1. Experiments were carried out on a tubular solar still integrated with stearic acid as a phase change material in Allahabad, India. 2. The daily energy efficiency was 21.87% and daily exergy efficiency was 0.857%. Productivity increased with increasing water temperature according to the correlation P=5.489Tw - 169.9, with an R2 value of 0.804. 3. The use of a phase change material increased nighttime productivity and the overall productivity of the solar still.

1. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print),
ISSN 0976 – 6359(Online), Volume 6, Issue 1, January (2015), pp. 42-46 © IAEME
42
EXPERIMENTAL STUDY OF A TUBULAR SOLAR STILL
WITH PHASE CHANGE MATERIAL
Ajeet Kumar Rai, Vivek Sachan
Mechanical Engineering Department, SSET, SHIATS Allahabad (UP) India
ABSTRACT
Experiments were carried out on tubular solar still in Allahabad climate conditions. Energy
storage medium is used in still to produce distillate in the off sunshine hours .A correlation is
developed for the productivity of a still using experimental results .The proposed correlation has
been validated with the experimental results .The regression coefficient approaches to unity and the
correlation may be perfect positive with least error .Energy and exergy efficiency of a system were
calculated .It is observed that productivity of solar still increase by 20% when energy storage
medium is used .
Keywords: Phase Change Material, Energy and Exergy efficiency, Correlation Coefficient.
INTRODUCTION
Although, more than two-thirds of the Earth surface is covered by water, many countries
suffer for shortage of portable water is a serious issue that many countries suffer from. Furthermore,
the worldwide rapid growth of industry and population has resulted in a large boom in demand for
fresh water. The solar still is an ideal source of fresh water for drinking purpose. It is one of the most
important and technically viable applications of solar energy. The production capacity of a simple
type still is in the range of 2–5 l/m2
/day [1]. This makes the system highly uneconomical. In solar
desalination process, the productivity of the solar still is very less compared to other conventional
desalination systems. Less productivity is the main drawback of solar still. For enhancing the
productivity of solar still phase change material are used as energy storage system. Phase change
material supply energy during off sunshine, particularly at night. Many researchers have investigated
the effect of PCM on the productivity of solar still theoretically and experimentally [2-15]. Exergy
analysis is based upon the second law of thermodynamics, which stipulates that all macroscopic
process are irreversible .Every such irreversible process entails a non recoverable loss of exergy
Analysis of exergy losses identifies possibility of improving the design of system. Ranjan et. al. have
performed exergy analysis of solar still and have found highest exergy destruction in the basin liner
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2. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print),
ISSN 0976 – 6359(Online), Volume 6, Issue 1, January (2015), pp. 42-46 © IAEME
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[16] use of phase change material below the basin liner minimizing the exergy loss. In the present
work stearic acid is used in the basin of tubular solar still to enhance the productivity of the still and
to minimize the losses.
EXPERIMENTAL SET UP
A prototype solar still having a horizontal tray which acts as absorber of 0.77 m2
was
designed and constructed. Tray was constructed using galvanized iron sheet of thickness 0.5 mm and
later on painted in black. The tray is surrounded by tubular structure made up of PVC sheet. The total
area of the PVC cover is 3.52 m2
. The still is formed by a tubular transparent surface made up of
PVC sheet. Testing was performed by placing the tubular solar still operating in sunlight for a 8 h
period. The work has led to the development of the tubular 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
tubular solar still has shown that the productivity of the system was substantially increased in
comparison with that of the basin type solar still. 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 set up
are shown in figure1.
Figure 1: Photograph of Tubular Solar Still
Performance of Solar Still
1. The expression for overall thermal efficiency (ηpassive)
ηpassive =
∑୫∗୐
୅౭⨜୍(୲)ୢ୲
m= Productivity, L latent heat of vaporization, Aw area, I(t) solar intensity

3. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print),
ISSN 0976 – 6359(Online), Volume 6, Issue 1, January (2015), pp. 42-46 © IAEME
44
2. ηex =
୉ଡ଼౛౬౗౦
୉ଡ଼౩౫౤
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
( ౐౗
౐౩
)4
]
The exergy output of a solar still can be written as
Exevap = m L[ 1 - (
౐౗
౐౩
)]
Ta ambient temperature, Ts sun temperature (6000 K)
RESULTS AND DISCUSSION
Fig.2: Variation of solar intensity with respect to time on a particular day in the month of March
Fig. 2 shows the variation of solar intensity on a particular day of testing the tubular solar still
in the month of March .The maximum intensity of 1000 W/m2
is received at 12:00 hrs.
Fig 3: Variation of wind speed with time on a particular day
Fig.3 shows the variation of wind speed on a particular a day in the month of March .The
maximum wind speed is 1.7 m/s at 2:00 hrs.
0
200
400
600
800
1000
1200
S0larIntensity(w/m2)
Time of a day(hr)
0
0.5
1
1.5
2
windspeed(m/s)
Time of a day (hr)

4. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print),
ISSN 0976 – 6359(Online), Volume 6, Issue 1, January (2015), pp. 42-46 © IAEME
45
Fig.4: Variations of water temperature, PCM temperature, basin temperature, condensing cover and
ambient temperature with respect to time on a particular day
Fig.4 shows the variations of water temperature, PCM temperature, basin temperature,
condensing cover and ambient temperature with time on a particular day. After sunshine, heat
transfer takes place from basin water to PCM. Water temperature starts decreasing in after noon but
water and PCM temperature equals at around 4 ‘O’ clock. When water temperature decreases, PCM
starts discharging heat to the water and nocturnal productivity increases.
Relationship between basin water temperature and distillate output
Fig.5: Variation of productivity with water temperature
During the experiments, the water temperature Tw was varied between 350
C and 590
C. The
following empirical relationships were obtained for mean hourly stationary productivity as function
of water temperature. P = 5.489Tw -169.9.
CONCLUSION
Experiments were carried out on a tubular solar still integrated with stearic acid as energy
storage material in Allahabad climatic condition. Some important conclusions were drawn:
• Daily energy efficiency of 21.87 % is obtained.
• Instantaneous exergy efficiency varies between 0.05 and 6.59.
• Daily exergy efficiency of 0.857 % is obtained.
0
10
20
30
40
50
60
70
Temprature(0c)
Time of a day (hr)
Tw
Tpcm
Tb
Tci
Tco
Ta
P= 5.498Tw - 169.9
R² = 0.804
0
20
40
60
80
100
120
140
0 10 20 30 40 50 60
Productivity(ml)
Tepmpature (oC )

5. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print),
ISSN 0976 – 6359(Online), Volume 6, Issue 1, January (2015), pp. 42-46 © IAEME
46
• An empirical relation for productivity P = 5.489Tw -169.9 is developed and the value of R2
is
equal to 0.804, shows good agreement with the experimental results.
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