Environmental Engineering Reference
In-Depth Information
Figure 2.4.14
Scheme of the considered SCPP, (from Petela, 2009).
-
application of eZergy balance for estimation of effect of gravity,
-
involving exchange of radiation energy and exergy between chimney and deck,
-
distinguishing the energy, exergy and eZergy losses to the environment and sky,
-
proposing the convective-radiative effective temperature concept for the surfaces.
As shown in Figure 2.4.14, the considered SCPP consists of a circular greenhouse
type collector and a tall chimney at its centre. Air flowing radially inwards under the
collector deck is heated from the collector floor and deck, and through a turbine enters
the chimney. A draft-driven environmental air (point 0) enters the collector through
the gap of height
H
e
. The collector floor of diameter
D
f
is under the transparent
deck which declines appropriately to ensure a constant radial cross-section area for
the radially directed flow of the air. The assumption of constant cross-section area in
the collector means that
π
·
D
1
/4, and so, the assumed value
H
e
allows for calculation of the inlet turbine diameter
D
1
=
D
f
·
H
e
=
π
·
D
1
·
H
1
=
π
·
D
f
)
0
.
5
and height
(4
·
H
e
·
H
1
=
D
1
/4. The collector floor preheats air from state 0 to state 1 (state 1 prevails in
the zone denoted with a dashed line). Preheated air (state 1) expands in the turbine to
state 2. The turbine inlet and outlet diameters are
D
1
and
D
2
, respectively. The height
of turbine is
H
T
;(
H
1
+
H
T
=
H
2
). Expanded air leaves the SCPP (at point 3) through
the chimney at height
H
3
.
For the established geometrical parameters of the collector-turbine-chimney sys-
tem, and for the constant thermodynamic input data, like solar radiation intensity
and environment parameters, the system spontaneously self-models in response to the
actual situation. This means that the buoyancy effect determines the flow rate of air
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