File Name: cup and bob viscometer .zip
Uzeology derived from Greek rheos meaning 'flow' and logos meaning 'science' is the study f the flow or deformation of matter under the influence of stress. Rheology can be applied solids completely resistant to deformation , liquids moderately resistant to deformation and gases completely nonresistant to deformation. Pharmaceutical processing operations such as mixing of materials, filling and packaging into containers 2.
GENG 303 FLUID MECHANICS LABORATORY
Uzeology derived from Greek rheos meaning 'flow' and logos meaning 'science' is the study f the flow or deformation of matter under the influence of stress.
Rheology can be applied solids completely resistant to deformation , liquids moderately resistant to deformation and gases completely nonresistant to deformation. Pharmaceutical processing operations such as mixing of materials, filling and packaging into containers 2. Removal of product from package such as pouring from a bottle, extrusion from a tube, spraying liquids from atomizers and passage from syringe needle 3. Topical application of product onto skin 4. Physical stability of suspensions, emulsions and semisolids 5.
Bioavailability, since viscosity has been shown to affect the absorption rate of drugs 6. Release of drug from dosage forms and delivery systems. Elasticity Pure elasticity is achieved if the shape of the body is restored once the force is withdrawn.
Elasticity is the property of solid materials and Hooke's law is used to describe the elastic deformation of solids. Hooke's law of elasticity If stress is directly proportional to strain, the body returns to its original shape and size, after the stress applied has been relieved. The proportionality between stress and strain is quantified by the constant known as the modulus of elasticity or Young's modulus E unit: pascal. Viscosity Pure viscosity or pure viscous flow occurs if there is continuous movement during the applied force, and no restorative motion occurs once the force is withdrawn.
Viscosity is the property of liquid materials to undergo permanent or irreversible deformation and is explained by Newton's law of viscous flow. Newton's law of viscous flow To understand the fundamental components of viscous flow, consider Figure 3.
TWoparallel planes are a distance dx apart; the viscous body is confined between the planes. When force, P, is applied the top, plane A. As a consequence, there exists a velocity gradient dvldx between the' planes.
This velocity gradient over a distance is known as the rate of shear, D dvldx. According to Newton's law of viscous flow: Velocity. Viscosity is the internal friction in the fluid, i. Conventionally, viscosity is represented by n. Then rearranging Eq. Viscosity is defined as the tangential force per unit area, in dyne per cm-.
For dilute aqueous solutions, the common unit becomes the centipoise poise , cp. The viscosity of water is about 1 cp. The SI unit of viscosity is pascal second. One pascal second is equal to 10 poise. Example 3. The oil had the same viscosity as that of water. In liquids, the fall in viscosity is due to decrease in the intramolecular forces of ction. The variation of viscosity with temperature is expressed by an equation analogous - e Arrhenius equation of chemical kinetics:.
Based on Newton's law -ewtonian. Fluids that follow n-Newtonian fluids do not haviour is shown in Figure. The classification of fluids based on their rheological 3. Rheogram: Plot of rate of shear 1. Simple liquids, either pure chemicals or solutions of as a function of shear stress.
Viscosity of such fluids is independent of the rate of shear but depends on composition, pressure and temperature. Rheogram and viscogram 1. For Newtonian fluids, the rheogram is linear and passes through the origin, indicating that minimal shear applied will induce shear see Figure 3. The slope of such a curve is the fluidity and the inverse of slope is the viscosity of the fluid. Shear stress and shear rate are directly proportional and therefore a single viscometric point can characterize the liquid rheology.
For Newtonian fluids, the viscogram is a straight line parallel to the axis of rate of shear, indicating that Newtonian viscosity is independent of the rate of shear see Figure 3. These fluids instantaneously adapt to changing shear stress.
Time-independent non-Newtonian fluid behaviour can be of three types: plasticity, pseudoplasticity and dilatancy. Plasticity 1. Plastic materials or Bingham plastics require an initial finite force, called yield value, before any rheological flow can start. At shear stress values below the yield value, such plastic materials substances behave as elastic solids exhibiting reversible deformation, and above the yield value, they behave as Newtonian systems.
Concentrated flocculated suspensions e. The rheogram of a Bingham plastic is represented by a straight line or curve on the stressshear rate plot being displaced from the origin by the yield value see Figure 3.
The slope of the linear portion is known as mobility, which is the inverse of plastic viscosity. Plastic viscosity is defined as the shearing stress in excess of yield value that has to be applied to induce a unit rate of shear. Reason Plasticity is often exhibited by concentrated flocculated suspension where particles are attracted by the force of flocculation van der Waals forces.
The shear force required to reak the force of flocculation between the particles contributes to yield value. Continued ear breaks further linkages, thus leading to decrease in apparent viscosity with increase hear. On exceeding the yield value, the shearing stress and rate of shear become directly roportional. The diagrammatic explanation of plastic behaviour is depicted in Figure 3. At shearing stress above the yield value, stress was found to increase linearly with rate of shear.
Shear-thinning behaviour is often referred to as pseudoplasticity. Pseudoplastic material tends to become more fluid the faster they are stirred. Weakly flocculated suspensions, polymeric solutions such as solution of tragacanth, sodium alginate and cellulose derivatives' and semisolid systems containing polymer component are examples of pseudoplastic materials.
Rheogram begins at the origin, indicating that the particle-particle bonds are too weak to withstand the applied shear stresses. The increase in the rate of shear is greater than the corresponding increase in shear stress, resulting in the rheogram being concave towards the shear-rate axis Fig.
A decrease in viscosity is observed with increase in shear rate Fig. The Ostwald-de Waele equation is used to describe pseudoplastic behaviour since a single value of viscosity cannot characterize the viscous behaviour of pseudoplastic materials.
In this equation, N is greater than 1 for pseudoplastic materials and less than 1 for dilatant materials. The equation is reduced to Newton's law when N is equal to 1. Reason Pseudoplastic flow is exhibited by polymeric solutions. In polymeric solutions, the flexible, long-chain macromolecules are in thermal agitation with water molecules. To attain the condition of minimum energy, the macromolecules tend to undergo coiling.
Furthermore, intramolecular hydrogen bonding may also cause bridging between individual adjacent molecules. Both these phenomena coiling and bridging develop degrees of interlocking, which is responsible for the high initial viscosity of these systems. Upon the application of shear, the macromolecule chains uncoil and align themselves in the direction of flow as shown in Figure 3.
The imposition of increasing shear rates reduces the entrapment of ater, thereby offering less resistance to flow and reduction in viscosity. On removal of shear suesses, Brownian motion re-establishes the coiled conformation and interparticle links instantaneously and the system returns to its high viscosity condition.
Thus, the restoration. The pseudoplastic behaviour of weekly flocculated suspensions, such as silica or alumina gel, is due to the development of three-dimensional 'house of card' crure in the presence of water.
Usually, most suspending agents exhibit similar capability Ior development of structure. Dilatancy 1. Shear-thickening behaviour is often referred to as dilatancy. Materials that increase in volume, i. Flow properties of dilatants are opposite to that of pseudoplastics.
Increase in the rate of shear is greater than the corresponding increment in shear stress Fig. Increase in viscosity is observed with increase in shear rate Fig. The Ostwald-de Waele equation used to describe pseudoplasticity is also applicable for dilatant materials.
As the degree of dilatancy increases, the value of N decreases. Reason At rest, the deflocculated particles do not tend to aggregate but are intimately packed with minimum interparticle volume.
The amount of vehicle what vehicle is sufficient to fill the volume, and to lubricate and allow the particles to slip past each other. At this stage, the material, being fluid, can be poured or stirred. On increasing shear stress, the particles bunch up together, take an open form of packing and develop large voids.
Since the amount of vehicle is constant, it cannot completely fill the void spaces and the suspension appears dry as if the suspended particles had expanded or dilated. With further increase in shear rates the. When shear is removed, the void volume decreases, the viscosity drops and the suspension appears wet again. The diagrammatic explanation of dilatant behaviour. However, if the suspended particles are large or if the suspension is viscous, the Brownian motion is too slow to restore the broken interparticle links instantaneously.
If the structure does not immediately recover, the descending rheogram will have lower stress values at each shear rate and the apparent viscosity will decrease even while the system is under constant shear.
Such a body is said to be thixotropic. Thixotropy is therefore time-dependent breakdown or the rebuilding of structure on standing, i. When kept undisturbed for an hour or two, it reverts to gel as the Brownian motion rebuilds the house of card structure.
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Capillary viscometer Ostwald viscometer Falling sphere viscometer Application:- Newtonian fluids Multipoint viscometer:-Equipment work at a several rate. The time of flow of the liquid under test is compared with the time required for a liquid of known viscosity. The tube with the jacket is then inverted, which places the ball at. The following equation is used to calculate the apparent viscosity of.
Viscosity Determination. Free pharmacy material. Viscosity is defined as the resistance in the flow of liquid. It is also defined as the internal friction between two layers of liquid which resists the flow of liquid. Then he defined the viscosity as the resistance in the flow of liquid at applied stress.
Capillary viscometer Ostwald viscometer Falling sphere viscometer Application:- Newtonian fluids Multipoint viscometer:-Equipment work at a several rate. The time of flow of the liquid under test is compared with the time required for a liquid of known viscosity. The tube with the jacket is then inverted, which places the ball at. The following equation is used to calculate the apparent viscosity of. The sample required is small 0.
A viscometer also called viscosimeter is an instrument used to measure the viscosity of a fluid. For liquids with viscosities which vary with flow conditions , an instrument called a rheometer is used. Thus, a rheometer can be considered as a special type of viscometer. In general, either the fluid remains stationary and an object moves through it, or the object is stationary and the fluid moves past it. The drag caused by relative motion of the fluid and a surface is a measure of the viscosity.
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