EGEE 304 exam 1 UPDATED Exam
Questions and CORRECT Answers
How does the science of heat transfer differ from the science of thermodynamics? - CORRECT
ANSWER - thermodynamics == amount of heat transfer as a system undergoes a process
from one equilibrium state to another.
Heat transfer == deals with the rate of heat transfer as well as the temperature distribution within
the system at a specified time.
What is the driving force for heat transfer, - CORRECT ANSWER - temperature difference
driving force for electric current flow - CORRECT ANSWER - electric potential difference
(voltage)
driving force for fluid flow - CORRECT ANSWER - pressure difference.
On a hot summer day, a student turns his fan on when he leaves his room in the morning. When
he returns
in the evening, will his room be warmer or cooler than the neighboring rooms? Why? Assume all
the doors
and windows are kept closed. - CORRECT ANSWER - Warmer. Because energy is added to
the room air in the form of electrical work.
Consider two identical rooms, one with a refrigerator in it and the other without one. If all the
doors and
windows are closed, will the room that contains the refrigerator be cooler or warmer than the
other room?
Why? - CORRECT ANSWER - Warmer. If we take the room that contains the refrigerator as
our system, we will see that electrical work is
supplied to this room to run the refrigerator, which is eventually dissipated to the room as waste
heat.
, Define thermal conductivity, and explain its significance in heat transfer. - CORRECT
ANSWER - the rate of heat transfer through a unit thickness of the material per unit area and
per unit temperature difference thermal conductivity of a material is a measure of how fast heat
will be conducted in that material.
How do the thermal conductivity of gases and liquids vary with temperature? - CORRECT
ANSWER - The thermal conductivity of gases is proportional to the square root of absolute
temperature. The thermal
conductivity of most liquids, decreases with increasing temperature, with water being a notable
exception.
What are the mechanisms of heat transfer? How are they distinguished from each other? -
CORRECT ANSWER - The mechanisms of heat transfer are conduction, convection and
radiation.
conduction - CORRECT ANSWER - the transfer of
energy from the more energetic particles of a substance to the adjacent less energetic ones as a
result of interactions between the particles.
Qcond = -kA dt/dx
convection - CORRECT ANSWER - mode of energy transfer between a solid surface and the
adjacent liquid or gas which is in motion, and it involves combined effects of conduction and
fluid motion.
Qconv = hAs(ts- tinfinty)
radiation - CORRECT ANSWER - energy emitted by matter in the form of electromagnetic
waves (or photons) as a result of the changes in the electronic configurations of the atoms or
molecules.
Qrad= e sigma As (Ts^4 - T^4 surr)
Questions and CORRECT Answers
How does the science of heat transfer differ from the science of thermodynamics? - CORRECT
ANSWER - thermodynamics == amount of heat transfer as a system undergoes a process
from one equilibrium state to another.
Heat transfer == deals with the rate of heat transfer as well as the temperature distribution within
the system at a specified time.
What is the driving force for heat transfer, - CORRECT ANSWER - temperature difference
driving force for electric current flow - CORRECT ANSWER - electric potential difference
(voltage)
driving force for fluid flow - CORRECT ANSWER - pressure difference.
On a hot summer day, a student turns his fan on when he leaves his room in the morning. When
he returns
in the evening, will his room be warmer or cooler than the neighboring rooms? Why? Assume all
the doors
and windows are kept closed. - CORRECT ANSWER - Warmer. Because energy is added to
the room air in the form of electrical work.
Consider two identical rooms, one with a refrigerator in it and the other without one. If all the
doors and
windows are closed, will the room that contains the refrigerator be cooler or warmer than the
other room?
Why? - CORRECT ANSWER - Warmer. If we take the room that contains the refrigerator as
our system, we will see that electrical work is
supplied to this room to run the refrigerator, which is eventually dissipated to the room as waste
heat.
, Define thermal conductivity, and explain its significance in heat transfer. - CORRECT
ANSWER - the rate of heat transfer through a unit thickness of the material per unit area and
per unit temperature difference thermal conductivity of a material is a measure of how fast heat
will be conducted in that material.
How do the thermal conductivity of gases and liquids vary with temperature? - CORRECT
ANSWER - The thermal conductivity of gases is proportional to the square root of absolute
temperature. The thermal
conductivity of most liquids, decreases with increasing temperature, with water being a notable
exception.
What are the mechanisms of heat transfer? How are they distinguished from each other? -
CORRECT ANSWER - The mechanisms of heat transfer are conduction, convection and
radiation.
conduction - CORRECT ANSWER - the transfer of
energy from the more energetic particles of a substance to the adjacent less energetic ones as a
result of interactions between the particles.
Qcond = -kA dt/dx
convection - CORRECT ANSWER - mode of energy transfer between a solid surface and the
adjacent liquid or gas which is in motion, and it involves combined effects of conduction and
fluid motion.
Qconv = hAs(ts- tinfinty)
radiation - CORRECT ANSWER - energy emitted by matter in the form of electromagnetic
waves (or photons) as a result of the changes in the electronic configurations of the atoms or
molecules.
Qrad= e sigma As (Ts^4 - T^4 surr)
