THERMAL CONDUCTIVITY: INTRODUCING
THE CONCEPT WHEN THERE IS NOT
MUCH INFRASTRUCTURE
L. J. MARTINEZ-MIRANDA
Dept. of Materials Science and Engineering
University of Maryland
College Park MD 20742-2115
OUTLINE
• WHAT ARE THE MAIN POINTS WE WANT THE STUDENTS TO
LEAVE WITH
• THE APPARATUS
– STUDENTS ARE ASKED ABOUT THE POSSIBLE PROBLEMS
– STUDENTS ARE ASKED FOR SUGGESTION ON HOW TO IMPROVE
IT
• ERROR CALCULATIONS
PURPOSE
• To measure the temperature differential across an
Al, a glass and a Cu slab.
• Using Al as reference, measure the power
dissipated dQ/dt across the slab based on the rate
of change of temperature as a function of position.
• Estimate the heat transfer, dQ at specific time
intervals, dt, for Al.
• Based on the number you obtain for Al, calculate
the thermal conductivity and heat transfer for
glass and Cu.
The students learn:
1.
2.
3.
4.
5.
What is thermal conductivity?
How does it vary between materials?
How does heat travel across a sample?
What is the error in the measurements?
How can the measurement be improved to make it
better?
Materials:
•Two thermometers
•Three 1.5 cm x 4.5 cm x 0.2 cm slabs of Al, Cu and glass
•Thermal conductivity apparatus, consisting of: 1. heater ( sautering
iron) , the produces a constant heat flow; 2. holder for the slabs: 3. a
ruler to measure the temperature at specific places.
Procedure
1. Using a ruler or a calliper, measure the cross-sectional are A of the Al,
the glass slide, and the Cu. Which A is the one we must measure.
2. Turn on the heater and wait a few minutes while it stabilizes. If it is on,
wait for a few minutes. Do not touch it: HOT HOT HOT.
3. Place the Al in the sample holder. Note: you must mark on the piece of
Al the location of the places where you will measure the temperature
(Why?).
4. Use the thermometer to record the temperature at these same two
places. Take 4 measurements, waiting 1 minute in between them.
5. Record the temperature, temperature gradient, and time of
measurement.
6. For Al, use the value for the thermal conductivity provided in table 7.19
in dePodesta’s book, and determine the power dissipated at each
reading
7. Using the time intervals for your reading, determine the heat dissipated
for the last three readings.
RESULTS
SUGGESTIONS
• ONCE STUDENTS FINISHED THE EXPERIMENT,
THEY WERE ASKED TO MAKE SUGGESTIONS OF
HOW TO IMPROVE THE DESIGN.
• THEY ARE ASKED TO SUBMIT DRAWINGS.
• WE HAVE INTEGRATED SOME OF THE
SUGGESTIONS OVER THE YEARS.
CONCLUSIONS
• WE WERE ABLE TO TEACH STUDENTS ABOUT
THERMAL CONDUCTIVITY
• STUDENTS APPLIED THEIR KNOWLEDGE OF
ERRORS IN ORDER TO DETERMINE HOW CLOSE
THEY WERE.
• STUDENTS WERE ASKED TO SUGGEST WAYS OF
IMPROVING THE DESIGN.