2.219. One mole of water being in equilibrium with a negligible
amount of its saturated vapour at a temperature T 1 was completely
converted into saturated vapour at a temperature T2. Find the ent-
ropy increment of the system. The vapour is assumed to be an ideal
gas, the specific volume of the liquid is negligible in comparison with
that of the vapour.2.7. Transport Phenomena
- Relative number of gas molecules traversing the distance s without col..
lisions:
NIN0=e–sik (2.7a)
where X is the mean free path. - Mean free path of a gas molecule:
X= _ 1 (^) (2.7b)
Y2 ad 2 n
where d is the effective diameter of a molecule, and n is the number of mole-
cules per unit volume.
- Coefficients of diffusion D, viscosity and heat conductivity x of gases:
D =^1 1
3(v) 2,
3= — (v4, x = — 3 (v)kpcv., (2.7c)where p is the gas density, and cir is its specific heat capacity at constant volume.- Friction force acting on a unit area of plates during their motion parallel
to each other in a highly rarefied gas:
F=^1
6
— p I ui — u 2 (2.7d)where u 1 and u 2 are the velocities of the plates.- Density of a thermal flux transferred between two walls by highly
rarefied gas:
q = 1 pcv Ti — T2 I, (2.7e)
where T 1 and T 2 are the temperatures of the walls.
2.220. Calculate what fraction of gas molecules
(a) traverses without collisions the distances exceeding the mean
free path X;
(b) has the free path values lying within the interval from X
to a.
2.221. A, narrow molecular beam makes its way into a vessel
filled with gas under low pressure. Find the mean free path of mole-
cules if the beam intensity decreases ri-fold over the distance Al.
2.222. Let adt be the probability of a gas molecule experiencing
a collision during the time interval dt; a is a constant. Find:
(a) the probability of a molecule experiencing no collisions during
the time interval t;
(b) the mean time interval between successive collisions.
2.223. Find the mean free path and the mean time interval be-
tween successive collisions of gaseous nitrogen molecules
(a) under standard conditions;
100