Heat Transfer Questions and Answers – Correlations for Forced Convection

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This set of Heat Transfer Multiple Choice Questions & Answers (MCQs) focuses on “Correlations For Forced Convection”.

1. The convective heat transfer coefficient in laminar flow over a flat plate
a) Increases with distance
b) Increases if a higher viscosity fluid is used
c) Increases if a denser fluid is used
d) Decreases with increase in free stream velocity
View Answer

Answer: c
Explanation: It mostly increases if a denser fluid is used.

2. For laminar flow over a flat plate, the average value of a Nusselt number is prescribed by the relation
Nu = 0.664 (Re) 0.5 (Pr) 0.33
Which of the following is then a false statement?
a) Density has to be increased four times
b) Plate length has to be decreased four times
c) Specific heat has to be increased four times
d) Dynamic viscosity has to be decreased sixteen times
View Answer

Answer: d
Explanation: The dynamic viscosity has an inverse relation to 1/6 power. To double the convective heat transfer coefficient, the dynamic viscosity has to be decreased 64 times.

3. For turbulent flow over a flat plate, the average value of Nusselt number is prescribed by the relation
Nu = 0.664 (Re) 0.5 (Pr) 0.33
Which of the following is then a false statement?
The average heat transfer coefficient increases as
a) 1/5 power of plate length
b) 2/3 power of thermal conductivity
c) 1/3 power of specific heat
d) 4/5 power of a free stream velocity
View Answer

Answer: a
Explanation: The average heat transfer coefficient reduces with length as 1/5th power of the length.
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4. A nuclear reactor with its core constructed of parallel vertical plates 2.25 m high and 1.5 m wide has been designed on free convection heating of liquid bismuth. Metallurgical considerations limit the maximum surface temperature of the plate to 975 degree Celsius and the lowest allowable temperature of bismuth is 325 degree Celsius. Estimate the maximum possible heat dissipation from both sides of each plate. The appropriate correlation for the convection coefficient is
Nu = 0.13 (Gr Pr) 1/3
a) 143 MW
b) 153 MW
c) 163 MW
d) 173 MV
View Answer

Answer: b
Explanation: Q = 2 h A d t = 153 MW.

5. Consider the above problem, find the value of Grashoff number
a) 101.3 * 10 12
b) 102.3 * 10 12
c) 103.3 * 10 12
d) 104.3 * 10 12
View Answer

Answer: d
Explanation: Grashof number = l 3 p 2 β g d t/µ 2.

6. A thin walled duct of 0.5 m diameter has been laid in an atmosphere of quiescent air at 15 degree Celsius and conveys a particular gas at 205 degree Celsius. Base your calculations on one meter length of the duct, estimate the convective coefficient of heat transfer
a) 5.086 W/m2 K
b) 6.086 W/m2 K
c) 7.086 W/m2 K
d) 8.086 W/m2 K
View Answer

Answer: a
Explanation: h = 1.37 (d t/l) 0.25 = 5.086 W/m2 K.

7. Free correction modulus is given by
a) p 2 β g c P
b) p 2 β g c P/k
c) p 2 β g c P/µ k
d) p 2 β g c P
View Answer

Answer: c
Explanation: It contains only fluid properties and is called the free convection modulus.
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8. The free convection coefficient is given by
h = C 1 d t m/l 1 – 3m
The value of exponent for laminar flow is
a) 0.5
b) 0.6
c) 0.7
d) 0.8
View Answer

Answer: a
Explanation: For laminar flow h = C 1 (d t/l) 0.25.

9. For inclined plates we multiply Grashoff number with
a) Cos 2 α
b) Sin 2 α
c) Sin α
d) Cos α
View Answer

Answer: d
Explanation: It should be multiplied with cos α, as α is angle with the horizontal.
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10. The free convection coefficient is given by
h = C 1 d t m/l 1 – 3m
The value of exponent for turbulent flow is
a) 0.43
b) 0.33
c) 0.23
d) 0.13
View Answer

Answer: b
Explanation: For turbulent flow h = C (d t).

Sanfoundry Global Education & Learning Series – Heat Transfer.

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

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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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