This set of Heat Transfer Multiple Choice Questions & Answers (MCQs) focuses on “Fourier Equation”.
1. The famous Fourier series is named after
a) Diller and Ryan
b) J.B. Joseph Fourier
c) Stefan- Boltzmann
d) Wein’s
View Answer
Explanation: He gave this theory in 1824.
2. Fourier law of heat conduction is best represented by
a) Q = -k A d t /d x
b) Q = k A d x/d t
c) Q = -k A
d) Q = k d t/d x
View Answer
Explanation: According to Fourier law of heat conduction, Q = -k A d t /d x.
3. Here are some assumptions that are made for Fourier law. Identify the wrong one
a) No internal heat generation
b) Steady state heat conduction
c) Non- linear temperature profile
d) Isotropic and homogenous material
View Answer
Explanation: It has constant temperature gradient and a linear temperature profile.
4. Consider the following statements:
The Fourier heat conduction equation
Q = -k A d t /d x
Presumes
i) Steady state conditions
ii) Constant value of thermal conductivity
iii) Uniform temperature at the wall surface
iv) One dimensional heat flow
Which of these statements are correct?
a) i, ii and iii
b) i, ii and iv
c) ii, iii and iv
d) i, iii and iv
View Answer
Explanation: Thermal conductivity is different for different materials.
5. The diagram shows heat conduction through a plane wall. The surface temperature is 475 K and it radiates heat to the surroundings at 335 K. If thermal conductivity of the material is 12.5 W/m degree, find the temperature gradient. Let convective coefficient be 80 W/m2 degree and radiation factor is 0.9
a) – 1052.4 degree celsius
b) – 2052.4 degree celsius
c) – 3052.4 degree celsius
d) – 4052.4 degree celsius
View Answer
Explanation: Heat conducted through the plate = convection heat losses + radiation heat losses. So, d t /d x = – 13155/12.5 = – 1052.4 degree Celsius.
6. Negative sign in Fourier heat conduction equation indicates
a) Heat always flow is in the direction of positive temperature gradient
b) Heat always flow in the direction of negative temperature gradient
c) No heat flow is there
d) Data is insufficient
View Answer
Explanation: The ratio d t/d x represents the change in temperature per unit thickness i.e. the temperature gradient. So it represents heat flow in the direction of negative temperature gradient.
7. Transmission of heat i.e. molecular is smallest in case of
a) Gases
b) Liquids
c) Alloys
d) Solids
View Answer
Explanation: In gases, atoms are arranged loosely, there is less molecular transmission of heat as compared to solids, liquids and alloys.
8. Which one is not the unit of thermal conductivity?
a) kcal/m hr K
b) KJ/m hr K
c) W/m s K
d) Cal/cm s K
View Answer
Explanation: Thermal conductivity = “energy per unit time, per unit length, and per unit temperature difference”. The SI unit for thermal conductivity is W/m K (watts per meter per Kelvin). However, there is an extra ‘s’ in the option “W/m s K”. The unit “kcal/m hr K” could also be specified as “kJ/m s K” or “Cal/cm s K”.
9. “Thermal conductivity represents the amount of heat conducted across the unit area when a temperature difference of one kelvin”.
a) True
b) False
View Answer
Explanation: It is across unit area and through unit distance.
10. Which of the following is the unit of thermal resistance?
a) degree/kcal
b) hour degree
c) s degree/kcal
d) degree/W
View Answer
Explanation: Thermal resistance is expressed in the unit’s hr degree/kcal, degree/W and s degree/J.
Sanfoundry Global Education & Learning Series – Heat Transfer.
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