Improving the productivity of solar still by using water fan and wind turbine
Introduction
Extracting the potable freshwater from saline/brackish water is a function of solar still that can be utilized. These devices are suitable for a single house or a small community for providing good quality drinking water. The productivity of fresh water by CSSs is limited as investigated by many researchers. In addition, thermal efficiency of CSSs is low (∼35–40%) with normal daily productivity of 3–4 L/m2 d (Yadav and Sudhakar, 2015).
Several techniques and designs have been developed to improve efficiency and productivity of CSSs, such as double-basin (Al-Karaghouli and Alnaser, 2004), multi-effect (Tanaka and Nakatake, 2007), regenerative (Abu-Arabi and Zurigat, 2005), stepped still (Ziabari et al., 2013), corrugated wick (Omara et al., 2015), tubular solar (Ahsan and Fukuhara, 2010), conical still (Gad et al., 2015), solar still with reflectors (Tanaka, 2010, Tanaka and Nakatake, 2009), rotating drum (Lilian et al., 2016), solar collectors (Voropoulos et al., 2003), with fins and sponges (Velmurugan et al., 2008), internal condenser (Al-Nimr and Dahdolan, 2015), and hybrid solar still (Voropoulos et al., 2003), special designs (hemispherical, spherical, triangular, concave, etc.) (Durkaieswaran and Kalidasa, 2015) and using nanofluids (Lovedeep and Tiwari, 2016). A review of different techniques and designs of various solar stills was made by (Mojtaba et al., 2016, Sivakumar and Ganapathy, 2013).
The various factors that affect the daily distillate of multiple-effect stills integrated with a solar collector were investigated by Tanaka and Nakatake (2007). Also, influence of inclination of external collector of conventional still in winter was conducted by the same researchers.
Ziabari et al. (2013) simulated a stepped still under two climatic conditions of Koshk and Bandar Abbas, Iran. Results demonstrated that the average productivity of freshwater was 6.7 L/m2/d, which was higher by 26% in comparison with the initial site (Koshk village). Ahsan and Fukuhara (2010) proposed a new model of heat and mass transfer of a tubular still. They found that, the heat balance of the humid air and the mass balance of the water vapor in the humid air were formulized for the first time.
Tanaka (2010) conducted a numerical study to investigate the effects of external reflectors and internal reflectors on the conventional still. He concluded that the daily productivity could be increased by inclining the external reflector forward in all seasons except for in summer become backward. A conventional solar still integrated with a rotating drum enhanced more daily distillate compared with a conventional one (Lilian et al., 2016). The speed of drum and saline water level were ranged from 0.25 to 4 rpm and 1 to 5 cm, respectively. They found that daily distillate is inversely proportional to drum speed.
A conventional still, a conventional collector and a storage tank were connected together (Voropoulos et al., 2003) to study the influence of augmentation on the solar still. The solar still inlet was connected to solar collector (fin type) as its outlet was fed to the solar still. They indicated that the productivity utilizing augmentation was improved by 52% with saline water as a feed. Al-Nimr and Dahdolan (2015) modeled a novel concentrated still that increases with an internal condenser and a porous evaporator, for different condenser and ambient temperatures, solar irradiations and wind speeds, using Microsoft Excel software. They concluded that a reduction in temperature of condenser and the speed of wind alleviated the efficiency and productivity of the solar still.
The daily distillate of still depends on the heat transfer mechanism and working temperature. The heat transfer coefficients can be increased by enhancing the thermo-physical properties of saline water. Suspension of nanoparticles into saline water is a simple technology which enhances the thermo-physical properties (Lovedeep and Tiwari, 2016).
The fresh water amount condensed in CSS depends on the glass cover temperatures and velocity of air flows on the outer surface of cover of glass. Al-Hinai et al. (2002) predicted dependency of solar still distillate on operational parameters and climatic by using a theoretical model. Their results showed that an increase of 1–3 m/s leads to 8% augmentation of distillate.
An experimental and theoretical study on a solar still was developed by Abu-Qudais et al. (1996). In this work, an increase in water productivity was observed when the velocity of air was higher than 1.5 m/s, and decreases for a velocity of air of 3 m/s. This means that any additional cooling reduced the water temperature in the basin, i.e. a slight breeze was sufficient to enhance the efficiency. An experimental research on a CSS was developed by Margarita et al. (2015). His results showed increments in the production and total efficiency when the velocity of air increases up to 5.5 m/s. Above this velocity, these increments were diminished. In addition, he concluded that the optimum velocity is achieved at 3.5 m/s.
Zeinab and Ashraf (2005) used a rotating shaft with horizontal axis introduced near to the water surface of the absorber of solar still to improve still performance. They used an electrical motor to rotate the shaft. Their results showed that the still thermal efficiency was improved by 5.5% at July, 5% at June, and 2.5% at May.
Eltawil and Zhengming (2009) presented a hybrid desalination system that constitutes of inclined solar water distillation (ISWD) and wind turbine (to rotating horizontal shaft) integrated with main solar still (MSS). The effect of change water depths (1, 2 and 3 cm), different flow rates of feeding water (25.0, 41.7 and 58.3 ml/min) and two modes of operation as due south and tracking the sun are consider. They indicated that the daily water productivity from the ISWD could be higher than the MSS by about 26.55–29.17%.
In our previous study (Kabeel et al., 2012), we have experimentally attempted to improve the fresh water production of CSS by using a rotating water fan with a vertical shaft. A photovoltaic system (PV) used to power a DC-motor, which used to rotate the water fan. The effect of the water fan speed (ranged from 30 to 45 rpm) and the saline water depth (ranged from 1 to 7 cm) on the performance of the still was studied. Experimental results indicated that the still production increases with fan speed and the maximum difference of yield between FSS and CSS is obtained at water depth of 3 cm (with fan rotation). In addition, we concluded that utilizing water fan enhances the yield by about 25% at a speed of 45 rpm, and a depth of 3 cm.
In the same study, some difficulties are created and not solved. The vertical shaft of rotating fan passes through the still base through ball bearing, so that this connection increases the chance of leaking. In addition, the initial cost of the PV system is high and the projected area of PV cell is considered in still efficiency calculations.
The aim of this study is solve the problems in our previous work. In the present work water fan powered by wind turbine is used to increase the distillate of CSS. The rotating shaft passes through back side wall of still, so there is not leaking. In addition, initial and maintenance costs are reduced. The new system has small space about previous system.
Section snippets
Experimental setup
To eliminate the influence of experimental conditions, two solar stills (FSS and CSS) were manufactured, Fig. 1. The FSS prepared with a water fan works with wind turbine.
Experimental procedures
The experimental tests were carried out at University of Prince Sattam bin Abdulaziz, KSA, and the tests were performed from 8 am to 6 pm during July and November 2015. Every 1 h the accompanying parameters were measured for various depths and various modes of experimentations: atmospheric temperature, solar irradiation, glass cover temperature, saline water temperature and water productivity, while the velocity of wind was measured every 0.5 h. The totally accumulated productivity is also
Experimental uncertainty analysis
The present study used the same method proposed by (Holman, 1994) for estimating the uncertainty in the results. Suppose a set of measurement is made in order to measure “n” number of experimental variables. These measurements are then used to calculate some desired result of the experiment (R). Thus
Let WR be the uncertainty in the result and W1, W2, W3,…..….................Wn be the uncertainties in the independent variables. The uncertainty in result is
Experimental results and discussion
Experimental results carried out in this study are used to discuss and put more shed on the effects of, water productivity, solar irradiation, wind velocity, water depth, daily efficiency and hourly efficiency.
Conclusions
Effect of incorporating wind turbine and water fan into conventional still was investigated to indicate how much this modification effects on solar still performance. In this study, the following points can be concluded:
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The daily amount of distillate is affected by the water depth and the wind turbine rotational speed.
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An effective method to enhance the rate of evaporation, and hence improving the freshwater production is proposed and is based on using a fan inside the solar still.
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The amount of
References (28)
- et al.
Year-round comparative study of three types of solar distillation units
Desalination
(2005) - et al.
Experimental study and numerical simulation of a solar still using an external condenser
Energy
(1996) - et al.
Mass and heat transfer model of tubular solar still
Sol. Energy
(2010) - et al.
Parametric investigation of a double-effect solar still in comparison with a single-effect solar still
Desalination
(2002) - et al.
Experimental comparative study of the performances of single and double basin solar-stills
Appl. Energy
(2004) - et al.
Modeling of a novel concentrated solar still enhanced with a porous evaporator and an internal condenser
Sol. Energy
(2015) - et al.
Various special designs of single basin passive solar still – a review
Renew. Sustain. Energy Rev.
(2015) - et al.
Wind turbine-inclined still collector integration with solar still for brackish water desalination
Desalination
(2009) - et al.
Thermal analysis of a conical solar still performance: an experimental study
Sol. Energy
(2015) - et al.
Effect of using nanofluids and providing vacuum on the yield of corrugated wick solar still
Energy Conserv. Manage.
(2015)
Influence of water depth on internal heat and mass transfer in a plastic solar still
Desalination
Different domestic designs of solar stills: a review
Renew. Sustain. Energy Rev.
Improvement techniques of solar still efficiency: a review
Renew. Sustain. Energy Rev.
Monthly optimum inclination of glass cover and external reflector of a basin type solar still with internal and external reflector
Sol. Energy
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Currently Prince Sattam bin Abdulaziz University, Saudi Arabia.