4C Lab
05/31/2007 03:30 PM
Thermal Conductivity
Goal: To determine the thermal conductivity of different materials.
Equipment List:
Pasco Thermal conductivity apparatus
ice mold with cover
materials to test: wood, lexan, masonite and sheet rock.
Pasco steam generator
vernier calipers
timer
two small cups to collect melted ice and condensing steam
triple beam balance
paper towels for clean up
Background: The thremal conductivity, k, is a constant whiuch measures how good a conductor of heat a
particular material is. The thermal conductivity is related to the heat transferred by:
k=
(Heat transferred)(Thickness of material)
(Area) (Time of heat transfer)(Temperature differential)
(1)
The technique for measuring thermal conductivity is straightforward. A slab of material to be tested is
clamped between a steam chamber, which maintains a constant temperature of 100o C , and a block of ice,
which maintains a constant temperature of 0o C. The heat transferred is measured by collecting the water
from the melting ice. The ice melts at a rate of 1 gram per 80 calories (3.34 x 105 J/kg) of heat flow (the
latent heat of melting for ice), or:
Delta Q = Lf delta m
(2)
Combining equations (1) and (2), the thermal conductivity, k, can be expressed:
k =
(mass of melted ice) (334000 J/kg)(thickness of material)
(area of ice)(time during which ice melted)(temp.differential)
(3)
Procedure:
Set up the apparatus as shown in the diagram -- don't attach the steam generator hose to the chamber
yet!
Measure and recored h, the thickness of the material
Mount the sample material onto the steam chamber. Take care that the sample material is flush against
the water channel, so water will not leak, then tighten the thumbscrews. (A bit of grease between the
channel and the sample will help create a good seal.)
Place the ice on top of the sample. It is not necessary to remove the ice from the mold. Just place the
open end of the mold against the sample, and let the ice slide out as the experiment proceeeds.
Let the ice sit for several minutes so it begins to melt and comes in full contact with the sample.
Then measure the diameter of the ice block. Record this value as d1 .
http://nebula.deanza.fhda.edu/physics/Dickson/4C/ThermalConductivity.html
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4C Lab
05/31/2007 03:30 PM
Obtain data for determining the ambient melting rate of the ice as follows:
Weigh a small container and record its mass
Collect the melting ice in the container for a measured time t a (~10 min.).
Weigh the container and water and record the mass
Find the mass of the water m wa .
Run steam into the steam chamber. Let the steam run for several minutes until temperatures stablize
so that the heat flow is steady. (Place a container under the drain spout of the steam chamber to
collect the water that escapes from the chamber.)
Now collect data for determining the melting rate of the ice with steam running into the steam
chamber.
Using the same small container as before, collect the melting ice for approximately 10 minutes.
Record the mass of the water, mw, which is equal to the mass of melted ice and t, the time.
Repeat to ensure consistent data.
Remeasure the diameter of the ice, d2 .
Repeat for a total of three samples.
Analysis:
1. Use dav = ½(d 1 + d2 ) to find th area over which the heat flow between the ice and steam chamber took
place, the area of the ice in contact with the sample material.
2. Calculate k using equation (3) for each trial. Remember, the ambient melting rate accounts for some part
of the mass of the water obtained during the steam cycle. Thus, the mass you collect in the cup while steam
is flowing into the chamber is larger by the amount of mass while sitting in the room.
http://nebula.deanza.fhda.edu/physics/Dickson/4C/ThermalConductivity.html
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4C Lab
05/31/2007 03:30 PM
3. Average your two k values for each material.
4. Compare your values with the following:
kwood = 0.18 ± 0.06 W/mK
ksheetrock = 0.24 ± 0.06 W/mK
kmasonite = 0.27 ± 0.06 W/mK
klexan = 0.241 ± 0.04 W/mK
Conclusion:
Review your results.
http://nebula.deanza.fhda.edu/physics/Dickson/4C/ThermalConductivity.html
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