Document Type
Thesis
Date of Award
5-31-1988
Degree Name
Master of Science in Mechanical Engineering - (M.S.)
Department
Mechanical Engineering
First Advisor
Avraham Harnoy
Second Advisor
E. S. Geskin
Third Advisor
Anthony D. Rosato
Abstract
The object of this study is to understand two important characteristics exhibited by viscoelastic fluids at high shear-rates, and analyse their influence on practical applications Viscoelastic fluids, such as polymer solutions, when subjected to high shear stress, behave in a manner which has not been sufficiently analytically explained In experimental studies, such fluids have shown.
(a) Stress relaxation.
(b) Decrease of viscosity with an increase in shear rate.
(c) Slight decrease of viscosity with temperature.
(d) Normal stress differences in shear flow.
In this thesis an analytical explanation is given for two (a and b ) of these features This will allow a better prediction of viscoelastic fluid behavior under practical conditions and enable us to use these properties to our advantage Analysis of these two characteristics is done separately in two sections of this thesis.
The first section analyses and interprets the effect of stress relaxation in viscoelastic lubricants on dynamically loaded, short journal bearings An earlier study on squeeze film between plates has been extended to a journal bearing The loci of the journal center subjected to a dynamic load is solved for Newtonian and viscoelastic lubricants The effect of viscoelasticity on the loci and its variation under different loading conditions is examined.
The results show a marked improvement in the performance of viscoelastic lubricants over Newtonian lubricants Under an unsteady load the journal center orbits show reduced eccentricity, attitude angle and travel of the journal due to the elasticity of the fluid. The results imply superior lubrication performance with a reduced rate of wear.
The second section examines the role of shear thinning (viscosity reduction), in boundary layer flow of viscoelastic fluids past a submerged cylinder, using the Power law Prior studies have been done for flow around a sphere with an assumed velocity distribution in the boundary layer. In this study the velocity distribution is calculated to ensure a more accurate analysis. It is of particular interest to see the fluid separation behavior, since it has a significant influence on the drag force for high Reynold's number flow. The location of the separation point for the flow is determined and compared to that of a Newtonian fluid flow.
The results show a shift in the fluid separation in the downstream direction for viscoelastic flow. This causes a more uniform pressure distribution around the cylinder and so reduces the drag. This is in quantitative agreement with previous experiments.
This characteristic behavior of viscoelastic fluids can be used in important engineering applications. The drag force on a body moving through water, like a ship or a submarine, may be reduced by coating them with a layer of polymer Also the frictional resistance to the flow of a fluid through a pipe, can be reduced by coating the inside of the pipe with a suitable polymer.
Recommended Citation
Sood, Sudarshan S., "Investigation of high shear-rate viscoelastic flow" (1988). Theses. 3221.
https://digitalcommons.njit.edu/theses/3221
