Flowing Heat

Matt Weisenberger, matt@caer.uky.edu

University of Kentucky,

Center for Applied Energy Research

2540 Research Park Dr., Lexington, KY 40511

859-257-0322

4th grade science experiment

Overview

• What is Heat?• Three Experiments

– (1) Thermal Diffusivity– (2) Thermal Expansion– (3) Heat Capacity

• Procedure Questions Materials &

Observations Results & Conclusions

What are Heat & Temperature?

• Heat is ENERGY• The more heat-energy within a

material, the hotter it will feel.• Heat always flows… from hotter areas

to cooler areas… not the reverse.• Temperature is a measurement of the

amount of heat within a material.• Materials that feel hot have a lot of heat

in them. You feel that heat flowing into your cool hand.

Experiment 1: Thermal Diffusivity

– What is thermal diffusivity?– Through which materials does heat

flow faster?

AnswerThermal diffusivity tells us how fast

heat is conducted through a material. Materials such as copper and steel conduct heat faster than materials such as wood and plastic.

Experiment 1: Materials

1. Hot plate

2. Rods of copper, glass, and graphite (about 2 in. long X 3/8 in. diameter)

3. Paraffin wax

Procedure1. Stand three rods, made of different

materials, with the exact same length (approx. 2 in. long) on a hot plate.

2. Turn the hot plate on “high.”3. Place a small sliver of wax on the

top surface of the rods and watch to see which rod melts the wax the fastest and which one the slowest.

– The material upon which the wax melts first has the highest thermal diffusivity.

– The material upon which the wax melts second has the second highest thermal diffusivity, etc.

Observations

Copperwax melts 2nd

Glasswax melts

3rd

Graphitewax melts 1st

Results & Conclusions

• Graphite had the highest thermal diffusivity.

• Copper had the 2nd highest thermal diffusivity.

• Glass had the lowest thermal diffusivity.

Experiment 2.Thermal Expansion

– What is thermal expansion?– Which materials expand more?

• AnswersHeat-energy causes the atoms of

a material to vibrate. As they vibrate, they push each other apart. This causes the material to expand.

Experiment 2: Materials1. Metal Tubing:

- copper: 8 ft long, about ¼ inch diameter, bendable- aluminum: 8 ft long, about ¼ inch diameter

2. Toothpicks (2)3. Colored tape4. Funnel5. Rubber hose with hose clamps (6 in. long with

a diameter that will fit snugly around tubing)6. Laboratory ring stand with clamp7. Wood blocks (about 2 in X 2 in X 2 in)8. Source of hot water9. Pitcher full of ice water10. Hot water vessel such as a teapot, coffee pot,

etc.11. Bucket

Experiment 2: Procedure1. Approximately 18 inches from one end,

bend each tube 90º (see photo on slide 12).

2. Rest the other end on a wooden block (see photo).

3. Vertically support the bent end using the laboratory ring stand (see photo).

4. Attach a funnel to the supported end using the rubber hose and clamp (see photo on slide 13).

5. Make several “toothpick flags” by wrapping a piece of colored tape around a toothpick so that it resembles a small flag (see photo on slide 14).

6. Place the toothpick end of the flag between the metal tube and wooden block (see slide 14 photo).

Experiment 2: Procedure7. Place the hot water vessel onto the hot

plate and bring to a boil.8. Place a bucket beneath the straight

end of the copper tube.9. While the students are looking at the

toothpick flag, pour some boiling water into the funnel and observe the amount and direction that the flag spins.

10. Next, pour the ice water into the funnel and observe the flag spinning in the opposite direction.

11. Repeat steps 8 – 10 with the aluminum tube.

Metal Tube Assembly

Funnel Assembly

Close-Up of “Toothpick Flag”

Conclusions

●The more the flag spins, the greater the thermal expansion of the metal tube, thus:1. Aluminum has the highest

thermal expansion2. Copper has the least thermal expansion

Helpful Hints & Observations

• Keep students away from the funnel and bucket when pouring the boiling water!

• It is helpful to put the tube assembly on a long table.

• When watching the flag spin, make a note of how many revolutions it spins.

Experiment 3.Heat Capacity

• Questions– What is heat capacity?

• AnswerThe amount of heat-energy

necessary to raise the temperature of 1g of a material 1ºC.

Experiment 3: Materials

1. Hot Plate2. Beaker or pan that can be used to

boil water3. Metal tongs4. Rods or cylinders of copper, plastic,

and graphite (approx. 1 in. diameter X 1 in. long)

5. Glass beakers (150 ml capacity)6. Thermometer or thermocouple7. Stopwatch (or ordinary watch that

can measure seconds)

Procedure1. Weigh three rods, of exactly the same

size, made of plastic, graphite, and copper and heat to 100ºC in boiling water.

2. Using tongs or tweezers drop one of the materials into 100ml of water that is at room temperature.

3. Measure the temperature increase of the water for 1 minute.– The material which most heats the

water has the highest heat capacity.4. Repeat for the other two materials.

Conclusions

• The Plastic has the highest heat capacity.

• The graphite has the 2nd highest heat capacity.

• The copper has the lowest heat capacity.

Helpful Hints & Observations

• Thermocouples work best, but if using a thermometer get one that can accurately measure small temperature changes.

Heat Flow in ActionQuestions

– How do thermal diffusivity, thermal expansion, and heat capacity work together? -- Thermal conductivity

– What is thermal conductivity?Answers

– The three heat experiments show how heat flow affects materials.

– The thermal conductivity is related to all three of the above and is a number that characterizes the speed at which, heat-energy flows through a material of constant area when one end is at a high temperature and the other is at a lower temperature.

Resources

Materials for most of these experiments can be purchased from hardware stores and scientific equipment suppliers such as Fisher Scientific and Ward’s. Another excellent source is McMaster Carr (www.macmaster.com)