Experimental and Numerical Analysis of a PCM-Supported ...
Experimental and Numerical Analysis of a PCM-Supported ...
Experimental and Numerical Analysis of a PCM-Supported ...
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size <strong>of</strong> the thermal buffer, melting temperature <strong>of</strong> <strong>PCM</strong> in the thermal buffer, <strong>and</strong><br />
brine concentration factor. The computation time was setup for the whole year with a<br />
time step 120 seconds using interpolation techniques to smoothly develop a time<br />
evolution <strong>of</strong> the average hourly input weather conditions over the entire time steps<br />
between the successive hours.<br />
The effects <strong>of</strong> transient weather conditions <strong>and</strong> climate on the system performance<br />
have been examined comparing between the two different locations in Egypt; Al-<br />
Arish, <strong>and</strong> Al-Kharga.<br />
8.3.1 Effect <strong>of</strong> brine concentration factor (r c )<br />
Figure 8.3 shows the variations <strong>of</strong> distillation rate <strong>and</strong> GOR under same operation<br />
conditions with the brine concentration factor for a solar collector area <strong>of</strong> 220 m 2 . The<br />
results reveal that the GOR increases as the brine concentration factor increases due<br />
to better heat recovery while the rate <strong>of</strong> distillate decreases at the same time. In<br />
closed water loop HDH processes, mixing <strong>of</strong> feed seawater <strong>and</strong> recirculated brine<br />
causes the degradation <strong>of</strong><br />
the solar collector’s thermal<br />
efficiency due to increasing<br />
the inlet brine temperature to<br />
the collector, <strong>and</strong> hence the<br />
inlet heat capacity flow rate<br />
to the HDH system<br />
decreases. The distillate rate<br />
peaks at a value <strong>of</strong> r c =2<br />
while the GOR peaks at a<br />
value <strong>of</strong> r c =3 beyond which<br />
the GOR saturates while the<br />
distillate rate continues to<br />
drop. Thus operating the<br />
plant at a value <strong>of</strong> r c >3 is not<br />
recommended under these<br />
circumstances.<br />
Figure 8.3: Effect <strong>of</strong> brine concentration ratio on<br />
the average-yearly distillate rate <strong>and</strong> GOR<br />
Further, scale formation is an important limiting factor to be considered when talking<br />
about brine circulation. The tendency <strong>of</strong> scale formation increases with increasing the<br />
recirculated fraction due to increasing the brine salinity. The threshold limit for this<br />
factor decreases in inverse proportion to the top brine temperature which can be<br />
reached in the plant. For instance, the threshold value for r c has been set at 1.5 for<br />
Multi-Stage Flash desalination plants working at a top brine temperature around<br />
110ºC to avoid serious scale formation problems. Since the top brine temperature<br />
level in HDH systems is designed at a maximum value <strong>of</strong> 85ºC, a higher threshold<br />
limit <strong>of</strong> r c up to 3 probably can be tolerated. However, since the variation <strong>of</strong> GOR is<br />
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