Page 317 - Wastewater Solids Incineration Systems

278 Wastewater Solids Incineration Systems

Or, upon simplification, lbf/sq ft lbf/sq ft (lbf/sq ft 47.88 Pa and lb/cu ft
3
16.02 kg/m ).
With this understanding of force and mass, the four basic quantities described
above can be used to define all other physical quantities within a mechanical system,
as illustrated in Table A.1 by way of common examples of secondary quantities.
2.1.2 Absolute Pressure and Temperature
The gases in combustion systems are typically at pressures and temperatures dif-
ferent from ambient conditions. Therefore, it is necessary to use absolute pressure
and temperature scales, where the lowest value is zero and not a negative number, to
adjust properties to actual process conditions.
2.1.2.1 Pressure
Pressure measurements that are not in absolute are typically referred to as gage or
gauge pressures. Standard atmospheric pressure is 14.696 lbf/sq in absolute (psia).
To convert any gage pressure (psig) to absolute (psia), simply add 14.696 (note that
psig 6.895 kPa). To convert this pressure to lbf/sq ft (psfa), simply multiply by
144 (note that 1 lbf/sq ft 0.0005 Pa). The following example converts a gage pres-
sure of 10 psig to an absolute pressure (psfa):
(10 psig 14.696) (144 sq in/sq ft) 3556.2 psia
2
(Note that sq in 0.000 645 2 m )
Other pressure units commonly encountered are
Inches of water column in H O (kPa),
2
Inches of mercury in Hg (kPa),
Ounces per square inch osi, and
Head (pumps), measured in feet of water column ft H O (meters [m] of head).
2
Densities of water and mercury used for converting pressure are as follows: den-
sity of water at 68°F equals 62.32 lb/cu ft and density of mercury at 68°F equals
848.71 lb/cu ft.
2.1.2.2 Temperature
Even though in this appendix U.S. customary units are used, the metric temperature
scale is quite commonly used in some venues. U.S. customary temperature units are
expressed in degrees Fahrenheit (°F); metric temperatures are expressed in degrees
Celsius (°C). Converting between Fahrenheit and Celsius temperatures is done as fol-
lows: °F 1.800 (°C) 32 and °C 0.5556 (°F 32).
Absolute temperature scales are degrees Rankine (°R) for Fahrenheit and degrees
Kelvin (K) for Celsius. Determining the absolute temperature is done by adding a