Environmental Engineering Reference
In-Depth Information
The measured efficiency is therefore lower than the catalog efficiency by about 8% for
x
=
0 and 9.3% for
x
= 0.05
o
C hr m
2
/kcal. The drop in collector efficiency of a group of
interconnected collectors can be attributed to the heat loss by internal piping and connectors.
In the basic design, the influence of dust deposition on the solar collectors was assumed
to cause a 10% loss of the incoming solar radiation. Measurements of the heat loss due to
dust effect carried out during plant operation showed that the influence of dust deposition has
a seasonal character with the loss in solar radiation varying from 4% during winter months to
as much as 20% in the summer. To account for the monthly variation of the dust effect in the
simulation program, a mathematical model was developed to estimate the dust effect from
month to month.
Heat loss from the collector piping system is another cause of heat loss that has to be
accounted f-cor. The piping system consists of insulated pipes varying in diameter from 30
mm to 125 mm as well as valves, pipe supports, expansion joints and safety valves. In the
basic design, heat loss from the piping system was estimated based only on heat loss from all
the pipes with heat loss from valves, supports, etc. neglected. Measurements were made to
estimate the total piping loss which takes into consideration all components of the piping
system. For a single block, the measured heat loss from the piping system was correlated by
the following formula:
Q
loss-m
= 66.6 (
T
w
-
T
a
)
1.3
kcal/hr
(66)
The theoretical (calculated) value of the piping heat loss excluding valves, supports, etc.
was estimated as:
Q
loss-c
= 93.5 (
T
w
-
T
a
) kcal/hr
(67)
For a (
T
w
-
T
a
) = 40
o
C , the measured heat loss is 2.15 times the theoretical value.
(b) The heat accumulator
The heat accumulator (HA) in the solar plant consists of 3 series-connected thermally
stratified vertical cylinders. Heat loss from the accumulator tanks was estimated in the basic
design as 1.05
o
C per day for a water temperature of 99
o
C and an ambient temperature of
30
o
C. For a storage capacity of 300 m
3
of water, the estimated daily heat loss is 315,000
kcal/day. Heat loss measurements from plant heat balance indicates that daily temperature
drop varies from month to month with the average yearly value of 2.61
o
C per day which is
more than double the value used in basic design. This value is also based on a water
temperature of 99
o
C and ambient temperature of 30
o
C.
(c) The MED evaporator.
As seen from table 21, the evaporator is the only piece of equipment in which the
performance in the basic design was upgraded in the simulation program: 20% up in water
production capacity, and 0.2 to 7.5% less in specific heat consumption. In the basic design,
the maximum evaporator capacity was 120 m
3
/day (5 m
3
/hr) and specific heat consumption is
43.8 kcal/kg- product at 35
o
C seawater temperature and 55,000 ppm salt concentration. This
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