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Melting Ice Cubes aka. Thermodynamics and Heat Transfer

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Melting Ice Cubes aka. Thermodynamics and Heat Transfer * * * You can increase Q by changing: Delta T make the plate hotter A increase the area k you can ... – PowerPoint PPT presentation

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Title: Melting Ice Cubes aka. Thermodynamics and Heat Transfer


1
Melting Ice Cubesaka. Thermodynamics and Heat
Transfer
2
Miracle Thaw
  • Is it really a miracle?
  • Lets check it out

3
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

4
Experiment Worksheet
5
  • 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.

6
  • 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?

7
Calculate Area
  • Trace ice cube
  • Measure chord length c
  • Measure height h

8
Calculate Area
  • Discuss the best way to locate the following
    measurements
  • Measure angle a
  • Measure the radius r
  • Calculate l

9
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.

10
  • 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.

11
  • 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?

12
  • Record
  • the finish time
  • temperature at the center of the puddle
  • outside edge of the plate
  • Share data with other groups.

13
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.

14
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

15
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?

16
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

17
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?

18
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 ?

19
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.

20
Miracle Thaw
  • Is it really a miracle?

21
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.

22
Suggestions for Higher Grades cont.
  • Create an interactive animated computer program
    that demonstrates the experiment.
  • Example
  • http//socrates.berkeley.edu7009/simple_machines/

23
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

24
Have Fun
25
Additional slides for advanced grades
26
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.

27
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)

28
Some Material Properties
29
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)

30
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.

31
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

32
Conservation of Energy
  • Better yet, we can solve for the final
    temperature of the steel to melt the ice

33
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.

34
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 ?

35
CONDUCTION
  • Heat flows through a material from
    molecule-to-molecule.
  • Fouriers Law

36
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

37
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 ?

38
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 ?

39
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
    ?

40
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.
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