Melting Ice Cubes aka. Thermodynamics and Heat Transfer

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Melting Ice Cubesaka. Thermodynamics and Heat
Transfer
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Miracle Thaw

• Is it really a miracle?
• Lets check it out

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Melting Ice Cubes Icebreaker J
First experiment objective Determine how fast
each different test material melts an ice cube
AND how the melting of the ice cube effects the
test materials temperature.

• Establish teams and have them create a company
  name
• Run first experiment

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Experiment Worksheet
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• What is the room temperature?
• Measure and record the temperature of each
  material.
• Measure the weight of the material being tested.
• 5th grade Convert the weight from pounds to
  kilograms
• 6th grade Calculate the mass of the material and
  compare it to the actual measurement.
• High school Compare methods for calculating mass
  and converting units. I.e., by hand, calculator,
  spreadsheet, draw 3-dimensionally on a CAD system
  and measure the properties, web
  (http//n93.cs.fiu.edu/measures/fulltable.asp),
  etc.

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• Calculate the area of the ice cube.
• Discuss
• What shape is the ice cube?
• What is the formula for this shape?
• What measurements will be needed?
• How can the necessary measurements be found?

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Calculate Area

• Trace ice cube
• Measure chord length c
• Measure height h

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Calculate Area

• Discuss the best way to locate the following
  measurements
• Measure angle a
• Measure the radius r
• Calculate l

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To Locate Center of Circle

• Rotate ice cube, overlapping the curved portion
  of the ice cube, and trace it again.
• Fold the circle in quarters to locate center or
  use a compass.

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• Area answers.
• Give your results to your teacher.
• Break into small groups and compare answers.
• Come up with one answer per group.
• Compare group answers.
• Using the initial readings, calculate the
  average.
• Compare the average to the group answers.
• The teacher will use this answer to calculate the
  volume of the ice cube.

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• Place the ice cube, side down, on the material.
• Time from the placement to completely melted.
• Students discuss
• Why is the ice cube melting?
• What is happening?
• How is it changing form?
• Where does the heat come from?

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• Record
• the finish time
• temperature at the center of the puddle
• outside edge of the plate
• Share data with other groups.

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Summary of First Experiment

• Where did the heat come from to melt each ice
  cube (from the test material or from the
  surrounding air) ?
• What makes one test material faster at melting
  the ice cube than another ?
• Why did the ice cubes move ?
• Level of answers will depend on grade level.

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Thermodynamics

• Greek words describe early forms of
  thermodynamics
• Therme (heat)
• Dynamics (power)
• Today it covers a wider spectrum of energy and
  energy transformation
• I.e., space shuttle to refrigeration

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Thermodynamics

• Is the interaction between energy and matter and
  it is everywhere
• Hair dryers and heat guns, irons, furnace, air
  conditioners, hot water tanks, etc.
• Also must be considered when designing computers,
  automobile engines, VCRs, CD players, dimmer
  switches, etc.
• What happens if
• a hair dryer gets too hot?
• a computer gets too hot?

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5th Grade

• Calculate DT (Delta Time - change in temperature
  of the material being tested.)
• (Tfinal - Tinitial)
• Compare student DT results to calculated DT,
  supplied by the teacher, in a line graph on graph
  paper or using a spreadsheet.
• Discuss the results

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5th Grade cont.

• Compare the amount of heat (Q) each material has
  available to the amount of heat required to melt
  the ice cube in a combination bar/line graph.
  (Data supplied by the teacher)
• Which material(s) did not have enough heat
  available to melt the ice cube?
• What can be done to increase the available heat?
• Do you see any correlations between the two
  graphs?

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Summary

• What test material was the best at melting ice
  cubes ?
• Did the color seem to effect the performance ?
• Why would an ice cube melt, even if the test
  material did not have enough energy to do it ?

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Thermodynamics

• Therefore, different materials are used to the
  transfer heat
• I.e., the material in the computer chip in the
  electric radio alarm clock is used to help keep
  the chip from overheating.

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Miracle Thaw

• Is it really a miracle?

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Suggestions for Higher Grades

• Complete 5th grade level mathematics, graphs,
  etc., only have the students calculate
• The volume and mass of the ice cube.
• The amount of heat generated by each material.
• How long a specific material will take to melt an
  ice cube.
• Calculate the volume and mass of the material
  being tested, and compared to actual measured
  weight.
• Discuss heat transfer in more depth.

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Suggestions for Higher Grades cont.

• Create an interactive animated computer program
  that demonstrates the experiment.
• Example
• http//socrates.berkeley.edu7009/simple_machines/
  

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Additional Exercises

• Compare the same material with different masses.
• Compare different materials with the same mass.
• Conduct a web search of items that use heat
  sinks.
• Examples
• Library of Thermodynamics Arizona State Univ.
• http//www.asu.edu/lib/noble/physics/thermo.htm
• Heating system (heat pipe sinks) and fans
• http//www.kita.or.kr/catalog/cheil/index.html
• Laptops
• http//www.indek.com/heatpipe/hp_app.htm
• Computers
• http//www.thermalloy.com/catalog/htm/dhs57.htm
• http//www.web_tronics.com/webtronics/heatredmouns
  .html
• http//www.heatsink.com/
• http//www.execpc.com/industrialelectronics/wakefl
  d/wakepg19.html
• http//www.marlow.com/d_heat.htm
• Dimmer
• http//home.swbell.net/evansjim/MyHomeRepair/Dimme
  rSwitch.htm
• http//www.thermalloy.com/catalog/htm/eprof41b.htm
  

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Have Fun
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Additional slides for advanced grades
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THERMODYNAMICS

• The science of energy (or its ability to cause
  changes), and
• The relationships among the properties of
  matter.
• HEAT, Q, is the form of energy which melted our
  ice cubes.
• In the SI system, we measure Q in Joules.

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THERMODYNAMICS

• Some important material properties
• m is the mass of the material (kg)
• V is the volume (m3)
• r is the density (kg/m3)
• C is the specific heat (J/kg-oC)

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Some Material Properties
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THERMODYNAMICS

• For a solid, Q m C DT
• This is the amount of heat corresponding to a
  change in temperature
• If you dont know the mass, calculate it from m
  r V
• DT is the change in temperature,
• (Tfinal - Tinitial)

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How much heat does it take to melt one of our ice
cubes ?

• If the ice cube is at 0oC,
• Latent Heat of Fusion (amount of energy needed
  to go from solid to liquid states.
• For water, that is 333,700 Joules/kg.
• If our ice cube is 0.01 kg, the heat required
  is 3,337 Joules.

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Do we have enough energy in our test materials to
do that ?

• Example
• A 0.5 kg. chunk of steel, starting at 22oC,
  releases 3255 Joules of heat when it is cooled to
  7oC.
• Q m C DT
• (0.5 kg)(434 Joules/kg-oC)(22-7 oC)
• 3255 Joules
• 3337 Joules is needed, therefore, there isnt
  enough heat to melt the ice cube

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Conservation of Energy

• Better yet, we can solve for the final
  temperature of the steel to melt the ice

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Conservation of Energy

• A 0.5 kg block of steel
• Cools from room temperature (22oC) to 6.62oC
• Gives up enough heat to melt a 0.01 kg ice cube.

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Heat Transfer

• is the flow of energy which happens when a
  difference in temperature exists.
• can happen between two bodies or even within a
  single body.
• What was the difference in temperature between
  our ice cubes and our test materials ?

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CONDUCTION

• Heat flows through a material from
  molecule-to-molecule.
• Fouriers Law

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Fouriers Law

• Q is the heat transfer rate
• k is a material property, thermal conductivity
• A is the area which heat flows through
• DT is the temperature difference
• Dx is the distance the heat must travel

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Fouriers Law

• How do you make the ice cubes melt faster ?
• What do the terms in Fouriers Law show us ?
• Which variables can you control ?

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Fouriers Law

• Fouriers Law tells us how fast heat will flow.
• Do we know if there is enough energy available
  in our test materials to melt our ice cube ?

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Fouriers Law

• The rate of heat flow is
• The steel block cools from 22oC to 6.62oC in
  melting the ice which is 0oC.
• As that happens, the value of DT decreases.
• Therefore, the rate of heat transfer to the ice
  decreases.
• How can we increase the rate for a given material
  ?

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GO TO WORK !!!

• Determine if your test materials have enough
  heat to melt an ice cube.
• Measure the rate (time) of heat transfer.
• Tabulate your experiment data.