Fantastic 4 Quiz

Question 1

As a newly-employed researcher in Berjaya Company, the manager requested you to calculate the capacity of a single-effect evaporator. You know that the area of this evaporator is 40m^2 and it has an overall heat transfer coefficient of 2500W/m^2K. The evaporator is used to concentrate an aqueous solution which contains 6% of solids at a feed temperature of 18°C to 20% solids. The saturated steam is going in with a pressure of 313 kPa while the evaporator is operating at a vacuum pressure of 76.27 kPa. The BPR (boiling point rise) is known to be 8K. Perform the calculation and inform the value of capacity to your manager. 
(Hint: Capacity is the amount of solvent vapourised per time)

Accepted Answer

2.33kg/s

Answer

1.00kg/s

Answer

4.53kg/s

Answer

5.00kg/s

Question 2

The Yeoh’s Company would like to produce concentrated grape juice for new-year sales. A 4% solids raw juice at 22°C is entered into a single-effect evaporator and the company plans to produce a 38% solids grape concentrate from the feed. The pressure in the evaporator is at an absolute pressure of 25kPa while the steam entering is at a gauge pressure of 130.8kPa. The boiling temperature of the grape juice in the evaporator is at 65°C. The overall heat transfer coefficient is known to be 390Jm^(-2) s^(-1) 〖°C〗^(-1) and the evaporator’s heat transfer surface area is approximately 10.5m^2. What is the flow rate of the raw juice need to be supplied to the evaporator to produce the desired product?

Accepted Answer

386.46 kg/hr

Answer

403.25 kg/hr

Answer

517.25 kg/hr

Answer

228.28 kg/hr

Question 3

A client requested you to replace the single effect evaporator in his factory with multiple effect evaporator (specifically triple effect evaporator). He told you that the evaporator is used to evaporate a solution with negligible boiling point rise using saturated steam at 232.1kPa. Meanwhile, the pressure in the last effect is 40kPa. Heat transfer coefficient are given as U1 = 1980W/m^2 K; U2 = 2042 W/m^2 K and U3 = 2166 W/m^2 K. Calculate the boiling point in each effect with the assumption that the heat transfer surface areas of each effect are equal.

Accepted Answer

T1= 58.75°C; T2= 59.27°C; T3= 60.22°C

Answer

T1= 58.75°C; T2= 38.44°C; T3= 45.87°C

Answer

T1= 17.06°C; T2= 16.54°C; T3= 15.59°C

Answer

T1= 20.02°C; T2= 54.43°C; T3= 60.22°C

Question 4

What is the difference between forward feed and backward feed of multiple effect evaporators?

Accepted Answer

In forward feed, the feed flows to the direction of vapour flow but in backward feed, feed flows opposite to the direction of vapour flow.

Answer

Forward feed reuses the latent heat of vapour but backward feed does not reuse the latent heat of vapour.

Answer

Forward feed is used for cold feed while backward feed is used for hot feed.

Answer

Forward feed decreases steam economy while backward feed increases steam economy.

Question 5

Which of the following statements is NOT TRUE about vertical tube evaporator?

Accepted Answer

The steam enters the tube and condenses and leaves out as condensate.

Answer

It is not applicable for liquids with high viscosity.

Answer

The liquid in the tube rises by natural circulation.

Answer

The natural circulation is caused by boiling and the decrease in density.

Question 6

Which sections below are involved in a typical evaporator?
I)	Separator
II)	Condenser
III)	Evaporating section
IV)	Heat exchanger

Accepted Answer

I, III, IV

Answer

I and II

Answer

I, II and III

Answer

II, III and IV

Question 7

To produce a product which doubled the initial feed solids concentration, an evaporator can be used. To investigate this, a 30% solution of NaOH in water is entered into the evaporator with a rate of 3899 kg/hr at a temperature of 55°C. The overall heat coefficient is 1200 W/m^2K. In the evaporator, the vapour space is having a pressure of 10kPa while the saturated steam has a pressure of 143.27kPa. Estimate the steam used and also the steam economy. 
(Hint: Cp of water is 1.893 kJ/kgK)

Accepted Answer

S = 2754.08 kJ/kg; Economy = 0.708

Answer

S = 1949.50 kJ/kg; Economy = 0.778

Answer

S = 2754.08 kJ/kg; Economy = 1.412

Answer

S = 1949.50 kJ/kg; Economy = 1.412

Question 8

Which of the following statements is NOT TRUE about drying?

Accepted Answer

It is the process of removal of large amount of water from solid material.

Answer

Removal of water can be done thermally.

Answer

Removal of water can be done by the centrifuging process.

Answer

It is the process of removal of small amount of water from solid material.

Question 9

In a room, the temperature of the air is known to be at 33.5°C while the pressure is 101.3kPa. The air contains water vapour and the partial pressure, P_A is found out to be 2.98kPa. You are required to estimate the humidity, saturation humidity and also the percentage humidity respectively.

Accepted Answer

0.0188 kg water/ kg air; 0.0336 kg H_2 O/ kg air; 55.95%

Answer

0.0188 kg water/ kg air; 0.0336 kg H_2 O/ kg air; 57.46%

Answer

0.0336 kg water/ kg air; 0.0188 kg H_2 O/ kg air; 57.46%

Answer

0.0336 kg water/ kg air; 0.0188 kg H_2 O/ kg air; 55.95%

Question 10

You are a research assistant in a laboratory and your research officer requested you to find out the humid heat and the humid volume of a dryer. Given the air entering the dryer is having a dew point of 302.2K and its dry bulb temperature is 343K. By using the humidity chart, find out the values.

Accepted Answer

1.056 kJ/kg dry air; 1.013m^3/ kg dry air

Answer

1.013 kJ/kg dry air; 1.056m^3/ kg dry air

Answer

2.078 kJ/kg dry air; 1.983m^3/ kg dry air

Answer

2.435 kJ/kg dry air; 1.983m^3/ kg dry air

Question 11

At 361K, the air stream is having a humidity H= 0.05 kg H_2 O/ kg dry air. It is in contact with an adiabatic saturator with water. Find the value of H and T if it is cooled and humidified to 80% saturation. For 100% saturation, are the H and T going to increase or decrease?

Accepted Answer

H= 0.067 kg H_2 O/ kg dry air; T= 321.5K; H will increase but T will decrease.

Answer

H= 0.067 kg H_2 O/ kg dry air; T= 48.5K; H will increase but T will decrease.

Answer

H= 0.055 kg H_2 O/ kg dry air; T= 48.5K; H will decrease and T will decrease.

Answer

H= 0.055 kg H_2 O/ kg dry air; T= 321.5K; H will decrease but T will increase.

Question 12

Why large chamber is preferable in spray dryer instead of small chamber?

Accepted Answer

To prevent particles from striking on sticking on wall.

Answer

To allow particles to stick on wall.

Answer

To allow drying to occur rapidly.

Answer

To increase the amount of end product.

Question 13

What are the steps in the formation of crystals?
I)	Precipitation
II)	Nucleation
III)	Growth to macroscopic size
IV)	Extraction

Accepted Answer

II and III

Answer

I and II

Answer

III and IV

Answer

II, III and IV

Question 14

We can measure the solubility in crystallisation by using polythermal method. What is meant by polythermal method?

Accepted Answer

Heating solutions initially containing excess solutes.

Answer

Adding solvents at constant temperature.

Answer

Adding solvents at constant pressure.

Answer

Heating solutions initially containing limited solutes.

Question 15

What do you think should be the main reason for the very low solubility of NaCl in benzene (C_6 H_6)?

Accepted Answer

Weak solvation of 〖Na〗^+ and 〖Cl〗^- by C_6 H_6.

Answer

Hydrogen bonding in C_6 H_6.

Answer

Strong solvent-solvent interaction.

Answer

Strength of the covalent bond in NaCl.

Question 16

Consider a reaction, X + Y --> Z . The rate for this reaction is k[X][Y]2. The three cubes above shows a reaction for the production of a mixture in which X is the yellow balls and Y is the black balls. Based on the rate law, which one either [X] or [Y] has a greater influence? Why?

Accepted Answer

Y has a greater influence.

Answer

X has a greater influence.

Answer

Both have the same influence.

Answer

Both have no influence.

Question 17

Pasteurization can be defined as the process of heating milk to high temperatures for a a period time in order to kill bacteria that is present in the milk. F&N Dairies (M) Sdn Bhd, uses pasteurization method to heat the milk to 650 C for 30 minutes. However, if it is heated to 750 C it only needs 15 seconds for the same result. Find the activation energy for this treatment of milk process. 
Hint : Use Arrhenius equation, rate is inversely proportional to time, R=8.314.

Accepted Answer

468181.23 J/mol

Answer

424130.50 J/mol

Answer

550748.62 J/mol

Answer

621328.45 J/mol

Question 18

A gas mixture enters a reactor with a flow rate of 4 dm3/s at 420K. The gas mixture contains equimolar of A and inerts at 12 atm. Given R=0.082dm3.atm/mol.K.
Determine the entering concentration of A, CAO.

Accepted Answer

0.174 mol/dm3

Answer

0.220 mol/dm3

Answer

0.183 mol/dm3

Answer

0.142 mol/dm3

Question 19

Consider a reaction taking place as shown above.
The activation energies for k1 and k2 are given to 120 and 30 kJ/mol respectively. Both the reactions are said to be first-order. Which of the following is the best choice in order to maximize the yield of B?

Accepted Answer

PFR at high temperature

Answer

PFR at low temperature

Answer

CSTR at high temperature

Answer

CSTR at low temperature

Question 20

N plug flow reactor which are in series with a total volume of V will give the same conversion as in a single plug flow reactor of volume ‘V’ for any order reactions.

Accepted Answer

True

Answer

False

Question 21

The rate constant of a chemical reaction decreases by decreasing the temperature. The production sulfur trioxide is shown in the reaction above.  Applying Le Chatelier’s Principle, will the amount of SO3(g) formed from a given amount of SO2(g) and O2(g)  be higher when at ________.

Accepted Answer

Low temperature

Answer

High temperature

Question 22

Najeb is a Malaysian student who weighs about 65kg. He eats rice everyday. He consumes about 6200kJ of food per day. Taking his main source of food as rice which is glucose, the overall reaction is shown above. Taking the density of a average human being as 1000kg/m3, find Najeb’s metabolic rate in terms of moles of oxygen consumed per meter cube of person per second.

Accepted Answer

0.00244 mol O2 used / m3.s

Answer

0.00132 mol O2 used / m3.s

Answer

0.00359 mol O2 used / m3.s

Answer

0.00141 mol O2 used / m3.s

Question 23

A -->  B+C
The exothermic reaction was carried out adiabatically and the above data was obtained.
It is given that the entering molar flow rate of A was 150 mol/min. At the end of the reaction, it is found that A was only 20% of its’ initial amount. Calculate the CSTR and PFR volume in this reaction.

Accepted Answer

CSTR: 9.6 dm3, PFR: 2.8 dm3

Answer

CSTR: 2.8 dm3, PFR: 9.6 dm3

Answer

CSTR: 2.4 dm3, PFR: 2.8 dm3

Question 24

In a chemical plant, a reactor with the following specifications is needed and you have been asked to design it: conversion after reactor 1, X1=0.1 and conversion after reactor 2, X2=0.6 with entering flowrate of 0.55 mol/s. What is the smallest volume of reactors series that you can achieve and how you are going to arrange the reactors?

Accepted Answer

CSTR ---> PFR

Answer

PFR ---> CSTR

Answer

PFR ---> PFR

Question 25

Space velocity

Accepted Answer

All of the above

Answer

describes the extensive operating characteristics of a tubular flow reactor.

Answer

is the maximum feed rate per unit volume of reactor for a given conversion.

Answer

is a measure of the ease of the reaction.

Question 26

Consider a reaction,  X + Y  Z       The rate for this reaction is k[X][Y]2. The three cubes above shows a reaction for the production of a mixture in which X is the yellow balls and Y is the black balls.  Which of the following order is of increasing rate of reaction?

Accepted Answer

Cube 3 > Cube 1 > Cube 2

Answer

Cube 2 > Cube 3 > Cube 1

Answer

Cube 1 > Cube 2 > Cube 3

Answer

Cube 3 > Cube 2 > Cube 1

Question 27

What is the similarity between all mole balances of reactors?

Accepted Answer

All have generation of the product in the system.

Answer

All have flow rate into the reactor.

Answer

All have accumulation at the end of the reactor system.

Question 28

Specific rate constant for a second order reaction

Accepted Answer

change with temperature

Answer

does not depend on temperature

Answer

depends on the nature of the reactants.

Answer

all of the above.

Question 29

An Associate Professor from University of Auckland carried an experiment to calculate the total heat transferred in a crystallizer. The details of the crystallizer is as follows. 
Feed= 5000Ibm at 200F
The concentrated solution comes out of the crystallizer at 60F.
The crystal produced is a sodium sulfate decahydrate with the yield of 3000Ibm.
The heat capacity of the feed is 0.90 btu/Ibm.F.
The heat of solution at 60F is (-26.48 btu/Ibm).