PART 3 - Transport Phenomena in Bioprocess System

Question 1

According to _____________________________ (1961), two correlations adequately explain their data regarding the absorption of gases that are sparingly soluble into liquids that subsequently chemically consume the gas.

Answer 1

Calderbank and Moo-Young

Question 2

There are two clear regimes of bubble-swarm mass-transfer, with a critical bubble diameter Dc indicating the boundary between them. Dc ≈ 2.5 mm when surfactants are not present:

Answer 2

Bigger bubbles
Smaller bubbles

Question 3

_________ bubbles than this are usually found in sieve-plate columns and agitated tanks containing pure water.

Answer 3

Bigger

Question 4

__________ bubbles are commonly observed in agitated vessels containing hydrophilic solutes in aqueous solution and sintered-plate columns.

Answer 4

Smaller

Question 5

What are the factors affecting bubble size?

Answer 5

1. Bubble formation
2. Bubble breakup
3. Bubble coalescence

Question 6

It is determined by instabilities in the gas stream that enters the liquid phase, which cause the stream to fragment into separate bubbles instead of moving continuously through the vessel.

Answer 6

Bubble formation

Question 7

It depends on the competition between surface tension, which stabilizes the bubble, and local fluid forces, which tend to tear the bubble apart.

Answer 7

Bubble breakup

Question 8

The probability of _______________________ depends on the properties of the gas-liquid interface.

Answer 8

bubble coalescence

Question 9

In real dispersions, like those involving bubbles in a liquid, often encounter a variety of bubble sizes rather than a uniform size throughout. This variation is known as a:

Answer 9

distribution of bubble sizes

Question 10

To characterize this distribution and provide a representative size, the ________________________________________ is utilized.

This is a surface-averaged measurement, offering a characteristic or mean size for the bubbles present in the dispersion.

Answer 10

Sauter mean bubble diameter (Dsm)

Question 11

___________ (1983) reviewed a number of studies on gas-liquid mass transfer in low viscosity fluids in agitated vessels.

The relationship fits the results of numerous experiments conducted in various vessels with various mixer configurations within a 20–40% range.

Answer 11

Van’t Riet

Question 12

What are the factors affecting KLa values in bioreactor ?

Answer 12

1. Estimation of Diffusivities
2. Ionic Strength
3. Surface-Active Agents
4. Effects of Electrolytes
5. Presence of Cells

Question 13

The __________________________________ is frequently used to compare the effectiveness of bioreactors and as an important scale-up factor.

Answer 13

volumetric mass transfer coefficient (kLa)

Question 14

______________ can be referred to as the measurement of the total concentration of ions in the solution, weighted by ion charge. It is denoted by 𝜇.

The greater the magnitude of the charge, the ________ the magnitude of the concentration, and thus the __________ the ionic strength.

Answer 14

Ionic strength

greater
greater

Question 15

Many biochemicals are ____________, meaning they contain hydrophilic and hydrophobic moieties that tend to concentrate at gas-liquid and liquid-liquid interfaces.

Answer 15

amphipathic

Question 16

What is a moiety?

Answer 16

A moiety is a part of the chemical structure of a molecule or compound that could include a substructure, such as a functional group.

Question 17

Most of kLa data published are gathered through physical absorption or desorption using clean water.

It is common knowledge that mechanical force-generated bubbles in electrolyte solutions are considerably _______ than those in pure water.

Answer 17

smaller

Question 18

The physical presence per se of microbial cells in the broth will affect the kLa values in ___________________________.

Answer 18

bubbling-type fermenters.

Question 19

The rates of oxygen absorption into aqueous suspensions of sterilized yeast cells were measured in:

Answer 19

(i) an unaerated stirred tank with a known free gas–liquid interfacial area.
(ii) a bubble column; and
(iii) an aerated stirred tank.

Question 20

Data acquired with scheme (i) showed that the kL values were only minimally affected by the presence of cells, whereas for schemes (ii) and (iii), the gas holdup and kLa values were decreased somewhat with increasing cell concentrations, due to increased bubble sizes.

Question 21

_______________ the fermentation broth ensures uniform air distribution within the medium. When you blend a solution, you introduce energy into the system.

Answer 21

Agitating

Question 22

Higher power input leads to ________ bubbles, thereby increasing the interfacial area. Consequently, the mass transfer coefficient is expected to be influenced by both the power input per unit volume of the fermentation broth and the gas’s superficial velocity.

Answer 22

smaller

Question 23

The discussion of agitation that follows pertains to fluids that exhibit characteristics similar to Newtonian fluids.

Question 24

Since mixing is a multifaceted process, the relevant factors are collectively evaluated using a dimensionless parameter called the ______________. This number is employed to describe the flow behavior.

Answer 24

Reynolds number (Re)

Question 25

Another set of dimensionless parameters employed to describe mixing in a container is the ________________, which incorporates **gravitational forces** into its calculation:

Answer 25

Froude number (Fr)

Question 26

_____________________ is influenced by fluid properties, including fluid density and viscosity, the agitator's rotational speed, and the impeller's diameter.

Answer 26

Power consumption

Question 27

Four Types of Agitators:

Answer 27

1. Turbine Disk (Rushton) 2. Turbine Inclined Blades 3. Propeller, marine type 4. Intermig

Question 28

To achieve **optimal mixing**, a turbine typically features between **four to six** blades. Turbines equipped with flat blades create a radial flow pattern, which proves effective for dispersing gas within the medium. In this process, the gas is introduced just beneath the impeller, drawn upward to the blades, and fragmented into consistent, small bubbles.

Answer 28

A. Turbine disk (Rushton)

Question 29

The most common type of agitator is turbine. It consists of several short blades mounted on a central shaft. The diameter of a turbine is normally 35–45% of the tank diameter.

Answer 29

B. Turbine inclined blades

Question 30

The propeller agitator with three blades rotates at relatively high speeds of 60–300 rps; highly efficient mixing is obtained. The generated flow pattern is axial flow since the fluid moves axially down to the center and up the side of the tank.

Answer 30

C. Propeller, marine type

Question 31

The intermig agitator represents a relatively new innovation in agitator design. It takes the form of an **axial pumping impeller with blades positioned at opposing angles** to each other. Comparing an intermig agitator to a disk turbine agitator, the former delivers a more uniform energy transfer to the liquid in the container. As a result, this agitator **requires lower power and less air input** to achieve equivalent mixing and the same mass transfer coefficient.

Answer 31

D. Intermig

Question 32

__________ is the science of deformation and flow. It is the study of how matter flows, often in a liquid state, but also in the case of "soft solids" or solids that deform under a specific force rather than bouncing back elastically

Answer 32

Rheology

Question 33

This fluid can be identifiable by a single viscosity coefficient at a particular temperature. In this case, viscosity varies with temperature but **remains constant with respect to strain rate**.

Answer 33

Newtonian Fluid

Question 33

This is a wide range of fluids whose **viscosity is influenced by strain rate** (the relative flow velocity). The categorization of these fluids is determined by how shear stress and shear rate are connected within the fluid.

Answer 33

Non-Newtonian Fluid

Question 34

This denotes how a material's deformation or strain changes over time.

Answer 34

Strain rate

Question 35

All gases, water, dispersions of gas in water, low-molecular-weight liquids, aqueous solutions of low-molecular-weight

Answer 35

Newtonian

Question 36

Rubber solutions, adhesives, polymer solutions, some greases, starch suspensions, cellulose acetate, mayonnaise, some soap and detergent slurries, some paper pulps, paints, wallpaper paste, biological fluids

Answer 36

Pseudoplastic

Question 37

Cornstarch-water mixture, quicksand

Answer 37

Dilatant

Question 38

Some plastic melts, margarine, cooking fats, some greases, toothpaste, some soap and detergent slurries, some paper pulps.

Answer 38

Bingham Plastic

Question 39

Blood, tomato sauce, orange juice, melted chocolate, printing ink

Answer 39

Casson Plastic