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Biochem Finals Period > Quiz 3 > Flashcards

Quiz 3 Flashcards

1
Q

Mass can be transferred from one place to another under the influence of a

A

concentration gradient

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2
Q

In biological multiphase systems, mass transfer takes place between

A

Two liquid phases, between a liquid and a solid phase, or between a gas and a liquid phase.

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3
Q

most large-scale fermentation processes are

A

aerobic

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4
Q

bioethanol and lactic acid production

A

anaerobic

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5
Q

Before being utilized, _________ must be moved via a sequence of processes from the
gas bulk onto the surfaces of cells.

A

oxygen

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6
Q

The solubility of oxygen within broth is typically _____

A

very low

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7
Q

During aerobic cultures and fermentations, improving _________is always
given priority

A

gas-liquid mass transfer

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8
Q

Example of transport resistances

A

Diffusion from bulk gas-liquid interface.
Movement through the gas-liquid interface.

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9
Q

Microbial cells themselves have some tendency to adsorb at

A

interfaces

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10
Q

__________concentration does not represent the oxygen supply for the
respiring microbes

A

the bulk dissolved O2

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11
Q

Mass transfer takes place by two basic processes

A

convection and diffusion

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12
Q

movement of component molecules in a mixture under the influence of a
concentration difference in the system

A

molecular diffusion

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13
Q

Diffusion of molecules occurs in the direction required to

A

eliminate the concentration gradient

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14
Q

It states that the molar flux of a component A relative to the average molal velocity of all
constituent JA is proportional to the concentration gradient dCA/dz

A

Fick’s first law of diffusion

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15
Q

Computing for diffusivity, When the solvent is water, Skelland (1974) recommends the use of the correlation
developed by

A

Othmer and Thakar

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16
Q

The three most common theories for mass transfer mechanisms are the

A

two-film theory, the surface renewal theory, and the penetration theory

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17
Q

This theory states that two fictitious films are present on either side of the interface that
causes the overall resistance to mass transfer and that takes place due to molecular diffusion

A

Two-Film Theory

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18
Q

In two-film theory, Concentration gradients are assumed to exist only in the

A

films

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19
Q

The two-film theory states that kl (mass-transfer coefficient) varies __________ as
the film thickness Ξ΄, whereas kl and DAB (diffusivity) are directly proportional to each other.

A

inversely

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20
Q

came up with the penetration theory in 1935

A

Higbie

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21
Q

assumes that turbulent eddies travel from the bulk to the interface and at the interface, they remain for an exposure time equal to t0.

A

Penetration theory

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22
Q

assumed by which the solute is assumed to penetrate a given eddy during its stay at the interface.

A

process of unsteady-state molecular diffusion

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23
Q

Penetration theory predicts that kl (mass-transfer coefficient) and the _______________ are directly proportional, whereas kl varies inversely as the ________

A

square root of DAB (molecular diffusivity); exposure time t0.

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24
Q

modified Higbie’s penetration theory for liquid phase mass transfer.

A

Danckwerts (1951)

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25
Q

states that a portion of the mass-transfer surface is replaced with a new surface by the motion of eddies near the surface assuming that the liquid elements at the interface are being randomly swapped by fresh elements from bulk and each of the liquid elements at the surface has the same probability of being substituted by a fresh element

A

surface renewal theory

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26
Q

Similar to the penetration theory, the mass
transfer coefficient is ___________ to the square root of diffusivity

A

directly proportional

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27
Q

at 1 atm of air and 25Β°C, the O2 collision rate at the surface is of the order of __________

A

10^24 molecules per square centimeter per second

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28
Q

At steady state, the oxygen transfer rate to the gas-liquid interface__________ its transfer rate
through the liquid-side film

A

equals

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29
Q

Thus, essentially all the resistance to mass transfer lies on the

A

liquid-film side

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30
Q

for the gas-phase mass-transfer coefficient Kg is approximately equal to kg if

A

M (distribution coefficient) is very small

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31
Q

Head space gas, in calculating oxygen absorption rate, is

A

not included

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32
Q

It is important to recognize that π‘„π‘œ2
is defined

A

β€œat a point

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33
Q

The maximum possible mass-transfer rate is simply found by setting

A

𝑐𝑙 = 0

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34
Q

all oxygen entering the bulk solution is assumed to be ________ consumed

A

rapidly

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35
Q

f π‘˜π‘™π‘Žπ‘π‘™ is much larger than π‘₯πœ‡π‘šπ‘Žπ‘₯/π‘Œπ‘œ2,
π‘Œπ‘œ2 , the main resistance to increased oxygen
consumption is ______________

A

microbial metabolism

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36
Q

If the main resistance to increased oxygen consumption is microbial metabolism, then the reaction appears to be

A

biochemically limited

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37
Q

the reverse inequality apparently leads to 𝑐𝑙 near zero, and the reactor seems to be in

A

the mass-transfer-limited mode

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38
Q

At steady state, the oxygen absorption and
consumption rates must_________

A

balance

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39
Q

If the cell metabolic machinery is saturate with oxygen, then sufficient oxygen is available to accept immediately all electron pairs which pass through the respiratory chain, so that some other biochemical process within the cell is

A

rate- limiting

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40
Q

In the batch-system results of Figure 4, a maximum in specific O2 demand occurs in the

A

early exponential phase

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41
Q

affects oxygen demand in a major way

A

carbon nutrient

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42
Q

generally metabolized more rapidly than other carbohydrate substances

A

glucose

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43
Q

The component parts of oxygen utilization by the cell include

A

cell maintenance, respiratory oxidation for further growth, and oxidation of substrates into related metabolic end products

44
Q

In metabolic stoichiometry, oxygen utilization for growth is typically coupled directly to

A

the amount of carbon-source substrate consumed

45
Q

Oxygen may also be consumed as a reactant in

A

biotransformation

46
Q

mass transfer between phases may often become the _________ of the overall
process rate

A

limiting step

47
Q

is used to improve mass transfer and also to insure homogeneous distribution of the nutrients in the liquid phase

A

Mixing ( by aeration and agitation )

48
Q

oxygen transport from the air is
necessary and obviously focused

A

aerobic systems

49
Q

the transport of
other gases such as methane or carbon dioxide usually takes place

A

anaerobic systems

50
Q

one of the most important nutrients for aerobic cells that need oxygen dissolved in
the broth for maintenance, growth and production of bioproducts

A

Oxygen

51
Q

in aerated bioreactors the critical limiting factor to providing the optimal environment is the

A

oxygen transfer rate (OTR)

52
Q

dependent on the vessel’s geometrical configuration and
the physical properties of the fluids

A

mass-transfer coefficient π‘˜L

53
Q

Three dimensionless numbers play a significant
role in the mass transfer process

A

(1) Sherwood Number, (2) Schmidt Number, and (3) Grashof Number.

54
Q

dimensionless number that represents the ratio of the convective mass transfer rate to the diffusive mass transfer rate

A

Sherwood number (Sh)

55
Q

Characteristic length, in bioprocessing applications, will be equivalent to the

A

diameter of the air bubbles

56
Q

A _____________ Sherwood number indicates that convection is the dominant mode of mass transfer

A

high

57
Q

A ____ Sherwood number indicates that diffusion is the dominant mode

A

low

58
Q

Describes the relationship between mass diffusivity over momentum diffusivity or vice versa

A

Schmidt number (Sc)

59
Q

this dimensionless number is most applicable to cases
that simultaneously involve mass and momentum diffusion

A

Schmidt number (Sc)

60
Q

often used to design and optimize
processes that involve mass transfer, such as aeration, fermentation, and filtration

A

Schmidt number (Sc)

61
Q

used to determine the rate of oxygen transfer from the air to a culture of
cells in a fermenter

A

Schmidt number (Sc)

62
Q

A _______ Schmidt number indicates that momentum transfer is more important than mass transfer, while a _______ Schmidt number indicates that mass transfer is more important than momentum transfer

A

High, low

63
Q

This number is mostly associated with the cases involving free (natural) convectio

A

Grashof Number (Gr)

64
Q

used to characterize the flow of fluids in bioreactors and other vessels

A

Grashof Number (Gr)

65
Q

A ________ Grashof number indicates that the flow is laminar, while a ______Grashof
number indicates that the flow is turbulent

A

low , high

66
Q

generally more effective at mixing
fluids, which can be important for bioprocesses that require good mixing, such as fermentation

A

Turbulent flow

67
Q

measure of how quickly an organism consumes oxygen

A

Oxygen-Absorption Rate (OAR)

68
Q

Oxygen-Absorption Rate (OAR) is also known as

A

Respiration Rate or Metabolic Rate

69
Q

OAR is typically measured in units of

A

milliliters of oxygen per minute per gram of body weight (ml O2/min/g BW)

70
Q

As oxygen is categorized as a sparingly soluble gas, the _______ is equal to e liquid-side individual mass transfer coefficient

A

overall mass transfer coefficient KL

71
Q

oxygen-transfer rate can be maximized by ___________ and air flow rate

A

minimizing the power consumption

72
Q

The oxygen absorption can be enhanced by increasing

A

interfacial area a, mass-transfer coefficient π‘˜πΏ
, and the concentration difference

73
Q

π‘˜πΏπ‘Ž is not a property of the ________, but a parameter of the _________

A

system; model adopted

74
Q

came up with the dynamic gassing out technique in 1979

A

Van’t Riet

75
Q

__________ monitors the change in the oxygen concentration, while an oxygen-rich liquid is deoxygenated by passing ________ through it

A

Dynamic gassing out technique, nitrogen

76
Q

usually used to measure the DO concentration

A

polarographic electrode

77
Q

It works by inducing an electrochemical
reaction with the dissolved oxygen, and the resulting electrical signal is proportional to the DO concentration

A

polarographic sensor

78
Q

In direct measurement technique, _______________ used to estimate the oxygen concentration in the gas stream entering and leaving the fermenter

A

a gaseous oxygen analyzer

79
Q

generally used to measure and evaluate the oxygen
concentration of the liquid in a fermenter

A

oxygen sensor

80
Q

largely depends on the size of the fermenter.

A

Difference in concentration term

81
Q

used the dynamic technique to estimate the π‘˜πΏπ‘Ž value for the oxygen transfer during an actual fermentation process with real culture medium and microorganisms

A

Taguchi and Humphrey

82
Q

implemented in a microorganism-rich aerated batch fermenter over which the
oxygen material balance is applied

A

Dynamic technique

83
Q

Despite a steady dissolved oxygen level in the fermenter, the oxygen concentration will be
_________ if the air supply is turned off

A

decreased sharply

84
Q

based on the oxidation of sodium
sulfite to sodium sulfate in the presence of catalyst (Cu++ or Co++)

A

Sodium sulfite oxidation method (Cooper et al., 1944)

85
Q

it is possible to determine the oxygen transfer rate by using an

A

Oxygen consuming chemical reaction

86
Q

Traditional sulfite method is based on the _______ by
oxygen

A

oxidation of sulfite to sulfate

87
Q

the rate of sulfite consumption is determined solely by the rate at which

A

oxygen is transferred from the gas phase

88
Q

The dissolved oxygen concentration, cO, is virtually ________ due to the very rapid reaction with sulfite

A

zero

89
Q

__________ is determined by measuring the concentration of sulfite in samples taken
at a set of time values after the start of the experiment

A

The reaction rate

90
Q

can be determined by adding an excess amount of iodine, and thereafter back-titrate with thiosulfate, using starch as an indicator

A

sulfite concentration in the samples

91
Q

may enhance the oxygen absorption, since the rapid chemical reaction may occur not only in the bulk liquid, but also in the liquid film

A

sulfite oxidation

92
Q

The significant coalescence-reducing effects of sulfite on the bulk liquid results in a_________specific interfacial area.

A

higher

93
Q

Both the enhancement of mass transfer due to reaction in the film, and the _________, may lead to an overestimation of π‘˜πΏa

A

coalescence-reducing effect of sulfite

94
Q

This method due to Hickman (1988) is, like the sulfite method, a chemical method

A

Hydrogen peroxide method

95
Q

the transfer of oxygen from the liquid to the gas phase is measured

A

Hydrogen peroxide method

96
Q

generated by the enzyme-catalyzed decomposition of hydrogen peroxide

A

oxygen

97
Q

At steady state, the rate of decomposition of hydrogen peroxide equals____________
from the liquid phase to the gas phase

A

half the rate of oxygen transfer

98
Q

calculated from the gas phase partial pressure of oxygen.

A

interfacial concentration of oxygen

99
Q

Hickman used the assumption of _______ of
both the liquid and the gas phase

A

complete back-mixing

100
Q

The risk of enhancing the mass transfer by reaction in the liquid film is _______ in h2o2 method

A

smaller

101
Q

the effect of the small added amount of catalase on the coalescence of the medium is _________ in h2o2 method

A

negligible

102
Q

The method has been applied with good results for π‘˜πΏπ‘Ž measurements in large industrial reactors,
also with viscous, non-Newtonian media

A

H2O2 method

103
Q

in fermentation processes is a common problem

A

Foam formation

104
Q

Foaming is controlled routinely in fermenters using a

A

foam sensor and
pump for automatic addition of antifoam agent

105
Q

Therefore, antifoam addition will be triggered more often if the working volume of the vessel is

A

increased

Biochem Finals Period (5 decks)

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