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Right answer is (C) Henry’s law

To explain: Solubility of AIR in water follows Henry’s Law – “the amount of air dissolved in a fluid is PROPORTIONAL to the pressure in the system” – and can be expressed as:

c = pg / kH

where, c = solubility of dissolved gas

kH = proportionality constant depending on the NATURE of the gas and the solvent

pg = partial pressure of gas (Pa, psi)

The solubility of OXYGEN in water is higher than the solubility of nitrogen. Air dissolved in water contains approximately 35.6% oxygen compared to 21% in air.

Correct option is (a) True

The explanation: In air-lift FERMENTERS, Medium circulation is also accomplished with bubble formation. kLa obtained in air-lift reactor will be LESS than bubble FERMENTER due to shorter contact TIME between bubble and medium.

Right choice is (a) True

The best I can explain: In a non-coalescing liquid, the bubbles REMAIN close to the SIZE produced at the back of the cavities. Because bubbles formed at the sparger are IMMEDIATELY drawn into the impeller zone, dispersion of gas in stirred vessels is largely independent of sparger design; when the sparger is located under the stirrer, it has been shown that sparger type does not SIGNIFICANTLY affect mass TRANSFER.

Correct OPTION is (a) Density

Explanation: The molecular TRANSFER equations of Newton’s law for fluid MOMENTUM, FOURIER’s law for heat, and Fick’s law for mass are very similar. One can convert from one transfer coefficient to another in order to COMPARE all three different transport phenomena.

Right OPTION is (c) Number of cells

For explanation: The concentration of cell increases during COURSE of batch culture and the total rate of OXYGEN uptake is proportional to the no. of cell present. The rate of oxygen consumption per cell also known as oxygen uptake rate (OUR):

QO = qox

Where: Qo = oxygen uptake rate per volume broth (gL^-1 s^-1)

qo = specific oxygen transfer rate (gg^-1 s^-1).

Right CHOICE is (a) mol m^−2 s^−1

Explanation: J is the “diffusion flux,” of which the dimension is amount of substance per unit area per unit time, so it is expressed in such UNITS as mol m^−2 s^−1. J MEASURES the amount of substance that will flow through a unit area during a unit time INTERVAL.

The CORRECT ANSWER is (a) 1.539×10^-5 m^2/sec

To EXPLAIN: DIFFUSIVITY of O^2 in the MIXTURE,

Right option is (c) 0.081 s^-1

The explanation: \(\bar{(C_{AL})}\) = 78% AIR SATURATION. Let us define t1 = 5s, CAL1 = 50%, T2 = 15 s and CAL2 = 66%. From the equation:

The correct option is (b) Obligate AEROBES

Easiest explanation: Most cells are aerobic and therefore need to be supplied with oxygen to GROW (obligate aerobes). Some find oxygen toxic and grow badly in its presence (obligate anaerobes), while OTHERS grow better when oxygen is present, but CONTINUE to do so if its absence (FACULTATIVE anaerobes).

Correct CHOICE is (a) Rate of OXYGEN transfer per UNIT VOLUME of fluid

The explanation is: NA is the rate of oxygen transfer per unit volume of fluid (gmol m^-3s^-I), NA is the rate of Oxygen transfer of component A.

Correct OPTION is (d) Radiation

For explanation I would say: Radiation is the FASTEST mode of transfer of HEAT, because radiation travels at the speed of light, which is very quick. The slowest mode of transfer of heat is CONDUCTION because it takes place from particle to particle. The fastest is radiation at the speed of light 3,00,000 km in ONE second.

The CORRECT choice is (a) True

For explanation: kL in FERMENTATION LIQUIDS is about 3-4×10^-4 m s^-1 for bubbles greater than 2-3 mm DIAMETER; this can be reduced to 1×10^-4m s^-1 for smaller bubbles depending on bubble rigidity. Once the bubbles are above 2-3 mm in size, kL is relatively constant and insensitive to conditions.

Right option is (c) Second law of thermodynamics

Explanation: Second Law of Thermodynamics states that It is not POSSIBLE for heat to flow from a colder body to a warmer body without any work having been done to accomplish this flow. Energy will not flow spontaneously from a low TEMPERATURE OBJECT to a HIGHER temperature object.

Correct CHOICE is (a) True

Explanation: Forced air heating and air conditioning are examples of heating (or COOLING) by convection. This is an effective way of BRINGING a hot (or cold) fluid to a different AREA. Convection transfers heat over a distance faster than conduction.

The CORRECT answer is (c) Mass transfer

The EXPLANATION: In single-phase SYSTEMS, the rate of mass transfer due to molecular diffusion is given by FICK’s law of diffusion, which STATES that mass flux is proportional to the concentration gradient.

Right answer is (a) 50 gl^-1

Explanation: Assume that addition of COPPER sulphate does not affect C*AL or kLa. If qo is reduced by a factor of 12.5/3 = 4.167, xmax is INCREASED to:

xmax = 4.167 (12 gl^-1) = 50 gl^-1

To achieve the calculated cell densities all other CONDITIONS must be favourable, e.g. sufficient substrate and TIME must be provided.

The correct answer is (c) Splashing and shaking

For explanation: Homebrewers have several aeration/oxygenation methods available to them: siphon sprays, whipping, splashing, shaking, pumping air through a stone with an aquarium pump, and injecting pure oxygen through a sintered stone. Pumping compressed air through a stone is not an efficient WAY to provide adequate levels of DO. Traditional splashing and shaking, although LABORIOUS, is fairly efficient at dissolving up to 8 ppm oxygen. To increase levels of oxygen, the CARBOY HEADSPACE can be purged with pure oxygen prior to shaking.

Correct choice is (a) True

The explanation is: Oxygen is a critical additive in brewing. Oxygen is the only necessary nutrient not naturally FOUND in wort. ADDING adequate oxygen to wort REQUIRES a fundamental understanding of why yeast NEED oxygen, how much oxygen they need, and how to get oxygen into solution and the factors affecting solubility of oxygen. Yeast use oxygen for cell membrane synthesis. Without oxygen, cell growth will be extremely limited. Yeast can only PRODUCE sterols and certain unsaturated fatty acids necessary for cell growth in the presence of oxygen.

Correct choice is (c) Increase VOLUME to the reactor

For explanation: The roles of the disengagement zone are to:

▪ add volume to the reactor,

▪ reduce FOAMING and

▪ MINIMISE RECIRCULATION of bubbles through the down COMER.

The correct choice is (c) 0.0227 g/liter

The explanation is: Since air mainly CONSISTS of NITROGEN and Oxygen – the air DISSOLVED in the water can be calculated as:

ca = (0.0089 g/litre) + (0.0138 g/litre)

= 0.0227 g/liter.

The correct choice is (b) Air-lift

To explain: There are two types of air-lift fermenters which are the internal loop and the external loop. The internal loop has a draft tube in its INNER tube, in which the up-flowing gasses liquid and the down-flowing liquid is separated by the draft tube. Draft tubes are USED in some processes to promote better MASS transfer, mixing and inducing circulatory motion to reduce bubble coalescence. The external loop has two streams flow in two separate pipes connected at TOP and bottom. In this way, the air-lift fermenters improve the CIRCULATION and oxygen transfer and equalize shear forces in the reactor.

Correct option is (b) False

The explanation: At STEADY state there can be no accumulation of OXYGEN at any location in the fermenter; therefore, the rate of oxygen TRANSFER from the bubbles MUST be equal to the rate of oxygen consumption by the cells.

Correct answer is (a) Hydrogen purification by palladium sheets

The best I can explain: A practical example of steady-state diffusion – the purification of hydrogen gas. ONE side of a THIN sheet of palladium metal is exposed to the impure gas composed of hydrogen and other gaseous species such as NITROGEN, oxygen, and water vapor. The hydrogen SELECTIVELY diffuses through the sheet to the opposite side, which is maintained at a CONSTANT and lower hydrogen pressure.

Correct choice is (C) 10 ppm

Easiest explanation: The solubility of OXYGEN in aqueous solutions at ambient temperature and PRESSURE is only about 10 ppm. This amount of oxygen is quickly CONSUMED in aerobic cultures and MUST be constantly replaced by sparging.

The correct answer is (b) m^2/s

Explanation: The units of thermal DIFFUSIVITY are length^2/time and a common set of SI units is m^2/sec (the use of cm or MM as the length scale is frequent as it allows REPORTING of values closer to the value ONE).

Right option is (a) Dynamic gassing out method

For explanation: This method HINGES on the measurement of the DISSOLVED OXYGEN concentration that is altered by absorption or desorption, facilitated by flushing with inert gases like nitrogen. The instantaneous dissolved oxygen concentration can be measured by using electrodes and kLa is hence ESTIMATED from the slope of the resulting PLOT.

The correct choice is (B) 0.0089 g/liter

Easiest EXPLANATION: Oxygen dissolved in the WATER at atmospheric PRESSURE can be calculated as:

c = PG / kH

co = (1 atm) 0.21 / (756.7 atm/(mol/litre)) (31.9988 g/mol)

= 0.0089 g/liter.

The correct option is (b) Dimensionless mass TRANSFER number

To elaborate: The Sherwood number (Sh) (also CALLED the mass transfer Nusselt number) is a dimensionless number used in mass-transfer operation. It represents the RATIO of the convective mass transfer to the rate of DIFFUSIVE mass transport, and is named in honor of Thomas Kilgore Sherwood.

The correct CHOICE is (c) Solvents are IMMISCIBLE

Best explanation: EQUILIBRIUM DISTRIBUTION of one solute between two phases is conveniently described in terms of the distribution LAW. At equilibrium, the ratio of solute concentrations in the two phases is given by the distribution coefficient or partition coefficient, m. The distribution law is accurate only if both solvents are immiscible and there is no chemical reaction.

Right OPTION is (d) 100%

For explanation I would say: If \(\BAR{C_{AL}}\) is TAKEN to be 70% air saturation:

The error in kLa is ALMOST 100%.

The correct answer is (a) LOW biomass yields

The explanation: Water with high concentrations of dissolved minerals such as salt will have a lower DO CONCENTRATION than fresh water at the same temperature. Low dissolved oxygen (DO) PRIMARILY results from EXCESSIVE ALGAE growth caused by phosphorus. As the algae die and decompose, the process consumes dissolved oxygen.

The correct choice is (b) Chemostat

To elaborate: A chemostat (from chemical environment is static) is a bioreactor to which fresh medium is continuously added, while culture liquid containing left over nutrients, METABOLIC END PRODUCTS and microorganisms are continuously removed at the same rate to keep the culture volume CONSTANT.

The correct OPTION is (a) Solid

Explanation: Convection cannot take place in most solids because neither bulk current flows nor significant diffusion of MATTER can take place. Diffusion of heat TAKES place in rigid solids, but that is called heat conduction. Convection, however, can take place in soft solids or mixtures where solid particles can MOVE PAST each other.

The correct option is (b) False

Easy explanation: Turbulence in FLUIDS produces bulk mixing on a scale equal to the smallest eddy size. Within the smallest eddies, flow is LARGELY streamline so that further mixing must occur by DIFFUSION of fluid components. Mixing on a MOLECULAR scale therefore relies on diffusion as the final step in the mixing process.