Environmental Engineering Reference
In-Depth Information
6.3 CODE TESTING
The code developed is tested using performance measurements for known collectors
from test carried out at SNL and presented in Dudley et al. (1994). The information
required to input to EES code is the following:
Direct normal irradiation (DNI) [W/m
2
]
1
2
Wind speed [m/s]
Ambient temperature [
◦
C]
3
Solar incidence angle [
◦
]
4
5
Coating absorptance [
−
]
Coating emittance at 100
◦
C[
−
6
]
Coating emittance at 400
◦
C[
−
7
]
8
Mirror reflectivity [
−
]
9
Glass envelope transmittance [
−
]
10
Annulus pressure or vacuum [
−
]
11
Annulus absolute pressure [kPa]
HTF flow rate [m
3
/s]
12
13
Type of heat transfer fluid
14
Receiver inside diameter [m]
15
Receiver outside diameter [m]
16
Glass envelope inside diameter [m]
17
Glass envelope outside diameter [m]
Collector aperture area [m
2
]
18
19
Shadowing [
−
]
20
Tracking error [
−
]
21
Dirt factor on glass envelope [
−
]
22
Dirt factor on mirror [
−
]
Collector inlet temperature [
◦
C].
23
A comparison of the performance of the code developed and the tests conducted
at SNL is shown in the following figures. Figures 6.3.1 and 6.3.2 show a comparison
of the actual efficiency and heat loss of the collector with the values determined from
the EES code developed, when vacuum exists in the receiver annulus.
Similar results for air in the receiver annulus are presented in Figures 6.3.3 and
6.3.4. In all cases the agreement between the experimental results and those obtained
by the EES code is acceptable. The agreement is better for the air case whereas in
both cases the difference increases with increasing operating temperature. It should be
noted that the relatively high percentage differences shown in Figure 6.3.2 are due to
the magnitude of the actual numbers considered and generally the model underesti-
mates the heat loss at high receiver temperatures and overestimates it at low receiver
temperatures. In general, the reason for the deviation presented in the case of heat loss
(Figures 6.3.2 and 6.3.4) is the possible dependence of the optical properties on the
temperature.
Finally, the code developed is used with the characteristics of the collector erected
at the premises of the Cyprus University of Technology and in particular at the
Archimedes Solar Energy Laboratory. The collector, shown in Figure 6.3.5, is supplied
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