L. J. MARTINEZ-MIRANDA Dept. of Materials Science and Engineering University of Maryland College Park MD THERMAL CONDUCTIVITY: INTRODUCING THE CONCEPT WHEN THERE IS NOT MUCH INFRASTRUCTURE

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.What is thermal conductivity? 2.How does it vary between materials? 3.How does heat travel across a sample? 4.What is the error in the measurements? 5.How can the measurement be improved to make it better?

Materials: Two thermometersTwo thermometers Three 1.5 cm x 4.5 cm x 0.2 cm slabs of Al, Cu and glassThree 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.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 CONDUCTIVITYWE WERE ABLE TO TEACH STUDENTS ABOUT THERMAL CONDUCTIVITY STUDENTS APPLIED THEIR KNOWLEDGE OF ERRORS IN ORDER TO DETERMINE HOW CLOSE THEY WERE.STUDENTS APPLIED THEIR KNOWLEDGE OF ERRORS IN ORDER TO DETERMINE HOW CLOSE THEY WERE. STUDENTS WERE ASKED TO SUGGEST WAYS OF IMPROVING THE DESIGN.STUDENTS WERE ASKED TO SUGGEST WAYS OF IMPROVING THE DESIGN.