Exploitation of solar energy in the process of purification of the land surface water

Transcription

1 International Journal of Computation and Applied Sciences IJOCAAS, Volume 5, Issue 1, August 218, ISSN: Exploitation of solar energy in the process of purification of the land surface water Jaafar A. Kadhum Abstract Humanity faces a major problem: the lack of drinking water around the world that can affect the human future. Solar distillation systems are a possible solution to this problem as solar energy is currently used in the production of clean water for laboratory applications, drinking, and for agricultural purposes, depending on the size of the system. In this study, some improvements are being made to increase the productivity of the solar distillation. Two types of solar distillers were constructed and tested. The first is a simple traditional solar tub, which can produce 3L/ m 2 D of distilled water in summer. Type II is characterized by its design in a graduated form and this design increases the surface area exposed to the sun, causing an increase of 22% of distilled water production. Index Terms Solar energy, distillation, salty water, productivity. T I. INTRODUCTION he limited availability of drinking water in many parts of the world is an old problem, and till now many regions of the world inhabitants are suffering from this problem. Historically, humans have always tried to treat salt and brackish water and convert it into potable water that can be used in drinking and agriculture [1, 2]. While global fresh water resources are shrinking, due to explosive population growth rates, as well as significant environmental pollution that is caused by human activities for energy production and industry [3, 4]. Fresh water can be defined as water containing dissolved salts less than about 1 milligrams per mg (mg/l) [5]. In principle, only shallow distillation allows pure water to evaporate from the basin and to be collected on the glass cover, leaving all particulate pollutants in the distilled basin [6]. In general, fresh water is water that contains trace amounts of soluble salts, especially sodium chloride [7]. Natural sources of fresh water are rain, lakes, streams, rivers, and groundwater with salt content of less than 5 ppm [8]. Saltwater is water that is naturally present in the ocean or sea and has a high salinity. Full-strength sea water contains 35 parts of salt, especially sodium chloride per 1, parts of water, while salinity is equal to 35 (p.p.t) equal to 3.5% [9]. Too much salinity in the water is detrimental to human health. Salinity is considered as 5 mg/litre but the lower the better it is, and up to 1 mg/l of salinity is considered the maximum human consumption in the long term [1]. Any value greater than 1, (mg/l) has long-term adverse health effects [11]. The distillation and desalination of water is not a new process but it is very old, as the old models are the fixed types that consist of a tank with black ground and transparent cover. It is not necessary to boil and distil water, and distillation is one of the many processes available to purify the water [12]. The freely available sun rays can provide the thermal energy that can be used to accomplish this process [13]. The benefit of solar radiation requires the use of more space to collect solar energy. Solar distillation systems can be large or small in size and are designed to serve one family with a capacity of 3 to 15 litres of drinking water per day, or designed to produce much more fresh water for the processing of a village or small town [14]. Solar-powered distillation systems are affordable and technologically low cost. Distilled solar is a simple device to obtain distilled drinking water and solar energy is used as fuel for this process [15]. These desalination units have low installation cost and no fuel consumption. However, solar distillates are characterized by two important factors: reduced production capacity of distilled water, and the need for large space to receive solar radiation [16]. Solar distillers consist of a rectangular basin with shallow water and a basin made of glass or reinforced plastic. The bottom of the basin is painted black to increase the absorption of solar radiation [17]. The distilled solar does not contain moving parts or filters and does not require any type of fuel [18]. The rising water vapour from the aquarium is condensed on the surface of a composite glass lid at the top of the aquarium and collects condensate water. Solar distillates are characterized by other industrial distillation systems that do not require any kind of energy, nor are skilled operators, they can be manufactured locally and do not require complex maintenance, and low cost to build and operate [19, 2]. The performance of the solar distillator depends on the availability of solar radiation. The amount of solar energy in Iraq is about 25 kw/m 2. So, Iraq is well qualified for solar distillation and can be a good solution for the production of fresh water [21]. The solar distillate can be placed on the roof of the building, in the garden, or anywhere as long as it reaches sufficient amount of sunlight [22]. Distilled water produced from the solar system is not commercially successful, because solar distillers use natural evaporation and condensation in a process similar to that of rain water [23]. This allows the natural ph level to produce excellent quality compared to steam distillation [23]. Pollution in the distilled basin causes some errors in the construction of the basin and there are several ways to reduce pollution from the materials in the basin itself [24]. Sodium bicarbonate can be added to the aquarium for several days to avoid most volatile substances [25]. Distillate parts must be manufactured from noble materials

2 International Journal of Computation and Applied Sciences IJOCAAS, Volume 5, Issue 1, August 218, ISSN: to prevent any bad or toxic effect on the water flowing through, even in high temperature conditions that may occur, so the relatively low-cost polyvinyl chloride plastic pipe is preferred [26]. Vinyl chloride has been identified as a carcinogen that can be harmful to workers in the manufacturing of ponds, so we must be very careful about the use of these substances in the drinking water system. It is therefore recommended to build distillation plants still water each of the heat-resistant glass materials [26, 27]. Solar distillers are a useful device for the production of potable water and are important for industrial application, hospitals and laboratories as well as for radiator and battery maintenance [28, 29]. To study the water distillation still as a thermal system, first the control volume must de applied as shown in Figure (1), and then consider the energy and mass balances around the system [3]. Fig. 1: Water distillation still as a thermal system Energy inters the system are [32]: a. Direct radiation of solar energy. b. Ambient and surrounding reflecting radiation energy. Energy leaves the system are [33]: a. Heat transfer from still walls by convection. b. Heat transfer to surrounding by radiation. c. Radiation lost energy to surrounding by reflection. d. Heat energy transfer to ground by conduction. e. Energy lost by clean water outlet. f. Energy lost with waste salty water. Due to the several number and complexity of the heat and mass transfer, included in the water still system it was seen that modelling the whole water still distillation system was too complex [34]. The sun energy is not constant with the time and, also due to the change of the sun location and the existence of dust and clouds, air pollution and etc, along the day. The unsteady state conditions are existed in all parameter of the water still distillation, so it is too difficult to get a mathematical formula with the unsteady state condition. So, depending on practical work will by better and more satisfaction in evaluation to approach the optimum system [35, 36]. Finally important notes must be considered during this study as follow: - The size of the still must with a standard size as 1 or 2 meter square. - The quantity of brine water in basin must be kept at minimum, because a lot of salty water in basin will absorb the solar radiation energy and remain the salty water temperature at low level. - The salty water basin walls must be insulated, because some heat energy will escape to ambient, that tend to redaction in still performance. - The temperature deference between glass upper surface of collector and salty water, must kept maximum as possible, it is the important parameter which defined the still performance. - The transparency of glass condenser cover must be of high quality to reduce the absorption of solar radiation which tends to heat the glass. - The distance between surface of salty water and glass lower surface must be kept at minimum as possible, to shortage the vapour transfer distance. - The glass collector thickness must be at minimum to increase the heat transfer of the condensed vapor to the surrounding. - Water distillation still must be placed in open space, with high wind speed, and under sun light for along period of time. - The incident angle of the solar light on glass collector surface must be kept vertical to reduce the reflectivity of the light on the glass surface. - The upper surface of the glass collector must be kept clean, because dust will absorb the light energy and tends to increase the glass temperature, this will reduce amount of condense water on hot dusty glass. - The water distillation still system must be completely closed, to prevent any escape of the vapour to the surrounding, only small pipe for salty water inlet and small pipe for clean water outlet. The aim of this study is to evaluate the enhancement in the productivity of a gradual basin solar distiller and comparing it of a simple single slope solar distiller with same collector area in two main seasons in Iraq, summer and winter. Any improvement or increase in the production of solar distillate is an added benefit to the distillation process. So, the proposed distiller will undergo an improvement to raise the efficiency of distillation to be suitable for work in the atmosphere of Iraq. II. EXPERIMENTAL SETUP Two solar distillers were fabricated and tested, to evaluate the best one of them and to determine to determine the possibility of improving the proposed distillate production. The first simplified type of glass was built as rectangular box; the upper transparent surface is inclined with 12 o. The glass box was painted with black color to absorb the sunlight radiation as shown in Fig. (2). Dimension and technical details of the basin are: o Basin cross section area 1 m 2 o Basin length 12 mm o Basin width 834 mm o Front height 1 mm o Rear height 2 mm o Salty water capacity 7 litre o Angle of glass collector 12 degree o Salty water maximum depth 7 mm

3 Temperature ( C) International Journal of Computation and Applied Sciences IJOCAAS, Volume 5, Issue 1, August 218, ISSN: o Constricted material, all from glass. A. Tests Procedure The two studied distillers were put on the roof of the Energy and Renewable Energies Technology Center in the University of Technology. The productivity of the two stills was measured twice a week for the studied period with conditions of shiny and no shadow from clouds or dust. The basin water temperature was measured also as well as the ambient temperature. The average of the measured data (temperature and productivity) was taken and compared. Fig. 2: Simple single slope rectangular glass basin The second model of distillation system, that has been constructed with technical specification as the Water vapour can move from the hot part which facing the sun to the cold part in opposite face of the system or we can say in shadow face, and the collector bed covered by charcoal to absorb the water and form the sun as shown in Fig. (3). III-RESULT AND DISCUSSION Fig. 4 shows the temperature distribution for winter season for the water in the distillers' basin and ambient temperature. The graduate distiller raise the water temperature in its basin compared to the simple single slope solar distiller and ambient air. This increase in the temperature comes from the increase in the basin area. This increase in the basin area has increased the overall gained temperature by 67.8%. 6 5 Ambeint temperature Fig. 4: The tested distillers' basin temperatures variation with time at winter season Fig. 3: Gradual solar distillation system with vapor circulation technology Dimension and Technical details as following: o Collector length. 12 mm o Collector width. 834 mm o Collector thickness. 12 mm o Collector bed covered by charcoal. o Make the bed as graduate surface to keep the o water in all side of the bad. Introduce sun-tracking system to keep the sun radiation fall vertically along the day. Experiments were conducted in Iraqi summer (June to August 217) and winter (mid November 217 to end of January 218) to verify the Iraqi climates effects on both distillers. Fig. 5 shows that the two tested distillers' temperatures rose highly at summer season compared to winter. The maximum achieved temperature was 7 C for graduate distiller water. Here we must concentrate on the high ambient temperature of Iraqi weathers at summer season as the maximum average temperature recorded for the testing period was 5 C. This high temperature inhibits the cooling of the glass, reducing the heat transferred to the air, and as a result negatively affected the distillation productivity.

4 Productivity (l/m 2 ) Temperature ( C) Productivity (l/m 2 ) International Journal of Computation and Applied Sciences IJOCAAS, Volume 5, Issue 1, August 218, ISSN: Summer Ambeint temperature Summer Fig. 5: The tested distillers' basin temperatures variation with time at summer season Fig. 6 represents the average productivity of the two tested distillers at winter season. In this season, the productivity of the graduate distiller exceeded the simple single slope solar distiller. This was because of the better heating of basin water for the graduate distiller. The average increase in productivity was 32.9%, which indicates that this distiller is better than the simple distillate in winter season of Iraq Winter Fig. 6: The tested distillers' productivity variation with time at winter season Fig. 7 declares the average productivity of the tested stills at summer season of Iraq. In the summer, the ambient temperature is high and also solar radiation intensity is high, which leads to higher water temperatures in the distilled basin as shown in the figure 5. However, during the period from 12 AM to 3 PM, the yield of the two distillates is less than expected. The reason for this is the high temperature of the condenser (distiller's glass) and because of the high temperature of the external atmosphere does not cool the glass to the desired level required, which reduces the distillation productivity. This phenomenon has been studied by Ref. [37] in detail and developed solutions. The reader interested in this issue can return to the reference above. Fig. 7: The tested distillers' productivity variation with time at summer season VI- CONCLUSION It seems that the use of small distillation stills is suitable solution for supplying a family by fresh water. The first and most important requirement for using solar distillation is satisfied, which is the high solar energy. Radiation density in Iraq is suitable for this application. The tests were conducted on two fabricated distillers. The performance of the two distillers declared that the single slope solar distiller type is simple and cheap. It does not require skilled workers to build it, low maintenance required with low fresh water production, as the maximum production of this type was about 3l/m2.D in average at winter season. It is not small quantity, it is sufficient for one person, especially if we know that it is cheap in price, simple to maintain and easy to constructed. So a collection of two or three units is sufficient to supply clean water for drinking and cooking purposes of one small family. The second distillation system is more complex but its productivity is higher than the first still at winter. Its defect is more complex in construction. It can produce about 4.5 L/m 2 D. This distiller has low productivity as the first one at summer due to difficulty of cooling the condenser (glass). REFERENCES [1] S.S. Dutt, K. Hiroaki, S. Kazunobu, "Phase change materials for low temperature solar thermal applications," Res. Rep. Fac. Eng. Mie Univ., vol. 29, pp.31-64, 24. [2] M.T. Chaibi, T. Jilar, "System performance and design of roofintegrated desalination in greenhouses," Proceedings at the ISES Solar World Congress, Gothenburg, 23. [3] M.T. Chaichan and K. I. Abass, "Productivity amelioration of solar water distillator linked with salt gradient pond," Tikrit Journal of Engineering Sciences, vol. 19, No. 4, pp , 212. [4] S.A. Kalogirou, "Sweeter desalination using renewable energy sources," Progress in Energy and Combustion Science Journal, vol. 31, No. 3, pp , 25. [5] M.M. El-Kassaby, "Parabolic type solar still," Renewable Energy, vol. 1, pp , [6] M.T. Chaichan & H. A. Kazem, "Using aluminum powder with PCM (paraffin wax) to enhance single slope solar water distillator productivity in Baghdad-Iraq winter weathers," International Journal of Renewable Energy Research, vol. 1, No. 5, pp , 215.

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