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Improved hot wire methodology for thermal conductivity measurement in liquids


E. Marin1, S. Alvarado1, G. Juarez1, A. Calderon1 and R. Ivanov2

1Centro de Investigación en Ciencia Aplicada y Tecnología Avanzada (CICATA), Instituto Politécnico Nacional (IPN), México D.F., México
2Facultad de Física, Universidad Autónoma de Zacatecas, Zacatecas, México

Keywords: hot wire technique, heat transfer, liquids, thermal conductivity
property: thermal conductivity
material: liquids

The technological development generates the need for information about thermal properties of materials such as the thermal conductivity. Often the amount of available data is poor, and sometimes a comparison between data reported by different laboratories and/or measured by different experimental techniques show huge scattering. This is due to several reasons, one of them deviations from the mathematical model serving as the basis of the experimental method. Thus the minimization of these deviations is always an impetus, and can be achieved from the theoretical or from the experimental point of view. From the several methods proposed for measurement of this parameter, the ancient hot wire technique is one of the most popular and well established. It is based on the measurement of the temporal history of the temperature rise caused by a linear heat source (hot wire) embedded in a test material. If the wire is heated by passing a constant electrical current through it, the rise in temperature will be dependent on the thermal conductivity of the medium surrounding it. In the most used approach this parameter can be determined straightforward from the linear part of a graph of the temperature rise, DT, as a function of the natural logarithm of the measurement time, t. In this paper we will describe the implementation of an automated hot wire apparatus designed for measurements on liquid samples. High purity Platinum was used as a hot wire element (0.0762 mm diameter and 14 cm long), allowing measurements in about 100 mL volume samples. In our approach the temperature rise is accurately determined using a high precision current source and a nanovoltmeter (instead of a commonly used Wheatstone bridge). Based in this experimental approach, we were able to propose a criterion to verify that we are working on the correct linear region of the curve DT versus ln(t). The usefulness of the device has been demonstrated with test liquid samples of well known thermal properties.


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