Chapter 1 |Mixing
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Questions and Answers

Why is mixing considered a fundamental step in most process sequences?

  • To create an ordered system of particles
  • To decrease heat transfer
  • To decrease the overall composition of the mixture
  • To randomize dissimilar particles within a system (correct)
  • Which term is synonymous with mixing according to the text?

  • Dissolution
  • Diffusion
  • Segregation
  • Blending (correct)
  • What is the main purpose of mixing in the context of pharmaceutical products?

  • To secure uniformity of composition (correct)
  • To increase segregation
  • To reduce physical and chemical reactions
  • To separate the components
  • In the mixing process, what happens to dissimilar particles within a system?

    <p>They are randomized</p> Signup and view all the answers

    Which of the following is NOT a reason for carrying out mixing in pharmaceutical manufacturing?

    <p>To promote segregation</p> Signup and view all the answers

    What additional process does agitation during mixing supplement in the context of chemical reactions?

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

    What are the two primary components of a liquid mixing system?

    <p>Tank and means of supplying energy</p> Signup and view all the answers

    Which component is used to direct the bulk movement of material in mixers?

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

    Which type of mixing is usually more feasible for limited volumes of materials?

    <p>Batch mixing</p> Signup and view all the answers

    How are impellers classified in terms of mixing liquids?

    <p>By the type of flow pattern they produce</p> Signup and view all the answers

    Which flow pattern is perpendicular to the impeller shaft?

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

    What serves to direct the flow of material within the vessel besides supplying power?

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

    What kind of mixing occurs when shear reduces the scale of segregation by thinning dissimilar layers?

    <p>Diffusive mixing</p> Signup and view all the answers

    How does diffusive mixing by diffusion reduce the intensity of segregation?

    <p>By exchanging positions of particles within the powder bed</p> Signup and view all the answers

    What equipment is used for rapid overall mixing involving tumbling motion?

    <p>Batch Tumblers/Blenders</p> Signup and view all the answers

    Which geometric form is NOT mentioned as a type of tumbler blender commercially available?

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

    In a tumbling mixer, what enhances the resulting tumbling motion?

    <p>Lifter blades or baffles</p> Signup and view all the answers

    What is the main effect of shear occurring between regions of different composition and parallel to their interface?

    <p>Reduces scale of segregation</p> Signup and view all the answers

    Which type of blender is recommended for precision blending?

    <p>Twin-shell blenders</p> Signup and view all the answers

    What type of motion is not conductive to efficient mixing in cubical and polyhedron-shaped blenders?

    <p>Sliding action</p> Signup and view all the answers

    What is a drawback associated with ribbon mixers?

    <p>Difficult to clean</p> Signup and view all the answers

    What type of motion characterizes the mixing pattern in double cone blenders?

    <p>Rolling motion</p> Signup and view all the answers

    Which mixer exhibits shearing action between moving blades and trough?

    <p>Agitator mixer</p> Signup and view all the answers

    What property of powders makes them difficult to mix due to agglomeration?

    <p>High forces of cohesion</p> Signup and view all the answers

    What is considered as a practical upper limit for the viscosity of materials that can be mixed using turbines or flat blade devices?

    <p>10 poise</p> Signup and view all the answers

    Which of the following statements is true about mixing thick creams, ointments, and pastes?

    <p>They have a high viscosity, making it difficult to generate turbulence within their bulk.</p> Signup and view all the answers

    What is a characteristic of turbines or flat blade mixing devices?

    <p>They are insensitive to changes in power consumption, density, and viscosity.</p> Signup and view all the answers

    In the mixing of two immiscible liquids, what is the primary mechanism involved?

    <p>Subdivision of one phase into globules and distributing them throughout the bulk fluid.</p> Signup and view all the answers

    What are the two primary forces involved in the mixing of two immiscible liquids?

    <p>Interfacial tension and shear forces</p> Signup and view all the answers

    How is the selection of mixing equipment determined for low-viscosity systems?

    <p>Based on the mechanism by which intense shearing forces can be generated</p> Signup and view all the answers

    What type of mixing involves systems where spontaneous, irreversible, and complete mixing would take place by diffusion?

    <p>Positive mixing</p> Signup and view all the answers

    Which type of mixing is more difficult to form and maintain, requiring a higher degree of mixing?

    <p>Negative mixing</p> Signup and view all the answers

    What occurs in neutral mixing systems unless acted upon by an external energy input?

    <p>Remain static</p> Signup and view all the answers

    Forces of shear during fluid mixing are generated by interactions between moving fluids and:

    <p>Solid surfaces</p> Signup and view all the answers

    What is the derivative of velocity with respect to distance measured normal to the direction of flow known as?

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

    What classification depends on the relationship between shear rates and applied stress for fluids?

    <p>Rheological classification</p> Signup and view all the answers

    What type of mixer is characterized by the development of a vortex at the center of the vessel?

    <p>Impeller mixer</p> Signup and view all the answers

    Which fluid mixing device induces tangential flow but does not produce mixing except near the tank walls?

    <p>Grid mixer</p> Signup and view all the answers

    What is the drawback associated with the formation of a vortex during mixing?

    <p>Increased likelihood of foaming</p> Signup and view all the answers

    Which device typically includes vanes, baffles, screws, grids, or combinations for efficient mixing?

    <p>Impeller mixer</p> Signup and view all the answers

    At what viscosity range is the formation of a vortex during mixing considered undesirable?

    <p>&lt; 20,000 cps</p> Signup and view all the answers

    Which type of flow pattern is characteristic of turbines with blades arranged perpendicular to the impeller shaft?

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

    What is the primary effect of a propeller in mixing liquids?

    <p>Producing axial flow</p> Signup and view all the answers

    How are turbines distinguished from propellers in terms of blade pitch?

    <p>Turbines have blades with varying pitch</p> Signup and view all the answers

    Which impeller type induces radial flow by centrifugal action?

    <p>Turbines with 90-degree blades</p> Signup and view all the answers

    What is a key characteristic of turbines' design that allows operation in highly viscous fluids?

    <p>Simple and rugged design</p> Signup and view all the answers

    In what type of fluid are propellers most efficient?

    <p>Low-viscosity liquids</p> Signup and view all the answers

    What type of flow pattern is induced primarily by the setup of propellers?

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

    What type of motion characterizes the mixing pattern in double cone blenders?

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

    Which blender type is NOT recommended for precision blending according to the text?

    <p>Planetary mixer</p> Signup and view all the answers

    What is the drawback associated with ribbon mixers mentioned in the text?

    <p>Higher power requirement</p> Signup and view all the answers

    Which type of mixing is NOT conducive to efficient mixing in cubical and polyhedron-shaped blenders?

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

    What additional mixing action occurs in twin-shell blenders during each revolution?

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

    What is a common drawback associated with sigma blade and planetary mixers mentioned in the text?

    <p>Relatively higher power requirement</p> Signup and view all the answers

    What is the practical upper limit of viscosity for the application of turbines or flat blade mixing devices?

    <p>15 poise</p> Signup and view all the answers

    What type of forces play a role in the mixing of two immiscible liquids?

    <p>Surface tension and shear forces</p> Signup and view all the answers

    How are high shear rates achieved in low-viscosity systems during mixing?

    <p>By passing the fluid under high pressure through small orifices</p> Signup and view all the answers

    What is the primary function of a turbine or flat blade design in mixing thick creams and ointments?

    <p>Generate turbulence within the bulk</p> Signup and view all the answers

    In a polyphase system, what is the effect of the first force on the globules within the fluid?

    <p>Maintains globule shape integrity</p> Signup and view all the answers

    Which factor influences the selection of equipment for generating intense shearing forces in liquid mixtures?

    <p>Viscosity of the liquids</p> Signup and view all the answers

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