Environmental Engineering Reference
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as waste. Based on the definition discussed in paragraph 2.3.4.2, the energy degree of
perfection
η
E
, of the considered photosynthesis:
n
SU
h
SU
η
E
=
(2.4.105)
γ
[
α
V
j
V
+
α
L
(
j
S
−
j
V
)]
+
n
CO
2
h
CO
2
+
n
w
h
w
whereas the exergy degree of perfection
η
B
, of the photosynthesis based on formula
(2.3.18):
n
SU
b
SU
η
B
=
(2.4.106)
γ
[
α
V
b
V
+
α
L
(
b
S
−
b
V
)]
+
n
CO
2
b
CO
2
+
n
w
b
w
Example 2.4.4.1
The following input values have been used in the exemplary
computations for the system presented in Figure 2.4.19:
=
-
Environment temperature
T
0
293 K,
=
-
Temperature difference
T
5K,
-
Relative humidity of environment air
ϕ
0
=
0
.
4,
-
Environment pressure
p
0
equal to the standard pressure
p
0
=
p
n
=
101
.
325 kPa,
-
Weakening radiation factor
γ
=
0
.
7,
-
Leaf absorptivity within PAR wavelength range
α
V
=
0
.
88,
-
Leaf absorptivity beyond the PAR range
α
L
=
0
.
05,
0
.
003 kW/(m
2
K),
-
Convective heat transfer coefficient
k
=
-
Mole fraction of sugar in biomass
z
SU
=
0
.
08.
The leaf temperature is
T
=
T
0
+
T
=
298 K and from equation (2.4.104) the
10
−
9
kmol/(m
2
s). The percentage terms of energy
and exergy equations (2.4.103) and (2.4.104), respectively, are shown in Fig. 2.4.20.
The 100% reference for the output terms is assumed as the input sum due to the
absorbed radiation and the substances of CO
2
and liquid water.
Thus the perfection degree value
η
E
sugar production rate
n
SU
=
3
.
21
·
=
35
.
4% is larger than
η
B
=
2
.
608% (by about
35
.
4
/
2
.
608
14 times) mainly because of the denominators in equations (2.4.105)
and (2.4.106). The exergy of liquid water, in the denominator of equation (2.4.106), is
positive whereas the energy of this water in the denominator of equation (2.4.105) is
negative, (the water vapor is assumed as the reference phase for enthalpy calculation).
The energy terms (Fig. 2.4.20, energy balance) show that the input consists of the
positive radiation energy (1459
.
8
≈
1485.2%)
liquid water enthalpy. The energy of the consumed carbon dioxide is zero because it
enters the system at the reference temperature
T
0
. The output energy terms show no
irreversible loss and the zero energy of both; the produced oxygen and released water
vapor leave the system at the reference temperature. Heat transferred by convection
and radiation are 65.3% and 6.4%, respectively. The energy of liquid water contained
in the produced biomass is negative (
+
125
.
4
=
1585
.
2%) and the negative (
−
−
7.1%) also because the vapor phase was assumed
as the reference substance for water.
The exergy input terms (Figure 2.4.20, exergy balance) are the absorbed radia-
tion (87
.
76
95
.
19%) and the water of positive value 4.81%. The exergies of
the delivered CO
2
, released O
2
and water vapor are zero because these gases, at the
+
7
.
43
=
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