Heat Transfer UPDATED Actual Questions
and CORRECT Answers
In a/an __________ system, energy can be transferred by heat and work but not mass. -
CORRECT ANSWER✔✔- Closed (control mass)
When heat transfer rate is expressed per unit area, it is called _______. - CORRECT
ANSWER✔✔- Heat flux
Write the name of the law that governs this expression and state which mode of heat transfer
is governed by it.
q" = -k*(dT/dx) - CORRECT ANSWER✔✔- Fourier's Law - (mode) conduction
Write the name of the law that governs this expression and state which mode of heat transfer
is governed by it.
q" = h*(Ts-Tinfin) - CORRECT ANSWER✔✔- Newton's Law of Cooling - (mode)
convection
Write the name of the law that governs this expression and state which mode of heat transfer
is governed by it.
q" max = σ*Ts^4 - CORRECT ANSWER✔✔- Stefen Boltzmann Law of Radiation - (mode)
radiation
The material property that is a ratio of material's ability to conduct heat to its ability to store
heat is called ______ and is represented by the letter(s)/symbol(s) _____. - CORRECT
ANSWER✔✔- Thermal Diffusivity (α) - ratio of thermal conductivity
Modify the general heat confuction equation for a 1D, steady state process with volumetric
heat generation and varying thermal conductivity.
, δ/δx (k*δT/δx) + δ/δy (k*δT/δy) + δ/δz (k*δT/δz) + qdot = ρ*cp*δT/δt - CORRECT
ANSWER✔✔- δ/δx (k*δT/δx) + qdot = 0
Modify the general heat confuction equation for a 1D, transient process having constant
properties and No volumetric heat generation.
δ/δx (k*δT/δx) + δ/δy (k*δT/δy) + δ/δz (k*δT/δz) + qdot = ρ*cp*δT/δt - CORRECT
ANSWER✔✔- δ2T/δx2 = (ρ*cp/k) δT/δt
Contact resistance arises due to what? - CORRECT ANSWER✔✔- Imperfect contact
between two surfaces (rough surfaces)
Name two ways to decrease contact resistance. - CORRECT ANSWER✔✔- - decrease
surface roughness
- use soft metallic insert
- use thermal grease
- use more conductive gases
- increase interface pressure
(True/False) Heat generation is actually other forms of energy that have been converted to
thermal energy. - CORRECT ANSWER✔✔- True
When heat transfer occurs by conduction in one direction and convection occurs
simultaneously in a perpendicular direction, it is called a/an _________ problem. -
CORRECT ANSWER✔✔- Extended surface
What is the purpose of a fin? - CORRECT ANSWER✔✔- To increase the heat transfer rate
from an object to the surrounding fluid by increasing surface area.
Define heat generation. - CORRECT ANSWER✔✔- Thermal energy that is converted from
another form of energy not included in the analysis.
and CORRECT Answers
In a/an __________ system, energy can be transferred by heat and work but not mass. -
CORRECT ANSWER✔✔- Closed (control mass)
When heat transfer rate is expressed per unit area, it is called _______. - CORRECT
ANSWER✔✔- Heat flux
Write the name of the law that governs this expression and state which mode of heat transfer
is governed by it.
q" = -k*(dT/dx) - CORRECT ANSWER✔✔- Fourier's Law - (mode) conduction
Write the name of the law that governs this expression and state which mode of heat transfer
is governed by it.
q" = h*(Ts-Tinfin) - CORRECT ANSWER✔✔- Newton's Law of Cooling - (mode)
convection
Write the name of the law that governs this expression and state which mode of heat transfer
is governed by it.
q" max = σ*Ts^4 - CORRECT ANSWER✔✔- Stefen Boltzmann Law of Radiation - (mode)
radiation
The material property that is a ratio of material's ability to conduct heat to its ability to store
heat is called ______ and is represented by the letter(s)/symbol(s) _____. - CORRECT
ANSWER✔✔- Thermal Diffusivity (α) - ratio of thermal conductivity
Modify the general heat confuction equation for a 1D, steady state process with volumetric
heat generation and varying thermal conductivity.
, δ/δx (k*δT/δx) + δ/δy (k*δT/δy) + δ/δz (k*δT/δz) + qdot = ρ*cp*δT/δt - CORRECT
ANSWER✔✔- δ/δx (k*δT/δx) + qdot = 0
Modify the general heat confuction equation for a 1D, transient process having constant
properties and No volumetric heat generation.
δ/δx (k*δT/δx) + δ/δy (k*δT/δy) + δ/δz (k*δT/δz) + qdot = ρ*cp*δT/δt - CORRECT
ANSWER✔✔- δ2T/δx2 = (ρ*cp/k) δT/δt
Contact resistance arises due to what? - CORRECT ANSWER✔✔- Imperfect contact
between two surfaces (rough surfaces)
Name two ways to decrease contact resistance. - CORRECT ANSWER✔✔- - decrease
surface roughness
- use soft metallic insert
- use thermal grease
- use more conductive gases
- increase interface pressure
(True/False) Heat generation is actually other forms of energy that have been converted to
thermal energy. - CORRECT ANSWER✔✔- True
When heat transfer occurs by conduction in one direction and convection occurs
simultaneously in a perpendicular direction, it is called a/an _________ problem. -
CORRECT ANSWER✔✔- Extended surface
What is the purpose of a fin? - CORRECT ANSWER✔✔- To increase the heat transfer rate
from an object to the surrounding fluid by increasing surface area.
Define heat generation. - CORRECT ANSWER✔✔- Thermal energy that is converted from
another form of energy not included in the analysis.
