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Probe Body and Thermal Contact Conductivity Affect Error of Heat Pulse Method Based on Infinite Line Source Approximation
Author(s) -
Liu Gang,
Si Bing C.,
Jiang Ai X.,
Li Bao G.,
Ren Tu S.,
Hu Ke L.
Publication year - 2012
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj2011.0228n
Subject(s) - thermal diffusivity , thermal conductivity , line source , radius , thermal conduction , analytical chemistry (journal) , thermal , materials science , line (geometry) , heat equation , volumetric heat capacity , thermodynamics , laser flash analysis , chemistry , soil science , mathematics , composite material , physics , heat transfer , heat flux , optics , geometry , environmental science , chromatography , mathematical analysis , computer security , computer science
The dual probe (DP) method is a widely used method for determining the thermal conductivity ( K ), the specific heat capacity ( c ), and the thermal diffusivity (α) of soil, but this method overestimates c , particularly for dry soil. The objective of this study is to examine if the probe body and the thermal contact conductivity ( H ) lead to biased estimation of the thermal properties by using the DP method. We used the analytical solution for cylindrical heat sources with the finite H value derived by Moench and Evans (1970). For an air‐dried sand sample with c = 756 J kg −1 K −1 , the experimental estimated c from the infinite line source (ILS) model for DP units, with the heater needles of 3.175 and 1.27 mm, is 953 J kg −1 K −1 and 904 J kg −1 K −1 , respectively. For 3.175‐ and 1.27‐mm heater needles, the c estimated by applying the ILS model to temperatures simulated using the Moench and Evans solution is 926 J kg −1 K −1 and 845 J kg −1 K −1 , respectively. Simulations suggest that both the existing of the finite probe body and H make contribution to the overestimation of c from the ILS model. The overestimation of c increases with the increase in the radius of the heater needle and decreases with the increase of H value. Using ILS could lead to substantial errors in the estimated c of dry soil.