Performance Evaluation of Single Slope Tilted Wick Solar Still with Varying Salt Concentrations

In this present article, a thorough study of a single-slope solar still has been conducted. The single slope solar still was modified with an inclined wick at 30°. The basin water was varied with different salt concentrations (0 %, 2 %, and 4 %). The study was performed for four different cases viz: (1) Conventional Solar Still (CSS) (2) Tilted wick Solar Still (TWSS) with 0 % salt concentration (3) TWSS with 2 % salt concentration (4) TWSS with 4 % salt concentration. The experiment was conducted under constant radiation of 500 W/m2 that was provided with the help of external panels. The functional correlation between basin water temperature (Tw) and time has been established. Moreover, from the obtained results best distillate output was acquired at 2 % salt concentration as the salt particles trapped inside the wick pores help to increase the evaporation rate effectively. The overall distillate output increased by 8.3 %, 17.5 %, and 8.5 % for Case 2, Case 3, and Case 4 when compared to Case 1 respectively.


INTRODUCTION
Water is the essential requirement of all living beings on the Earth, but around 2/3 rd the world's population is facing severe water scarcity at least once a month in the year.The rapid increase in the world's population, poor water management plans, and limited sources of fresh water lead to depletion of fresh potable water sources and shifted the world towards a water crisis.Generally, near coastal areas the availability of fresh water is limited, and their population depends on nearby sources, transportation of fresh water, and mainly on ocean water.The transported water is not economical and feasible for the long term so; they need in place solution to combat the current scenario.The ocean water contains high salinity in the form of TDS of more than 35 ppb (parts per billion).However, it can be desalinated economically for further household uses with the help of solar energy.Other than this, solar energy has been widely used in various sectors such as collectors, solar driers, solar stills, and so on [1 -3].
Solar still is a simple device to get fresh distilled water from brine water, using solar energy as a fuel.Impure water is poured into the thermally insulated black-painted basin, covered with transparent air-tight film.The solar radiation is passed through the film to the basin water, resulting in the increasing temperature of the basin water.The increase in water temperature leads to the evaporation of basin impure water and that evaporated water condenses over the inner surface of the transparent film by releasing its latent heat and drops down through the inner surface to the distillate channel.Moreover, solar still has several advantages such as simple design, cost economical, low maintenance, environment friendly, and so on, but it has some disadvantages also, like low productivity and high cost of modification [4].1285 (2024) 012002 IOP Publishing doi:10.1088/1755-1315/1285/1/012002 2 Number of researchers contributed in this field to enhance the overall distillate of the solar still by enhancing evaporation as well as condensation rate and by lowering the price of desalinated ocean water by modification in design [4], introducing heat exchangers [5 -7], collector [8], wick [9 -14], reflectors [15], sprinkler [16 -18] or adding various nanoparticles [19][20][21][22].Moreover, Agarwal et al. [23] experimented on conventional solar still (CSS) by integrating multiple V-shaped floating wick.The Maximum daily yield for modified solar still (MSS) in summer and winter was found to be 6.20kg/m 2 and 3.23kg/m 2 .Furthermore, an experiment was performed on double basin single slope solar still (DBSSSS) by introducing hollow fins, wick fins, and without fins for two cases of partially submerged fins and completely submerged fins in brackish water.For partially submerged fins, the hollow fins show better productivity, while fully submerged wick fins seemed to be more economical and effective [24].
Tanaka [25] performed a theoretical investigation over vertical multi-effect solar still with a sponge-based tilted wick for better productivity.Bisht et al. [26] experimented with floating black die cotton wick and solar pond with CSS.
The diurnal distillate of MSS was improved by 53.55% compared to CSS. [27] found a 32% improvement in distillate output of MSS compared to CSS with porous wick type solar still by introducing forced condensation.Few researchers found black cotton wick Ahmed et al. [28] reported a significant improvement with black cotton wick with inclined solar still.Lee et al. [29] reported a 7 % distillate improvement with a multi effect diffusion solar distiller and wick plate.Essa et al. [30] reported 114.2 % improvement with convex-shaped absorber tubular solar still (TSS), jute wick, and nano composites.Lawrence et al. [31] experimented on single slope tilted wick solar still (SSTWSS) by the addition of 0.12% concentration of NiO nanoparticles prepared by stem and leaf extraction.The total productivity of the stills was found to be 4.2 L/m 2 , 5.75 L/m 2 and 5.8L /m 2 for without nanoparticles, with leaf extract NiO nanoparticles and stem extract NiO nanoparticles respectively.Modi et al. [32] performed a theoretical investigation on single slope double basin solar still (SSDBSS) with jute and black cotton cloth pile at 1cm and 2cm water depth.
The productivity of the jute wick pile was high compared to the black cotton wick pile at 1 cm & 2 cm water depth by 18.03% and 21.46 %.Shanab et al. [33] modified a pyramid solar distiller (PSD) with CuO nano phase change material (NPCM) and four reflectors, results were compared with the distillate productivity of CSS.The productivity was increased by 154.38 % for modified PSD compared to CSS.Chaurasiya et al. [34] performed a theoretical investigation and concluded that single slope single basin passive solar still (SSSBPSS) integrated with Fresnel lens can enhance productivity by 638.02 % compared to reference solar still.Abbaspour et al. [35] performed a theoretical investigation on vertical solar still (VSS)according to the obtained results 10-15 partitions in VSS can decrease the productivity of still.Elbar et al. [36] conducted experimentation on hybrid solar still comprised of a solar panel for heating saline water and a porous material (black steel wool fiber).Maximum daily productivity for a hybrid solar system with 60% preheated saline water was found to be 3.534kg/m 2 and daily efficiency of 38.07%compared to CSS.Harahsheh et al. [37] conducted an experimentation on double slope solar still (DSSS) with phase change material (PCM) integrated with an external collector can enhance productivity up to 4 times the reference still.Evadason et al. [38] investigated the productivity of twin wedge-shaped still, which was found 51.5% more compared to CSS.Moreover, the cost for purifying 1 Liter of water was 0.028$/L for twin wedge-shaped still.Nagaraju et al. [39] experimented on SSSS by introducing sand troughs for heat storage at 1cm, 2cm, and 3cm water depth.The maximum productivity was found to be 0.2L/m 2 and 0.453L/m 2 for cases without and with heat storage at 1cm water depth.Fayaz et al. [40] blended 7 wt.% of titanium metallic particles with black paint on the absorber plate and recorded an 11.87% increase in the temperature of the aluminum plate when compared to the normal black paint absorber plate.Ojo et al. [41] experimented to purify industrial wastewater with the help of solar still and the results were compared with water potable standards of the WHO (World Health Organization).Maatki et al. [42] performed a numerical investigation on triangular solar still with water base CNT by two-stage natural circulation.The results showed a 15% increase in heat transfer compared to a single stage.Muftah et al. [43] pointed out various methods to enhance the performance of solar stills and concluded the distillate productivity of single slope solar still (SSSS) is better than double slope solar still (DSSS).Karthikeyan et al. [44] experimented with 3cm water depth and 45° glass inclination on solar still with different absorber materials and thermocol insulation.The productivity and efficiency of still were found to be 2.92L/m² and 4.9% with aluminum oxide nanoparticles.
Investigation on solar stills shows reflectors, condensers, porous absorbing materials, water depth, solar intensity, ambient temperature, insulation materials, wick materials, and fins can be used to increase the productivity of the still at low cost [45].However, among this wick is the low-cost modification which can show a significant improvement in the distillate yield of the solar still.Based on above literature review it was remarked that the introduction of wick to the still shows significant improvement in the distillate yield of the solar still.To obtain the actual improvement with different saltwater concentration (0 %, 2 %, and 4 %) to overcome freshwater challenges in coastal areas.In this study, a TWSS was fabricated and experimented with three different salt concentrations (0%, 2%, and 4%) of water.
So an experimental study was conducted to improvement in distillate by using a Khes cloth wick.

Materials
A stainless steel with grade 304 (26 gauge) was purchased from the industrial area of Chandigarh and has excellent corrosion resistant properties Table 1 shows the chemical compositions of stainless steel.18 mm of wooden ply was used to support the setup.The basin and internal reflector of the still were made of stainlesssteel sheet of 26-gauge thickness.The setup was well insulated with 3inch and 4inch foam from both sides, bottom, and front to prevent thermal losses [10].A black painted GI sheet of 0.5mm thickness was used to support the wick.
Wick was placed according to the latitude of the location to capture the maximum possible sun radiations.A pump is used to supply water to the wick with a mass flow rate of 0.3 g/s.The 5mm toughened glass was placed at an angle of 45° sealed with a rubber gasket [5].To prevent any further losses silicon was used moreover, Figure 1 and Table 2 show the systematic 2-D diagram and dimensions of the experimental solar still.

METHODS
The experiments were performed (with wick) at three different salt concentrations (0%, 2%, and 4%) as tabulated in Table 4.The obtained productivity for MSS was compared to CSS.The setup was preliminary investigated for three days at a fixed mass flow rate of 0.3 g/s.The water depth of the still was kept constant at 2cm, however, the mass flow rate of water from the pump to the tilted wick was kept fixed in order to keep the wick completely wet.10kg of with and without salt concentration water was poured into the basin.Table 3 shows the different concentrations of salt in water.The weight of obtained potable water was measured with the help of an electronic weighing machine having a range up to 1kg with an error of ±0.001g.The external radiation panel with 21 bulbs having a 5000-watt rating was used to evaporate water.The radiation from the external panel can be adjusted with the help of a knob.The radiation is set to a constant 500w/m² for 8 hours.Additionally, K-Type thermocouples, solarimeter, and data logger was used to sense temperature, and solar radiation, and record data at different point of the timeduring experiment as shown in Figure 2.
The experiment was conducted in indoor conditions, under an external radiation panel which was kept fixed at 500 W/m 2 at Chandigarh University for the latitude of 30.7698°N and longitude of 76.5756°E for four different cases viz: (1) CSS (2) TWSS with 0 % salt concentration (3) TWSS with 2 % salt concentration (4) TWSS with 4 % salt concentration as shown in Table 3.To obtain the effect of salt concentration (0%, 2%, and 4%) on the distillate productivity of MSS, every morning the basin was filled with 10kg of water (with and without salt).The experimentation on setup was performed from 9 am -5 pm.

Results and Discussions
The effect of different salt concentrations on the MSS is discussed in this section.Figure 3 shows the hourly variation of basin water temperature (Tw) for different cases.It can be observed that Tw is the function of time.Constant radiations from the panels increase the Tw of all the cases.For case 1 the lowest Tw was found initially but the graph line shifted upwards with time and found to be a maximum 47.2˚C in evening.However, for case 2 initially, the Tw was low as compared to CSS as the tilted wick was placed over the basin water, and was not directly exposed to the radiation.
Moreover, with the time the Tw increases, the excess water from the pump to the tilted wick rolls down to the basin and further increases the temperature of the Tw.The maximum basin water temperature (Tw) of 59.3 ˚C was attained for Case 2 which was 25.6 % more compared to Case 1. Furthermore, the addition of 2 % salt concentration increases the Tw, at initial hours the temperature was high compared to Case 2, but with the passage of time, the graph line shows similar behavior as Case 2 and found maximum at late hours.The brine water was pumped to tilted wick, the salt particles from the water trapped inside the pores of the wick and excess water rolled down.The salt particles inside the pores store heat and increase the temperature of the tilted wick and poured water.The maximum basin water temperature (Tw) of 61.2˚C was attained for Case 3 and shows 29.6 % increase in Tw.Likewise, in Case 3, in Case 4 the salt concentration was increased up to 4 %.The addition of salt concentration directly affects the Tw however, during early morning and evening the Tw was high compared to other cases and reached up to 67.3 ˚C which is found to be 42.5 % more compared to CSS, moreover, it can be noticed that with increase in salt concentration in basin decreases heat capacity and show significant improvement in basin water temperature.Figure 4 shows the variation of inner glass temperature (Tig) for different cases.It can be observed from the graph that Tig is also the function of time moreover, with the time the Tig increases and is found to be maximum in the evening due to constant radiation of 500 W/m 2 from the external panel.The minimum Tig was found for Case 1 compared to other cases while highest was found for Case 4. The maximum Tig for Case 1 was found in the evening and attained 54.1 ˚C.However, introducing the wick to CSS (Case 2) increases the Tig, as the convective heat from the wick increases Tig and found to be 63˚C at evening 4:00 -5:00 pm, which was found to be 16.4 % more compared to Case 1.Moreover, for Case 3the graph line shows approximately a similar pattern as Case 1.However, it was high at 11:00 -12:00 am compared to CSS but after that it follows the linear increase in temperature and found a maximum 56 ˚C temperature which was found to be 3.  Figure 5 shows the variation in wick temperature (Twi) for MSS.Initially, at early morning the temperature of the wick for all the cases was approximately similar but with time Twi increases and was found to be maximum in evening.In the initial hours of the experiment, the temperature rose abruptly because the wick was inclined at 30˚ accordingly parallel to the radiation panel which helps to achieve maximum.Moreover, a maximum temperature of 67.  of tilted wick on the distillate productivity for saline water conditions by processing water with different salt concentrations (0 %, 2 %, and 4%).Based on the experimentation following conclusions were derived: 1.The provided constant radiation from the external panel helps to achieve better productivity.
2. Wick placement was parallel to the external radiation panel so that the wick could receive maximum radiation.
3. The addition of tilted wick and salt concentration increases the basin water temperature compared to conventional solar still.
4. 2 % salt concentration shows the best distillate output due to an increase in evaporation rate with the help of tilted wick and an increase in surface tension of brine water.
6. Nanotechnology can be incorporated into the arrangement to increase the still's yield.
7. Distillate output can be improved by storing heat throughout the day to increase night productivity.Either a latent heat storage medium or a sensible heat storage medium can be used.
8. Artificial intelligence can be integrated with the solar still.

Figure 2
Figure 2 Solar Still with External Radiation Panel

Figure 3
Figure 3 Variations in Basin Water Temperature (Tw) 1 % more compared to Case 1.Likewise, in Case 3 initially the Tig for Case 4 was below CSS but after 1:00 pm the graph shows a rapid increase in the Tig and was found to be maximum compared to other Cases.The maximum temperature of 63.3˚C was attained by Case 4 which was found to be 16.8 % more compared to Case 1.

Figure 4
Figure 4 Variation in Temperature of Inner Glass (Tig)

Figure 6 Figure 7
Figure 6 Variations in Hourly Distillate Productivity

Table 3 :
Salt Concentrations in Water

Table 4 :
Experimental Cases