Environmental Engineering Reference
In-Depth Information
Figure 6.2.1
Collector receiver model a) nomenclature, b) energy balance and c) thermal resistance
network for the cross-section of the receiver.
losses have been omitted for clarity. The optical losses are due to imperfections in the
collector mirrors, tracking errors, shading and cleanliness of the mirror and receiver
glazing. The incoming solar energy, which effectively is equal to the solar energy input
minus any optical losses, is absorbed by the glass envelope (q
go,SolAbs
) and receiver pipe
(q
po,SolAbs
). Most of the energy that is absorbed by the receiver is conducted through the
receiver pipe material (q
pi-po,cond
) and eventually transferred to the HTF by convection
(q
f-pi,conv
). The remaining energy is transmitted back to the glass envelope by con-
vection (q
po-gi,conv
) and radiation (q
po-gi,rad
). The energy reaching the glass cover from
radiation and convection then passes through the glass envelope wall by conduction
(q
gi-go,cond
) and along with the energy absorbed by the glass envelope wall (q
go,SolAbs
)is
lost to the environment by convection to ambient air (q
go-a,conv
) and radiation towards
the sky (q
go-s,rad
).
The energy balance equations are determined by considering that the energy
is conserved at each surface of the receiver cross-section, shown in Figure 6.2.1.
Therefore:
q
f-pi,conv
=
q
pi-po,cond
(6.2.1)
q
po,SolAbs
=
q
po-gi,conv
+
q
po-gi,rad
+
q
pi-po,cond
(6.2.2)
q
po-gi,conv
+
q
po-gi,rad
=
q
gi-go,cond
(6.2.3)
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