Transcript Keep the Heat Thermodynamics

Keep the Heat
Thermodynamics
Teams bring an insulated device built
prior to the competition that:



Fits in a 15.0 cm x15.0 cm x15.0 cm cube
Constructed of any material except any type
of foam, bubblewrap, or commercial
insulation
Holds a 250 ml beaker, that is easily
inserted.
Insulated Device Continued





Has a hole in the top that is at least 1.5 cm
in diameter and all the way through the topmust stay open
Hole must be at least 2.5 cm above beaker
Contains no energy source
Not different that room temperature
Penalities: 10 points for each violation in
construction
Two Part Event

Part 1 Device Testing
Heat retention score (if negative set to zero for
scoring)
((internal temp / external temp)-1) x 25
Prediction score
(1-(abs (internal final temp - predicted final temp /
final internal temp) x 50
Plot score 10 Points max
Ice Water Bonus (Level C)
Volume used /4
Max 12.5 pts
Part 2 Written test
Worth 50 points
Topics include
 Temperature conversions
 Heat units
 Thermal conductivity
 Heat capacity
 Specific heat
 Laws of thermodynamics
 History of thermodynamics
 Thermodynamics processes
Bring to the Competition
Must bring: (For full points)

Insulated Device

Identical 250 ml beaker (Pyrex or similar)

Eye protection (Chemical splash proof goggles)

Graphs or plots (Minimum of 4)

Writing utensils

May Bring:

Notes secured in a 3 ring binder, nothing loose

Calculators, supplies and tools
Graphs or Plots
 Worth 10 Points Total
 “May” submit up to 4 for scoring (1 point each)
 Team name and student names: 2points
 Axis labeled and Title : 2 points
 Appropriate units and increments : 2 points
 Team may have to explain how data was collected
and also how it will be used.
 May have to be submitted before tournament
 Have a duplicate set for team to use
Example of Plots
The Competition
 After impound supervisor will announce




Cooling time 20-40 minutes
Room temperature
Water bath temp 60o – 90o C
Volume of water 50 ml -150 ml
 25 ml increments at regional
 10ml increments at state
 1ml increments at national
Competition Continued
 Teams will be given water in both beakers
then places one beaker in their device.
 At C Level may add ice water up to 50 ml
 Teams may use their own thermometers
 Teams must then predict the final
temperature at time allotted.
 Team spends remaining time to do written
test
Written Test Topics
 Temperature conversions
 Heat units
 Thermal conductivity
 Heat capacity
 Specific heat
 Laws of thermodynamics
 History of thermodynamics
 Thermodynamics processes
Temperature conversion
Heat Units







The most common units for heat are
BTU (Btu) - British Thermal Unit
Calorie
Joule
BTU - British Thermal Unit
The unit of heat in the imperial system - the BTU - is
the amount of heat required to raise the temperature of one pound
of water through 1oF (58.5oF - 59.5oF) at sea level (30 inches of
mercury).
 1 Btu (British thermal unit) = 1055.06 J = 107.6 kpm = 2.931 10-4
kWh = 0.252 kcal = 778.16 ft.lbf = 1.0551010 ergs = 252 cal = 0.293
watt-hours
 An item using one kilowatt-hour of electricity generates 3412 Btu.
Heat Units continued
 A calorie is commonly defined as
 the amount of heat required to raise the temperature





of one gram of water 1oC
the kilogram calorie, large calorie, food calorie,
Calorie (capital C) or just calorie (lowercase c) is the
amount of energy required to raise the temperature of
one kilogram of water by one degree Celsius
1 kcal = 4186.8 J = 426.9 kp.m = 1.163 10-3 kWh =
3.088 ft.lbf = 3.9683 Btu = 1000 cal
Be aware that alternative definitions exists - in short:
Thermochemical calorie
The calorie is outdated and commonly replaced by
the SI-unit Joule.
Heat units continued
 Joule
 The unit of heat in the SI-system the Joule is
 a unit of energy equal to the work done when a force
of one newton acts through a distance of one meter
 4.184 joule of heat energy (or one calorie) is required
to raise the temperature of a unit weight (1 g) of
water from 0oC to 1oC, or from 32oF to 33.8oF
 1 J (Joule) = 0.1020 kpm = 2.778 10-7 kWh = 2.389
10-4 kcal = 0.7376 ft.lbf = 1 kg.m2/s2 = 1 watt second
= 1 Nm = 1 ft.lb = 9.478 10-4 Btu
Heat conductivity
 How a material will allow heat to pass
through:
Heat Capacity
 The amount of heat needed to change a
substance’s temperature
 Commonly called specific heat
Laws of Thermodynamics
Laws of Thermodynamics
 First Law of Thermodynamics
 The first law of thermodynamics is the
application of the conservation of energy
principle to heat and thermodynamic
processes:

2nd Law of Thermodynamics
 The Second Law essentially says that it is impossible
to obtain a process where the unique effect is the
subtraction of a positive heat from a reservoir and the
production of a positive work. Energy exhibits
entropy. It moves away form its source.. You cannot
keep a continual flow of heat to work to heat to work
without adding energy to the system. In machine
terms, you have to add energy to get more work, and
the ratio of heat to work will never equal 100% due to
energy expanding away from its source.
2nd law continued
Entropy
 Energy flows from high energy to low energy
with some lost to environment
3rd Law of Thermodynamics
 It says all processes cease as temperature
approaches absolute zero. This is the
temperature at which molecules cease
movement, cease producing kinetic energy. In
other words, there is no energy.
Thermodynamic Processes
Equations that may help



























Calorimetry
Heat required to change temperature: Q = mcΔT
Heat required to change phase: Q = mL
Ideal Gas Law: PV = nRT (in Kelvin)
Boyle's LawConstant TemperaturePV = constantP1V1=P2V2Charles/Gay Lussac LawConstant PressureV/T =
constantV1/T1=V2/T2
0th Law: Two objects, each in thermal equilibrium with a third object, are in thermal equilibrium with each other.
Math Example: If A = C and B = C, then A = B.
1st Law: The change in internal energy of a system equals the difference between the heat taken in by the system and the work
done by the system.
Formula: ΔU = Q - W (in Kelvin)
Adiabatic
no heat flow
Q=0
ΔU = W
Isothermal
no temp change
ΔT = 0 so ΔU = 0
Q=W
Isochoric
no volume change
ΔV = 0 so W = 0
ΔU = Q
Isobaric
no pressure change
ΔP = 0
W=PΔV
Team Checklist/ Data Sheet














Team # _________ Team Name______________
Competitors names ________________ and ___________
2a Competitors Must bring insulating device, 2 identical 250 ml Pyrex beakers,
eye protection, plots, writing utensils.
2a Competitors May bring: notes, parts/supplies, calculators
2a All references materials must be secured in 2 ring binder
2d The teams device, parts, and any supplies must be impounded before the
event starts
2d Eye protection does not need to be impounded
2e Competitiors must wear eye protection during set up and loading of devices
with water
3 Device fits in in a 15cm x 15cm x 15cm cube
3a Device is made of allowed materials
3c Device can accommodate 250 ml beaker
3d Device has a hole>=1.5 cm diameter, ,2.5 cm above beaker
3e Device has no energy sources
3f Device is not significantly different from room temp
Device Testing Data
 Predicted Internal Beaker Temp. ________
 Final Internal Beaker Temp .
 Final External Beaker Temp.
 Ice Water added in ml (C level)
________
________
________
Web Resources
 Equation cheat sheet:
http://www.bing.com/images/search?q=Thermod
ynamics+Equation+Sheet&view=detail&id=D35E
C8C097C0FCF787987BA0BB06AEA7DE27646
8
 Simple explanation of the laws of
thermodynamics
http://www.physicsplanet.com/articles/threelaws-of-thermodynamics
Web resources
 Videos on thermodynamics :
http://www.khanacademy.org/science/physics/
thermodynamics/v/thermodynamics--part1?playlist=Physics