Pdf general weissenberg effect in free surface rheometry. Weisenberg effect article about weisenberg effect by the. This is a direct consequence of the normal stress that acts like a hoop stress around the rod the effect is named after karl weissenberg. Close encounters of the polymer kind lesson close encounters lesson handout for students answer key polymers weissenberg effect entropy enthlapic interactions assessment 1. The behavior of the free surface was noted as a function of time and rotational speed.
The weissenberg effect in molten polymers sciencedirect. The higherorder theory of the weissenberg effect is developed as a perturbation of the state of rest. General weissenberg effect in free surface rheometry part ii. We show here, however, that the effect can occur with simple newtonian fluids. Pdf general weissenberg effect in free surface rheometry part ii. These data agree with the results of investigations of fixed supramolecular structures, for example, with the work of anderson, give information on the dynamics of the behavior of polymer structures from the moment of their appearance, and reflect the actual. Shearing in the flow of the liquid concentrically around the rotating rod causes the component of the stress normal to the circular flow direction to become greater in magnitude compared to the two other mutually perpendicular components. Viscoelastic fluids weissenberg effect viscoelastic fluids, such as dough and certain polymers, tend to climb up rotating shafts instead of drawing down a vortex. The high weissenberg number problem a 30 year old mystery. With the advantages of a higher lengthwall thickness ratio and a more stable free surface compared to those of the traditional weissenberg effect twe, the microscale w. This phenomenon is related to the elasticity of the fluid. The numerical technique is based on the projection method to simulate viscoelastic twophase. The relaxation time weissenberg number, we when we is small additional newtonian viscosity. General weissenberg effect in free surface rheometry part.
Instead of being driven away from a spinning object, it starts climbing. Corrections to capillary flow michigan technological university. They deter mined the climbing constant for these fluids and further extended the definition of the weissenberg effect to include the deformed free surface on. Weissenberg effect in the thick white of the hens egg nature. The oldroyd a and the walters a fluids display the negative weissenberg effect. The weissenberg effect makes liquid climb like spaghetti. A newtonian liquid was observed to climb up a rotating shaft whose tip was initially just in contact with the liquid surface.
Weissenberg effect article about weissenberg effect by the. This effect is due to the normal stresses that the shear induces. The hollow bob 20 a is attached to a bob shaft 10 a and is submerged in a test fluid 40 a. Rotating a rod in a ferrofluid above some critical angular velocity exhibits this phenomenon. On the weissenberg effect of turbulence article pdf available in theoretical and applied mechanics letters 94. This effect is usually illustrated by a ferrofluid magnetic fluid, as in this demonstration. The normal stress effect of a viscoelastic fluid generated in a viscometric flow, i.
In the weissenberg effect, a nonnewtonian fluid tends to climb up the walls of a spinning rod. These data agree with the results of investigations of fixed supramolecular structures, for example, with the work of anderson, give information on the dynamics of the behavior of polymer structures from the moment of their appearance, and reflect the actual processes. Evidence that it is a numerical phenomenon but inconclusive whether higher resolution delays of promotes breakdown. Viscoelasticity was found to have little effect for. This is called the weissenberg effect and is very difficult to model. This discrepancies can be rooted to the definition of the climbing constant. The photograph shows the flow of a solution of polyisobutylene. Normalstress coefficients and rod climbing in colloidal dispersions. Weissenberg effect and its dependence upon the experimental.
In your own words, describe what enthalpic and entropic interactions are. The experiment was performed by matt mason and jaden t. In the case of the resin with the lowest molecular weight and the highest. Secondary flows associated with the weissenberg effect nature. The perturbation induces a slowmotion expansion of the stress into rivlinericksen tensors in combinations which are completely characterized by five viscoelastic parameters. Jul 14, 2007 the three different fluids shown in the video, all of which exhibit the weissenberg effect, are. The deborah and weissenberg numbers rob poole school of engineering university of liverpool, united kingdom since their introduction to the literature nearly fifty years ago the deborah and weissenberg numbers have proved invaluable for rheologists in quantifying viscoelastic effects. A hollow bob 20 a with a plurality of circumferentially spaced holes 30 a. In this work a finite difference scheme to simulate the weissenberg effect is presented. This is a direct consequence of the normal stress that acts like a hoop stress around the rod. The effect of viscoelasticity on the stability of a pulmonary.
Normal stresses and weissenberg effect, journal of rheology. The perturbation is given in powers of the angular frequency. Corrections to capillary flow slip at the wall mooney analysis. The weissenberg effect is a phenomenon that occurs when a spinning rod is inserted into a solution of elastic liquid. The reason for this breakdown has remained somewhat of a mystery. The three different fluids shown in the video, all of which exhibit the weissenberg effect, are.
Video a shows a rod, with its end immersed in this fluid, being rotated. Higherorder theory of the weissenberg effect journal of. The weissenberg effect or rodclimbing experiment in this video clip a dilute 0. Download free acrobat reader dc software, the only pdf viewer that lets you read, search, print, and interact with virtually any type of pdf file. This phenomenon occurred when the rotation speed was increased above a. Lecture 16 free surface flows applied computational fluid. General weissenberg effect in free surface rheometry part i.
Normal stresses and weissenberg effect normal stresses and weissenberg effect kundu, pijush k. Dec 16, 2007 this experiment is an attempt to create the weissenberg effect in common fluids by spinning a stainless steel rod in a fluid reservoir. A theory for surface elevation in the weissenberg effect. A couette flow generated by a cylinder rotating perpendicular to the free surface of a fluid is considered and the equations of motion are solved to yield an expression for the surface shape in the vicinity of the rod. Preliminary results indicate that the same stabilizing effect occurs with fem as well 9. This paper reports the results of an experimental investigation to determine the climbing constants of viscoelastic liquids in the rotating rod geometry with two layers of viscoelastic liquids and the results of an investigation which describes the effects of eccentricity on the free surface shape of a nonnewtonian liquid in motion between eccentric cylinders. How to do the weissenberg effect science experiment science. One manifestation of normal stresses is the appearance of rod climbing the weissenberg effect in a system where a rotating shaft is immersed in a. Weissenberg method article about weissenberg method by the.
However, when a rotating rod is immersed in a concentrated polymer melt or solution, the meniscus climbs the rod. The microscale weissenberg effect for highviscosity solution. The ratio t r t f is a dimensionless number of particular significance in the study of flow of nonnewtonian fluids. One of the main challenges imposed in this simulation is to provide numerical methods which achieve high elasticity rate and that represent the correct shape of the free surface. Such rob climbing behaviour is referred to as the weissenberg effect. The flow of a secondorder fluid with a free surface between two coaxially mounted cylinders of finite length, the inner one of which is rotating, is being. In the experiment a rod is rotated with its end immersed in the fluid outlined above.
The weissenberg number ws is named after karl weissenberg, an early worker in the field of nonnewtonian fluids. Oct 08, 2008 the climbing effect of a viscoelastic fluid when stirred by a spinning rod is well documented and known as weissenberg effect wei et al, 2006. In order to understand weissenbergs contribution to xray crystallography it is necessary to appreciate the background to the subject when he entered it around 1922. In this work, a comparison of the flow around a spinning disk for a newtonian and a nonnewtonian liquids. Rod climbing the weissenberg effect a dilute solution 0. Weissenberg effect, which is commonly observed whenever a stirring rod is rotated normal to the free surface of a concentrated polymer solution. We have observed that this effect can appear when the fluid is stirred without a rod. On the emergence of weissenberg effect, the gel was stirred manually for one and a half hours. An alteration of the normal stresses in a nonnewtonian fluid on account of elasticity, so that such a fluid, when placed between two concentric, rotating.
Close encounter of the polymer kind teachengineering. The steady free surface motion of a layered medium of viscoelastic fluids driven by a vertical rotating rod and the free surface motion of a viscoelastic fluid between vertical, eccentric, rotating cylinders is solved by means of domain. Instead of being thrown outward, the solution is drawn towards the rod and rises up around it. This paper reports the results of an experimental investigation to determine the climbing constants of viscoelastic liquids in the rotating rod geometry with two. By means of the weissenberg effect data on the deformation and cohesion of polymer structures in shear flow may be obtained. A method of studying crystal structure by xray diffraction in which the crystal is rotated in a beam of xrays, and a photographic film is moved parallel to the axis of rotation. Possibility of using the weissenberg effect to investigate. The fluid model chosen is one for which the shear stress. Weissenberg effect the weissenberg effect is the instance where a polymer travels up a rod, in contrast to say water that moves away from the rod as it spins. Vu department of chemical engineering, mcgill university, 3480 university street, montreal, quebec h3a 2a7 canada received july 14,1977 summary the climb of viscoelastic liquids up a. Us9157846b1 bob for testing rheology and overcoming the.
Rod climbing the weissenberg effect nonnewtonian fluid. The free surface on a liquid between cylinders rotating at different speeds. Transportation of highly viscous solutions at the picoliter level with a rapid dynamic response is paramount for micronanofabrication. Weissenbergs influence on crystallography professor h.
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