conduction:
convection:
emissivity:
greenhouse effect:
heat of sublimation:
heat:
kilocalorie:
latent heat coefficient:
mechanical equivalent of heat:
net rate of heat transfer by radiation:
radiation:
radiation:
rate of conductive heat transfer:
Stefan-Boltzmann law of radiation:
specific heat:
sublimation:
thermal conductivity:
Problem-Solving Strategies for the Methods of Heat Transfer
- Examine the situation to determine what type of heat transfer is involved.
- Identify the type(s) of heat transfer—conduction, convection, or radiation.
- Identify exactly what needs to be determined in the problem (identify the unknowns). A written list is very useful.
- Make a list of what is given or can be inferred from the problem as stated (identify the knowns).
- Solve the appropriate equation for the quantity to be determined (the unknown).
- For conduction, equation
Q
t=
kA(T 2 −T 1 )
d
is appropriate.Table 14.3lists thermal conductivities. For convection, determine the amount
of matter moved and use equationQ=mcΔT, to calculate the heat transfer involved in the temperature change of the fluid. If a phase
change accompanies convection, equationQ=mLforQ=mLvis appropriate to find the heat transfer involved in the phase change.
Table 14.2lists information relevant to phase change. For radiation, equation
Qnet
t
=σeA⎛⎝T 24 −T 14 ⎞⎠gives the net heat transfer rate.
- Insert the knowns along with their units into the appropriate equation and obtain numerical solutions complete with units.
- Check the answer to see if it is reasonable. Does it make sense?
Glossary
heat transfer through stationary matter by physical contact
heat transfer by the macroscopic movement of fluid
measure of how well an object radiates
warming of the Earth that is due to gases such as carbon dioxide and methane that absorb infrared radiation from the Earth’s
surface and reradiate it in all directions, thus sending a fraction of it back toward the surface of the Earth
the energy required to change a substance from the solid phase to the vapor phase
the spontaneous transfer of energy due to a temperature difference
1 kilocalorie = 1000 calories
a physical constant equal to the amount of heat transferred for every 1 kg of a substance during the change in phase of
the substance
the work needed to produce the same effects as heat transfer
is
Qnet
t
=σeA⎛⎝T 24 −T 14 ⎞⎠
heat transfer which occurs when microwaves, infrared radiation, visible light, or other electromagnetic radiation is emitted or absorbed
energy transferred by electromagnetic waves directly as a result of a temperature difference
rate of heat transfer from one material to another
Q
t
=σeAT^4 ,whereσis the Stefan-Boltzmann constant,Ais the surface area of the object,Tis the
absolute temperature, andeis the emissivity
the amount of heat necessary to change the temperature of 1.00 kg of a substance by 1.00 ºC
the transition from the solid phase to the vapor phase
the property of a material’s ability to conduct heat
Section Summary
14.1 Heat
- Heat and work are the two distinct methods of energy transfer.
- Heat is energy transferred solely due to a temperature difference.
- Any energy unit can be used for heat transfer, and the most common are kilocalorie (kcal) and joule (J).
• Kilocalorie is defined to be the energy needed to change the temperature of 1.00 kg of water between14.5ºCand15.5ºC.
• The mechanical equivalent of this heat transfer is1.00 kcal = 4186 J.
14.2 Temperature Change and Heat Capacity
• The transfer of heatQthat leads to a changeΔTin the temperature of a body with massmisQ=mcΔT, wherecis the specific heat of
the material. This relationship can also be considered as the definition of specific heat.
14.3 Phase Change and Latent Heat
CHAPTER 14 | HEAT AND HEAT TRANSFER METHODS 497
