Suchergebnisse

A general equation is derived for the pressure dependance of the rotational thermal conductivity. The result differs from the equation obtained in the preceding note, in that it takes into account the temperature jump at the wall. It should thus remain valid down to rather low pressures (≈1 mm Hg for an apparatus with a wall separation of 0,1 cm.).

Experiments have shown that the thermal conductivities λ of monoatomic (He, A) and diatomic (H2, O2) gases differ markedly. This can be explained if the rotational and vibrational thermal conductivities λr vanish at low pressures, when the distance covered by a molecule between two « active » collisions (leading to a rotational-translational, or vibrational-translational energy transfer) is larger that the dimensions of the apparatus.
We recall the usual interpretation of this phenomenon ; discuss the catalytic effect of the wall and the influence of the simultaneous occurence of more than one reaction with different rates, on the rotational and vibrational heat transfers. We also show that the λr pressure dependance in a cylindrical apparatus (our experimental case), and in a parallel plate system, should be nearly identical, if the separation between the hot and cold boundaries is the same, and if the diameters of the two coaxial cylinders are of the same order of magnitude (in the ratio 1/2 or larger). We assume, in this note, that the boundary temperature in the gas is equal to that af the wall. The effect of the temperature jump at the wall will be discussed in the following communication (II).