Using Cryogenics to Teach Temperature and Heat Transfer

micefunctionalUrban and Civil

Nov 15, 2013 (3 years and 6 months ago)

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“Using Cryogenics to Teach
Temperature and Heat Exchange”

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http://mathinscien
ce.info





Using Cryogenics to Teach Temperature and
Heat Transfer


James Beasley, Educator, Mathematics & Science Center


Developed with funding from the Mathematics & Science Center as part of the course,
Chemistry for Middle S
chool Teachers
, Summer 2004


Curriculum

Physical Science, Chemistry


Key Concepts



Temperature, temperature scales, heat and heat transfer



Phase change, freezing and boiling point, vaporization, condensation,
conduction and convection



Overview

Liquid

nitrogen is applied to materials such as metals, rubber balls,
bananas, balloons and flowers. Demonstrations relate basic physical
properties of matter, changes of state, and the effect of “icy cold” on
humans and everyday objects.


Materials



Dewar for
liquid nitrogen



4 Styrofoam cups in a holder



Large beaker



One
-
half banana



Balloons (small round or long)



Flowers (daisies or carnations)



Tuning forks (2, same key)



Lead bell (2” x 2” square lead sheet, string & metal washers)



Solid rubber ball (“bouncy bal
l”)



Racquet ball (hollow rubber ball)



Gloves, goggles



Student work sheets (Optional)


Safety

Instructor and volunteers should always wear protective gloves and
goggles when handling or assisting with liquid nitrogen.


Time

Demonstration



45 min

Group
ing

n/a





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Procedure

1. Introduce the cryogenic liquid as a very special sample of matter by
holding up a Styrofoam cup of liquid nitrogen. Ask students to define the
word
matter
.

2. Hold the cup so students may see the vapors pouring from the top.
Ask s
tudents whether they think the substance is hot or cold. Ask them
what observation(s) helped them draw that conclusion. Discuss
differences in the behavior of hot and cold vapors. Students should
decide the substance must be cold because the vapors are fa
lling toward
the floor. Hot vapors rise.



3. Discuss the difference between a
gas

and a
vapor
?



4. Ask for additional observations. What is forming on the outside of the
cup? The cool liquid
condenses

the moisture in the air around the cup.


5. As
k students to define the term
molecule
.


6. Tell the class that this substance is one of only seven elements that
occur normally as
diatomic molecules.
The seven elements are
hydrogen, nitrogen, oxygen, fluorine, chlorine, bromine, and iodine.



7. Define
cryogenic
s.
Cryos

is a Greek word meaning “icy cold”;
genic

means produces or generates. Therefore, cryogenics means that which
produces “icy cold” conditions.


8. CAREFULLY pour some liquid nitrogen from a cup onto the floor or a
table top. Ask for obser
vations. What happened to the liquid? Why did it
sizzle and evaporate? Compared to the temperature of this liquid, the
floor (or table, etc.) is very hot. Touching a warmer surface causes the
liquid nitrogen to boil away. The nitrogen absorbed heat from t
he warmer
surface. Heat is a form of
energy

transferred because of a difference in
temperature. Discuss
conductio
n and
convection
.


9. Discuss the three most common
states of matter.

(
solid, liquid, gas
)
Why is water sometimes a solid, sometimes a liqui
d, and at other times a
gas? (depends on temperature or heat content)


10. Ask, “What is
temperature
?” The average kinetic energy of
molecules in matter or a measure of how rapidly the molecules are
moving.


11. The temperature of liquid nitrogen is
-
320

F or
-
196

C. Remember
water freezes at +32

F or 0

C. Discuss safety associated with
cryogenic liquids.


12. Discuss
gas laws

(Optional).

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13.
Perform balloon experiment
:
Put some liquid nitrogen into a
beaker. Blow up a small balloon. Explain
that the balloon is rigid now
because the gas particles inside are colliding with each other and with
the elastic walls of the balloon. If a blown up balloon is released, the gas
particles escape and the balloon collapses. There are no longer enough
gas p
articles colliding with the sides of the balloon to exert the pressure
necessary for it to be inflated. What may happen to a balloon left in your
car on a hot July 4
th

afternoon? (It will expand and/or burst.) What may
happen on a cold winter night? (It ma
y shrink.) Look what happens when
I put this balloon in the liquid nitrogen. Discuss why the balloon shrinks
while in the liquid nitrogen but then inflates again when waved in the air
outside the liquid nitrogen container. Note the balloon retains its
ela
sticity.


14.
Test tuning fork
: Demonstrate that both tuning forks sound the
same. Have a student put one of the tuning forks into a cup of liquid
nitrogen. Ask the class to predict what will happen when the tuning fork
is removed from the nitrogen and t
he tests are repeated. Retest.


15.
Test lead bell
: Have a student shake the lead bell and then put the
lead bell into another cup of liquid nitrogen. Ask the class to predict what
will happen when the tuning fork is removed from the nitrogen and the
test
is repeated. Retest.


16.
Test banana
: Tell student to hammer the nail into the block of wood
using a banana hammer. Stop student before he/she hits the nail with
the banana and ask do they really think that is going to work. What might
we do to make it wo
rk? Put the banana into the liquid nitrogen. Ask the
class to predict what will happen when the banana is removed from the
nitrogen and used to hammer the nail. Test the banana. Let the student
drive the nail into the board using the flat end of the banan
a.


17.
Test flower
: Ask student to lightly tap a flower on the table top. Do
you hear anything when you tap it? Put the flower into a cup of liquid
nitrogen. Ask the class to predict what will happen when the flower is
removed from the nitrogen and the t
est is repeated. Retest.


18.
Test hard rubber ball and racquetball

:
Bounce both balls. Put
each ball into a cup of liquid nitrogen. Ask the class to predict what will
happen when the balls are removed from the nitrogen and the test is
repeated. Retest ho
w well they bounce after they are quick frozen.
“Bouncy ball” should bounce, but like a glass marble. The racquet ball
should implode with a loud pop.



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19.
Discuss practical uses of cryogenics
:



Food Preservation
: Freeze dried f
ood and frogs.



Medicine
:

Freeze warts, preserve whole blood, corneas, etc.

Scientists hope to develop the technology to freeze organs or
even human beings while we search for a cure for diseases like
cancer but we haven’t perfected that yet.



Band Instruments
: Brass instruments are

placed in a container
that has been
cooled down using liquid nitrogen. The treated
metal is cooled at a prescribed rate to prevent thermal shock. It
has been documented that this kind of treatment improves the
overall resonance, enables loud notes to be p
layed at the same
intensity with less effort, and allows moving parts to last longer
and work more efficiently.



Sports
: Skate blades

treated in this manner stay sharp longer
with less material removed during sharpening. A t
reated metal
golf club head give
s better distance.



Saw Blades
: Saw blades, including chain saw cutting teeth, that
have been cryogenically treated, stay sharp much longer saving
time and money.




Superconductivity:
Set the black disc in the cut
-
off cup bottom.
Place a small magnet on
top of the disc. Place the cup bottom
and its contents on top of another inverted cup. Slowly pour liquid
nitrogen over the disc and magnet until the magnet levitates. The
disc becomes a
superconductor

at very low temperatures. The
magnet induces an el
ectric current in the disc that has a magnetic
field exactly opposite to that of the top magnet. The top magnet is
pushed up
-

or levitated. This is call a
HTS

or
high temperature
superconductor
. Originally helium at 4.2K was used to induce
superconducti
vity. Helium is much less abundant than nitrogen
and the very cold temperature needed was not as practical. Use
the plastic tongs to gently flip the magnet. Place the cup on the
demonstration table and let students pass by and observe the
levitation.


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Assessment

1.

What are the three most common states of matter? Can you
name a fourth state of matter?

2.

What are diatomic molecules? List all seven of them.

3.

Why did the balloon shrink and then re
-
inflate?

4.

Temperature is a measure of what? What is another way

of
stating this?

5.

Based on what you saw happening on the outside of the cups
filled with liquid nitrogen, how would you say that clouds are
formed?



Answers to
Assessment
Questions










1.

The three most common states of matter are solid, liquid and
gas.
Plasma is a fourth state of matter.

2.

Diatomic molecules are elements which normally occur in nature
as two atoms bonded together. The seven diatomic molecules
are hydrogen, nitrogen, oxygen, fluorine, chlorine, bromine and
iodine.

3.

The balloon shrunk w
hen the air molecules in the balloon gave up
their heat to the liquid nitrogen, slowed down and compacted
together. The balloon inflated when the compacted air molecules
absorbed heat energy from the air in the room and changed back
to a gas.

4.

Temperature
is a measure of how fast molecules are moving.
Temperature is a measure of the average kinetic energy of
matter.

5.

As water vapor ascends to higher altitudes, the temperature
decreases. The water molecules give up their heat to the
surrounding air and chan
ge state from a gas to the liquid droplets
that form a cloud.



Alternate Demos

Select from the experiments described on the following websites to teach
concepts of temperature, states of matter and heat exchange:


Fun Dry Ice Projects

http://oror.essortment.com/dryiceprojects_opl.htm


The Saturday Scientists

http://www.west.net/~science/co2.htm



Dry Ice: Simply Sublime!

http://tlc.ousd.k12.ca.us/~acody/Dry_Ice.html

From, Cody’s Science Education Zone