W_20_Rheology(medium+hard)
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Questions and Answers

What does a falling sphere viscometer primarily measure?

  • The dynamic viscosity of a fluid (correct)
  • The thermal conductivity of liquids
  • The specific heat of a solid
  • The density of gases

    • Which law is utilized in a falling sphere viscometer to determine viscosity?

  • Bernoulli's principle
  • Archimedes' principle
  • Newton's second law
  • Stokes' law (correct)

    • In the context of the rotational rheometer, what is typically adjusted to measure viscosity?

  • The temperature of the fluid
  • The speed of the rotating plates (correct)
  • The pressure applied to the sample
  • The volume of the fluid sample

    • What is the main configuration of a rotational rheometer?

    <p>Two parallel plates or a cone and plate</p> Signup and view all the answers

    What factors are involved in the calculation of viscosity using Stokes' law?

    <p>Mass of the sphere and acceleration due to gravity</p> Signup and view all the answers

    What is a key characteristic of non-Newtonian fluids observed in a rotational rheometer?

    <p>Variable viscosity depending on shear rate</p> Signup and view all the answers

    What is the formula for shear stress according to the provided content?

    <p>$ au = F / A$</p> Signup and view all the answers

    What parameter is denoted by 'n' in the equation for dynamic viscosity?

    <p>Viscosity coefficient</p> Signup and view all the answers

    How is the shear strain defined in the context provided?

    <p>$ ext{strain} = rac{ ext{displacement}}{ ext{height}}$</p> Signup and view all the answers

    In the provided context, what does shear strain rate represent?

    <p>The ratio of velocity of the top layer to height</p> Signup and view all the answers

    Why is an Ostwald U tube viscometer typically used?

    <p>To calculate dynamic viscosity of fluids</p> Signup and view all the answers

    What does the displacement caused by shear indicate?

    <p>It reflects the resultant strain in a specific time</p> Signup and view all the answers

    What unit is used to measure shear stress in the context provided?

    <p>Newtons per meter squared (N/m²)</p> Signup and view all the answers

    What does the top layer's velocity relate to in shear stress testing?

    <p>The height of the sample</p> Signup and view all the answers

    Which of the following correctly defines shear stress rate?

    <p>$ ext{shear stress rate} = rac{V}{ ext{height}}$</p> Signup and view all the answers

    Which variable is part of the shear stress formula?

    <p>Area</p> Signup and view all the answers

    What is the unit of dynamic viscosity in the SI system?

    <p>Pascal second</p> Signup and view all the answers

    In the context of fluid flow, what type of flow is characterized as Newtonian?

    <p>Laminar flow</p> Signup and view all the answers

    What does the term 'shear stress' refer to in fluid dynamics?

    <p>Force per unit area acting parallel to the flow</p> Signup and view all the answers

    Which instrument is commonly used to measure viscosity in a laboratory setting?

    <p>Viscometer</p> Signup and view all the answers

    Which of the following expressions correctly represents the relationship between shear stress and shear strain?

    <p>Shear stress = viscosity * shear strain rate</p> Signup and view all the answers

    How is kinematic viscosity defined?

    <p>Dynamic viscosity divided by density</p> Signup and view all the answers

    What does a higher viscosity indicate about a fluid's flow characteristics?

    <p>The fluid offers more resistance to flow</p> Signup and view all the answers

    At what flow velocity is a Newtonian fluid defined?

    <p>Constant, regardless of shear stress</p> Signup and view all the answers

    What type of flow exhibits a decrease in viscosity when shear stress is applied?

    <p>Shear-thinning flow</p> Signup and view all the answers

    Which substance is an example of Bingham flow?

    <p>Toothpaste</p> Signup and view all the answers

    In shear-thickening fluids, how does viscosity change with applied shear stress?

    <p>Increases as shear stress increases</p> Signup and view all the answers

    Which equation represents the power law for non-Newtonian fluids?

    <p>$ au = n imes r'$</p> Signup and view all the answers

    What characterizes non-Newtonian fluids in relation to shear stress?

    <p>Their viscosity depends on the rate of applied shear stress</p> Signup and view all the answers

    Which type of flow requires a yield stress to begin flowing?

    <p>Bingham flow</p> Signup and view all the answers

    An example of a shear-thinning fluid is:

    <p>Ketchup</p> Signup and view all the answers

    What is the behavior of a shear-thickening fluid when shear rate is applied?

    <p>It becomes more viscous</p> Signup and view all the answers

    What is the result of shear thickening flow at high shear rates?

    <p>Viscosity increases significantly.</p> Signup and view all the answers

    Which flow behavior begins after a yield stress is exceeded?

    <p>Bingham flow</p> Signup and view all the answers

    Which term describes time-dependent shear thinning behavior?

    <p>Thixotropy</p> Signup and view all the answers

    What happens to viscosity during thixotropic behavior when the material is mixed?

    <p>Viscosity decreases gradually.</p> Signup and view all the answers

    At what point does Bingham flow behave like Newtonian flow?

    <p>Once the yield stress is surpassed.</p> Signup and view all the answers

    What kind of substances exhibit pseudoplastic flow?

    <p>Decrease in viscosity with increased shear.</p> Signup and view all the answers

    Which feature distinguishes Newtonian flow from other types of flow?

    <p>Constant viscosity regardless of shear rate.</p> Signup and view all the answers

    How does increasing shear rate affect shear thinning materials?

    <p>Viscosity gradually decreases.</p> Signup and view all the answers

    What effect does temperature have on viscosity according to the content?

    <p>Decreases viscosity</p> Signup and view all the answers

    Which of the following describes a Newtonian fluid?

    <p>Viscosity remains constant regardless of shear stress</p> Signup and view all the answers

    What is shear stress in the context of viscosity?

    <p>The resistance of a fluid to flow</p> Signup and view all the answers

    What distinguishes a thixotropic system from a Newtonian system?

    <p>Thixotropic viscosity decreases over time under constant shear</p> Signup and view all the answers

    What happens to viscosity as pressure increases?

    <p>Viscosity increases</p> Signup and view all the answers

    Which of the following is an example of a Newtonian fluid?

    <p>Water</p> Signup and view all the answers

    In terms of viscosity, what does 'shear rate' refer to?

    <p>The rate at which velocity changes in a fluid over time</p> Signup and view all the answers

    How does the viscosity of a thixotropic fluid behave over time under a constant shear?

    <p>Decreases gradually</p> Signup and view all the answers

    What is the primary focus of rheology in terms of material behavior?

    <p>The analysis of deformation and flow in materials</p> Signup and view all the answers

    Which of the following aspects is NOT a primary use of rheological measurements?

    <p>Predicting thermal expansion</p> Signup and view all the answers

    In the context of rheology, what does the term 'viscoelasticity' refer to?

    <p>The combined elastic and viscous response of a material</p> Signup and view all the answers

    What is an essential aspect of quality control that can be influenced by rheological measurements?

    <p>The physical stability and consistency of products</p> Signup and view all the answers

    How can rheological measurements contribute to process optimization?

    <p>By understanding material behavior under stress and strains</p> Signup and view all the answers

    Which of the following issues can poor rheological behavior indicate?

    <p>Inconsistent ingredient proportions</p> Signup and view all the answers

    What does an understanding of viscosity contribute to in terms of product formulation?

    <p>Ensuring compatibility with patient administration</p> Signup and view all the answers

    Which outcome is indicative of high viscosity during a rheological evaluation?

    <p>Resistance to flow and deformation</p> Signup and view all the answers

    Which statement accurately characterizes a Newtonian fluid?

    <p>It exhibits a constant viscosity regardless of shear stress.</p> Signup and view all the answers

    What is a primary characteristic of thixotropic materials?

    <p>Viscosity decreases with time under constant shear.</p> Signup and view all the answers

    How does pressure affect the viscosity of fluids generally?

    <p>Viscosity can increase or decrease depending on the fluid type.</p> Signup and view all the answers

    What distinguishes a shear-thinning fluid from other fluid types?

    <p>Its viscosity decreases with increasing shear rate.</p> Signup and view all the answers

    Which term best describes a fluid that behaves like a Newtonian fluid when above a certain threshold?

    <p>Bingham plastic</p> Signup and view all the answers

    What phenomenon occurs in a shear-thickening fluid at high shear rates?

    <p>Viscosity increases dramatically.</p> Signup and view all the answers

    Which component is essential in calculating viscosity?

    <p>Shear rate</p> Signup and view all the answers

    What is the role of temperature in the behavior of fluids concerning viscosity?

    <p>Increased temperature typically leads to reduced viscosity.</p> Signup and view all the answers

    What is the relationship between shear stress and shear strain rate?

    <p>Shear stress is defined as the product of shear strain and viscosity.</p> Signup and view all the answers

    In a viscometric study, how is shear strain typically defined?

    <p>As the total displacement due to shear over a specific height.</p> Signup and view all the answers

    How is the shear strain rate mathematically described?

    <p>As velocity of the top layer divided by height.</p> Signup and view all the answers

    What does the term 'shear stress' measure in fluids?

    <p>The internal friction within the fluid due to motion.</p> Signup and view all the answers

    What unit is commonly used to express shear stress in the context provided?

    <p>Pascals (Pa)</p> Signup and view all the answers

    What does a higher phase angle indicate about a material?

    <p>The material is more viscous.</p> Signup and view all the answers

    When discussing shear stress, which variable is NOT involved in the calculation?

    <p>Velocity of the fluid</p> Signup and view all the answers

    Which statement accurately reflects the relationship between phase angle and material properties?

    <p>A lower phase angle correlates with higher elasticity.</p> Signup and view all the answers

    What is the significance of the ratio of fluid displacement caused by shear?

    <p>It affects the fluid's flow characteristics and behavior.</p> Signup and view all the answers

    In the context of complex modulus, what does a higher loss modulus signify?

    <p>The material has more viscous characteristics.</p> Signup and view all the answers

    What is implied when the phase angle is at 0 degrees?

    <p>The material behaves elastically without viscosity.</p> Signup and view all the answers

    What does the term 'viscometry' refer to in the context provided?

    <p>The measurement and analysis of viscosity.</p> Signup and view all the answers

    How does complex modulus relate to the nature of the liquid sample?

    <p>It shows the material's elastic and viscous responses under stress.</p> Signup and view all the answers

    What type of flow requires an applied pressure to initiate its movement?

    <p>Bingham flow</p> Signup and view all the answers

    Which characteristic is true of shear-thinning fluids?

    <p>Flow can begin immediately upon application of shear stress.</p> Signup and view all the answers

    In non-Newtonian fluids, which behavior is associated with a decrease in viscosity over time when subjected to a constant shear rate?

    <p>Thixotropic behavior</p> Signup and view all the answers

    Under what condition does a shear-thickening fluid show an increase in viscosity?

    <p>At higher shear rates</p> Signup and view all the answers

    What distinguishes a non-Newtonian fluid from a Newtonian fluid?

    <p>Non-Newtonian fluids' viscosity depends on shear rate.</p> Signup and view all the answers

    Which fluid behavior starts flowing only after exceeding a specific yield stress?

    <p>Bingham flow</p> Signup and view all the answers

    What occurs to the viscosity of a thixotropic fluid under constant shear?

    <p>It decreases over time.</p> Signup and view all the answers

    What phase angle indicates a purely elastic material according to the given content?

    <p>0 degrees</p> Signup and view all the answers

    Which behavior is expected from materials that exhibit viscoelasticity?

    <p>Both elastic and viscous behavior</p> Signup and view all the answers

    Which condition must be met for a material to flow in a concentrated suspension during application?

    <p>It must resemble a liquid</p> Signup and view all the answers

    Under what stress condition does flow begin in materials that exhibit yield stress?

    <p>After a certain shear stress is applied</p> Signup and view all the answers

    What distinguishes the behavior of a viscoelastic material during storage compared to application?

    <p>It acts like a solid during storage and a fluid during application</p> Signup and view all the answers

    Which statement best describes the relationship between shear stress and shear rate in elastic materials?

    <p>Shear stress is directly proportional to shear rate</p> Signup and view all the answers

    What is a defining characteristic of materials in which shear stress and shear strain are at a phase angle of 0?

    <p>They respond instantaneously to applied stress</p> Signup and view all the answers

    In the context provided, what happens when shear strain is applied to viscoelastic materials over time?

    <p>They may transition between viscous and elastic behavior</p> Signup and view all the answers

    Study Notes

    Rheology

    • Rheology is the science of deformation and flow
    • Viscometry is the measurement of a fluid's resistance to flow

    Viscometry Testing

    • Rheological measurements describe the flow behavior of liquids and semisolids
    • Insights into viscosity, elasticity, and viscoelasticity help understand material structure (raw materials and finished products)

    Quality Control

    • Physical stability, consistency of quality, patient compatibility, and drug bioavailability are crucial
    • Differences can indicate contamination, poor mixing, or variability
    • Adhesive performance of transdermal patches is a key factor

    Process Optimization

    • Understanding how materials behave under stress and strain is vital
    • Selecting suitable equipment is crucial

    Product Development

    • Optimizing flow, spreading, and firmness are important factors

    Predicting Behavior

    • Predicting behavior under different conditions (temperature and pressure) is essential
    • Research into different conditions and molecular structures and interactions with new materials is critical

    Research and Development

    • Exploring molecular structure, interactions, and new materials is a key aspect

    Newton's Experiment

    • Shear stress = Force/area
    • Shear strain = Displacement/time
    • Shear strain rate = Velocity of top layer/height

    Viscometry - Definition of Terms

    • Shear stress (σ) = Torsional force/area (N/m²)
    • Shear strain rate (γ̇) = Shear strain in a certain time (s⁻¹)
    • Viscosity (η) = Shear stress/shear rate (Pa·s)
    • Shear strain (γ) = Displacement/gap

    Dynamic Viscosity (η)

    • Dynamic viscosity (η) is measured in Nm² or Pa·s
    • Kinetic viscosity (ν) is measured in m²/s

    Newtonian Flow

    • Newtonian fluids have constant viscosity regardless of applied shear stress
    • Resistance to flow does not change with speed or force of flow
    • Graph of shear stress vs shear rate is linear; gradient = viscosity
    • Equipment for measuring Newtonian flow includes capillary viscometers and falling sphere viscometers

    Capillary Viscometer Question

    • Calculate the dynamic viscosity of a Newtonian liquid using a capillary viscometer, given the density of the liquid and instrument constant

    Ostwald U-Tube Viscometer

    • Measures the time for a liquid to flow under gravity from one point to another
    • Records time for flow from C to D
    • Calculating dynamic viscosity: n = k * ρ * t

    Falling Sphere Viscometer

    • Device used to calculate the dynamic viscosity of a fluid by measuring the time required for a sphere to fall a certain distance through the fluid
    • Using Stokes law

    Rotational Rheometer

    • Used for non-Newtonian flow measurement
    • Upper mobile plate parallel to lower stationary plate.
    • Experimental settings include plate size, gap size, and temperature.

    Factors Affecting Viscosity

    • Temperature (T): Increased temperature decreases viscosity
    • Pressure (P): Increased pressure increases viscosity
    • Time (t): Time affects viscosity in non-Newtonian systems
    • Shear stress (σ): Affects viscosity in both Newtonian and non-Newtonian systems

    Newtonian System

    • Viscosity remains constant regardless of applied shear stress
    • Viscosity changes with rate of shear
    • Flow behavior is linear (shear stress and shear rate)
    • Equation: σ/γ̇ = η (constant)

    Non-Newtonian System

    • Viscosity changes with shear stress or strain rate
    • Shear stress dependent viscosity - Shear-thinning flow (e.g., cream) - Shear-thickening flow (e.g., concentrated suspensions) - Bingham flow (e.g., toothpaste, needs applied pressure)
    • Time dependent viscosity - Thixotropic flow (e.g., bentonite, ketchup)

    Shear-Thinning Flow

    • Viscosity decreases as shear rate increases
    • Flow begins as soon as shear stress is applied
    • Viscosity is high at low shear rates and low at high shear rates
    • Power law equation: η = Kγⁿ (where n < 1)

    Shear-Thickening Flow

    • Viscosity increases as shear rate increases
    • Opposite behavior to shear thinning flow
    • Power law equation: η = Kγⁿ (where n > 1)

    Bingham Flow

    • Yield stress is required before flow begins
    • Newtonian flow begins when yield stress is reached

    Thixotropic Behavior

    • Time-dependent shear-thinning
    • Viscosity decreases with time under applied stress and increases on removal of stress
    • Hysteresis loop shows time dependence

    Viscoelasticity in Products

    • Many materials exhibit viscoelasticity (viscous and elastic)
    • During storage, it needs to behave like a solid to prevent sedimentation; during application, it needs to flow like a fluid

    Oscillation Principles

    • Phase angle (δ) measures elasticity; higher angle indicates more viscous and lower angle indicates more elastic qualities

    Parameters in Oscillation

    • Complex modulus (G*) shows liquid-like or solid-like nature of sample
    • Loss modulus (G'') indicates liquid-like nature of sample
    • Storage modulus (G') indicates solid-like nature of sample
    • Dynamic viscosity is related to shear viscosity

    Test Modes

    • Rotational rheometers have various test modes, including viscometry (shear), oscillation, creep, and recovery
    • Dry (elastic) versus soak (viscous/inelastic)
    • Complex viscoelastic behavior (vector sum of moduli)

    Oscillation Measurement Types

    • Amplitude sweep: Linear viscoelastic region identification; measures inherent structure
    • Frequency sweep: Useful for liquid, gels, and hydrogel films, with a specific analysis
    • Temperature sweep
    • Time experiment (thixotropic)
    • Creep tests: constant stress applied over a period of time

    Creep Test

    • Constant stress is applied over an extended period
    • Monitoring the resulting strain provides information on material behavior under stress.

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    Rheology W20 PDF

    Description

    Test your knowledge on viscosity measurement techniques, including the use of falling sphere viscometers and rotational rheometers. This quiz covers key concepts such as Stokes' law, shear stress, and characteristics of non-Newtonian fluids. Perfect for students and professionals in the field of fluid dynamics.

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