BAB V. KESIMPULAN DAN SARAN
5.2 Saran
Saran dari penulis untuk memperbaiki penelitian-penelitian berikutnya, antara lain :
1. Perlunya menggunakan pompa yang dapat mengalirkan air pada laju aliran rendah, dan konstan.
2. Agar diperoleh data yang lebih valid, baik bila menggunakan sensor temperatur pada setiap sekat untuk mengetahui secara detail temperatur air pada setiap sekat.
52
DAFTAR PUSTAKA
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55
LAMPIRAN
Lampiran 2. Tabel Sifat Air, dan Uap Jenuh
Lampiran 3. Tabel Sifat Air (Cair Jenuh)
Lampiran 4. Draf artikel yang telah dideseminasikan dalam ICSAS 2019
Effects of Water Heating Time on the Efficiency of
a Wick-Covered Partition Solar Still
Dimas Hanung Pamungkas
1, a)and F. A. Rusdi Sambada
1, b)1
Department of Mechanical Engineering, Faculty of Science and Technology, Sanata Dharma University, Yogyakarta, Indonesia
a)Corresponding author: dimashanung@gmail.com b)
sambada@engineer.com
Abstract. Clean water is a rare thing to find because many water sources are contaminated with
wasting product from industry. One way to get drinkable water from contaminated water is by distillation using solar energy. The type of distillation that is widely used is basin and wick type absorber. The basin type has an advantage on the small loss of heat energy coming out of the distillation tool, but has low effectiveness on evaporation process. While the type of wick absorber has a higher effectiveness, but there is a loss energy coming out of the distillation tool greater than the basin type. This study aims to discover the effect of water heating time on the efficiency of solar water distillation. This research uses an experimental method by making model which is combining the advantages of basin and wick type absorber become a wick-covered partition solar still. Variables varied in this study are (1) the type of solar still with water is accommodated and flowed on each partition, and (2) the type of solar still with and without any wasted energy out of the solar still. Our results show that variations without any loss of energy and water are accommodated at a volume of 100 ml in each partition have efficiency up to 67.7%.
INTRODUCTION
In maintaining survival, humans will not escape the use of water. Humans need water for their daily needs such as washing, cooking, bathing, and so on. Water is also an irreplaceable basic human need, that is drinking. About 72.4% of human body consists of water (Forbes, 2012). Therefore, the need for clean water is very absolute. However, the availability of clean water is a problem nowadays.
The scarcity of clean water is caused by the increasing amount of water pollution, both river and groundwater, along with the development of technology, and industry. This water pollution causes water quality to decrease until it cannot function according to its designation (Goel, 2006). Indonesian people, especially in remote areas, are accustomed to consuming groundwater and river water directly. This condition is the beginning of the emergence of various problems, especially problems related to human health. Based on data from UNICEF Indonesia (Indonesia, 2012), poor sanitation and water hygiene have caused child mortality due to diarrhea to reach 88% worldwide.
One way to get clean water that can be consumed directly from contaminated water is through the water distillation process with solar energy or usually called solar still. Solar energy is used to accelerate the 2 main processes in solar still, those are evaporation, and condensation. Of the various variations of solar still devices, the type of basin, and the type of wick absorber are the most commonly used. Basin type solar still is the type of distillation that has the simplest construction but its efficiency value is lower than wick type (Udhayabharathi et al., 2015). While in wick type absorber, there is a considerable loss of energy in the form of hot water coming out of the tool before completely evaporating.
Several studies on basin type, and the wick type absorber of solar still and its variations have been carried out. Sodha et al. (Sodha et al., 1981) conducted a study on a wick type solar still with
a double fabric type. From the study, distillation results were obtained at 2.5 l/m2.day, with an overall efficiency of 34%. Distillation by combining the wick type absorber, and the basin has been carried out by Minasian and Al-Karaghouli (Minasian and Al-Karaghouli, 1995). This type gives 85% more results than distillation types of wick absorber or basin type. The combination of basin, and wick type absorber, using 6 partition installed along the absorber area proved to provide an efficiency increase of 60.3% compared to conventional wick type distillation (Christian, 2018). The solar still productivity itself depends on several parameters such as weather conditions, tool position, glass slope, steam leak, and other operational parameters (Garg and Mann, 1977). They explained that the results of distillation of solar energy were directly proportional to the total intensity of the sun, ambient air temperature, and wind speed. However, the productivity of distillation is not affected by atmospheric vapor pressure.
Based on research that has been done, the factors that influence the efficiency of solar still include the influence of materials, and the form of absorber (Naim and Abd El Kawi, 2003). Other factors are the effect of the slope of the cover glass, and the thickness of the water (Garg and Mann, 1977). The study showed optimum results on glass slope of 10°, and increased yields that were directly proportional to the decrease in water thickness above 1 cm. Further research on the effect of water thickness, and slope of glass on heat transfer is carried out by Tiwari and Tiwari(Tiwari and Tiwari, 2006), and Ahmed and Ibrahim(Ahmed and Ibrahim, 2016). The third factor is the influence of the thickness of the glass cover (Panchal and Shah, 2012). They explained that the increase in efficiency of the distillation device is directly proportional to the thinner thickness of the glass. In this study, testing was carried out with variations in glass thickness of 4 mm, 8 mm and 12 mm. The optimum efficiency results were obtained in the thickness of the 4 mm glass cover. The fourth factor is the different temperature between absorber and the cover glass. The optimum efficiency will be obtained if the surface temperature of the absorber gets higher, and conversely the surface temperature of the cover glass gets lower (Abdenacer and Nafila, 2007).
Based on the studies mentioned above, this study will extend the duration of water heating process in the absorber so that the evaporation process can take place optimally. Water will flow from the fist partition to the next partition in the zigzag direction. So that the water will gradually warm up until the last partition. This study will vary the amount of water flow rate to obtain maximum efficiency. Thus, it is expected that the results of distilled water can increase the performance value of the wick-covered partition solar still.
METHODOLOGY
FIGURE 1. Cross-sectional view of the schematic arrangement of experiment. Information:
(1) cover glass, (2) dirty water, (3) absorber, (4) distilled water channel, (5) distilled water container, (6) supporting framework, (7) dirty water supply tank, (8) faucet, (9) unevaporated
water channel, (10) unevaporated water container, (11) wick, (12) hose.
A cross sectional view of schematic diagram of the wick-covered partition solar still shown in Fig. 1. Water reservoirs on this wick-covered partition solar still made from multiplexes measuring 73 cm x 55 cm with a thickness of 3.6 cm. Absorber is made of aluminum plate with a size of 69 cm x 51 cm. As an insulator, aluminum plates are coated using black rubber of the same size as
3 mm thick. The absorber wall is made of multiplex with 3 cm thick, and the entire inner surface, and outside of the wall are covered with 3 mm thick of black rubber as an insulator. The partition used is made of 6 pieces of aluminum elbow plate. The partition is installed along with the absorber in the same distance between the partition, which is 11.6 cm, and the partition is 2.5 cm height. The cover glass used has a thickness of 3 mm. Data retrieval is done indoors using a solar simulation tool in the duration of data retrieval for 2 hours. The solar simulation tool consists of 6 lights with each lamp having a power of 375 W. The lamp is mounted in an iron frame which is positioned parallel to the slope of the absorber. The distance between the lamp and the cover glass is 50 cm. Figure 2 shown the solar simulation tool.
FIGURE 2. The solar simulation used in this research. Information: (1) wick, (2) dirty water,
(3) lamp, (4) absorber, (5) unevaporated water container, (6) distilled water container, (7) hose, (8) dirty water supply tank, (9) supporting framework, (10) partition, (11) water pump. The tool scheme in the research of wick-covered partition solar still consists of 2 configurations, those are:
1. Wick-covered partition solar still with dirty water is accommodated on each partition (without any input water flow).
2. Wick-covered partition solar still with the zigzag flow direction, and the water comes out of the distillation through the last partition.
The parameters varied are:
1. Four variations of the water volume collected in each partition (100, 150, and 300 ml). 2. Three variations of the flow rate of water flowing in the absorber with zig-zag flow, and
issued through the last partitions (0.30, 0.45, and 0.90 liters/hour).
In this study, the following variables were measured every 10 seconds for 2-hour data retrieval, including:
1. Intake water temperature, Tin (°C) 2. Water out temperature, Tout (°C) 3. Outer glass temperature, Tc (°C) 4. Water temperature, Tw (°C) 5. Distilled water volume, m (liter)
6. The amount of solar energy (lights) received, G (watt/m2) 7. Duration of data retrieval, t (second)
Water and glass temperature was measured using Dallas Semiconductor Temperature Sensors (TDS), operated by Arduino microcontroller, having at least 0.01°C. The distilled output was recorded with the help of the sensor level. The solar intensity was measured with the help of a calibrated solar meter. The sun's heat value for all types of variations is considered constant because the number and position of the lights used in each variation were same.
The final result of this study is to know the efficiency value of a distillation device with related variations. Efficiency is defined as the ratio of the amount of energy used for the evaporation process to the amount of solar energy that comes during the heating process (Arismunandar, 1995):
∫ (1)
where mg is the result of distilled water (kg), hfg is the latent heat of evaporation (kJ/kg), AC is the area of the distillation (m2), G is the amount of solar energy coming (W/m2), and dt is the length of heating time (seconds). In this analysis, loss of heat energy through the side, and the base of the absorber can be negligible. Then, the energy balance in water (Jansen, 1985) produces:
(2)
Some heat energy from the absorber will be transferred to the glass using convection, radiation, and evaporation. The process of heat transfer by convection can be calculated by the equation:
(
) (3) where qconv is the energy wasted from glass to the environment (W/m2), Ta is the temperature of water (°C), Tk is the temperature of the glass (°C), Pw, and Pc is the partial pressure of steam at water, and glass (N/m2). Meanwhile, energy for evaporation (qvap) can be calculated by equation:
( )
( ) (4)
The results of distillation water can be calculated based on the value obtained from evaporation energy (qvap). The rate of distillation (mvap) can be searched by relationship:
(5)
The energy used during the heating process (qc) can be calculated using equation (6):
(6)
where mw is the mass flow rate of water (kg/s), Cp is the specific heat of water at constant pressure (kJ/kg°C), and ΔT is the difference in temperature of the inlet water, and the temperature of the water coming out of the distillation (°C).
RESULTS AND DISCUSSION
Data that has been obtained, then processed using Eq. 1 to Eq. 6. Then, carried out an analysis based on the total mass of water used for 2 hours of data retrieval.
From Fig 3, it can be seen that the best results are obtained in variations with the minimum total mass of water (600 ml). These results apply both to variations with water that is contained in the partitions and in variations with flowing water. This happens because water with a small volume has a thin layer of water. Heating process of the thin layer of water will be faster (Ladouy and Khabbazi, 2015). Meanwhile, at a larger volume of water, the heating process will be longer because the water layer has a greater thickness.
In addition, the use of wick installed on each partition serves to create a thin layer of water. Through the capillary nature of wick, water will be distributed vertically. So, the absorber area that can be used to heat the water becomes wider. In variations with large volumes of water, water will covered almost the entire surface of the wick. As a result, the wick that should be used to speed up the evaporation process does not function optimally.
If we look at the same amount of total mass of water, variations with accommodated water always give higher results than variations with flowing water. The results obtained also showed a significant difference. This happens because water of flowing conditions will only fill the lower part of the partitions. So that the wick is not able to distribute water to a higher part. Areas that are useful for the heating process will also be reduced.
FIGURE 3. The results of distilled water based on variations in the amount of total mass of
water used during data retrieval.
FIGURE 4. Efficiency based on variations in the amount of total mass of water used during
data retrieval.
The presence of water coming out of the last partitions is also a loss of energy. Since, the water that comes out is hot water that cannot be evaporated during the course of water from the first partitions to the last partitions. Besides, the flow rate that is too high causes the water heating process to not run optimally. It will take longer time to evaporate water with a greater thickness. Seen in Figure 3, the condition of the total mass of water is 1800 ml, the results obtained are very small.
Based on Equation 1, the efficiency of solar still will be directly proportional to the distilled water produced. So, the highest efficiency value was obtained in the variation of water collected with the volume in each partition of 100 ml (67.68%). In variation with the water are flowed in a zigzag direction and removed from the last partitions, the maximum efficiency value for the total mass of water used during data collection was 600 ml (56.68%).
The performance of the solar still itself is influenced by several factors, including the differences between glass temperature and absorber temperature, qvap and qconv. Figure 5 to Figure 7 shows the value of the temperature difference between the absorber and the glass during the
343,5 337,9 303 286,5 257,2 179,5 0 50 100 150 200 250 300 350 400 600 900 1800 Resul t o f Dis tilled Wa ter ( m l)
Total mass of water (ml)
Without any flowing water
Water flowing in the absorber with zigzag flow, and issued through the last partitions 67,68 66,61 59,91 56,68 51,01 35,69 0 10 20 30 40 50 60 70 80 600 900 1800 E ff iciency ( %)
Total mass of water (ml)
Without any flowing water
Water flowing in the absorber with zigzag flow, and issued through the last partitions
duration of data retrieval. Glass temperature difference and temperature absorber are given the symbol ΔT. This ΔT value is very influential on the evaporation process, and condensation.
FIGURE 5. The average of ΔT every 10 minutes in variations of 600 ml total mass of water.
FIGURE 6. The average of ΔT every 10 minutes in variations of 900 ml total mass of water. In the first few minutes, ΔT in all variations is negative. This happens because all parts of the water have not been fully heated. The value of ΔT which is above the horizontal axis, shows the start of the results of distilled water. From Figure 5 to Figure 7, we know that the temperature of the water accommodated in the partitions is always lower. This event occurs because the water heating process in variations with zigzag flow is a gradual warming. So that the water will experience an increase in temperature as the water runs from the first partition to the next partitions. However, in the last few minutes, the line will almost coincide. This happens because of accommodated water which can act as heat storage. So that when the water has been fully heated, the increase in temperature of the absorber becomes higher.
-4 -3 -2 -1 0 1 2 3 4 5 6 10 20 30 40 50 60 70 80 90 100 110 120 ΔT ( °C) Time (minute)
Without any flowing water
Water flowing in the absorber with zigzag flow, and issued through the last partitions
-6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 10 20 30 40 50 60 70 80 90 100 110 120 ΔT ( °C) Time (minute)
Without any flowing water
Water flowing in the absorber with zigzag flow, and issued through the last partitions
FIGURE 7. The average of ΔT every 10 minutes in variations of 1800 ml total mass of water.