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Right option is (a) True

To ELABORATE: A bioreactor is divided in a working volume and a headspace volume. The working volume is the FRACTION of the total volume TAKEN up by the medium, microbes, and gas bubbles. The remaining volume is called the headspace. Typically, the working volume will be 70-80% of the total fermenter volume. This value will however depend on the rate of foam formation during the reactor. If the medium or the fermentation has a tendency to foam, then a larger headspace and SMALLER working volume will need to be USED.

The correct option is (b) False

Easiest explanation: Note that it is very important that an “instrument AIR” compressor is not USED. Instrument air is typically generated at higher pressures but is aspirated with oil. Instrument air compressors are used for pneumatic control. Air compressors used for large scale bioreactors typically produce air at 250 kPa. The air should be dry and oil free so as to not block the inlet air FILTER or contaminate the medium.

Correct CHOICE is (b) 1 rps

For explanation I would SAY: N = REVOLUTIONS per sec (rps). The AGITATION speed is given in the example as 60 revolutions per minute, which when divided by 60 seconds/minute yields:

N = 60 rpm / 60 = 1 rps.

Right choice is (a) 977,035

Explanation: NRE = Reynolds number for AGITATED liquids = ( D^2 * N * ρB / μB).

NRe = (3.02 * 3,600 * 64.0 / 2.12)

NRe = 977,035.

Right answer is (a) True

The best explanation: VISCOSITY increases with INCREASING pressure because the amount of free volume in the internal structure decreases due to compression. Consequently, the molecules can move LESS freely and the internal friction FORCES increase. The result is an INCREASED flow resistance.

The CORRECT OPTION is (a) 4.62 m

For explanation I WOULD SAY: Agitator Impeller Diameter, D = 33 % of tank diameter = 14 * 33% m = 4.62 m.

The correct option is (b) False

Easy explanation: Liquids into which gas is sparged have reduced power requirements. Gas BUBBLES decrease the DENSITY of the fluid. The presence of bubbles also affects the hydrodynamic behaviour of fluid around the impeller. LARGE gas-filled cavities develop BEHIND the stirrer blades in aerated liquids; these cavities reduce the resistance to fluid flow and decrease the drag COEFFICIENT of the impeller. With sparging, the power consumed could be reduced to as little as half the ungassed value, depending on gas flow rate.

Right choice is (C) 0.5 N/m^2

Easiest EXPLANATION: Given: Shear velocity u = 0.25 m/s,

shear stress y = 0.125/s

dynamic VISCOSITY μ = 2 Ns/m^2

The shearing stress is given by,

F = μ A u/y

F = 2 Ns/m^2 × 0.125 /s

F = 0.5 N/m^2

Therefore, the shearing stress is 0.5 N/m^2.

The correct ANSWER is (b) 2463 m^3

The explanation is: FLUID Height in Tank , H = 16 m and DIAMETER of tank, D = 14 m

Slurry volume in tank = π * D^2*H/4 =π * (14)^2*16 / 4 = 2463 m^3.

Right answer is (a) True

For EXPLANATION: Thixotropic behaviour is not uncommon in cultures CONTAINING fungal mycelia or EXTRACELLULAR microbial POLYSACCHARIDES, and APPEARS to be related to reversible ‘structure’ effects associ – ated with the orientation of cells and macromolecules in the fluid.

Correct option is (c) inertial forces to VISCOUS forces

For explanation: The Reynolds number is the ratio of inertial forces to viscous forces WITHIN a fluid which is subjected to relative internal movement due to different fluid velocities, in which is KNOWN as a boundary layer in the case of a BOUNDING SURFACE such as the interior of a pipe.

Correct answer is (b) False

Easiest EXPLANATION: An important concept in fluid MECHANICS is that liquids, like water and OIL, cannot be compressed much when you push down on them in an enclosed CONTAINER. So, liquids are CONSIDERED to be incompressible fluids.

Correct ANSWER is (a) 30.11 cSt

The BEST I can explain: V = μ/ρ = 0.0241/800 = 30.11×10-6 m^2/s or 30.11 cSt.

The correct answer is (c) Negative normal STRESS and zero SHEAR stress

For explanation: Fluid with zero shear stress within it is known as static fluid. When ever fluid moves it undergoes CONTINUOUS deformation DUE to shear (caused due to VISCOSITY of the fluid). So when the fluid is in rest no shear stress develops and only normal stress exists. So static fluid has zero shear stress.

Correct choice is (c) 1698 cm/s

Explanation: The FLOW RATE (A1v1) of the WATER APPROACHING the constriction must be equal to the flow rate leaving the hose (A2v2). This gives:

v2 = \(\FRAC{A_1 v_1}{A_2}\)

= \(\frac{(\pi)(106.1)}{(\pi)(0.5/2)^2}\)

= 1698 cm/s.

Right answer is (a) 5.3 Hp

For EXPLANATION: The correlations calculate the DELIVERED Power to the fluid. This must be corrected BACK to the agitator motor and account for efficiency LOSSES in the motor, gearbox, and bearings.

PDelivered = (NP ρB * N^3 * DA^5) / GC

PDelivered = 6 * 64 * 1^3 * 3^5 / 32.2

PDelivered = 2,898 ft-lb/sec

or using 550 ft-lb/sec per Hp,

PDelivered = 5.3 Hp.

The correct choice is (a) Temperature

To explain: Along with the shear rate, temperature really is the dominating INFLUENCE. The higher the temperature is, the lower a substance’s VISCOSITY is. CONSEQUENTLY, decreasing temperature causes an increase in viscosity. For some FLUIDS a decrease of 1°C already causes a 10 % increase in viscosity.

Right answer is (b) LESS than 3°

Best explanation: The angle Φ between the plate and cone is very small, usually less than 3°, and the FLUID to be measured is located in this small gap. Large cone angles are not used for ROUTINE work for a VARIETY of reasons, the most important being that analysis of the results for non-Newtonian fluids WOULD be complex or impossible.

The correct choice is (b) False

Easy explanation: When a shear force is EXERTED on some fluids, the apparent VISCOSITY EITHER increases or decreases with duration of the force. If apparent viscosity increases with time, the fluid is SAID to be rheopectic; rheopectic fluids are relatively rare in OCCURRENCE. If apparent viscosity decreases with time the fluid is thixotropic.

Right OPTION is (b) False

Explanation: If the viscosity of the fluid is increased, the size of the smallest eddies also increases. INCREASING the fluid viscosity should, THEREFORE, reduce SHEAR DAMAGE in bioreactors.

The correct OPTION is (c) Turbulent flow

Best explanation: The slower the flow the more closely the streamlines represent actual MOTION. SLOW FLUID flow is therefore called streamline or laminar flow. In fast motion, fluid particles frequently cross and recross the streamlines. This motion is called turbulent flow and is characterized by FORMATION of eddies.

The correct answer is (a) Study of MATERIALS with both solid and fluid characteristics

Easy explanation: It is the study of the flow of matter, primarily in a liquid state, but also as “soft SOLIDS” or solids under conditions in which they respond with plastic flow rather than DEFORMING elastically in response to an applied FORCE. It is a BRANCH of physics which deals with the deformation and flow of materials, both solids and liquids.

Right option is (b) 1.29 × 10^-6 m^2s^-1

Easiest explanation: Damage due to eddies is avoided if the \(K \ddot{o}\) 1mogorov scale remains greater than 2/3-1/2 the diameter of the beads. LET US determine the stirrer speed required to create eddies with size, λ = 2/3 (120 μm) = 80 μm = 8 x 10^-5 RN. The stirrer power producing eddies of this dimension can be estimated:

Kinematic viscosity, v = \(\frac{\MU}{\rho} = \frac{1.3×10^{-3} kg \,m^{-1} s^{-1}}{1010 \,kgm^{-3}}\) = 1.29 × 10^-6 m^2s^-1.

Correct option is (d) LESS than 2100

For explanation: One of the most significant outcomes of REYNOLDS’ experiments is that there is a critical Reynolds number which marks the UPPER boundary for laminar flow in pipes. In SMOOTH pipes, laminar flow is encountered at Reynolds numbers less than 2100. Under normal conditions, flow is turbulent at Re above about 4000. Between 2100 and 4000 is the transition region where flow may be either laminar or turbulent depending on conditions at the entrance of the pipe and other variables.

Correct choice is (d) It provides PROTECTION and SURFACE area

Explanation: The microcarrier beads are used to increase the number of adherent CELLS per flask and are EITHER dextran or glass based, they come in a range of densities and SIZES. The beads are buoyant and therefore can be used with spinner culture flasks. The surface area available for cell growth on these beads is huge. It is a support matrix allowing for the growth of adherent cells in bioreactors.

Correct answer is (b) Stirred Tank fermenter

To explain I WOULD say: Mixing is usually carried out in a stirred tank; Stirred tanks are usually cylindrical in shape. If possible, the base of the tank is rounded at the edges rather than angled; this ELIMINATES sharp CORNERS and pockets into which fluid currents may not penetrate and DISCOURAGES formation of stagnant REGIONS.

Correct option is (d) Dilatant

Easy explanation: When physicochemical interactions create bonds that are STRONG enough to resist breakage during shear, this mechanism WOULD dominate and dilatant (shear-thickening) behavior is observed. Shear-thinning fluids are used for lubrication and paints and require less VOLUME. Its VISCOSITY increases as the shear rate increases.

Right answer is (b) Decrease

Best explanation: The SIZE of the particles of a substance will greatly affect its viscosity. Small particles can move more EASILY past each other and can therefore flow FASTER, meaning they have a lower viscosity. Large particles would MEAN a higher viscosity.

The CORRECT OPTION is (d) 6.6 Hp

Best EXPLANATION: PMotor = PDelivered / ( 1 – Losses )

PMotor = 5.3 / ( 1 – 0.20 )

PMotor = 6.6 Hp.

The CORRECT answer is (a) Increase

To elaborate: A gas’s viscosity increases when heated (more energy causing more MOVEMENT + THEREFORE more friction because particles are hitting each other). DECREASES when COOLED.

Right choice is (b) 50

For explanation I would SAY: Ten poise equal one pascal SECOND [Pa s] MAKING the centipoise [CP] and millipascal second [MPA s] identical.

1 Pa-s = 10 P

So,

5 Pa-s = 50 P.

The correct option is (d) 0.894 cm

To ELABORATE: The area is PROPORTIONAL to the square of diameter, so:

v1d1^2 = v2d2^2

d2^2 = v1d1^2 / V2 = \(\frac{(4 \frac{m}{s})(2cm)^2}{(20 cm)^2}\)

d2 = 0.894 cm

Correct answer is (a) True

To EXPLAIN I would SAY: Particles of the same substance have an attractive force on ONE another. Some substances have a strong attraction while some substances have a weaker attraction. The STRONGER the attraction of particles, the higher the VISCOSITY.

The correct OPTION is (c) 0.917

The BEST I can EXPLAIN: Given DATA: Volume = 5 m^3

Weight = 45 kN

Specific weight of water = 9.807 kN/m^3

The correct option is (a) True

Best explanation: The LAMINAR region extends to higher REYNOLDS numbers in pseudoplastic fluids than in NEWTONIAN systems. At Rei below 10 and above 200 the results for Newtonian and non-Newtonian fluids are essentially the same; in the intermediate range, pseudoplastic liquids consume LESS power than Newtonian fluids. Flow patterns in pseudoplastic and Newtonian fluids differ significantly. Even when there is high turbulence near the IMPELLER in pseudoplastic systems, the bulk liquid may be moving very slowly and consuming relatively little power.

Correct ANSWER is (a) 106.1 cm/s

To EXPLAIN: The cross-sectional area of the hose will be GIVEN by:

A1 = π r^2 = π (2 cm/2)^2 = π cm^2

To FIND the velocity, v1, we use

Flow rate = A1 v1 = 20.0 L/min = \(\FRAC{20.0 × 10^3 cm^3}{60.0 s}\)

v1 = \(\frac{20.0 × \frac{10^3 cm^3}{60.0s}}{\pi cm^2}\)

= 106.1 cm/s

Right option is (b) False

Explanation: Simple circular flow of liquid around the shaft is generally disadvantageous and should be AVOIDED. In circular flow, liquid moves in a STREAMLINE fashion and there is little mixing between fluid at different heights in the tank. Circular flow also LEADS to vortex development. At high impeller SPEEDS, the vortex may reach down to the impeller so that gas from the surrounding atmosphere is drawn into the liquid; this is generally undesirable as it produces very high mechanical stresses in the stirrer shaft, bearings and seal. PREVENTION of circular flow has a high priority in design of mixing systems, and is usually achieved by installing baffles which interrupt the circular flow pattern and create turbulence in the fluid.

The correct option is (a) 1.46 N/m^3

To explain I would say: GIVEN DATA: Velocity profile V = 5y^2 + y;

μ = 8.35 poise

Substituting y=7.5 on the above equation, we get SHEAR stress at RESPECTIVE depths.

τ = 1.46 N/m^3.