20120140503001

International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 –
6480(Print), ISSN 0976 – 6499(Online) Volume 5, Issue 3, March (2014), pp. 01-08, © IAEME
1
EXPERIMENTAL STUDY OF A TUBULAR SOLAR STILL INTEGRATED
WITH A FAN
Ihsan Mohammed Khudhur*, Dr. Ajeet Kumar Rai**
*Technical College Kirkuk, Foundation of Technical Education,
Ministry of Higher Education and Scientific Research, Republic of Iraq
**Department of Mechanical Engineering SSET, SHIATS- DU Allahabad (U.P) INDIA- 211007
ABSTRACT
In this commutation, an attempt has been made to increase the productivity of a tubular solar
still. A tubular solar still was designed fabricated and tested in the Allahabad climatic conditions.
Basin was made up of GI sheet and painted black to increase its absorptivity. Condensing cover
made of polycarbonate sheet. Number of experiment was conducted to read the behavioral variation
inside the still. A fan is used to increase the rate of evaporation and condensation inside the still. It is
observed that by using fan inside the still, daily productivity increased by 8.5%.
Keywords: Tubular Solar Still, Condensing Cover Temperature, Heat & Mass Transfer Coefficient.
INTRODUCTION
Water production from a solar still is expressed as the amount of produced distilled water
per day per unit of basin surface. Water production depends strongly by the amount of the falling
solar energy. In a given location, it depends by the existing climatic conditions and the time of the
day and year. So, it takes maximum values during sunny and warm days of summer and midday and
it takes minimum values in winter time. Since solar energy per unit surface is standard by nature,
production of a given installation increases only with the increase of the surface of the still. The
output of a one-stage solar still is within 1-2 l/m2
per basin area per day in winter time and within 3-4
l/m2
per basin area per day for summer time(Cooper,1969, .Malik et. al, 1982, E.E. Delyannis,
1991,Guinn, 1992, O.A. Hamed, et. Al., 1993). Efficiency of solar stills varies in the range of 25-
40% in winter time and in the range of 30-60% in summer time, depending of course on the design,
construction and environmental and operating conditions.
INTERNATIONAL JOURNAL OF ADVANCED RESEARCH IN ENGINEERING
AND TECHNOLOGY (IJARET)
ISSN 0976 - 6480 (Print)
ISSN 0976 - 6499 (Online)
Volume 5, Issue 3, March (2014), pp. 01-08
© IAEME: www.iaeme.com/ijaret.asp
Journal Impact Factor (2014): 4.1710 (Calculated by GISI)
www.jifactor.com
IJARET
© I A E M E

2
The solar distillation systems, which differ mainly in the geometry of the distillation unit, in
the used materials and in the several techniques for the increase of output, are continuous objects of
research work. However, all designs and types are based on the same operation principle. The
simplest unit for solar distillation is the one-stage solar still. These units are placed either in the
ground or on bases. The low productivity of solar stills has leaded the researchers to several efforts to
increase productivity. These are focused on the design of the several parts of the solar still,
concerning the geometry, the material, the operating parameters or the use of techniques to increase
productivity. Tubular Solar Still (TSS) consists of a transparent tubular cover made of polycarbonate
and a trough inside the cover. Consequently, the weight of the TSS became much lighter than that of
the basin type with a glass cover. The TSS, therefore, can be easily built on-site without using special
tools. This easy assembly helps shortening of water transportation distance. The scope of the efforts
on the design of the solar still is to find the optimum parameters concerning the productivity of the
solar still. A basic parameter in the output of solar stills is their geometry, mainly concerned on the
shape and the slope of the transparent cover. For the determination of the slope of the cover the
installation area, the volume of the air-tight area inside the still and the type of the cover material
have to be taken into account. Transmittance of the material takes the maximum values when solar
radiation falls vertically on the cover, whereas it is decreased significantly with the increase of
incidence angle of solar radiation. For the mild climate zones this means large volumes of air-tight
area inside the still, which decreases the output. On the contrary, small slopes mean smaller volumes
of air-tight area inside the still which increases output, however there is the danger of increased
losses due to the falling of water condensate back to the mass of the saline water in the basin before
it is collected as output. It has been reported that there is an optimum slope of the cover, concerning
the water production. This lies between 100
and 250
for regions with mild climate, whereas for hot
regions it is between 350
Akash, et al., (2000). But in other reports it is said that in hot regions the
optimum slope of the still cover is around 150
(S. Kumar et al. 2000). Moreover, the thickness of the
cover plays important role in the output because the increase of thickness means decrease of the
transmittance of the cover to solar energy. It has also been reported that the increase of thickness
causes reduction on the output larger than the output that would mean the respective reduction of the
transmittance of the cover. Finally, the use of double cover reduces the output by 25-30% and it
increases also the cost of the solar still. The output of the solar still increases when the distance
between the basin and the surface where condensation takes place decreases (Satcunanathan and
Hansen, 1973). However, in some other experiments it has been seen that the influence of this
distance is not crucial for low values of solar radiation. The material of the basin plays important role
in the output of the solar still. It has been reported that the use of black plastic wick increase the
output by 38 - 60%. Akash, et al., (1998). Other absorbing materials for the still basin, black rubber
can also be used with an increase of output of about 20%. Generally speaking, the increase of the
absorptance of the basin material increases the still output. The depth of the saline water is also an
important factor for the still output. It has been reported that it does not play important role in well
insulated stills, but it has significant influence in not insulated ones, especially in smaller depths (
Fath, 1996; Kumar, et al., 2000). It has been reported also that for water depth of more than 10 cm
there is not essential change in the distilled water productivity, when all other parameters are kept
steady. Insulation of the basin plays important role in the output of the system, and its effect is seen
mainly in smaller water depths. It has been shown that the decrease of the heat loss coefficient
through the bottom and the sides from the value of 4 W/m2
C to the value of 2 or 1 W/m2
C it brings
an increase in water production by 20% or 34% respectively Fath, (1996). The effect of climatic
parameters wind on the performance of a single basin type solar still has been studied by different
researchers. Soliman, (1972), has studied the effect of water and ambient temperatures, wind velocity
and angle of inclination of the cover on the performance of the still is shown by means of tables and

3
graphs. This leads to the explanation that at low water temperatures, the rate of evaporation is low.
Whereas at high water temperatures, increasing wind speed will increase the ratio of rate of
evaporation to the total heat transfer through the cover. Nafey, et al., (1997), has studied the various
parameters affecting the solar still productivity. In this work, investigation of the main parameters
affecting solar still performance under the conditions of Suez gulf was considered. A general
equation relating the dependent and independent variables which control the daily productivity of a
single slope solar still is developed. This equation could be used to predict the daily productivity
with a reasonable confidence level (max. error ±5%). Hinai, et al. (2002) formulated a mathematical
model to predict the productivity of a simple solar still under different climatic, design and
operational parameters in Oman. The shallow water basin, 230 cover tilt angle, 0.1 m insulation
thickness and asphalt coating of the solar still were found to be the optimum design parameters that
produced an average annual solar still yield of 4.15 kg/m2 day. Investigators’ ideas about the effect
of wind on solar stills vary (telkes,1956; Lof et al. 1961; Hollands 1963) state that increasing wind
velocity causes a decrease in the output Cooper (1969) points out that increasing wind velocity
causes an increase, the influence of wind on output is unimportant. that wind blowing over the glass
cover causes faster evaporation. As the wind velocity increases, the convective heat transfer
coefficient from the glass cover to ambient air increases and simultaneously the glass cover
temperature decreases. Due to this, the temperature difference between water surface and the glass
cover increases and ultimately the yield of the solar still increases as compared to stagnant ambient
air conditions. As the wind velocity over the solar still increases, the distillate yield of the solar still
increases continuously. The wind velocity is more effective in summer and at higher water masses
and it was found tobe10and8m/s on typical summer and winter days, respectively .It was found that
productivity increases with the increase of wind speed up to atypical velocity beyond which the
increase in productivity becomes insignificant El-sebaii (2000)
EXPERIMENTAL SETUP
A prototype solar still having a horizontal tray which acts as absorber of 0.62 m2
was
designed and constructed rai et al. (2013). Tray was constructed using galvanized iron sheet of
thickness 0.5mm and later on painted in black. The try is surrounded by tubular structure made up of
Polycarbonate sheet. The total area of the Polycarbonate cover is 2.6 m2
. The still is formed a tubular
transparent surface made up of Polycarbonate sheet. Testing was performed by placing the tubular
solar still operating in sunlight for a 24-h period. The work has led to the development of the tubular
solar still and to an 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 other type of
basin type solar still. The present study was concerned with the modified design of TSS and
development of models with improved rate of evaporation and condensation on the inner surface of
the tubular cover. Copper-Constantan thermocouples are used, along with a digital temperature
indicator, to record the condensing cover temperature, water temperature and water vapor
temperature in the experimental setup. These thermocouples, over a prolonged usage period, tend to
deviate from the actual data. 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 figure. 1.
To find the effect of addition of a fan in the TSS, number of readings was taken on this setup for
different seasons of Indian climatic conditions. For a particular day in the month of February,
readings taken with and without the addition of a fan are shown in the table 1and table 2.

4
Fig.1. Photograph of Tubular Solar Still
Table 1: Observations without fan in Tubular solar still
T
TIME
T1 ˚
GLASS
T2 ˚
GLASS
T3 ˚
BASIN
T4 ˚
WATER
T5˚
INLET
FPC
T6 ˚
OUTLET
FPC
T7˚
VAP
UP
T8˚
VAP
DOWN
T9˚
AMB.
air
WIND
Velocity
M/S
Distal
ltion
ML
Solar
Intens.
MW/2
08:30 22 19 26 27 39 32 30 26 19 0.5 0 34
09:00 33 26 30 31 39 46 45 30 21 0.5 10 42
09:30 38 29 34 34 39 61 52 33 23 0.8 34 54
10:00 42 32 38 39 39 75 61 36 24 1.1 35 61
10:30 48 35 43 43 40 80 62 37 25 1.0 47 74
11:00 50 37 46 46 41 83 72 40 25 1.0 66 82
11:30 52 39 49 49 41 83 74 42 26 1.0 87 84
12:00 54 41 50 50 41 83 75 42 27 1.0 99 88
12:30 56 43 52 52 43 84 76 44 28 1.2 118 91
01:00 54 41 51 51 43 83 74 43 29 1.0 121 86
01:30 53 42 53 52 46 83 75 44 30 1.0 125 85
02:00 52 42 52 52 48 83 76 44 31 1.2 120 77
02:30 48 41 51 51 50 81 74 44 32 1.1 116 68
03:00 49 41 50 50 51 74 61 43 31 1.5 106 57
03:30 46 41 49 49 52 71 70 42 30 1.1 95 42
04:00 42 39 47 47 52 62 67 41 29 1.0 87 31
04:30 36 34 42 42 51 51 61 39 27 1.0 64 19
05:00 32 31 38 39 51 41 58 36 26 1.0 48 9

5
Table 2: Observations with fan in Tubular solar still
RESULTS AND DISCUSSION
The variation of vapor temperature inside the solar still above and below the basin at a water
depths of 2 cm are shown in fig.2. As the vapor leaves the water surface its tendency is to rise up, it
reaches to top cover surface and starts condensing. The presence of vapor particle below the basin
are less, due to this reason temperature below the basin is low which is shown in fig. 2 by Tbb (
temperature of vapor below the basin). A large temperature difference exit between temperature of
vapor above the basin and temperature below basin.
Fig. 2: Variation of Temperature with and without fan with time of a day on 12 February 2014 water
depth 2 cm
T
TIME
T1 ˚
GLASS
T2 ˚
GLASS
T3 ˚
BASIN
T4 ˚
WATER
T5˚
INLET
FPC
T6 ˚
OUTLET
FPC
T7˚
VAP
UP
T8˚
VAP
DOWN
T9˚
AMB.
air
WIND
Velocit
M/S
Distal
ltion
ML
Solar
Intens.
MW/C
M2
08:30 22 17 15 15 40 42 28 21 14 0.8 0 33
09:00 31 22 24 25 40 61 33 26 16 0.8 20 52
09:30 33 24 27 27 40 72 31 29 18 1.0 35 65
10:00 38 27 32 32 41 83 37 33 18 1.3 45 70
10:30 42 30 37 36 42 84 41 36 19 1.2 50 74
11:00 45 31 41 39 42 89 43 39 20 1.4 63 82
11:30 47 33 43 42 42 90 45 40 21 1.3 80 90
12:00 49 34 45 43 44 85 47 41 22 1.2 109 96
12:30 51 37 48 46 46 89 52 40 23 1.3 115 94
01:00 51 38 49 47 48 82 54 41 24 1.5 117 88
01:30 49 36 48 46 47 81 52 40 25 1.2 122 84
02:00 46 36 48 46 45 80 58 40 26 1.1 144 79
02:30 46 36 47 45 45 80 47 39 25 1.4 115 71
03:00 43 36 46 45 46 81 44 39 24 1.7 110 62
03:30 38 32 43 42 45 73 42 38 24 1.7 107 52
04:00 36 31 41 40 45 62 41 38 24 1.1 100 42
04:30 31 28 38 36 45 53 40 38 23 1.2 99 22
05:00 28 26 35 33 45 39 36 35 22 1.2 65 9

6
Fig. 2 shows the varation temperature of vapor above the basin and below the basin inside the
basin with and without fan at water depth of 2 cm. Temperature of above the basin is higher without
fan than Temperature of vapor above the basin with fan because of forced convection inside the still.
Fig.3: Variation of temperature with and without fan with time of a day on February 2014 water
depth 2 cm
Fig.3 shows the temperature of cover with and without fan. Cover temperature decreases
when fan is used. A maximum of 15% temperature of the cover is reduced by using the fan.
Temperature of vapor above the basin is higher without fan than Temperature of vapor above the
basin with fan. Because of air velocity temperature of condensing cover decrease which increase
∆T(TW-TC). Which increase the total productivity of the still.
Fig. 4: Variation of Productivity with and without fan February 2014 water depth 2 cm
Fig.4 shows the productivity of tubular solar still in natural convection mode and in forced
convection mode. Forced convection is induced inside the still with the addition of a fan. It is
observed that the day time productivity increase by 8.56%and for night productivity is increased by
7.95%

7
CONCLUSION
A modified tubular solar still is designed, fabricated and tested in Allahabad climatic
condition. Temperature above the basin and below the basin are quiet different inside the tubular
solar still. A fan is used to push the vapor from hot zone towards the cold zone and towards the
condensing cover side thereby increasing the rate of evaporation and condensation inside the tubular
solar still. An increase in water temperature and decrease in condensing cover temperature is
recorded. Day time productivity increases by 8.56% and with use of this fan night time production
increases by7.95%.
REFERENCES
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