Environmental Engineering Reference
In-Depth Information
The heat collection efficiency is expressed by the following polynomial equation
Q
2
η
≡
c
=
a
+
b
x
+
c
x
(7)
c
A
I
c
t
a
,
b
, and
c
are constants and
x
is a parameter defined as
T
+
T
c
1
c
2
−
T
a
2
x
=
(8)
I
t
where
T
a
is the ambient air temperature and
I
t
is the solar radiation
on
a tilted surface.
Susbstituting the expression for
Q
c
from Eq. 6 and the expression for
x
from Eq. 8 into Eq. 7
we get a relationship for the collector outlet temperature,
T
c2
in terms of the collector inlet
temperature, ambient temperature, solar radiation and collector absorber area
2
2
C
T
+
2
C
T
+
C
=
0
(9)
1
c
2
c
3
2
where
C
1
, C
2
and
C
3
are given by the following expressions
C
1
=
c A
c
C
2
=
c A
c
(
T
c1
- 2
T
a
) +
b
A
c
I
t
- 2
m
c
I
t
C
3
=
c
A
c
(
T
c1
2
T
a
)
2
+ 2
b
A
c
I
t
(
T
c1
- 2
T
a
) + 4
a
A
c
I
t
2
+ 4
m
c
C
p
I
t
T
c1
Using the constants
a
,
b
, and
c
and for given values for
T
c1
,
T
a
and
I
t
,
eqn 9 can be solved for
T
c2
to give
−
C
−
C
2
2
−
C
C
2
1
3
T
c
=
2
C
1
with the above equations, the hourly values of the outlet water temperature
T
c2
can be derived
if the hourly inlet water temperature,
T
c1
, is given.
5.3. Calculating the Performance of the Evaporator
The performance of the evaporator consists of estimating the overall heat transfer
coefficients (OHTC) of the first effect (heater), the other evaporator effects (2
nd
- 18
th
effects), the 17 preheaters and the condenser as well as evaluating the economy (or specific
heat consumption) of the evaporator. The list of measurements carried out for the evaporator
are shown in table 4.
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