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Heat Transfer SmartBook 3 Questions and
Answers (Expert Solutions)
Q: Identify the true statements about heat conduction in a wall if the air temperatures
inside and outside the house remain constant., 🗹🗹: A small thickness of the wall
causes the temperature gradient in that direction to be large.
Heat transfer through the wall of a house can be modeled as steady and one-
dimensional.
Q: Calculate the rate of change of the energy of the wall (dEwalldt) if the rate of heat
transfer into the wall (Q˙in)is 60 W and the rate of heat transfer out of the wall (Q˙out)
is 43 W., 🗹🗹: 17 W
Q: A plane concrete wall has a thickness of 0.3 m and area of cross-section 25 m2. The
thermal conductivity of concrete is 1.09 W/(m·K). The temperature on one side of the
wall (T1) is 32°C and the other side (T2) is 17°C. Calculate the rate of heat conduction
through the plane wall., 🗹🗹: Reason:
(Q˙cond) = ((A) x Thermal conductivity (k) xTemperature difference (T1 −
T2)/Thickness (L)) that yields
(Q˙cond)=1362.5 W
Q: The Fourier's law for heat conduction for the plane wall shown in the figure is given
by _____. Q˙cond is the rate of conduction heat transfer, k is the average thermal
conductivity, A is the cross-sectional area of the material, T1 − T2 is the temperature
difference, and L is the wall thickness., 🗹🗹: Q˙cond = kA x (T1 − T2)L
Q: The unit of conduction resistance is _____., 🗹🗹: kelvin(K)/watt(W)
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Q: Identify the true statements about heat conduction through a wall if the air
temperatures between the inner and outer surfaces of the walls of the house are the
same., 🗹🗹: There is no heat transfer through the wall from the top to the bottom.
There is no heat transfer through the wall from left to right.
Q: Rank the following values of the rate of heat transfer (Q˙in)Q˙in into a wall and the
rate of change of the energy (dEwalldt)dEwalldt of the plane wall from the smallest to
largest order of rate of heat transfer (Q˙out)Q˙out out of the wall. Place the smallest
value on top., 🗹🗹: 1) 17
2) 15
3)9
Q: A square-steel section of cross-sectional area 0.24 m2m2, thickness 0.075 m, and the
thermal conductivity 50.2 W/(m·K)W/(m·K) is subjected to a temperature difference of
20 K between its two faces. Calculate the heat transfer rate through the section if it acts
like a plane wall., 🗹🗹: 3212.8 W
Q: Identify the true statements about Fourier's law of heat conduction., 🗹🗹: The rate
of heat transfer is directly proportional to the temperature difference.
The rate of heat transfer is directly proportional to the thermal conductivity.
The rate of heat transfer is inversely proportional to the length of heat conduction.
Q: A plane wall has thickness 0.1 m, cross-sectional area 1.2 m2, and thermal
conductivity 0.8 W/(m⋅K). Calculate the conduction resistance of the material., 🗹🗹:
0.104 KW
Q: The energy balance equation for a plane wall section is given by _____. Q˙inQ˙in is the
rate of heat transfer into the wall, Q˙outQ˙out is the rate of heat transfer out of the wall,
dEwalldtdEwalldt is the rate of change of the energy of the wall., 🗹🗹: Q˙inQ˙in -
Q˙outQ˙out = dEwalldt
Q: The rate of convective heat transfer between a solid and a fluid can be calculated
using the formula ______, where Q˙convQ˙conv is the rate of convection heat transfer,
T∞T∞ is the temperature of the solid, TsTs is the temperature of the liquid, and
RconvRconv is the convection resistance., 🗹🗹: Q˙conv = Ts − T∞Rconv
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Q: The SI unit for rate of heat transfer (Q˙cond)(Q˙cond) is _____., 🗹🗹: watt (W)
Q: For a plane wall, the conduction resistance (Rwall)Rwall is 11.90 × 10-310-3 K/W,
the thermal conductivity (k)k is 2.10 W/(m⋅K), and the thickness (L)L is 0.05 m.
Calculate the cross-sectional area of the wall., 🗹🗹: 2 m2
Q: For a plane wall system, if the convection heat transfer coefficient (h)h is 14
Wm2⋅KWm2⋅K and the convection resistance (Rconv)Rconv is 2.1 KWKW, calculate the
area of solid (As)As., 🗹🗹: 0.034 m2
Q: Identify the types of heat transfer models for heat transfer through the wall of a
house if the air temperature in and outside the house remain constant., 🗹🗹: Steady
One-dimensional
Q: Calculate the radiation resistance for a piece of coal with radiation heat transfer
coefficient 7.33 W/(m2⋅K) and the surface area 1.2 m2., 🗹🗹: 0.11 KW
Q: For a plane wall system, the convection heat transfer rate (Qconv)Qconv is 20 W and
the convection resistance (Rconv)Rconv is 0.77 K/W, calculate the temperature
difference (Ts − T∞)Ts - T∞ between the plane wall and the surrounding fluid., 🗹🗹:
15.4 K
Q: The unit of the radiation heat transfer coefficient (hrad)hrad is _____., 🗹🗹:
watt(meter)2kelvin
Q: A hot aluminum rod is allowed to cool in air. The combined heat transfer coefficient
(hcombined)hcombined for this model is given by _____, where hradhrad is the radiation
heat transfer coefficient and hconvhconv is the convection heat transfer coefficient.,
🗹🗹: hrad + hconv
Q: True or false: The equation for convection resistance RconvRconv = 1h×As1h×As is
valid only when the surfaces are plane. h is the convection heat transfer coefficient and
As is the cross-sectional area of the solid., 🗹🗹: False
Heat Transfer SmartBook 3 Questions and
Answers (Expert Solutions)
Q: Identify the true statements about heat conduction in a wall if the air temperatures
inside and outside the house remain constant., 🗹🗹: A small thickness of the wall
causes the temperature gradient in that direction to be large.
Heat transfer through the wall of a house can be modeled as steady and one-
dimensional.
Q: Calculate the rate of change of the energy of the wall (dEwalldt) if the rate of heat
transfer into the wall (Q˙in)is 60 W and the rate of heat transfer out of the wall (Q˙out)
is 43 W., 🗹🗹: 17 W
Q: A plane concrete wall has a thickness of 0.3 m and area of cross-section 25 m2. The
thermal conductivity of concrete is 1.09 W/(m·K). The temperature on one side of the
wall (T1) is 32°C and the other side (T2) is 17°C. Calculate the rate of heat conduction
through the plane wall., 🗹🗹: Reason:
(Q˙cond) = ((A) x Thermal conductivity (k) xTemperature difference (T1 −
T2)/Thickness (L)) that yields
(Q˙cond)=1362.5 W
Q: The Fourier's law for heat conduction for the plane wall shown in the figure is given
by _____. Q˙cond is the rate of conduction heat transfer, k is the average thermal
conductivity, A is the cross-sectional area of the material, T1 − T2 is the temperature
difference, and L is the wall thickness., 🗹🗹: Q˙cond = kA x (T1 − T2)L
Q: The unit of conduction resistance is _____., 🗹🗹: kelvin(K)/watt(W)
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Q: Identify the true statements about heat conduction through a wall if the air
temperatures between the inner and outer surfaces of the walls of the house are the
same., 🗹🗹: There is no heat transfer through the wall from the top to the bottom.
There is no heat transfer through the wall from left to right.
Q: Rank the following values of the rate of heat transfer (Q˙in)Q˙in into a wall and the
rate of change of the energy (dEwalldt)dEwalldt of the plane wall from the smallest to
largest order of rate of heat transfer (Q˙out)Q˙out out of the wall. Place the smallest
value on top., 🗹🗹: 1) 17
2) 15
3)9
Q: A square-steel section of cross-sectional area 0.24 m2m2, thickness 0.075 m, and the
thermal conductivity 50.2 W/(m·K)W/(m·K) is subjected to a temperature difference of
20 K between its two faces. Calculate the heat transfer rate through the section if it acts
like a plane wall., 🗹🗹: 3212.8 W
Q: Identify the true statements about Fourier's law of heat conduction., 🗹🗹: The rate
of heat transfer is directly proportional to the temperature difference.
The rate of heat transfer is directly proportional to the thermal conductivity.
The rate of heat transfer is inversely proportional to the length of heat conduction.
Q: A plane wall has thickness 0.1 m, cross-sectional area 1.2 m2, and thermal
conductivity 0.8 W/(m⋅K). Calculate the conduction resistance of the material., 🗹🗹:
0.104 KW
Q: The energy balance equation for a plane wall section is given by _____. Q˙inQ˙in is the
rate of heat transfer into the wall, Q˙outQ˙out is the rate of heat transfer out of the wall,
dEwalldtdEwalldt is the rate of change of the energy of the wall., 🗹🗹: Q˙inQ˙in -
Q˙outQ˙out = dEwalldt
Q: The rate of convective heat transfer between a solid and a fluid can be calculated
using the formula ______, where Q˙convQ˙conv is the rate of convection heat transfer,
T∞T∞ is the temperature of the solid, TsTs is the temperature of the liquid, and
RconvRconv is the convection resistance., 🗹🗹: Q˙conv = Ts − T∞Rconv
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Q: The SI unit for rate of heat transfer (Q˙cond)(Q˙cond) is _____., 🗹🗹: watt (W)
Q: For a plane wall, the conduction resistance (Rwall)Rwall is 11.90 × 10-310-3 K/W,
the thermal conductivity (k)k is 2.10 W/(m⋅K), and the thickness (L)L is 0.05 m.
Calculate the cross-sectional area of the wall., 🗹🗹: 2 m2
Q: For a plane wall system, if the convection heat transfer coefficient (h)h is 14
Wm2⋅KWm2⋅K and the convection resistance (Rconv)Rconv is 2.1 KWKW, calculate the
area of solid (As)As., 🗹🗹: 0.034 m2
Q: Identify the types of heat transfer models for heat transfer through the wall of a
house if the air temperature in and outside the house remain constant., 🗹🗹: Steady
One-dimensional
Q: Calculate the radiation resistance for a piece of coal with radiation heat transfer
coefficient 7.33 W/(m2⋅K) and the surface area 1.2 m2., 🗹🗹: 0.11 KW
Q: For a plane wall system, the convection heat transfer rate (Qconv)Qconv is 20 W and
the convection resistance (Rconv)Rconv is 0.77 K/W, calculate the temperature
difference (Ts − T∞)Ts - T∞ between the plane wall and the surrounding fluid., 🗹🗹:
15.4 K
Q: The unit of the radiation heat transfer coefficient (hrad)hrad is _____., 🗹🗹:
watt(meter)2kelvin
Q: A hot aluminum rod is allowed to cool in air. The combined heat transfer coefficient
(hcombined)hcombined for this model is given by _____, where hradhrad is the radiation
heat transfer coefficient and hconvhconv is the convection heat transfer coefficient.,
🗹🗹: hrad + hconv
Q: True or false: The equation for convection resistance RconvRconv = 1h×As1h×As is
valid only when the surfaces are plane. h is the convection heat transfer coefficient and
As is the cross-sectional area of the solid., 🗹🗹: False
