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Soil Science Society of America Journal Abstract -

Air Entrapment as a Possible Source of Error in the Use of a Cylindrical Heat Probe1


This article in SSSAJ

  1. Vol. 37 No. 6, p. 828-832
    Received: Mar 27, 1973
    Accepted: July 17, 1973

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  1. N. K. Nagpal and
  2. L. Boersma2



The cylindrical heat probe is frequently used to measure the thermal conductivity of soils. Its theory is based on the assumption of zero thermal contact resistance at the probe surface. Noncompliance with this assumption could result from air entrapment at the probe surface, at the time of inserting the probe into the porous material. Results of studies are reported which show that the use of the heat probe can yield erroneous results which can be explained on the basis of air entrapment at the probe surface. Additional experiments were carried out to seek information regarding the relationship between thermal conductivity and soil water content for materials made up of different particle sizes. The porous media used consisted of three glass bead size fractions with diameters of 53–74, 74–105, and 149–210 µm obtained by dry sieving. Results of the experiments indicated that at the ambient temperature of 26C the relationship between thermal conductivity and water content was the same for the three size fractions. Experiments were not conducted at other ambient temperatures.

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