Let's take a closer look at this and see what it really
CHANGE OF STATE--The change of any matter
means. If you apply pressure to a gas, the volume will
from one state (solid, liquid, or vapor) to another.
decrease proportionally. Thus, if you double the
COMPRESSION--The act of increasing the
pressure exerted on a gas, its volume will become half
pressure and temperature of a substance by decreasing
of what it was. On the other hand, if you reduce the
its volume.
pressure exerted on a gas by one-half, the volume of
that gas will double.
CONDENSATION--The process by which a
vapor changes state to a liquid when heat is removed
Remember, the temperature must remain constant.
from the vapor.
If the temperature goes up or down, then Boyle's law
does not apply.
CONDUCTION--Heat transfer from molecule to
molecule within a substance or between two substances
Charles' Law
that are in physical contact with each other.
CONVECTION--Heat transfer through some
Charles' law states: "At a constant pressure, the
easily circulated medium (usually liquid or vapor). As
volume of a compressed gas varies directly to the
the medium moves, it carries contained heat energy,
absolute temperature; at a constant volume, pressure
which is then transferred to the surroundings.
varies directly to the absolute temperature."
DEHUMIDIFY--To reduce the quantity of water
Now, let us consider what this means. If you raise
vapor in a given space.
the temperature of a compressed gas, the volume will
increase proportionally with the increase in tempera-
EVAPORATION--The process by which a liquid
ture. The effect works in reverse if you decrease the
changes state to a vapor when heat is added to the
temperature.
liquid.
An example of the effect of this law is seen in the
HEAT--A basic form of energy that is transferred
downstroke of the piston of an internal combustion
by virtue of a temperature difference. Heat always
engine. As the air-fuel mixture is ignited, the
flows from a hot object to a cold object; the greater the
temperature increases and the volume of gas in the
temperature difference, the faster the flow. Heat cannot
cylinder expands, pushing the piston down.
be created or destroyed--only transferred.
HEAT OF CONDENSATION--The latent heat
Dalton's Law
given up by a substance as it changes state from a vapor
to a liquid.
Dalton's law states: "The total pressure of a con-
fined mixture of gases is the sum of the pressures of
HEAT OF FUSION--The latent heat absorbed as
each of the gases in the mixture."
a substance changes from a solid to a liquid.
This means that if you have a mixture of gases in a
HEAT OF VAPORIZATION--The latent heat
cylinder, the pressure in the cylinder is a total of all the
absorbed by a substance as it changes state from a
pressures of all the gases in that cylinder. For example,
liquid to a vapor.
if you have a cylinder that contains 10 psi of oxygen, 20
LATENT HEAT--Heat applied to, or removed
psi of nitrogen, 35 psi of carbon dioxide, and 65 psi of
from, a substance that causes a change in the physical
helium, the total pressure in the cylinder will equal 130
state of the substance, but not in its temperature.
psi. Also, each gas in the cylinder will act as if it were in
the cylinder alone.
REFRIGERATION CYCLE--The complete
course of operation of a refrigerant (from starting
TERMINOLOGY
point back to starting point) in a closed refrigeration
system.
The following terms apply to the science of
refrigeration and air conditioning.
SENSIBLE HEAT--Heat applied to, or removed
from, a substance that causes a change in the tem-
BRITISH THERMAL UNIT--The amount of
perature of the substance, but not in its state.
heat required to produce a temperature change of 1F in
1 pound of pure water at sea level pressure.
SUPERHEAT--Heat added to a vapor above the
boiling point of the liquid that produced the vapor. The
11-5
