In this work, an attempt has been made to study the effect of condensing cover material on the productivity of single basin solar still. Glass and acrylic sheet of 5 mm thickness were used as a condensing cover. Experiments were conducted on single basin single slope solar still with water depth of 1cm in the basin. Convective and evaporative heat transfer coefficients were calculated for 30 minutes time interval. When the glass is used as condensing cover daily energy and exergy efficiency were recorded as 36.43% and 2.73%, where as it is recorded as 16.84% and 1.52% when acrylic sheet used as a condensing cover.

1. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print),
ISSN 0976 – 6359(Online), Volume 5, Issue 5, May (2014), pp. 99-107 © IAEME
99
STUDY OF EFFECT OF CONDENSING COVER MATERIALS ON THE
PERFORMANCE OF A SOLAR STILL
Parmendra Singh, Dr. Ajeet Kumar Rai, Vivek Sachan
MED, SSET, Sam Higginbottom Institute of Agriculture Technology and Sciences,
Allahabad (U.P.), India
ABSTRACT
In this work, an attempt has been made to study the effect of condensing cover material on
the productivity of single basin solar still. Glass and acrylic sheet of 5 mm thickness were used as a
condensing cover. Experiments were conducted on single basin single slope solar still with water
depth of 1cm in the basin. Convective and evaporative heat transfer coefficients were calculated for
30 minutes time interval. When the glass is used as condensing cover daily energy and exergy
efficiency were recorded as 36.43% and 2.73%, where as it is recorded as 16.84% and 1.52% when
acrylic sheet used as a condensing cover.
Keywords: Condensing Cover Materials, Energy and Exergy Efficiency.
INTRODUCTION
Desalination is a process to produce the distilled water from brackish/saline water for the use
of medical, drinking and charging of the batteries, etc. purposes by using solar energy called solar
still. The solar distillation systems are mainly classified as passive and active solar still. In passive
solar still, the water in basin is heated directly by solar radiation i.e., without feeding an external
energy but in active solar still an additional thermal energy is feed in to the basin of passive solar still
to increase basin water temperature.
One of the major challenges for putting solar still in practice is to work with the undesirable
properties of glass as a material for mass production for solar stills [1]. Glass is heavy, brittle and has
high replacement costs. On the other hand, plastic is light weight, relatively unbreakable, easy to
transport and easy to process. Historically, plastic solar stills have been commercially more
successful than glass solar stills and have sold over 400,000 units [2]. Still, due to higher amount of
water production among other materials, glass has been the superior choice of material for its use as
condensation surface inside a solar still. Factors like the type of material, roughness, inclination,
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2. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print),
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shape, transmittance, wiping and vibration of the condensing surface were found to have a significant
impact on the production of water from the solar still [3-7]. The effect of condensing surface was
covered in more detail [1-7]. The use of mechanically modified plastic against glass lowered the
production of water by 18%[1]. The production of water from a solar still was found to be directly
proportional to the thickness and thermal conductivity of condensing surface. The production of
water decreased by 7% with an increase in glass thickness from 2 mm to 6 mm. The use of copper
metal against plastic increased the production of water by 18%. [4] Dincer reported the relation
between energy and exergy, exergy and environment, energy and sustainable development, and
energy policy making and exergy in detail. The results obtain by Rosen et al[9]. suggested that
exergy should be utilized by engineers and scientists, as well as decision making and policy makers,
involved in green energy and technologies in tandem with other objectives and constraints. In the
literature, the exergy analysis of a passive solar still is carried out by Nunez et al.[10] in Mexico.
There are very limited studies on the exergetic evaluation of active solar desalination system in the
literature. Garcia-Rodriguez and Gomez-Camacho[11] performed an exergy analysis of a solar multi-
effect distillation system (SOL-14 plant) located in Almeria solar research centre in southeastern
Spain. Similarly Sow et al.[12] carried out energetic and exergetic analysis of a triple effect distiller
by solar energy. This work quantifies power consumption per unit mass of pure water. Show et al.
obtain exergetic efficiencies between 16-26% for a triple effect system. The exergetic analysis has
been widely used in design, simulation and performance evaluation of energy systems reported by
Hepbsali[13]. Hepbasli[13] made a key review on exergetic analysis and assessment of renewable
energy resources for sustainable future for solar collector, solar thermal power plant, solar cooker,
solar drying, solar desalination and hybrid PV collector. In the present work a single slope solar still
is tested with two different condensing cover materials experimentally and their energy and exergy
analysis is also performed.
EXPERIMENTAL SET-UP
A prototype single slope solar still having a horizontal tray which acts as absorber of 1 m2
was designed and constructed. Tray was constructed using galvanized iron sheet of thickness 0.5 mm
and later on painted in black. Testing was performed by placing the Single slope solar still operating
in sunlight for a 24-h period. The work has led to the development of the single solar still and to a
technical improvement. In order to achieve the maximum yield from the system, the still orientation
should be the direction at which the highest average incident solar radiation is obtained.
Experimental investigation of the Single slope solar still has shown that the productivity of the
system was substantially increased in comparison with that of the basin type solar still. The present
study was concerned with the energy and exergy efficiency based on evaporation from the water
surface and based on condensation on the inner surface of the Single slope cover. Copper –
constantan thermocouples are used, along with a digital temperature indicator, to record the glass
temperature, water temperature and water vapor temperature in the experimental setup. These
thermocouples, over a prolonged usage period, tend to deviate from the actual temperature.
Therefore, they were calibrated with respect to a standard thermometer. A view of the condensing
chamber and photograph of the experimental setup are shown in figure.1

3. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print),
ISSN 0976 – 6359(Online), Volume 5, Issue 5, May (2014), pp. 99-107 © IAEME
101
Fig.1: Experimental setup of single slope solar Fig.2: Experimental setup of single slope solar
Still with glass as a condensing cover still with acrylic as a condensing cover
Performance of single slope solar still
Energy efficiency
Instantaneous efficiency
The expression for instantaneous efficiency (ηi)
ηi =
୫ୣ౭‫୐כ‬
୍ሺ୲ሻ‫כ‬୅౭
Overall thermal efficiency
The expression for overall thermal efficiency (ηpassive)
ηpassive =
∑ ୫‫୐כ‬
ୟ౭୍ሺ୲ሻୢ୲
Exergy efficiency
The general exergy balance for solar still can be written, Hepbalsi (2006)
ΣExin - ΣExout = Exdes
or
Exsun – (Exevap + Exwork) = Exdest
The exergy input to the solar still is radiation and can be written as
Exsun = Exin =Aw * I (t)*[1 - ర
య
( ౐౗
౐౩
) + భ
య
ሺ౐౗
౐౩
ሻ4
]
The exergy output of a solar still can be written as
Exevap =Aw* hew*(Tw – Tc )*[1 -ሺ ౐౗
౐౭
ሻ]
The exergy of work rate for solar still
Exwork = 0
The exergy destructed in solar still can be written as
Exdest = Mw*Cw *(Tw – Ta)*[1 -ሺ ౐౗
౐౭
ሻ]
The exergy efficiency of solar still us defined, Hapbalsi (2006)
ηex =
୉୶ୣ୰୥୷ ୭୳୲୮୳୲ ୭୤ ୱ୭୪ୟ୰ ୱ୲୧୪୪
୉୶ୣ୰୥୷ ୧୬୮୳୲ ୭୤ ୱ୭୪ୟ୰ ୱ୲୧୪୪
ሺ୉୶౛౬౗౦ሻ
ሺ୉୶౟౤ሻ

4. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print),
ISSN 0976 – 6359(Online), Volume 5, Issue 5, May (2014), pp. 99-107 © IAEME
102
RESULTS AND DISCUSSION
Number of readings was taken on the setup and data were analyzed for two different days in a
month.
Fig.3: Variation of Solar intensity with time of a day
Fig.3 shows the Variation of solar intensity with time on two different days of
experimentation in the month of April.
Fig.4: Variation of wind speed with time of a day
0
200
400
600
800
1000
1200
1400
Solarintensity(w/m2)
Time of a day (hr)
I(t)a
I(t)g
0
1
2
3
4
5
6
Windspeed(m/s)
Time of a day (hr)
Va
Vg

5. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print),
ISSN 0976 – 6359(Online), Volume 5, Issue 5, May (2014), pp. 99-107 © IAEME
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Fig.4 shows the Variation of wind speed with time on two different days of experimentation
under consideration. Average wind speed on 01/04/2014 was 2.4166 and average wind speed on
23/04/2014 was 1.411 m/s.
Fig.5: Variation of temperature with time of a day
Fig.5 shows the Variation of temperature with time, water temperature with acrylic
condensing cover is higher than water temperature with glass cover. Inner condensing cover
temperature of acrylic sheet is higher than that of glass cover.
Fig.6: Variation of convective heat transfer with time of a day
0
10
20
30
40
50
60
70
80
Temprature0C
Time of a day
Twg
Tag
Tgi
Twa
Taa
Tai
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
Evaporativeheattransfer
coefficient(w/m2)
Time of a day(hr)
hcwa(PM)
hcwa(DM)
hcwg(PM)
hcwg(DM)

6. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print),
ISSN 0976 – 6359(Online), Volume 5, Issue 5, May (2014), pp. 99-107 © IAEME
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Fig.6 shows the variation of convective heat transfer coefficient with time. Evaporative heat
transfer coefficient (PM) is higher than evaporative heat transfer coefficient (DM).
Fig.7: Variation of evaporative heat transfer coefficient with time
Fig.7 shows the variation of convective heat transfer coefficient with time. Evaporative heat
transfer coefficient is higher when glass is used as condensing cover. The maximum value of exergy
efficiency of glass cover is 6.64% whereas it is 3.54% for acrylic sheet condensing cover.
Fig.8: Variation of energy efficiency with time of a day
0
10
20
30
40
50
60
70
80
90
100
Evaporativeheattransfer
coefficient(w/m2)
Time of a day(hr)
hewa(PM)
hewa(DM)
hewg(PM)
hewg(DM)
0
10
20
30
40
50
60
Energyefficiency(η)
Time of a day (hr)
ηg
ηa

7. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print),
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Fig.8 shows the variation of energy efficiency with time. Energy efficiency is higher when
glass is used as a condensing cover. The maximum value of energy efficiency of glass cover is
50.37% whereas it is for acrylic sheet condensing cover 29.13%.
Fig.9: Variation of exergy efficiency with time of a day
Fig.9 shows the variation of exergy efficiency with time. Exergy efficiency is higher when
glass is used as condensing cover. The maximum value of exergy efficiency of glass cover is 6.64%
whereas it is for acrylic sheet condensing cover 3.54%.
Fig.10: Variation of distillate with time of a day
0
1
2
3
4
5
6
7
ExergyEfficiency(η)
Time of a day (hr)
Exa
Exg
0
0.1
0.2
0.3
0.4
0.5
0.6
Distillate(kg)
Time of day(hr)
mthg
mexpg
mtha
mexpa

8. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print),
ISSN 0976 – 6359(Online), Volume 5, Issue 5, May (2014), pp. 99-107 © IAEME
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Fig.10 shows the theoretical and experimental distillate with time for glass and acrylic sheet
used as a condensing cover.
Fig.11: Variation of distillate with time of a day
Fig.10 shows the variation of experimental distillate output with time. It is observed that the
daily productivity is higher when glass is used as the condensing cover than acrylic sheet condensing
cover. A maximum of 3.925 liter/day is obtained with glass cover in comparison to 2.310 liter/day
when acrylic sheet is used.
CONCLUSION
A single slope solar still with different condensing cover material is tasted in the premises of
SHIATS-DU Allahabad. Energy and Exergy analysis of the system is performed to find the
maximum energy efficiency and exergy efficiency of the system. The following points can be
concluded from the present work.
• The exergy efficiency of a single slope solar still is lower than energy efficiency it is due to
lower evaporative heat transfer rate.
• The maximum instantaneous energy efficiency for solar still with glass as a condensing cover
is 50.30% when as it is 29.136% for acrylic sheet condensing cover.
• The maximum instantaneous energy efficiency for solar still is 6.64% when glass is used as a
condensing cover and 3.54% when acrylic sheet condensing cover.
• Daily productivity increased by 71% when glass is used for condensing cover.
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pg

9. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print),
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