Page 16 - Reciprocating Compressors Operation Maintenance

Reciprocating Compressors and Their Applications 3

Charles' Law states that at constant pressure, the volume of an ideal
gas will increase as the temperature increases.
If heat is applied to a gas it will expand, and the pressure will remain
the same. This law assumes the absence of friction or the presence of an
applied force.

Yi-Ik VL_VL
or
vTTi~ T ~T;~
2
Amonton's Law states that at constant volume, the pressure of an ideal
gas will increase as the temperature increases.

Ik = Jk or JJL = JjL
P, T, T 2 T,

Gas and Vapor

By definition, a gas is that fluid form of substance in which the sub-
stance can expand indefinitely and completely fill its container. A vapor
is a gasified liquid or solid—a substance in gaseous form.
The terms gas and vapor are generally used interchangeably.

To understand how gases and gas mixtures behave, it is necessary to rec-
ognize that gases consist of individual molecules of the various gas compo-
nents, widely separated compared to their size. These molecules are always
traveling at high speed; they strike against the walls of the enclosing vessel
and produce what we know as pressure. Refer to Figure 1-1.
Temperature affects average molecule speed. When heat is added to a
fixed volume of gas, the molecules travel faster, and hit the containing
walls of the vessel more often and with greater force. See Figure 1-2. This
then produces a greater pressure. This is consistent with Amonton's Law.
If the enclosed vessel is fitted with a piston so that the gas can be
squeezed into a smaller space, the molecule travel is now restricted. The
molecules now hit the walls with a greater frequency, increasing the
pressure, consistent with Boyle's Law. See Figure 1-3.
However, moving the piston also delivers energy to the molecules,
causing them to move with increasing velocity. As with heating, this