Solar Energy 144 (2017) 71–78
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Solar Energy
journal homepage: www.elsevier.com/locate/solener
Observational study of modified solar still coupled with oil serpentine
loop from cylindrical parabolic concentrator and phase changing
material under basin
A.E. Kabeel ⇑, Mohamed Abdelgaied
Mechanical Power Engineering Department, Faculty of Engineering, Tanta University, Egypt
a r t i c l e
i n f o
Article history:
Received 17 December 2015
Received in revised form 30 June 2016
Accepted 4 January 2017
Available online 11 January 2017
Keywords:
Cylindrical parabolic concentrator
Solar desalination
Developed solar still
Oil heat exchanger
Phase change material
Productivity enhancement
a b s t r a c t
The performance of a cylindrical parabolic concentrator with focal pipe - coupled with a developed solar
still with (oil heat exchanger, Phase Change Material (PCM)) have been experimentally investigated to
improve the freshwater productivity. The cylindrical parabolic concentrator with focal pipe and oil heat
exchanger (serpentine loop) represent the external heat source to increase the temperatures of the basin
water and PCM. The PCM used as a heat storage medium. The influences of high heat exchanger oil temperature on the performance of the developed solar still are experimental investigated. A comparison
between a developed solar still and the convenstional solar still is carried out to evaluate the enhancement in the freshwater productivity under the same ambient conditions. The experimental results indicated that, the freshwater productivity approximately reached 10.77 L/m2 day for the developed solar
still, while its value is recorded 4.48 L/m2 day for conventional solar still. The freshwater productivity
of the developed solar still is 140.4% higher than that of the conventional solar still in average. Also,
the daily efficiency approximately reached 25.73% for the developed solar still, while its value is recorded
46% for conventional solar still. The percentage decrease in the daily efficiency for the developed solar
still about 44% compared to the convenstional solar still in average. In the present experimental work
the estimated cost of one liter of freshwater productivity reaches approximately 0.1359 LE (0.0174 $)
and 0.1378 LE (0.0177 $) for developed solar still and conventional solar still, respectively. This results
is obtained during the period from June to August 2015 under the Egyptian conditions.
Ó 2017 Elsevier Ltd. All rights reserved.
1. Introduction
The availability of freshwater on the earth’s surface is decreasing day by day, due to the continued increase in population density
and rapid development in the industry. Therefore, it was necessary
to use solar energy in the desalination of sea water to overcome
this problem. Solar stills represent a good option and a simple
technique compared to the other distillation methods.
The main problem encountered with the solar stills are the low
productivity of freshwater, and that is within the limits 2.5–5 L/m2
day. The basin water depth is important factor affecting on the productivity of the solar stills. Phadatare and Verma (2007) studied
the behavior of a single basin solar still at different water depth.
This study showed that, the freshwater productivity of the solar
⇑ Corresponding author.
E-mail
addresses:
(A.E. Kabeel).
kabeel6@hotmail.com,
http://dx.doi.org/10.1016/j.solener.2017.01.007
0038-092X/Ó 2017 Elsevier Ltd. All rights reserved.
kabeel6@f-eng.tanta.edu.eg
still decrease with the increase in the basin water depth. Tripathi
and Tiwari (2005) experimentally studied the impacts of water
depths on the productivity for passive and active solar stills. This
study showed that, the convective heat transfer coefficient
between the inner glass cover and basin water depends on the
water depth. After the sunset the productivity increases for
increase the water depths. Rajamanickam and Ragupathy (2012)
studied the effect of water depths on the productivity for a double
slope and a single slope solar stills. This study showed that, the
productivity of the still decreases with increase the basin water
depth. Khalifa and Ahmad Hamood (2009) experimentally studied
the impacts of water depths on the freshwater productivity of still.
This study showed that, the still productivity decreased by 48% for
increase the water depth from 1 to 10 cm. Tiwari and Tiwari (2006)
experimentally studied the effects of water depths on the evaporative mass transfer coefficient for a passive single-slope solar still.
Tiwari and Tiwari (2007) studied the effects of water depths on
the productivity for a single slope passive solar still. They found
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A.E. Kabeel, M. Abdelgaied / Solar Energy 144 (2017) 71–78
that, increasing the water depth decreases the still productivity up
to depths of about 10 cm but at greater depths than this the productivity becomes almost constant.
The water evaporation rate depends on the free area of saline
water in basin still. Abu-Hijileh Bassam and Rababa’h Himzeh
(2003) use the sponge cubes in the basin water to increase the free
area of the saline water, their results showed an improvement in
the distillate water productivity. Velmurugan et al. (2008a,b,
2009) found that, the use of the sponges in a single basin still
and stepped still improved the productivity by 15.3%.
The freshwater productivity of solar still depends on the temperature difference between basin water and glass cover. AbdelRehim and Lasheen (2007) studied the performance of modified
solar stills includes a solar energy concentrator. This study showed
that, the productivity of modified system is 18% higher than that of
conventional solar still. Sanjay and Sinha (1996) experimentally
studied the behavior of a double slope solar still integrated with
cylindrical parabolic concentrator. This study showed that, a double slope solar still integrated with cylindrical parabolic concentrator gives the maximum productivity at all basin water depth, the
rate of increase was about 94% higher than that of conventional
solar still in average. The performance of the solar still integrated
with flate plate solar collector have been conducted by Tiwari
et al. (2009), Lawrence and Tiwari (1990), Yadav (1991), Tiris
et al. (1998). These studies showed that, the distillate water productivity of the solar still integrated with flate plate solar collector
is higher than that of a conventional solar still. Singh et al. (2016)
experimentally studied the performance of active solar still integrated with two hybrid PVT collectors. Jahangiri Mamouri et al.
(2014) experimentally evaluated the performance of a single basin
solar still with evacuated tube collectors and achieved the efficiency of 22.9%. They also found the optimum depth of water as
the length of the heat pipe condenser. Kargar Sharif Abad et al.
(2013) used flat plate collectors and pulsating heat pipes in conjunction with the solar still and achieved the maximum yield of
0.875 L/m2 h. Feilizadeh et al. (2015) studied the effect of the number of flat collectors on multi-stage solar stills. This study showed
that, in the summer, 48% and 23% more productivity were obtained
by adding the second and third collector, respectively.
Singh et al. (2001) experimentally studied the productivity of a
double slope active solar still and photovoltaic integrated flat plate
collector. This study showed that, the production rate has been
accelerated to 1.4 times than the single slope active solar still
and photovoltaic. Dev and Tiwari (2012) experimentally studied
the productivity of an evacuated tubular collector integrated solar
still. This study showed that, the daily productivity of an evacuated
tubular collector integrated solar still higher than that of a single
slope solar still. Singh et al. (2012) numerically and experimentally
studied the performance of a double slope active solar still with
two flat plate collectors connected to the basin of solar still.
Singh et al. (2013) numerically studied the performance of a solar
still integrated with evacuated tube collector in natural mode. The
results show that, the overall energy and exergy efficiencies has
been found to be in the range of 5.1–54.4% and 0.15–8.25% respectively at 0.03 m water depth. Kumar et al. (2014) numerically studied the productivity of a single slope solar still integrated with an
evacuated tube collector. This study showed that, the optimum
daily productivity has been obtained as 3.9 kg with energy and
exergy efficiencies as 33.8% and 2.6% respectively. Tiwari et al.
(2015) presented an exergoeconomic and enviroeconomic analyses
of partially covered photovoltaic thermal flat plate collector integrated solar stills.
Abdel-Rehim and Lasheen (2005) studied the effect of packed
layer and rotating shaft installed close to the basin water surface
on the productivity of modified solar stills. This study showed that,
the productivity of modified solar still using packed layer as simple
thermal storage system was increased from 5% to 7.5%, while it was
increased from 2.5% to 5.5% for the modified one using rotating
shaft compared to conventional still. Nafey et al. (2001) experimentally studied the effect of black rubber and black gravel materials on
the productivity of a single basin sloped solar still, their results
showed that the black gravel (20–30 mm size) improves the productivity by 19% and the black rubber (10 mm thick) improves
the productivity by 20%. Naim and El Kawi (2003) studied the effect
of charcoal particles on the productivity of the solar still. Different
factors such as size range of charcoal particles, brine flow rate,
and still inclination to the horizontal have been investigated.
Also, the phase change materials used to enhance the freshwater productivity of solar still. Many researchers (El-Sebaii et al.,
2009; Radhawan, 2004) studied the impact of the PCM on the productivity of a basin still and stepped still, respectively. Dashtban
and Tabrizi (2011) studied the effect of the PCM on the performance of cascade solar still. Arunkumar et al.(2013)studied the
effect of PCM on the productivity of the concentrator-coupled
hemispherical basin still. The results show that, the freshwater
productivity with PCM is 26% higher than that without PCM.
Kabeel and Abdelgaied (2016) experimentally studied the effect
of PCM on the performance of a solar still, their results showed that
the daily freshwater productivity for solar still with PCM is 67.18%
higher than that of the conventional solar still. Kabeel et al. (2016)
experimentally studied the performance of a double passes solar
air collector–coupled modified solar still with PCM, their results
showed that the daily productivity for a double passes solar air collector–coupled modified solar still with PCMis 108% higher than
that of the conventional still.
Due to the low freshwater productivity of the solar stills, these
studies aims to improve the productivity of the solar still, by using
a cylindrical parabolic concentrator with focal pipe - coupled with
a developed solar still with (oil heat exchanger, Phase Change
Material (PCM)). Oil is flowing in a closed cycle through the heat
exchanger and focal pipe by using small pump. The PCM that acts
as latent and sensible heat storage system. The PCM used in the
present work is the Paraffin wax because of wide availability and
low cost. The basin water in the developed solar still is heated
directly by solar radiation absorped by absorber plate and also,
by the high oil temperature flow through the heat exchanger.
The effect of high oil temperature on the performance of developed
solar still are experimentally investigated. A comparison between a
developed solar still and the convenstional solar still is carried out
to evaluate the enhancement in the freshwater productivity under
the same ambient conditions.
2. Experimental work
In the present experimental work, two solar stills were
designed, fabricated and constructed to compare the freshwater
productivity of the solar desalination. The present experimental
work was carried out in Faculty of Engineering-Tanta University,
Egypt (Latitude 30.47°N and longitude 31°E) in the period from
June to August 2015. The experimental measurements were carried out from 6:00 am to 10:00 pm. One of them is a developed
solar still with (oil heat exchanger, Phase Change Material (PCM))
- integrated with a cylindrical parabolic concentrator with focal
pipe and the other is the conventional solar still as shown in Figs. 1
and 2. Fig. 1 shows the schematic diagram of the present exprimental work. In addition, Fig. 2 shows a photo of the present exprimental work.
As shown in Fig. 1, a conventional solar still has a basin area of
0.72 m2 (0.6 m 1.2 m). The basin still made from a galvanized
iron sheet of 1.5 mm thick. The elevations of low-side wall and
the high-side wall have been kept at 0.12 m and 0.47 m,
A.E. Kabeel, M. Abdelgaied / Solar Energy 144 (2017) 71–78
73
Fig. 1. Schematic diagram of the present exprimental work.
respectively. The whole inside surface of the basin still is coated
with black paint to increase the absorptivity of solar radiation.
Also, the surface of the basin still was insulated from the side
and bottom walls with low thermal conductivity fiber glass of
5 cm thick to reduce the heat energy loss from the basin still to
the ambient. The still cover is made of commercial glass, with a
thickness of 3 mm, and it is inclined by 30.47° to the horizontal.
The silicon used as a bonding material to prevent any leakage
between the basin box and the glass cover. The feed water tank
is placed 1 m above the basin still to feed the saline water to the
basin still. The feed water tank is connected to basin still by water
pipe line. A check valve is integrated at the pipe line entrance to
regulate the saline water flow rate.
The developed solar still with (oil heat exchanger, PCM) - integrated with a cylindrical parabolic concentrator with focal pipe
consists of oil heat exchanger (serpentine loop), PCM reservoir,
absorber surface, feed water tank, glass cover, insulation, cylindrical parabolic concentrator with focal pipe and measuring devices.
The saline water tank is located about 1 m above the basin still
to feed saline water to basin still. The absorber vessel made from
copper sheet 0.54 m 1.14 m 6 cm height (0.4 mm thick)
located inside the basin still, the basin still made from a galvanized
iron sheet of 0.6 m 1.2 m (1.5 mm thick). The gap between the
absorber vessel and basin still is filled with a phase change material (PCM) as a thermal energy storage medium with 3 cm thick.
The vertical depth of low-side wall and the high-side wall have
been kept at 0.12 m and 0.47 m, respectively. The whole inside surface of the absorber vessel and the basin still are coated with black
paint to increase the absorptivity of solar radiation. Also, the surface of the basin still was insulated from the bottom and side walls
with low thermal conductivity fiber glass of 5 cm thick to reduce
the heat energy loss from the basin still to the ambient. The developed solar still cover is made of commercial glass, with a thickness
of 3 mm, and it is inclined by 30.47° to the horizontal. The silicon
used as a bonding material to prevent any leakage between the
basin still and the glass cover.
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A.E. Kabeel, M. Abdelgaied / Solar Energy 144 (2017) 71–78
Fig. 2. A photo of the present exprimental work.
A phase change material reservoir, with 3 cm thick, is installed
with the developed solar still, beneath the absorber plate and filled
by PCM. The PCM reservoir located in the gap between the copper
absorber vessel and the basin still. The PCM represents a latent and
sensible heat energy storage medium. In this work the Paraffin wax
with a mass of 17.5 kg is used as a PCM because of its wide availability and its low cost. The properties of Paraffin wax is indicated
in Table 1.
A cylindrical parabolic concentrator used as a reflector system
that concentrates sunlight on the receiver tube. The cylindrical
parabolic concentrator has a dimension of 1.2 m wide and 2 m long
with 90° opening angle, an aluminum reflector with a special solar
coating used as a reflective material. The receiver consists of a
absorber copper tube 2 m long and 1.9 cm diameter covered by
glass evacuated tube 2 m long and 3.8 cm diameter, the vacuum
between the copper tube and glass cover used to decrease the heat
losses (suppress natural convection).
Oil heat exchanger (oil serpentine loop), consists of a single
tube with 12 passes, the oil flow inside the copper tube 1.252 cm
diameter and 8.4 m long. The copper tube of the oil heat exchanger
is immersed in the basin water. The copper serpentine loop is
coated with black paint to increase the absorptivity of solar radiation during sunlight. The oil serpentine heat exchanger immersed
in water of basin still. The electric pump used to pumping the oil
through the oil serpentine heat exchanger.
3. The daily efficiency of the solar stills
The daily efficiency, gd was obtained by the sum of hourly condensate production mp, multiplied by the latent heat Lw at average
Table 1
Paraffin wax properties (Haji-Sheikh et al., 1982).
Properties
Values
Melting temperature (°C)
Latent heat (kJ/kg)
Solid/liquid heat capacity (kJ/kg °C)
Solid/liquid density (kg/m3)
Coefficient of thermal conductivity (W/m °C)
56
226
2.95/2.51
818/760
0.24
basin water temperature Tw, hence the results was divided by the
average solar radiation I(t) over the whole absorber area A:
gd ¼
P
mp Lw
A IðtÞ
ð1Þ
where the latent heat Lw followed by El-Dessouky and Ettouney
(2002):
Lw ¼ 103 ½2501:9 2:40706 Tw þ 1:192217 103 T2w
1:5863 105 T3w ð2Þ
4. Experimental measurements
In the present exprimental work the intensity of solar radiation,
ambient temperature, glass cover temperature, saline water temperature, absorber plate temperature, PCM temperature, inlet heat
exchanger oil temperature, outlet heat exchanger oil temperature
and distilled water temperature are measured every 1 h. During
the each test, freshwater productivity is measured periodically
every 1 h. The oil flow rate remain constant at 6 L/min, the properties of the oil used in the present work are listed in Table 2. The
depth of the saline water remains constant at 2 cm during the
experiments in the both developed solar still and conventional
solar still. All exprimental measurements aims to evaluate the performance of the both developed solar still and conventional solar
still under the ambient conditions of Tanta City-Egypt. In the
developed solar still the cylindrical parabolic concentrator with
focal pipe and serpentine loop represent the external heat source
to increase the temperatures of the basin water and PCM. The
PCM used as a heat storage medium. In the first stage the heat is
stored in PCM as a sensible heat until it reaches to the melting
Table 2
Thermal properties of thermal oil at 20 °C.
Properties
Value
Density q (kg/m )
Viscosity l (Pa s)
Thermal Conductivity K (W/m K)
Specific heat capacity CP (kJ/kg. °C)
3
850
0.0686
0.14
1.966
A.E. Kabeel, M. Abdelgaied / Solar Energy 144 (2017) 71–78
75
point. In this state, the PCM starts to melt and after completing the
melting, the heat will be stored in PCM as a sensible heat. The PCM
will represent a source of heat for the basin water during the periods of low solar radiation intensity and during the night.
5. Error analysis
In the present experimental work the several parameters were
measured in the both developed solar still and conventional solar
still. This parameters include; the temperatures at all points (ambient temperature, inlet heat exchanger oil temperature, outlet heat
exchanger oil temperature, glass cover temperature, saline water
temperature, absorber plate temperature, PCM temperature) were
measured by K-type thermocouples which integrated with a G4LCUEA modular programmable logic control (MPLC); thermal oil
flow rate are measured by EZ-view flowmeter; wind velocity are
measured by vane anemometer; total solar radiation are measured
by solarimeter and the amount of freshwater are measured by calibrated flask. The accuracy for different used measuring instruments is summarized in the following table, Table 3. The
uncertainty in the present exprimental results can be calculated
according to the procedure explained by Barford (1990). The
uncertainty is defined as the root sum square of the fixed error
of the instrumentation and the random error observed during different measurements. Accordingly, the errors of the calculated
daily efficiency and daily productivity are ±0.6%, ±0.11%,
respectively.
Fig. 3. Hourly solar radiation intensity and temperature variations for the developed solar still and conventional solar still, 24-6-2015.
6. Experimental results and discussion
In the present experimental work, depending on the ambient
conditions during the period from June to August 2015, the wind
velocity varied from 0.4 to 5.2 m/s and the intensity of solar radiation varied from 225 to 1100 W/m2. For the developed solar still
the oil flow rate in the heat exchanger remains constant at
6 L/min. The behavior of the developed solar still and the conventional solar still are tested at a same water depth of 2 cm and under
the same ambient conditions.
In Figs. 3 and 4, the variation of the inlet heat exchanger oil
temperature, PCM temperature, glass cover temperature, basin
water temperature, ambient temperature and solar radiation
intensity of stills are shown with time. The freshwater productivity
of stills depends on the intensity of the solar radiation and the
ambient temperature. As shown in Figs. 3 and 4 the both ambient
temperature and solar radiation intensity increases to the maximum value at the midday and decrease after that gradually.
Fig. 3 shows that for the developed solar still the basin water temperature was 30 °C at 6:00 am and increased up to 92 °C at
1:00 pm, the inlet heat exchanger oil temperature was 37 °C at
6:00 am and increased up to 103 °C at 1:00 pm, while the PCM
temperature and the glass cover temperature in the range of
28–88 °C and 27–51 °C, respectively. On the other hand, for the
conventional solar still the basin water temperature was 27 °C at
6:00 am and increased up to 79 °C at 1:00 pm, while the glass
cover temperature in the range of 27–49 °C. Also, Fig. 4 shows that,
for the developed solar still the basin water temperature was 30 °C
Table 3
Error analysis for various experimental devices.
Device
Accuracy
Range
Error
EZ-view flowmeter
Solarimeter
Vane anemometer
Thermocouples
Calibrated flask
±0.05 L/min
±1 W/m2
±0.1 m/s
±1 °C
±5 ml
2–15 L/min
0–5000 W/m2
0.4–30 m/s
200: 1250 °C
0–2000 ml
0.83%
0.15%
3.5%
1.52%
0.77%
Fig. 4. Hourly solar radiation intensity and temperature variations for the developed solar still and conventional solar still, 30-7-2015.
at 6:00 am and increased up to 94 °C at 1:00 pm, the inlet heat
exchanger oil temperature was 37 °C at 6:00 am and increased
up to 105 °C at 1:00 pm, while the PCM temperature and the glass
cover temperature in the range of 28–90 °C and 27–52 °C, respectively. On the other hand, for the conventional solar still the basin
water temperature was 27 °C at 6:00 am and increased up to 80 °C
at 1:00 pm, while the glass cover temperature in the range of
27–50 °C. The previous results indicate that, the temperatures of
measured points are gradually increased until they reach their
maximum values in the midday and decrease after that gradually.
The basin water temperature of the developed solar still is
higher than that of the conventional solar still by about 3–24 °C,
this is mainly due to, the high temperature of oil inlet to the heat
exchanger, as well as, due to the PCM. In addition to, the high solar
radiation intensity absorbed in the both copper absorber plate and
copper serpentine loop for the developed solar still with (oil heat
exchanger, PCM).
The hourly freshwater productivity for both developed solar
still and conventional solar still during the period from 6:00 am
to 10:00 pm are shown in Figs. 5 and 6. This figure shows that
the hourly freshwater productivity for the developed solar still is
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A.E. Kabeel, M. Abdelgaied / Solar Energy 144 (2017) 71–78
still is higher than that for conventional solar still, due to impacts
of both the high temperature of oil inlet to the heat exchanger and
PCM on evaporation rate. This mainly because, the evaporation
rate increases with increase the basin water temperature, the
increase in the basin water temperature due to the high temperature of oil inlet to the heat exchanger. Also; the PCM represents a
source of heat after the sunset and during the night. The results
show that the high temperature of oil inlet to the heat exchanger
and PCM increase the freshwater productivity for the developed
solar still with (oil heat exchanger, PCM).
Figs. 7 and 8 show the accumulated freshwater productivity for
the developed solar still and conventional solar still. This figure
shows that, the accumulated freshwater productivity for
developed solar still is higher than that of conventional solar still
along the day. As shown in Fig. 7 the accumulated freshwater
Fig. 5. Variation of hourly freshwater productivity for developed solar still and
conventional solar still, 24-6-2015.
Fig. 7. The accumulated freshwater productivity for developed solar still and
conventional solar still, 24-6-2015.
Fig. 6. Variation of hourly freshwater productivity for developed solar still and
conventional solar still, 30-7-2015.
higher than that of the conventional solar still, where the high temperature of basin water increase the evaporation rate in the developed solar still. The increase in the basin water temperature due to
the high temperature of oil inlet to the heat exchanger of developed solar still, as well as, due to the PCM. The PCM vessel represents a source of heat during the periods of low solar radiation
intensity and during the night. Also, Fig. 5 shows the freshwater
productivities of the two stills were around 0.0 at 6:00 am, while
freshwater productivities recorded 1.24 L/m2 hour and 0.8 L/m2
hour at 1:00 pm for developed solar still and conventional solar
still, respectively on the date 24-6-2015. Fig. 6 shows the freshwater productivities of the two stills were around 0.0 at 6:00 am,
while freshwater productivities recorded 1.26 L/m2 hour and
0.81 L/m2 hour at 1:00 pm for developed solar still and conventional solar still, respectively on the date 30-7-2015. The results
show that, the hourly freshwater productivity of developed solar
Fig. 8. The accumulated freshwater productivity for developed solar still and
conventional solar still, 30-7-2015.
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A.E. Kabeel, M. Abdelgaied / Solar Energy 144 (2017) 71–78
Table 4
Daily productivity, productivity rise and daily efficiency for some testing days.
Daily productivity (L/m2)
Date
24/06/2015
29/06/2015
06/07/2015
10/07/2015
29/07/2015
30/07/2015
10/08/2015
Conventional solar still
Developed solar still
4.41
4.44
4.45
4.46
4.48
4.48
4.47
10.6
10.66
10.72
10.73
10.77
10.77
10.75
productivities up to almost 10.6 L/m2 day and 4.41 L/m2 day for
developed solar still and conventional solar still, respectively. The
increase in accumulated freshwater productivity for developed
solar still was 140.36% higher than that for conventional solar still.
Also, Fig. 8 shows that, the accumulated freshwater productivities
up to almost 10.77 L/m2 day and 4.48 L/m2 day for developed solar
still and conventional solar still, respectively. The recorded rate of
increase was about 140.4% higher than that of conventional solar
still. This increase is due to the high temperature of oil inlet to
the heat exchanger and the PCM, where their use increases the
evaporation rate in the developed solar still with (oil heat exchanger, PCM).
Table 4 shows the accumulated freshwater productivity,
productivity rise and daily efficiency for the developed solar still
and conventional solar still. As shown in Table 4 the average value
of the accumulated productivity reaches 10.77 L/m2 day and
4.48 L/m2 day for developed solar still and conventional solar still,
respectively. The percentage increases in freshwater productivity
for the developed solar still than the conventional solar still was
in the range 140.1–140.9%. The daily efficiency for the conventional solar still is higher than that of developed solar still. The
average daily efficiency reaches 25.73% and 46% for developed
solar still and conventional solar still, respectively. The percentage
decreases in the daily efficiency for using developed solar still
about 44% compared to the conventional solar still.
Daily productivity rise %
Daily efficiency %
Conventional solar still
Developed solar still
140.36
140.1
140.9
140.6
140.4
140.4
140.5
45.6
45.9
46
46.1
46.3
46.3
46.2
25.46
25.6
25.75
25.77
25.87
25.87
25.82
Table 5
Details of cost analysis for two solar stills.
Life, n
Interest per year i, %
Capital cost P, LE
Salvage value S, LE
Capital recovery factor CRF
Sinking fund factor, SFF
Fixed annual cost FAC, LE
Annual salvage value ASV, LE
Annual operating and maintenance cost, LE
Total annual cost TAC, LE
Annual freshwater productivity, L
Annual cost per one liter of distilled
water productivity, AC/L
AOMC ¼ 30% FAC
Conventional
solar still
Developed
solar still
10
12
750
150
0.177
0.057
132.75
8.55
39.82
144.15
1190
0.1378LE/L
(0.0177 $/L)
10
12
2050
410
0.177
0.057
362.85
23.37
108.85
393.91
3298
0.1359 LE/L
(0.0174 $/L)
ð7Þ
The annual operating and maintenance cost (AOMC) is taken
30% of (FAC)
ASV ¼ S SFF
ð8Þ
Here the salvage value (S) of the system is taken as 20% of the
capital cost (P) of the system.
The sinking fund factor (SFF) can be expressed as:
i
n
ði þ 1Þ 1
ð9Þ
7. Economic analysis
SFF ¼
Economic analysis of a two solar stills are presented in this section. The minimum average daily productivity can be estimated
9.7 L/m2 day and 3.5 L/m2 day for developed solar still and conventional solar still, respectively. Assume solar still operate 340 days
in the year, where the sun rise along the year in Egypt. Economic
analysis is carried out to estimate the annual cost per liter of distilled water (AC/L) in the present system using Eq. (3).
Table 5 give the details of cost analysis, which shows that the
estimated cost of one liter of freshwater productivity reaches
approximately 0.1359 LE (0.0174 $) and 0.1378 LE (0.0177 $) for
developed solar still and conventional solar still, respectively.
TAC=L ¼
TAC
M
ð3Þ
Total annual cost (TAC) is calculated by using the fixed annual
cost (FAC), annual operating and maintenance cost (AOMC) and
annual salvage value (ASV) as follows by Fath et al. (2003):
TAC ¼ FAC þ AOMC ASV
ð4Þ
FAC ¼ P ðCRFÞ
ð5Þ
where (P) is the capital cost.
The capital recovery factor (CRF) expressed as,
n
CRF ¼
i ð1 þ iÞ
n
ð1 þ iÞ 1
ð6Þ
The interest per year (i) and the number of life years of the system (n) are assumed as 12% and life time 10 years.
8. Conclusions
A developed solar still with (oil heat exchanger, Phase Change
Material (PCM)) - integrated with a cylindrical parabolic concentrator with focal pipe was designed, fabricated and constructed
to improve the still freshwater productivity. In the developed solar
still, the cylindrical parabolic concentrator with focal pipe and oil
heat exchanger represent the external heat source to increase the
temperatures of the basin water and PCM. The PCM used as a heat
storage medium. A comparison between developed solar still and
convenstional solar still are carried out to evaluate the development in the freshwater productivity under the same ambient conditions of the Tanta city (Egypt). The exprimental results showed
that the accumulated freshwater productivity for developed solar
still is higher than that of convenstional solar still. The daily productivity reached approximately 10.77 L/m2 for the developed
solar still while its value was 4.48 L/m2 for the convenstional solar
still. The percentage increases in freshwater productivity for the
developed solar still than the conventional solar still was in the
78
A.E. Kabeel, M. Abdelgaied / Solar Energy 144 (2017) 71–78
range 140.1–140.9%during the period from June to August 2015
(Egypt). The average daily efficiency reaches 25.73% and 46% for
developed solar still and convenstional solar still, respectively.
The percentage decreases in the daily efficiency for using developed solar still about 44% compared to the convenstional solar still.
In the present work the estimated cost of one liter of distillate
water productivity reaches approximately 0.1359 LE (0.0174 $)
and 0.1378 LE (0.0177 $) for developed solar still and convenstional solar still, respectively.
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