Viscosity measurement of Flow, Classification and type

measurement of Viscosity
Classification,
instrument used for viscosity measurement

1. Measurment of Viscosity PRESENTATION By Maheshkumar Kadam Assistant Professor MGM College of Food Technology Gandheli Chhtrapati Sambhaji Nagar Maharashtra

2. Classification Of Viscosity or fluid Viscosity is the measure of a substance's resistance to motion under an applied force – as per the definition . Viscosity = shear stress/shear rate The result is typically expressed in  centipoise ( cP ), which is the equivalent of 1 mPa s ( milli pascal second).  Shear stress is the force per unit area required to move one layer of fluid in relation to another. Shear rate is the measure of the change in speed at which intermediate layers move with respect to one another This applies to absolute viscosity. For kinematic viscosity, the measurement is different, as we will explain later. For many liquids, the stress that causes flow is directly proportional to the rate of shear strain. The shear stress divided by the shear rate is constant for a given fluid, at a specific temperature. This constant is the dynamic or absolute viscosity. But you can also simply refer to it as the viscosity of a material. A simple way of seeing viscosity is as the thickness of a fluid, but when you look at fluids with different densities, the clearest way of describing viscosity is as resistance to flow. Difference Between Kinematic And Dynamic Viscosity Properties Kinematic Viscosity Dynamic Viscosity Also known as Diffusivity of momentum Absolute Viscosity Represents Inertia as well as viscous force The viscous force of the fluid Symbol ν μ Ratio The ratio of dynamic viscosity to density The ratio of shear stress to shear strain Used When inertia, as well as viscous force, is dominant When viscous force is dominant Density Dependent Independent Unit m2/s Ns/m2

3. What is Viscosity Viscosity is the measure of a substance's resistance to motion under an applied force – as per the definition . Viscosity = shear stress/shear rate The result is typically expressed in  centipoise ( cP ), which is the equivalent of 1 mPa s ( milli pascal second).  Shear stress is the force per unit area required to move one layer of fluid in relation to another. Shear rate is the measure of the change in speed at which intermediate layers move with respect to one another This applies to absolute viscosity. For kinematic viscosity, the measurement is different, as we will explain later. For many liquids, the stress that causes flow is directly proportional to the rate of shear strain. The shear stress divided by the shear rate is constant for a given fluid, at a specific temperature. This constant is the dynamic or absolute viscosity. But you can also simply refer to it as the viscosity of a material. A simple way of seeing viscosity is as the thickness of a fluid, but when you look at fluids with different densities, the clearest way of describing viscosity is as resistance to flow. Difference Between Kinematic And Dynamic Viscosity Properties Kinematic Viscosity Dynamic Viscosity Also known as Diffusivity of momentum Absolute Viscosity Represents Inertia as well as viscous force The viscous force of the fluid Symbol ν μ Ratio The ratio of dynamic viscosity to density The ratio of shear stress to shear strain Used When inertia, as well as viscous force, is dominant When viscous force is dominant Density Dependent Independent Unit m2/s Ns/m2

4. Classification of fluids Fluids are classified into two major types depending on the relationship between shear stress and the rate of the strain . These two types of fluids are: Newtonian fluids – those fluids for which viscosity does not depend on the  stress rate. An example is water. Where stress is directly proportional to rate of strain or Fluid with a constant viscosity at a fixed temperature and pressure. A Newtonian fluid's viscosity remains constant, no matter the amount of shear applied for a constant temperature.. These fluids have a linear relationship between viscosity and shear stress. They obey the Newton’s law of viscosity, which is τ= µdu/ dy The constant of proportionality is known as the viscosity. τ = shear stress exerted by the fluid ("drag ") μ = fluid viscosity - a constant of proportionality du/ dy = velocity gradient perpendicular to the direction of shear.

5. Classification of fluids Non-Newtonian fluids – those fluids for which viscosity is independent of the stress rate. Some examples are blood and paint In   Physics   and Chemistry   , a non-Newtonian fluid is a  fluid that does not follow  Newton's law of viscosity , that is, it has variable viscosity dependent on stress. In particular, the viscosity of non-Newtonian fluids can change when subjected to force. Ketchup, for example, becomes runnier when shaken and is thus a non-Newtonian fluid. Many salt solutions and molten polymers are non-Newtonian fluids, as are many commonly found substances such as custard ,  toothpaste,  starch suspensions , corn starch, paint, blood, melted butter and shampoo. Most commonly, the viscosity (the gradual deformation by shear or tensile stresses) of non-Newtonian fluids is dependent on shear rate or shear rate history. Some non-Newtonian fluids with shear-independent viscosity, however, still exhibit normal stress-differences or other non-Newtonian behavior

6. Types of Non Newtonian Viscosity 6 . This type   of fluid will display a decreasing viscosity with an increasing shear rate. • Probably the most common of the non-Newtonian fluids, pseudo-plastics include paints, emulsions, and dispersions of many types. • This type of flow behavior is sometimes called "shear-thinning . Increasing viscosity  with an increase in rate of Share characterizes the dilatant fluid . Although rarer than pseudo plasticity, dilatancy is frequently observed in fluids containing high levels of deflocculated solids, such as clay slurries, Milk Chocolate with butter powder compounds and sand/water mixtures . Most liquid return their original Consistency as soon as agitation stops • Dilatancy is also referred to as shear-thickening flow behavior. A time-independent relation Pseodoplastic Dilantants This type  of fluid will behave as a solid under static conditions. • A certain amount of force must be applied to the fluid before any flow is induced; this force is called the yield stress (f'). • Tomato catsup is a good example of this type fluid; its yield value will often make it refuse to pour from the bottle until the bottle is shaken or struck, allowing the catsup to gush freely. • Once the yield value is exceeded and flow begins, plastic fluids may display Newtonian, pseudo plastic, or dilatant flow characteristics a time-dependent relation It’sa Reversible isothermal Gel-so-gel Transformation i.e those gets that break up on shake and reset on standing here structure brak down and viscosity decease with continued shear stress (incudes most of Cream) Rheopectic Here structure Build up and Viscosity Increase with Continued with Shear Stress Viscoelastic These material have viscous and elastic properties at the same time. When shear stress is removed the material never fully return to its original Shape as there is a permanent deformation (Dough, Cheese, Gelled food ) a time-independent relation Plastic(Bingham Plastic) Thixotrophy & Rheopectic Stress Shear rate

7. Classification of fluids Fluids are classified into two major types depending on the relationship between shear stress and the rate of the strain . These two types of fluids are: Newtonian fluids – those fluids for which viscosity does not depend on the  stress rate. An example is water. Where stress is directly proportional to rate of strain or Fluid with a constant viscosity at a fixed temperature and pressure. A Newtonian fluid's viscosity remains constant, no matter the amount of shear applied for a constant temperature.. These fluids have a linear relationship between viscosity and shear stress. They obey the Newton’s law of viscosity, which is τ= µdu/ dy The constant of proportionality is known as the viscosity. τ = shear stress exerted by the fluid ("drag ") μ = fluid viscosity - a constant of proportionality du/ dy = velocity gradient perpendicular to the direction of shear.

8. Measurement of Viscosity Most widely Used method for Determination of Viscosity pure Fluids Capillary action occurs when a liquid moves through a small tube without the need for external force. This is due to: Adhesion  – The attraction between the liquid molecules and the tube’s surface. Cohesion  – The attraction between liquid molecules that helps them move together Surface Tension  – The tendency of a liquid to form a shape due to intermolecular forces Result calculated by time required for liquid to flow through capillary a given distance immersed in constant temperature water bath.(Relative Viscosity ) Density of Liquid , calculations as kinematic viscometer, rate of flow, is slow in capillary Driving force of liquid and hydrostatic head of liquid is not constant Flow Through Capillary Tube Ostwald Viscometer

9. Measurement of Viscosity When discussing flow through an orifice, viscosity refers to the fluid's resistance to flow, which significantly impacts the flow rate through the orifice; meaning, a fluid with higher viscosity will experience a lower flow rate This Instrument Generally used to Measure the consistency of tomato past . Material possessing high yield value may required considerable hydrostatic head to produce suitable flow Result are reported in time to flow a definite volume of material through the orifices of a shear capillary tube under constant temperature Flow Through Orifices when passing through an orifice compared to a less viscous fluid, due to increased internal friction within the fluid itself Higher viscosity leads to a larger pressure drop across the orifice, resulting in a reduced flow rate When calculating flow rate through an orifice, the viscosity of the fluid must be considered and often incorporated into a correction factor to account for its influence Along with viscosity, other fluid properties like density and temperature also play a role in the flow characteristics through an orifice. 

10. causing a pressure drop due to the increased velocity of the fluid as it passes through the restricted area, which is the primary principle behind an "orifice plate" instrument used to measure flow rate in industrial applications; essentially, the pressure difference across the orifice is measured and used to calculate the flow rate based on Bernoulli's equation. Used for highly Mobile Materials Definite volume flow through orifice of short capillary under constant temperature Viscosity increased by using pressurized system different rates of shear can be imposed Flow through an orifice" refers to the movement of a fluid through a small opening (orifice) in a pipe or other barrier, Flow Through Capillary Orifice Pressure for 10gm 5-10lb Falling Ball Viscometer Falling Ball Viscometer depends on the measurement of the Time required for the a weight to fall through a tube of the Material being tested. Weight may vary from spherical to dic -shaped Specific gravity of the weight which increase the driving force. Gardner mobile-meter work on same principle It measure Consistency by time required for a ball fall between Two reference points. Result are calculated time divide by distance traveled by the falling ball Viscosity = Time of Travels *Weight of ball Distance Travelled Type of Measurement of Viscosity

11. causing a pressure drop due to the increased velocity of the fluid as it passes through the restricted area, which is the primary principle behind an "orifice plate" instrument used to measure flow rate in industrial applications; essentially, the pressure difference across the orifice is measured and used to calculate the flow rate based on Bernoulli's equation. Used for highly Mobile Materials Definite volume flow through orifice of short capillary under constant temperature Viscosity increased by using pressurized system different rates of shear can be imposed Flow through an orifice" refers to the movement of a fluid through a small opening (orifice) in a pipe or other barrier, Flow Through Capillary Orifice Pressure for 10gm 5-10lb Roratation of Spildle and Cylinder in test Material Rotation of cylinder in test material the measurement of resistance to rotation of Spindle or cylindrical immersed in the test material is the basis of a several industrial viscometer most instrument of this type can be classed also as a torsion viscometer since the results are obtained by a measurement of a torque on the rotary part of the instrument The measurement of Torque by the calibrating spring on the spindle rotating at a constant speed in the test material is the principal operation of the Brookfield synchroelectric visometer are noted in term of centrpoise it is Geared for different rate of shares help to find range of measurement materials can be measured at different rate of shares it is also useful for determine the presence of thyrotrophic, dilatant and rheological properties A Brookfield viscometer uses rotational viscometer to measure the viscosity of a fluid. It measures the torque required to rotate a spindle in a fluid. The torque is applied through a calibrated spring. The amount of torque required to rotate the spindle is proportional to the viscosity of the fluid A spindle is immersed in the fluid The spindle is rotated at a defined speed The force required to maintain the speed is measured The force is used to calculate the viscosity of the fluid Brookfield viscometers can be used to measure the viscosity of a variety of fluids, including non-Newtonian fluids. Non-Newtonian fluids are fluids whose viscosity depends on the conditions of agitation The stormer viscometer. Type of Measurement of Viscosity

12. Type of Measurement of Viscosity 12 Power consumption The degree of Spread or flow of material in given period of time is basic principle (Ketchup, paste Puree ) Bostwick Consistometer Measurement of Distance over which the material flow on a level surface under its own weight during given time interval Adams Consistometer The degree of spread or flow of the product in all direction in a given time The consistency of product can also be determined by recording total power consumption necessary to drive mixture or other type of a Shearing instrument a certain number of revolution the power consumed can be recorded by a microwatt hour meter brabender farinograph operated on a similar principle in that torque use on the motor housing providers measurement of consistency it is widely used in serial chemistry and baking industry the door character can be identified by its ability to absorb more or less water the farinograph major record these absorption consistency and also the stability and elasticity of the day last of dough This instrument is used for testing gelatin glues, pectin and jelly strength Bloom Gelometer is used to determine Stuffiness for measuring Jelly Strength. Penetrometer measure the degree of penetration tomato past Penetration in to test material Ultrasonic vibration measure viscosity of product electronically by means of magnetostrictive sensing element which vibrates longitudinally Ultrasonic vabration Spread or Flow of Material

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