Page 31 - Advanced Mine Ventilation

14 Advanced Mine Ventilation

number of neutrons and protons making up the atomic nucleus. These weights
expressed in grams are called gram atomic weights.

1.6.2 Avogadro’s Number

Avogadro’s law says that equal volumes of different gases at the same pressure and
temperature contain the same number of molecules. The number of molecules in
1 g-molecular weight of a substance is 6.02 10 23 ( 1%).

1.6.3 British Thermal Unit
It is the quantity of heat required to raise the temperature of one pound of water by 1

of Fahrenheit at, or near, its point of maximum density (39.1 F).
1.6.4 Critical Temperature and Pressure

Critical temperature is that temperature above which a gas cannot be liquefied by pres-
sure alone. The pressure under which a substance may exist as gas in equilibrium with
liquid at the critical temperature is the critical pressure.

1.6.5 Density
It is the concentration of matter, measured by mass per unit volume. It is expressed as
3
lb/ft .
1.6.6 Dew Point

It is the temperature at which condensation of vapor in the air takes place.

1.6.7 Enthalpy or Heat Content
It is a thermodynamic quantity equal to the sum of internal energy in a system plus the
product of the pressureevolume work done on the system.
Thus:

H ¼ E þ pv (Btu/lb)
Where
H ¼ enthalpy or heat content
E ¼ internal energy of the system
p ¼ pressure
v ¼ volume

1.6.8 Entropy

It is the capacity factor for isothermally unavailable energy. The increase in the entropy
of a body, ds, during an infinitesimal stage of a reversible process is equal to the