Performance analysis of solar still with cow dung cakes and blue metal stones

Abstract

The aims of this paper is to investigate the effects of various materials inside the solar still on the increase of the productivity of potable water. Here, blue metal stones and cow dung cakes were used as materials. To investigate their effect, three identical solar stills with an effective area of 1 m square made from locally available materials were tested in climate conditions of Mehsana (23°50′ N 72° 23′). The first and second solar stills were filled with blue metal, stones and cow dung cakes, while the third one was taken as a reference which consisted of only blue paint at the basin. The experiments show that blue metal stones have the highest distillate output at daytime, followed by cow dung cakes solar still and reference solar still. On the other hand, the overall distillate output of blue metal stones and cow dung cakes at daytime as well as at night were 35% and 20% compared with that of reference solar still.

Graphical abstract

Keywords

blue metal stones / cow dung cakes / distillate output / solar still / solar intensity

1 Introduction

Solar distillation represents a most attractive and simple technique among other distillation processes and is especially suited to small and tiny units at locations where solar energy is considerably abundant. Mehsana, a district of Gujarat, located in the north, contains abundant amount of solar energy [1−10] and is the best location of the solar thermal experiments due to tropics of cancer passing nearer to Mehsana, hence several research works have done on solar still for increment in distillate ouptut [11−20]. The design of a solar still requires the optimization of many factors such as brine depth, tight seal to prevent vapor leakage, thermal insulation, cover slope, shape and the material of the still. In spite of several technologies found in this area, affordable and simple processes have not yet been evolved [21]. The construction of a single basin solar still is very simple [22]. A black painted basin contains brackish or seawater, which is enclosed in a completely airtight area formed by transparent cover. Incident solar radiation passes through the transparent cover. The blue basin absorbs the radiation. Consequently, the water contained in the basin, is heated up and evaporates in the saturated conditions inside the still. The water vapor rises until it is exposed to the cooler inner surface of the cover [23]. Tripathi and Tiwari [24] have worked on the effect of water depth on internal heat and mass transfer or active and passive solar still. They have contributed their work in effect on water depth and have found the optimum water depth on the performance of active and passive solar still. Kalidasa Murugavel et al. [25] have made experiments on a double slope solar still. They have maintained a thin layer of water inside the solar still to investigate its performance. They have also used wick materials such as light cotton cloth, sponge sheets, and porous materials such as natural rock and quantized rock as special materials. They found that among all the parameters, cotton, jute to maintain constant water depth and detailed output or productivity is increased. Tripathi and Tiwari [26] have investigated the effect of water depth on internal heat and mass transfer process for active solar desalination. They have made thermal modeling of active solar still and applied energy balance equation for the active solar still. Moreover, they have solved the problem of how constant water depth or water firm can increase the heat and mass transfer. They have increased detailed output from the solar still. Tiwari and Tiwari [27] have conducted an investigation of thermal modeling based on solar fraction and experimental study of the annual and seasonal performance of a single slope passive solar still. They have taken variable as water depth and shown the effect of water depth on the performance of a solar still as per the annual and seasonal performance. Srithar and Mani [23] have made an investigation on single basin solar still with deep basin. They have taken variable of water depth and shown the effects when the depth of the water is increased and found out that constant film of the water inside the basin liner can increase the detailed output. They have also taken variable of glass cover and proved that the reduced thickness of glass can help to increase the solar insolation and detailed output is increased. Tiwari and Tiwari [27] have made double condensing chamber in a single basin solar still. They have confirmed that double condensing chamber solar still for a typical winter season of Delhi gives 46% higher output than single slope conventional chamber, and that double slope solar still is more economical in large-scale production to provide drinking water in remote areas [28]. Some researcher used single slope solar stills for many useful purposes. Hanson et al. [29] have demonstrated that their single basin stills are very successful in removing non-volatile contamination from the urine. Their stills have also successfully removed the bacteria.

The purpose of this paper is to assess the consequence of different materials on solar still to enhance the distillate output. These materials are blue metal stones and cow dung cakes bought from Mehsana, Gujarat, India.

2 Experimental setup

Figure 1 shows the experimental setup fabricated by using locally available materials. Three single basin solar stills were made up and tested in climate conditions of Mehsana, Gujarat. The first solar still was covered with blue metal stones with a thickness of 10 mm over the basin surface. The second one was covered with cow dung cakes with an average diameter of 6 cm and a thickness of 0.3 cm, and the third one was considered as reference still. Each solar still had an area of 1 m² consisting of a basin liner made up of MS plate having a maximum height of 120 mm and a thickness 15 mm. And each solar still was made in such a way that it never suffered from the corrosion problem. The basin was made waterproof using carpet, and airtight. The top of the basin was covered with transparent toughened glass with a thickness of 4 mm inclined by nearly 20 degrees with the horizontal. The spacing between the glass cover and the basin water surface was 70 mm to120  mm. The slope of the glass cover did not affect the rate at which the distillate ran down its inner surface to the collection trough. The glass cover that was no more than 50 mm to 70 mm thick from the water surface allowed the still to operate efficiently. Therefore, the glass-to-water distance increased the heat loss because the convection became greater, making the still efficiency. The top was sealed tightly using silicone sealer to bring down the vapor leakage. Figure 2 illustrates the blue metal stones and Figure 3 demonstrates the cow dung cakes used in the present experiment.

3 Experimental procedure

All experiments started from 7:00 am to 7:00 am of the next day. The parameters such as inner glass cover temperature, vapor temperature, water temperature, ambient temperature, distillate output, and solar insolation were measured at each hour.

The water, glass and vapor temperatures were recorded with the help of calibrated copper constantan thermocouples and digital temperature indicator. A total of 9 K type thermocouples were used in the measurement. The ambient temperature was measured by a calibrated mercury in glass thermometer. The distillate output was recorded with the help of a calibrated solarimeter while the wind speed was measured by an anemometer. Table 1 lists the accuracies and errors for various measuring instruments used in the experiments. Table 2 shows the physical properties of vapor used in the experiment.

4 Results and discussion

The performance analysis of three solar stills was conducted using blue metal stones and cow dung patties. Figure 4 depicts different temperatures such as the inner glass cover temperature, vapor temperature, basin temperature and ambient temperature. It shows the hourly variations of 30 mm constant water depth with in a storage tank of 15 L on June 10, 2011. It can be understood from Fig. 4 that water basin water temperature, inner glass cover temperature and vapor temperature gradually increase from 7 am to 12 pm and then decrease due to less direct radiation falling on the solar still. It also proves that the basin vapor temperature is higher compared with basin water temperature and inner glass cover temperature. Differences of temperature between basin water and inner glass cover temperature cause to produce distillate output of water inside the solar still. As the temperature difference increases, the distillate output from the solar still increases.

Figure 5 shows the relation between distillate output (kg) and time (h). It demonstrates that the distillate output rate varies from early break of the day until the afternoon due to more availability of direct radiation during the summer condition of June. It also indicates that the hourly variations of distillate output is least for conventional solar still followed by the solar still filled with cow dung cakes and solar still filled with blue metal stones. Blue metal stones possesses the high heat storage capacity hence, it brings a higher amount of distillate output. Cow dung cakes are porous, hence they can store the heat during sunshine hours. They are black in color, hence the temperature in solar still containing cow dung cakes would be higher compared with metal stones. Due to the higher heat storing capacity, the solar still which is filled with blue metal stones absorbs the maximum amount of solar radiation in the morning and evening and increases the distillate output. Hence, it is observed from Fig. 5 that the solar still filled with blue metal stones increases the distillate output in the evening when the sunshine is low and also at night when the sun is not in the sky. Hence, the nocturnal (night time) production is also increased by the solar still filled with blue metal stones. Therefore, the productivity of the solar still containing blue metal stone is increased by up to 12% compared with the conventional solar still while the solar still filled with cow dung cakes is increased by up to 5% compared with the conventional solar still. The solar still filled with blue metal stones has the ability to restrict sudden release of stored energy to the basin water than the conventional solar still compared with other two solar stills. Its surface temperature is higher than that of the solar still filled with cow dung cakes as well as the conventional solar still. Hence, the overall production of distillate water from the solar still filled with blue metal stones is 35% and that from the solar still filled with cow dung cakes is 20% higher compared with the conventional solar still.

To obtain pure water from unclean water by using solar energy requires an evaporation process. To evaporate the water inside the solar still requires solar energy. Hence, the evaporation process is responsible for purifying water. Therefore, the basin water inside the solar still plays a significant part. As the evaporation inside solar still increases, the vapor temperature and distillate output increase from the solar still. Figure 6 shows the variations of basin water temperatures of the three kinds of solar stills. It is observed from Fig. 6 that the conventional solar still linearly increases the basin water temperature from 7:00 am to 2:00 pm. The solar still filled with cow dung cakes has a higher basin water temperature due to its property called porosity. But the solar still filled with blue metal stones has a much higher temperature compared with the conventional solar still and the solar still filled with cow dung cakes. Figure 6 shows that a temperature of close to 81°C is achieved at 2:00 pm due to the higher amount of solar radiation incident for increment in distillate output. It also demonstrates that the heat gained by low metal stones retains inside and due to low sunshine hours between 4: 00 pm to 6:00 pm, which makes good basin water temperature.

The establishment of water vapor has equal importance like basin water temperature. Water vapor possesses lower density, and it will get condensed due to cooler regions of ice cover and the start of the formation of fresh water. Referable to the inclined surface glass cover, it will trickle down and pour into the distillate water trough. Such water is called pure water. Figure 7 shows the variations of vapor temperatures of different solar stills. A uniform increase in vapor temperature of conventional solar still is achieved from 7: 00 am to 12:00 pm due to the increase in solar insolation. The vapor temperature produced by the solar still filled with cow dung cakes also increases. But compared with the conventional solar still, a maximum vapor temperature of 52°C is produced by the solar still filled with blue metal stones. Due to the higher heat storage of blue metallic stones compared with the solar still filled with cow dung cakes and the conventional solar still, the vapor temperature of the solar still filled with blue metal stones increases. Figure 8 shows the variations of distillate output of 7 days of operation in climate conditions of Mehsana, Gujarat. It registers that the average distillate output of the conventional solar still is 2.2 kg, whereas that of the solar still filled with cow dung cakes is 2.85 kg and that of the solar still filled with blue metal stones is 2.95 kg. Hence, the distillate output of the solar still filled with blue metal stones is increased by 35% and that of the solar still filled with cow dung cakes is increased by 20% compared with the conventional solar still.

5 Conclusions

Three identical solar stills, one filled with blue metal stones, the other with cow dung cakes, and the third conventional, have been constructed to evaluate distillate output from them. The following conclusions can be reached based on the experiment.

1) An increase in distillate output of water was noted with the increase of temperature difference in basin water and inner glass cover.

2) The highest temperature of basin water was obtained by the solar still filled with blue metal stones compared with the one filled with cow dung cakes and the conventional one.

3) The highest vapor temperature was also obtained by the solar still filled with blue metal stones compared with the other two solar stills.

4) The distillate output of a solar still having blue metal, stones of increased up to 35% compared with conventional solar still.

5) The distillate output of the solar still filled with cow dung cakes was increased by up to 20% compared with the conventional one.

6) The heat storing capacity of blue metal stones is higher compared with cow dung cakes to be used as a mild steel basin of conventional solar still.

7) Blue metal stone is a better material which can store energy during sunlight hours.

8) Blue metal stone is a safer material to gain distillate output at night time, so it can lead to nocturnal production.

References

[1] Panchal H N, Shah P K. Modelling and verification of single slope solar still using ANSYS-CFX. International Journal of Energy and Environment, 2011, 2(6): 985–998

[2] Panchal H N, Shah P K. Investigation on solar stills having floating plates. International Journal of Energy and Environment Engineering, 2012, 3(1): 8–12

[3] Panchal H N, Doshi M, Thakor K, Patel A. Experimental investigation on coupling evacuated heat pipe collector on single basin single slope solar still productivity. International Journal of Mechanical Engineering & Technology, 2011, 2(1): 1–9

[4] Panchal H N, Shah P K. Effect of varying glass cover thickness on performance of solar still: in a winter climate conditions. International Journal of Renewable Energy Research, 2012, 1(4): 212–223

[5] Panchal H N, Shah P K. Enhancement of distillate output of double basin solar still with vacuum tubes. Frontiers in Energy, 2014, 8(1): 101–109

[6] Panchal H N, Doshi M, Patel A, Thakor K. Experimental investigation on coupling evacuated heat pipe collector on single basin single slope solar still productivity. International Journal of Mechanical Engineering & Technology, 2011, 2(1): 1–9

[7] Panchal H N, Shah P K. Modeling and verification of hemispherical solar still using ANSYS CFD. International Journal of Energy and Environment, 2013, 4(3): 427–440

[8] Panchal H N, Patel M I, Patel B, Goswami R, Doshi M. A comparative analysis of single slope solar still coupled with flat plate collector and passive solar still. International Journal of Research and Reviews in Applied Sciences, 2011, 7(2): 111–116

[9] Panchal H N, Doshi M, Chavda P, Goswami R. Effect of cow dung cakes inside basin on heat transfer coefficients and productivity of single basin single slope solar still. International Journal of Applied Engineering Research, 2011, 1(4): 675–690

[10] Panchal H N. Experimental investigation of varying parameters affecting on double slope single basin solar still. International Journal of Advances in Engineering Sciences, 2011, 2(1): 17–21

[11] Panchal H N, Shah P K. Enhancement of upper basin distillate output by attachment of vacuum tubes with double-basin solar still. Desalination and Water Treatment

[12] Zala B, Dodia K, Panchal H N. Present status of solar still: a critical review. International Journal of Research Review in Engineering Science and Technology, 2013, 2(1): 6–11

[13] Panchal H N, Shah P K. Performance analysis of double basin solar still with evacuated tubes. Applied Solar Energy, 2013, 49(3): 174–179

[14] Panchal H N, Shah P K. Performance improvement of solar stills via experimental investigation. International Journal of Advanced Design and Manufacturing Technology, 2013, 5(5): 19–23

[15] Panchal H N, Patel P. Energy absorbing materials used in solar still for enhancement in distillate output: a review. International Journal of Ambient Energy, 2015

[16] Panchal H N, Shah P K. Char performance analysis of different energy absorbing plates on solar stills. Iranica Journal of Energy & Environment, 2011, 2(4): 297–301

[17] Panchal H N, Shah P K. Experimental and ANSYS CFD simulation analysis of hemispherical solar still. IIRE International Journal of Renewable Energy, 2013, 8(1): 1–14

[18] Panchal H N, Thakar N S, Thakkar V N. Performance analysis of various parameters on glass cover of solar distiller-experimental study. International Journal of Advance Engineering and Research Development, 2014, 1(3): 1–12

[19] Panchal H N. Experimental analysis of different absorber plates on performance of double slope solar still. International Journal of Engineering Science and Technology, 2010, 2(11): 6626–6629

[20] Panchal H N, Patel P, Mevada R, Patel H. Reviews on different energy absorbing materials for performance analysis of solar still. International Journal of Advance Engineering and Research Development, 2014, 1(11): 62–66

[21] Prasad P R, Pujitha P, Venkata Rajeev B G, Vikky K. Energy efficient solar water still. International Journal of ChemTech Research, 2011, 3(4): 1781–1787

[22] Namprakai P, Hirunlabh J, Kiatsiriroat T. Ethyl alcohol distillation in a basin solar still. Renewable Energy, 1997, 11(2): 169–175

[23] Srithar K, Mani A. Analysis of a single cover FRP flat plate collector for treating tannery effluent. Applied Thermal Engineering, 2004, 24(5–6): 873–883

[24] Tripathi R, Tiwari G N. Thermal modeling of passive and active solar stills for different depths by using concept of solar fraction. Solar Energy, 2006, 80(8): 956–967

[25] Kalidasa Murugavel K. Chockalingam Kn K S K, Srithar K. An experimental study on single basin double slope simulation solar still with thin layer of water in the basin. Desalination, 2008, 220(1–3): 687–693

[26] Tripathi R, Tiwari G N. Effect of water depth on internal heat and mass transfer for active solar distillation. Desalination, 2005, 173(2): 187–200

[27] Tiwari A K, Tiwari G N. Thermal modeling based on solar fraction and experimental study of the annual and seasonal performance of a single slope passive solar still: the effect of water depths. Desalination, 2007, 207(1–3): 184–204

[28] Garg H P, Prakash J. Solar Energy. Wiley Sons, 2000, 165–190

[29] Hanson A, Zachritz W, Stevens K, Mimbela L, Polka R, Cisneros L. Distillate water quality of a single-basin solar still: laboratory and field studies. Solar Energy, 2004, 76(5): 635–645

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