Environmental Engineering Reference
In-Depth Information
Table 3.2.1
General thermodynamic quantities and balance equations.
Specific enthalpy
h
=
u
+
vP
s
2
−
s
1
=
c
ln
T
2
T
1
−
R
ln
P
2
Specific entropy
P
1
Specific exergy*
ex
i
=
[(
h
i
−
h
0
)
−
T
0
(
s
i
−
s
0
)]
1
−
T
0
T
Ex
th
=
Thermal exergy
×
Q
(
m
i
h
i
)
in
=
(
m
i
h
i
)
out
+
Q
+
W
Energy balance
(
m
i
ex
i
)
in
=
(
m
i
ex
i
)
out
+
Ex
de
+
Ex
th
Exergy balance
En
out
En
in
Energy efficiency
η
en
=
Ex
out
Ex
in
*Based on changes in chemical formulation specific chemical exergy is added.
Exergy efficiency
η
ex
=
3.3 CASE STUDIES
In this section several studies are presented which highlight the use of solar energy
systems. Detailed energy and exergy analyses are also presented in order to help model
integrated solar energy systems. In the first case study a solar energy system is integrated
with an Organic Rankine Cycle (ORC) for producing power, in the second study a
solar PV/T system is modeled for power and heat production, in the third study a solar
PV/T system is integrated with an electrolyzer and absorption system for hydrogen and
cooling production.
3.3.1 Case study 1: Exergy analysis of an integrated solar,
ORC system for power production
In this case study, a detailed energy and exergy model of an integrated solar ORC is
presented for power production. Operating parameters such as ambient temperature,
area of solar energy system and pressure at state 4 are varied to see their effect on
energy and exergy efficiencies.
3.3.1.1 System description
An integrated solar thermal ORC system for power production studied in this case
study is shown in Figure 3.3.1. Air at state 1 returning from the boiler is passed
through the solar thermal collector. In the solar thermal collector, the solar flux hitting
the collector is absorbed by the air passing through the collector. The air at high
temperature leaving the solar collector at state 2 enters the boiler where it loses heat to
the isobutane coming in at state 4. Isobutane coming in at state 4, after gaining heat
from state 2 leaves the boiler at state 3 to enter the turbine. In the turbine, the pressure
and temperature of the isobutane is dropped and isobutane leaves at state 6 to enter
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