This set of Heat Transfer Operations Puzzles focuses on “Shell and Tube Heat Exchangers – Miscellaneous Questions”.
1. Which one of the following dirt factor should we assign to the HE for two moderately clean streams?
a) UD = 20, UC = 30
b) UD = 40, UC = 50
c) UD = 50, UC = 60
d) UD = 100, UC = 110
View Answer
Explanation: We should always assign the higher value of Rd so that the cleaning is done beforehand. Here the maximum value of Rd is for minimum U, i.e. we have Rd = (30-20)/30×20 = 0.0167 is the highest for UD = 20, UC = 30.
2. A heat exchanger was required to cool a liquid from 150℃ to 110℃, but the outlet temperature was increased by 3℃ every month for same heat transfer. What should have been the fouling factor if UD = 80?
a) 94
b) 49
c) 85
d) 90
View Answer
Explanation: We can tell that for the heat transferred to be equal, UD×47 = UC×40 or UC = 80×47/40 = 94.
3. Which one of the following formula is correct for return losses?
a) \(\frac{4N}{S} \frac{V^2}{2g}\)
b) \(\frac{4N}{S} \frac{V^2}{2}\)
c) \(\frac{4N}{S} \frac{V^2}{g}\)
d) \(\frac{N}{S} \frac{V^2}{2g}\)
View Answer
Explanation: For a shell and tube heat exchanger the head loss for every turn of the Tube is known as the return loss which is represented as H = \(\frac{4N}{S} \frac{V^2}{2g}\).
4. When steam is used on the tube side of the Heat Exchanger, then the allowable pressure drop should be less than _____ P.S.I.
a) 1
b) 2
c) 3
d) 4
View Answer
Explanation: If we keep a very high pressure drop for the steam then there would be unnecessary condensation of the steam decreasing the Heat transfer coefficient.
5. When we want to have extremely small pressure drop for the shell side and also desire to provide support to the tubes, which one the following setup should we use?
a) Segmental Baffles
b) Doughnut Baffles
c) Orifice Baffles
d) Support Plates
View Answer
Explanation: Use of any kind of baffle leads to a very high pressure drop due to which in operations with low pressure drop we do not use baffles rather using support plates are better options.
6. The more the number of shell and tube passes, less is the value of Correction Factor.
a) True
b) False
View Answer
Explanation: The more the number of shell and tube passes, more is the difficulty or error in calculating their temperature differences, hence more is the LMTD and hence more is the correction factor.
7. What is term S in the formula for Return Loss for tubes in a Shell and Tube Heat Exchanger?
H = \(\frac{4N}{S} \frac{V^2}{2g}\).
a) Specific gravity
b) Density
c) Specific heat capacity
d) Specific heat
View Answer
Explanation: The term S in the formula \(\frac{4N}{S} \frac{V^2}{2g}\) stands for the specific gravity of the fluid flowing through the tube at that instant.
8. What is the minimum baffle spacing for a Shell and Tube Heat Exchanger?
a) ID of Shell
b) ID of Tube
c) ID of Shell/5
d) ID of Shell/4
View Answer
Explanation: For baffles to be employed, these limitations arise due to the fact that lesser spacing increases leakage between the bundles and the baffles. Hence the minimum spacing should be ID of Shell/5.
9. What is the maximum baffle spacing for a Shell and Tube Heat Exchanger?
a) ID of Shell
b) ID of Tube
c) ID of Shell/5
d) ID of Shell/4
View Answer
Explanation: For baffles to be employed, these limitations arise due to the fact that larger spacing increases more axial flow in the shell than across the bundle. Hence the maximum spacing should be ID of Shell.
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