抄録
A method of measuring thermal conductivity in varying state of temperature is described.
A thin and long cylinder is considered, in a large homogeneous medium of uniform temperature. If the surface of unit length of the cylinder is heated at a constant rate of H cal/sec and if the rise of temperature at the axis of the cylinder from time t1 to time t2 is θ2-θ1, the conductivity k of the medium is derived as
_??_
provided that the radius of the cylinder is very small.
Measurements are made electrically and the time needed for one observation is 1_??_30 min depending on the states of material used. Experiments were carried out for values of k ranging from 5×10-5 of air to 2×10-2 of Hg.
By plotting θ vs ln t, and finding the minimum time tmin required for the relation to become linear, the thermal diffusivity K of the medium is found for the product Ktmin assumes a constant value. Further, by measuring k and tmin for any given material, an estimation of its specific heat cp can be made by the relation K=k/ρcp where ρ is the density.
