Exergy analysis of solar radiation processes - Solar Energy Sciences and Engineering Applications - page 70

Heat Q 1 − 2 , at temperature T S , is the sum of the portions of emission of surface 1
reaching surface 2, thus:

1

Q 1 − 2 = E 1 ϕ 1 − 2 ε 2 (2.4.65)

1 − ϕ 2 − 2 ρ 2

Heat Q 2 − 2 at temperature T 2 , is the sum of the portions of emission of surface 2
reaching surface 2, thus:

1

Q 2 − 2 = E 2 ϕ 2 − 2 ε 2 (2.4.66)

1 − ϕ 2 − 2 ρ 2

Heat Q 3 − 2 at temperature T 3 , is the sum of the portions of emission of surface 3
reaching surface 2, thus:

1

Q 3 − 2 = E 3 ϕ 3 − 2 ε 2 (2.4.67)

1 − ϕ 2 − 2 ρ 2

Heat Q 1 − 3 , at temperature T S , which is the sum of the totally absorbed irradiation
which reaches surface 3 at view factor ϕ 1 − 3 , and the totally absorbed irradiation parts
reflected from surface 2, can be determined as follows:

1

Q 1 − 3 = Iϕ 1 − 3 + Iϕ 1 − 2 ρ 2 ϕ 2 − 3 (2.4.68)

1 − ϕ 2 − 2 ρ 2

Heat Q 2 − 3 at temperature T 2 , is the sum of the portions of emission of surface 2
reaching surface 3, thus:

1

Q 2 − 3 = E 2 ϕ 2 − 3 (2.4.69)

1 − ϕ 2 − 2 ρ 2

Heat Q 3 − 3 at temperature T 3 , is the sum of the portions of emission of surface 3
reflected from surface 2 to surface 3:

1

Q 3 − 3 = E 3 ϕ 3 − 2 ρ 2 ϕ 2 − 3 (2.4.70)

1 − ϕ 2 − 2 ρ 2

As shown in the exergy part of the present paragraph even the assumption on
the black surfaces 1 and 3 for exergetic consideration required far more equations
in comparison to the respective energetic considerations developed for the system in
which only one black surface 1 was assumed. Obviously, exergetic consideration of the
system with only one black surface 1 would require developing of significantly more
equations in comparison to the considerations presented in this paragraph.
Comparison of the energy and exergy balances for the considered SCPC, at the
assumed ε 3 = 1, is presented in Table 2.4.4. In the both analyses the radiation escaping

from the SCPC is estimated at a relatively high level, (energy: 68 . 34 + 4 . 43 = 72 . 77%

and exergy 57 . 069 57 . 226%). The energy analysis allows for split-

ting the escaping radiation loss according to the radiosity of surface 2 and 3, whereas

+ 0 . 026 + 0 . 132 =