Umm Al-Qura University
College of Engineering & Islamic Architecture
Mechanical Engineering Department
Course # 804314-2 : Heat Transfer (1)
Home-Work 1
Student’s Name: ______________________________________ ID#: _____________ Group: __
Multiple Choices: Circle the letter which best answers the question.
1.
The following are correct except
a.
2.
3.
Particles in solids bump into each other when heated
b.
Conduction is best in solids because the particles are very close
c.
Fluids will not conduct very well because the particles are not attached or close
d.
The ice in drinks gives some of its heat energy to the drink
The following are correct except
a.
A solid take up room on expansion but mass remains the same
b.
Density of solids increases as temperature increases
c.
Density of solids decreases as temperature increases
d.
Infrared radiation (IR) does not need medium to travel through
The following are correct except
a.
Wood and Plastics are good insulators but poor conductors
b.
Metals used in making cooking utensils are good conductors but poor insulators
c.
Conduction happen best in fluids than solids
d.
Conduction happens best in solids than in fluids
e. Liquids and gases are known as fluid
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3. Which of the following is or are correct? When a fluid (liquid or gas) is heated
4.
5.
a.
Temperature increases
b.
The fluid expands
c.
The fluid becomes less dense as it take up more space
d.
Mass of fluid remains the same as volume increases
e.
All of the above
All the following are correct except
a. All hot object or things give out or emit Infrared Radiation
b. Infrared radiation does not require a medium to travel through
c. The convection currents, less dense liquids rises up and cooler liquids moves in
to take its place
d. Thermal energy is not needed to change a solid to liquid
e. Heat and Temperature are not the same but related in a way
The amount of Thermal energy or heat energy in an object depends on the following except
a. its temperature
b. nature of material it is made from
c. Its volume or density
d. Its mass
6.
The following information about boiling point are correct except
a. Thermal energy is needed for change of state from liquid to gas
b. Boiling point is that temperature a liquid will start to change from liquid to gas
c. Is the temperature when evaporation is fast
d. Boiling point is the same for all liquids
e. Boiling point of pure water is 100 °C
7.
What means of heat transfer does not require a medium?
a. Conduction
b. Convection
c. Radiation
d. All means of heat transfer require a medium
Transfer of heat by the mixing and motion of macroscopic portions of a fluid is called
____________ heat transfer.
a. Conduction
8.
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b. Convection
c. Radiation
d. Thermodynamics
9.
Transfer of heat by electromagnetic radiation that arises due to the temperature of a body
is called ____________ heat transfer.
a. Conduction
a. Convection
b. Radiation
c. thermodynamic
10.
Transfer of heat by the interactions of atoms or molecules of the material through which
the heat is being transferred is called ____________ heat transfer.
a. conduction
b. convection
c. radiation
d. thermodynamic
11.
Transfer of heat by the motion and mixing caused by density variation resulting from
temperature differences within a fluid is called____________ .
a. condensation
b. natural convection
c. forced convection
d. boiling
13. The rate of heat transfer per unit area is called ____________.
a. thermal conductivity
b. heat flux
c. emissivity
d. black body radiation
14. When you put your hand in a cup of ice water, your hand feels cold. This is because
___________.
a. your hand gains the coldness from the ice water
b. your hand loses thermal energy to the ice water
c. the ice water loses thermal energy to your hand
d. the ice water loses the coldness to your hand
15. A hot object warms a cool object. Which of the following statements about the relationship
between temperature and thermal energy in this case is correct?
a. Temperature flows from the hot object to the cold object.
b. Temperature flows from the object with the most thermal energy to the object
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16.
with the least thermal energy.
c. The object with the most thermal energy always has the highest temperature.
d. Energy flows from the object with the highest temperature to the object with the
lowest temperature.
Heat from the sun reaches Earth by
a.
b.
c.
d.
Convection
Radiation
Conduction
none of the above
17. A steel slab with area A and no internal heat generation is at steady state with temperature
T1 on one side and temperature T2 on the other side. The thermal conduction coefficient of steel
is k. What is the thermal resistance of the slab (the thickness is L)?
a.
b.
c.
d.
k(T1-T2)/L
kA(T1-T2)/L
L/(kA)
k/L
18. The inner and outer radii of a spherical cell are 1 cm and 2 cm, respectively. The thermal
conductivity of the shell is 1 W/m.K. Calculate the heat transfer through the cell if the
temperatures of the inner and outer surfaces are 200°C and 100°C, respectively.
a. 25.0 W
b. 50.2 W
c. 37.3 W
d. 100.2 W
e. 12.5 W
19. Calculate the heat conducted through a 0.2 m thick industrial furnace wall made of fireclay
brick. Measurements made during steady-state operation showed that the wall temperatures
inside and outside the furnace 1500 and 1100 K respectively. The length of the wall is 1.2 m and
the height is 1 m.
a.
b.
c.
d.
4.08 W
4800 W
4.08 kW
4800 kW
20. A steel slab with area A and no internal heat generation is at steady state with temperature T 1
on one side and temperature T2 on the other side. The thermal conduction coefficient of steel is
k. What is the thermal resistance of the slab?
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a. k(T1-T2)/L
b. kA(T1-T2)/L
c. L/(kA)
d. k/L
21. The units of heat flux are:
a.
b.
c.
d.
e.
Watts
Joules
Joules/m2
Watts/m2
Joules/kg K
22. In which of these is free convection the dominant mechanism of heat transfer?
a.
b.
c.
d.
e.
Heat transfer to a piston head in a diesel engine combustion chamber
Heat transfer from the inside of a fan-cooled p.c.
Heat transfer to a solar heating panel
Heat transfer on the inside of a central heating panel radiator
Heat transfer on the outside of a central heating panel radiator
23. Which of these statements is not true?
a.
b.
c.
d.
e.
Conduction can occurs in liquids
Conduction only occurs in solids
Thermal radiation can travel through empty space
Convection cannot occur in solids
Gases do not absorb thermal radiation
24. What is the heat flow through a brick wall of area 10 m2, thickness 0.2 m, k = 0.1 W/mK
with a surface temperature on one side of 20 °C and 10 °C on the other?
a.
b.
c.
d.
e.
f.
50 Watts
50 Joules
50 Joules/m2
50 Watts /m2
200 Watts
200 Watts /m2
25. Which of these statements is not true: Heat transfer by radiation….
a. only occurs in outer surface
b. is negligible in free convection
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c. is a fluid phenomenon and travels at the speed of the fluid
d. is an acoustic phenomenon and travels at the speed of sound
e. is an electromagnetic phenomenon and travels at the speed of light
26. Calculate the net thermal radiation heat transfer (heat flux) between two surfaces. Surface A,
has a temperature of 100 °C and Surface B, 200 °C. Assuming they are sufficiently close so that
all the radiation leaving A is intercepted by B and vise-versa. Assume that also black-body
behavior.
a.
b.
c.
d.
e.
f.
27.
The different modes of heat transfer are:
a.
b.
c.
d.
e.
28.
85 W
85 W/m2
1740 W
1740 W/m2
200 Watts
None of these
Forced convection, free convection and mixed convection
Conduction, radiation and convection
Combined forced and free convection
Combined laminar and turbulent flow
Condensation, boiling, free convection and forced convection
Mixed convection refers to:
a.
b.
c.
d.
29.
Combined convection and radiation
Combined convection and conduction
Combined forced and free convection
Combined laminar and turbulent flow
e. Combined forced convection and condensation
The thermal diffusivity,α , is defined as:
a.
b.
c.
d.
e.
30.
= µ/Cpk
= kCp/ρ
= k/ρCp
= hL/k
= L/k
Two identical bodies radiate heat to each other. One body is at 30 °C and the other at 250
°C. The emissivity of both is 0.7. What is the net heat transfer per square meter?
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a. 2.635 kW
b. 4.8 kW
c. 2.635 kW
d. 4.8 W
31. Arrange the following materials from the highest to the lowest thermal conductivity:
Air
Alloys
pure metal
nonmetallic
Water
Rank
32. A certain insulation has a thermal conductivity of 10 W/m°C. What thickness is necessary to
effect a temperature drop of 500 °C for a heat transfer rate of 400 W/m2?
Answer:
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33. Consider steady-state conditions from one-dimensional conduction in a plane wall having a
thermal conductivity k = 10 W/mK and thickness L = 0.2 m, with no internal generation.
T1
T2
Figure 1
x
0
L
Determine the unknown quantities for each case, indicating the direction of the heat flux.
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Case
T1 (oC)
T2 (oC)
(K/m)
Heat Flux q
Direction
(W/m2)
A
-40
B
25
-10
0
C
50
D
10
E
-100
2000
-20
-5000
33. Air at 20 °C blows over a hot plate 50 by 75 cm maintained at 250 °C. The heat transfer rate
is 2.5 kW. Calculate the convection heat transfer coefficient.
Answer:
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34. Calculate the net thermal radiation heat transfer (heat flux) between two surfaces. Surface A,
has a temperature of 100 °C and Surface B, 200 °C. Assuming they are sufficiently close so that
all the radiation leaving A is intercepted by B and vise-versa. Assume that also black-body
behavior.
Answer:
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