On transient hot-wire measurement of the thermal conductivity of electrolytic solutions

P. Baruël

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    In its "classical" form the transient hot-wire method for measurement of the thermal conductivity of liquids is not suitable for measurements on electrolytic solutions. In this report is described a new modification of the method, permitting measurements on all electrolytic solutions whose decomposition voltage is not quite extremely low (i. e. a few tenths of volts). Till now extension of the method to include measurements on electrolytes has as Jar as the author knows only been carried through in 2 works, namely by Alas and van der Held et al., the hot wire having been surrounded with an electrically insulating layer. The latter work was later revoked by one of the authors (in co-operation with others). For practical and theoretical reasons Alas uses a thin layer that is dissolved by bases, and that work therefore confines itself to measurements on solutions of
    salts. In the present work the electrical insulation round the hot wire is avoided by modification of the measuring cell and the circuit so that the voltage applied to the cell is made to balance with the counter-electromotive force from the electrolytic polarization when a short pulse of current has passed through the liquid. A naked wire can therefore be used in the liquid, which, when balance has been obtained, cannot carry electric current. A technique has been worked out for "blank experiments" in which the platinum hot wire is replaced by a manganin wire. In such blank experiments electric disturbances at measurement on electrolytic solutions will reveal themselves if they are present. For experimental verification of the applicability of the method measurements were made on aqueous solutions of KBr, NaCl, NaOH, and H2SO4, all in the concentrations 0.5, 1, 1.5, and 2 N. For most of these the thermal conductivity is known from the literature, measured by other methods. The agreement is good. The method can be used on the strongest bases, e. g. about 20 N NaOH, as well as on acids and salt solutions. The present report builds upon an earlier report by the same author, which contains the necessary circuit analysis and presents the method of calculation. Thi? method differs somewhat from those of earlier authors because the modification necessitated a break with the "classical" principle that the thinnest possible wire (e. g. 20 μm in diameter) should be used. In this work a wire diameter of 500 μm is used. This further resulted in
    a very robust cell construction.
    Original languageEnglish
    Place of PublicationRoskilde, Denmark
    PublisherRisø National Laboratory
    Number of pages65
    ISBN (Print)8755001564
    Publication statusPublished - 1972
    SeriesDenmark. Forskningscenter Risoe. Risoe-R


    • Risø-R-264
    • Risø-264
    • Risø report 264


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