A calorimeter capable of measuring the heat capacity of 1 mg size samples from
4.2 to greater than 100 K has been designed, constructed, and tested. The sample is
bonded to the end of a 0.002 inch diameter, 0.5 cm long chromel-constantan
thermocouple (type E) and heated optically with a laser and fiber optic. An advantage of
this calorimeter is the low addenda heat capacity of the thermocouple. The
thermocouple, which serves not only as the temperature sensor of the sample but also as
the thermal link between the sample and a constant temperature reservoir, is anchored to
a copper block, which acts as the constant temperature reservoir. Heat capacity is
determined from the temperature rate of decay of the sample using a sweep method.
The sample is heated to an initial temperature above the block temperature by the
laser. The laser is then turned off and the sample temperature is allowed to decay to the
block temperature. By measuring the temperature of the sample as a function of time and
relating it to the thermal conductivity of the thermocouple in a separate experiment, the
sample's heat capacity can be determined. The thermal conductivity of the thermocouple
is determined by performing an experiment with a sample of known heat capacity.
A design model created with a spreadsheet helped to determine what size
thermocouple should be used as well as the best materials and dimensions of the
components that make up the calorimeter. The model was also useful in determining the
nature of a calorimetry experiment and helped determine how high above the block
temperature the sample should be heated, how low the pressure inside the calorimeter
should be, and how much time a calorimetry experiment would require.
Experiments using copper samples have confirmed the validity of the design. The
results of an experiment using a 1.1 mg copper sample agree (within expected
uncertainty) with the accepted heat capacity of copper from 7 to 100 K. One factor in the
uncertainty is the large heat capacity of the grease (Apiezon N) used to bond the sample
to the tip of the thermocouple, especially below 15 K. / Graduation date: 1994
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/37205 |
| Date | 04 August 1993 |
| Creators | Wolochuk, Lee |
| Contributors | Warnes, William H. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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