Salinity gradient solar ponds - Solar Energy Sciences and Engineering Applications - page 205

Figure 7.3.4 In-pond (left) and external (right) heat exchangers at RMIT University, Melbourne,
Australia.
the best practice will be to prevent and outbreak of algae pond in the first place. Earlier
studies have shown that adding copper sulphate to the solar pond water or making
the solar pond water more acidic will help reduce the algae growth (Gasulla et al.,
2011). Acidification of the pond provides a simple and reliable maintenance method
for preventing or inhibiting algal blooms and maintaining high transparency. The pH
level of the pond should be monitored and hydrochloric acid added to keep the level
below 5.5. Another approach is to add brine shrimp to the pond to feed off and hence
control the algae level (Wang and Seyed-Yagoobi, 1995; Malik et al., 2011).
7.3.3 Heat extraction
The main purpose of a solar pond is to supply heat and this heat is stored in the storage
zone of the pond, and this is in addition to the heat that is stored in the gradient layer.
There are different ways in which heat can be extracted from the storage zone of the
solar pond. In the case of a large solar pond external heat exchangers are used with
hot brine being extracted from the storage zone; after it passes through the external
heat exchanger this brine is pumped back. In the case of small solar ponds in-pond
heat exchangers are better suited, made from plastic tubes or copper nickel tubes
(Jaefarzadeh, 2006). Figure 7.3.4 shows the in-pond and external heat exchangers in
the 50 m 2 solar pond at RMIT University, Melbourne, Australia. The most common
method of heat extraction from solar ponds is pumping hot brine from the storage
zone through a diffuser located just below its interface with the gradient zone to a
heat exchanger located near the pond. After delivering heat to the heat exchanger, the
cooler brine is returned to the bottom of the pond. This brine removal and return can
be accomplished without causing instability in the gradient layer. The pond must also
always be operated with the salt concentration in the storage zone below the saturation
level. Otherwise there can be some crystallisation of salt in the pipes, pumps and other
equipment used in the heat extraction system, especially when it is not operating. The
resulting blockages can be difficult to remove. Alternatively heat can be extracted using
in-pond heat exchangers. For instance, use of plastic pipes connected to weights on