Advances on the hot wire technique

The hot wire technique is considered to be an effective and accurate means of determining the thermal conductivity of ceramic materials. However, specifically for materials of high thermal conductivity, the appropriate time interval to be considered in calculations is a decisive factor for getting accurate and consistent results. In this work, a numerical simulation model is proposed with the purpose of determining the minimum and maximum measuring time for the hot wire parallel technique. Nevertheless, the factor that limits the application of the hot wire technique for high thermal conductivity materials is the maximum measuring time for the experimental thermal transient registration. An alternative experimental arrangement is then proposed for materials with thermal conductivity higher than 15 W/mK. In this technique, the time interval considered for the calculations may be several times bigger than that one corresponding to the parallel technique, what means in practice that it may be applicable for materials with higher thermal conductivities. Fourteen different specimens of refractory materials, and four polymers, with thermal conductivities ranging from 0.04 to 14 W/mK, in shape of rectangular parallelepipeds were employed in the experimental programme. An empirical equation determining minimum and maximum measuring times is also obtained for the hot wire parallel technique. In this work is also proposed a technique of insulation of the hot wire, what makes possible its application to electrical conducting materials. (c) 2007 Elsevier Ltd. All rights reserved.