The solar still is a simple device used for obtaining fresh water for small scale demand. Due to intermittent nature of solar energy, solar still s are not continuous in nature. To make them operative for non-sunshine hours energy storage mediums are used. In the present work an attempt has been made to utilize the energy storage capacity of Lauric acid to enhance the performance of solar still. Experiments were carried out on single basin double slope solar still in the premises of SHIATS, Allahabad in the month of February. It is observed that the nocturnal distillate output is increased by more than 17% when Lauricacid is used as energy storage medium.

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EXPERIMENTAL INVESTIGATION OF A SOLAR STILL
USING LAURIC ACID AS A ENERGY STORAGE MEDIUM
Maheep Kumar*, Ajeet Kumar Rai**, Vivek Sachan**
*Department of Mechanical Engineering, NIU, Greater Noida.
**Department of Mechanical Engineering, SSET, SHIATS Allahabad, U.P. India
ABSTRACT
The solar still is a simple device used for obtaining fresh water for small scale demand. Due
to intermittent nature of solar energy, solar stills are not continuous in nature. To make them
operative for non-sunshine hours energy storage mediums are used. In the present work an attempt
has been made to utilize the energy storage capacity of Lauric acid to enhance the performance of
solar still. Experiments were carried out on single basin double slope solar still in the premises of
SHIATS, Allahabad in the month of February. It is observed that the nocturnal distillate output is
increased by more than 17% when Lauric acid is used as energy storage medium.
Key words: Solar Distillation, Energy Storage Mediums.
INTRODUCTION
There is acute shortage of fresh drinking water in remote, coastal and rural areas of many
countries. The only nearly inexhaustible source of water is the oceans. Their main drawback,
however, is their high salinity. Therefore, it would be attractive to tackle the water -shortage problem
with desalination of this water. Desalinize in general means to remove salt from seawater or
generally saline water. Desalination processes require significant quantities of energy to achieve
separation of salt from seawater. If desalination is accomplished by conventional technology, then it
will require burning of substantial quantities of fossil fuels. Given that conventional sources of
energy are polluting, sources of energy that are not polluting will have to be developed. Fortunately,
there are many parts of the world that are short of water but have exploitable renewable sources of
energy that could be used to drive desalination processes. Solar thermal energy is the most available
renewable source of energy. The sun consists of hot gases and has a diameter of 1.39 × 109
m; it has
an effective blackbody temperature of 5762 K, the temperature in its central region ranges between
8× 106
and 40× 106
K. The Sun emits energy at a rate of 3.8 × 1023
kW, of which, approximately 1.8
× 10kW is transmitted to the earth; only 60% of this amount reaches the earth’s surface. The other
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40% is reflected back and absorbed by the atmosphere. If 0.1% of this energy is converted with
efficiency of 10%, then it can generate amount of energy equivalent to four times of the world’s total
generated electricity. Moreover, the total annual solar radiation falling on the earth is more than 7500
times of the world’s total annual primary energy consumption that is 450 EJ. There is 3,400,000 EJ,
approximately, of total annual solar radiation reaches the surface of the earth which is greater than all
the estimated conventional energy sources.
The use of solar energy is a promising option for desalination of saline water. Solar
distillation systems for desalination of saline water are extensively discussed in literature. A single
basin solar still is a very simple solar device. This can be fabricated easily with locally available
materials. The maintenance is also cheap and no skilled labor is required. Because of its low
productivity it is not popularly used. Number of works are undertaken to improve the productivity of
the still. Since solar energy is not continuously available distillate production is also not continuous.
Therefore producing distillate during non-sunshine hours by using thermal energy storage mediums
is one of the options. Thermal energy can be stored as sensible heat, latent heat or combination of
these two. Materials that can store latent heat during the phase transition are known as phase change
materials. Latent heat of phase change material is many orders higher than the specific heat of
materials. Therefore PCM can share 2-3 times more heat or cold per volume or per mass as can be
stored as sensible heat in water in a temperature interval of 20 0
C. Lorsh et al, Lane et al and
Humphries and Griggs have suggested a wide range of PC Ms that can be selected as a storage
media. In order to select the most suitable PCM as a storage media some criterias are also mentioned
by Furbo and Svendsen, Lane, Abhat have given a detailed classification of PCMs along with their
properties. Dincer and Rosen have also exercised the same. Rai et al have reviewed work on PCMs
and their wide range of applications. Naim et al constructed a novel continuous single stage solar still
with PCM. They reported that the productivity of a solar still can be greatly enhanced by the use of a
PCM integrated to the still. Shukla et al and Rai et al have used PCM as a energy storage medium to
study the performance of a solar still. In the present study, performance of a double slope solar still
with Lauric acid as PCM has been investigated in outdoor conditions in the month of February.
Melting temperature of Lauric acid is 490
C and latent heat of fusion is 178 kJ/kg.
EXPERIMENTAL SETUP AND PROCEDURE
Set-up
Figure 1 shows the photograph of double slope solar still (DSS). Two DSS of same size and
shape are taken for experimentation on the same plateform. one DSS is kept normal while other is
equipped with PCM at its base. The DSS consist of a passive solar distillation unit with a glazing
glass cover of thickness 3mm, inclined at 260
having an area of 0.048m x 0.096m. The glass covers
are used to transmit solar energy and to preserve heat. It works as a condensing surface for the vapor
generated in the basin. The basin of the still is made up of Galvanized iron. The effective area of the
basin is 0.72 m2
. 2 kg of Lauric acis as PCM is spread in the basin. A separate tray made of
Aluminum is used to store water for distillation. Air tight contact is made between water basin
(Aluminium tray) and the PCM. Thermocouples were attached in different locations of the still to
record the temperature of glass covers on east side and west side, water temperature in the basin,
basin temperature, temperature of PCM and atmospheric temperature. A distillate channel was
provided at each end of the basin for the collection of distillate output. The distillate was collected in
a bottle and then measured by graduated cylinder. Solarimeter is used to measure the solar intensity
on east and west side glass covers. Anemomter is used to measure the wind velocity.

3. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 –
6480(Print), ISSN 0976 – 6499(Online), Volume 5, Issue 12, December (2014), pp. 35-40 © IAEME
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Figure :1 Experimental Set up of Double Slope Solar Still With Lauric Acid
Procedure
The experiments were conducted in the premises of SHIATS Allahabad, UP, India. All
experiments were started at 8:30 AM at local time. Copper-Constantan thermocouples with 10
least
count were used to measure the temperature of water basin, PCM, east and west side glass covers
and atmosphere. Thermocouples were caliberated using ZEAL thermometer. The distillate output
was recorded with the help of a measuring cylinder of least count 1 ml. The solar intensity was
measured with the help of caliberated solarimeter of least count 2 mW/m2
. The effect of use of phase
change material is also studied by comparative analysis.
PRODUCTIVITY OF SOLAR STILL
Energy balance equations are given by the different components of a solar still without PCM
by Shukla et al [5], and Rai et al [6] and with PCM by El-Sebaii et al.[14]. The hourly and daily
productivity of solar still is given by the expressions
Mewh=hewh(Tw-Tgin)/L (1)
Mewd=Σ24hMewh (2)
RESULTS AND DISCUSSION
Fig.2 shows the variation of solar intensity falling on a particular day on the east and west
side of the glass covers of double slope solar still. Since the both the solar stills are kept on the same
plateform and their orientations are also the same, solar intensity on east side and west side glass
covers are also found same. Solar intensity falling through the east side glass cover is found higher
till 3:00PM. Maximum value of solar intensity is received on the east side glass cover at around
11:00AM. Variation of wind velocity is also shown in fig 3.

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Figure 2: Variation of solar intensity with time of a day
Figure 3: Variation of wind velocity with time of a day
Figure 4: Variation of temperatures with time of a day
Fig 4 shows the variation of temperatures of different elements of double slope solar still. As
it is expected water temperature is found higher due to green house effect whereas PCM temperature
is found lower due to low heat transfer from bottom of the water basin. But case reversed in night,
and the amount of heat stored by PCM is transferred back to the water. Temperature of PCM is
found higher till 10:00 ‘o’ clock in the morning. Fig 5 shows the variation of distillate output

5. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 –
6480(Print), ISSN 0976 – 6499(Online), Volume 5, Issue 12, December (2014), pp. 35-40 © IAEME
39
measured in every half an hour from both systems. It is observed that the distillate output from the
still with PCM is higher. A 8.2% rise in the daytime output is measured with the still in which Lauric
acid is used. Nocturnal output is also measured from both the systems. It is observed that 17.7%
more distillate is obtained with the still equipped with PCM. This is because energy absorbed by
PCM as latent heat of fusion in day time is released in night during solidification of PCM. This
released heat enhances the production of distillate in night.
Figure 5: Variation of distillate output with time of a day
CONCLUSION
In the present work an attempt has been made to enhance the productivity of solar still with
the help of a energy storage medium beneath the water basin. Experiments were carried out on two
identical solar still. A comparison is made between the performance of two stills with and without
energy storage medium. Lauric acid, a phase change material, is used as a energy storage medium in
the solar still. It is observed that an overall 13% rise in productivity is obtained when PCM is used in
the solar still. This will further improve in summer season when there is high temperature in the day
time for a longer duration.
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