Relative Measurements of Thermal Conductivities of Metals Using Non-stationary Hot-wire Method with Insulated-coated Probe

Abstract

The non stationary, hot wire method has been developed for use with an insulated, coated probe in order to determine thermal conductivities of metals. This development was carried out using both simulation and experimentation. The simulations of the temperature increase ( DT ) of the heater were carried out using various solid samples (Al, V, Ag and W). Experiments were carried out using hot strip and hot wire probes to determine DT from the voltage change ( DV ) using the four terminal method. Measurements of DT on solid Fe, Ni and Ti were made using hot strip probes with coatings of (i) silica (ca. 5 mm thickness) and (ii) mica (20 300 mm thickness). Similarly, experiments were carried out on liquid Hg and Ga using hot wire probes with coatings of (i) silica (ca. 5 mm thickness) and (ii) alumina based material (170 470 mm thickness). The results of simulations and experiments have shown:(1) The following equation applies to dDV/d ln t (t: time) obtained using an identical probe: dDV/d ln t＝A(I 3 ･a T ･R 273 ･X T /4p)･(1/l)＋B where dDV/d ln t is an average slope for the time period 1 2 s, l is the thermal conductivity at a certain temperature (T ), I is the current supplied to the heater, a T is the temperature coefficient of electric resistivity of the heater at T K, R 273 is the resistance between the potential leads for the four terminal method of the heater at 273 K, X T is the resistance per unit length of the heater at T K, and A and B are probe constants.(2) The probe constants are independent of temperature. Thus equations for other temperatures (T 1 ) can be obtained by replacing temperature dependent terms a T and X T in the above equation by those for T 1 as follows: dDV/d ln t＝A(I 3 ･a T1 ･R 273 ･X T1 /4p)･(1/l)＋B Using these relations, the thermal conductivity of liquid Ga was determined over the temperature range (310 500 K). It has also been found that determination of the thermal conductivity is unaŠected by coating thickness providing that the thickness of the insulating layer is ＜ca. 300 mm.

Thermal Conductivity of 2CaO·SiO₂ Bearing Solid Solution

“…This method is called hot wire/strip method, 8) which can determine the thermal conductivity on the bases of the tendency of heat diffusion from the heating material, namely, hot wire or strip, obtained by monitoring the temperature elevation. The schematic diagram of the experimental set-up is shown in Fig.…”