DESIGN FABRICATION AND PERFORMANCE ANALYSIS OF CONCAVE SOLAR STILL

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1 DESIGN FABRICATION AND PERFORMANCE ANALYSIS OF CONCAVE SOLAR STILL A.VembathuRajesh 1*, C.Mathalai Sundaram 1, V.Sivaganesan 1, B.Nagarajan 1, M.Pradeep 1, 1 Department of Mechanical Engineering, Nadar Saraswathi College of Engineering & Technology, Theni, Tamil Nadu, India. *Corresponding Author ID: avr.krj@gmail.com ABSTRACT The amount of distillate water from a solar still depends on different parameters. The evaporative surface area and glass cover temperature are the most effective parameters. Increasing the surface area or decreasing the cover temperature will enhance the distillate output. In this work, a weir concave type solar still with four glass cover surfaces is studied experimentally. The main advantage of using four glass cover surface is to increase the amount of solar radiation falling on the evaporative surface. Most of the day time, there is a temperature difference between the four still glass sides and the evaporative surface which allow more vapor to condensate on the lower glass cover surface. Results have shown that the average distillate productivity during the day time is approximately 4 L/m2 with a system efficiency of 0.38 at solar noon. It is higher than the conventional type solar still. Keywords: Solar still, Concave Basin Solar still, Pyramid Solar still 1. INTRODUCTION SOLAR DISTILLATION Solar distillation has been used for many years, usually for comparatively small plant outputs. Over the years, substantial research has been carried out to find out ways into improving the efficiency of the process. Research work has been carried out in many parts of the world. Solar distillation uses, in common with all distillation processes, the evaporation and condensation modes, but unlike other processes energy consumption is not a recurrent cost but is incorporated in the capital cost of the solar collector. The solar still therefore, is of a simple design, construction and maintenance with ease of operation. It is best suitable for regions of the world with high solar intensities. The mechanism of operation is based on the transmitting, absorption and reflective properties of glass and other transparent materials. The glass has the property of transmitting incident short-wave solar radiation which passes through the glass, the glass being a medium of transfer of heat, into the still to heat the brine. However, the re-radiated wavelengths from the heated water surface are infra-red and very little of it is transmitted back through the glass. Today, producing volumes of pure potable water is not only technically feasible but equally economically viable using the desalination of seawater. The challenge though has been to produce potable water for rural communities for drinking and sanitation to help meet the Millennium Develoent Goal without compromising standards. In meeting the challenges of the provision of potable water for drinking and sanitation, huge desalination plants have been built. The introduction of dual-power plants were also deployed to reduce the cost of electricity and water which could impact negatively on the populace. Schematic diagram of a basin-type solar still Exhaust heat from power plants were also deployed as an alternative for running desalination systems. These are large desalination systems though. However, not all water demands are coupled with the need for additional electric power. Solar energy may be deployed to produce fresh water from The sea. This may be accomplished in a large system or in a simple basintype solar desalination unit. On a practical basis, certain things ought to be taken into consideration while designing and operating a solar still. For instance, shallow basins require large expanse of land. This land 70

2 has to be cleared and leveled in readiness for the installation of the still; obviously this attracts some additional cost. Oftentimes and because the water to be treated is salt water, salt crystals build up on the dry part of the basins. This can reduce the overall absorption area of the basin, thereby impacting negatively on the effective basin area. Leakage can cause distillate to leak back into the basin or even leak out of the basin. It is equally necessary to flush the still basin on a regular basis so as to remove accumulated salts and microbes that might have grown in the brines. The use of algaecides might also be encouraged to control the growth of algae. 2. LITERATURE REVIEW A.K.Desai et al. [1] made an attempt to study the process and performance of conventional and concave solar still. This paper carries out comparative analysis of conventional and concave basin solar stills. It has been observed that the productivity is very low up to noon but increased at after noon and also observed that the efficiency of concave basin is higher. The amount of water distillate per hour is more in concave basin type solar still. E. Kabeel et al. [2] made an attempt to increase the efficiency of the solar still by increasing the surface area or decreasing the cover temperature of condensing surface. The amount of distillate water from a solar still depends on different parameters. The evaporative surface area and glass cover temperature are the most effective parameters. Increasing the surface area or decreasing the cover temperature will enhance the distillate output. In this work, a weir concave type solar still with four glass cover surfaces is studied experimentally. The main advantage of using four glass cover surface is to increase the amount of solar radiation falling on the evaporative surface. Most of the day time, there is a temperature difference between the four still glass sides and the evaporative surface which allow more vapor to condensate on the lower glass cover surface. Results have shown that the average distillate productivity during the day time is approximately 4 L/m 2 with a system efficiency of 0.38 at solar noon. It is higher than the conventional type solar still. Dr. S. Shanmuga Priya et al. [3] made an attempt to improve the efficiency of the solar still by using the different absorbing materials Solar distillation can be used effectively to produce portable water using sea water, but its low efficiency has restricted its utilization. It could be still employed at hot climatic geographical locations such as India effectively to produce portable drinking water. The purpose of this paper is to study the effect of different absorbing materials on distillate production under the climatic condition of India so as achieve maximum distillate. Single-basin four slope solar still with an effective insulation area of 0.6m 2 was used to carry out the investigation. Experimental results as expected showed that the distillate production increased with different absorbing materials as compared to distillate production without any absorbing materials. Ink and dye were used as absorbing materials and results were compared against distillation with any absorbing materials. M. Umamaheswaran et al. [4] presented a study on the details the construction, testing and analysis of parabolic trough collector/reflector configuration for small scale domestic purpose water distillation application. Ground water is heated by the solar radiation as it circulates along the solar collector within an absorber pipe in order to generate steam directly into the absorber pipe. The generated steam is condensed and collected. The parabolic trough can deliver heat at temperature ranging from 200 C C for applications such as desalination. Since medium concentration ratios are attainable one axis sun tracking is required. Direct steam generation increases thermodynamic efficiency. Heat exchangers are eliminated which reduces the overall cost and also harmful effects of the oil to the environment is also eliminated. Khaled M. S. et al. [5] presented a new concept of active vibratory solar still. Firstly, a flexible packed stretched media is installed in the bottom of the basin to increase the efficiency of the still. Secondly, a vibratory harmonic effect is applied. The flexible packed media is formed from stretched helical coiled copper wires, which is considered as a good media for heat absorbing and transferring and as simple thermal storage system. Also, a vibrator (resonator) is installed in the middle of the system structure. The target of using the vibrator is to generate forced vibration to excite the flexible 71

3 packed media to break the boundary layer and surface tension of the saline water and improve convective heat transfer, and also to excite the condensed polycarbonate glass cover to assist the condensed droplets to slide down before it becomes bigger and possibly falls down in the basin, thus increasing the water vaporization and condensation. The performance is compared with the conventional solar stills (CSS). The vibratory excitation effect is accounted by the new parameter 'vibratory performance gain'. The productivity due to added backed helical wires is found to be 3.4 l/m² day, with efficiency of about 35 %, and the productivity with vibration is increased to be 5.8 l/m²day and the average daily efficiency is about 60%. The nocturnal production ranges are found from 38 to 57 %. Nilamkumar S et al. [6] compared the different solar stills which are stepwise basin solar still, pyramid solar still and concave/convex basin solar still are taken with its different parameters(glass thickness, glass and water temp difference, absorber plate area, and free surface area of the water these will affect productivity and efficiency of the solar still, due to different designs of solar still, its parameter changes and to find out that which one is the bestest designs compare to others. In this paper the pyramid type solar still is studied with or without fan within three days. The effect of air motion inside the solar still of 3m^2 area was studied experimentally by ali air was allowed to circulate inside the still by placing a fan which consume negligible power, the results shows that the effect of forced convection inside the solar still increase the productivity of the solar still due to turbulence which is created due to fan studied by ali, also it is notable that the productivity increases with increase in Reynolds no. but it falls after maximum value. Hitesh N Panchal et al. [7] studied that single basin solar still is a very simple solar device used for converting available brackish or wastewater into potable water. This device can be fabricated easily with locally available materials. The maintenance is also cheap and no skilled labor is required. This device can be a suitable solution to solve drinking water problem. Because of its low productivity, it is not popularly used. Numbers of works are undertaken to improve the productivity of the Solar still. The aim of this research has been to study the effect of various parameters on performance of double slope solar still.. This Paper represents the work on solar still by using different parameters like Water Depth inside the solar still; sprinkler and various dies. In addition, how black die can increase the effective output of the solar still, sprinkler used to increase the condensation rate and lower depth of water level can increase the productivity of solar still are proved. Husham M. Ahmed [8] made an attempt to explore ways to increase distillation productivity of conventional, simple basin type solar still. Therefore, three identical simple type solar stills were designed, manufactured, and tested under the actual environment in Bahrain during July, two of which, are connected with external passive condensers. The first is a conventional still, and was used as a reference for comparison. In the second still, two passive condensers were connected in parallel, only to the upper part of the back of the still. While in the third still, another two condensers were connected in parallel to, both, upper and lower parts of the back of the solar still. It has been found that the still incorporating condensers connected only to the upper part of the back of the still yielded an increase of 15.1% of the distilled water production rate. The still incorporating condensers connected to the upper and lower parts of the back of the still yielded an increase of 30.54% in the production rate of distilled water. Hitesh N Panchal, et al. [9] studied that potable water is water which is fit for consumption by humans and other animals. It is also called drinking water, in a reference to its intended use. Water may be naturally potable, as is the case with pristine springs, or it may need to be treated in order to be safe. In either instance, the safety of water is assessed with tests which look for potentially harmful contaminants. Solar still is a device which converts saline water into drinkable water. This paper represents experiment conducted on hemispherical solar still in climate conditions of Mehsana, Gujarat. Results show that distillate output of hemispherical solar still is 3.2 liter per meter square per day. S. Madhu Ali et al. [10] presented the effect of two different photo- catalysts (PC s) on solar desalination. A double slope single basin solar- still with basin area 72

4 of 1m 2 is used for desalination. PC s are the chemical which enhances the evaporation rate of water in solarstill in the presence of sun light without reacting with water and without getting consumed. In this work the performance of solar- still was investigated by using two different PC s 1) granular activated carbon (GAC) and 2) Pbo 2, by varying the weight concentration. The performance of solar- still was investigated with 0.5 kg GAC, 1kg GAC, and by coating the base of solar- still with 0.5 kg Pbo 2 and 1 kg GAC. The output from the still was considerably increased by the use of PC s. 3. EXPERIMENTAL SETUP AND PROCEDURE 3.1. Fabrication of concave solar still Solar still is an uncommonly used method of water distillation process used to produce drinkable water in efficient and minimal cost method. This method is more efficient because of its low cost even very hard water can also be converted into drinkable water in easy way. However, the amount of water vaporized and condensed is minimum for the operating period of the still. Even though it s a better method of water distillation process due to no need of fossil fuels and its use only solar energy which is easily and hugely available at everywhere for the water distillation process. A concave type solar still is designed and constructed for the purpose of experimental work. Figure 1 shows a schematic diagram of the designed solar still and a photograph of this solar still is shown in Fig. 2. The basin of the solar still is a concave with a square aperture of 0.6m X 0.6m. It is fabricated from galvanized iron steel of 2.95 mm. thick. The bottom and sides of the basin are insulated by 0.5 cm thickness thermo coal surrounded by a wood 6 mm thickness. The basin depth of concave surface is 16 cm. The basin surface is coated with black materials such as black silicone gel, black paint or black ink to absorb maximum solar radiation. The four sides of glass cover are of ordinary window glass of 2 mm thickness with a tilt angle of 45 degrees to the horizontal surface. The distillate water is collected by a aluminium channel fixed on the sides at the lower end of the glass cover and is taken out through a rubber tube to two slight canes as shown in the figure. The whole system is made vapor tight using silicone rubber as a sealant to prevent any vapor leakage. The experimental setup is suitably instrumented to measure the temperatures at different points of the still and the amount of distillate. The temperature of the still is measured by the thermometer. The amount of distillate collected can be read in the distillate collecting slight canes which are graduated in ml. The still is fabricated from galvanized iron, aluminium channels and normal window glass the basin and square aperture of stills base is made by means of welding the glasses are dimensioned and cut for the required shape of triangular to get a pyramid shape of condensing surface, the four glasses are cut like the glasses are in same dimension and shape to produce the pyramid shape, then the four glasses are assembled together in pyramid shape using the adhesive materials. After assembling the glasses in pyramid shape, the distillate collecting channels are prepared to collect the distillate drawn from condensing surface, the collecting channels are made from the aluminium L and T shaped channels, the channels are prepared in a square form which is in the form of bottom of pyramid shape glass assembly, the channels assembled in square shape by using the screws and bolt nuts the collecting surface of still is mounted into the condensing surface by using the adhesive materials then the joining surface of the glasses and the collecting channels are made vapor tight by using the silicone gel as a sealant in the outer side of the collecting channels. The square aperture of the still is surrounded by the wood of thickness 6 mm and the bottom of the still also surrounded by the wood, the woods which are surrounds the square aperture and bottom of still are joined by the adhesives. The square aperture of the still and the glass and collecting channel assembly are mounted together by the screws, the screws are gripped the assembly by screwing the screws into the wooden box. The assembly is made vapor tight by using the silicone gel as sealant. Table.1. Details of instruments Sl. No. Instrument Range Use 1 Thermometer c To measure the temperature of the glasses and water 73

5 2 Distance Scale International Journal of Emerging Technology and Innovative Engineering 0-15 cm To measure the depth of the water in the stills basin 3 Slight canes ml To measure the amount of distillate collected Table. 2. Details of materials Sl. No. Particulars Materials Numbers Dimensional details (mm) 1 Basin Galvanized iron x 613 Fig 2: Layout of the experimental setup 2 Square aperture Galvanized iron x Condensing surface Glass 4 Δ 300 x Cover box Wood x160 5 Bottom cover Wood x Distillate collecting channel Aluminium with L shape 4 - Fig 3: A photograph of the experimental solar still 7 Glass seating channel Aluminium with T and L shape 4-8 Collecting tube Rubber 8 - Fig 4: The vaporizing stage Fig 1: Schematic Diagram of the still 74

6 the day. The temperature of the glasses in the four sides of the condensing surface are noticed at every hour of the experiment, the amount of water collected are read in the slight canes and noted down. The noted temperature of glasses and amount of distillate collected are tabulated. The temperature of the input water inside the still is also noted and then the solar radiation intensity at every hour is noted down, the temperature of the condensing surface is noted in tables at every hour of the experiments. 4.2 Solar still with silicone gel as absorbing material 4. PROCEDURE Fig 5: Condensation starting stage Fig 6: Water condensing stage 4.1 Solar still without absorbing material: The solar still is fabricated as discussed above and then the still is placed into a place where the suns radiation can reach into the still without any trouble the still is filled with salty water and allowed to evaporate, the evaporated water is get condensed into water droplets the condensed water droplets are drawn into the aluminium distillate collecting channels the water droplets drawn are continuously drawn into the distillate collecting channels. The collected distillate in the channels is flow into the holes provided in the collecting channels, and then the condensed water is collected in the slight canes which are graduated in ml. The still is filled with the water of depth 5 cm height, for this height of water the still occupies 12.4 liters of water. The 5 cm depth of water is allowed to get heated and evaporated. The table 3 shows the readings absorbed, the fig 7 shows the temperature variation of In this setup the stills basin and the square aperture are coated with the silicone gel as absorbing material to improve the radiation absorption of the solar still. The black color silicone is coated into the absorbing area to increase the radiation absorption will increase the absorption rate of the solar still. The still is filled with the water of depth 5 cm height, for this height of water the still occupies 12.4 liters of water. The 5 cm depth of water is allowed to get heated and evaporated. The table 4 shows the readings absorbed, the figure 8 shows the temperature variation of the day. The temperature of the glasses in the four sides of the condensing surface are noticed at every hour of the experiment, the amount of water collected are read in the slight canes and noted down. The noted temperature of glasses and amount of distillate collected are tabulated. The temperature of the input water inside the still is also noted and then the solar radiation intensity at every hour is noted down, the temperature of the condensing surface is noted in tables at every hour of the experiments. 4.3 Solar still using the black and white paint as absorption materials In this setup the stills basin is coated with the black paint as absorbing material and the white paint is coated into the square aperture of the still to increase the radiation absorption of the solar still. The still is filled with the water of depth 5 cm height, for this height of water the still occupies 12.4 liters of water. The 5 cm depth of water is allowed to get heated and evaporated. The table 5 shows the readings absorbed, the figure 8 shows the temperature variation of the day. The temperature of the glasses in the four sides of the condensing surface are noticed at every hour of the 75

7 experiment, the amount of water collected are read in the slight canes and noted down. The noted temperature of glasses and amount of distillate collected are tabulated. The temperature of the input water inside the still is also noted and then the solar radiation intensity at every hour is noted down, the temperature of the condensing surface is noted in tables at every hour of the experiments. 5. READINGS AND TABULATION Table 3. Readings absorbed experiment done without absorbing material with 5cm depth of water Glass 1(C) Water in temp (C) Atm Temp. (C) Radiation W/m2 Maximum temperature of water in basin Minimum temperature of water in basin Amount of distillate collected 72 0 c 35 0 c 400ml Absorbing Material Without absorbing material Time/ Place 11 am 12 noon 13 Date 17/3/ Water depth 5 cm Glass 1(C) Glass 2(C) Glass 1(C) Glass 1(C) Water in temp (C) Atm Temp. (C) Radiation W/m2 Maximum temperature of water in basin Minimum temperature of water in basin Amount of distillate collected 67 0 C 31 0 C 350 ml Table 4. Readings absorbed when using silicone as absorbing material with 5cm depth of water. Absorbing material Black silicone gel Time/ Place 11 am 12 noon 13 Date 18/3/ Water depth 5 cm Glass 1(C) Glass 2(C) Glass 1(C) Table 5. Readings absorbed using black and white paint as absorber with 5cm depth of water Absorbing material Black and white paint Date 19/3/2014 Water depth 5 cm Time/ Place 11 am 12 noon Glass 1(C) Glass 2(C) Glass 1(C) Glass 1(C) Water in temp (C) Atm. Temp. (C) Radiation W/m2 Maximum temperature of water in basin 72 0 c Minimum temperature of water in basin 35 0 c Amount of distillate collected 400ml The table 5 shows the readings absorbed, the figure 8 shows the temperature variation of the day. The temperature of the glasses in the four sides of the condensing surface are noticed at every hour of the experiment, the amount of water collected are read in the slight canes and noted down. The noted temperature of glasses and amount of distillate collected are tabulated. The temperature of the input water inside the still is also noted and then the solar radiation intensity at every hour is noted down, the temperature of the condensing surface is noted in tables at every hour of the experiments. 6. CALCULATION 76

8 Area of basin, International Journal of Emerging Technology and Innovative Engineering A=0.88 m Efficiency of still without absorbing material with 5cm water depth η =APH/3600G A-collecting surface area in m 2 G-solar radiation in w/m 2 H-latent heat of water, P-collecting water in liter = / = 33% 6.2 Efficiency of still using black silicone with 5cm water depth η =APH/3600G = / = 43% 6.3 Efficiency of still using black and white paint with 5cm water depth η =APH/3600G = / = 29% 7 RESULTS AND DISCUSSON The temperature difference between the glass cover for all sides and the water is kept up to late afternoon. This temperature difference helps the vapor to condensate on the lower glass surface and hence condensing more vapors and hence increasing the collected water. Fig 7: Graph of hourly variation of temperature during the day 6.2 GRAPH OF DISTILLATE OUT Figure 8 shows the variation of distillate output and total solar radiation intensity during the day time. The amount of total solar radiation incident on the still surface depends on the time of the day. The solar radiation varies along the hours after sunrise till a maximum value at mid day then decreases. These solar radiation data are used to calculate the solar still efficiency. These figures indicate that the effect of solar radiation intensity on still productivity is pronounced. 77

9 Fig 9: Water collected as a function of the hour of day 8. CONCLUSIONS In this work, a concave basin pyramid type solar still was, fabricated and experimentally tested during daytime for three days under outdoors of summer climatic conditions. It was found that, the daily distillate water produced from the still ranged from approximately 350 ml to 400 ml for seven hours per day. The daily efficiency of the still varies for different absorbing materials. The efficiency of solar still for without absorbing material for water depth about 5 cm is 33%, with black paint as absorbing material for water depth about 5 cm is 38%. The experimental results indicated that the still with black paint as absorbing material has the highest efficiency of 38% than the still without any absorbing materials for the same water depth. The effect of saline water depth on the still efficiency was also studied. And also it is concluded that the solar still efficiency with black paint as absorbing material for water depth of 5 cm has the better efficiency. Fig 8: Hourly variation of distillate output during the day It was observed that the distillation improved with varying absorbing materials. Improvement was observed with variation of absorbing materials. Rate of evaporation not remained same when the different absorbing materials are used. Volumetric Rates obtained with silicone, black and white and without absorbing material are compared with results obtained in each situation shown in Figure REFERENCES [1] Nilamkumar S Patelsolar still, Effect of various parameters on different types of solar still: Case Study, International Journal of Innovative 78

10 Research in Science, Engineering and Technology, Vienna, Austria, pp [2] Delyannis, E. and Belessiotis, V., 2001, Solar energy and desalination, in Advances in solar energy, An annual review of research and develoent, Goswami, D.Y. (Ed.), 14, American Solar Energy Society, Inc, Boulder, Colorado, pp [3] Saleh-hrabsheh, Theoretical and experimental analysis of water desalination system using low grade solar heat, Ph.D. dissertation Graduate school of the University of Florid. [4] Husham M. Ahmed, 1998, Experimental Investigation of solar stills connected to External passive condensers, 1998; 14(1-4) [5] H.E.S. Fath, Desalination, Solar distillation: a promising alternative for water provision with free energy, simple technology and a clean environment, 116 (1998) [6] Nilamkumar S Patelsand H.M. Salah, Experimental and numerical analysis of a tube-type networked solar still for desert technology, Bull. Nagoya University, 43, (1990) [7] G.N. Tiwari and M.A. Noor, Characteristics of solar stills, Int. J. Solar Energy, 18 (1996) [8] S. Kumar and G.N. Tiwari, Optimization of collector and basin areas for a higher yield for active solar stills, Desalination, 116 (1998) 1 9. [9] K. Murase, S. Komiyama, A. Ikeya and Y. Furukawa, Develoent of Multi-effect Membrane Solar Distillator, Bull. Soc. Sea Water Sci., 54 (2000)