MULTIPLE EFFECT DISTILLATION OF SEAWATER WATER USING SOLAR ENERGY - THE CASE OF ABU DHABI SOLAR DESALINATION PLANT - Energy Research Developments: Tidal Energy, Energy Efficiency and Solar Energy - page 26

increased during winter months compared to summer months and also increases during the
month where the plant experiences several shutdowns either emergency shutdown or
automatic shutdown due to insufficient accumulator charge. Months where the plant has been
in emergency shutdown for long periods of pump maintenance, for example, can have
accumulator loss exceeding 8%.

Table 10. Monthly heat loss from the heat accumulator as a
percentage of incident solar radiation (data of 1985)

Month Jan. Mar. May Jun. Sep. Nov. Dec.

Heat loss % 5.6 6.3 5.0 4.6 5.6 5.3 6.6

7.2.2. Thermal Stratification Ratio
The thermal stratification ratio is the ratio of the mass of the strata of water in the heat
accumulator where a temperature gradient exists to the total mass of water inside the
accumulator. The total mass of water inside the 3 accumulator tanks is essentially constant at
300 m 3 . The thickness of the temperature gradient strata is measured using the temperature
sensor (RTD) located in the middle of tank # 2 (mid-temperature tank). The heat accumulator
operates in two main modes: the simultaneous heat collection and discharge mode during day
periods and the discharge mode during night periods. Table 11 shows the percentage thermal
stratification ratio for each of these two modes for a number of days. During the heat
discharge mode (at night), the temperature gradient strata averages 19.5 m 3 which
corresponds to a stratification ratio of 6.5%. During the simultaneous heat collection and
discharge mode (during day time) this strata averages 21.9 m 3 which corresponds to a
stratification ratio of 7.3%.

Table 11. Thermal stratification ratio of heat accumulator (data of 1985)

Heat
discharge

Simultaneous heat
collection and discharge

Date

Jan. 14 4.6% 6.0%

Jan. 15 3.8% 7.9%

Jan. 19 4.6% 4.8%

Feb. 2 6.7% 8.1

Feb. 13 6.6% 6.1%

Feb. 20 6.1% 8.3%

Mar. 10 10.6% 6.3%

Mar. 20 8.8% 3.9%

Mar. 29 6.5% 5.8%

Apr. 4 9.4% 5.7%

Apr. 10 7.2% 7.6%

Apr. 20 1.7% 11.5%

May 3 6.4% 8.9%

May 11 5.6% 9.2%

May 20 8.3% 9.3%

Average 6.5% 7.3%