1. When a highly corrosive and reactive substance is used in the operation we prefer to use__________
a) Full helical coils
b) Full conventional jacket
c) Ringlet Coil
d) Semi helical coil
Explanation: When it comes to handling corrosive substances, a jacket has the advantage that there are no extra construction materials or metal surface in contact with the process other than the vessel wall.
2. For the manufacture of pharmaceuticals, when we want to minimize contamination, we prefer to use__________
a) Full helical coils
b) Full conventional jacket
c) Ringlet Coil
d) Semi helical coil
Explanation: For the manufacture of pharmaceuticals, where we work with fine chemicals and performance products, a jacket minimizes contamination as there are no extra surfaces to clean unlike coils.
3. A jacket has a lower heat transfer rate and coefficient than a coil.
a) True
b) False
Explanation: Jackets usually have thick walls and low surface area which greatly impacts its heat transfer coefficient.
4. Which of the following is not a factor for jacketed vessel’s low heat transfer rate?
a) Thick Wall
b) Low surface Area
c) Quality of material
d) Surface not in contact with vessel
Explanation: The quality of material used is always high yet as we use jackets the other three options are true which leads to the overall degradation of the heat transfer rate
5. For exothermic reactions, which setup is best suited for an agitated vessel?
a) Full conventional jacket
b) Dimpled jacket
c) Full helical coils
d) Half-pipe jacket
Explanation: When we are considering exothermic reactions, a jacketed vessel has the disadvantage that the area/volume ratio decreases with increasing scale, hence in this case we require a high heat transfer area which is usually provided by coils.
6. Why are agitated vessels usually used in batch manufacture?
a) Necessary to calculate the time to heat or cool a batch
b) Because batch processes occur in vessels
c) It avoids harmful reactions
d) It supports endothermic reactions
Explanation: Agitated vessels usually used in batch manufacture because we need to calculate the time to heat or cool a batch so that highly exothermic reactions can be carried out with proper care.
7. The rate of change of temperature in an agitated vessel can be represented as which one of the following?
a) \(\frac{\delta T}{\delta t} = \frac{UA}{MCp}(T-Ts)\)
b) \(\frac{\delta T}{\delta t} = \frac{UA}{MCp}(Ts-T)\)
c) \(\frac{\delta T}{\delta t} = \frac{MCp}{UA}(Ts-T)\)
d) \(\frac{\delta T}{\delta t} = \frac{MCp}{UA(Ts-T)}\)
Explanation: This is because Q = UA(Ts-T) = MCp \(\frac{\delta T}{\delta t}\). Hence, \(\frac{\delta T}{\delta t} = \frac{UA}{MCp}\)(Ts-T)
8. What is the term X in the following equation?
\(\frac{\delta T}{\delta t}= \frac{UA}{MCp}(X-T)\)
a) Service side temperature
b) Process side temperature
c) Service side temperature difference
d) Process side temperature difference
Explanation: In the equation of temperature gradient with time, the two temperature terms are Ts and t, where Ts is the Service side constant temperature and T is the temperature at time t.
9. Which one of the following is correct expression for calculating time ‘t’ to reach temperature T ?
a) \(t=\frac{MCp(Ts-To)}{UA(Ts-T)}\)
b) \(t=\frac{MCp(Ts-T)}{UA(Ts-To)}\)
c) \(t=\frac{UA(Ts-To)}{MCp(Ts-T)}\)
d) \(t=\frac{MCp}{UA}log\frac{Ts-To}{Ts-T}\)
Explanation: This is because Q = UA(Ts-T) = MCp \(\frac{\delta T}{\delta t}\). Hence, \(\frac{\delta T}{\delta t} = \frac{UA}{MCp}(Ts-T)\), integrating both sides, ln(Ts – T)= UA/MCp(t) or \(t=\frac{MCp}{UA}log(\frac{Ts-To}{Ts-T})\).
10. For agitated vessels, what is the correct expression for the Overall Heat Transfer Coefficient?
a) \(\frac{1}{U} = \frac{1}{hAb}+\frac{X}{K}+\frac{1}{hAc}\)
b) \(\frac{1}{U} = \frac{1}{hAb}+\frac{K}{X}+\frac{1}{hAc}\)
c) \(\frac{1}{U} = \frac{1}{hAb}+\frac{1}{K}+\frac{1}{hAc}\)
d) \(\frac{1}{U} = \frac{1}{hAb}+\frac{1}{KX}+\frac{1}{hAc}\)
Explanation: The overall heat transfer coefficient is the combination of convective and conductive one. The first being on the process side hAb, heat transfer coefficient h and transfer area Ab, similarly the wall with X/K with X as vessel wall thickness and K=conductivity, and finally service side hAc.