Questions and answers for exam Preparation

MCQs

Total Questions : 234 | Page 2 of 24 pages

Question 11. If the stirring speed increased from 300 to 500 rpm leads to an increase in the reaction rate by two folds. Then it may be concluded that

the reaction was mass transfer limited at 300 rpm
the reaction was mass transfer limited at 500 rpm
the reaction did not involve any mass transfer step
the movement of molecules in the reactor at 300 rpm occurred due to diffusion alone

Discuss Question

Answer: Option A. -> the reaction was mass transfer limited at 300 rpm
Answer: (a).the reaction was mass transfer limited at 300 rpm

Question 12. An increase in the heat transfer in the stirred tank reactor will be observed at

higher cooling water temperature
higher stirrer speed
the removal of baffles from the reactor
slower stirrer speed

Discuss Question

Answer: Option B. -> higher stirrer speed
Answer: (b).higher stirrer speed

Question 13. Turbulent flow range of mixing speed is obtained for

Rei<10
10<Rei<10⁴
Rei>10⁴
None of these

Discuss Question

Answer: Option C. -> Rei>10⁴
Answer: (c).Rei>10⁴

Question 14. For laminar flow, Reynolds number is correlated with power number as (where K, a constant which depends on the container geometry and shape of stirrer; Rei is Reynolds number for agitator; Di, stirrer diameter and N, stirrer speed)

Np = K(Rei)¹
Np = N2Di(Rei)¹
Np = K(Rei)
Np = KNDi(Rei)²

Discuss Question

Answer: Option A. -> Np = K(Rei)¹
Answer: (a).Np = K(Rei)¹

Question 15. The effect of increasing the stirrer speed in an unbaffled stirred tank reactor is that

a small increase in stirrer speed will cause the liquid to enter the turbulent flow regime
as the stirrer speed increases, the liquid will continue to circulate and then become turbulent
as the stirrer speed increases, the liquid will continue to circulate. Eventually a vortex will form.
A vortex will form at low stirrer speeds. As the stirrer speed increases the liquid will start to circulate

Discuss Question

Answer: Option C. -> as the stirrer speed increases, the liquid will continue to circulate. Eventually a vortex will form.
Answer: (c).as the stirrer speed increases, the liquid will continue to circulate. Eventually a vortex will form.

Question 16. Which of the following(s) is/are non-mechanically agitated reactors?

Stirrer tank reactor
Bubble column
Air lift reactor
Both (b) and (c)

Discuss Question

Answer: Option D. -> Both (b) and (c)
Answer: (d).Both (b) and (c)

Question 17. The volume of liquid (VL) in a cylindrical reactor can be calculated from the liquid height (HL) and tank diameter (Dt) using the following equation

VL = 4/3 x π x HL x Dt³/8
VL= HL x π x Dt²/4
VL= HL x π x Dt²
VL = 4 x π x Dt²

Discuss Question

Answer: Option B. -> VL= HL x π x Dt²/4
Answer: (b).VL= HL x π x Dt²/4

Question 18. Power number is ratio of

imposed forced to intertial force
bouyant force to inertial force
gravitation force to inertial force
imposed force to gravitational force

Discuss Question

Answer: Option A. -> imposed forced to intertial force
Answer: (a).imposed forced to intertial force

Question 19. The average fractional gas hold up (H) can be given as (where Zf and Zl are the level of aerated and clear liquid respectively)

H = (Zf-Zl)/Zf
H = Zf/Zl
H = Zf/ZfZl
H =(Zf+Zl)/Zf

Discuss Question

Answer: Option A. -> H = (Zf-Zl)/Zf
Answer: (a).H = (Zf-Zl)/Zf

Question 20. Which of the following best explains the reasons for using axial flow impellers in crystallization and precipitation reactions?

Crystal and precipitates are not too small, so as to ensure easy separation of the solids from the mother liquor
Crystals and precipitates are thoroughly broken down, so as to ensure easy separation of the solids from the mother liquor
Both (a) and (b)
Axial flow impellers provide low shear, energy efficient mixing conditions

Discuss Question

Answer: Option A. -> Crystal and precipitates are not too small, so as to ensure easy separation of the solids from the mother liquor
Answer: (a).Crystal and precipitates are not too small, so as to ensure easy separation of the solids from the mother liquor