Environmental Engineering Reference
In-Depth Information
total radiation which leaves a surface and includes emission of the considered surface as
well as all reflected radiations arriving from other surfaces of the system. The concept
of radiosity is convenient for energy calculation, however it cannot be used for exergy
considerations because it does not distinguish the temperatures of the components of
the radiosity. The radiosity
J
1
of the imagined surface 1 equals the irradiation
I
:
J
1
=
I
(2.4.38)
and another independent equation on the radiosity is also included into calculations:
J
2
=
E
2
+
ρ
2
(
ϕ
1
−
2
J
1
+
ϕ
2
−
2
J
2
+
ϕ
3
−
2
J
3
)
(2.4.39)
It is assumed that the reflector is very thin so the uniform temperature
T
2
prevails
through the whole reflector thickness and on the inner and outer side of the reflector.
Thus the heat
Q
2,
c
transferred from both sides of the reflector is:
Q
2,
c
=
2
A
2
k
2
(
T
2
−
T
o
)
(2.4.40)
and heat radiating from the outer side of reflector to the environment is:
A
2
ε
2
σ
(
T
2
−
T
o
)
Q
2,
r
=
(2.4.41)
where
k
2
is the convective heat transfer coefficient and
T
0
is the environment
temperature.
Heat
Q
3,
c
transferred by convection from surface 3 to the environment is:
Q
3,
c
=
A
3
k
3
(
T
3
−
T
o
)
(2.4.42)
and the useful heat
Q
3,
u
transferred through the wall of the cooking pot is:
A
3
k
3
(
T
3
Q
3,
u
=
−
T
w
)
(2.4.43)
where
k
3
is the convective heat transfer coefficient,
T
w
is the absolute temperature
of water in the cooking pot and
k
3
is the heat transfer coefficient, which takes into
account the conductive heat transfer through the cooking pot wall and convective heat
transfer from the inner cooking pot surface to the water.
The equations system (2.4.32)-(2.4.43) can be solved by successive iterations. The
energy analysis of the SCPC can be carried out based on the evaluation of the terms in
the following energy conservation equation for the whole SCPC:
ϕ
2
−
1
J
2
+
ϕ
3
−
1
J
3
+
Q
2,
c
+
Q
2,
r
+
Q
3,
c
+
Q
3,
u
=
I
(2.4.44)
The first two terms in equation (2.4.44) represent radiation energy escaping from
the SCPC due to the radiosities of surfaces 2, (
ϕ
2,1
·
J
3
). Dividing the
both sides of equation (2.4.44) by
I
, the percentage values
β
of the equation terms can
J
2
), and 3 (
ϕ
3,1
·
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