Melting Ice Cubes

aka. Thermodynamics and Heat Transfer 1

Miracle Thaw

 Is it really a miracle?

 Let’s check it out… 2

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 material’s temperature.

 Establish teams and have them create a company name  Run first experiment 3

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.

– 5 th grade: Convert the weight from pounds to kilograms – 6 th 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. 5

 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

A

 1 2 [ ( )]  Measure chord length: c =  Measure height: h = 7

A

 1 2 [ ( )]

Calculate Area

 Discuss the best way to locate the following measurements: – Measure angle: α = – Measure the radius: r =  Calculate l

l

 .

r

 8

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 14

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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5

th

Grade

 Calculate D T (Delta Time - change in temperature of the material being tested.)  – (T final - T initial ) Compare student D T results to calculated D T, supplied by the teacher, in a line graph on graph paper or using a spreadsheet.

– Discuss the results 16

5

th

Grade con’t.

 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. 19

Miracle Thaw

 Is it really a miracle?

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Suggestions for Higher Grades

 Complete 5 th 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

con’t.

 Create an interactive animated computer program that demonstrates the experiment.

– Example: – http://socrates.berkeley.edu:7009/simple_machines/ 22

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/wakefld/wakepg19.html

http://www.marlow.com/d_heat.htm

– Dimmer » http://home.swbell.net/evansjim/MyHomeRepair/DimmerSwitch.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 (m 3 ) r is the density (kg/m 3 ) C is the specific heat (J/kg o C) 27

Some Material Properties

Material Steel Iron Aluminum Copper Lead Pyrex Glass Brick Pine Wood Plywood Ice (near 0 o C) Water (near 0 o C) Density (kg/m 7,850 7,870 2,770 8,930 11,340 2,225 1,920 640 545 920 1,000 3 ) Specific Heat (J/kg 434 447 875 385 129 835 o 835 2,805 1,215 2,040 4,230 C) Latent Heat of Fusion for Solid/Liquid Water: 333,700 J/kg Thermal Conductivity (W/m o C) 60 73 177 401 35 1.4

0.72

0.15

0.12

1.88

0.57

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THERMODYNAMICS

 For a solid, Q = m C D T  This is the amount of heat corresponding to a change in temperature  If you don’t know the mass, calculate it from: m = r V  D T is the change in temperature, (T final - T initial ) 29

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

 If the ice cube is at 0 o C,  “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 22 o C,  releases 3255 Joules of heat when it is cooled to 7 o C.

Q = m C D T = (0.5 kg)(434 Joules/kg o C)(22-7 o C) = 3255 Joules  3337 Joules is needed, therefore, there isn’t enough heat to melt the ice cube 31

Conservation of Energy

Better yet, we can solve for the final temperature of the steel to melt the ice: D     Q m C  T final  T initial  3337 Joules D T kg )( 434 Joules kg  o C )  22  o C   o C o C 32

Conservation of Energy

 A 0.5 kg block of steel  Cools from room temperature (22 o C) to 6.62

o C  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.



Fourier’s Law:

Q  k A D T D x 35

Fourier’s Law

Q  k A D T D x  Q is the heat transfer rate  k is a material property, thermal conductivity    A is the area which heat flows through D T is the temperature difference D x is the distance the heat must travel 36

Fourier’s Law

Q  k A D T D x

How do you make the ice cubes melt faster ?

What do the terms in Fourier’s Law show us ?

Which variables can you control ?

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Fourier’s Law

Q  k A D T D x  Fourier’s 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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Fourier’s Law

The rate of heat flow is: Q  k A D T D x  The steel block cools from 22 o C to 6.62

o C in melting the ice which is 0 o C.  As that happens, the value of D T 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.

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