Page 32 - Advanced Mine Ventilation

Underground Coal Mine Atmosphere 15

infinitesimal amount of heat, Q, absorbed divided by the absolute temperature of the
body, T.
Thus for a reversible process:

Q

ds ¼ Btu=lb= F
T
1.6.9 Mole Volume
The volume occupied by a mole or a gram molecular weight of any gas at standard
conditions is 22.414 L.

1.6.10 Relative Humidity
It is the ratio of the quantity of water vapor present in the atmosphere to the quan-
tity which would saturate it at the existing temperature. It is also the ratio of the
pressure of water vapor present to the pressure of saturated water vapor at the
same temperature.

1.6.11 Specific Heat

Heat required to raise the temperature of unit weight of a gas by 1 F at constant pres-
sure (C p ) or volume (C v ) and is measured in Btu/lb F.

1.6.12 Viscosity
2
It is the drag or shear resistance of air to motion. It is measured in lbs/ft . This is also
called absolute (m) viscosity. Absolute viscosity divided by mass density is called ki-
nematic viscosity (y).

Problems

1.1 Calculate the height of a column of dry air equivalent to 1 psi pressure. Assume standard
conditions for atmospheric pressure and temperature.
1.2 Repeat the above calculation for water.
1.3 Calculate the density of air at 10,000 ft. Assume air density at sea level is equal to
3
0.075 lb/ft .
1.4 Calculate the maximum allowable respirable dust concentration in a coal mine if the respi-
rable dust contains (a) 10%, (b) 15%, and (c) 20% silica.
1.5 Calculate the specific gravity of methane, ethane, propane, hydrogen, carbon dioxide, nitro-
gen, and oxygen if the specific gravity of air is 1.00. (Hint: specific gravity is proportional to
the molecular weight).