This set of Heat Transfer Operations Multiple Choice Questions & Answers (MCQs) focuses on “Agitated Vessels – Transient Heating and Cooling”.
Explanation: In the diagram we observe the coils to be covering the vessel and not inside it, hence these setups are called Jacketed Vessel.
2. The resistance equation for the cold fluid is R = __________
Explanation: The resistance on the cold side is equal to the convective resistance to the colder side having area Ac and coefficient hc. Hence resistance = 1/hcAc.
3. What is the term N in the following equation?
NRe = Reynolds number for agitated liquids = (LA2 × N × ρB / μB).
a) Agitator Speed
b) Number of turns in coil
c) Number of turns in jacket coil
d) Number of passes in jacket
Explanation: In the Reynolds number for agitated liquids, we consider the total liquid volume that passes a particular point in some period of time, for which we require the agitator speed in RPM. Hence the term N is number of turns the agitator makes in specific period of time.
Explanation: The temperature gradient for an ideally mixed agitator is usually linear, as we usually don’t achieve ideality in practice, the given plot is best suited.
5. If ADC is the fouling deposit area on the vessel side, then what is its resistance?
a) R = 1/hADC
b) R = 1/hDCADC
c) R = 1/hDCAT
d) R = 1/hTADC
Explanation: The resistance of the surface is due to the covering fouled area only which has a heat transfer coefficient of hDC. Hence the correct expression is R = 1/hDCADC.
6. If the Nusselt Number for the jacket side is calculated then what is the definition of Dj?
NNu = Nusselt number of jacket fluid = (hJ * DJ / kJ).
a) Diameter of jacket tubes
b) Equivalent cross flow diameter of the jacket
c) Diameter of the vessel
d) Difference of the diameter of jacket and vessel
Explanation: The term Dj stands for the equivalent cross flow diameter of the jacket which is slightly greater than the vessel diameter and is equal to the closed surface transferring heat.
7. What is the term Γ in the following equation?
NRe Film = Reynolds number for the condensate film.
NRe Film = 4Γ / μJ
a) Condensate loading rate
b) Condensate removing rate
c) Vapour Removal rate
d) Vapour Loading rate
Explanation: The term given above is defined as the condensate loading rate which is measured as the mass rate of condensate per perimeter of vessel jacket.
Explanation: In the diagram we observe the coils to be covering the half the portion inside the vessel and not outside it, hence these setups are called Internal coil Vessel.
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