engleski

Determination of thermal conductivity by transient hot wire method

Thermal property data are important for the engineering solutions of the heat transfer problems. There are many cases in which thermal conductivity of the studied material is not available, eg. cement materials of different compositions during setting and hardening. Furthermore, these materials are wet and porous and in order to prevent development of humidity gradients under imposed thermal gradients, one finds transient measurement methods as preferable. This work describes a developed apparatus and a transient Hot Wire (HW) method to obtain the thermal conductivity of dry and wet materials. Single, thin platinum wire is used as both a constant power heater and temperature sensor. The result obtained from measurement is the temperature development of the HW during heating period, which is described by a theoretical model. The thermal conductivity of the material under study is obtained by the solution of the parameter estimation problem, utilizing the Levenberg-Marquardt method of optimization. The results of the method evaluation on reference materials indicated an accuracy of 3% and a precision of 0.7% (for 95% confidence). The reference materials used were gelatinous water (Agar gel 0.7%), glycerol and Ottawa (quartz) sand. The values of the thermal conductivity for fresh calcium aluminate cement pastes with water to cement mass ratio of 30 and 40 % are documented. The systematic error arising due to the measured sample electrical conductivity is calculated to be less than 0.5% for the experimental configuration used.

thermal conductivity; hot wire method; reference materials; electrical conductivity; calcium aluminate cement

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