Page 899 - Fundamentals of Water Treatment Unit Processes : Physical, Chemical, and Biological

854 Appendix H: Dissolved Gases

120
110
100
Atmospheric pressure (kPa) 70 Y=M0+M1*x + M8*x +M9*x 9
90
80
...
8
101.3
M0
60
M1
–0.011944
50
M2
5.3142e-07
40
M4
8.246e-15
30
–2.3906e-18
M5
20 M3 –1.3476e-11
M6 2.0382e-22
10 R 1
0
0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000
Elevation (m)
FIGURE H.2 Atmospheric pressure as function of elevation above sea level. (Figure plotted and regression equation from data as obtained
in Lide, D. R. (Ed.), Handbook of Chemistry and Physics, 77th edn., CRC Press, Inc., Boca Raton, FL, pp. 14-17, 1996.)
M3 ¼ 1.3476 10 11 H.1.6 WATER VAPOR
M4 ¼ 8.2464 10 15 Figure H.3 gives the vapor pressure of water at temperatures
M5 ¼ 2.3906 10 18 from 08C to 1008C. The plot is given as reference for calcu-
M6 ¼ 2.0382 10 22
lations requiring vapor pressure data. Equation H.9, also a
polynomial describes the relationship, i.e.,
The same data as given by Lide for pressure also provided
temperature and density for different elevations. The tempera- P(vapor) ¼ M0 þ M1 Z þ M2 Z þ M3 Z 3
2
ture data showed a decline in elevation as given by Equation 4 5 6
H.7, which was also a best fit of the data by the Kladiograph þ M4 Z þ M5 Z þ M6 Z (H:9)
software,
where
P(vapor) is the pressure of water vapor in equilibrium with
T(K) ¼ 1:2105 9:7673 10 04 Z (H:7)
water surface (kPa)
M0, M1, M2, M3, M4, M5, M6 are polynomial coeffi-
where T(K) is the temperature (K). cients for vapor pressure versus Z
The associated density is depicted accurately by Equation
H.8, also showing a decline with elevation, i.e.,
M0 M1 M2 M3 M4 M5 M6

r(air) ¼ 1:2105 9:7673 10 04 Z (H:8) 0.61052 0.044905 1.3613 3.0315 1.9829 3.5164 2.7009
10 03 10 05 10 07 10 09 10 12
3
where r(air) is the density of air (kg=m ).
As a matter of interest, to cross reference with the utility of
the ideal gas law, the density of a gas is a function of H.2 GAS SOLUBILITY IN WATER: HENRY’S LAW
temperature and pressure and can be calculated by the pres-
The solubility of a gas in water is given by Henry’s law,
sure and temperature data, i.e., r(molar) ¼ n=V ¼ P=RT and
3 which has utility for innumerable situations. Although simple
r(kg=m ) ¼ r(molar) MW(air)=1000. The value for MW(air)
and clear, implementation of Henry’s law may be complicated
is given in Table H.1.
artificially. Reasons are (1) Henry’s law has two forms, and
(2) a variety of units for Henry’s constant are in use,
(3) Henry’s constant data are scattered in the literature.
H.1.5 COMPOSITION OF AMBIENT AIR
In this section, Henry’s law is defined, applications are
Another interest is to know the composition of ambient air. illustrated, and the issues that complicate its use are addressed.
Table H.1 gives the sea level composition of a dry atmos- Hopefully, its pure simplicity is not obscured by the compli-
phere. Such data are required when applying Henry’s law to cating issues. First, however, Henry’s law has some interesting
problems involving atmospheric gases. background that later was tied to thermodynamic theory.