Energy matrices, enviroeconomic and exergoeconomic analysis of passive double slope solar still with water based nanofluids

Energy matrices, enviroeconomic and exergoeconomic analysis of passive double slope solar still with water based nanofluids

Desalination 409 (2017) 66–79 Contents lists available at ScienceDirect Desalination journal homepage: www.elsevier.com/locate/desal Energy matrice...

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Desalination 409 (2017) 66–79

Contents lists available at ScienceDirect

Desalination journal homepage: www.elsevier.com/locate/desal

Energy matrices, enviroeconomic and exergoeconomic analysis of passive double slope solar still with water based nanofluids Lovedeep Sahota a,⁎, Shyam a, G.N. Tiwari b a b

Centre for Energy Studies, Indian Institute of Technology Delhi, Hauz Khas, New Delhi 110016, India Bag Energy Research Society (BERS), SODHA BERS COMPLEX, Plot No. 51, Mahamana Nagar, Karaudi, Varanasi, UP 221005, India

H I G H L I G H T S • Concentration of metallic Al2O3, TiO2, and CuO nanoparticles and basin fluid (BF/NF) mass of passive DSSS system has been optimized for each month. • Annual energy, exergy, and productivity of the system have been estimated for the system with purposed water based nanolfuids. • Energy matrices, enviroeconomic and exergoeconomic analysis has been carried out.

a r t i c l e

i n f o

Article history: Received 16 July 2016 Received in revised form 26 December 2016 Accepted 11 January 2017 Available online xxxx Keywords: Exergoeconomic parameter Energy matrices Nanofluids

a b s t r a c t Nanofluids are the new generation of ultrafast heat transfer fluids due to their exceptional thermo-physical and optical properties and attracted attention of the researchers worldwide in recent times. Worldwide, research is underway to utilize the advances of nanotechnology for potable water production. In the present communication, the energy matrices, enviroeconomic analysis, and exergoeconomic analysis of passive double slope solar still (DSSS) has been carried out incorporating Al2O3, TiO2 and CuO-water based nanofluids. Significant enhancement in the annual productivity (Al2O3 19.10%; TiO2 10.38%; and CuO 5.25%), energy (Al2O3 26.76%; TiO2 19.36%; and CuO 12.96%), and exergy (Al2O3 37.77%; TiO2 25.55%; and CuO 11.99%) of passive DSSS system with nanofluids has been observed in comparison to the still with basefluid (water) only. On the basis of energy and exergy, the energy payback time (EPBT), energy production factor (EPF), life cycle conversion efficiency (LCCE), environmental cost and exergoeconomic parameter has been estimated for different interest rates (i=4%,8%,and 10%) and life span (maximum 50 years) of the passive DSSS loaded with proposed three different water based nanofluids. © 2017 Elsevier B.V. All rights reserved.

1. Introduction Potable water is the most important element and one of the vital factors for sustenance of the life of all creatures on the earth. Deficiency of potable water is the most important concern for the mankind in most of the parts of the world especially in the arid regions and costal area. In recent times, various techniques have been employed which converts the filthy or contaminated water into the potable water. Among all these techniques solar distillation is the simplest, environment friendly and cost effective method used to produce drinking water on utilizing the non-conventional source of energy (renewable source of energy solar energy). Solar distillation systems are divided into two groups' viz. passive solar stills and active solar stills. In the past few decades, various researchers studied the passive and active solar stills in detail and ⁎ Corresponding author. E-mail address: [email protected] (L. Sahota).

http://dx.doi.org/10.1016/j.desal.2017.01.012 0011-9164/© 2017 Elsevier B.V. All rights reserved.

concluded that passive solar stills perform better than the active solar stills [1–5]. In recent times, researchers employed different designs of the passive solar stills (step-basin, multi-basin, hemispherical, spherical, V-shape, concave, tubular, triangular pyramid, inclined wick type, stand alone, tubular etc.) in order to improve the still productivity [6–16]. From the literature, it has been concluded that passive single slope solar still performs better than passive double slope solar still on the basis of annual yield, annual energy, annual exergy and exergoeconomic parameter. On the other hand passive double slope solar still perform better than passive single slope solar stills on the basis of productivity [17]. Moreover, on the basis of second law of thermodynamics, various researchers carried the energy and exergy analysis of the stills on the basis to optimize the design and operating parameters [18–25]. In recent times, advances in nano-science and engineering gives hope to find the smart and promising solutions of the various current problems including water purification which can be diminished using nano-absorbents, nano-catalysts, bioactive nanoparticless (NPs), nano-

L. Sahota et al. / Desalination 409 (2017) 66–79

powders, nanotubes etc. Worldwide, theoretical and experimental research work has been performed by various researchers in solar applications utilizing nanofluids. These are the new generation of ultrafast heat transfer fluids due to their exceptional thermo-physical and optical properties. These properties of the nanofluids can be improved by tailoring the size and shape of NPs in a particular hostfluid or basefluid which shows that it is good opportunity to improve the system performance by incorporating the precise nanofluids. Therefore, researchers have made attempts to study the thermo-physical and optical properties of various nanofluids [26–34]; and the performance of solar devices with nanofluids i.e. flat plate collectors and heat exchangers [35–42]. Very few literatures have been found on the solar stills incorporating nanofluids. Kabeel et al. [43] experimentally studied the performance of vacuum fan coupled single slope solar still using Al2O3-water based nanofluid. Elango et al. [44] experimetally studied the performance of single slope solar still by incorporating Al2O3, TiO2, and ZnO-water based nanofluids. Omara et al. [45] studied the effect of nanofluids and vacuum on the performance of convensional solar still and corrugated wick type solar still. Sahota and Tiwari [46] studied the performance of passive DSSS system with Al2O3-water based nanofluid for three different concentrations of NPs (0.04%, 0.08%. 0.12%). Furthermore, Sahota and Tiwari [47] developed the characteristic equation for basefluid (water) and Al2O3, TiO2, and CuO-water based nanofluids to study the performance of passive DSSS. It has been found that the solar still with Al2O3-water based nanofluid gives better productivity of the passive DSSS system in comparison to other studied nanofluids. Shashir et al. [48] experimentally studied the improvement in the performance of solar still using graphite and copper oxide micro flakes (nanoparticles) and different cooling flow rates over the toughen glass cover. They examined different concentrations of micro flakes (0.125 % − 2%), different basin water depths (0.25cm − 5cm), and different flow rates over the toughen glass cooling cover (1 − 12kg/h). They reported 44.91% and 53.95% improvement in the productivity of the solar still using copper oxide and graphite particles respectively. Whereas, the enhancement in productivity is found to be 47.80% and 57.60% with water flow over the toughen glass cover as a cooling for copper oxide and graphite particles respectively in comparison to conventional solar still. It is very important to analyze the life cycle cost of the system as it help designers to fabricate the system in cost effective manner. The life cycle cost analysis of active and passive solar stills have been carried by the various researchers worldwide. Kumar and Tiwari [49] investigated the life cycle cost analysis of single slope hybrid (PV/T) active solar still for 0.05m basin water depth. The comparative cost of the potable water obtained from passive solar still (Rs .0.70/kg) is found to be less than hybrid (PV/T) active solar still (Rs .1.93/kg) for the system life span of 30 years. Tiwari et al. [50] studied the exergoeconomic and enviroeconomic analysis of active solar still. Their purposed system (PVT-FPC) meets the daily demand of potable water during the sunshine hours. On the basis of annual performance, Singh et al. [17] reported the comparative study of life cycle of passive single slope and double slope solar stills with the effect of energy matrices. They have found 0.144 kW h/Rs . and 0.137 kW h/Rs.per unit cost for single and double slope passive solar stills respectively based on exergoeconomic parameter. In literature, the exergoeconomic and envireconomic analysis of photovoltaic solar systems has also been carried out by the researchers using basefluid (water) [41,42]. Said et al. [51] studied the energy and exergy analysis of flat plate collectors by incorporating different sizes (13nm and 20nm) of Al2O3-water based nanofluid. They reported that for 0.1% volume concentration and 1.5kg/min mass flow rate, Al2O3water based nanofluid (13nm) shows higher energy efficiency (73.76%) as compared to Al2O3-water based nanofluid (20nm) which gives 70.7% energy efficiency. It is credited to the better thermo-physical and optical properties of the nanofluids at smaller diameter. Mahian et al. [52] discusses the economic and environment consideration of solar collectors and water heating systems in their detailed review on the applications of nanofluids in solar energy. Otanicar and Golden

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[53] performed the comparative study on the solar collectors using basefluid (water) and nanfluids to investigate the environmental and economic aspects. They have found that the capital cost and maintenance costs have been found to be $120 and 20$ higher respectively in solar collector using nanofluids in comparison to the basefluid. From the enviroeconomic point of view, they reported that nanofluids based solar collectors neutralizes 74kg of CO2 emission in comparison to the conversional collectors over its life span of 15 years. Khullar and Tyagi [54] investigated the environmental impact on concentrating solar water heat system using nanofluids; and reported that CO2 emissions have been reduced by approximately 2.2 × 103kg of CO2/household/year. Faizal et al. [55] studied the energy economic and environmental analysis of flat plate solar collector using CuO, SiO2, TiO2, and Al2O3 water based nanofluids. The CuO nanofluid gives better thermal performance among others due to its higher density, thermal conductivity and lower specific heat. They reported that CuO, SiO2, TiO2, and Al2O3 nanofluids saved around 10,239kg , 8625kg , 8857kg and 8618kg total weight respectively or 1000 units of solar collectors. Moreover, their study concluded that (a) each solar nanofluid based collector saves an average of 220MJ of embodied energy (b) 2.4 years payback period is found with nanofluid based solar collector as compared to the conventional collector (2.49 years) and (c) an average of 170kg less CO2 emissions with manufacturing of nanofluid based collector. None of the researcher has studied the life cycle cost analysis of passive solar stills by incorporating nanofluids. In present communication, annual performance and cost analysis of the passive double slope solar still using Al2O3, TiO2, and CuO-water based nanofluids has been carried out corresponding to the optimized values of the basin fluid (BF/NF) mass and concentration of assisting nanoparticles of each particular month (Table 3). The energy matrices i.e. the energy production factor (EPF), energy payback time (EPBT), and life cycle conversion efficiency (LCCE) considering the initial investment, salvage value, maintenance cost, interest rate and life span of the still into account have also been evaluated. 2. System description The East-West oriented systematic view of conventional double slope solar still (DSSS) filled with water based nanofluid is depicted in Fig. 1. The assisting NPs in the basefluid (water) of passive DSSS system enhance the internal heat transfer rates as well as optical properties. These optical properties can be altered by regulating the physical dimensions. The strong interaction of light (electromagnetic waves) with NPs is credited to the conducting electrons on the surface of NPs which causes oscillations on exciting the light at particular wavelength. This oscillatory behavior is responsible for the infrequent strong scattering and absorption properties. Material's dielectric properties are exceptionally imperative and play a vital role in the intensity and placement of the plasmon resonances. Therefore, nanofluids directly absorb the penetrated solar radiation due to toning among its optical absorption spectrum and the solar radiation spectrum. It is evident that the wavelength corresponding to maximum extinction swings towards the longer wavelength side on raising the NP size. At high concentration, the assisting NPs spread more in the given basin nanofluid volume; consequently, the availability of high surface area transfers the more heat from the NPs to the surrounding nanofluid which intern elevates its temperature. Hence, the mutual effect of transfer of energy by the assisted NPs and the blackened surface (direct transfer) increases the nanofluid temperature. As fluid temperature increases, evaporation of basefluid (water) starts and vapors (via heat transfer mechanism) at the inner surface of the cover get condensed after releasing its latent heat to the cover. Eventually, the trickled condensed water is collected in the measuring jars through the channels fixed at the lower ends of the cover under the gravity. Here, it is important to mention that though the mixing of NPs in the basefluid of the conventional solar stills enhances the productivity but it makes the system more complex due to

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L. Sahota et al. / Desalination 409 (2017) 66–79

Fig. 1. Systematic view of passive double slope solar still loaded with metallic nanoparticles.

the problem of sedimentation, dispersion and clustering of NPs which demands or causes complex maintenance of the still. Therefore, some advance and sophisticated equipment have been required to overcome this issue which may increase the cost of the conversional solar stills. Moreover, the separation of nanoparticles from the rejected brine is one of the issues which also cause complex maintenance of the solar stills. Various separation methods have been developed depends on the size, shape, volume fraction, and thermo-physical properties of the nanoparticles; and type/class and thermo-physical properties of the basefluid. Among all, filtration, centrifugation, electrophoresis, magnetic separation, chromatography, and chemical methods are the most widely used techniques for this purpose. Therefore, incorporation of NPs sets the constraints to reuse the rejected brine over a longer period with additional saline water (according to the requirement) in the still to avoid the complexity issue.



 T giE

T goE ¼

Kg Lg



 þ h1gE T a

h1gE þ



 T giW

and T goW ¼

Kg Lg

Kg Lg



 þ h1gW T a

h1gW þ

Kg Lg

Solving the energy balance equations of different components of the present system still, one can obtain the following first order differential equation; dT f 0 þ aT f ¼ f ðt Þ dt The solution of above first equation for the fluid (BF/NF) temperature of the system can be expressed as 0

 f ðt Þ  1−e−aΔt þ T f 0 e−aΔt a

3. Mathematical formulation

Tf ¼

Following assumptions have been taken into account for the analysis of passive DSSS:

where, Tf0 is the basin basefluid (water) temperature at t = 0.

(a) All processes in the system are in quasi steady state. (b) There is no temperature stratification between the layers of fluid (BF/NF) in the system. (c) The heat capacity of the absorbing material, the insulation (bottom and sides), and the glass cover is negligible. (d) The system is vapor leakage proof. (e) NPs are well dispersed in the basefluid; and no sedimentation and clustering of NPs takes place. Following Sahota and Tiwari [46,47], the temperature of inner and outer surface of the top glass cover of the east and west side of the still can be expressed as

T giE

   0  Aþ TfB A þ T f B0 and T giW ¼ ¼ H H

 a¼

ð3Þ

 C 11 þ C 33 ½C 22 þ T a C 33 þ C 44  0 ; and f ðt Þ ¼ MfCf Mf Cf

All the unknowns in above equations are given in Appendix A. From Cooper and Dunkle model, the generalized expression of internal evaporative and convective heat transfer coefficients are given below as  hef ¼ ð0:016273Þhcf

P f −P gi T f −T gi

 ð4Þ

5144 2 where, P gi ¼ exp½25:317−ðT gi5144 þ273Þ and P f ¼ exp½25:317−ðT f þ273Þ ðN=m Þ

hcf ¼ ð0:844ÞðΔT Þ1=3 ð1Þ

ð2Þ

ð5Þ ðP f −P gi ÞðT f þ273Þ

where; ΔT ¼ ðT f −T gi Þ þ ½

2:689105 −P f



L. Sahota et al. / Desalination 409 (2017) 66–79

(

Internal radiative heat transfer coefficient is given as hrf ¼ ∈eff σ

h

2  2 i   T f þ 273 þ T gi þ 273 T f þ T gi þ 546

Eth;ex ¼ ð6Þ

 T f þ 273 T giE þ 273   )  T f þ 273 Ab þ hef ;W T f −T giW −ðT a þ 273Þ ln T giW þ 273 hef ;E

 

69

T f −T giE −ðT a þ 273Þ ln



ð11Þ

where; ∈1eff ¼ ∈1f þ ∈1g −1: The natural convective heat transfer coefficient (hnc) from basin to fluid surface has been obtained from the following relation of Nusselt number (Nu); ðNuÞ f ¼

hnc X ¼ C ðGrPr Þn ¼ C ðRaÞn k

ð7Þ 2 3

where, Grashof number: ðGrÞ f ¼ ½gβρμL2

ΔT

 ; Prandlt number: ð PrÞ f ¼ f

μC ð k pÞ f

Rayleigh number, Ra = GrPr; and for horizontal plate facing upward, C = 0.54 and n =¼. External radiative HTC from east and west side of the glass cover is given as h

hrgaE

4  4 i ∈g σ T giE þ 273 − T sky þ 273  and hrgaW ¼ T g −T a h 4  4 i ∈g σ T giW þ 273 − T sky þ 273  ¼ T g −T a

ð12Þ

The hourly temperature variation, heat transfer coefficients, energy and exergy; and yield from the passive DSSS system loaded with basefluid and all three different water based nanofluids have been obtained using the following correlations of thermo-physical properties (density, specific heat, conductivity, and viscosity) of basefluid [56] and naofluids (Table 2): Density (ρ) ρbf ¼ 999:79 þ 0:0683  T bf −0:0107  T 2bf þ 0:00082 −5  T 3bf  T 2:5 bf −2:303  10

ð13Þ

Specific heat (C)

ð8Þ

2 C bf ¼ 4:217−0:00561  T bf þ 0:00129  T 1:5 bf −0:000115  T bf

þ 4:149  10−6  T 2:5 bf

ð14Þ

Conductivity (k)

where, Tsky = Ta − 6 External convective HTC can be expressed as; hcga ¼ 2:8 þ 3V

 _ _ w ¼ q1g  3600 ¼ h1g T f −T g  3600 M L L

ð9Þ

−6 kbf ¼ 0:565 þ 0:00263  T bf −0:000125  T 1:5 bf −1:515  10 2 0:5  T bf −0:000941  T bf

ð15Þ

Viscosity (μ) Hourly energy and exergy of the system are given as; Eth;en

    ¼ hef ;E T f −T giE þ hef ;W T f −T giW Ab

ð10Þ

1 ð16Þ μ bf ¼

557:82−19:408  T bf þ 0:136  T 2bf −3:116  10−4  T 3bf

4. Methodology The climatic data of each month of the New Delhi Climate has been obtained from IMD, Pune, India. Liu and Jordan formulae have been used to evaluate the solar radiation of different weather conditions (a, b, c, and d-type) of all the months for 30° inclination (north latitude) of the east and west side of the glass cover with the help of MATLAB 2012a. Four types of weather conditions (a, b, c, and d type) are defined as follows (IMD Pune, India): ▪ Type ‘a’ – for clear days – sunshine hours are available for greater than or equal to 9 h per day, and if diffuse radiation is b50% or N25% of global radiation. ▪ Type ‘b’ – hazy days – sunshine hours are available in between 7 and 9 h per day and if diffuse radiation is b 50% or N 25% of global radiation. ▪ Type ‘c’ – hazy and cloudy days – sunshine hours are available in between 5 and 7 h per day, and if diffuse radiation is b75% or N 50% of global radiation. ▪ Type ‘d’ – cloudy days – sunshine hours are available in less than or equal to 5 h per day, and if diffuse radiation is N75% of global radiation. Specification of different components of the passive DSSS is given in Table 1. Following methodology has been adopted to study the cost analysis of passive DSSS system using basefluid (water) and Al2O3, TiO2, and CuOwater based nanofluids. I. Temperature of inner (TgiE, TgiW) and outer surface (TgOE, TgOW) of the glass cover, internal (hef, hcf,hrf, and hnc) and external (hrgaE,hrgaW, hcgaE, and hcgaW) heat transfer coefficients, and fluid (BF/NF) temperature (Tf) has been evaluated using Eqs. (1)–(9). II. Concentration of the loaded NPs and fluid (BF/NF) mass in the still basin has been optimized for each month. _ Þ, energy (Eth,en), and exergy III. Corresponding to the optimized concentration of NPs and fluid (BF/NF) mass, the total monthly productivity ðM w

(Eth,ex) have been estimated. IV. After estimating annual energy, exergy and productivity (yield), the exergoeconomic parameter and energy matrices (EPBT, EPF and LCCE) have been evaluated.

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L. Sahota et al. / Desalination 409 (2017) 66–79

The flow chart of methodology is given below for better understanding;

5. Energy matrices

On the basis of energy and exergy, EPBT can be expressed as [57];

The energy matrices viz. energy payback time (EPBT), energy production factor (EPF), and life cycle conversion efficiency (LCCE) has been used to study the performance of the passive double slope solar still (DSSS). For any efficient and productive renewable energy system, the energy produced by the system in its entire life span must be higher than the energy utilized by it during manufacturing. Consequently, it is essential to evaluate these parameters for renewable energy technology.

5.1. Energy payback time (EPBT) EPBT of the passive DSSS system defines the time period needed to recuperate the total energy exhausted in the material preparation for the system fabrication.

Table 1 Numerical constants used in computation for passive DSSS. Dimensions of passive DSSS AgE σ AgW Cbf Ab hsg hlb hub X θ Kg KB Lg Lb

Constants

Numerical value 1.025 m × 1.025 m 5.67 × 10−8 (W/m2K4) 1.025 m × 1.025 m

4188 (J/Kg ° C) 2 m×1 m 0.5 m 0.22 m 0.534 m 1.5 m 300 0.780 (W/m ° C) 0.035(W/m ° C) 0.004 m 0.005 m

dp αg αb αbf ∈g

20 × 10−9m 0.05 0.8 0.6 0.95

ðEPBT Þen ¼

Embodied energy in ðEin Þ  Annual energy out Eout;ann

ð21Þ

ðEPBT Þex ¼

Embodied energy in ðEin Þ  Annual exergy out Eex;ann

ð22Þ

The amount of energy consumed for preparation of the materials for the system fabrication defines its energy payback time period such that it depends on the embodied energy and the annual energy output (productivity) obtained from the system. The information about the energy densities of diverse materials is essentially required for the estimation of the embodied energy of various components of the system. In general, it is the required time span to cover up the amount of energy expended for the system preparation which is utilized during the system and its components fabrication. The embodied energy of different components of the passive DSSS system is presented in Table 4. The energy density of NPs is very low in comparison to the other components of the system; consequently the embodied energy of the NPs is neglected [52]. The annual productivity (yield) of the system obtained from the basefluid (water) and studied water based nanofluids is given in Table 5. To make the system cost effective, it should be attempted to keep the value of EPBT as low as possible. On the basis of energy and exergy, the EPBT of passive DSSS system has been estimated using Eqs. (13)–(14) for basefluid and all three different nanofluids and presented in Table 7(a-d). 5.2. Energy production factor (EPF) The energy production factor determines the overall performance of the system. The EPF on the basis of energy and exergy can be expressed as [57]; "

ðEPF Þen

Embodied energy in ðEin Þ  ¼ Annual energy out Eout;ann

#−1 ð23Þ

L. Sahota et al. / Desalination 409 (2017) 66–79

71

Table 2 Thermo-physical properties of Al2O3, TiO2, CuO-water based nanofluids. Quantity

Expression

Specific heat

C nf ¼ 0:8429 ð1 þ 50nf Þ ð1 þ 50p Þ ð1 þ 100p Þ 15 b dp b 50nm; 0 b φp b 4%; 20 b Tnf b 50 ° C (Al2O3, and CuO-water) [62]

−0:3037

T

C

d

0:4167

2:272

φ

D

p C nf ¼ ½Aðφp ÞB ðT nf ÞC ðC p;bf Þ C p;bf

A= 1.387 , B = − 0.00425 , C = 0.001124 , D = − 0.21159 dp = 21nm; 0 b φp b 8%; 15 b Tnf b 65 ° C (TiO2-water) [63] ρnf = φpρp + (1 − φp)ρbf [64]

Density Thermal conductivity

k

p knf ¼ kbf ½1 þ ð1:0112Þφp þ ð2:4375Þφp ðdp 47 Þ−ð0:0248Þφp ð0:613 Þ ðnmÞ

0 b φp b 10%; 20 b Tnf b 70 ° C; 11 b dp b 150nm (Al2O3-water) [65] k

knf ¼ kbf ½1 þ ð0:135Þð kbfp Þ

0:273

0:547

T

ðφp Þ0:467 ð 20nf Þ

ðdp100 Þ ðnmÞ

0:234



0 b φp b 10%; 20 b Tnf b 70 ° C; 11 b dp b 150nm (TiO2-water) [66] μ

knf ¼ kbf ½0:9843 þ ð0:398Þð φp Þ0:467 ðμ nf Þ

0:0235

bf

1 ðdp ðnmÞ Þ

0:2246

φ

φ2

φ

−ð3:951Þð T nfp Þ þ ð34:034ÞðT 3p Þ þ 32:51ðT 2p Þ nf

nf

0 b φp b 10%; 20 b Tnf b 70 ° C; 11 b dp b 150nm (CuO-water) [65] Viscosity

2 μ nf ¼ −0:4491 þ ð28:837 T nf Þ þ 0:547φp −0:163φp þ

φ 2 ð23:653ÞðT nfp Þ

φp

φ

2

φ3

þ ð0:0132Þ φ3p −ð2354:7ÞðT 3 Þ þ ð23:498Þð dpp Þ −ð3:018Þð 2p Þ dp

nf

11 ≤ φp ≤9 ; 13 ≤dp ≤ 130nm ; 20 ≤ Tnf ≤90 ° C (Al2O3-water) [65] μ nf ¼ μ bf ½ð1 þ φp Þ11:3 ð1 þ

T nf −0:038 ð1 70 Þ

d

p þ 170 Þ

−0:061



10 ≤ φp ≤4 ; 20 ≤dp ≤ 170nm ; 0 ≤ T ≤ 70 ° C (TiO2-water) [67] ð

247:8

μ nf ¼ ð2:414  10−5 Þ10 T nf −140 Thermal expansion coefficient

" ðEPF Þex ¼

Embodied energy in ðEin Þ  Annual exergy out Eex;ann

#−1 ð24Þ

The EPF of passive DSSS system has been evaluated on the basis of energy and exergy for basefluid and all three different nanofluids for different life spans (maximum 50 years) of the still (Table 7(a–d)). 5.3. Life cycle conversion efficiency (LCCE) Life cycle conversion efficiency is the net output of the system with respect to the solar radiation falling on the system during the whole life span of the system. The life cycle conversion efficiency of passive DSSS system can be expressed as [57]; 

Een;ann  n −Ein Esol;ann  n

ð25Þ

Eex;ann  n −Ein ¼ Esol;ann  n

ð26Þ

ðLCCEÞen ¼ 

ðLCCEÞex

Þ

10 ≤ φp ≤10 % ; 11 ≤ dp ≤ 150nm ; 20 ≤T ≤ 70 ° C (CuO-water) [65] βnf = (1 − φp)βbf + φpβp [68,69]

where, Een,ann is the annual solar energy output, Ein is the embodied energy, Esol,ann is the annual solar energy retrieved by the still, Eex ,ann is the annual exergy gain, and n is life span of the still. The LCCE of passive DSSS system has been estimated for basefluid and all three different nanofluids on the basis of energy and exergy (Table 7(a-d)). 6. Enviroeconomic analysis (environmental cost) It is based upon the cost of CO2 emission and propels to utilize the non-conventional sources of energy such that renewable technology which does not emit carbon to the environment. The amount of CO2 emitted per kWh is approximately 0.960 kg [58]. On considering the transmission (20%) and distribution losses (40%), the amount of CO2 emitted per kWh comes out to be 2.0 kg. The amount of CO2 mitigated per annum (φCO2) can be expressed as [59];

On the basis of energy; φCO2 ¼

On the basis of exergy φCO2 ¼ Table 3 Optimized values of the basin fluid (BF/NF) mass and concentration of nanoparticles (Al2O3, TiO2, and CuO) for the passive DSSS corresponding to the each month. Month

January February March April May June July August September October November December

Basin fluid (BF/NF) mass

Concentration (φp) of metallic nanoparticles (%)

Mw (kg)

Al2O3

TiO2

CuO

20 25 35 35 40 40 35 35 35 35 30 20

0.158 0.185 0.254 0.258 0.272 0.263 0.221 0.212 0.236 0.247 0.175 0.143

0.072 0.095 0.169 0.173 0.187 0.166 0.136 0.123 0.147 0.153 0.084 0.059

0.052 0.079 0.119 0.127 0.153 0.131 0.115 0.106 0.122 0.128 0.069 0.044

ψCO2 =0:38  Een;ann

ð27Þ

103 ψCO2  Eex;ann

ð28Þ

103

where, ψCO2 is the amount of CO2 emitted per unit electricity or average CO2 equivalent intensity for electricity generation from coal (2.04 kg CO2/kWh).

Table 4 Embodied energy of different components of passive double slope passive solar still [17]. Double slope solar still Name of component

Mass of component (kg)

Energy density (kWh/kg)

Embodied energy (kWh)

GRP body GI angle iron Glass cover Total embodied energy

34.59 30.00 20.7

25.64 13.88 8.72

775.61 416.40 180.50 1372.51

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L. Sahota et al. / Desalination 409 (2017) 66–79

Table 5 Annual yield, energy, and exergy obtained from basefluid (water) and three different nanofluids. Outputs

Water

Al2O3-water

TiO2-water

CuO-water

Annual yield (East) (kg) Annual yield (West) (kg) Total annual yield (kg) Total thermal energy (kWh) Total thermal exergy (kWh)

602.66 639.23 1241.89 1101.64 82.29

722.79 755.86 1483.65 1396.51 113.25

671.40 699.46 1370.86 1314.93 103.32

644.46 662.75 1307.21 1244.43 92.164

The environmental cost or environmental parameter (ZCO2) is given as Z CO2 ¼ φCO2  zCO2

ð29Þ

where, zCO2 is the international carbon price (14.5 $ per ton of CO2). The amount of CO2 mitigated per annum and the environmental cost (carbon credits) of passive DSSS system has been estimated for the basefluid and all three different water based nanofluids on the basis of energy and exergy (Table 8).

7. Exergoeconomic analysis It is an economic analysis method based on exergy. It is a combination of exergy analysis with the cost analysis to improve the performance of renewable energy systems. It enables the designers to find an alternative ways or techniques to improve the system performance from the cost point of view. The exergoeconomic parameter (Rex) based on exergy for passive DSSS system can be expressed as [60,61]; Rex ¼

Eex;ann UAC

ð30Þ

where, Eex , ann is the annual exergy gain and UAC is the uniform annual cost of passive DSSS. The generalized expressions of uniform annual cost (UAC), net present value (NPV), shrinking fund factor (SFF), and capital recovery factor (CRF) are given below; UAC ¼ ðNPV  CRF Þ þ ðMS  CRF Þ−S  SFF

ð31Þ

h i NPV ¼ P þ R1  ðCRF Þn þ Rn1  ðSFF Þn1 þ Rn2  ðSFF Þn2 þ …Rnk  ðSFF Þnk −S  ðSFF Þn

ð32Þ

CRF ¼ F CR;i;n ¼

iði þ 1Þn ði þ 1Þn −1

ð33Þ

SFF ¼ F SR;i;n ¼

i ði þ 1Þn −1

ð34Þ

where, P is the present cost, S is the salvage value, MS is the maintenance cost, n is the life span of the still and Rnk is the replacement factor. The replacement period of NPs has been chosen as one year whereas the replacement periods of other still components i.e. paint and silicone gel has been taken as five years. The systematic diagram for this is shown below;

The cost and salvage value of different components of passive DSSS system are given in Table 6. The values of UAC, NPV, SFF, CRF, and exergoeconomic parameter (Rex) of passive DSSS system for basefluid and three different water based nanofluids has been evaluated and presented in Table 9.

L. Sahota et al. / Desalination 409 (2017) 66–79 Table 6 Cost and salvage value of different components of the passive DSSS. Parameters

FRP body @ 340/kg Glass cover (1.15 m2) Iron stand Inlet/Outlet nozzle Iron clamp Gaskets Silicon gel Labor and other changes Total cost of the still 100 g Al2O3 nanoparticles (b50 nm) 100 g TiO2 nanoparticles (10 − 25 nm) 100 g CuO nanoparticles (b20 − 55 nm) Salvage value of the system after 30 years without nanoparticles, if inflation remains @ 4 % . Salvage value of the system after 50 years without nanoparticles, if inflation remains @ 4 % . Salvage value of the system after 30 years with nanoparticles, if inflation remains @ 4 % . Salvage value of the system after 50 years with nanoparticles, if inflation remains @ 4 % .

Table 7 Energy matrices on the basis of energy and exergy.

Cost

Years

Energy Matrices

(Rs.)

($)

Energy

10 ,200 800 1000 200 250 200 200 4000 16,850 4500 7200 7425 5140

151.51 11.88 14.85 2.97 3.71 2.97 2.97 59.41 250.29 66.84 106.95 109.25 76.35

EPF

11 ,264

167.32

Al2O3 TiO2 CuO Al2O3 TiO2 CuO

73

9067.2 11 , 972 15 , 650 19 , 867 26 , 232 34 , 291

134.68 177.83 232.47 295.11 389.66 509.37

⁎1 US $ = 67.32 Rs. on 07/08/2016.

8. Results and discussion The concentration of assisting NPs and the fluid (BF/NF) mass has been optimized corresponding to the climatic conditions of each month. The values of optimized fluid (BF/NF) mass and concentration of NPs (Al2O3, TiO2, and CuO) for different months is given in Table 3. Both the basin fluid (BF/NF) mass and concentration of NPs have been found to be higher for the months of higher solar radiations (May and June). The optimal range of the basin fluid (BF/NF) mass has been found to be 20kg ≤ Mw ≤ 40kg. Whereas, the optimized values of the assisting NPs Al2O3, TiO2, and CuO have been found to be in the range of 0.143 % ≤ φp ≤ 0.272%; 0.059 % ≤ φp ≤ 0.187%; and 0.044 % ≤ φp ≤ 0.153% respectively. It is inferred that the lower values of optimized basin fluid (BF/NF) mass are corresponds to the months of low solar radiations. It is credited to the fact that penetrated solar radiation utilized by the basin liner increases the fluid temperature on exploiting the sensible heat and the remaining heat is accountable for the mechanism of evaporation. Consequently, the evaporation mechanism further slowdown in case of higher basin fluid mass due to more utilization of more sensible heat and therefore the optimal values corresponds to the lower values of the basin fluid mass for the months of low incident solar radiations. The monthly variation of maximum temperature difference (ΔT)max between the basefluid and all three different water based nanofluids corresponding to the optimized parameters of that particular month is shown in Fig. 2. The value of (Δ T)max has been found to be higher for Al2O3-water based nanofluid than the other studied water based nanofluids (TiO2-water, and CuO-water). It is credited to the superior thermo-physical properties of Al2O3-water based nanofluid as explained earlier (system description). Also, the peak of the curves of all three studied nanofluids occurs for the months of higher solar radiation. The temperature (and hence conductivity) of NPs increases more during the sunshine hours due to their direct absorption ability. Consequently, the combined effect (basin liner and NPs) raises the temperature of the nanofluids in the system. The monthly productivity obtained from the basefluid and proposed nanofluids corresponding to the optimized parameters is presented in Fig. 4. The productivity of west side of the system has been found to be marginally higher than the east side of the system. Furthermore, the productivity is found to be higher for the month of May for Al2O3-

Exergy LCCE

EPBT

EPF

LCCE

EPBT

(a) Basefluid (water) 1 0.80 5 4.01 10 8.02 15 12.04 20 16.05 25 20.06 30 24.07 40 32.10 50 40.13

−0.080 0.245 0.285 0.299 0.306 0.310 0.313 0.316 0.318

1.24

0.06 0.30 0.60 0.90 1.20 1.49 1.80 2.39 2.99

−0.382 −0.057 −0.016 −0.003 0.004 0.008 0.011 0.014 0.016

16.67

(b) Al2O3-water 1 1.017 5 5.08 10 10.17 15 15.26 20 20.34 25 25.43 30 30.52 40 40.69 50 50.87

0.0071 0.332 0.373 0.386 0.393 0.397 0.400 0.403 0.405

0.982

0.082 0.412 0.825 1.237 1.650 2.062 2.475 3.300 4.125

−0.373 −0.0478 −0.0712 0.0064 0.0132 0.0173 0.0200 0.0234 0.0254

12.11

(c) TiO2-water 1 0.958 5 4.79 10 9.59 15 14.37 20 19.16 25 23.95 30 28.74 40 38.32 50 47.90

−0.017 0.308 0.349 0.362 0.369 0.373 0.376 0.379 0.381

1.043

0.075 0.376 0.752 1.129 1.505 1.881 2.258 3.011 3.763

−0.376 −0.0507 −0.0101 0.0035 0.0103 0.0144 0.0171 0.0205 0.0225

13.28

(d) CuO-water 1 0.906 5 4.533 10 9.066 15 13.60 20 18.13 25 22.66 30 27.20 40 36.26 50 45.33

−0.03798 0.288 0.328 0.342 0.349 0.353 0.355 0.358 0.361

1.103

0.0671 0.335 0.671 1.007 1.343 1.678 2.014 2.686 3.357

−0.379 −0.054 −0.0133 0.0002 0.0070 0.0111 0.1380 0.0172 0.0192

14.89

water based nanofluid than the other studied nanofluids for both the east and west side of the system. Significant improvement in the annual productivity of the system has been observed by incorporating nanofluids (Al2O3 19.10%; TiO2 10.38%; and CuO 5.25%) in comparison to the still with basefluid only (Table 5). The variation of annual productivity (yield) with different types of weather conditions is presented in Fig. 5. The productivity obtained from the east and west side of the passive DSSS using basefluid and studied water-based nanofluids is shown in Fig. 5(a) and (b) respectively. The productivity of the west side of system has been found to be marginally higher than the east side for all different weather conditions (a, b, c, and d-type). It has been perceived that the system productivity using Al2O3-water based nanofluid found to be higher in comparison to the other studied nanofluids for all the weather conditions. It is due to the low temperature of the west side glass surface after noon hours which enhance the temperature difference between the fluid (BF/NF) surface and the inner surface of the glass cover. The hourly variation of temperature of the inner surface of the toughen glass cover of the east side (TgiE) and west side TgiW) of the DSSS loaded with basefluid for the month of May (summer condition) and January (winter conditions) is shown in Fig. 3. The results are found to be in good agreement with the results of Singh et al. [17]. Similar variations have been observed in the glass cover temperature for the nanofluids. The c-type weather conditions have been found to be more suitable to use the solar still as it gives better productivity in

74

L. Sahota et al. / Desalination 409 (2017) 66–79

Table 8 Enviroeconomic analysis of the passive DSSS on the basis of thermal energy and exergy. Basefluid/Nanofluid

Environmental cost Energy

Exergy

Energy production cost

Baefluid Water-Al2O3 Water-TiO2 Water-CuO

(Rs.)

($)

5508.2 6982.5 6574.6 6222.1

91.80 116.73 109.57 103.70

CO2 mitigated (tones)

5.91 7.49 7.05 6.68

Environmental cost (carbon credits)

Exergy production cost

(Rs.)

($)

(Rs.)

($)

5145.2 6522.4 6141.4 5812.1

85.75 108.7 102.35 96.86

411.45 566.25 516.6 460.82

6.86 9.44 8.61 7.68

CO2 mitigated (tones)

0.167 0.231 0.210 0.188

Environmental cost (carbon credits) (Rs.)

($)

146.04 200.99 188.37 163.57

2.43 3.50 3.05 2.71

⁎Average unit electricity cost is taken Rs. 5/kWh (7–8 US cents per kWh). ⁎1 US $ = 67.32 Rs. on 07/08/2016.

comparison to other weather conditions for all three different water based nanofluids. It is credited to availability of higher number of clear days for c-type weather conditions in each month of the year. Further, the monthly variation of energy and exergy of passive DSSS is shown in Fig. 6(a) and (b) respectively. Both energy and exergy has been found to be higher for the month of May for Al2O3-water based nanofluid (Eth , en 1396.51 kWh ; and Eth , en113.25 kWh) in comparison to the basefluid (Eth , en 1101.64 kWh ; and Eth , en82.89 kWh) and other studied nanofluids. The computed values of energy and exergy of the passive DSSS loaded with basefluid and studied three different nanofluids has been presented in Table 5. On the basis of energy and exergy, the energy payback time of the passive DSSS system for basefluid and all three different water based nanofluids has been evaluated (Table 7(a–d)). The EPBT has been found to be lower for Al2O3-water based nanofluid ((EPBT)en 0.982 year; (EPBT)ex 12.11 year) than the other studied nanofluids and found to be higher for basefluid ((EPBT)en 1.24 year; (EPBT)ex 16.67 year) as shown in Fig. 7. The variation of energy production factor (EPF) with life span of the passive DSSS system is depicted in Fig. 8. It has been observed that the EPF of the system increases with increase in life span of the system. On the basis of both energy and exergy, the

Table 9 Net present value, capital recovery factor, shrinking fund factor, uniform annual cost, and unit cost obtained for the passive DSSS with basefluid and water-based three different nanofluids. Years Interest NPV (n) rate, i (%) (Rs.) Basefluid (water)

30 50 30 50 30 50 Al2O3-water 30 50 30 50 30 50 TiO2-water 30 50 30 50 30 50 CuO-water 30 50 30 50 30 50

4 4 8 8 10 10 4 4 8 8 10 10 4 4 8 8 10 10 4 4 8 8 10 10

19,536 19,884 18,115 18,141 17,778 17,786 183,150 198,510 109,460 110,510 91,964 92,266 238,970 258,970 142,920 144,290 120,120 120,510 292,890 299,900 185,290 185,290 155,760 155,760

CRF

SFF

UnaCost Rex (Rs.) (kWh/Rs . )

0.0578 0.0466 0.0888 0.0817 0.1061 0.1009 0.0578 0.0466 0.088 0.0817 0.1061 0.1009 0.0578 0.0466 0.088 0.0817 0.1061 0.1009 0.0578 0.0466 0.088 0.0817 0.1061 0.1009

0.0178 0.0066 0.0088 0.0017 0.0061 0.0009 0.0178 0.0066 0.0088 0.0017 0.0061 0.0009 0.0178 0.0066 0.0088 0.0017 0.0061 0.0009 0.0178 0.0066 0.0088 0.0017 0.0061 0.0009

1135.5 930.23 1617.9 1491.1 1896.4 1803.9 10,598 9245.3 9731.7 9041.9 9766.0 9315.9 13,825 12,060 12,704 11,803 12,752 12,165 17,913 14,419 16,467 15,154 16,534 15,720

13.69 11.23 19.60 17.85 22.72 21.73 90.91 83.33 90.91 83.33 90.91 83.33 135.1 117.64 123.45 114.94 123.45 117.64 196.07 156.25 178.57 166.66 178.57 169.49

EPF has been found to be higher for Al2O3-water based nanofluid in comparison to the other studied water based nanofuids and basefluid. It is credited to the fact that the passive DSSS system gives higher values of energy and exergy for the Al2O3 NPs loaded passive DSSS system. For 50 year life span of the system, the EPF for Al2O3-water based nanofluid has been found to be 50.87 and 4.125 respectively on the basis of energy and exergy. The estimated EPF on the energy and exergy for passive DSSS system loaded with basefluid and all three different water based nanofluids for different life span of the system is given in Table 7(a–d). The variation of life cycle conversion efficiency (LCCE) with life span of the passive DSSS system is presented in Fig. 9. The LCCE of the system for the basfluid and all three different water based nanofluids has been evaluated on the basis of energy and exergy and it has been perceived that the LCCE increases with increase in life span of the system. It is found to be higher for the system loaded with Al2O3-NPs followed by TiO2 and CuO –NPs and hostlfuid loaded system. On the basis of energy and exergy respectively, it is found to be 40.5% and 2.54% for Al2O3water based nanofluid; and 31.8% and 1.6% for the system with basefluid for 50 year life span of the system (Table 7(a–d)). The amount of CO2 mitigated per annum and the environmental cost (carbon credits) has been estimated for the passive DSSS system loaded with basefluid and all three different water based nanofluids on the basis of energy and exergy (Table 8). The amount of CO2 mitigated per annum has been found to be higher for Al2O3-water based nanofluid (energy basis-2.84 t; exergy basis-0.231 t) followed by other studied nanofluids and basefluid (energy basis-2.25 t; exergy basis-0.167 t).

Fig. 2. Monthly variation of maximum temperature difference (typical day of each month) among the basefluid and water based all three different nanofluids.

L. Sahota et al. / Desalination 409 (2017) 66–79

Fig. 3. Hourly variation of temperature of the inner surface of the toughen glass cover of the east side (TgiE) and west side TgiW) of the DSSS for the month of May (summer condition) and January (winter conditions) using basefluid.

75

The environmental cost has also been found higher for Al2O3-water based nanofluid (energy basis-Rs. 2478.53; exergy basis-Rs. 200.99) in comparison to the other studied water based nanofluids and basefluid (energy basis-Rs. 1955.19; exergy basis-Rs. 146.04). Moreover, the exergoeconomic analysis of the present system has been carried out and the computed results are presented in Table 9. The uniform annual cost (UAC), net present value (NPV), shrinking fund factor (SFF), capital recovery factor (CRF), and exergoeconomic parameter (R ex ) of passive DSSS system for basefluid and three different water based nanofluids has been evaluated for different interest rates (i = 4%, 8%, and 10%) and life span of the system (n = 30 yeras, and 50 years). It has been observed the NPV decreases with increase in interest rate for fixed life span of the system while it increases with increase in life span of the system for fixed interest rate. For given life span and interest rate, the NPV has been found to be higher for Al2O3-water based nanofluid than the other studied nanofluids and basefluid. On the other hand, the uniform annual cost (UAC) increases with increase in interest rate for the fixed life span of the system and it falls with increase in life span of the system for fixed interest rate. The UAC has been found to be significantly higher for the system loaded with nanofluids. The exergoeconomic parameter has been evaluated for both the 30 years and 50 years life span of the passive DSSS system incorporating

Fig. 4. Monthly variation of productivity (yield) obtained from the basefluid (water) and nanofluid of the (a) east and (b) west side of passive DSSS.

Fig. 5. Variation of annual productivity (yield) with different types of weather conditions for the (a) east and (b) west side of passive DSSS for the basefluid (water) and all three different water-based nanofluids.

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L. Sahota et al. / Desalination 409 (2017) 66–79

Fig. 6. Monthly variation of (a) energy and (b) exergy of passive DSSS for the basefluid (water) and all three different water-based nanofluids.

water based nanofluids and basefluid (Table 9). It has been found that the exergoeconomic parameter (Rex) decreases gradually with increase in interest rate in case of DSSS system loaded with basefluid only. This gradual variation in the Rex with interest rate has been credited to the fact that the value of UAC increases with increase in interest rate for the fixed life span of the system. Whereas, very minimal variation in exergoeconomic parameter has been observed in case of passive DSSS system loaded with nanofluids. It happens due to significantly higher values of uniform annual cost of the system with nanofluids in comparison to the basefluid loaded DSSS system. The Rex of the present system loaded with basefluid has been found to be 11.23 Rs ./kWh for 4% interest rate and 50 years life span of the system. Whereas, the significantly higher values of the exergoeconomic parameter (Rex) of the system loaded with Al2O3, TiO2, and CuO-water based nanofluids has been found to be 83.33 , 117.64 , and 156.25 Rs . /kWh respectively for the same parameters (i = 4%, and n = 50 years). The exergoeconomic parameter has been found to be higher for the system with all three different nanofluids in comparison to the conventional basefluid loaded system. It is credited to the higher values of UAC of the system incorporating nanofluids for given interest rate and life span of the passive DSSS system.

Fig. 7. Energy payback time (EPBT) on the basis of energy and exergy for the basefluid and all three different nanofluids.

9. Conclusions Annual performance and cost analysis of the passive DSSS system loaded with assisting Al2O3, TiO2, and CuO-nanoparticles has been carried out on the basis of energy and exergy. Following conclusions has been withdrawn from the present study: (a) The optimization of concentration of Al2O3, TiO2, and CuO NPs; and fluid (BF/NF) mass depends on the climatic conditions (solar intensity and ambient temperature). The optimal range of the basin fluid (BF/NF) mass has been found to be 20kg ≤ Mw ≤ 40kg whereas, the optimized values of the assisting NPs Al 2O3, TiO2, and CuO have been found to be in the range of 0.143 % ≤ φp ≤ 0.272%; 0.059 % ≤ φp ≤ 0.187%; and 0.044 % ≤ φp ≤ 0.153% respectively throughout the year. (b) The annual productivity, energy, and exergy were found to be significantly higher for the passive DSSS system loaded with nanofluids following the order of Al2O3 N TiO2 N CuO-water based nanofluid. Furthermore, these parameters has been found higher for the c-type weather conditions due to availability of maximum number of clear days for this condition.

Fig. 8. Variation of energy production factor (EPF) with life span of the still on the basis of energy and exergy for the basefluid and all three different nanofluids.

L. Sahota et al. / Desalination 409 (2017) 66–79

77

Fig. 9. Variation of life cycle conversion efficiency (LCCE) with life span of the passive DSSS system on the basis of (a) energy, and (b) exergy for basefluid and all three different water-based nanofluids.

(c) On the basis of both energy and exergy, the EPBT and EPF has been found to be lower and higher respectively for the system with Al2O3 NPs in comparison to the other studied nanofluids and basefluid. The LCCE of the system increases with increase in life span of the system and found to be higher again for Al2O3-water based nanofluid. (d) On the basis of both energy and exergy, the amount of CO 2 mitigated and environmental cost per annum has been found to be higher for Al2O3-water based nanofluid followed by other studied nanofluids and basefluid. On the other hand, the estimated exergoeconomic parameter has been found to be significantly higher for the studied water based nanofluids loaded in the system in comparison to the conventional basefluid.

hb,f hnc hEW Uga Uba ∈g ∈f ∈eff σ AgE

Recommendation

AgW

The performance of active solar still can be studied by incorporating nanofluids with heat exchanger. Furthermore, the effect of NP size and shape on the system performance can be investigated for the active and passive solar stills.

Ab As θ Δt Ta Tf TgiE

Nomenclature Fraction of solar energy absorbed by condensing cover αg Fraction of solar energy absorbed by the fluid αf Volume fraction of NP (%) φp Diameter of NP (m) dp expansion coefficient of NP (K−1) βp expansion coefficient of the fluid (K−1) βf Dynamic viscosity of the fluid, (Ns/m2) μf Density of NP, (kg/m3) ρp Density of the fluid, (kg/m3) ρf Conductivity of NP (W/mK) kp Conductivity of the fluid, (W/mK) kf Specific heat of NP, (J/kgK) Cp Specific heat of the fluid, (J/kgK) Cf Mass of the fluid in the basin of solar still Mf _w Hourly yield (kg/hr) M Internal evaporative heat transfer coefficient on east side, hef,E (W/m2K) Internal evaporative heat transfer coefficient on west side, hef,W (W/m2K) Total external heat transfer coefficient, (W/m2K) h1g Heat transfer coefficient between basin liner and ambient air, hba (W/m2K)

TgiW TgoE TgoW L Kg Lg ISE ISW I(t) UgaE UgaW Pf X S Rex

Heat transfer coefficient between basin liner and basefluid, (W/m2K) Natural convective heat transfer coefficient, (W/m2K) Internal radiative heat transfer coefficient between east and west condensing cover, (W/m2K) Overall heat transfer coefficient between condensing cover and ambient air, (W/m2K) Overall heat transfer coefficient between basin liner and ambient air, (W/m2K) Emissivity of condensing cover Emissivity of the fluid Effective emissivity of fluid Stefan-Boltzmann's constant, (W/m2K4) Surface area of condensing cover of east side of solar still, (m2) Surface area of condensing cover of west side of solar still, (m2) Basin area of solar still, (m2) Area of solar still, (m2) Inclination angle of glass cover, (degree) Time interval (second) Ambient temperature, (°C) Fluid temperature, (°C) Inner condensing cover temperature of east side of solar still, (°C) Inner condensing cover temperature of west side solar still, (°C) Outer condensing cover temperature of east side of solar still, (°C) Outer condensing cover temperature of west side solar still, (°C) Latent heat of vaporization, (J/kg) Conductivity of condensing cover, (W/m° C) Thickness of condensing cover, (m) Solar intensity on east side of condensing cover, (W/m2) Solar intensity on west side of condensing cover, (W/m2) Total solar intensity on cover, (W/m2) Overall heat transfer coefficient between outer glass cover of east side and ambient (W/m2K) Overall heat transfer coefficient between outer condensing cover of west side and ambient air, (W/m2K) Partial saturated vapor pressure of the fluid, (N/m2) Characteristic length, (m) Salvage value of the system Exergoeconomic parameter

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L. Sahota et al. / Desalination 409 (2017) 66–79

Subscripts a b v gi f p ex en e c r th sol E W ann

Ambient Basin surface Vapor Inner condensing cover Fluid Particle Exergy Energy Evaporative Convective Radiative Solar East side West side Annual

Abbreviation BF

Basefluid

NF HTC EPBT EPF NPV DSSS LCCE UAC CRF SRF NP

Nanofluid Heat transfer coefficients Energy payback time Energy production factor Net present value Double slope solar still Life cycle conversion efficiency Uniform annual cost Capital recovery factor Shrinking fund factor Nnaoparticle

Appendix A

A = C1U2 + C2 A0 ¼ C 01 U 1 þ C 2 0 B ¼ ðh1 f ;E U 2 þ h1 f ;W hEW AgE ÞðA2b Þ B0 ¼ ðh1 f ;W U 1 þ h1 f ;E hEW AgE ÞðA2b Þ C1 = αg ISE AgE + UgaETaAgE

C2 = αg ISW hEWAgEAgW + UgaWTahEWAgEAgW C 1 0 ¼ α g ISW AgE þ U gaW T a AgW

U 2 ¼ h1 f ;W ðA2b Þ þ hEW AgW þ U gaW AgW 0

C 11 ¼ ðA2b Þ½h1 f ;E ð1− HB Þ þ h1 f ;W ð1− BH Þ ðA2b ÞðISE

C 22 ¼ þ I SW Þðα f þ 2α b U ga Þ C33 = UbaAb C 44 ¼ ðA2b ÞðH1 Þðh1 f ;E A þ h1 f ;W A0 Þ # " K

h1gE ð Lgg Þ

U gaE ¼

K

ð Lgg Þþh1gE

" U gaW ¼

K

h1gW ð Lgg Þ

#

K ð Lgg Þþh1gW

C 2 0 ¼ α g ISE hEW AgE AgW þ U gaE T a hEW AgE AgW

U ga ¼

H = U1U2 − h2EWAgEAgW

U ba ¼ ðh b; fþhba Þ

ðI SE þISW Þhb; f 2ðhb; f þhba Þ h

b; f

h

ba

U 1 ¼ h1bf ;E ðA2b Þ þ hEW AgE þ U gaE AgE

References [1] J.A. Eibling, S.G. Talbert, G.O.G. Lof, Solar stills for community use - digest of technology, Sol. Energy 13 (1971) 263–276. [2] H.P. Garg, H.S. Mann, Effect of climatic, operational and design parameters on the year round performance of single-sloped and double-sloped solar still under Indian arid zone conditions, Sol. Energy 18 (1976) 159–163. [3] M.A.S. Malik, G.N. Tiwari, A. Kumar, M.S. Sodha, Solar Distillation, first ed. Pregamon Press, UK, 1982. [4] G.N. Tiwari, Recent advances in solar distillation, in: K. Raj, K.P. Maheshwari, R.L. Sawhney (Eds.), Solar Energy and Energy Conservation, Wiley, Eastern, New Delhi 1992, pp. 32–149 (Chap. 2). [5] G.N. Tiwari, H.N. Singh, R. Tripathi, Present status of solar distillation, Sol. Energy 75 (2003) 367–373. [6] A. Trad, A. Kaabi, Effect of orientation on the performance of a symmetric solar still with a double effect solar still (comparison study), Desalination 329 (2013) 68–77.

[7] T. Arunkumar, R. Jayaprakash, D. Denkenberger, A. Ahsan, M.S. Okundamiya, S. Kumar, H. Tanaka, H.S. Aybar, An experimental study on a hemispherical solar still, Desalination 286 (2012) 342–348. [8] R. Sathyamurthy, H.J. Kennady, P.K. Nagarajan, A. Ahsan, Factors affecting the performance of triangular pyramid solar still, Desalination 344 (2014) 383–390. [9] T. Rajaseenivasan, K.K. Murugavel, Theoretical and experimental investigation on double basin double slope solar still, Desalination 319 (2013) 25–32. [10] P.U. Suneesh, R. Jayaprakash, T. Arunkumar, D. Denkenberger, Effect of air flow on “V” type solar still with cotton gauze cooling, Desalination 337 (2014) 1–5. [11] H.E. Gad, S.S. El-Din, A.A. Hussien, K. Ramzy, Analysis of a conical solar still performance: an experimental study, Sol. Energy 122 (2015) 900–909. [12] A.E. Kabeel, Performance of solar still with a concave wick evaporation surface, Energy 34 (2009) 1504–1509. [13] A.S. Abdullah, Improving the performance of stepped solar still, Desalination 319 (2013) 60–65. [14] F.T. Farshad, M. Dashtban, M. Hamid, Experimental investigation of a weir-type cascade solar still with built-in latent heat energy storage system, Desalination 260 (2010) 248–253. [15] A. Ahsan, T. Fukuhara, Mass and heat transfer model of Tubular Solar Still, Sol. Energy 84 (2010) 1147–1156. [16] S. Gorjian, B. Ghobadian, T.T. Hashjin, A. Banakar, Experimental performance evaluation of a stand-alone point-focus parabolic solar still, Desalination 352 (2014) 1–17. [17] D.B. Singh, G.N. Tiwari, I.M. Al-Helal, V.K. Dwivedi, J.K. Yadav, Effect of energy matrices on life cycle cost analysis of passive solar stills, Sol. Energy 134 (2016) 9–22. [18] I. Dincer, The role of exergy in energy policy making, Energ Policy 30 (2002) 137–149. [19] V.K. Dwivedi, Performance Study of Various Designs of Solar Stills(Ph.D thesis) IIT, New Delhi (India), 2009. [20] J.C. Torchia-Nuñez, M.A. Porta-Ga'ndarab, J.G. Cervantes-de Gortaria, Exergy analysis of a passive solar still, Renew. Energy 33 (2007) 608–616. [21] S. Vaithilingam, G.S. Esakkimuthu, Energy and exergy analysis of single slope passive solar still: an experimental investigation, Desalin. Water Treat. (2014) 1–12. [22] A. Hepbalsi, A key review on exegetic analysis and assessment of renewable energy sources for sustainable future, Renew. Sustain. Energy 12 (2007) 593–661. [23] R.V. Singh, R. Dev, M.M. Hasan, G.N. Tiwari, Comparative energy and exergy analysis of various passive solar distillation systems, World Renewable Energy Congress, Solar Applications, Linkoping, Sweden 2011, pp. 8–13. [24] M.R. Rajamanickam, A. Ragupathy, Influence of water depth on internal heat and mass transfer in a double slope solar still, Energy Procedia 14 (2012) 1701–1708. [25] G.N. Tiwari, A. Dimri, A. Chel, Parametric study of an active and passive solar distillation system: energy and exergy analysis, Desalination 242 (2009) 1–18. [26] K.H. Solangi, S.N. Kazi, M.R. Luhur, A. Badarudin, A. Amiri, R. Sadri, M.N.M. Zubir, S. Gharehkhani, K.H. Teng, A comprehensive review of thermo-physical properties and convective heat transfer to nanofluids, Energy 89 (2015) 1065–1086. [27] R.A. Taylor, P.E. Phelan, T.E. Otanicar, R. Adrian, R. Prasher, Nanofluid optical property characterization: towards efficient direct absorption solar collectors, Nanoscale Res. Lett. 6 (2011) 225. [28] G. Colangelo, E. Favale, P. Miglietta, A. de-Risi, M. Milanese, D. Laforgia, Experimental test of an innovative high concentration nanofluid solar collector, Appl. Energy 154 (2015) 874–881. [29] G. Colangelo, E. Favale, P. Miglietta, A. de-Risi, D. Laforgia, A new solution for reduced sedimentation flat panel solar thermal collector using nanofluids, Appl. Energy 111 (2013) 80–93. [30] R. Said, A. Saidur, Hepbasli, N.A. Rahim, New thermo-physical properties of water based TiO2 nanofluid-the hysteresis phenomenon revisited, Int. Commun. Heat Mass Transf. 58 (2014) 85–95. [31] R. Said, R. Saidur, N.A. Rahim, Optical properties of metal oxides based nanofluids, Int. Commun. Heat Mass Transf. 59 (2014) 46–54. [32] M. Du, G.H. Tang, Optical property of nanofluids with particle agglomeration, Sol. Energy 122 (2015) 864–872. [33] A.A. Hussien, M.Z. Abdullah, M.A. Al-Nimr, Single-phase heat transfer enhancement in micro/minichannels using nanofluids: theory and applications, Appl. Energy 164 (2016) 733–755. [34] M.S. Hossain, R. Saidur, M.F.M. Sabri, Z. Said, S. Hassani, Spotlight on available optical properties and models of nanofluids: a review, Renew. Sust. Energ. Rev. 43 (2015) 750–762. [35] S.Z. Heris, M.N. Esfahany, S.G. Etemad, Experimental investigation of convective heat transfer of Al2O3-water nanofluid in circular tube, Int. J. Heat Fluid Flow 28 (2007) 203–210. [36] J. Albadr, S. Tayal, M. Alasadi, Heat transfer through heat exchanger using Al2O3 nanofluid at different concentrations, Case Studies in Thermal Engineering 1 (2013) 38–44. [37] O. Mahian, A. Kianifar, A.Z. Sahin, S. Wongwises, Entropy generation during Al2O3water nanofluid flow in a solar collector: effects of tube roughness, NP size, and different thermophysical models, Int. J. Heat Mass Transf. 78 (2014) 64–75. [38] I.I. Ryzhkov, A.V. Minakov, The effect of NP diffusion and thermophoresis on convective heat transfer of nanofluid in a circular tube, Int. J. Heat Mass Transf. 77 (2014) 956–969. [39] Z. Said, R. Saidur, A. Hepbasli, N.A. Rahim, New thermophysical properties of water based TiO2 nanofluid-the hysteresis phenomenon revisited, Int. Commun. Heat Mass Transf. 58 (2014) 85–95. [40] Z. Said, R. Saidur, N.A. Rahim, Optical properties of metal oxides based nanofluids, Int. Commun. Heat Mass Transf. 59 (2014) 46–54. [41] R.S. Vajjha, D.K. Das, A review and analysis on influence of temperature and concentration of nanofluids on thermophysical properties, heat transfer and pumping power, Int. J. Heat Mass Transf. 55 (2012) 4063–4078.

L. Sahota et al. / Desalination 409 (2017) 66–79 [42] G. Huminic, A. Huminic, Application of nanofluids in heat exchangers: a review, Renew. Sust. Energ. Rev. 16 (2015) 5625–5638. [43] A.E. Kabeel, Z.M. Omara, F.A. Essa, Enhancement of modified solar still integrated with external condenser using nanofluids: an experimental approach, Energy Convers. Manag. 78 (2014) 493–498. [44] T. Elango, A. Kannan, K.K. Murugavel, Performance study on single basin single slope solar still with different water nanofluids, Desalination 360 (2015) 45–51. [45] Z.M. Omara, A.E. Kabeel, F.A. Essa, Effect of using nanofluids and providing vacuum on the yield of corrugated wick solar still, Energy Convers. Manag. 103 (2015) 965–972. [46] L. Sahota, G.N. Tiwari, Effect of Al2O3 NPs on the performance of passive double slope solar still, Sol, Energy 130 (2016) 260–272. [47] L. Sahota, G.N. Tiwari, Effect of nanofluids on the performance of passive double slope solar still: a comparative study using characteristic curve, Desalination 388 (2016) 9–21. [48] S.W. Sharshir, G. Peng, L. Wu, N. Yang, F.A. Essa, A.H. Elsheikhd, S.I.T. Mohamede, A.E. Kabeel, Enhancing the Solar Still Performance Using Nanofluids and Glass Cover Cooling: Experimental Study, Appl. Therm. Eng. 113 (2017) 684–693. [49] S. Kumar, G.N. Tiwari, Life cycle cost analysis of single slope hybrid (PV/T) active solar still, Appl. Energy 86 (2009) 1995–2004. [50] G.N. Tiwari, J.K. Yadav, D.B. Singh, I.M. Al-Helal, A.M. Abdel-Ghany, Exergoeconomic and enviroeconomic analyses of partially covered photovoltaic flat plate collector active solar distillation system, Desalination 367 (2015) 186–196. [51] Z. Said, R. Saidur, N.A. Rahim, Energy and exergy analysis of a flat plate solar collector using different sizes of aluminium oxide based nanofluid, J. Clean. Prod. 133 (2016) 518–530. [52] O. Mahian, A. Kianifar, S.A. Kalogirou, I. Pop, S. Wongwises, A review of the applications of nanofluids in solar energy, Int. J. Heat Mass Transf. 57 (2013) 582–594. [53] T.P. Otanicar, J. Golden, Comparative environmental and economic analysis of conventional and nanofluid solar hot water technologies, Environ. Sci. Technol. 43 (2009) 6082–6087. [54] V. Khullar, H. Tyagi, A study on environmental impact of nanofluid based concentrating solar water heating system, Int. J. Environ. Stud. 69 (2012) 220–232. [55] M. Faizal, R. Saidur, S. Mekhilef, M.A. Alim, Energy, economic and environmental analysis of metal oxides nanofluid for flat-plate solar collector, Energy Convers. Manag. 76 (2013) 162–168.

79

[56] C. Popiel, J. Wojtkowiak, Simple formulas for thermo-physical properties of liquid water for heat transfer calculations (from 0 °C to 150 °C), Heat Transf. Eng. 19 (1998) 87–101. [57] G.N. Tiwari, R.K. Mishra, Advanced Renewable Energy Sources, RSC Publishing Cambridge, UK, 2012. [58] B.K. Sovacool, Valuing the greenhouse gas emissions from nuclear power: a critical survey, Energ Policy 36 (2008) 2940–2953. [59] B.J. Huang, T.H. Lin, W.C. Hung, F.S. Sun, Performance evaluation of solar photovoltaic/thermal systems, Sol. Energy 70 (2001) 443–448. [60] P.J. Axaopoulos, E.D. Fylladitakis, Performance and economic evaluation of a hybrid photovoltaic/solar system for residential applications, Energy Build. 65 (2013) 488–496. [61] S. Agrawal, G.N. Tiwari, Enviroeconomic analysis and energy matrices of glazed hybrid photovoltaic module air collector, Sol. Energy 92 (2013) 139–146. [62] Y.R. Sekhar, K. Sharma, Study of viscosity and specific heat capacity characteristics of water-based Al2O3 nanofluids at low particle concentrations, J. Exp. Nanosci. 10 (2015) 86–102. [63] T. Yiamsawasd, A.S. Dalkilic, S. Wongwises, Measurement of specific heat of nanofluids, Curr. Nanosci. 8 (2012) 939–944. [64] B.C. Pak, Y.I. Cho, Hydrodynamic and heat transfer study of dispersed fluids with submicron oxide particles, Exp. Heat Transf. J. Therm. Energy Gener. Transp. Storage Convers. 11 (1998) 151–170. [65] K. Khanafer, K. Vafai, A critical synthesis of thermo-physical characteristics of nanofluids, Int. J. Heat Mass Transf. 54 (2011) 4410–4428. [66] H.E. Patel, T. Sundararajan, S.K. Das, An experimental investigation into the thermal conductivity enhancement in oxide and nanofluids, J. Nanopart. Res. 12 (2010) 1015–1031. [67] K. Sharma, P. Sarma, W. Azmi, R. Mamat, K. Kadirgama, Correlations to predict friction and forced convection heat transfer coefficients of water based nanofluids for turbulent flow in a tube, Int. J. Microsci. Nanoscale Therm. Fluid Transp. Phenom. 3 (2010) 283–308. [68] K.S. Wang, J.H. Lee, S.P. Jang, Buoyancy-driven heat transfer of water-based Al2O3 nanofluids in a rectangular cavity, Int. J. Heat Mass Transf. 50 (2007) 4003–4010. [69] C.J. Ho, M.W. Chen, Z.W. Li, Numerical simulation of natural convection of nanofluid in a square enclosure: effects due to uncertainties of viscosity and thermal conductivity, Int. J. Heat Mass Transf. 51 (2008) 4506–4516.