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A remark on the theory of measuring thermal diffusivity by the modified Angstrom's methodA theory of the measurement of the thermal diffusivity of a sample by the modified Angstrom method is developed for the case in which radiative heat loss from the end surface of the sample is not negligible, and applied to measurements performed on lunar samples. Formulas allowing sample thermal diffusivity to be determined from the amplitude decay and phase lag of a temperature wave traveling through the sample are derived for a flat disk sample for which only heat loss from the end surface is important, and a sample of finite diameter and length for which heat loss through the end and side surfaces must be considered. It is noted that in the case of a flat disk, measurements at a single angular frequency of the temperature wave are sufficient, while the sample of finite diameter and length requires measurements at two discrete angular frequencies. Comparison of the values of the thermal diffusivities of two lunar samples of dimensions approximately 1 x 1 x 2 cm derived by the present methods and by the Angstrom theory for a finite bar reveals them to differ by not more than 5%, and indicates that more refined data are required as the measurement theory becomes more complicated.
Document ID
19810060091
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Horai, K.-I.
(Lamont-Doherty Geological Observatory Palisades, NY, United States)
Date Acquired
August 11, 2013
Publication Date
August 10, 1981
Publication Information
Publication: Journal of Geophysical Research
Volume: 86
Subject Category
Lunar And Planetary Exploration
Accession Number
81A44495
Funding Number(s)
CONTRACT_GRANT: NGR-33-008-177
Distribution Limits
Public
Copyright
Other

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