Transport Phenomena in Bioprocess Engineering
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What is the primary focus of studying transport phenomena in bioprocess systems?

  • Understanding chemical reaction rates only
  • Studying how substances move during biochemical processes (correct)
  • Analyzing nutrient efficiency in plants
  • Evaluating equipment performance in isolation

    • Which of the following is a factor influencing oxygen transfer efficiency in bioreactor systems?

  • Temperature gradients within the solution (correct)
  • The concentration of carbon dioxide only
  • The viscosity of the growth medium (correct)
  • Size of the bioreactor tank

    • What does the volumetric mass transfer coefficient (KLa) indicate?

  • Momentum transfer between fluids
  • The rate of heat loss in bioreactors
  • The effectiveness of oxygen transfer (correct)
  • Efficiency of solute concentration

    • Which method is typically used to determine oxygen transfer rates in bioreactors?

    <p>Applying the mass balance approach</p> Signup and view all the answers

    Which phenomenon can dominate the overall rate of solute processing in a reaction volume?

    <p>Physical-transport phenomena</p> Signup and view all the answers

    How can foam formation impact oxygen transfer in bioprocesses?

    <p>It can reduce oxygen transfer efficiency</p> Signup and view all the answers

    What is momentum transport primarily related to in bioprocess engineering?

    <p>Fluid dynamics and circulation</p> Signup and view all the answers

    What is one of the key roles of transport phenomena in biochemical engineering?

    <p>To design efficient bioprocesses</p> Signup and view all the answers

    What was the percentage decrease in kL when 10 ppm of sodium lauryl sulfate (SLS) was added?

    <p>56 percent</p> Signup and view all the answers

    What is the primary characteristic of passive transport?

    <p>It occurs naturally from high to low concentration.</p> Signup and view all the answers

    At what concentration of surfactant did the lowest kLa' value occur?

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

    What happened to the value of kLa' with increasing concentrations of surfactant?

    <p>It plateaued after a certain point</p> Signup and view all the answers

    Which type of transport requires energy to move substances across membranes?

    <p>Active transport</p> Signup and view all the answers

    How much did kLa' increase with the addition of 4.0 ppm of sodium dodecyl sulfate?

    <p>400 percent</p> Signup and view all the answers

    Which resistance is encountered first during the transport of a gas bubble into a cell?

    <p>Diffusion from bulk gas to gas-liquid interface</p> Signup and view all the answers

    What effect does cellular activity have on gas transport efficiency?

    <p>It decreases the transport resistances.</p> Signup and view all the answers

    What is the approximate reduction in kL typically observed with the addition of surfactants?

    <p>60 percent</p> Signup and view all the answers

    What effect do electrolytes have on bubble size in mechanical force-generated bubbles?

    <p>They decrease bubble size</p> Signup and view all the answers

    Which of the following is NOT a factor affecting the efficiency of gas transfer?

    <p>Concentration of the gas in the atmosphere</p> Signup and view all the answers

    What happens to the sixth resistance in gas transport if microbial cells are individual rather than aggregated?

    <p>It does not occur during transfer.</p> Signup and view all the answers

    What effect does electrostatic potential at the surface of aqueous electrolyte solutions have?

    <p>It decreases the rate of bubble coalescence</p> Signup and view all the answers

    What is recommended when using correlations for kL values obtained with surfactants?

    <p>To substitute them with experimental values whenever feasible</p> Signup and view all the answers

    What role do microbial cells have at the gas-liquid interface during gas transport?

    <p>They create a barrier preventing diffusion.</p> Signup and view all the answers

    What is the main process involved in the transport of solute across the cell envelope?

    <p>Active transport</p> Signup and view all the answers

    What assumption does the penetration theory make about turbulent eddies?

    <p>They remain at the interface for a specific time, t0.</p> Signup and view all the answers

    How is the mass transfer coefficient (kL) related to molecular diffusivity (DAB) in the penetration theory?

    <p>It is directly proportional to the square root of molecular diffusivity.</p> Signup and view all the answers

    What modification did Danckwerts make to Higbie's penetration theory?

    <p>He modified it for liquid phase mass transfer.</p> Signup and view all the answers

    What is the relationship between exposure time (t0) and the mass transfer coefficient in penetration theory?

    <p>It is inversely proportional.</p> Signup and view all the answers

    According to penetration theory, what allows the solute to penetrate the eddy at the interface?

    <p>Unsteady-state molecular diffusion.</p> Signup and view all the answers

    What is a key element of the surface renewal theory?

    <p>It focuses on surface renewal events in mass transfer.</p> Signup and view all the answers

    Which equation represents the relationship used in the penetration theory?

    <p>$k_L = 2 \frac{D}{\pi t_0}$</p> Signup and view all the answers

    What does the constant D represent in the equation related to mass transfer coefficient?

    <p>The diffusivity of the solute.</p> Signup and view all the answers

    What is one advantage of the dynamic pressure method in kLa measurement?

    <p>It eliminates the need for gas composition adjustments.</p> Signup and view all the answers

    Why is the sulfite oxidation method generally discouraged for measuring kLa?

    <p>Results vary unpredictably with operating conditions.</p> Signup and view all the answers

    What complicates measurements in the dynamic pressure method?

    <p>Changes in bubble size after a pressure shift.</p> Signup and view all the answers

    What is a key aspect of modifying methods used to estimate kLa?

    <p>Integrating mass transfer processes and liquid film resistance.</p> Signup and view all the answers

    How does bubble size influence kLa measurements in salt solutions?

    <p>It affects the coalescence properties of bubbles.</p> Signup and view all the answers

    What technique is often compared to the sulfite oxidation method for measuring kLa?

    <p>Dynamic pressure method.</p> Signup and view all the answers

    What impact does the oxygen probe's pressure tolerance have on kLa measurement?

    <p>Allows for accurate readings during pressure fluctuations.</p> Signup and view all the answers

    What is a common issue when applying the simple dynamic method for kLa measurement?

    <p>Complications with gas hold-up.</p> Signup and view all the answers

    What is the relationship between the diffusivity of A in B and the correlation suggested by Othmer and Thakar for water?

    <p>It requires specific SI units for accuracy.</p> Signup and view all the answers

    What does the variable $D°$ represent in the provided equations?

    <p>Diffusivity of A in B in a very dilute solution.</p> Signup and view all the answers

    How is the association factor ($\xi$) for the solvent water described in the content?

    <p>2.26 for water.</p> Signup and view all the answers

    Which of these parameters is NOT part of the equations provided?

    <p>Density of the solvent.</p> Signup and view all the answers

    What is the experimental value given for the diffusivity of oxygen in water at 25°C?

    <p>$2.5 imes 10^{-9} m^2/s$</p> Signup and view all the answers

    Which correlation is suggested for use with water as the solvent?

    <p>Othmer and Thakar correlation.</p> Signup and view all the answers

    Why should the equations for $D°$ not be considered for concentrated solutions?

    <p>They are derived from experimental values in dilute conditions.</p> Signup and view all the answers

    What unit is specified for the viscosity ($oldsymbol{ u}$) in the equations?

    <p>kg/m·s</p> Signup and view all the answers

    In the context of the equations, what does the term $V$ represent?

    <p>Solute molecular volume at the normal boiling point.</p> Signup and view all the answers

    What is a common misconception regarding the application of the discussed equations?

    <p>All solvents exhibit the same association factors.</p> Signup and view all the answers

    Study Notes

    Introduction

    • Biological systems grow increasingly complex as they scale from molecular to fluid volumes.
    • Transport phenomena can be a major factor affecting overall reaction rates in large biological systems.

    Learning Objectives

    • Understanding transport phenomena in bioprocess systems
    • Identifying methods to determine oxygen transfer rates in bioreactors
    • Understanding the volumetric mass transfer coefficient (KLa) and its effect on oxygen transfer efficiency
    • Recognizing factors influencing oxygen transfer efficiency and their effect on cell culture performance
    • Evaluating the impact of foam formation and anti-foam agents on oxygen transfer efficiency

    Gas-Liquid Mass Transfer in Cellular Systems

    • Transport phenomena involves the movement of substances like fluids, heat, or particles during chemical and biochemical processes.

    • Principles of transport are fundamental to the design and operation of bioprocesses.

    • Momentum transport (fluid dynamics): important processes like blood circulation and mixing in bioreactors

    • Mass transport: important for movement of chemical species, like oxygen transport to aerobic microorganisms

    • Energy (heat) transport: critical for processes like reactor sterilization and temperature control.

    Determination of Oxygen Transfer Rates

    • Aerobic cultures require a continuous oxygen supply for cell growth and metabolic activity.
    • Insufficient oxygen can damage or kill cells.
    • Engineers utilize aeration to maintain optimal oxygen levels.

    Determination of KLa values

    • The volumetric mass transfer coefficient (kLa) is a crucial parameter in bioreactors.
    • It characterizes the efficiency of oxygen transfer from the gas phase to the liquid phase.

    Factors Affecting KLa values in bioreactors

    • Degree of Agitation: Increased power input generally means smaller bubbles, enhancing oxygen transfer but exceeding optimal levels may be detrimental to microorganisms.

    • Medium Culture Rheology: The viscosity of the medium impacts mass transfer rates; non-Newtonian fluids exhibit various viscosities in different conditions.

    Effects of Foam and Anti-foam on Oxygen Transfer

    • Foaming can affect the gas-liquid interface's effective area for oxygen transfer, affecting oxygen uptake rates
    • Factors like surface-active substances, hydrodynamic conditions, and cell/product concentration can affect foam generation and stability.
    • Anti-foam agents help control foam and thus maintaining steady oxygen supply to the culture.

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    Description

    This quiz focuses on the fundamental concepts of transport phenomena within bioprocess systems. Questions explore topics such as oxygen transfer efficiency, volumetric mass transfer coefficient (KLa), and the effects of surfactants on bioreactor performance. Dive deep into the principles that govern the movement of substances in biochemical engineering.

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