Productivity enhancement of Evacuated Tubes solar still of different water depth: Thermal modelling and an Experimental analysis.

Abstract

In this research article, the author has conducted the comparative thermal experimental analysis and investigation on Conventional still and Modified Evacuated Tubes solar still with different water volume of 30 and 50 Litre in Basin, in respect of Energy Balance Equation. The various variable elements have been taken into account and duly calculated for both the stills i.e. active still and passive still, based on thermal modelling. The variables calculated comprise inner glass surface temperature, distillate yield, basin water temperature etc. The entire study has been carried out at Akison’s Solar Equipments Pvt. Ltd., Shirwal, Maharashtra, India (latitude18.14° N: longitude 73.97° E), with adequate instrumental infrastructure setup appropriate for the purpose. The investigation concluded that there is substantial escalation of. 242% and 246% at 0.03 and 0.05m of water depth respectively in the yields obtained from Modified Evacuated Tubes solar still in comparison of Conventional still. It has been observed that theoretical outcomes from thermal modelling and the outcomes attained from experiments done for simple and modified stills are in respectable consensus.

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Productivity enhancement of Evacuated Tubes solar still of different
water depth: Thermal modelling and an Experimental analysis.
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ICFEST 2020
IOP Conf. Series: Materials Science and Engineering 1065 (2021) 012013
IOP Publishing
doi:10.1088/1757-899X/1065/1/012013
1
Productivity enhancement of Evacuated Tubes solar still of
different water depth: Thermal modelling and an Experimental
analysis.
Sunil More1, Joseph Daniel2
Research Scholar1, Associate Professor2, Department of Mechanical Engineering, School of
Mechanical Engineering (SMEC), VIT University-Chennai, Tamil
nadu, India
Email-sunil.more33@gmail.com
Abstract. In this research article, the author has conducted the comparative thermal experimental
analysis and investigation on Conventional still and Modified Evacuated Tubes solar still with
different water volume of 30 and 50 Litre in Basin,
in respect of Energy Balance Equation. The
various variable elements have been taken into account and duly calculated for both the stills i.e.
active still and passive still, based on thermal modelling. The variables calculated comprise inner
glass surface temperature, distillate yield, basin water temperature etc. The entire study has been
carried out at Akison’s Solar Equipments Pvt. Ltd., Shirwal, Maharashtra, India (latitude18.14° N:
longitude 73.97° E), with adequate instrumental infrastructure setup appropriate for the purpose. The
investigation concluded that there is substantial escalation of. 242% and 246% at 0.03 and 0.05m of
water depth respectively in the yields obtained from Modified Evacuated Tubes solar still in
comparison of Conventional still. It has been observed that theoretical outcomes from thermal
modelling and the outcomes attained from experiments done for simple and modified stills are in
respectable consensus.
1. Introduction.
Water establishes the primary component for the endurance of life on planet earth and the reduction of
drinkable water source, attributed to various reasons such as rapid increase in population, industrial
revolution, climate changes resulting in frequent droughts, underground pollution, is quite alarming. Earth
surface comprises 71% of water and out of that, most of it, say around 98.8% of it, is not fit for human
consumption. That leaves only 2.5% of total the water available on earth fit for drinking. [1]
There are different methods are available to get distilled water but these various methods of water
distillation require fossil fuels and electricity. Solar distillation is one of the simplest and eco-friendly
technique which uses solar energy as renewable form of energy and it is also non-polluting. So, it is
effectively used in costal and remote areas where electricity is unavailable t
o reduce water scarcity problem.
Solar Still is an environment friendly green energy device, categorized into Active and Passive Solar
Still, in which solar energy is primarily employed for purification of water via distillation practice. The

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difference between Active and ‘Passive Solar Still being that in former, in comparison to the latter,
additional thermal energy is also utilized to gain potable water. The outcome of the Passive Solar Still is
quite less and to increase the desirable outcomes, a lot of research work has been poured into the issue to
develop various techniques.
Dimri et al [2] carried out experimental work on the Conventional solar still with copper, glass and
plastic as ‘condensing cover material’ and came to conclusion that the highest outcome was obtained with
copper due to its higher thermal conductivity. Rai and Tiwari [3] performed experiment on ‘Solar Still’
accompanied with ‘Flat Plate Collector’ and observed that the productivity got accelerated by 24%. In the
experiment carried out by Velmurugan et al.[4], a mini solar pond combined with a Conventional
Still
was
constructed and the observations came out that the outcome rate of water in a Solar Still with sponge and
combined with a Mini Solar Pond and Ordinary Solar Still were 3.14 and 4.65 kg/m2/day respectively,
escalating productivity thereby by 48%. Badran et al and Tiris et al [5, 6]
utilized
a Flat Plate Collector with
a Single Basin Solar Still and observed 52% escalation in the production of drinkable water. Dashtban M et
al [7] experimented using the Latent Heat Thermal Energy Storage System in a specially designed Weir
Type Cascade Solar
Still, to increase the outcome. Prabahar et al [8] studied Modified Double Slope Solar
Still. An escalation by 14% in outcome was noticed by utilizing Flat Plate Collector’, an escalation of 10%
with sponge and 17% by sponge and Flat Plate Collector.
H. Kargar Sharif Abad et.al.[9] i
ntroduced a Solar Desalination System by using a
Pulsating Heat
Pipe and noticed 875 ml/(m2.h) increase in outcome. Z. M. Omara et al, [10] experimented on developed
Solar Still with Solar Concentrator. The productivity was increased by 244% and 347% respectively without
and with preheating of the brackish water. An inclined solar system was mo
delled and simulated by Hikmet
S.Aybar [11] .The result showed that the system generated distilled water of 3.5-5.4 Litre/m2 and also
maximum temperature of hot water reached to 600C. Hitesh N. Panchal [12] worked on double basin solar
still combined with Vacuum
Tubes and Black Granite Gravel
placed in basin water to enhance the
productivity. Anil Kr. Tiwari et.al [13] performed experiment on Conventional Solar Still for different water
volumes with cover inclination angle of 300 and also thermal modelling of the system was carried out. The
experimental yield was
found in good agreement with theoretical values obtained from thermal modelling.
Hitesh N. Panchal [14] worked on the Evacuated Tube Solar Still and noticed a considerable increase in the
average distillate output. Rahul Dev et.al [15] conducted experiment on an Inver
ted Absorber Solar Still
(IASS) and Conventional Solar Still (SS) at diverse levels of water depth and they found that higher basin
water temperature and yield was obtained with IASS as compared with simple still.
Under Natural Circulation Mode. K. Sampathkumar et al [16] experimentally and theoretically
studied Evacuated Tube Solar Still. The results concluded that the performance of Evacuated Tube Solar
Still is much higher than the Conventional Solar Still throughout the year. It was observed by Selcuk Selimli
et al [17] that the productivity was considerably enhanced by about 62.5%, when Solar
Vacuum
Tube was
integrated with Simple Solar Still. An experiment was carried out by Ali.F. Muftaha et al [18] on Stepped
Solar Still integrated with internal and external reflectors, external condensers along with absorber
materials, which yielded 29% escalation in the daily outcome of modified solar still. K
. Sampathkumar
[19]
worked on Vacuum tube solar still and noticed that daily outcome was increased by 49.7% and it increased
further to 59.48% when coupled with black stones and vacuum tubes. Lilian Malaeb et al [20] studied
analytically the modified still with rotating drum to optimize the performance and concluded a noticeable
escalation in the productivity was observed in comparison of a Conventional Solar
Still
.
Hence to enhance the yield from Solar Still, various methods are tried by researchers like use of
Flat Plate Collector, concentrating collector, heat pipes, reflectors and internal and external condensers, air

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blower with solar still. Also provide vacuum condition in still, incorporate the phase change materials,
sensible heat storage and Nano materials, wick materials and dyes in basin water. Evacuated tube solar still
is more efficient as there is no loss of energy through vacuum. The solar radiations are positively tracked
continuously through- out the day due to its cylindrical shape. The incident angle of sunlight on the
cylindrical tubes is at 900 thought the day; hence the peak absorption is always for it so it’s thermal
performance is higher than other collectors.
The core objectives of the research are:
• Thermal modelling of Conventional Solar Still and Evacuated Tubes Solar Still with natural circulation
for
different water
depth in Basin.
• Validation of the values like hourly inner glass surface temperature, basin water temperature and distillate
yield with Experimental values.
• To evaluate the potential of active solar still by comparing its performance parameters with conventional
still.
2. Experiment.
The experiment set was designed and installed at Akison’s Solar Systems Pvt. Ltd. at Shirwal
(Latitude18.14° N: Longitude 73.97° E), Maharashtra (India) and as shown in Fig.1.For the experiment
Solar Still Basin used with inner side painted in black up to 10mm high so that it could absorb maximum
solar radiation. It is made up of galvanized iron plates, 1.5mm thick and 1m × 1m area, with bottom and all
sides of it are comprised of Rockwool insulation (50mm thick) with thermal conductivity of 0.045W/mK to
achieve minimum heat loss
from it. A toughened glass (4mm thick) was fixed, at upper side of Solar Still at
190 angles, in accordance with horizontal axis (Latitude of Shirwal), which acts as condensing surface. The
glass was tightened with solar still by a silicon rubber sealant to prevent the vapour
leakage from the system.
The condensate water from inclined glass cover was collected in U shape mild steel channel which is located
at lower side of solar still. A rubber pipe was utilized to accumulate distillate in measuring jar from
collection tray. A hole had been drilled in Solar Still body to attach ‘K Type Constantan Thermocouples’ to
measure basin, water and inner glass cover temperature respectively. The same material and Dimensions
was used for active solar still. Total 13 holes of diameter 0.063 m were made at the
bottom end of front wall
of the Solar Still to attach the one end of same number of Evacuated tubes with specifications of length
1.8m, outer diameter 0.058 m, inner diameter 0.047m and glass thickness of 0.0016m, with the help of
rubber gaskets, at an angle of 300
with horizontal surface, and whose other ends were fixed at
a metal frame
connected to the Solar Still stand again at 300 angle.
3. Instrumentation.
 For the accurate measurement of radiation from sun incident on the ‘Solar Still’ surface, a calibrated
solarimeter was used with a range of 0-1200 W/m2 & accuracy of
2
1/Wm
.

For accurate measurement of water temperature in the basin, inner glass cover and ambient temperature, ‘K
type Thermocouples ‘were used with accuracy of
0
0.1 C
.
 For measurement of wind velocity, an ‘Anemometer’ with range of 0-15m/sec & accuracy of
0.2 / secm
was used.
 A plastic jar of 1 litre capacity with an accuracy of
10ml
was used to collect the distillate yield.
Extensive experiments were carried out on both Simple solar Still and Active Solar Still with water depths
precisely 0.03m and 0.05m during May 2019 from 9 am to 6 pm on clear sunny days.
Dimensions of experimental set up are shown in Table No.1

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Figure 1. Schematic diagram of the experimental setup.
Table 1. Dimensions of experimental set up
Particulars
value
Simple Solar Still and Active Solar Still Area. (As and Aa)
1m2
Evacuated Tubes Area integrated with Solar Still (Al)
3.455 m2
Absorber area of evacuated tubes. (AET)
1.099m2
Solar still outer area.
1 m× 1m
Glass cover inclination to horizontal.
19 0
Length of each evacuated tubes
1.8 m.
Inner diameter of evacuated tubes
0.047 m
Outer diameter of evacuated tubes
0.058 m
Glass thickness in each evacuated tube.
0.0016m
Table 2.
List of various ‘Constants and Designs’ parameters employed in theoretical modelling.
Parameters
Value
Parameters
Value
αb
0.36
Cw
4190 J /Kg 0 K
αg
0.05
hw
250 W/m2K
αw
0.34
t
3600 s
FR
0.831
σ
5.67× 10-8 W/ m2K
Mw
30 and 50 kg
(α) e
0.8
εeff
0.82
ULC
2.44 W/ m2K
Li
0.05m
htg
5.7+3.8 Va, Va=4 m/sec
Ki
0.045 W/ mK
L
2.25 ×105 J/Kg

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4. Thermal modelling:
The Thermal Model of Conventional Solar Still and Evacuated Tubes Solar Still is developed by utilizing
First Law of Thermodynamics.
For analysis the following assumptions are made:
 No vapour leakage in Solar Still.
 Glass cover, basin liner and insulation are having negligible heat capacity.
 Steady state condition is reached at every hour.
 Across the glass cover of the Solar Still and Basin water of the ‘Solar Still, no temperature gradient
exists.
 No change in the water level inside the Solar Still Basin throughout the experiment. It is maintained
constant.
 Inside the glass cover, it has been assumed that only film type condensation of water occurs.
4.1 Energy Balance of Glass Cover
'[ ]
cw ew rw
g effs cg rg
I qqq qq

 
'()()
g effs tw w g tg g a
IhTThTT


(1)
The rate at which glass absorbs solar energy and sum of energies transferred from water surface via
radiation, convection & evaporation to glass are equivalent to energy lost by glass to atmosphere via
convection & radiation.
tw cw ew rw
hhhh
The ‘Convective Heat Transfer Coefficient’ between water and glass [21] has been given by
1/3
3
( ) ( 273)
0.884 [( ) ]
268.9 10
wg w
cw w g
w
PP T
hTT P



(2)
The ‘
Evaporative Heat Transfer Coefficient’
between water and glass [21] has been given by
3
16.273 10 ( )
cw w g
ew
wg
hP P
hTT

 


(3)
The ‘Radiative Heat Transfer Coefficient’ between water and glass [21] has been given by
22
( 273) ( 273) ( 546)
rw eff w w g
hTTgTT

   
(4)
Where
eff

= The ‘Effective Emissivity
’
between the water surface and the glass cover has been taken [22]
as 0.82.
The total ‘Heat Transfer Coefficient’ between glass and atmosphere [23] is given by
5.7 3.8( )
tg
hv
(5)
V has been
taken as 4 m/sec for numerical calculations.
The ‘glass cover temperature’
g
T
is derived from energy balance equation as
'
g effs tw w tg g
g
tw tg
IhThT
Thh




(6)

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4.2 Energy Balance for Basin Liner
The energy transferred to water by convection and conduction energy lost from bottom and sides of the
basin are equivalent to the rate of solar energy absorbed by basin
'(1')(1')
b g w effs w b
Iqq
 
 
'(1')(1') ( ) ( )
b g w effs w b w b b a
IhTThTT
 
 
(7)
The ‘Convective Heat Transfer’ between basin and water is given by [4]
()
wwbw
qhTT
(
8)
The ‘Convective Heat Transfer Coefficient’ between basin and water is taken as 135 W/m2 K. [4].
The ‘Conductive Heat Transfer’ between basin and atmosphere is given by (22)
()
bbba
qhTT
(9)
The ‘Basin Liner Temperature’
b
T
is derived from ‘
Energy Balance Equation’
of the basin liner
'
effs w w b b
b
wb
bI h T h T
Thh




(10)
Where
'b


=
'(1')(1')
bg w
 

4.3 Energy balance of water mass for ‘Simple Solar Still’
The heat deposited due to solar energy in water and the heat transferred to glass cover is equivalent to the
radiation energy absorbed by water mass in basin and convective heat gained from basin liner.
' (1 ' ) ( ) [ ]
W
w g effs w W cw ew rw
dT
I q MC qqq
dt

 
(11)
Substituting Equations 6 and 10 in Equation 11, the following Differential Equation is obtained.
()aT
dTw
dt wft
(12)
Where
()
effs
w
UA
aMC

&
() ()
effs effs
w
IA UA Ta
ft MC


Expressions for
effs
UA
&
effs
IA
are given in the Appendix
To obtain the approximate analytical solution, the following assumptions have been made. The time interval
(0 )ttt
is small
a is constant during the time interval
t
1) The function
()ft
is constant i.e.
()ft
=
()ft
for the time interval between 0 and
t
In equation 12, by using initial condition at
0t
,
(0)Tw t Two
, the expression for water temperature
is derived as
()
[1 ]
at at
ft
Tw e Twoe
a


(13)
The following expression is used for deriving the hourly yield:

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,()
3600
ew g w g
ew s
hTT
mA
L


(14)
4.4 Energy Balance of water mass for Solar Still with evacuated tubes
The Radiation Energy absorbed by water mass in basin and Convective Heat gained from basin liner and
heat energy supplied to basin water from Evacuated tubes is equivalent to the heat stored in water and heat
transfer to glass cover.
' (1 ' ) ( ) [ ]
W
w g effs w u W cw ew rw
dT
I qQMC qqq
dt

 
(15)
The Thermal Energy supplied to the Solar Still via Evacuated Tubes has been given by [22]
[ ( ) ( ) ( ) ]
L
u R e effe LE w a
ET
A
QF TI U TT
A

 
(16)
Substituting equations 6 and 10 in Equation 15, the following differential equation has been obtained.
()aT
dTw
dt wft
Where
()
effe
w
UA
aMC

and
() ()
effe effe
w
IA UA Ta
ft MC


Expression for
effe
UA
and
effe
IA
are given in the Appendix.
To derive the approximate analytical solution, the same assumptions were made as in the case of Simple
Solar Still. By using initial condition at
0t
,
(0)Tw t Two
The expression for
Water
Temperature has been obtained as
()
[1 ]
at at
ft
Tw e Twoe
a


MATLAB 14’ which is primarily used for computing various Heat Transfer Coefficient has been utilized
to develop the Thermal Model. In order to compute various Heat Transfer
Coefficients,
the values of various
designs and climatic parameters are prerequisites and which are duly provided in Table 2. The values of
Heat Transfer Coefficients are further utilized for computing the theoretical values of inner glass surface
temperature, water temperature and hourly yield, by giving initial values of glass and water temperature.
The values of solar radiation and ambient temperature have taken with respect to daily observation. Figure
2 represents a flow chart
for computation of theoretical values.

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Figure 2. Flow Chart representing ‘Computer Model of Solar Still’

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Table 3. Ambient (Ta), Water (Tw) and Inner Glass cover Temperature (Tg) for 0.03-meter water
depth solar still.
Time
of the
Day
Ambient Temperature
T
a(o C)
Water Temperature
Tw (o C)
Inner Glass cover Temperature
T
g (o C)
Passive Still
(31-05-19)
Active Still
(29-05-19)
Passive Still
(31-05-19)
Active Still
(29-05-19)
Passive Still
(31-05-19)
Active Still
(29-05-19)
9
33
36
40
44
42
45
10
37
39
47
55
49
54
11
40
40
58
69
58
62
12
41
41
65
76
63
70
13
43
42
72
84
67
75
14
42
42
74
88
68
79
15
41
43
72
89
64
81
16
40
42
69
86
59
77
17
35
39
58
82
48
72
18
33
35
53
75
42
63
Table 4. Ambient (Ta), Water (Tw) and Inner Glass cover Temperature (Tg) for 0.05-meter water depth
solar still
Time
of the
Day
Ambient Temperature
Ta (o C)
Water Temperature
T
w (o C)
Inner Glass cover
Temperature T
g (o C)
Passive Still
(01-06-19)
Active Still
(30
-05-
19)
Passive Still
(01
-06-
19)
Active Still
(30
-05-
19)
Passive
Still
(01-06-19)
Active Still
(30-05-19)
9
32
35
31
41
35
40
10
33
36
37
49
42
47
11
35
38
45
60
46
55
12
36
39
53
70
55
63
13
37
40
59
78
58
71
14
40
41
64
83
60
75
15
41
43
65
85
59
78
16
39
41
64
86
56
77
17
38
40
61
82
53
73
18
36
35
57
75
49
65
5. Result and Discussion.
In this experiment, various values derived from Theoretical Modelling were tested, verified and validated
with experimental results for
various water depths for
both Active and Passive Solar Still. The hourly
variations of water and glass temperatures for Evacuated Tubes Solar Still and Conventional Solar Still with
0.03 m water depth have been demonstrated in Figure 3 and 4, wherein it has been revealed that the

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maximum temperature of water (89 oC) and glass (81 oC) are obtained in Evacuated Tubes Solar Still at 15
hours, which are considerably higher than the Simple Solar Still’s water (74 oC ) and glass (68 oC)
temperatures at 14 hours for the same water depth.
Figure 3. Hourly variation of theoretical and experimental water temperature for 0.03 m water depth solar
still.
Figure 4. Hourly variation of theoretical and experimental glass temperature for 0.03 m water depth solar
still.
From figure 5 and 6 ,we can perceive that the maximum temperatures of water (86o C) and glass
(77o C) have been obtained in Evacuated Tubes Solar Still at 16 hours, which are considerably greater than

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the Simple Solar Still water(65oC ) and glass (59 oC) temperatures at 15 hours for 0.05 m water depth.
Water and glass temperature values are higher in Evacuated Tubes Solar Still for both the water depths. It
is because the Evacuated Tubes provide extra thermal energy to basin water. Also it could be observed from
figure 1 to 4 that the theoretical values of water and glass temperatures support the corresponding values
with experimental results
and are in good agreement.
Figure 5. Hourly variation of theoretical and experimental water temperature for 0.05 m water depth solar
still.
Figure 6. Hourly variation of theoretical and experimental glass temperature for 0.05 m water depth solar
still.

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It also has been discovered that in early hours, the hourly theoretical values of glass and water
temperatures are higher, as in theoretical calculations heat losses are not considered. But in the evening
hours, the experimental values of water and glass cover temperature are higher as they hold the heat as
stored energy. It also has been observed that as the water depth increased from 0.03 to 0.05 m for both
Active and Passive Solar Still, the maximum water and glass temperature attainment time was shifted to 1
hour later as more time is required
to achieve maximum temperature for more water mass.
Figure 7 and 8 reveals the hourly variation of convective, evaporative, radiative heat transfer
coefficients, respectively, for both Simple Solar Still and Evacuated Tubes Solar Still of 30 Litre water in
Basin. The results show that the Evaporative Heat Transfer Coefficient escalates
with time and in the
afternoon hours a decreasing trend is observed in its value attributed to lower temperatures in the evening.
It can be duly observed from figures 7 and 8 that, the values of Evaporative (137W/m2K),
Convective (3.07 W/m2K) and Radiative (8.93W/m2K) heat transfer coefficient are high in Solar Stills
integrated with Evacuated Tubes
than the Simple Solar Still having values of Evaporative (41W/m2K),
Convective (2.30 W/m2K) and Radiative (7.16W/m2K) heat transfer coefficient respectively. Due to higher
temperature difference between water and glass in the Evacuated Tubes Solar Still attributed to additional
thermal energy provided
by evacuated tubes, the values of different heat transfer coefficients are higher in
Evacuated Tubes Solar Still.
Figure 7. Hourly variation of heat transfer coefficient for 0.03 m water depth simple solar still.

ICFEST 2020
IOP Conf. Series: Materials Science and Engineering 1065 (2021) 012013
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doi:10.1088/1757-899X/1065/1/012013
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Figure 8. Hourly variation of heat transfer coefficient for 0.03 m water depth solar still with evacuated
tubes.
Figure 9 and 10 represents the hourly variation in respect of yield obtained from Simple Solar Still
and Active Solar Still for 0.03 m and 0.05 m water depths respectively. It has been observed that as water
depth was increased, the total yield from the Solar Still was decreased for both stills. The higher water depth
increases water mass in basin, which results in more time consumption for evaporation. For this reason, the
basin water temperature and evaporation rate are found less in higher water depth Solar Still, which leads
to decrease in its output. The maximum values of hourly output for Evacuated Tubes Solar Still were 0.88
Litre/m2 / hr. and 0.770 Litre/m2/ hr for 0.03 and 0.05 water depths respectively.
Figure 9. Hourly variation of experimental yield for 0.03 m water depth solar still.

ICFEST 2020
IOP Conf. Series: Materials Science and Engineering 1065 (2021) 012013
IOP Publishing
doi:10.1088/1757-899X/1065/1/012013
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Figure 10. Hourly variation of experimental yield for 0.05 m water depth solar still.
6. Conclusion.
The Thermal Modelling of Conventional Still and Evacuated Tubes Solar Still has been
experimentally confirmed and duly validated for 30 and 50 Litre of water in
the research
. The following
points are highlighted on the basis of experimental and theoretical results:
1. The average water temperature of an Evacuated Tubes Solar Still was found to be increased by 15o C
and 21o C for 0.03m and 0.05 m water depths respectively.
2. Due to additional heat energy supplied by evacuated tubes, the basin water temperature
was found to be
increased in Active Solar Still which further leads to increase in its productivity.
3. The yield of Evacuated Tubes Solar Still has been found as 7.61 & 7.535 Litre/m2/day for 0.03m and
0.05 m water depths respectively, while for Simple Solar Still, it wa
s 3.15 and 3.055 Lit
re/m2/day for
0.03m and 0.05 m water depth respectively.
4. The total and evaporative heat transfer coefficient for an Evacuated Tubes Solar Still has been found
very high, attributed to the higher water temperature difference as compared to conventional Still for
both the respective water depths.
5.
A fairly good agreement has been found between theoretical results obtained fr
om Thermal Modelling
and the Experimental results for both the Solar Stills.

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doi:10.1088/1757-899X/1065/1/012013
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7. References
[1] Gleick, P.H. Water in Crisis: A Guide to the World’s Freshwater Resources; Oxford University Press:
New York ,NY, USA, 1993
[2] Dimri V. ,Sarkar B., Singh U.,and Tiwari G.N. 2008. Effect of condensing cover material on yield of
an active solar still: an experimental validation. Desalination 227: 178-189.
[3] Rai.S.N., and G.N. Tiwari,1983
Single basin solar still coupled with flat plate collector .Energy
Conversion and Management 23 (4) :145-149.
[4] Velmurugan, V, Srithar, K., Solar Stills Integrated with a Mini Solar Pond Analytical Simulation and
Experimental Validation, Desalination 216 (2007), 1-3, pp. 232-241
[5] Ali A. Badran, Ahmad A. Al
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Hallaq, Imad A. Eyal Salman, Mohammad Z. Odat. A Solar Still
Augmented with a Flat Plate Collector Desalination 172 (2005) 3 pp.227-234.
[6] Tiris C. Tiris M. Y Erdalli M. Sohmen Experiental Studies on a Solar Still Coupled with a Flat-Plate
Collector and a Single Basin Still Energy Conversion and Management 39 (1998) 8, pp. 853-856.
[7] Dashtban M, Tabrizi FF,Thermal analysis of a weir-type cascade solar still integrated with PCM storage.
Desalination 2011 279 415–22.
[8] J.Prabahar, Dr.T.Balusamy,Varghese M John, Enhancement of Productivity on Double Slope Single
Basin Solar Still by Flat Plate Collector and Sponge
Applied Mechanics and Materials Vols. 813
-814
(2015) pp 690-694.
[9] H. Kargar Sharif Abad , M. Ghiasi , S. Jahangiri Mamouri , M.B. Shafii, A novel integrated solar
desalination system with a pulsating heat pipe Desalination 311 (2013) 206– 210
[10] Z.M. Omara a, Mohamed A. Eltawil. Hybrid of solar dish concentrator, new boiler and simple solar
collector for brackish water desalination. Desalination 326 (2013) 62–
68.
[11] Hikmet S.. Aybar , Mathematical modeling of an inclined solar water distillation system Desalination
190 (2006) 63–70
[12] Hitesh N.Panchal ,Enhancement of distillate output of double basin solar still with vacuum tubes
Journal of King Saud University-Engineering Sciences (2015) 27,170-175
[13]
Anil Kr. Tiwari, G.N. Tiwari , Thermal modeling based on solar fraction and experimental
study of the
annual and seasonal performance of a single slope passive solar still: The effect of water depths
Desalination 207 (2007) 184–204
[14] Hitesh Panchal.,Anuradha Awasthi, Theoretical modelling and experimental analysis of solar still
integrated with evacuated tubes Heat and Mass Transfer (2016)
[15]
Rahul Dev , Sabah A. Abdul-Wahab , G.N. Tiwari, Performance study of the inverted absorber solar
still with water depth and total dissolved solid. Applied Energy 88 (2011) 252–264
[16] K. Sampathkumar, T. V. Arjunan, M. Eswaramoorthy, and P. Senthilkumar, Thermal Modelling of a
Solar Still Coupled with Evacuated Tube Collector under Natural Circulation Mode. Energy Sources,
Part A 35:1441
–
1455, 2013.
[17] Selcuk Selimli, Ziyaddin Recebli, Semra Ulker, Solar vacuum tube integrated seawater distillation - an
experimental study facta universities , Vol. 14 No 1 2016 pp. 113 – 120.
[18] Ali.F. Muftah, K. Sopiana, M.A. Alghoulc,
Performance of basin type stepped solar still
enhanced
with superior design concepts. Desalination (2017).
[19] Sampathkumar Karuppusamy, An Experimental Study on Single Basin Solar Still Augmented with
Evacuated tubes. Thermal Science: Year 2012 Vol. 16 No.2 pp. 573-581
[20] Lilian Malaeb, Kamel Aboughali , George M. Ayoub , Modelling of a modified solar still system with
enhanced productivity. Solar Energy 125 (2016) 360–372.

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doi:10.1088/1757-899X/1065/1/012013
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[21] D. W. Medugu , L. G. Ndatuwong, Theoretical analysis of water distillation using solar still
International Journal of Physical Sciences Vol. 4 (11) pp. 705-712, November, 2009.
[22] Tiwari G.N.,Dimri V.,Singh U.,Chel A., and Sarkar B., 2007 Comparative thermal performance
evaluation of an active solar distillation system International Journal
of Energy Research 31:1465
-1482
[23] Duffie J.A. and W.A. Beckman 1991. Solar engineering of thermal processes. Wiley Publication.
8. Appendices.
For the purpose of numerical analysis of Simple Solar Still and Evacuated Tubes Solar Still, the below
mentioned Heat Transfer Equations have been employed.
The design parameters of Evacuated Tubes Solar Still has been calculated in the following
expressions.
()() ()
() [' ' ' ]
()
Aeffe ET R e effe effe
wtw
effe b w g
w b tw tg
IAF It
hh
Where hh h h
 
   



The expression of
Aeffs
U
for Simple Solar Still
Where
Aeffs b t
wb
b
wb
tw tg
t
tw tg
UUU
hh
Uhh
hh
Uhh





The expression of
Aeffe
U
for Solar Still integrated with Evacuated Tubes
Aeffe b t L R LC
UUUAFU
9. Nomenclature.
English Letters
AL Area of solar still, m2
AET Diameter of outer glass ×total length of the tubes, m2
Cw Specific heat capacity of Basin water, J/kg K
F
R Heat removal factor
hb Basin liner overall heat transfer coefficient, W/m2K
hw Convective heat transfer coefficient from basin liner to water, W/m2K
hcw Convective heat transfer coefficient from water to glass cover, W/m2K
hew Evaporative heat transfer coefficient from water to glass cover, W/m2K
hrw Radiative heat transfer coefficient from water to glass cover, W/m2K

ICFEST 2020
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doi:10.1088/1757-899X/1065/1/012013
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htg Total heat transfer coefficient from glass cover to ambient, W/m2K
htw Total heat transfer coefficient from water to glass cover, W/m2K
I Intensity of solar radiation, W/m2
Ki Thermal conductivity of insulation material, W/m K
L Latent heat of vaporization, J/kg
Li
Thickness of insulation material, m
Lg Thickness of glass covers, m
Mw Mass of water in the basin, kg
Mew Total distillate output from passive solar still at end of each day (kg)
Pg Partial vapor pressure at inner surface glass temperature, N/m2
Pw Partial vapor pressure at water temperature, N/m2
Qu U
seful thermal energy gain by vacuum
tubes, W/m2
t Time, s
Ta Ambient air temperature, K
Tb Basin temperature, K
Tg Glass inner surface cover temperature, K
Tw Water temperature, K
Ub Overall bottom heat
loss coefficient
, W/m2K
Ut Overall top heat loss coefficient, W/m2K
v Wind velocity, (m/s)
Greek Letters
α Fraction of energy absorbed
τ Absorptance-transmittance product
σ Stefan Boltzman constant,
ε Emissivity
Subscripts
b Basin liner
e Evacuated tubes
eff Effective
g Glass cover
s Solar still
w Water
0 Initial