Research Article. An Experimental Study of a Single Surface Solar Water Distiller

Transcription

1 International Journal of Engineering & Technology Sciences (IJETS) 1 (2): 84-95, ISSN Academic Research Online Publisher Research Article An Experimental Study of a Single Surface Solar Water Distiller Aburime B.A a, Kwasi-Effah C.C b* and Egware O.H c* a,b,c Department of Mechanical Engineering, University of Benin, P.M.B 1154, Benin City, Nigeria *Corresponding author collinshicent@yahoo.com, henryegware@yahoo.com ARTICLE INFO Article history Revised:1May Accepted:23May Keywords: Solar water distiller, Energy, efficiency, Rural, Renewable, Health. A b s t r a c t The availability of fresh water resources and their quality is essential to improve human health in rural areas of numerous developing countries worldwide. In this paper, an experimental single slope solar water distiller with an active surface area of 0.192m2 was evaluated. The data used was obtained from daily recording of temperature, average volume evaporated and energy of hourly in 8 days in the month of November 2011(16th 23rd). Result showed that the average volume distilled per day is approximately liters and liters on non - incorporating and incorporating a reflector respectively. The solar still consist of an air-tight basin, in which saline or contaminated water is evaporated and condensed on the top cover for collection. The solar water distiller has shown to be a viable alternative for distilled water production. The energy source is renewable and environmentally friendly. Academic Research Online Publisher. All rights reserved. Nomenclature: Q e = the amount of energy utilized in vaporizing water in the still (J/m 2 ), L = latent heat of vaporization of water (J/kg), n = solar still efficiency, Qt = the amount of incident solar energy in the still (J/m 2 ), M e =daily solar still production 1. Introduction The inadequate access to fresh water resources or the inappropriate quality of these same resources is a common problem in developing countries [1]. Improving the availability of fresh water resources and its quality with simple technological innovations can therefore contribute to a rapid enhancement in the livelihoods of the rural population in these areas. Solar water distillation is a simple, yet effective, technology that has long been used to provide potable water in many remote areas of arid and semi-arid developing countries [2]. The first known

2 use of solar stills dates back to the 16 th century, when Arab alchemist used this system to distil water on a small scale [3] The principle The basic principle behind solar distillation is simple and replicates the natural process purification [4]. A solar still is an air tight basin that contains saline or contaminated water (i.e. feed water). It is enclosed by a transparent top cover, usually of glass or plastic, which allows incident solar radiation to pass through. The inner surface of the basin is usually blackened to increase the efficiency of the system by absorbing more of the incident solar radiation [5]. The feed water heat up, then starts to evaporate and subsequently condenses on the inside of the top cover, which is at a lower temperature as it is in contact with the ambient air. The condensed water (i.e. the distillate) trickles down the cover and is collected in an interior trough and then stored in a separate basin [6]. This system is also known as passive solar still, as it operates solely on sun s radiation [7]. The following happens inside the distiller unit: the part of the solar radiation that is not reflected nor absorbed by the cover is transmitted inside the solar still, where it is furthered reflected and absorbed by the water mass [8]. The amount of solar radiation that is absorbed is a function of the absorptivity and depth of the water. The remaining energy eventually reaches the blackened basin liner, where it is mostly absorbed and converted into thermal energy [8] Design In the last decades, several designs for the solar stills have been proposed and investigated. The common objective behind these new designs is to maximize the output by increasing the efficiency of the system. It is possible to classify the passive solar stills as: basin, wick, diffusion or other type of stills [9].There are numerous variations on the single basin still, but the two main categories are single slope and double slope stills. The main difference between these two types of still is that the cover of the double-slope still is of a roof-type, while the single slope still presents just one inclined cover plate. Latitude is one of the factors that determine whether single or double slope still should be used. At latitudes lower than 20, single slope stills with equator facing cover are recommended [10].Since Nigeria is located in Latitude 4 and 14 North, the single slope is preferred for our design. However, both types of still can successfully be used. 85 P age

3 2. Experimental procedures 2.1. Materials and mix design The experimental single surface solar still isometric view showing all it components is represented in Figure 1. The solar still basin has a top cover made of glass, arranged in form of a roof of a house, with an interior surface coated with a back paint. The interior surface improves absorption of the sun s rays. Feed water is poured into the still to partially fill the basin. The glass cover allows the solar radiation (short wave) to pass into the still, which is mostly absorbed by the blackened base. A reflector of a parabola shape made of plane mirror is used to increase the isolation of the sun rays in the still. The water begins to heat up and the moisture content of the air trapped between the water surface and the glass cover increases. The base also radiates energy in the infra red region (long waves) which is reflected back into the still by the glass cover, trapping the solar energy inside the still (the green house effect). The heated water vapour evaporates from the basin and condenses on the inside of the glass cover. Condensed water trickles down the inclined glass cover to an interior collection trough and out to a storage bottle. Every morning the still is filled with some quantity of dirty water to be purified for each day. The still will continue to produce distillate after 50 minutes down until the water temperature cools down. The basin should be clean every day to flush out impurity left. General operation is represented in block diagram as shown in Figure 1. The operation is simple and requires placing the still where there are sun s rays. Still are modular and for greater water requirements, several stills can be connected together in series or parallel as desired Solar Still Production and Efficiency The intensity of solar energy falling on the still is the most important parameter affecting production. The daily solar still production, Me Q L e = (1) Qe The solar still efficiency, η = x 100 (2) Q Equation 2 can also be expressed as n = t actual mass evaporated maximum possible water x 100 % 86 P age

4 Fig. 1. Isometric view of a Single Surface Solar water Distiller; 1. Reflector, 2. Rollers, 3. Stand, 4. Casing silver coated, 5. Outlet channel, 6. Trough or Basin, 7. Rectangular shaped glass, 8. Right Angle Triangular shaped glass, 9. Inlet channel, 10. Sun, 11. Sun rays, 12. Galvanized metal sheet coated black. Solar Energy Dirty Water Single Surface Still Distill Water Fig 2. Block Diagram of a Single Surface Solar Still Operation Having fabricated a portable single surface solar still distiller with an active surface area of 0.192m 2, an experimental analysis was carried out in duration of about 16 day during the dry season (November, 2011). Using A complete metrological data, experimental data were used to analyze it in other to find out the efficiency of the system and volume of distilled water produced on the basis of incorporating a reflector and not incorporating a reflector under the same weather conditions. 87 P age

5 3. Results and Discussion 3.1. Experimental Data The data used when obtained from the daily recording of temperature, average volume evaporated and energy of hourly in 8 days in the month of November 2011(16 th 23 rd ). The data for reflector not incorporated and reflector incorporated are shown In Tables 1 and 2 respectively. The values produced variation with time are in Tables 1 and 2 are similar, therefore Day 1 is used to represent the changes. The volume evaporated with time for Day 1 Reflector not incorporated and Reflector incorporated are represented in Figures 3 and 4 respectively. Table1: Average Irradiation, Volume and Data As At November 2011 Reflector Not Incorporated Day 1 Day 2 Time GMT (hrs) Average Day P age

6 Day 4 Day 5 Day 6 Day 7 Day P age

7 Table 2: Average Irradiation, Volume and Data As At November 2011 Reflector Incorporated Day 1 Day 2 Day 3 Day 4 Day 5 Time (hrs) Average P age

8 Day 6 Day 7 Day Volume 100 hour Time (Hr) Fig. 3. Change in Volume of Water Evaporated per hour with Time For Reflector Not Incorporated. 91 P age

9 Volume hour (ml) Time (Hr) Fig. 4: Change in Volume of Water Evaporated per hour with Time For Reflector Incorporated. 3.2 Analysis of Data The data from Tables 1 and 2 are analyzed using their mean values and Equations 1 and 2 are applied. From Table 1, Average sum energy irradiated by sun for 8 days = W/m 2 Total volume evaporated within 8 days =4681mL Average Total volume evaporated =585.13ml = L = kg Amount of energy required to vaporize 1Kg = 2260kJ Area of the unit= 0.53x0.363 = 0.192m 2 Thus, x x3600 = kJ/hr Since the duration time is 9hrs, Total average amount of energy transferred by the sun to water = kJ/hr x 9hr = kJ Applying Equation 1, Maximum possible water vapor = kJ/2260 =1.430kg Using Equation 2, Efficiency of the unit =actual mass evaporated/maximum possible water vapor x 100 = 0.585/1.44 x Page

10 =40.63% Also, from Table 2, average sum energy irradiated by sun for 8 days = 519W/m 2 Total volume evaporated within 8 days =6770 Average Total volume evaporated =846.25ml = L = kg Amount of energy required to vaporize 1Kg = 2260kJ Thus, x 1055 x x = J/hr = kJ/hr Since the duration time is 9hrs, total average amount of energy transferred by the sun to water = kJ/hr x 9hr = kJ Thus, Maximum possible water vapor = kJ/2260 =1.44kg Efficiency of the unit =actual mass evaporated/maximum possible water vapor x 100 = /1.44 x 100 =58.77% Percentage increase in efficiency (% increase in n) = incorporated reflector efficency non incorporated reflector efficiency non incorporated reflector efficiency x 100 % (3) Percentage increase in efficiency= ( )/40.63=44.65% From the analysis, it was observed that the efficiency of the single slope with reflector not incorporated is 40.63% and reflector incorporated is %. The efficiency of the solar still has shown to increase by 44.65% with the incorporation of a reflector. This purely indicates that the efficiency of the solar still increases with the increase in solar irradiance. Figures 3 and 4 reveals that the reflector increases the water quantity produced in Day 1. More Volume was produced at high temperature and high except Day 1 and 2 when reflector was incorporated. These 93 P age

11 conform to the rules of heat transfer. The result shows that heat is absorbed by system, explained well by the greater volume collected at the end of each experiment. 4. Conclusion An experimental single slope solar water distiller with an active surface area of 0.192m 2 has been evaluated. The average volume distilled daily was found to be L and L on not incorporating and incorporating a reflector respectively. However, the degree of irradiance is has shown to be of major effect on the efficiency of the system. The efficiency of the system was found to be 40.65% and 58.77% on not incorporating a reflector and incorporating a reflector respectively. It is essential to note that the solar still will only produce the expected output when it is fully airtight. However, the results presented above indicate that solar still is a viable measure for the improvement of the portable water quantity and quality especially in rural area. References [1] AHayek I. The effect of using different designs of solar stills on water distillation. Elsevier: Desalination 2006; 1(167): [2] Hanson A et al. Distillate water quality of a single-basin solar still: laboratory and field studies. Elsevier: Solar Energy 2004; 1(76): [3] Malik MAS, Tiwari, GN, Kumar A, Sodha MS. Solar distillation. Pergamon press Ltd, United Kingdom 1982; 1(1): [4] Badran OO, Abu-Khader MM. Evaluating thermal performance of a single slope solar still. Heat Mass transfer 2007; 1 (43): [5] Tiwari GN, Singh HN, Tripathi R. Present status of solar distillation. Elsevier: Solar Energy 2003; 75: [6] Al-Hayek I, Badran OO. The effect of using different designs of solar stills on water distillation. Elsevier: Desalination 2004; 1(169): [7] Tiwari GN, Singh HN. Solar distillation. Solar Energy Conversion and Photoenergy Systems 2004; 1(2): [8] Fath HES. Solar distillation: a promising alternative for water provision with free energy, simple technology and clean environment. Elsevier: Desalination 1998;1( 166): P age

12 [9] Flendrig LM, Shah B, Subrahmaniam N, Ramakrishnan V. Low cost thermoformed solar still water purifier for D&E countries. Elsevier: physics ans Chemistry of the Earth2009;1(34): [10] Kalidasa Murugavel K, Chockalingam KSK, Srithar K. Progress in improving the effectiveness of the single basin passive solar still. Elsevier: Desalination 1998; 1(220): P age