NAME:___________________________
DATE:____________
PERIOD:_____
Principles of Engineering
Unit 1.3.3 – Introduction to Thermodynamics
work
heat
flow
energy
The study of the effects of _______,
_______
_______,
and _________
on a system.
thermal
Movement of __________
energy.
Engineers use thermodynamics in systems ranging from nuclear power plants to electrical components.
Thermal Energy vs. Temperature
Thermal
Energy
__________ ___________
is kinetic energy in transit from one object to another due to temperature
difference. (measured in joules)
Temperature
_______________
is the average kinetic energy of particles in an object – not the total amount of
kinetic energy particles. (measured in degrees)
Temperature Scales
Scale
Freezing Point
(Water)
Celsius
0
Boiling Point
(Water)
100
Fahrenheit
32
212
Kelvin
273
373
Matter is made up of molecules
_____________ in motion (kinetic energy)
An increase in temperatureincreases
___________ motion.
A decrease in temperaturedecreases
___________ motion.
Absolute
Zero _______ occurs when all kinetic energy is removed from a object. 0 K = -273° C
_____________
Thermodynamic Equilibrium
thermal ___________
equilibrium is obtained when touching objects within a system reach the same
_______
_____ temperature.
loses
When thermal equilibrium is reached, the system ________
its ability to do work.
Zeroth
law
__________
______ of Thermodynamics: If two systems are separately found to be in thermal
equilibrium with a third system, the first two systems are in thermal equilibrium with each other.
1st Law of Thermodynamics
Law of energy conservation applied to a thermal system.
form
location
cannot
Thermal energy can change _______ and __________,
but it __________
be created or destroyed.
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thermal energy
Thermal energy can be increased within a system by adding _________
_______ (heat) or by performing
work
_______ in a system.
Example: Using a Bicycle Pump
coming out
Pumping the handle results in what? Air
________
Mechanical
_______________ energy is applied to the system.
thermal
Mechanical energy is converted into __________
energy through friction (the pump becomes hot).
The total increase in internal energy of the system is equal to what?
mechanical
The applied ______________
energy.
2nd Law of Thermodynamics
hot
cold
Thermal energy flows from ______
to _______.
to pizza
When you touch a frozen pizza with your hand, thermal energy flows in what direction? hand
______________
pizza to hand
When you touch a cooked pizza with your hand, thermal energy flows in what direction? _____________
Entrophy
__________ is the measure of how evenly distributed heat is within a system.
disorder
A system tends to go from order
________ to ___________.
Firewood has low entropy (molecules in order) when stacked and high entropy when burning (molecules
in disorder).
The total amount of energy in the world does not change, but the availability of that energy constantly
decreases.
Thermal Energy (heat) Transfer
The transfer or movement of thermal energy.
Most common types of transfer:
Convection
Conduction
_______________
_______________
100% efficiency is unattainable.
Radiation
_______________
irreversible
ALL processes are ________________.
Convection
fluid
The transfer of thermal energy by movement of ________
(liquid or gas).
dense
rises
When fluid is heated, it expands
_________, becomes less ________,
and ________.
Conduction
mollecule
The transfer of thermal energy within an object or between objects from ___________
to
molecule
____________.
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Thermal Energy Transfer Equations
Q = m . c . ΔT
Q = energy transfer (Joules)
m = mass of the material (kilograms)
Cp = specific heat capacity of the material (J / kg C )
T = temperature
Δ = difference
P = Q/Δt
P = k.A.ΔT/L
k = P . L / A . VT
P = rate of energy transfer (Watts)
Q = energy transfer (Joules)
t = time (seconds)
k = thermal conductivity
A = area of thermal conductivity
L = thickness of material
T = temperature
Δ = difference
Calculating Energy Transfer
Calculate the energy transferred when a block of aluminum at 80.0°C is placed in 1.00 liter (1kg) of water
at 25.0°C if the final temperature becomes 30.0°C.
Q = m  Cp  ΔT QAl = Qwater
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Calculating Energy Transfer
P=
Q
Δt
P = kA
ΔT
L
J
• 2m
Q    0.10 s× m×°C

2
  5°C  
•
  • 3600s
  0.04m  
U-Value
Thermal Conductivity of a Material
Overall heat coefficient.
conduct
The measure of a material’s ability to __________
heat.
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R-Value
Thermal Resistance of a Material
resist
The measure of a material’s ability to ________
heat.
higher
The higher
_________ the R-value, the __________
the resistance.
R = 1/U
U= P/AVT
Bulk R-value = R-value Object 1 + R-value Object 2 + … = Total R-Value
Calculating R-Value
Determine the R-value of the wall cavity below:
Thermal Energy Transfer
Radiation
medium
The process by which energy is transmitted through a __________,
including empty space, as
electromagnetic
_____________________
waves.
Stefan’s Law
lose
All objects _______
and gain
______ thermal energy by electromagnetic radiation.
Pnet = σAe(T24 - T14 )
P = radiated energy transfer
σ = Stefan's constant = 5.6696x10-8
A = area
W
m2 ×K 4
e  emissivity constant
T  temperature in Kelvin
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Prior to dressing for school, a student watches the morning weather to decide what clothes to wear. The
bedroom is 65ºF and the student’s skin is 91.4ºF. Determine the net energy transfer from the student’s
body during the 15.0 minutes spent watching the morning weather. Note: Skin emissivity is 0.90, and the
surface area of the student is 1.30m2.
Geothermal Energy
beneath
Energy generated from the thermal energy stored ___________
the Earth’s surface.
atmosphere
Also refers to the heat that is collected from the _________________;
for instance, near the oceans.
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