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1.	What is the first – order decay?(a) The rate of loss of the pollutant is constant(b) The rate of loss of the reactant is constant(c) The rate of loss of the pollutant is directly proportional to its concentration(d) The rate of loss of the reactant is directly proportional to its concentrationThe question was posed to me during an interview for a job.This is a very interesting question from Solving Unsteady topic in division Unsteady – State Material and Energy Balances of Bioprocess Engineering
Answer» The CORRECT CHOICE is (c) The rate of LOSS of the pollutant is directly proportional to its concentration For explanation: First – order decay is the rate of loss of the pollutant is directly proportional to its concentration: \|dc/dt\|reaction = -KC For such a pollutant, mreaction = – V kC.

2.	The units for the log mean temperature difference are __________(a) 1 / °C(b) °C(c) 1/2 °C(d) DimensionlessThis question was posed to me in my homework.This key question is from Solving Unsteady topic in chapter Unsteady – State Material and Energy Balances of Bioprocess Engineering
Answer» The correct option is (b) °C To elaborate: In the particular system, whatever unit is ASSIGNED to temperature, the same is the unit of LMTD. It is just a SPECIAL kind of temperature difference. Logarithmic mean temperature difference. LMTD is a logarithmic average of the temperature difference between the hot and COLD streams in heat EXCHANGER. Its unit is whatever is the unit of the temperature. °F or °C or KELVIN.

3.	” A balloon is filled with air at a steady rate.” Which process can be correct for this condition?(a) Semi – batch(b) Batch(c) Fed – batch(d) ContinuousThis question was posed to me at a job interview.The above asked question is from Solving Unsteady topic in section Unsteady – State Material and Energy Balances of Bioprocess Engineering
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4.	The fouling factor is _________(a) Is a safety factor(b) Accounts for all resistances due to mass transfer(c) Is a dimensionless number(d) Accounts for all resistances due to heat transferI have been asked this question in an online quiz.I want to ask this question from Solving Unsteady topic in section Unsteady – State Material and Energy Balances of Bioprocess Engineering
Answer» Right answer is (d) Accounts for all resistances due to HEAT transfer The explanation: The FOULING factor REPRESENTS the theoretical resistance to heat flow due to a build-up of a LAYER of dirt or other fouling substance on the tube SURFACES of the heat exchanger, but they are often overstated by the end user in an attempt to minimise the frequency of cleaning. In reality, if the wrong fouling factor is used, cleaning may actually be required more frequently.

5.	A compound dissolves in water at a rate proportional to the product of the amount of undissolved solid and the difference between the concentration in a saturated solution and the actual solution; i.e., Csat – C(t). A saturated solution of this compound contains 40 g per 100 g of water. In a test run starting with 20 kg of undissolved compound in 100 kg of water, it was found that 5 kg dissolved in 3 hr. if the test continues, how many kg of compound will remain undissolved after 7 hr? Assume that the system is isothermal.(a) 11.56 kg(b) 10.72 kg(c) 11.76 kg(d) 10.52 kgI had been asked this question by my school teacher while I was bunking the class.I'm obligated to ask this question of Solving Unsteady topic in section Unsteady – State Material and Energy Balances of Bioprocess Engineering
Answer» Correct option is (b) 10.72 kg To elaborate: Definitions of variables USED: C = kg dissolved compound/ kg water Cs = saturated m = mass of undissolved solid mo = initial mass of solid W = kg of water C7= 0.093 and m: mo – C7.100 kg m = 10.72 kg.

6.	Which of the following is not an example of batch process?(a) Cooking(b) Specialty chemicals(c) Refining(d) BrewingThis question was posed to me in an interview for job.My question is taken from Solving Unsteady topic in portion Unsteady – State Material and Energy Balances of Bioprocess Engineering
Answer» The correct OPTION is (C) Refining To explain I would say: Refining is a continuous process as feed and products flow continuously through process. SYSTEM is open, and usually modeled as STEADY flow. Examples: PETROLEUM refining (except coking, blending).

7.	“All of the coolant is at a uniform temperature, Tc”, is this statement correct according to the assumptions for the Unsteady-state energy balance?(a) True(b) FalseThis question was posed to me in an interview.My question is taken from Solving Unsteady in division Unsteady – State Material and Energy Balances of Bioprocess Engineering
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8.	“All of the coolant is at a uniform temperature, Tc”, is this statement correct according to the assumptions for the Unsteady-state energy balance?(a) True(b) FalseThis question was addressed to me at a job interview.My question is from Solving Unsteady in division Unsteady – State Material and Energy Balances of Bioprocess Engineering
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9.	“All of the coolant is at a uniform temperature, Tc”, is this statement correct according to the assumptions for the Unsteady-state energy balance?(a) True(b) FalseI got this question in a national level competition.My question comes from Solving Unsteady topic in division Unsteady – State Material and Energy Balances of Bioprocess Engineering
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10.	“Chemical reactions or phase changes occur” is this statement applicable for unsteady state energy balance?(a) True(b) FalseI have been asked this question in an international level competition.This interesting question is from Solving Unsteady topic in portion Unsteady – State Material and Energy Balances of Bioprocess Engineering
Answer» Right choice is (b) False To explain I WOULD say: No CHEMICAL reactions or phase changes occur as the system is well mixed with uniform temperature and COMPOSITION. Properties of the outlet stream are therefore the same as within the system and MIXTURES and solutions are ideal.

11.	The evaporator economy is dependent on the ________(a) Heat transfer rate(b) Mass transfer rate(c) Energy balance considerations(d) Mass balance considerationsThis question was posed to me in examination.My query is from Solving Unsteady topic in section Unsteady – State Material and Energy Balances of Bioprocess Engineering
Answer» Right choice is (a) Heat transfer rate Best EXPLANATION: There are three main measures of EVAPORATOR performance: Capacity (kg vaporized/time), Economy (kg vaporized/ kg steam input), Steam consumption (kg/hr). The performance of a evaporator is EVALUATED by the capacity and the economy. The rate of heat transfer q through the heating surface of an evaporator, by the DEFINITION of overall heat transfer coefficient, is product of three factors i) The area of heat transfer surface A ii) The overall heat transfer coefficient U iii) The overall temperature dropΔT Q = U * A * ΔT.

12.	Due to algal growth in a water supply reservoir in a neighborhood, the water has acquired an unpleasant taste. The compound is non-degradable, and the water utility has decided that the best way to deal with the situation is simply to flush the contaminant out of the system. The reservoir contains 11,000 m^3 of water, and the proposal is to pump 300 m^3/h of clean water through the system and discharge the effluent to the sewer system until 95% of the offending compound has been removed. If the reservoir is intensely mixed, how much flushing water will be required?(a) 30, 000 m^3(b) 33, 000 m^3(c) 35, 000 m^3(d) 39, 000 m^3The question was posed to me in an interview for internship.My query is from Solving Unsteady topic in division Unsteady – State Material and Energy Balances of Bioprocess Engineering
Answer» Right OPTION is (b) 33, 000 m^3 The explanation is: The compound is non-reactive and therefore behaves as a tracer. The contaminant concentration in the flushing water is zero. When 95% of the contaminant has been flushed out, the concentration will be 5% of the initial concentration, so:

13.	Which one process is not a transient process?(a) Fed- batch(b) Batch(c) Continuous(d) Semi- batchThis question was posed to me in an interview for job.My doubt stems from Solving Unsteady in division Unsteady – State Material and Energy Balances of Bioprocess Engineering
Answer» Correct ANSWER is (a) Fed- BATCH Easy EXPLANATION: Batch, semi-batch and continuous are transient as when they are start up, shut down or become transient at other times due to planned or unexpected changes in OPERATING CONDITIONS.

14.	Which of the following is the steady state condition based on the water tank concept?(a) Qin ≠ Qout(b) Qin = Qout(c) Qin > Qout(d) Qin < QoutThis question was posed to me during an online interview.My question is based upon Solving Unsteady in division Unsteady – State Material and Energy Balances of Bioprocess Engineering
Answer» CORRECT choice is (b) Qin = QOUT Explanation: Water FLOWS in = Water flows out; If Qin = Qout: Steady state (No accumulation) No INCREASE in level, mass, volume etc. In time, there is no change in the system.