- Heat and Molecular Physics 61
if the liquid passes through the tubes inthe counterflow, assuming that the heat
transferred per unit time through a unit
area element is proportional to the temper-
ature difference, the proportionality factor
being k. The thermal conductivity of the
liquid in the direction of its flow should be
neglected.
2.19*. A closed cylindrical vessel of base
area S contains a substance in the gaseous
state outside the gravitational field of the
Earth. The mass of the gas is M and its
pressure is p such that P <Psat, where
Peat is the saturated vapour pressure at a
given temperature. The vessel starts mov-
ing with an acceleration a directed along
the axis of the cylinder. The temperature is
maintained constant.
Determine the mass m lig of the liquidcondensed as a result of motion in the ves-
sel.
2.20. The saturated water vapour pressure
on a planet is Po = 760 mmHg.
Determine the vapour density p.
2.21. In cold weather, water vapour can beseen in the exhaled air. If the door of a warm
but is opened on a chilly day, fog rushes in-
to the hut.
Explain these phenomena.2.22*. A vessel of volume V = 2 1 contains
= 2 g of hydrogen and some amountof water. The pressure in the vessel is
pi = 17 x 10 5 Pa. The vessel is heated so
that the pressure in it increases to pt26 x 10 (^5) Pa, and water partially evapo-