- Email: [email protected]
Efficiency analysis of tank-type water distillation system integrated with hot water collector
Thermal Science and Engineering Progress 3 (2017) 24–30
Contents lists available at ScienceDirect
Thermal Science and Engineering Progress journal homepage: www.elsevier.com/locate/tsep
Efficiency analysis of tank-type water distillation system integrated with hot water collector Emin El a, Gülsßah Çakmak b,⇑, Cengiz Yıldız b a b
Vocational School of Technical Sciences, Bitlis Eren University, 13000 Bitlis, Turkey Department of Mechanical Engineering, Firat University, 23119 Elazig, Turkey
a r t i c l e
i n f o
Article history: Received 20 January 2017 Received in revised form 16 March 2017 Accepted 31 May 2017
Keywords: Solar still Energy efficiency Drinking water Tank type distiller
a b s t r a c t In this study, besides the hot water, it was also aimed to obtain distilled water from solar still water heating systems, which are widely used in obtaining hot water. For this purpose, a new type of distiller was obtained by making modifications, which enable us to obtain distilled water, on a solar still water heating system having flat-surface panel collector and vertical tank and operating as a closed system. The designed system was tested under both natural convection and forced convection at flow rates of 30 kg/h and 50 kg/h. As a result of performed experiments, the temperature, productivity, and distilled water production amounts were calculated for the designed system. It was determined that the temperature of hot water obtained was sufficient for daily use. According to the results, as the highest amount of water, 1.820 kg/day distilled water was obtained form also the natural convection system. In order to determine the drinkability of distilled water, the laboratory analyses were carried out, and it was found that the water meets EC standards. Thus, the clean and hot water was obtained at the same time from the designed system under real weather conditions. Ó 2017 Published by Elsevier Ltd.
1. Introduction Population growth, industrialization and active agricultural activities lead to the depletion of limited underground and surface water resources of the world, and increase the environmental problems. The shortage of potable water is an important problem, and the actual underground water stock is brackish in general and cannot be used as potable water as is. Gradual depletion of energy and water resources of the world and non-usefulness of the existing resources bring the energy and water procurement into the forefront. Renewable energy is the type of energy coming into the forefront with its characteristics such as, when appropriate technologies are used, having no pollutant effect and being local and environment-friendly. Even though the energy has an important role in development of human being, it is only a part of the whole. But, the water is a vital necessity that has to be met always. Water, which is our most vital requirement, has vital importance in terms of all our social activities. For purifying the dirty water, many methods are used, but all of those methods require a significant amount of energy. The energy
⇑ Corresponding author. E-mail address: [email protected] (G. Çakmak). http://dx.doi.org/10.1016/j.tsep.2017.05.012 2451-9049/Ó 2017 Published by Elsevier Ltd.
resources to be used in purification process such as oil, natural gas, and electricity have both high costs and lead to environmental pollution. The studies carried out in recent years aimed to increase the use of renewable energy resources as energy source. Mamlook et al. [1] compared the performances of various solar energy implementations. They carried out a study, where they utilized fuzzy logic on solar water distillation, solar water heating, photovoltaic and solar electricity production methods. Those methods were compared from the aspects of efficiency and costs. They determined that the solar water distillation was the best method in terms of the costs. Voropoulos et al. [2] experimentally examined the solar water distiller integrated with a storage tank under realistic conditions by keeping the water temperature stable at different water levels. The distillation system consisted of an asymmetrical pool-type distiller and the storage tanks under the distiller. The amount of water obtained from hot-water storage tank in 24-h was reported to be higher than that obtained from classical pool-type distillation system. Al-Hayek and Badran [3] experimentally examined 2 different solar water distillation systems, and investigated the parameters affecting the production via water distillation. One of the systems they used was asymmetrical greenhouse-type distillation system with mirrors in inner walls, while another system was symmetrical greenhouse-type distillation system. As a result of their
E. El et al. / Thermal Science and Engineering Progress 3 (2017) 24–30
experimental research, they reported that 20% more water was obtained from asymmetrical greenhouse-type water distillation system in proportion to symmetrical system. At the end of their study, they showed that the radiation was effective on the temperature at the surface of water in both of systems, and that the amount of water obtained from distillation system increased as the water depth decreased. Ben-Amara et al. [4] designed a new-type solar collector for distilling process. They examined the parameters such as solar radiation, wind speed, temperature of the medium, mass flow, air intake moisture and temperature that are effective on collector efficiency. As a result, they optimized the collector for the new solar water distillation system. Dayem [5] examined the numerical and experimental performance of classical solar water distilling systems based on very efficient condensation and vaporization cycle. Distillation room consisted of moistener and dehumidifier units. The air circulation in those 2 sections was provided via natural convection. The cold water was pre-heated inside, and then exposed to temperature change within the solar collector. It was determined that water can be produced 241 days a year in this system. Tripathi and Tiwari [6] carried out experiments at different depths for active and passive solar pools. In active distillation process, in order to increase the temperature difference between glass and water surface, they pumped the hot water to the bottom of pool. In passive system, no pump was utilized. For those systems utilized, they made comparisons at various depths and modes in parameters such as water, inner glass, outer glass, vaporization, temperature, radiation, and amount of the water obtained. Zamen et al. [7] optimized the solar energy system for desalinating the water. The aim of this optimization was to decrease the cost of obtaining clean water. The results obtained according to the solutions obtained from cost objective function were reported to be lower than those obtained from other objective functions. Esfahani et al. [8] attempted to produce a portable solar water distiller. By comparing the summer and winter results, they determined that the efficiency in summer was higher than winter efficiency. Tsilingiris [9] developed a new theoretical model for estimating the mass transportation in solar water distillation systems. The model he used was based on the Chilton-Colburn simulation that can be applied for wide range of Prandtl and Schmidt pure numbers. In order to perform comparative verification, he utilized a series of experimental results, which were obtained from passive solar water distillation system under summer conditions at higher process temperatures, for examining the higher process temperature conditions. Ahsan et al. [10] made a comparison by designing two Tubular Solar Still (TSS) obtained using a vinyl chloride layer and a polyethylene film cover as a transparent tube cover. According to the results obtained, the hourly evaporation, condensation and production flows are explained by the proportions of moist air temperature and relative humidity fraction. In order to estimate the hourly production flow at the end of their work, they proposed an empirical equation based on this relationship. Al-Sulttani et al. [11] designed, produced and tested a new double-slope solar still hybrid with rubber scrapers (DSSSHS) and a double-slope solar still (DSSS). The proposed DSSSHS design utilizes the advantages of using a small slope of the backing cover, which allows for higher solar radiation to penetrate. The maximum recorded value of the total internal heat transfer coefficient for the DSSSHS was found to be 38.754 W/m2 °C and the daily yield to be 4.24 L/m2 day with productivity improvement of 63%. Feilizadeh et al. [12] investigated separately, the effects of water depth and the water surface-cover distance (WCD) and examined
25
effects of water depth on the performance of solar stills with the same WCD. It was found that WCD can affect the amount of distillate yield up to 26%. In addition, the solar stills with various water depths were mathematically modelled and the rates of their productivity were predicted. The theoretical results were compared with the current experimental data and it was found that there is a good agreement between the present theoretical predictions and experimental observations. Rahbar and Esfahani [13] obtained the optimum geometric condition for increasing the productivity in a single-slope solar still by using theoretical and numerical methods. Their results indicate that for a fixed length of a solar still, the productivity increases with decrease in the specific height. In addition, they observed identical trends for both water productivity and convective heat transfer coefficient. In this study, besides the hot water, it was also aimed to obtain distilled water from solar still water heating systems, which are widely used in obtaining hot water. For this purpose, a new type of distiller was obtained by making modifications, which enabled us to obtain distilled water, on a solar water heating system having flat-surface panel collector and vertical tank and operating as a closed system. The designed system was tested under both natural convection and forced convection at flow rates of 30 kg/h and 50 kg/h, and the results were presented.
2. Materials and method 2.1. Experimental set-up In this study, a tank-type solar water distillation system integrated with hot water collector was designed and manufactured. The designed experimental setting was assembled at terrace of Heat Engineering Lab of Machinery Engineering Department of Engineering Faculty of Fırat University in the way preventing the shadowing. The experiments were carried out between July and October months under climate conditions of Elazıg˘. This system was designed as natural convection and forced convection, and then tested.
Fig. 1. Tank-type water distiller integrated with hot water collector. 1. City water inlet, 2. Hot liquid glass jar, 3. Hot liquid inlet, 4. Insulation, 5. Distilled water collection channel, 6. Collector, 7. Pyranometer, 8. Top serpentine (Cold), 9. Distilled water outlet, 10. Hot water outlet, 11. Bottom serpentine (Hot), 12. Measure, 13. Hot liquid outlet, 14. Thermocouple, 15. Digital thermometer, 16. Circulation, 17. Rotameter.
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E. El et al. / Thermal Science and Engineering Progress 3 (2017) 24–30
This system consists of planar collector collecting solar energy, tank type distiller, insulated pipes linking those 2 parts, pump, and measurement components (Fig. 1). The solar collector used in system was the planar solar collector that is used in traditional solar water heating system. In distillation system, the standard planar solar energy hot water collector with aluminum pipes and wings (dimensions of 930 1930 87.5 mm and surface area 1.8 m2 gross and 1.6 m2 net) was preferred. In design of tank-type water distiller used in this system, differently from traditional solar water heating systems, a top serpentine for ensuring the condensation at the top of tank and a distilled water collection channel for removing the condensation water from the system were utilized. Furthermore, through a plumbing system installed in insulation layer between inner sheet and outer sheet iron of the tank, the water circulated in serpentine was directed into the tank. Tank-type water distiller was manufactured from 0.8 mm-thick chrome-nickel material at width of 400 mm and height of 1050 mm in cylinder form. Heat insulation was prepared with 40 mm-thick poly-urethane material. In this system, the city water entering into tank passes firstly from top serpentine and cools the serpentine. And then, through a plumbing system passing through insulation layer, it reaches the tank from tank’s bottom and is collected there. The liquid heated with solar collector is used as the heat sources of this system. Hot liquid coming from collector and passing from bottom serpentine evaporates the city water gathering within the tank. Vaporizing city water condenses by contacting with top serpentine, which is cold, and the distilled water is obtained. That distilled water gathers in distilled water collection channel, and is removed from the system through a plumber system (Fig. 2).
In order to ensure the circulation of the water in system, the WELKO – LRS40 4S/130 model circulation pump was utilized. This pump can be operated at 0 °C–+100 °C temperature and under 10 bars of operation pressure, it has 3 speed levels, its maximum flow rate is 150 L/h, and maximum pump head is 4 m. Rotameter was used in order to determine the flow rate of liquid circulating in forced-convection systems, and particular rotameter used can measure the flow rates between 0 and 200 L/h. In measuring the density of solar radiation, the pyranometer manufactured by Kipp and Zonen (CC12) was used. The pyranometer was placed at an appropriate angle that is suitable for operation angle of the system, and the measurements were performed in 30 min of interval. In order to measure the temperatures of the determined points, Elimko E680 model 16-channel digital thermometer with universal inlet, inlet and outlet of which can be programmed by the user, was used. Under favor of that thermometer, the measurements can be made with J, K, T, E, and PT-100. In this study, the 0.5 mm-diameter J type thermocouples were used. Using the parameters leading to error during the distillation experiments, the total error was determined. In order to determine the total error in any parameter, the total error value was calculated by considering the constant errors, production errors and random error in accordance with the formula below [14],
h i1=2 Wth ¼ ðx1 Þ2 þ ðx2 Þ2 þ . . . . . . ðx1 Þ2
ð1Þ
During the experiments, the total errors were calculated and are presented in Table 1. Furthermore, the distilled water obtained from distiller per hour was calculated according the formula below;
mew ¼
hew ðTw Tg Þ3600 L
ð2Þ
Daily output of the distiller was calculated by multiplying the sum of condensation per hour with the hidden vaporization and then dividing to the radiation density per efficient collector surface area [15]
g¼
mew :L I A:3600
ð3Þ
The efficiency in the system using the pump is calculated by the following equation;
g¼
mew L IA3600 þ Wp:Dt
ð4Þ
2.2. Analysis of results Tank-type distiller experiments were carried out in September under climate conditions of Elazıg˘ city. At the end of the experiments, the amounts of distilled water produced in natural convec-
Table 1 Total errors occurring during the distillation experiments.
Fig. 2. Tank-type water distiller (1. City water inlet, 2. Distilled water outlet, 3. Hot water outlet, 4. Hot liquid inlet, 5. Insulation, 6. Top serpentine (Cold), 7. Distilled water collection channel, 8. Bottom serpentine (Hot), 9.Cold water inlet, 10. Hot liquid outlet).
Parameters leading to error
Total error
Total Total Total Total Total Total Total Total Total Total
±0.173 °C ±0.173 °C ±0.173 °C ±0.173 °C ±0.1 min ±0.1 min ±0.1 min ±0.1 min ±4.062 ml ±0.86 kg/h
error in measuring the temperature at collector inlet error in measuring the temperature at collector outlet error in measuring the tank temperature error in measuring the medium temperature periodical error in measuring the production periodical error in reading the temperature values periodical error in measuring the air temperature periodical error in measuring the radiation periodical error in measuring the fresh water produced periodical error in measuring the flow rate
E. El et al. / Thermal Science and Engineering Progress 3 (2017) 24–30
tion and forced convection systems and the efficiencies of systems were compared. The experiments carried out on forced convection system with 38° of collector angle were performed at 2 different flow rates (30 kg/h and 50 kg/h). In Fig. 3, the changes in natural convection tank-type water distiller’s collector inlet (Tkg), collector outlet (Tkç), tank water temperature (Td) and medium temperature (Tç) and the radiation intensity are shown. Accordingly, the highest temperature values measured in system were 92 °C on 13:00 at collector outlet, 62 °C on 15:30 at collector inlet, 78 °C on 14:30 at tank. The total amount of distilled water produced in system in daytime is 1410 ml. As a result of measurements carried out at 30 min. interval, the highest amount of distilled water (110 ml) was obtained on 15.00 (Fig. 4). As seen in figures, the increase in radiation intensity between 08.30 and 11.30 increased the temperature of water in tank, and consequently the amount of vaporization increased. The increase
27
in vaporization increased the amount of distilled water production. Although a decrease between 11.30 and 15.00 h was observed, the amount of distilled water produced increased under favor of thermal capacity of the water in tank. The amount of production peaked on 15.00, and then decreased as the temperature increased. After the sunset, the production continued due to the thermal storage capacity of the water within the tank. The distilled water produced in system during the night is 410 ml. The total amount of distilled water produced in system reached at 1820 ml/day (Fig. 4). In Fig. 5, the temperature change of the forced convection tanktype water distiller (30 kg/h) is shown. Accordingly, the highest temperature values measured were 92 °C on 13:30 at collector outlet, 69 °C on 15:30 at collector inlet, and 74 °C on tank at 14:00. The amount of distilled water produced in system during daytime is 1318 ml. As a result of measurements made at 30 min. interval, the highest amount of distilled water obtained during daytime was between 14.00 and 14.30 (106 ml) (Fig. 6). The
Fig. 3. The changes of temperature and radiation intensity in natural convection tank-type water distiller experiments.
Fig. 4. The amount of distilled water produced in natural convection tank-type water distiller.
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E. El et al. / Thermal Science and Engineering Progress 3 (2017) 24–30
Fig. 5. Temperature change in forced convection (30 kg/h) tank-type water distiller.
Fig. 6. The amount of distilled water produced in forced convection (30 kg/h) tank-type water distiller.
amount of distilled water produced in system during the night was 368 ml. Total amount of distilled water was 1686 ml/day. In Fig. 7, the temperature change in forced convection (50 kg/h) tank-type water distilled is shown. In Fig. 7, it is seen that the collector outlet temperature increased up to 12.30 and then decreased, and that the collector inlet temperature increased up to 16.00 and then decreased. The collector outlet temperature was measured to be 78 °C on 12:30, the collector inlet temperature was measured to be 63.3 °C on 16:00, and tank temperature was measured to be 71 °C on 13.30. In Fig. 8, the amounts of distilled water production in tank-type water distiller are presented at 30 min. interval. Accordingly, the amount of distilled water production in system during daytime showed increase up to 14.00, and then decreased. The highest amount of distilled water produced throughout the day was measured to be 110 ml on 14:00. The amount of distilled water production at the end of the day was measured to be 1232 ml. The amount of distilled water production in system during daytime was 1232 ml, and 336 ml in nighttime. The total amount was 1568 ml.
Considering all 3 cases, it can be seen that the temperature in the tank decreased from natural convection to forced convection due to the increase in flow rate. The total amount of distilled water decreased from 1820 ml to 1568 ml as the flow rate increased. Accordingly, by using Eq. (3), efficiencies were calculated for 3 systems, and presented in Fig. 9. Accordingly, the efficiencies of the systems increased throughout the daytime. On 17.00, the efficiencies were calculated to be 63.54% in 30 kg/h flow rate and 59.76% in 50 kg/h flow rate in forced convection systems and 83.15% in natural convection system. The reason that the efficiency of natural convection system is that the temperature of the water in tank was higher than other systems. In their study, Rajaseenivasan et al. [16] examined the performance of the single basin solar still by means of preheating the saline water using an integrated flat plate collector arrangement. They determined that the productivity of 1 m2 basin area of a conventional single slope single basin still to be 37%. In conventional single slope single basin still, 3.62 kg/day of water was distilled.
E. El et al. / Thermal Science and Engineering Progress 3 (2017) 24–30
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Fig. 7. Temperature change in forced convection (50 kg/h) tank-type water distiller.
Fig. 8. The amount of distilled water produced in forced convection (50 kg/h) tank-type water distiller.
The productivity of the single slope flat plate collector basin still (FPCB still that they developed was determined to be 60%. In this study, the productivity and the amount of water produced were determined to be 51.47% and 2.389 kg/day for 1 m2 basin area of a conventional single slope single basin still. For the tank-type distiller system that was developed, the productivity values obtained at natural convection and forced convection at 30 kg/h and 50 kg/h flow rates were found to be 83.15%, 63.54% and 59.76%, respectively. In this study, a standard solar still distiller, which is widely used, was modified to a solar still water heating system. For this reason, the collector surface area was set to be 1.8 m2. As a result of that, besides the hot water, also the distilled water was obtained from the designed tank-type distiller system. As seen in figures, the temperature of obtained water was sufficient for daily use. Thus, the clean and hot water was obtained at the same time under real weather conditions. According to the results, as the highest
amount of water, 1.820 kg/day distilled water was obtained form also the natural convection system. Since the circulation is slow in natural convection systems, the temperature of the water in tank is higher. For this reason, depending on the level of vaporization, higher amount of distilled water was obtained. But, in natural convection solar still system, the capacity of producing hot water is limited [17]. For this reason, forced convection system is more frequently preferred. In designed system, the level of distilled water obtained was found to be higher in natural convection. But, since the hot water production capacity was less, the system was found to be suitable for obtaining both hot and distilled water. While calculating the productivity values of forced convection systems, the pump power was also taken into account. Moreover, during the experiments, in order to determine the drinkability of distilled water obtained from tank-type water distiller combined with hot water collector, the water samples taken from distilled water under hygienic conditions were analyzed in
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E. El et al. / Thermal Science and Engineering Progress 3 (2017) 24–30
Fig. 9. Efficiencies of natural convection and forced convection tank-type water distillers.
References
Table 2 Analysis results of distilled water. Parameters
Distilled water
Drinking water standards, EC
pH Color Blur, NTU Ammonium nitrogen, mg/L Hardness, mg/L CaCO3
7.0 Colorless 1 0.2 70
6.5–9.5 Colorless 1 0.05–0.5 61–120
laboratory, and the results are presented in Table 2. In Table 2, it is seen that the water meets the EC standards.
3. Conclusions In this study, a tank-type distiller system combined with hot water collector was designed and, besides the hot water, also the distilled water was obtained from designed system. The designed system was tested under both natural and forced convections. The total amount of distilled water production in natural convection systems was found to be 1820 ml/day, while the same value in forced convection systems was 1686 ml/day at 30 kg/h flow rate and 1568 ml/day at 50 kg/h flow rate. The efficiency reached at 83.15% in natural convection system, and 63.54% at 30 kg/h flow rate and 59.76% at 50 kg/h in forced convection systems. Due to the storage water temperature, natural convection system’s efficiency was found to be higher than forced convection systems. It was determined that the temperature of obtained water was good enough for daily use. Hence, in addition to heating the water, the distilled water can be produced with solar water heating systems in regions with lack of potable water.
Acknowledgement This work was supported under the Coordination Unit of Scientific Research Projects of Fırat University, Project No: MF.11.10.
[1] R. Mamlook, B.A. Akash, S. Nijmeh, Fuzzy sets programming to perform evaluation of solar systems in Jordan, Energy Convers. Manage. 42 (2001) 1717–1726. [2] K. Voropoulos, E. Mathioulakis, V. Belessiotis, Experimental investigation of the behavior of a solar still coupled with hot water storage tank, Desalination 156 (3) (2003) 15–322. [3] I. A1-Hayek, O.O. Badran, The effect of using different designs of solar stills on water distillation, Desalination 169 (2004) 121–127. [4] M. Ben-Amara, I. Houcine, A.A. Guizani, M. Maalej, Efficiency investigation of a new-design air solar plate collector used in a humidification–dehumidification desalination process, Renewable Energy 30 (2005) 1309–1327. [5] A.M. Abdel Dayem, Experimental and numerical performance of a multi-effect condensation-evaporation solar water distillation system, Energy 31 (2006) 2710–2727. [6] R. Tripathi, G.N. Tiwari, Thermal modelling of passive and solar stills for different depths of water by using the concept of solar fraction, Sol. Energy 80 (2006) 956–967. [7] M. Zamen, M. Amidpour, S.M. Soufari, Cost optimization of a solar humidification–dehumidification desalination unit using mathematical programming, Desalination 239 (2009) 92–99. [8] A.J. Esfahani, N. Rahbar, M. Lavvaf, Utilization of thermoelectric cooling in a portable active solar still, an experimental study on winter days, Desalination 269 (2011) 198–205. [9] P.T. Tsilingiris, The application and experimental validation of a heat and mass transfer analogy model for the prediction of mass transfer in solar distillation systems, Appl. Therm. Eng. 50 (2013) 422–428. [10] A. Ahsan, Kh.M.S. Islam, T. Fukuhara, A.H. Ghazali, Experimental study on evaporation, condensation and production of a new tubular solar still, Desalination 260 (2010) 172–179. [11] A.O. Al-Sulttani, A. Ahsan, A. Rahman, N.N.N. Daud, S. Idrus, Heat transfer coefficients and yield analysis of a double-slope solar still hybrid with rubber scrapers: an experimental and theoretical study, Desalination 407 (2017) 61– 74. [12] M. Feilizadeh, M.R.K. Estahbanati, A. Ahsan, K. Jafarpur, A. Mersaghian, Effects of water and basin depths in single basin solar stills: an experimental and theoretical study, Energy Convers. Manage. 122 (2016) 174–181. [13] N. Rahbar, J.A. Esfahani, Productivity estimation of a single-slope solar still: theoretical and numerical analysis, Energy 49 (2013) 289–297. [14] J.P. Holman, Experimental Methods for Engineers, McGrawHill Book Company, 1971, pp. 37–52. [15] A.A. Badran, A.A. A1-Hallaq, I.A. Eyal Salman, M.Z. Odat, A solar still augmented with a flat-plate collector, Desalination 172 (2005) 227–234. [16] T. Rajaseenivasan, P.N. Raja, K. Srithar, An experimental investigation on a solar still with an integrated flat plate collector, Desalination 347 (2014) 131– 137. [17] S. Agı, H. Günerhan, Sıvılı düzlemsel günesß kolektörlerinde verim artırma olanakları, Tesisat Mühendislig˘i Dergisi 86 (2005) 15–30.
Contents lists available at ScienceDirect
Thermal Science and Engineering Progress journal homepage: www.elsevier.com/locate/tsep
Efficiency analysis of tank-type water distillation system integrated with hot water collector Emin El a, Gülsßah Çakmak b,⇑, Cengiz Yıldız b a b
Vocational School of Technical Sciences, Bitlis Eren University, 13000 Bitlis, Turkey Department of Mechanical Engineering, Firat University, 23119 Elazig, Turkey
a r t i c l e
i n f o
Article history: Received 20 January 2017 Received in revised form 16 March 2017 Accepted 31 May 2017
Keywords: Solar still Energy efficiency Drinking water Tank type distiller
a b s t r a c t In this study, besides the hot water, it was also aimed to obtain distilled water from solar still water heating systems, which are widely used in obtaining hot water. For this purpose, a new type of distiller was obtained by making modifications, which enable us to obtain distilled water, on a solar still water heating system having flat-surface panel collector and vertical tank and operating as a closed system. The designed system was tested under both natural convection and forced convection at flow rates of 30 kg/h and 50 kg/h. As a result of performed experiments, the temperature, productivity, and distilled water production amounts were calculated for the designed system. It was determined that the temperature of hot water obtained was sufficient for daily use. According to the results, as the highest amount of water, 1.820 kg/day distilled water was obtained form also the natural convection system. In order to determine the drinkability of distilled water, the laboratory analyses were carried out, and it was found that the water meets EC standards. Thus, the clean and hot water was obtained at the same time from the designed system under real weather conditions. Ó 2017 Published by Elsevier Ltd.
1. Introduction Population growth, industrialization and active agricultural activities lead to the depletion of limited underground and surface water resources of the world, and increase the environmental problems. The shortage of potable water is an important problem, and the actual underground water stock is brackish in general and cannot be used as potable water as is. Gradual depletion of energy and water resources of the world and non-usefulness of the existing resources bring the energy and water procurement into the forefront. Renewable energy is the type of energy coming into the forefront with its characteristics such as, when appropriate technologies are used, having no pollutant effect and being local and environment-friendly. Even though the energy has an important role in development of human being, it is only a part of the whole. But, the water is a vital necessity that has to be met always. Water, which is our most vital requirement, has vital importance in terms of all our social activities. For purifying the dirty water, many methods are used, but all of those methods require a significant amount of energy. The energy
⇑ Corresponding author. E-mail address: [email protected] (G. Çakmak). http://dx.doi.org/10.1016/j.tsep.2017.05.012 2451-9049/Ó 2017 Published by Elsevier Ltd.
resources to be used in purification process such as oil, natural gas, and electricity have both high costs and lead to environmental pollution. The studies carried out in recent years aimed to increase the use of renewable energy resources as energy source. Mamlook et al. [1] compared the performances of various solar energy implementations. They carried out a study, where they utilized fuzzy logic on solar water distillation, solar water heating, photovoltaic and solar electricity production methods. Those methods were compared from the aspects of efficiency and costs. They determined that the solar water distillation was the best method in terms of the costs. Voropoulos et al. [2] experimentally examined the solar water distiller integrated with a storage tank under realistic conditions by keeping the water temperature stable at different water levels. The distillation system consisted of an asymmetrical pool-type distiller and the storage tanks under the distiller. The amount of water obtained from hot-water storage tank in 24-h was reported to be higher than that obtained from classical pool-type distillation system. Al-Hayek and Badran [3] experimentally examined 2 different solar water distillation systems, and investigated the parameters affecting the production via water distillation. One of the systems they used was asymmetrical greenhouse-type distillation system with mirrors in inner walls, while another system was symmetrical greenhouse-type distillation system. As a result of their
E. El et al. / Thermal Science and Engineering Progress 3 (2017) 24–30
experimental research, they reported that 20% more water was obtained from asymmetrical greenhouse-type water distillation system in proportion to symmetrical system. At the end of their study, they showed that the radiation was effective on the temperature at the surface of water in both of systems, and that the amount of water obtained from distillation system increased as the water depth decreased. Ben-Amara et al. [4] designed a new-type solar collector for distilling process. They examined the parameters such as solar radiation, wind speed, temperature of the medium, mass flow, air intake moisture and temperature that are effective on collector efficiency. As a result, they optimized the collector for the new solar water distillation system. Dayem [5] examined the numerical and experimental performance of classical solar water distilling systems based on very efficient condensation and vaporization cycle. Distillation room consisted of moistener and dehumidifier units. The air circulation in those 2 sections was provided via natural convection. The cold water was pre-heated inside, and then exposed to temperature change within the solar collector. It was determined that water can be produced 241 days a year in this system. Tripathi and Tiwari [6] carried out experiments at different depths for active and passive solar pools. In active distillation process, in order to increase the temperature difference between glass and water surface, they pumped the hot water to the bottom of pool. In passive system, no pump was utilized. For those systems utilized, they made comparisons at various depths and modes in parameters such as water, inner glass, outer glass, vaporization, temperature, radiation, and amount of the water obtained. Zamen et al. [7] optimized the solar energy system for desalinating the water. The aim of this optimization was to decrease the cost of obtaining clean water. The results obtained according to the solutions obtained from cost objective function were reported to be lower than those obtained from other objective functions. Esfahani et al. [8] attempted to produce a portable solar water distiller. By comparing the summer and winter results, they determined that the efficiency in summer was higher than winter efficiency. Tsilingiris [9] developed a new theoretical model for estimating the mass transportation in solar water distillation systems. The model he used was based on the Chilton-Colburn simulation that can be applied for wide range of Prandtl and Schmidt pure numbers. In order to perform comparative verification, he utilized a series of experimental results, which were obtained from passive solar water distillation system under summer conditions at higher process temperatures, for examining the higher process temperature conditions. Ahsan et al. [10] made a comparison by designing two Tubular Solar Still (TSS) obtained using a vinyl chloride layer and a polyethylene film cover as a transparent tube cover. According to the results obtained, the hourly evaporation, condensation and production flows are explained by the proportions of moist air temperature and relative humidity fraction. In order to estimate the hourly production flow at the end of their work, they proposed an empirical equation based on this relationship. Al-Sulttani et al. [11] designed, produced and tested a new double-slope solar still hybrid with rubber scrapers (DSSSHS) and a double-slope solar still (DSSS). The proposed DSSSHS design utilizes the advantages of using a small slope of the backing cover, which allows for higher solar radiation to penetrate. The maximum recorded value of the total internal heat transfer coefficient for the DSSSHS was found to be 38.754 W/m2 °C and the daily yield to be 4.24 L/m2 day with productivity improvement of 63%. Feilizadeh et al. [12] investigated separately, the effects of water depth and the water surface-cover distance (WCD) and examined
25
effects of water depth on the performance of solar stills with the same WCD. It was found that WCD can affect the amount of distillate yield up to 26%. In addition, the solar stills with various water depths were mathematically modelled and the rates of their productivity were predicted. The theoretical results were compared with the current experimental data and it was found that there is a good agreement between the present theoretical predictions and experimental observations. Rahbar and Esfahani [13] obtained the optimum geometric condition for increasing the productivity in a single-slope solar still by using theoretical and numerical methods. Their results indicate that for a fixed length of a solar still, the productivity increases with decrease in the specific height. In addition, they observed identical trends for both water productivity and convective heat transfer coefficient. In this study, besides the hot water, it was also aimed to obtain distilled water from solar still water heating systems, which are widely used in obtaining hot water. For this purpose, a new type of distiller was obtained by making modifications, which enabled us to obtain distilled water, on a solar water heating system having flat-surface panel collector and vertical tank and operating as a closed system. The designed system was tested under both natural convection and forced convection at flow rates of 30 kg/h and 50 kg/h, and the results were presented.
2. Materials and method 2.1. Experimental set-up In this study, a tank-type solar water distillation system integrated with hot water collector was designed and manufactured. The designed experimental setting was assembled at terrace of Heat Engineering Lab of Machinery Engineering Department of Engineering Faculty of Fırat University in the way preventing the shadowing. The experiments were carried out between July and October months under climate conditions of Elazıg˘. This system was designed as natural convection and forced convection, and then tested.
Fig. 1. Tank-type water distiller integrated with hot water collector. 1. City water inlet, 2. Hot liquid glass jar, 3. Hot liquid inlet, 4. Insulation, 5. Distilled water collection channel, 6. Collector, 7. Pyranometer, 8. Top serpentine (Cold), 9. Distilled water outlet, 10. Hot water outlet, 11. Bottom serpentine (Hot), 12. Measure, 13. Hot liquid outlet, 14. Thermocouple, 15. Digital thermometer, 16. Circulation, 17. Rotameter.
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This system consists of planar collector collecting solar energy, tank type distiller, insulated pipes linking those 2 parts, pump, and measurement components (Fig. 1). The solar collector used in system was the planar solar collector that is used in traditional solar water heating system. In distillation system, the standard planar solar energy hot water collector with aluminum pipes and wings (dimensions of 930 1930 87.5 mm and surface area 1.8 m2 gross and 1.6 m2 net) was preferred. In design of tank-type water distiller used in this system, differently from traditional solar water heating systems, a top serpentine for ensuring the condensation at the top of tank and a distilled water collection channel for removing the condensation water from the system were utilized. Furthermore, through a plumbing system installed in insulation layer between inner sheet and outer sheet iron of the tank, the water circulated in serpentine was directed into the tank. Tank-type water distiller was manufactured from 0.8 mm-thick chrome-nickel material at width of 400 mm and height of 1050 mm in cylinder form. Heat insulation was prepared with 40 mm-thick poly-urethane material. In this system, the city water entering into tank passes firstly from top serpentine and cools the serpentine. And then, through a plumbing system passing through insulation layer, it reaches the tank from tank’s bottom and is collected there. The liquid heated with solar collector is used as the heat sources of this system. Hot liquid coming from collector and passing from bottom serpentine evaporates the city water gathering within the tank. Vaporizing city water condenses by contacting with top serpentine, which is cold, and the distilled water is obtained. That distilled water gathers in distilled water collection channel, and is removed from the system through a plumber system (Fig. 2).
In order to ensure the circulation of the water in system, the WELKO – LRS40 4S/130 model circulation pump was utilized. This pump can be operated at 0 °C–+100 °C temperature and under 10 bars of operation pressure, it has 3 speed levels, its maximum flow rate is 150 L/h, and maximum pump head is 4 m. Rotameter was used in order to determine the flow rate of liquid circulating in forced-convection systems, and particular rotameter used can measure the flow rates between 0 and 200 L/h. In measuring the density of solar radiation, the pyranometer manufactured by Kipp and Zonen (CC12) was used. The pyranometer was placed at an appropriate angle that is suitable for operation angle of the system, and the measurements were performed in 30 min of interval. In order to measure the temperatures of the determined points, Elimko E680 model 16-channel digital thermometer with universal inlet, inlet and outlet of which can be programmed by the user, was used. Under favor of that thermometer, the measurements can be made with J, K, T, E, and PT-100. In this study, the 0.5 mm-diameter J type thermocouples were used. Using the parameters leading to error during the distillation experiments, the total error was determined. In order to determine the total error in any parameter, the total error value was calculated by considering the constant errors, production errors and random error in accordance with the formula below [14],
h i1=2 Wth ¼ ðx1 Þ2 þ ðx2 Þ2 þ . . . . . . ðx1 Þ2
ð1Þ
During the experiments, the total errors were calculated and are presented in Table 1. Furthermore, the distilled water obtained from distiller per hour was calculated according the formula below;
mew ¼
hew ðTw Tg Þ3600 L
ð2Þ
Daily output of the distiller was calculated by multiplying the sum of condensation per hour with the hidden vaporization and then dividing to the radiation density per efficient collector surface area [15]
g¼
mew :L I A:3600
ð3Þ
The efficiency in the system using the pump is calculated by the following equation;
g¼
mew L IA3600 þ Wp:Dt
ð4Þ
2.2. Analysis of results Tank-type distiller experiments were carried out in September under climate conditions of Elazıg˘ city. At the end of the experiments, the amounts of distilled water produced in natural convec-
Table 1 Total errors occurring during the distillation experiments.
Fig. 2. Tank-type water distiller (1. City water inlet, 2. Distilled water outlet, 3. Hot water outlet, 4. Hot liquid inlet, 5. Insulation, 6. Top serpentine (Cold), 7. Distilled water collection channel, 8. Bottom serpentine (Hot), 9.Cold water inlet, 10. Hot liquid outlet).
Parameters leading to error
Total error
Total Total Total Total Total Total Total Total Total Total
±0.173 °C ±0.173 °C ±0.173 °C ±0.173 °C ±0.1 min ±0.1 min ±0.1 min ±0.1 min ±4.062 ml ±0.86 kg/h
error in measuring the temperature at collector inlet error in measuring the temperature at collector outlet error in measuring the tank temperature error in measuring the medium temperature periodical error in measuring the production periodical error in reading the temperature values periodical error in measuring the air temperature periodical error in measuring the radiation periodical error in measuring the fresh water produced periodical error in measuring the flow rate
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tion and forced convection systems and the efficiencies of systems were compared. The experiments carried out on forced convection system with 38° of collector angle were performed at 2 different flow rates (30 kg/h and 50 kg/h). In Fig. 3, the changes in natural convection tank-type water distiller’s collector inlet (Tkg), collector outlet (Tkç), tank water temperature (Td) and medium temperature (Tç) and the radiation intensity are shown. Accordingly, the highest temperature values measured in system were 92 °C on 13:00 at collector outlet, 62 °C on 15:30 at collector inlet, 78 °C on 14:30 at tank. The total amount of distilled water produced in system in daytime is 1410 ml. As a result of measurements carried out at 30 min. interval, the highest amount of distilled water (110 ml) was obtained on 15.00 (Fig. 4). As seen in figures, the increase in radiation intensity between 08.30 and 11.30 increased the temperature of water in tank, and consequently the amount of vaporization increased. The increase
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in vaporization increased the amount of distilled water production. Although a decrease between 11.30 and 15.00 h was observed, the amount of distilled water produced increased under favor of thermal capacity of the water in tank. The amount of production peaked on 15.00, and then decreased as the temperature increased. After the sunset, the production continued due to the thermal storage capacity of the water within the tank. The distilled water produced in system during the night is 410 ml. The total amount of distilled water produced in system reached at 1820 ml/day (Fig. 4). In Fig. 5, the temperature change of the forced convection tanktype water distiller (30 kg/h) is shown. Accordingly, the highest temperature values measured were 92 °C on 13:30 at collector outlet, 69 °C on 15:30 at collector inlet, and 74 °C on tank at 14:00. The amount of distilled water produced in system during daytime is 1318 ml. As a result of measurements made at 30 min. interval, the highest amount of distilled water obtained during daytime was between 14.00 and 14.30 (106 ml) (Fig. 6). The
Fig. 3. The changes of temperature and radiation intensity in natural convection tank-type water distiller experiments.
Fig. 4. The amount of distilled water produced in natural convection tank-type water distiller.
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Fig. 5. Temperature change in forced convection (30 kg/h) tank-type water distiller.
Fig. 6. The amount of distilled water produced in forced convection (30 kg/h) tank-type water distiller.
amount of distilled water produced in system during the night was 368 ml. Total amount of distilled water was 1686 ml/day. In Fig. 7, the temperature change in forced convection (50 kg/h) tank-type water distilled is shown. In Fig. 7, it is seen that the collector outlet temperature increased up to 12.30 and then decreased, and that the collector inlet temperature increased up to 16.00 and then decreased. The collector outlet temperature was measured to be 78 °C on 12:30, the collector inlet temperature was measured to be 63.3 °C on 16:00, and tank temperature was measured to be 71 °C on 13.30. In Fig. 8, the amounts of distilled water production in tank-type water distiller are presented at 30 min. interval. Accordingly, the amount of distilled water production in system during daytime showed increase up to 14.00, and then decreased. The highest amount of distilled water produced throughout the day was measured to be 110 ml on 14:00. The amount of distilled water production at the end of the day was measured to be 1232 ml. The amount of distilled water production in system during daytime was 1232 ml, and 336 ml in nighttime. The total amount was 1568 ml.
Considering all 3 cases, it can be seen that the temperature in the tank decreased from natural convection to forced convection due to the increase in flow rate. The total amount of distilled water decreased from 1820 ml to 1568 ml as the flow rate increased. Accordingly, by using Eq. (3), efficiencies were calculated for 3 systems, and presented in Fig. 9. Accordingly, the efficiencies of the systems increased throughout the daytime. On 17.00, the efficiencies were calculated to be 63.54% in 30 kg/h flow rate and 59.76% in 50 kg/h flow rate in forced convection systems and 83.15% in natural convection system. The reason that the efficiency of natural convection system is that the temperature of the water in tank was higher than other systems. In their study, Rajaseenivasan et al. [16] examined the performance of the single basin solar still by means of preheating the saline water using an integrated flat plate collector arrangement. They determined that the productivity of 1 m2 basin area of a conventional single slope single basin still to be 37%. In conventional single slope single basin still, 3.62 kg/day of water was distilled.
E. El et al. / Thermal Science and Engineering Progress 3 (2017) 24–30
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Fig. 7. Temperature change in forced convection (50 kg/h) tank-type water distiller.
Fig. 8. The amount of distilled water produced in forced convection (50 kg/h) tank-type water distiller.
The productivity of the single slope flat plate collector basin still (FPCB still that they developed was determined to be 60%. In this study, the productivity and the amount of water produced were determined to be 51.47% and 2.389 kg/day for 1 m2 basin area of a conventional single slope single basin still. For the tank-type distiller system that was developed, the productivity values obtained at natural convection and forced convection at 30 kg/h and 50 kg/h flow rates were found to be 83.15%, 63.54% and 59.76%, respectively. In this study, a standard solar still distiller, which is widely used, was modified to a solar still water heating system. For this reason, the collector surface area was set to be 1.8 m2. As a result of that, besides the hot water, also the distilled water was obtained from the designed tank-type distiller system. As seen in figures, the temperature of obtained water was sufficient for daily use. Thus, the clean and hot water was obtained at the same time under real weather conditions. According to the results, as the highest
amount of water, 1.820 kg/day distilled water was obtained form also the natural convection system. Since the circulation is slow in natural convection systems, the temperature of the water in tank is higher. For this reason, depending on the level of vaporization, higher amount of distilled water was obtained. But, in natural convection solar still system, the capacity of producing hot water is limited [17]. For this reason, forced convection system is more frequently preferred. In designed system, the level of distilled water obtained was found to be higher in natural convection. But, since the hot water production capacity was less, the system was found to be suitable for obtaining both hot and distilled water. While calculating the productivity values of forced convection systems, the pump power was also taken into account. Moreover, during the experiments, in order to determine the drinkability of distilled water obtained from tank-type water distiller combined with hot water collector, the water samples taken from distilled water under hygienic conditions were analyzed in
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Fig. 9. Efficiencies of natural convection and forced convection tank-type water distillers.
References
Table 2 Analysis results of distilled water. Parameters
Distilled water
Drinking water standards, EC
pH Color Blur, NTU Ammonium nitrogen, mg/L Hardness, mg/L CaCO3
7.0 Colorless 1 0.2 70
6.5–9.5 Colorless 1 0.05–0.5 61–120
laboratory, and the results are presented in Table 2. In Table 2, it is seen that the water meets the EC standards.
3. Conclusions In this study, a tank-type distiller system combined with hot water collector was designed and, besides the hot water, also the distilled water was obtained from designed system. The designed system was tested under both natural and forced convections. The total amount of distilled water production in natural convection systems was found to be 1820 ml/day, while the same value in forced convection systems was 1686 ml/day at 30 kg/h flow rate and 1568 ml/day at 50 kg/h flow rate. The efficiency reached at 83.15% in natural convection system, and 63.54% at 30 kg/h flow rate and 59.76% at 50 kg/h in forced convection systems. Due to the storage water temperature, natural convection system’s efficiency was found to be higher than forced convection systems. It was determined that the temperature of obtained water was good enough for daily use. Hence, in addition to heating the water, the distilled water can be produced with solar water heating systems in regions with lack of potable water.
Acknowledgement This work was supported under the Coordination Unit of Scientific Research Projects of Fırat University, Project No: MF.11.10.
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