Productivity enhancement of solar still by using porous absorber with bubble-wrap insulation

Accepted Manuscript Productivity enhancement of solar still by using porous absorber with bubble-wrap insulation

T. Arunkumar, A.E. Kabeel, Kaiwalya Raj, David Denkenberger, Ravishankar Sathyamurthy, P. Ragupathy, R. Velraj PII:

S0959-6526(18)31545-2

DOI:

10.1016/j.jclepro.2018.05.199

Reference:

JCLP 13056

To appear in:

Journal of Cleaner Production

Received Date:

14 January 2018

Accepted Date:

23 May 2018

Please cite this article as: T. Arunkumar, A.E. Kabeel, Kaiwalya Raj, David Denkenberger, Ravishankar Sathyamurthy, P. Ragupathy, R. Velraj, Productivity enhancement of solar still by using porous absorber with bubble-wrap insulation, Journal of Cleaner Production (2018), doi: 10.1016/j.jclepro.2018.05.199

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ACCEPTED MANUSCRIPT

Graphical Abstract

insulation front view, and (b) bottom view

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Productivity enhancement of solar still by using porous absorber with bubble-wrap insulation

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T. Arunkumar*1, A.E. Kabeel*2, Kaiwalya Raj1, David Denkenberger3, Ravishankar

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Sathyamurthy2,4,5, P. Ragupathy6, R. Velraj1

1

1Institute

5 6 7 8 9 10 11 12 13

for Energy Studies, CEG, Anna University, Chennai-600 025, Tamilnadu, India of Mechanical Power Engineering, Tanta University, Egypt 3Department of Civil and Architectural Engineering, Tennessee State University, Nashville, TN, USA 4Department of Mechanical Engineering, S.A. Engineering College, Chennai, Tamilndu, India 5Centre for excellence in energy and nano technology, S.A. Engineering College, Chennai, Tamilndu, India 6Aksheyaa College of Engineering, Pulidivakkam, Kancheepuram-603 314, Tamilnadu, India

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Abstract

15

The present work involves a solar water de-salting system with carbon impregnated foam

16

(CIF) with bubble-wrap (BW) insulation for fresh water productivity enhancement. The said

17

solar water de-salting system is single slope solar still (SSSS) of area 0.50 m2. Four identical

18

SSSSs were constructed and the performance was evaluated in the same climatic conditions

19

of Chennai (13.08°N latitude, 80.27°E longitude). The CIF of diameter 0.17 m and thickness

20

of 0.015 m was allowed to float on the water surface. Since the CIF was open pore and

21

hydrophilic, the floating absorbers acted as thermal storage and increased the evaporative

22

surface area of the basin. The temperature distributions on the floating absorbers are

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investigated with computational fluid dynamics (CFD) analysis. The result shows that the

24

simulation of temperature distribution has good agreement with experimentally recorded

25

data. Three modes of operation were tested: (i) SSSS without insulation, (ii) SSSS with BW

26

insulation and (iii) SSSS-CIF with BW insulation. The results were compared with a

27

conventional solar still (CSS) with sawdust insulation. The climatic parameters like wind,

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ambient temperature, solar radiation and internal temperatures of the SSSS were measured at

29

frequent intervals of time. The water quality tests were carried out and their results were

2Department

1

Corresponding author: [email protected] (AE. Kabeel), [email protected] (T. Arunkumar) [email protected] (Kaiwalya Raj), [email protected] (David Denkenberger), [email protected] (Ravishankar Sathyamurthy), [email protected] (P. Ragupathy), and [email protected] (R. Velraj). 1

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compared with rain water samples. The results showed that the productivity of the SSSS

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without insulation, SSSS with BW insulation, SSSS-CIF with BW insulation and CSS with

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sawdust insulation are 1.9 l/m2/day, 2.3 l/m2/day, 3.1 l/m2/day and 2.2 l/m2/day, respectively.

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Keywords: single slope solar still; carbon impregnated foam; bubble wrap, desalination

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1. Introduction

36

Prof. Stephen Hawking says that people must colonize another planet in next 100

37

years due to serious climate change, population growth and overdue asteroid strikes (Kharpal

38

and Arjun 2017). At the same time, ground water levels are decreasing at an accelerating rate

39

(Shiao et al. 2015). It is our responsibility to bring clean water to the next generation. A

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sustainable way of producing fresh water is solar desalination with brackish water input with

41

minimal CO2 emissions. Solar stills are very well studied over last 30 years by scientists

42

worldwide. The basic idea is sunlight passing through a clear cover and being absorbed by a

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black basin containing salty water. This heats the water, which evaporates and then

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condenses on the cooler cover above. The pure water drains off and is collected. This

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technology is old but effective for the present and future scenarios in remote places.

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Renewable energy is a cleaner way of producing desalinated water in remote and arid regions

47

(Koroneos et al. 2007). Chafidz et al. (2016) designed and developed the portable and hybrid

48

solar-powered distillation system for generating freshwater in arid regions and coastal areas

49

in Saudi Arabia. The result concluded that the fresh water output from the sustainable solar-

50

powered distillation system was 11.53 L/h.

51

Manokar et al. (2018) experimentally studied a photovoltaic-thermal (PVT) solar still

52

varying two parameters: (i) with and without insulation, and (ii) with and without water flow

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over the cover. The dimension of the solar still was 1810 mm × 920 mm × 150 mm. The

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basin of the solar still consisted of a polycrystalline PV panel of efficiency of 13-16%. The

55

result concluded that the sustainable production of an inclined solar panel solar still with side

56

wall insulation was 7.3 kg/m2/day. Abujazar et al. (2018) tested a stepped solar still for sea

57

water desalination. A cascaded forward neural network (CFNN) was also developed for

58

predicting the productivity of the distillation. The result was that the CFNN had more

59

accurate productivity results than the methods of root mean square error (RMSE), mean

60

absolute percentage error (MAPE) and mean bias error (MBE). Kabeel et al. (2018) 2

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experimentally studied graphite in the basin of a solar still. The dimensions of the solar still

62

was 112cm×76cm. The result was that the solar still with graphite sheet gives a yield of 7.73

63

l/m2/day, which is higher than that of the conventional solar still (4.41 l/m2/day). Kabeel et

64

al. (2017) experimentally studied the modified pyramid type solar still with phase change

65

material in the v-corrugated absorber. Two identical solar stills are designed and constructed

66

for experiments. The result concluded that the PCM equipped v-corrugated absorber solar

67

still demonstrates a productivity of 6.6 l/m2/day versus a conventional pyramid solar still of

68

3.5 l/m2/day.

69

Velmurugan et al. (2008) conducted experiments in a single basin solar still with

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sponge cubes, a wick and fins. In this work, 450 sponges of dimensions 20 mm×35 mm×35

71

mm were used. Also five fins with the dimensions of 35 mm×900 mm×1 mm were used in

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the basin. The results showed that the solar still with fins enhanced the productivity. Kannan

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et al. (2014) studied a solar absorption still with different absorbing materials in the basin.

74

The materials used were sponges, gravel, sand, and black rubber pieces. The results showed

75

that the combination of vapor absorption solar still with sponge, sand, and black rubber

76

pieces enhanced the system productivity. Samuel et al. (2016) conducted experiments on a

77

solar still with low cost energy storage materials. The absorbing materials used were spheres

78

and different colored sponges. Each sphere was filled with 127 g of rock salt. The test results

79

showed that the solar still with spheres enhanced the system performance and gave the

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highest productivity of 3.7 kg/m2/day.

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An innovative desalination technique was Ghasemi et al. (2014) experimentally

82

testing a double layer structure with bubble-wrap (BW) insulation to enhance steam

83

generation under concentrated solar illumination of 10 kW/m2. They used an exfoliated

84

graphite layer of thickness 5 mm placed on carbon foam of 10 mm thickness. Both graphite

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and carbon foams are hydrophilic in nature to promote capillary rise of water to the top

86

surface. The result showed that the combination of graphite layer and carbon foam yields

87

solar thermal conversion efficiency of 85%, while generating steam in open air. Sharshir et

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al. (2017) experimentally studied a modified single slope solar still with graphite flakes in

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the basin. The modifications were graphite nano particles, phase change materials and top

90

cover cooling. Three identical solar stills were designed and tested in the same climatic

91

conditions. The results show that the combined effect of graphite flakes, phase change 3

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materials and cover cooling enhanced the system productivity by 73.8%. Dev et al. (2011)

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studied an inverted absorber solar still that directs sunlight to the underside of the water

94

basin. This has the advantage of the sunlight not heating the clear cover with its absorption as

95

in a simple still. This author also studied a single slope solar still, and for both stills varied

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water depths and total dissolved solids. The results show that the inverted absorber enhanced

97

the solar still productivity.

98

Sathyamurthy et al. (2017) reviewed the integration of collectors into various solar

99

still designs to augment the productivity. The top cover cooling effects of different solar still

100

designs were reviewed by Omara et al. (2017). Different water and air flow cooling

101

techniques were investigated. Based on the validation, the air flow and water flow over the

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tubular and single slope solar still (SSSS) enhanced the productivity. The flow of water/air

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affects the glass cover temperature and increases the temperature difference (Tw-Tg). Kabeel

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et al. (2017) reviewed the three important heat exchange enhancements in solar stills. They

105

are (1) heat transfer through PCM, (2) different absorbing materials and (3) cooling

106

techniques on the top cover.

107

Mahian et al. (2017) experimentally studied a solar still with SiO2 and Cu water based

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nanofluids. Two identical flat plate collectors (FPCs) were connected with a SSSS’s heat

109

exchanger in series mode. After heating, a pump moved the nano fluids into the SSSS via

110

pipes to enhance the heat transfer as well as productivity. Two different size of nanoparticles

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(7 nm and 40 nm), two depths of basin water (4 cm and 8 cm) and two mass flow rates (0.04

112

kg/s and 0.12 kg/s) were examined. A mathematical model was also developed and validated

113

with experimental results. It was found that the Cu water based nanofluids had higher

114

evaporation rate than SiO2 nanofluids. Vinothkumar and Kasturi Bai (2008) experimentally

115

studied a SSSS for tap water and sea water distillation. The physical and chemical water

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quality test results were that the water quality were compliant with the United States

117

Environmental Protection Agency (EPA) standard.

118

Many researchers tested solar stills with different absorbing materials. Absorbing

119

materials play a significant role in increasing the evaporation surface area as well as basin

120

internal thermal storage. Examples include solar stills with dye in the basin conducted by

121

Sodha et al. (1980); Dutt et al. (1989) studied wick on the basin, Minasian and Al-karaghouli

122

(1995); Shukla and Sorayan (2005); Janarthanan et al. (2005); Rajaseenivasan et al. (2015); 4

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Kabeel (2009); Sakthivel et al. (2010); Srivastava and Agrawal (2013); El-Sebaii and

124

Shalaby (2015); Janarthanan et al. (2006); Hansen et al. (2015), charcoal pieces, Okeke et

125

al. (1990), rubber scraps by Al-Sulttani et al. (2017), internal reflectors, Estahbanti et al.

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(2016); Hiroshi (2011), sponge cubes Hijleh et al. (2003); Arjunan et al. (2011); Bhardwaj et

127

al. (2015), porous basin Madani and Zaki (1995), nano composite energy storage

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Elfasakhany (2016) and presence of baffles El-Sebaii (2006); Ravishankar et al. (2015).

129

Setoodeh et al. (2011) studied the heat transfer coefficient of a solar still using computational

130

fluid dynamics (CFD). The result were that the simulated results were in good agreement

131

with experiments. Khare et al. (2017) investigated the performance of a single slope solar

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still using CFD. The simulation result of water temperature and productivity was in

133

agreement with the experiments.

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The present paper is the first time that recyclable BW has been used as an insulation

135

material for a solar still. BW insulation is a very good insulator due to presence of small air

136

pockets. For future work, BW could be a good insulation material for other low temperature

137

solar thermal applications. Carbon impregnated foam (CIF) can be manufactured with a

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polyurethane open pore foam that has carbon particles coating the interior surfaces. In the

139

present work, CIFs are tested in a SSSS with BW as an insulating material. The temperature

140

distribution of the floating absorber is investigated with a CFD analysis. Based on the review

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of various solar still designs, the testing of a solar still with BW insulation had not been

142

conducted before (the above cited BW study was for steam production). In this experimental

143

work, four identical solar stills were constructed and tested under the same climatic

144

conditions. Three modes of operation were studied experimentally: (i) SSSS without

145

insulation, (ii) SSSS with BW, and (iii) SSSS-CIF with BW. The results are compared with a

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conventional solar still (CSS) with sawdust insulation (Mohamad et al. 1995) and

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conclusions are drawn.

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2. Materials and Methods

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The solar stills were designed and tested at the Institute for Energy Studies, Anna

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University, Chennai, India during the month of April to June, 2017. Four SSSSs of

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horizontal dimensions 0.71 m × 0.71 m were designed. The material used for the making of

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solar still is galvanized iron and coated with black paint (solar absorptivity αb ~0.95). The 5

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SSSS was initialized at 3 cm water depth each morning. The cover material was glass (3 mm

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thickness, αg=0.05, and εg=0.94), and its hydrophilic property prevented distilled water from

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falling back into the basin. It is not advisable to pour the saline water by opening the top

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cover and closing it again because there would be significant radiative, convective, and

158

evaporative losses. Therefore, a fill port was used instead. Four pieces of CIFs floated on the

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water surface to increase the evaporation area of the basin. The details of the foam absorber

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are shown in Fig. 1. Fig. 2 (a-c) shows photographic views of the foam absorbers (a) top

161

view, (b) side view and (c) zoomed-in view. Generally, CIFs are used in water purifiers and

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fish tank filters. The radius of the CIFs is 0.085 m. The total volume of the four CIFs is 1028

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cm3 (See Table 1). The sides and bottom of the SSSS walls are properly insulated with BW

164

(Ghasemi et al. 2014) of thickness 30 mm (Khalifa and Hamood 2009). The visible

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transmittance of the BW sheet was 80% (Ni et al. 2016). The thermocouples were placed at

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representative places in the solar stills to record the temperature of the various segments. The

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parameters including water temperature (Tw), internal air temperature (Tair), inner cover

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temperature (Tic), and carbon impregnated foam temperature (TCIF) are measured with PT-

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100 (RTD sensing devices) with an accuracy of ±0.1°C. The HP-Agilent 34970A, Data

170

Acquisition System (DAS) with an accuracy of ±1°C was used to record and log the solar

171

radiation (Pyranometer- HUKSEFLUX CP02), at a scanning rate of 1 minute throughout the

172

experiment (Fig. 3). The wind velocity was measured by using a digital anemometer (AVM-

173

03) of accuracy ±2%. A total dissolved solids (TDS) meter (TDS-3 & ±2%), electrical

174

conductivity (EC) meter (VKTECH & ±2%), and pH meter (Hanna pH & ±0.1pH) were used

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to test the water quality from the solar still. A digital weighing balance (Healthsense, ±0.1kg)

176

was used to calculate the water holding capacity of foams and sponge. Table. 2 summarizes

177

the list of instruments used and their accuracy values. A plastic rectangular strip of length of

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0.75 m was used to collect the condensed water on the inner glass cover. Four clean

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BorosilTM measuring jars were used to collect the fresh water from the strip. At the end of

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each day, the top covers of the solar stills were wiped clean with PVA sponges. The

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schematic view of the four solar still designs is shown in Fig. 4 (A-D). The BW insulation

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wrap over the solar still (top and bottom) is shown in Fig. 5 (a-b). Fig. 6 shows the pictorial

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view of the SSSS designs on the open terrace. A view of the foam absorber in the solar still is

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shown in Fig. 7 (a-c). 6

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3. Mathematical model

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The following steps outline the simulation of the CIF in the solar still. Here, the

188

steady state temperature distribution of the CIF is studied with an energy equation. The

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continuity equations and momentum equations are neglected because there is no flow in the

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CIF absorber.

191 192

3.1. Energy equation

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 (  E )  .keff T  S h t

194

where ρ is the density, keff is the effective conductivity and Sh is the heat source.

(1)

195 196

3.2 Boundary and initial conditions

197

The side walls were assumed to be adiabatic; hence no heat losses occur in solar still to

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ambient (See Table 3). In addition there is no leakage in the system. The physical properties

199

of solids, and liquids such as specific heat, thermal conductivity and density were taken as

200

constant. Further assumptions included that there is no temperature gradient across the basin

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water and glass cover of the solar still. A grid independence study has been performed and

202

analyzed. The convergence criteria for the computational solution are determined and set as

203

10-6 for the governing equations.

204

The radiative heat transfer from CIF to glass is given by Setoodeh et al. (2011)

205

hr ,CIF   CIF . (TCIF  273) 2  (Tg  273) 2  TCIF  Tg  546 

206

Note that hr radiation heat transfer coefficient (W/m2K), ε is the emissivity, σ is the Stefan-

207

Boltzmann constant (5.670×10-8W/m2 K4), T is the temperature of CIF (°C), and Tg is the

208

glass cover temperature (°C).

209

Where

 CIF  210

1

g



1

 CIF

(2)

1

211

Heat gained by the CIF is given in the equation by

212

mCIF C p CIF .

dTCIF  I CIF g ACIF  qloss  qr ,CIF  g dt

(3) 7

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Note that mCIF is the mass of the floating absorber, Cp is specific heat capacity, T is

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temperature (°C), q is the heat transfer coefficient (W/m2K), α is the CIF absorptivity, τ is the

215 216

transmissivity of glass, and ACIF is the area of the CIF. The convective heat transfer coefficient between water and glass is estimated as,  Tw  273.15  pw  pg    0.884 Tw  Tg     268900  pw   

1/3

217 218

hc , w g

The evaporative heat transfer coefficient between water and glass is given as

219

Setoodeh et al. (2011) ,

220

  Pw  Pg    he , w g  16.27 103  hc , w g   Tw  Tg  

221

222 223 224

(4)

(5)

Where pw  e

pg  e

 5144   25.314   Tw  273.15  

 5144   25.314    T  273.15  g 

Where Pw and Pg are partial pressure of water and glass (N/m2).

225 226

4. Tested water quality analysis

227

The water quality was tested in situ. Three important parameters including TDS

228

(ppm), electrical conductivity (μS/cm) and pH were tested. The tap water is feed in to the

229

solar still (Feilizadeh et al. 2011). The water samples were collected before and after

230

treatment from the solar still and the results are shown in Table. 4. A TDS meter, pH meter

231

and EC meter were used to test the water samples instantly. Before desalination, the level of

232

TDS was 927 ppm. After desalination, it was reduced to 10 ppm (Arunkumar et al. 2012)

233

Before treatment, the level of EC was 867 μS/cm. After treatment, it was reduced to

234

34μS/cm. The level of pH before and after treatment was 6.4 and 7.4, respectively. The rain

235

water samples were collected on 16 June 2017 in a clean measuring jar. The TDS, EC and

236

pH of the tested rain water samples were 36 ppm, 16 μS/cm and 6.5. The tested results of

237

desalinated sample and rain water sample are acceptable for drinking (Samuel et al. 2016).

238

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5. Results and Discussion

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The experimental part of this study includes solar radiation, ambient temperature,

241

temperature records in the still, CFD analysis, water-holding capacity of materials and fresh

242

water productivity.

243 244

5.1 Effect of climatic conditions

245

Fig. 8 shows the variation of solar radiation and ambient temperature with respect to

246

time. The fresh water productivity of any solar desalination unit depends upon the solar

247

radiation and ambient temperature. The highest recorded solar radiation over the tilted solar

248

still and ambient temperature (on 2017.06.02) were 842 W/m2 and 41.7°C, respectively. The

249

average solar insolation for Chennai (13.0821°N Latitude & 80.2702°E Longitude) is good

250

from February to May (See Appendix 1). The 13° South inclined top cover directly faces the

251

sun at solar noon on March 21. In Chennai, the sun position in the sky at solar noon varies

252

from 36.45° South to 10.45° North in Dec 21 and June 21, respectively. As far as the solar

253

radiation over the tilted surface is concerned, the best time to conduct the experiment should

254

be from February to April. But on the other hand, due to greater day length from March-

255

June (See Appendix 2), it is better to perform the experiment in these months. The higher

256

the direct solar radiation is, the higher the yield is (Sahota et al. 2017). Although June has the

257

greatest day length, due to clouds, the average intensity of solar radiation is less. It is

258

concluded from our observation that the best time to perform the desalination experiment in

259

Chennai is from March to May. The wind conditions were also recorded during the

260

experiment. There are many factors that affect the solar stills productivity such as water

261

depth, thickness of the glass, height of the walls, and angle of inclination. The effect of

262

ambient temperature and wind also plays a significant role in the productivity.

263

5.2 Variation of recorded solar still temperature

264

Fig. 9 (a) shows the results of measured water temperature (Tw), internal air

265

temperature (Tair), and inner cover temperature (Tic) of SSSS without insulation (See Table.5)

266

The recorded maximum of Tw, Tair, and Tic are 59.1°C, 55.5°C, and 50.5°C, respectively. Fig.

267

9 (b) shows the measured temperature profile of SSSS with BW insulation (See Table 6).

268

The maximum recorded temperatures of Tw, Tair, and Tic are 70.3°C, 69°C, and 65.7°C,

269

respectively. Fig. 9 (c) shows the variation of Tw, Tair, Tic, and TCIF of SSSS-CIF with BW 9

ACCEPTED MANUSCRIPT 270

insulation (See Table 7). The maximum reached Tw and TCIF are 70.4°C & 71.9°C. Fig. 9 (d)

271

shows the temperature variations of CSS with wooden insulation (See Table 8). The recorded

272

maximum of Tw, Tair, and Tic are 68.7°C, 66°C, and 60°C, respectively. Based on the results

273

of all the experiments, the SSSS-CIF with BW insulation shows the highest temperature. The

274

recorded temperature profile of the conventional single slope solar still for similar ambient

275

conditions, area and with wooden insulation is shown in Fig. 9(d). It clearly shows that the

276

solar still with insulation increase the temperature of water by 23% as compared to solar still

277

without insulation as the loss of heat from the basin to the surrounding is reduced.

278

The hourly variation in evaporative heat transfer coefficient (hew) for the tested

279

configurations is shown in Fig 10. The evaporative heat transfer coefficient is calculated

280

using Equation (4) and (5). It can be observed that the solar still without any kind of

281

insulation has ~1/3 lower evaporative coefficient inside the basin as compared to solar still

282

with insulation and CIF porous medium. A maximum of 47.5 W/m2K evaporative heat

283

transfer coefficient is observed in the case of solar still with CIF and bubble wrap insulation.

284

5.3 CFD simulation results

285

The CFD analysis was carried out using ANSYS Fluent 15.0. The mesh geometry of

286

the CIF is shown in Fig. 11. The simulation of the floating absorber temperature distribution

287

is predicted by using CFD analysis (Fig. 12). The major objective of this CFD simulation is

288

to analyze the temperature distribution on the floating absorber. The time taken to complete

289

the simulation process is 4-5 hours. The parameters used to solve the temperature distribution

290

on the foam are given in Table. 9. The experimental and simulation result of maximum

291

recorded floating absorber temperature is 71.5°C and 73°C, respectively. The temperature

292

profiles of the CIFs are investigated with CFD analysis and the simulation results show good

293

agreement with the measured result.

294

5.4 Fresh water productivity in the solar stills

295

Fig. 13 shows the fresh water productivity of solar still designs correlated with solar

296

radiation. The productivity of the SSSS without insulation, SSSS with BW insulation, SSSS-

297

CIF with BW insulation and CSS with sawdust insulation are 1.9 l/m2/day, 2.3 l/m2/day, 3.1

298

l/m2/day and 2.2 l/m2/day, respectively. The SSSS-BW insulation shows a slight

299

enhancement over the CSS with wooden insulation. Normally, a wooden frame with glass

300

wool or sawdust insulation is traditionally used in SSSS. But some factors compromise the 10

ACCEPTED MANUSCRIPT 301

wooden frame and sawdust insulation. They include (i) basin leakage, (ii) leakage in fresh

302

water channel and (iii) excessive precipitation if the system is not sealed adequately.

303

5.5 Effect of BW and floating absorber

304

The BW is nothing more than pockets of air wrapped in polymer. The air inside a

305

confined space acts as a poor conductor of heat, which in turn reduces heat loss to

306

surroundings. The air inside a confined space inhibits convection. Here, the SSSS is tightly

307

packed with BW of thickness 30 mm to reduce the heat loss. Due to the heat trapped by the

308

BW insulation, Tw, Tair, and Tic and are the maximum for all the configurations. If the

309

temperature difference (∆T) between Tw and Tic is lower, this causes a decrease in

310

productivity (Arunkumar et al. 2012). The hydrophilic interconnected CIFs occupied a

311

surface area of 0.214 m2 in the 0.50 m2 basin. The advantages of the CIFs are: (i) acting as an

312

internal heat storage element, and (ii) increasing the evaporation area of the basin. The

313

interconnected CIFs consist of a large quantity of air out of the water, so their thermal

314

conductivity is low there. However, in the water, because they are hydrophilic, they fill with

315

water. Still, because it is difficult for the water to move in the pores, the thermal conductivity

316

is lower than free water. This coupled with the solar absorption increases the temperature on

317

the top side of the CIFs. The SSSS is an airtight container. The interconnected CIFs float on

318

the water surface and they increase the evaporation (the hydrophilic nature allows the

319

capillary flow of water from bottom to spreading out over the top side for ease of

320

evaporation). The water vapor condenses on the inner glass cover and trickles down due to

321

gravity. Because the CIF is hydrophilic, the wetted surface area increases above that of open

322

water (Ghasemi et al. 2014). This increases the evaporation rate, enhancing the productivity.

323

5.6 Effect of water holding capacity of foams and sponge

324

Table. 10 show the comparison of water-holding capacity of polyurethane foams,

325

PVA sponges and CIFs (Figs.14-15). Sponges are made with many holes connected

326

throughout (open pore) to hold lot of water for various applications. The air portions are

327

replaced by water when the sponges contact a water surface. Due to their hydrophilic nature,

328

the water quickly spreads throughout the sponge. The tested results of water holding capacity

329

reveals that the PVA sponge can hold more water per dry mass than the other materials. The

330

PVA sponge is physically hard when dry and becomes soft when it gets wet. Carbon foams

331

are as good at holding water. The behavior of the CIF and sponge are interesting in the 11

ACCEPTED MANUSCRIPT 332

presence of solar radiation. The top surface of the sponges seems to be dry even as it is

333

saturated with water. Therefore, more energy is needed to evaporate the water from the

334

inside of the sponge cubes. In CIFs, the structural arrangement is such that the top is wet

335

when placed in water. This shows than the CIF allows fluid movement from the bottom to

336

the top surface. So the CIFs help to ease evaporation of water and pave a path to more fresh

337

water production.

338

5.7 Cost Comparison

339

The cost of the SSSS-CIF with BW insulation is shown in Table. 11. The overall

340

assumptions are a device life of 15 years, an equivalent of 80% sunny days, and an interest

341

rate of 6%. The total cost of the fabricated solar still without insulation would have been

342

approximately 34 USD for 1 m2. With an output of 1.92 l/m2/day, this is approximately

343

0.0060 $/l water, the baseline. Adding plywood insulation increased cost by 60%, but only

344

increased output by 10%, so the water was 0.0086 $/l, which is worse than baseline. On the

345

other hand, adding BW insulation increased cost by only 5%, but increased output by 22%,

346

so the water was 0.0051 $/l, an improvement from the baseline. Finally, adding both BW

347

insulation and the CIF increased cost of the baseline by 62%, but only increased output by

348

37%, so the water was 0.0064 $/l. Therefore, the minimum cost water was produced by the

349

BW insulation without the CIF absorber.

350 351

6. Comparison of previous results with present work

352

The comparisons of different insulation materials used by the researchers are shown

353

in Table. 12. The effect of insulation thickness on the productivity is studied by Khalifa and

354

Hamood (2009). They maintained three different insulation thicknesses of 30 mm, 60 mm

355

and 100 mm. The results were that the insulation thickness plays a significant role in the

356

productivity up to a thickness of 60 mm. From the detailed review of previous results,

357

sawdust (0.08 W/m.K), glass wool (0.04 W/m.K) and plywood (0.13W/m.K) are widely used

358

in solar stills to reduce the heat loss to surroundings. Denkenberger and Pearce concluded via

359

modeling that varying the insulation thermal resistance from 1 to 4 ºC/(W/m2) changed

360

output 19% (Pearce et al. 2016). The advantages of the BW (0.02 W/m.K) insulation are low

361

cost (1 m2~0.23$) and that it is easy to wrap around the unit. The BW insulation acted as a

362

water proof layer for the solar still during rainy days. Based on the comparisons, BW 12

ACCEPTED MANUSCRIPT 363

insulation in a SSSS moderately increases the productivity of solar still, but there could

364

easily be confounding factors. Fig. 16 shows the cost per litre (CPL) of previous results

365

(Rajaseenivasan and Murugavel 2013); (El-Agouz 2014); (Omara et al. 2011); (Abdullah and

366

Badran 2008); (Ansari et al. 2013); (Fath et al. 2003); (Wassouf et al. 2011); (Suneesh et al.

367

2014); (Kabeel 2009) with single slope solar stills. It is concluded from the chart that all of

368

the embodiments tested in this paper were lower distilled water cost than previous work. The

369

lowest cost of water was with BW and no foam absorber.

370 371

7. Conclusions

372

The effect of floating absorbers and BW insulation on the SSSS is experimentally

373

tested under Indian climatic conditions. Four identical solar stills are designed and tested in

374

the same environment to reach a concrete conclusion. Three modes of operation were studied

375

experimentally: (i) SSSS without insulation, (ii) SSSS with BW insulation, and (iii) SSSS-

376

CIF with BW. The 4 pieces of CIF are floated on the water surface. The results are compared

377

with a CSS with sawdust insulation.

378 379

 The temperature profiles of the CIFs are investigated with CFD analysis and the simulation results show good agreement with the measured result.

380

 The productivities of the SSSS without insulation, SSSS with BW insulation, SSSS-

381

CIF with BW insulation, and CSS were 1.9 l/m2/day, 2.3 l/m2/day, 3.1 l/m2/day and

382

2.2 l/m2/day respectively.

383 384

 The combination of internal heat storage (CIF) and heat trap (BW) yields superior performance.

385

 The BW insulation enhanced the productivity by 22% over solar still without

386

insulation. The SSSS-BW-CIF combination increased the productivity of 24% over

387

SSSS with BW insulation. The SSSS with BW insulation enhanced the productivity

388

of 10% over the SSSS with wooden insulation.

389

 The hydrophilic nature and interconnected carbon impregnated absorbers enhanced

390

fresh water productivity in the SSSS. The foams increase the evaporation surface area

391

of the basin.

13

ACCEPTED MANUSCRIPT 392

 Preliminary water quality tests were conducted and the results are in the acceptable

393

range suggested by the World Health Organization (WHO) and the Indian standard

394

specification.

395 396 397 398

 The pockets of air in the BW act as a poor thermal conductor and restrict the heat loss to surroundings. This is easier to use than other traditional alternatives.  Solar desalination is a low global warming impact method of producing safe drinking water.

399 400

8. Implications for theory and practice of cleaner production/sustainability

401

In remote areas and regions, fresh water is often trucked in. This consumes finite fossil fuels

402

and produces greenhouse gases. A much cleaner way of producing freshwater is with solar

403

energy. A promising way of doing this is with solar stills. This paper shows a promising new

404

technique to increase the productivity of solar stills.

405 406 407 408 409 410 411 412

9. Future work  The evaporative heat transfer from solar still as well as CIF could be simulated by using CFD analysis.  Graphite flakes (GF) could be used to form a layer on the CIF to increase the thermal conductivity.  Selective Copper Oxide coating could be applied on the top of CIF to reduce radiation loss and increase temperature of the foam segment.

413 414 415 416 417 418 419 420 421 422 14

ACCEPTED MANUSCRIPT 423

Appendix 1

424

Incident angle of beam radiation over the 13° south tilted glazing cos   sin  sin  .cos   cos  .cos .cos  .sin   cos  cos  .cos .cos   sin  .cos  .sin  

425

(A)

 cos  .sin  .sin .sin  426

Where θ is the incidence angle (°), ϕ is the latitude in (°), δ is the declination angle (°), γ is

427

the surface azimuth angle(°) and ω is the hour angle (°)South facing glazing angle, γ=0,

428

Incidence angle at solar noon, ω = 0

429

Then Equation (A) becomes,

430

cos   sin  .sin      cos  .cos    

431

Since ϕ=β=13°, Eq. (B) becomes,

432

cos   cos 

433

Declination angle,

434

  23.45sin 

435

Where δ is the declination angle (°) and n is the number of days in the year

(B)

(C)  360  (284  n)   365 

(D)

February 22

March 22

April 22

n=53

n=80

n=112

δ=-10.87°

δ=0°

δ=11.93°

From Eq. (B), θ=10.87°

From Eq. (B), θ=0°

From Eq. (B), θ=11.93°

436 437

Angle made by the beam radiation with the normal to the glazing surface at noon are 10.87°,

438

0° and 11.93° on Feb 22, April 22 and March 22 respectively. It clearly shows that on March

439

22, the solar beam radiation at the noon will be normal to the tilted glazing.

440 441 442 443 444 445 446 15

ACCEPTED MANUSCRIPT 447

Appendix 2

448

Day length calculation for March 22-June 22 and Dec 22.

449

Hour angle s  cos 1 ( tan  .tan  )

450

Where ωs is the hour angle corresponds to sunrise or sunset, ϕ is the latitude in (°) and δ is

451

the declination angle (°).

452

  23.45sin 

453

Day length (DL)= DL 

(E)

 360  (284  n)   365  2 s  15

(F)

March 22

April 22

May 22

June 22

July 22

December 22

n=81

n=112

n=142

n=173

n=203

n=356

By Eq. (D),

By Eq. (D),

By

By Eq. (D),

By Eq. (D),

δ=0°

δ=11.93°

δ=20.34°

δ=23.45°

δ=20.24°

δ=-23.45°

By Eq. (E),

By Eq. (E),

By Eq.(E),

By Eq.(E),

By Eq.(E),

By Eq.(E),

ωs=90°

ωs=92.79°

ωs=94.91°

ωs=95.75°

ωs=94.88°

ωs=84.25°

By Eq.(F),

By Eq.(F),

By Eq.(F),

By Eq.(F),

By Eq.(F),

By Eq.(F),

DL=12 h

DL= 12 h &

DL=12 h & 39

DL= 12 h & DL= 12 h & DL= 11 h &

22 min

min

45 min

Eq.

(D), By Eq. (D),

39 min

14 min

454 455

By calculation, it is clear that the day length will increase up to a maximum of 12 hours

456

45min on June 22 and further it will decrease. A minimum day length of 11 h 14 min is

457

calculated for December 22.

458 459 460 461 462 463 464 465 466 16

ACCEPTED MANUSCRIPT 467

10. Nomenclature

468

A

-

Area (m2)

469

Cp

-

Specific heat capacity (J/kg.K)

470

E

-

Energy (J)

471

h

-

Heat transfer coefficient (W/m2K)

472

I(t)

-

Incident solar radiation (W/m2)

473

k

-

Thermal conductivity (W/m.K)

474

L

-

Latent heat of vaporization (J/kg)

475

m

-

mass (kg)

476

P

-

Partial pressure (N/m2)

477

n

-

number of days

478

T

-

Temperature (°C)

479

V

-

Wind velocity (m/s)

480

q

-

heat transfer coefficient (W/m2.K)

481 482

Greek

483

α

-

Absorptivity

484

μ

-

Viscosity (kg/m/s)

485

ε

-

Emissivity

486

ρ

-

Density (kg/m3)

487

σ

-

Stefan-Boltzmann constant = 5.67×10-8 W/m2K4

488

τ

-

solar transmittance of glazing

489

∆

-

temperature difference

490

θ

-

incidence angle (°),

491

ϕ

-

latitude in (°),

492

δ

-

declination angle (°),

493

γ

-

surface azimuth angle(°),

494

ω

-

hour angle (°)

495 496 497

Subscripts 17

ACCEPTED MANUSCRIPT 498

amb

-

ambient

499

air

-

internal air

500

b

-

basin

501

c

-

convection

502

CIF

-

carbon impregnated foam

503

e

-

evaporation

504

eff

-

effective

505

g

-

glass

506

ic

-

inner cover

507

loss

-

loss

508

r

-

radiation

509

s

-

sunrise or sunset

510

w

-

water

511 512

Abbreviation

513

BW

-

Bubble-wrap

514

CFM

-

Cubic foot/minute

515

CPC

-

Compound parabolic concentrator

516

CPL

-

Cost per litre

517

CIF

-

Carbon impregnated foam

518

CSS

-

Conventional solar still

519

CFD

-

Computational fluid dynamics

520

DAS

-

Data acquisition system

521

DL

-

Day length

522

EC

-

Electrical conductivity (μS/cm)

523

GF

-

Graphite flake

524

PPI

-

Pores per inch

525

PVA

-

Polyvinyl Alcohol

526

RTD

-

Resistance temperature detector

527

SSSS

-

Single slope solar still

528

TDS

-

Total dissolved solids (ppm) 18

ACCEPTED MANUSCRIPT 529 530 531

11. Acknowledgement

532

This study received grant from University Grant Commission (UGC), Government of

533

India. Ref. No. F.4-2/2016 (BSR)/PH/14-15/0124 dated on 01 July 2016.

534 535 536

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integrating solar collectors to solar still. Renew. Sustain. Energy Rev. 77,1069-1097.

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Ravishankar Sathyamurthy., Nagarajan, P.K., El-Agouz., Jaiganesh, V., Sathish Khanna, P.,

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2015. Experimental investigation on a semi-circular trough-absorber solar still with

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baffles for fresh water production. Energ. Convers. Manag. 97,235-242.

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Sakthivel, M., Shanmugasundaram, S., Alwarsamy, T., 2010. An experimental study on a

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regenerative solar still with energy storage medium-jute cloth. Desalination 264,24-31.

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Samuel Hansen, R., Surya Narayanan, C., Kalidasa Murugavel, K., 2015. Performance

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analysis on inclined solar still with different new wick materials and wire mesh.

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Desalination 358,1-8.

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Sharshir, S.W., Guilong Peng., Lirong Wu., Essa F.A., Kabeel, A.E., Nuo Yang., 2017. The

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effects of flak graphite nanoparticles, phase change material and film cooling on the

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solar still performance. Appl. Energy 191,358-366.

696 697 698 699 700 701 702 703 704

Shukla, S.K., Sorayan, V.P.S., 2005. Thermal modeling of solar stills: an experimental validation. Renew. Energ. 30,683-699. Sodha, M.S., Kumar, A., Tiwari G.N., Pandey, G.C., 1980. Effect of dye on the performance of a solar still. Appl. Energy 7,147-162. Suneesh, P.U., Jayaprakash, R., Arunkumar, T., David Denkenberger., 2014. Effect of air flow on “V” type solar still with cotton gauze cooling. Desalination 337,1-5. Tanaka Hiroshi., 2011. Solar thermal collector augmented by flat plate booster reflector: Optimum inclination of collector and reflector. Appl. Energy 88,1395-1404. Tien Shiao, Andrew Maddocks, Chris Carson and Emma Loizeaudx, 3 maps explain India’s

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growing water risks, http://www.wri.org/blog/2015/02/3-maps-explain-

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Vaibhav Rai Khare., Abhay Pratap Singh., Hemant Kumar., Rahul Khatri., 2017. Modeling

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and performance enhancement of single slope solar still using CFD. Energy Procedia

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722 723 724 725 726 727 728 729 730 731 732 733 734 735 736 737 738 739 740 741 25

ACCEPTED MANUSCRIPT 742

Table. 1

743

Details of a single CIF S.No. Parameters

Values

1

Volume

257 cm3

2

Diameter

0.17 m

3

Thermal conductivity

0.25 W/m K

4

Pores per inch (PPI)

10-65 PPI

5

Mass

9g

6

Color

Black

744 745 Table. 2 746 Accuracy of the measuring instruments

S.No.

Instrument

Model/Make

Accuracy

Range

1

Data Acquisition System

HP-Agilent 34970A

±1°C

0-100°C

2

Pyranometer

HUKSEFLUX CP02

±5 W/m2

0-1750 W/m2

3

K-type thermocouples

GENERIC

±0.1°C

0-100°C

4

Anemometer

AVM-03

±2%

0-9990 CFM

5

Measuring jar

Borosil

±10 ml

0-1000 ml

6

TDS meter

TDS-3

±2%

0-99990 ppm

7

EC meter

VKTECH

±2%

0-99990 µS/cm

8

pH meter

Hanna pH

±0.1 pH

0.0-14 pH

9

Digital weighing balance

Healthsense

±0.1kg

1-5000 g

747 748

Table. 3

749

Boundary zone type and conditions S.No.

Zone

Zone type

Description

1

Top CIF surface

Wall

h = 10 W/m2

2

Bottom CIF surface

Wall

T = 303-344 K

3

Side CIF surface

Wall

T = 303-344 K

750 751 26

752

Table. 4

753

Tested water quality results EC TDS, ppm (WHO, 2003)

(μS/cm)

pH (WHO 2007)

Before

After

Acceptable Before

treatment treatment level 927

14

Less than 300

After

Acceptable Before

treatment treatment level 6.4

7.4

6.5-8.5

754 755 756 757 758 759 760 761 762 763 764 765 27

After

37

water

on 16.06.2017.

Acceptable

treatment treatment level 867

rain

samples are collected

(WHO 2011)

S.No.

1

Tested

0-800

TDS (ppm) 36

pH 6.5

EC (μS/cm) 16

766

Table. 5

767

Hourly variation of measured values for SSSS without insulation (2017/06/02) Sl.No.

I (W/m2)

Tamb (°C)

V (m/s)

Tw (°C)

Tair (°C)

Tic (°C)

9:00 9:30 10:00 10:30 11:00 11:30 12:00 12:30 13:00 13:30 14:00 14:30 15:00 15:30 16:00 16:30 17:00 17:30

580 650 715 754 810 844 857 855 842 806 746 672 590 494 395 308 185 135

26 26.6 34.5 35.4 36.2 36.1 36.3 36 36 36 36.4 35.2 34.5 34.8 36.3 34.5 33.7 33

1.02 2.985 0.82 3.819 3.268 2.926 0.795 2.8 1.05 1.3 2.305 1.869 1.789 1.322 2.159 1.025 3.531 2.309

34 37 41 44 46 50.5 53 55.5 57.2 58.5 59.1 55.6 51.5 49.5 47.5 45 44 42

33 35.5 40.5 43.5 46 48 51 52 55.5 55 54 52.5 49 48.6 47 44.5 43.5 41

33.5 35 36.5 39 42 43.5 46 48.5 50 50.5 50 49.5 48.5 47 45 42.5 40 39

768 769 770 771 772 28

Pd (ml/m2/day) 0 40 48 72 80 100 112 128 148 156 164 156 148 136 128 112 100 76

773

Table. 6

774

Hourly variation of measured values for SSSS with BW insulation (2017/06/02) Sl.No.

I (W/m2)

Tamb(°C)

V (m/s)

Tw (°C)

Tair (°C)

Tic (°C)

9:00 9:30 10:00 10:30 11:00 11:30 12:00 12:30 13:00 13:30 14:00 14:30 15:00 15:30 16:00 16:30 17:00 17:30

580 650 715 754 810 844 857 855 842 806 746 672 590 494 395 308 185 135

26 26.6 34.5 35.4 36.2 36.1 36.3 36 36 36 36.4 35.2 34.5 34.8 36.3 34.5 33.7 33

1.02 2.985 0.82 3.819 3.268 2.926 0.795 2.8 1.05 1.3 2.305 1.869 1.789 1.322 2.159 1.025 3.531 2.309

47.3 48.6 51.9 58.6 61.1 63.5 67.6 68.3 69.2 69.8 70.3 69.5 68.9 66.5 64.1 59.8 51.6 50

47.1 48.3 50.3 56.4 59.4 62.1 65 66.4 66.9 67.8 69 68.3 67.8 66.3 63.9 60.2 56.4 55

46 47.8 49.3 54.8 56.5 58.5 60.6 62.8 63.3 64.7 65.7 63.9 62.2 60.2 59.9 55.6 52 51

775 776 777 778 779 29

Pd (ml/m2/day) 0 40 64 88 112 128 152 160 172 184 188 184 176 164 144 134 112 92

780

Table. 6

781

Hourly variation of measured values for SSSS-CIF with BW insulation (2017/06/02) Sl.No.

I (W/m2)

Tamb (°C)

V (m/s)

Tw (°C)

TCIF (°C)

Tair (°C)

Tic (°C)

9:00 9:30 10:00 10:30 11:00 11:30 12:00 12:30 13:00 13:30 14:00 14:30 15:00 15:30 16:00 16:30 17:00 17:30

580 650 715 754 810 844 857 855 842 806 746 672 590 494 395 308 185 135

26 26.6 34.5 35.4 36.2 36.1 36.3 36 36 36 36.4 35.2 34.5 34.8 36.3 34.5 33.7 33

1.02 2.985 0.82 3.819 3.268 2.926 0.795 2.8 1.05 1.3 2.305 1.869 1.789 1.322 2.159 1.025 3.531 2.309

46.7 48.1 49.2 54.2 59.9 62.7 66 69.3 68.9 70 70.4 71 70 69.1 65.7 63.4 59.7 54.8

47.2 49.7 51.5 56.5 62.1 64.8 67.8 68.9 69.7 70.8 71.9 71.5 69.2 68.1 66 64 60 55.2

49.8 53.1 54.8 58.9 62.4 64.7 68.3 69 68.5 69 70.1 69.3 68.2 68.4 64 60.6 55 52.6

46 47.4 48.6 54.3 58.9 60 62 63.4 64 64.7 65.2 63.5 62.8 61.9 60 56.9 54 53.1

782 783 784 785 786 30

Pd (ml/m2/day) 0 52 100 136 180 212 234 242 250 250 232 216 196 176 156 140 122 96

787

Table. 8

788

Hourly variation of measured values for SSSS with wooden insulation (2017/06/02) Sl.No.

I (W/m2)

Tamb (°C)

V (m/s)

Tw (°C)

Tair (°C)

Tic (°C)

9:00 9:30 10:00 10:30 11:00 11:30 12:00 12:30 13:00 13:30 14:00 14:30 15:00 15:30 16:00 16:30 17:00 17:30

580 650 715 754 810 844 857 855 842 806 746 672 590 494 395 308 185 135

26 26.6 34.5 35.4 36.2 36.1 36.3 36 36 36 36.4 35.2 34.5 34.8 36.3 34.5 33.7 33

1.02 2.985 0.82 3.819 3.268 2.926 0.795 2.8 1.05 1.3 2.305 1.869 1.789 1.322 2.159 1.025 3.531 2.309

43.1 47.6 53 58.4 62.5 65.1 67 68.7 68.1 67.5 66.4 60.9 57.4 54.2 51 47.8 44.6 41.4

45.6 48.8 54 57.8 61.9 63.4 64 66 64.6 64.5 62.6 59.4 56.1 52.4 48 43.6 39.2 34.8

48 51.5 53.9 55.9 56.6 58 59.4 60 59 58.8 57.6 57 56.1 53 50 47 44 41

31

Pd (ml/m2/day) 0 40 60 80 100 120 140 148 160 168 180 180 168 152 140 124 108 84

ACCEPTED MANUSCRIPT Table. 9 Parameters used for simulation S.No. Parameters

Value

Unit

Water 1

Density (ρ)

998.2

kg/m3

2

Specific heat capacity (Cp)

4182

J/kg.K

3

Thermal conductivity (k)

0.6

W/m.K

4

Viscosity

0.001003 Pa.s

5

Molecular weight

18.052

g/mol

Glass 6

Density (ρ)

2500

kg/m3

7

Specific heat capacity (Cp)

750

J/kg.K

8

Thermal conductivity (k)

1.05

W/m.K

CIF absorber 9

Density (ρ)

35

kg/m3

10

Specific heat capacity (Cp)

1200

J/kg.K

11

Thermal conductivity (k)

0.25

W/m.K

700

W/m2

Climatic parameters 12

Solar radiation I(t)

13

Ambient temperature (Tamb) 29

32

°C

ACCEPTED MANUSCRIPT

Table. 10 Water holding capacity of foams and sponge S.No

1 2

Material type Polyurethane foam (high density) Polyurethane foam (low density)

Volume of

Dry

Wet

Weight

the

weight

weight

difference

material

in grams

in grams

in gram

599 cm3

23

412

389

16.91

857 cm3

7

625

618

88.28

Water Held (Wt. diff.÷ Dry Wt.)

3

PVA sponge

222 cm3

31

422

391

12.61

4

CIF

257 cm3

9

257

248

27.55

Table. 11 Cost analysis of experimented solar still designs Components -US$ for 1 m2 still Galvanized iron Top cover Black paint Fresh water port Labor charge Bubble wrap Wooden and saw dust insulation CIF Absorber Pipes Total L/m2/day $/L water Cost increases Output increases

SSSS Without insulation 15 3 1.56 0.7 12.5 N/A N/A N/A 0.78 33.54 1.924 0.0060 -

33

SSSS with BW

SSSS-CIF with BW

15 3 1.56 0.7 12.5 1.55 N/A N/A 0.78 35.09 2.34 0.0051 5% 22%

15 3 1.56 0.7 12.5 1.55 N/A 19.4 0.78 54.49 2.9 0.0064 62% 37%

SSSS with saw dust insulation 15 3 1.56 0.7 13 0 19.46 N/A 0.78 53.5 2.124 0.0086 60% 10%

804 805

Table. 12

806

Comparison of previous work with different insulation material used in the solar still S.No. 1 2

Author Ganaraj et al. (2017), India Rajaseenivasan et al. (2017), India

Solar still design

Thickness/Insulation Productivity

Year/Month

of

experimentation

Single slope solar still

20 mm/saw dust

2345 ml/day

April-May 2016

Single slope solar still

0.025 m/glass wool

3.19 kg/day

June 2014-April 2015

3

Gupta et al. (2016), India

Single slope solar still

20 mm/glass wool

2940 ml/day

April 2015

4

Sharshir et al (2017), China

Single slope solar still

5 mm/ glass wool

2116 ml/day

Nov-Dec 2015

5

Rabhi et al. (2017), Tunisia

Single slope solar still

Plywood

2.34 l/m2

Jan 2016

6

Jamil and Akhtar (2017), India

Single slope solar still

25 mm/glass wool

2.24 l/m2

March to June, 2015

7

Arunkumar et al. (2016), India

Single slope solar still

Saw dust

2.100 l/day

Jan to Nov 2013

8

Arunkumar et al. (2016), India

Single slope solar still

Saw dust

1.600 l/day

May 2012

9

Present work

Single slope solar still

30 mm/bubble-wrap

2.3 l/m2/day

April to June 2017

10

Present work

Single slope solar still

No insulation

1.9 l/m2/day

April to June 2017

807 808 809

34

ACCEPTED MANUSCRIPT

Fig. 1. Details of CIF absorber

Fig. 2. (a) Photograph of CIF top view, (b) side view, and (c) zoomed view (pores) 35

ACCEPTED MANUSCRIPT

Fig. 3. Photographic view of Pyranometer

36

Fig. 4. [A] SSSS without insulation, [B] SSSS with BW insulation, [C] SSSS-CIF with BW insulation, and [D] Conventional solar still

37

ACCEPTED MANUSCRIPT

Fig. 5. (a) Pictorial view of BW insulation front view, and (b) bottom view

Fig. 6. Pictorial view of experimental setup with temperature indicators

Fig. 7. Snapshot of (a) SSSS-CIF with BW, (b) CIF in the basin and (c) trace of larger condensation water marks under the cover 38

ACCEPTED MANUSCRIPT

Fig. 8. Graphical view of solar radiation and ambient temperature with respect to time

39

ACCEPTED MANUSCRIPT

Fig. 9 (a). Temperature profile of SSSS without insulation, (b) Temperature profile of SSSS with BW insulation, (c) Temperature profile of SSSS-CIF with BW insulation and, (d) Temperature profile of CSS

40

ACCEPTED MANUSCRIPT

Fig. 10. Evaporative heat transfer coefficient

Fig. 11 Mesh view of CIF

41

ACCEPTED MANUSCRIPT

Fig. 12. Temperature distribution of floating absorber in the solar still

42

ACCEPTED MANUSCRIPT

Fig. 13. Productivity with respect to solar still experiments

Fig. 14. Photograph of PVA sponge, polyurethane sponges and CIF

43

ACCEPTED MANUSCRIPT

Fig. 15. Photographic view of water holding capacity (dry and wet) of foams and sponges

44

ACCEPTED MANUSCRIPT

Fig. 16. Economics of previous results as compared with present work

45

ACCEPTED MANUSCRIPT

Highlights  The temperature distribution of the floating absorber was investigated with CFD.  CFD showed good agreement with experiment.  Carbon impregnated foam increased productivity by 35%.  Bubble-wrap is found to be an inexpensive insulation material.

ACCEPTED MANUSCRIPT Table. 6 Hourly variation of measured values for SSSS with BW insulation (2017/06/02) I (W/m2) 580 650 715 754 810 844 857 855 842 806 746 672 590 494 395 308 185 135

Sl.No. 9:00 9:30 10:00 10:30 11:00 11:30 12:00 12:30 13:00 13:30 14:00 14:30 15:00 15:30 16:00 16:30 17:00 17:30

Tamb(°C) 26 26.6 34.5 35.4 36.2 36.1 36.3 36 36 36 36.4 35.2 34.5 34.8 36.3 34.5 33.7 33

V (m/s) 1.02 2.985 0.82 3.819 3.268 2.926 0.795 2.8 1.05 1.3 2.305 1.869 1.789 1.322 2.159 1.025 3.531 2.309

Tw (°C) 47.3 48.6 51.9 58.6 61.1 63.5 67.6 68.3 69.2 69.8 70.3 69.5 68.9 66.5 64.1 59.8 51.6 50

Tair (°C) 47.1 48.3 50.3 56.4 59.4 62.1 65 66.4 66.9 67.8 69 68.3 67.8 66.3 63.9 60.2 56.4 55

Tic (°C) 46 47.8 49.3 54.8 56.5 58.5 60.6 62.8 63.3 64.7 65.7 63.9 62.2 60.2 59.9 55.6 52 51

Pd (ml/m2/day) 0 40 64 88 112 128 152 160 172 184 188 184 176 164 144 134 112 92

Table. 7 Hourly variation of measured values for SSSS-CIF with BW insulation (2017/06/02) Sl.No. 9:00 9:30 10:00 10:30 11:00 11:30 12:00 12:30 13:00 13:30 14:00

I (W/m2) 580 650 715 754 810 844 857 855 842 806 746

Tamb (°C) 26 26.6 34.5 35.4 36.2 36.1 36.3 36 36 36 36.4

V (m/s) 1.02 2.985 0.82 3.819 3.268 2.926 0.795 2.8 1.05 1.3 2.305

Tw (°C) 46.7 48.1 49.2 54.2 59.9 62.7 66 69.3 68.9 70 70.4

TCIF (°C) 47.2 49.7 51.5 56.5 62.1 64.8 67.8 68.9 69.7 70.8 71.9

Tair (°C) 49.8 53.1 54.8 58.9 62.4 64.7 68.3 69 68.5 69 70.1

Tic (°C) 46 47.4 48.6 54.3 58.9 60 62 63.4 64 64.7 65.2

Pd (ml/m2/day) 0 52 100 136 180 212 234 242 250 250 232

ACCEPTED MANUSCRIPT 14:30 15:00 15:30 16:00 16:30 17:00 17:30

672 590 494 395 308 185 135

35.2 34.5 34.8 36.3 34.5 33.7 33

1.869 1.789 1.322 2.159 1.025 3.531 2.309

71 70 69.1 65.7 63.4 59.7 54.8

71.5 69.2 68.1 66 64 60 55.2

69.3 68.2 68.4 64 60.6 55 52.6

63.5 62.8 61.9 60 56.9 54 53.1

216 196 176 156 140 122 96