Heat Transfer Operations Questions and Answers – Condensers Recap

This set of Heat Transfer Operations Multiple Choice Questions & Answers (MCQs) focuses on “Condensers Recap”.

1. What is the expression for heat transfer coefficient for a vertically placed condenser?
a) hVER=0.943\([\frac{K^3 p^2 g h_{fg}}{μx(T_{sat} – T_L)}]^{0.25}\)
b) hVER=0.743\([\frac{K^3 p^2 g h_{fg}}{μx(T_{sat} – T_L)}]^{0.25}\)
c) hVER=0.723\([\frac{K^3 p^2 g h_{fg}}{μx(T_{sat} – T_L)} ]^{0.25}\)
d) hVER=0.725\([\frac{K^3 p^2 g h_{fg}}{μx(T_{sat} – T_L) }]^{0.25}\)
View Answer

Answer: a
Explanation: The heat transfer coefficients given by Nusselt’s theory for film-wise condensation on the surface of vertical tubes is as follows,
hVER=0.943\([\frac{K^3 p^2 g h_{fg}}{μx(T_{sat} – T_L)}]^{0.25}\)

2. What is the expression for heat transfer coefficient for a horizontally placed condenser?
a) hHOR=0.943\([\frac{K^3 p^2 g h_{fg}}{μx(T_{sat} – T_L)}]^{0.25}\)
b) hHOR=0.743\([\frac{K^3 p^2 g h_{fg}}{μx(T_{sat} – T_L)}]^{0.25}\)
c) hHOR=0.723\([\frac{K^3 p^2 g h_{fg}}{μx(T_{sat} – T_L)}]^{0.25}\)
d) hHOR=0.725\([\frac{K^3 p^2 g h_{fg}}{μx(T_{sat} – T_L)}]^{0.25}\)
View Answer

Answer: d
Explanation: The heat transfer coefficients given by Nusselt’s theory for film-wise condensation on the surface of horizontal tubes is as follows,
hHOR=0.725\([\frac{K^3 p^2 g h_{fg}}{μx(T_{sat} – T_L)}]^{0.25}\)

3. As thermal conductivity kF increases, the heat transfer coefficient ________
a) Increases
b) Decreases
c) Remains same
d) Jumps to a high value
View Answer

Answer: a
Explanation: As thermal conductivity kf increases, the heat transfer coefficient increases since thermal resistance of the condensate film decreases.
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4. If there is a decrease in viscosity, the heat transfer coefficient ____________
a) Increase
b) Decrease
c) Remains same
d) Becomes zero
View Answer

Answer: a
Explanation: If the viscosity decreases or density increases, it will offer less frictional resistance and cause quick draining of the condensate, thereby causing an increase in heat transfer coefficient.

5. A high value of latent heat hfg means that the heat transfer coefficient would __________
a) Increase
b) Decrease
c) Remains same
d) Becomes zero
View Answer

Answer: a
Explanation: A high value of latent heat means that for each kilo-Watt of heat transfer occurred, there will be thinner condensate thickness and hence the heat transfer coefficient augments.

6. An increase in diameter means a _________ heat transfer coefficient.
a) Larger
b) Smaller
c) Zero
d) Infinite
View Answer

Answer: b
Explanation: If the diameter increases then the thickness of the film at the bottom increases and hence a smaller heat transfer coefficient.

7. A large value of temperature difference will lead to more condensation and hence a __________ heat transfer coefficient
a) Larger
b) Smaller
c) Zero
d) Infinite
View Answer

Answer: b
Explanation: A large temperature difference will lead to more condensation on the wall and bigger condensate thickness which will lead to a small heat transfer coefficient.
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8. An increase in number of tubes will lead to larger condensate thickness in the lower tubes leading to ____________ heat transfer coefficient
a) Larger
b) Smaller
c) Zero
d) Infinite
View Answer

Answer: b
Explanation: If the number of tubes increases then the condensate thickness too increases in the lower tubes leading to smaller heat transfer coefficient.

9. If the condensation occurs at the outside surface of the tubes, then the equation for the heat transfer coefficient does not change.
a) True
b) False
View Answer

Answer: b
Explanation: The constant of multiplication in the equation changes and the new equation is =
hVER=1.13\([\frac{K^3 p^2 g h_{fg}}{μx(T_{sat} – T_L)}]^{0.25}\)
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10. If the condensation occurs at the outside surface of the tubes, then the equation for the heat transfer coefficient cab be represented as which one of the following?
a) hVER=0.943\([\frac{K^3 p^2 g h_{fg}}{μx(T_{sat} – T_L)}]^{0.25}\)
b) hVER=1.13\([\frac{K^3 p^2 g h_{fg}}{μx(T_{sat} – T_L)} ]^{0.25}\)
c) hVER=0.723\([\frac{K^3 p^2 g h_{fg}}{μx(T_{sat} – T_L)} ]^{0.25}\)
d) hVER=0.725\([\frac{K^3 p^2 g h_{fg}}{μx(T_{sat} – T_L) }]^{0.25}\)
View Answer

Answer: b
Explanation: When the condensation occurs outside the tube surface the film formed is less thick and easily wiped which increases the heat transfer coefficient compared to the inner tube condensation, hence the constant is higher here.

Sanfoundry Global Education & Learning Series – Heat Transfer Operations.

To practice all areas of Heat Transfer Operations, here is complete set of 1000+ Multiple Choice Questions and Answers.

If you find a mistake in question / option / answer, kindly take a screenshot and email to [email protected]

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Manish Bhojasia - Founder & CTO at Sanfoundry
Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He lives in Bangalore, and focuses on development of Linux Kernel, SAN Technologies, Advanced C, Data Structures & Alogrithms. Stay connected with him at LinkedIn.

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