This set of Basic Chemical Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Flow Rate”.

1. Which of the following is the unit of flow rate?

a) Kg/s

b) Liters/s

c) Moles/s

d) All of the mentioned

View answer

Explanation: Mass flow rate = m/t, => unit = kg/s, volumetric flow rate = V/t, => unit = Liters/s, molar rate = n/t, => unit = moles/s.

2. Which of the following is not conserved for the flow of an incompressible liquid in a pipe with variable area?

a) Mass

b) Volume

c) Velocity

d) Flow Rate

View answer

Explanation: According to the equation of continuity, the product of area and velocity remains constant throughout the pipe, since the area of the pipe is variable, so the velocity if the liquid is variable.

3. What is the mass flow rate of a liquid flowing through a pipe of which 100 grams of water was collected in 10 seconds?

a) 0.01 kg/s

b) 0.05 kg/s

c) 0.1 kg/s

d) 0.5 kg/s

View answer

Explanation: mass flow rate = 0.1/ 10 = 0.01 kg/s.

4. What is the volumetric flow rate if 100 kg of water is collected in 10 seconds? (Density of water = 1000 kg/m3)

a) 0.1 m^{3}/s

b) 0.2 m^{3}/s

c) 0.01 m^{3}/s

d) 0.02 m^{3}/s

View answer

Explanation: volume of water collected = 100/1000 = 0.1 m

^{3}, => volumetric flow rate = 0.1/10 = 0.01 m

^{3}/s.

5. A liquid is flowing through a pipe of cross section 4 m^{2} at a rate of 4 kg/s, at a point pipe is divided into two pipes of areas of equal areas, what will be the ratio of flow rate in both the pipes?

a) 1:3

b) 1:1

c) 1:2

d) 2:3

View answer

Explanation: Since areas of the pipes are equal, by continuity equation flow will divide equally in the pipes, so their ratio will be 1:1.

6. The velocity of water in a pipe of area 5 m^{2} is 10 m/s, what will be the flow rate of water?

a) 25 m^{3}/s

b) 50 m^{3}/s

c) 75 m^{3}/s

d) 100 m^{3}/s

View answer

Explanation: Flow rate = area*velocity = 5*10 = 50 m

^{3}/s.

7. A liquid of density 0.1 kg/m^{3} is flowing through a pipe at a rate of 15 kg/s, what will be the area of the pipe if the fluid velocity is 5 m/s?

a) 30 m^{2}

b) 45 m^{2}

c) 75 m^{2}

d) 90 m^{2}

View answer

Explanation: Volumetric flow rate of the liquid = 15/0.1 = 150 m

^{3}/s, => Area of pipe = 150/5 = 30 m

^{2}.

8. 1 mole of Carbon dioxide enters in a reactor at a rate of 0.25 kg/s and leaves it at the rate of 1 kg/s, what are the number of moles of carbon dioxide leaves the reactor?

a) 0.25

b) 0.5

c) 0.75

d) 1

View answer

Explanation: Applying reaction equilibrium equation, 1*0.25 = n*1, => n = 0.25.

9. A Composition of carbon dioxide, oxygen and nitrogen with mole ratio 1:2:5 with 4 moles of oxygen, enters a reactor with a flow rate of 100 kg/s, the ratio of rates of leaving the reactor of the three is 5:2:1, and 5 moles of nitrogen leaves the reactor, what is the total number of moles leaving the reactor?

a) 6.1

b) 6.2

c) 6.3

d) 6.4

View answer

Explanation: number of moles of carbon dioxide, oxygen and nitrogen are 2, 4 and 10 respectively, let the leaving flow rates of carbon dioxide, oxygen and nitrogen are 5y, 2y and y respectively, => for nitrogen, 10*100 = y*5 => y = 200 kg/s, => for oxygen, 4*100 = 400*n => n = 1, for carbon dioxide, 2*100 = 1000*n => n = 0.2, => total number of moles leaving the reactor = 5 + 1 + 0.2 = 6.2.

10. 10 moles of oxygen divides and enters two reactors flow rate 45 kg/s and leaves the reactors at the flow rates of 6 kg/s and 9 kg/s, what are number of moles of oxygen that leaves the reactor with 9 kg/s?

a) 180

b) 450

c) 60

d) 90

View answer

Explanation: Let number of moles entering and leaving the second reactor be n

_{1}and n

_{2}respectively, applying reaction equilibrium equation to whole system, => 10*45 = n*(6 + 9), => n = 30, => Applying reaction equilibrium equation to both the reactors separately, => n

_{1}*45 = n

_{2}*9 => n

_{2}= 5n

_{1}, and (10 – n

_{1})*45 = (30 – n

_{2})*6, Solving both equations we get n

_{2}= 90.

11. 10 Kg/s of a fluid with density 10 Kg/m^{3} is passed into a tank of capacity 50 m3, how much time will it take to fill the tank?

a) 5 Second

b) 50 Second

c) 500 Second

d) 5000 Second

View answer

Explanation: Flow rate of fluid = 10/10 = 1 m

^{3}/s, => Time = 50/1 = 50 second.

12. 15 Kg/s of a fluid with density 5 Kg/m^{3} is passed into a tank of capacity 30 m^{3}, how much time will it take to fill the tank?

a) 3 Second

b) 10 Second

c) 30 Second

d) 100 Second

View answer

Explanation: Flow rate of fluid = 15/5 = 3 m

^{3}/s, => Time = 30/3 = 10 second.

13. 20 Kg/s of a fluid with density 5 Kg/m^{3} is passed into a tank of capacity 60 m^{3}, how much time will it take to fill the tank?

a) 5 Second

b) 10 Second

c) 15 Second

d) 20 Second

View answer

Explanation: Flow rate of fluid = 20/5 = 4 m

^{3}/s, => Time = 60/4 = 15 second.

14. 16 grams of oxygen is passed in the process in 5 minutes, what is the molar flow rate?

a) 0.1 mole/min

b) 1 mole/min

c) 10 mole/min

d) 16 mole/min

View answer

Explanation: Flow rate of fluid = (16/32)/5 = 0.1 mole/min.

15. 24 grams of CH4 is passed in the process in 3 minutes, what is the molar flow rate?

a) 0.1 mole/min

b) 0.3 mole/min

c) 0.5 mole/min

d) 0.7 mole/min

View answer

Explanation: Flow rate of fluid = (24/16)/3 = 0.5 mole/min.

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