting equipment. Representation of characteristic curve of stresses to velocity gradient at a variable concentration as characteristic curves of stresses to concentration at variable rota-tional speed of the wall is reported. Comparison of the latter with the characteristics of the known concentration meters demonstrates their good quality convergence. A scheme of the floccules collapse in a shear flow is also represented. Application of the known formulas of fluid mechanics to this scheme, taking into consideration the experimental characteristics, shows analytical and graphical dependencies of increase of the degree of mass dispersion (floc size reduction) of various concentrations with increasing velocity gradient that corre-sponds to the known data.

Authors

Yu. A. Tikhonov, Doctor of Engineering, Professor 

Affiliation

Saint Petersburg State Technological University of Plant Polymers, Ivana Chernyh street, 4, Saint Petersbuгg, 198095, Russia; e-mail: tamara_tpt@mail.ru

Keywords

shear, velocity gradient, viscosity, concentration of mass, size of flocculation, the boundary layer thickness.

References

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