Exergy analysis of solar radiation processes - Solar Energy Sciences and Engineering Applications - page 82

environment. Solar exergy reflected from the deck is b R = 5%. The possibility of

negative value of physical exergy ( b a ) of air was discussed in paragraph 2.2.3.1.
EZergy analysis uses mechanical exergy component for air. Exergy balance equa-
tions for floor and deck do not contain terms for substance. These two equations,
(2.4.81) and (2.4.82), remain unchanged because they contain only terms of the radia-
tion and convection heat for which the gravitational effect is not considered. However,
the exergy balance equations, (2.4.83), (2.4.84) and (2.4.85), considered for heating
air in collector, turbine and chimney, are modified by adding the gravity input.

e R =

G a + B f - a = Z 1 a + B w 1 + B a − d + B a (2.4.88)

G T + Z 1 a + B w 1 = Z 2 a + B w 2 + B P + B T (2.4.89)

G ch + Z 2 a + B w 2 + B f − ch = Z 3 a + B w 3 + B cv + B ch − 0 + B ch (2.4.90)

where G a , G T and G ch are the gravity inputs in eZergy balance for the collector air,
turbine and chimney, respectively. Note that in eZergy balance equation the potential
exergy does not appear as a separate term because this exergy is interpreted by eZergy
of substance.
To more easily distinguish it from the traditional exergy ( B or b ), the eZergy is
denoted by Z ,W,or z ,%. Denotations of other exergy magnitudes remain unchanged
because their values are unchanged. However, eZergy of air generally differs from
exergy of air; Z a ≥

B a :

Z a = max( B p + B H , B a ) (2.4.91)

where B p is the potential exergy, ( B p E p ), B a is the traditional physical exergy of

air calculated from formula (s). Magnitude B H is the physical exergy calculated also
based on equation (s), however, for the environment parameters (temperature T H and
pressure p H ) prevailing at the altitude H :

=

m c p ( T a − T H c p ln T a

p
p H

B H = T H ) −

T H −

R ln (2.4.92)

According to the interpolation formulae given by Petela (2009b):

10 6 ρ 6 . 02353 · 10 − 3
a

10 6 H = 1 . 215485 · − 1 . 214 · (2.4.93)

and the interpolated atmospheric parameters at altitude H :

10 − 7 H 2 10 − 12 H 3

T H = 288 . 16 − 0 . 0093 H + 3 . 2739 · − 2 . 9861 · (2.4.94)

101235 e 1 . 322 · 10 − 4 H p H = (2.4.95)

The computation results of exergy balances with use of eZergy are shown in
the bands diagram (Figure 2.4.18). The solar radiation exergy B S = 32 . 41 MW,

assumed as 100%, arriving at the deck is distributed between five SCPP components
in the case of using substance eZergy. The eZergy streams Z , W, are represented by

Z S =