Biomedical Engineering Reference
In-Depth Information
TABLE 15.2
Saturated Water Ice (for temperature below 0
C), Liquid Water (for temperature above 0
C),
and Vapor. Compiled from fundamentals. American Society of Heating, Refrigerating, and
Air-Conditioning Engineers, 1967 and 1972, and 1967 ASME Steam TablesdCont'd
Temperature
Specific volume
Enthalpy
Entropy, J/(kg
,
K)
Condensed
state, 10
L
3
m
3
/kg
Vapor
pressure, kPa
Vapor,
m
3
/kg
Condensed
state, J/kg
Vapor,
10
6
J/kg
Condensed
state
C
F
Vapor
10
1
10
5
71.111
160
3.2691
1.0235
4.824
2.9763
2.6288
968.4
7740.0
10
1
10
5
76.667
170
4.1317
1.0270
3.874
3.2091
2.6381
1035.4
7659.6
10
1
10
5
82.222
180
5.1786
1.0307
3.135
3.4424
2.6474
1101.5
7582.6
10
1
10
5
87.778
190
6.4397
1.0346
2.557
3.6760
2.6565
1166.8
7508.5
10
1
10
5
93.333
200
7.9469
1.0386
2.100
3.9097
2.6656
1230.9
7437.3
10
1
10
5
98.889
210
9.7374
1.0429
1.737
4.1437
2.6742
1294.1
7368.7
10
2
10
5
100.000
212
1.0133
1.0437
1.673
4.1907
2.6760
1306.7
7355.3
15.3.1. Water Cycle
The water cycle (known scientifically as the hydrologic cycle) refers to the continuous
exchange of water within the hydrosphere, between the atmosphere, soil water, surface
water, ground water, and plants.
Fig. 15.5
shows a schematic of the water movement on
Earth. Water moves perpetually through each of these regions in the water cycle consisting
of following transfer processes:
Evaporation from oceans, lakes, rivers, and other water bodies into the air and
transpiration from land plants and animals into air.
Precipitation from water vapor condensing from the air and falling onto the Earth's
surface: land or ocean.
Runoff from the land usually reaching the sea.
Water evaporation rate depends on the temperature, humidity in the air, and turbulence
near the water surface. In general, the water evaporation rate is given by
N
A
¼ k
p
ðp
0
A
p
A
Þ
(15.1)
where N
A
is the flux of water vapor leaving the water surface, k
p
is the mass transfer coeffi-
cient,
p
0
A
is the saturation water vapor pressure, and p
A
is the average vapor pressure in
the air.
The mass transfer coefficient k
p
is a function of the water vapor diffusivity (in air),
temperature gradient, wind conditions, and turbulence in the air (especially near the water
surface). Waves on water also increase the evaporation rate as the effective surface area
increases.
Advection of water vapor in atmosphere is strongly dependent on the wind or pressure/
temperature differences between locations. Macromotion of air causes extensive mixing in
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