Basic Separation Techniques and Sedimentation
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Questions and Answers

What occurs after the brief acceleration period in Type 1 settling?

  • The sedimentation rate remains constant immediately.
  • The sediment begins to rise to the surface.
  • The rate of sedimentation increases indefinitely.
  • The interface moves downwards at a constant rate. (correct)

    • What happens when the interface approaches the layer of sediment in Type 1 settling?

  • The rate of fall decreases until the critical settling point is reached. (correct)
  • The sediment continues to separate from the liquid.
  • The suspension becomes fully homogenized.
  • The liquid begins to separate from the solid particles.

    • Which factor does NOT affect the rate of sedimentation?

  • Temperature of the liquid. (correct)
  • Shape of the vessel.
  • Diameter of the containing vessel.
  • Height of the suspension.

    • In Type 2 settling, what characterizes the sedimentation process?

    <p>There is a gradual decrease in the sedimentation rate.</p> Signup and view all the answers

    What is formed at the critical settling point in Type 1 settling?

    <p>A direct interface between sediment and clear liquid.</p> Signup and view all the answers

    What is the primary characteristic of the separation process of a chemical mixture into pure components?

    <p>It requires energy input.</p> Signup and view all the answers

    Which separation technique involves the transfer of species between vapor and liquid phases?

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

    What type of separation technique adds another fluid phase to selectively absorb certain species from the feed?

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

    Which method uses a polymer membrane to exploit differences in species permeabilities?

    <p>Gas permeation</p> Signup and view all the answers

    What is the common characteristic of the separation technique depicted as using a solid agent?

    <p>It exploits species adsorbability.</p> Signup and view all the answers

    Which of the following is considered less common but of growing importance in separation techniques?

    <p>Barrier techniques</p> Signup and view all the answers

    What does crystallization primarily exploit for the separation of species?

    <p>Differences in melting points</p> Signup and view all the answers

    In liquid-liquid extraction, what characteristic must the added phase possess?

    <p>It must be immiscible with the feed phase.</p> Signup and view all the answers

    What is the primary purpose of thickening in the sedimentation process?

    <p>To increase the concentration of suspended solids</p> Signup and view all the answers

    Which process involves the partial separation of suspended solid particles from a liquid by gravity?

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

    During sedimentation, what happens to the sedimentation rate once the critical settling point is reached?

    <p>It falls</p> Signup and view all the answers

    What characterizes the sedimentation process in a scenario with a wide range of particle sizes?

    <p>Progressively decreasing sedimentation rate</p> Signup and view all the answers

    In the sedimentation process, what is typically seen at zone D?

    <p>Layer of sediment</p> Signup and view all the answers

    Which of the following external fields is particularly noted for its use in separating proteins?

    <p>Electrical field</p> Signup and view all the answers

    What is the end product of the clarification phase in sedimentation?

    <p>Clear effluent</p> Signup and view all the answers

    How is the sedimentation rate described before reaching the critical settling point?

    <p>It remains constant</p> Signup and view all the answers

    What is the terminal velocity of a particle in a fluid defined as?

    <p>The velocity that balances all forces acting on the particle</p> Signup and view all the answers

    How does the presence of large particles affect a concentrated suspension?

    <p>They increase the viscosity of the fluid.</p> Signup and view all the answers

    What happens to the apparent settling velocity in a concentrated suspension?

    <p>It is less than the actual velocity.</p> Signup and view all the answers

    Which factor does NOT influence the calculation of the drag coefficient?

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

    What is the form of the equation relating the drag force and the drag coefficient?

    <p>$F_d = C_d \times A_p \times \rho$</p> Signup and view all the answers

    What physical principle primarily affects the behavior of particles in a fluid suspension?

    <p>Buoyant force</p> Signup and view all the answers

    When does hindered settling occur?

    <p>When particles collide with each other or walls</p> Signup and view all the answers

    What aspect of fluid motion influences the velocity gradients near particles?

    <p>Flow spaces around the particles</p> Signup and view all the answers

    At which Reynolds number does Stokes' law apply?

    <p>Re &lt; 2</p> Signup and view all the answers

    What is the drag coefficient for Reynolds numbers between 500 and 200,000?

    <p>0.44</p> Signup and view all the answers

    In which region is the settling velocity given by $u_s = \frac{0.153g d^3 (\rho_s - \rho_f)}{\rho_f \mu}$?

    <p>Transitional region</p> Signup and view all the answers

    What is the empirical equation to determine settling for particle sizes using the highest Reynolds number?

    <p>K_c = 34.81 \frac{d^6}{\mu_f}</p> Signup and view all the answers

    What is the drag force equation applicable for Reynolds numbers between 500 and 200,000?

    <p>F_d = 0.055 \pi d^6 u \rho_f</p> Signup and view all the answers

    What defines the criterion for the empirical equation in determining settling velocity?

    <p>The highest Reynolds number for which the equation applies</p> Signup and view all the answers

    What does the constant K_c depend on?

    <p>Particle size and viscosity</p> Signup and view all the answers

    If a particle is in a low Reynolds number region, which equation best describes the settling velocity?

    <p>u_s = 0.153g d^3 / (\rho_f \mu)</p> Signup and view all the answers

    Study Notes

    Basic Separation Techniques

    • Separation of chemical mixtures is not a spontaneous process, requiring energy input
    • Multiphase mixtures are often separated into individual phases first
    • Common separation techniques are diagrammed in Figure 1.1
      • Separation by phase creation (Figure 1.1a)
      • Separation by phase addition (Figure 1.1b)
      • Separation by barrier (Figure 1.1c)
      • Separation by solid agent (Figure 1.1d)
      • Separation by force field or gradient (Figure 1.1e)
    • The most common technique creates a second, immiscible phase (Figure 1.1a)

    Sedimentation

    • Mechanical separation of one bulk phase from another

    • Separates suspended solids from a liquid via gravity settling

    • Operations include thickening and clarification

    • Thickening increases solid concentration

    • Clarification produces a clear effluent (liquid)

    • Sedimentation occurs in one or two ways (Figure 2a)

      • Clear liquid (A)
      • Suspension (B)
      • Gradual increase in concentration (C)
      • Sediment layer (D)

    • Sedimentation rate varies with particle size distribution (Figure 2b)

    Settling Velocity

    • Terminal velocity (ut) is the velocity at which a particle stops accelerating due to gravity
    • Drag force and buoyant force balance gravity force
    • Settling velocity affected by fluid height, vessel diameter, volumetric concentration, and shape (of the vessel)

    Reynolds Number Region

    • Stokes' law (Equation 3) applies at low Reynolds numbers (NRe < ~2)
    • For intermediate Reynolds numbers (500 to 200,000), drag coefficient is relatively constant for spherical particles
    • Newton's Law is applicable for higher Reynolds numbers
    • Ranges of equations for different Reynolds numbers (Table 2)

    Flocculation

    • Enhances sedimentation by causing small particles to aggregate into larger, faster-settling flocs
    • Coagulation and flocculation may occur sequentially or concurrently
    • Flocculation is the agglomeration of flocs formed during coagulation
    • Figure 3 shows the process of coagulation, flocculation, and subsequent sedimentation

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    CHE 301 Sedimentation PDF

    Description

    This quiz explores fundamental techniques used in separating chemical mixtures, emphasizing energy requirements and various methodologies. Key focus areas include multiphase mixtures, sedimentation processes, and operational strategies like thickening and clarification. Test your knowledge on the principles and applications of these separation techniques.

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