| dc.description |
The rate of energy transfer between parallel flat plates is evaluated
when the (stagnant) gas between them is polyatomic with one inert internal
mode. Deviations of the thermal conductivity from the complete equilibrium
(Eucken) value are expressed in terms of the inert mode relaxation time
and the effectiveness of the walls in exciting or de-exciting this mode.
The results are obtained via a linear theory consistent with small
temperature differences between the plates.
It is found that the Eucken-value of conductivity could be exceeded
if the relaxation times are non-zero and the plates very effective in
exciting the inert mode. 1Nhen relaxation times are very short the effect
of the walls on the energy transfer rate is small, but the malls make
their presence felt by distorting the temperature profiles in "boundary
layers" adjacent to the walls which are of order VDT in thickness
(D = diffusion coefficient, r = relaxation time). This result is
analogous to Hirschfelderts (1956) for the case of chemical reactions.
For experimental measurement of conductivity in a hot wire cell type
of apparatus it is shown that extrapolation of measured reciprocal
conductivities to zero reciprocal pressure should lead to the full Eucken
value. It is also shown that the slope of reciprocal apparent (measured)
conductivity versus reciprocal pressure curves is a function of relaxation
time as well as of the accommodation coefficients. It is quite possible
that the relaxation effect here is comparable with the temperature jump
effects, even for rotation in diatomic molecules. |
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