ABSTRACT
This study experimentally investigates the inclined solar still (ISS) with the incorporation of fins and natural bio-jute cloth under dynamic flow. Experiments are conducted on bright sunny summer days in Coimbatore, Tamil Nadu, India. The newly developed ISS features greatly support passive solar desalination. An increase in mass flow rate (Mf) increases heat transfer meticulously pointing out 0.65, 0.8, and 1 kg/min case absorber, and the water temperature difference is within 3°C. An Mf of 0.285 kg/min is secure for the maximum water temperature reach and clean water yield of 70°C and 4.1 kg/m2, respectively, along with jute cloth, it was 1.6 kg/m2 more against without jute cloth. The presence of a jute cloth cumulative water yield of 2.5 kg/m2 at 0.635 kg/min is very close to the absence of a wick cumulative yield of 2.3 kg/m2 during 0.285 kg/min. From these results, the authors conclude higher Mf is feasible to increase the still performance and clean water yield. The implementation of a fully renewable passive solar still is strongly recommended to attain renewable and sustainable desalination.
HIGHLIGHTS
The proposed modification of the still and wick substantially increases the water yield and reinforces the passive solar still desalination.
The presence of jute cloth has multiple benefits, such as porosity, and the height of the capillary effect enhance the evaporative rate by effective contact-making to absorber fin–wick–water.
A higher mass flow rate makes it possible to increase the still performance and clean water yield.
NOMENCLATURE
INTRODUCTION
Around the world, all countries face water stress, and per capita water availability has been rapidly decreasing; conversely, water consumption keeps increasing. Hence, the world is in fear, and serious action steps are being taken against water scarcity. Among them, scientists are making big efforts toward wastewater treatment, analyzing the reasons for wastewater production rate and their negative effects. Every year, approximately 380 billion m3 of wastewater is generated worldwide, and by the end of 2030, this number is estimated to rise by 24%. Furthermore, by 2050, it is expected to reach a 51% increase. Of the water available on Earth, 97% is in the ocean, which is salty and cannot be used for drinking. Therefore, although abundant water resources are available, the problem is that nearly 99% of water on Earth is unpotable. Nearly 37% of the world's population lives in coastal areas, and these people face significant potable water issues (Luo et al. 2022). Drinking water is essential for our overall health and well-being. It plays a vital role in various bodily functions and is necessary for survival. Water helps maintain bodily fluids' balance, which is crucial for proper hydration. It helps regulate body temperature, aids in digestion, and carries nutrients to the cells. Water is essential for the proper digestion and absorption of food. It helps break down food particles, facilitates the movement of nutrients through the digestive system, and prevents constipation. Dehydration can lead to fatigue and reduced energy levels. Drinking enough water helps to maintain optimal energy levels and improves overall physical and mental performance (Senthil Kumar et al. 2022; Banoqitah et al. 2023; Dhasan et al. 2023; Sathyamurthy 2023a, 2023b; Sathyamurthy et al. 2023, 2024a, 2024b).
Water scarcity and wastewater mismanagement cause a lack of sanitation problems, resulting in waterborne diseases and affecting aquatic life. Sustainable water treatment is the only solution to meet the present demand for water. Solar desalination is the greener pathway to attaining clean water. The energy paths to feed solar water desalination are divided into direct (thermal) and indirect (photovoltaic (PV)) methods. Indirect methods are expensive and slightly associated with pollution (Zhang et al. 2023). Membrane-type desalination is better based on performance against solar desalination; however, it needs pressure-precise membrane medium and auxiliary equipment. Moreover, dissolving the salt and other ingredients in the feed water is absent (Bamasag et al. 2022). In solar desalination, pure water is recovered notably from the process fully powered by solar radiation. Due to solar radiation possessing pasteurization, germicidal effects of wastewater are removed. The water analysis result revealed that distilled water from solar desalination is fit for drinking. Solar still (SS) gets attention under direct solar desalination. Ideal parts, simple configuration, powered by fully renewable energy, pollution free, and easy to make with localized materials are the key factors to further the development of passive solar. With the SS, saline water changes into potable water by evaporation and condensation of any water by the radiation of sun (Chauhan et al. 2021). It can be installed at any location with solar radiation, and it is highly useful in the coastal area. An SS can commonly be categorized into active and passive types. Active types are proposed and exhibit slightly higher performance compared with passive stills, due to the external heat supply incorporated such as photovoltaics, concentric collectors, and reflectors.
An SS is a type of technology that uses the power of the sun to produce clean drinking water from contaminated sources. The technology has several advantages that make it an ideal solution for communities or individuals who lack access to clean drinking water. One of the key advantages of SSs is their simplicity. The basic design of an SS consists of a shallow basin or pit covered with a clear material, such as glass or plastic. Contaminated water is poured into the basin, and the sun's rays heat it, causing it to evaporate. The resulting water vapor condenses on the inner side of the clear material and drips down into a collection container. Another advantage of SSs is their portability. SSs can be easily constructed from readily available materials and transported to remote or disaster-stricken areas where clean drinking water is required. They can also be used in various settings, from homes and schools to hospitals and refugee camps. SSs are also environmentally friendly. Unlike traditional water treatment methods, which often rely on chemicals or energy-intensive processes, SSs rely solely on the power of the sun. This means that they produce no harmful byproducts and have minimal environmental impact.
An inclined solar still (ISS) is a type of SS designed to improve the efficiency of the existing basic SS design. In an ISS, the basin or pit containing the contaminated water is angled to face the sun at an optimal angle. This allows more sun rays to be focused on the water, which increases the evaporation rate and improves the system's overall efficiency. In addition to the angled basin, ISSs may include reflective surfaces or other features that help direct more sunlight onto the water. This can further increase the efficiency of the still and make it particularly important in areas with low levels of sunlight.
In recent years, solar cookers, thermoelectric modules (TEMs), and various power sources have assisted with SSs resulting in a slightly higher yield against conventional solar stills (CSSs), but passive systems are really wanted to mitigate the issues on clean water; hence, passive SS upgradation has received much more priority due to its user convenience (Chaurasiya et al. 2022). More space occupancy and productivity rates are against commercialization even now (Yousef & Hassan 2019); however, researchers are fully open to the development of passive SS. Passive SS is sub-diversified by various aspects, mainly various geometric modifications (single and double basin or slope, pyramid, tubular, inclined, and hybrid). The ISS is claiming extra attention by reason of the faster heating of the feed water, which is capable of presenting a better angle to solar radiation, maximizing effective area, and minimizing the reflection (Prakash & Velmurugan 2015). Typically, the performance of an SS depends on a wide range of factors such as still configuration, absorber basin, glass cover material and thickness, feed water temperature, water thickness, water to cover the distance, water velocity, mass flow rate (Mf), solar intensity, wind velocity, location and angle of the still, and climate condition (Jathar et al. 2022). Some researchers propose the integration of SS strategies. Kabeel et al. (2019) proposed CSS with the integration of ISS and investigated the water depth and Mf against productivity for CSS, ISS, and CSS-ISS. The results revealed that the water yield of CSS, ISS, and CSS-ISS under the constant depth of 0.02 m was found to be 4.24, 5.024, and 6.2 kg, respectively. The performance of CSS based on past literature was capable of extracting 1–2 kg/m2; however, the authors adopted many strategies and steadily increased productivity. Increasing the surface area of feed water is an effective step for enhancing productivity. Fins and wick materials get attention for valorization due to their superiority in surface area. In addition, the wick material acts as a sensible heat storage material, and usually is composed of black cotton, jute cloth, wood, rock (Shoeibi et al. 2022), and plastics (Dumka et al. 2020). Nagarajan et al. (2017) studied the performance of ISS with baffle plates both experimentally and theoretically. The results revealed that the baffle plate still achieved 1.6 times more yield than without the baffle plate. The maximum yield of 5.4 kg/m2 day was recorded with the solar intensity of 675 W/m2 with baffle plate. Panchal et al. (2020) investigated the effect of fins made by waste wind chime pipe for CSS. The results exhibited a water yield of 2.375 and 2.322 L/day on average. It was found that increases of about 26.7% and 24.195 were observed from the SS without fin. Moreover, this study compared vertical and inclined fin performance results, and there was no significant difference between them. Kabeel et al. (2020) investigated the effect of hollow copper fins in a pyramid-shaped SS. As a result of the study, they concluded that hollow fins enhance daily productivity at 5.75 L/m2, which was 43% higher than the CSS daily yield of 4.03 L/m2. In addition, using phase change material (PCM) enhanced productivity further by 8.1 L/m2, which was 101.5% higher. Alatawi et al. (2022) analyzed the fin effects on the thermal performance of tubular solar still (TSS). The results revealed that fin incorporation in the TSS yielded 5.722 L/m2 per day, which was 44.8% higher than bare TSS. Overall, the design improved the efficiency to 41.1%, and production cost reduction was 40.7% using the proposed technique. Sharon et al. (2020) investigated the ISS with a stepped basin and black blended wooden wick. The results revealed how the wick impacted the productivity. It increased when compared with the base plate, and the daily productivity was 5 L/m2. Hansen et al. (2015) investigated the effect of different wick materials on different basin configurations of ISS such as wood pulp paper, wick, wicking water coral fleece fabric, and polystyrene sponge and different basins such as flat absorber, stepped absorber, and stepped absorber with wire mesh. The results revealed a higher value of water yield of 4.28 L/day was achieved by wire mesh in the stepped absorber plate of the ISS compared with the water coral fleece wick material. In addition, it was found that the water coral fleece porosity, absorbency, capillary rise, and heat transfer coefficient were 69.7%, 2 s, 10 mm/h, and 34.21 W/m2°C, respectively. Ramalingam et al. (2021) studied the ISS with a stepped basin with dried coconut coir disk wick material. The results showed that the ISS with this wick material enhanced the water yield from 28 to 69.5% compared with CSS. In addition, the proposed coconut coir disk had a porosity of 73.25%, an absorbency of 2 s, a capillary rise of 10 mm/h, and a heat transfer coefficient of 37.21 W/m2K. Thermal conductivity, heat transfer coefficient, capillary rise, porosity, water repellence, and water absorptivity were the influential parameters of wick performance inside an SS (Pal et al. 2017). Modi & Modi (2019) investigated single-slope and double-basin SSs with small piles of jute cloth and black cotton, which influenced water yield. Based on the study result, it was determined that jute cloth enhanced the clean water yield by 18.03% compared with black cotton.
Incorporating a latent heat storage material like PCM was identified to enhance productivity substantially as it can absorb the heat energy during high solar intensity periods and release it during lower solar intensity periods. Al-Harahsheh et al. (2022) investigated the effect of sodium thiosulfate pentahydrate PCM on still performance. The results showed that the clean water produced per day was improved to 4.34 m2. However, paraffin wax is preferred by many studies due to its low cost and availability. Suraparaju & Natarajan (2021a, 2021b) investigated the effect of water depth, paraffin wax, and pin fins in a single-basin SS. As a result, the PCM as energy storage in the modified still generated 3.75 L/m2 per day against the bare still, which was 1 L/m2 higher on a daily basis. Omara et al. (2020) concluded a considerable amount of literature used paraffin wax as it plays a crucial role in enhancing the productivity of SSs. PCM encapsulated with sensible heat storage materials augmented yield significantly. Kabeel et al. (2018a, 2018b) evaluated the organic and inorganic PCMs and notably found the thickness of a PCM does not significantly influence productivity; hence, a lower thickness is recommended from an economic point of view. However, this study first focuses on the fin and wick performance in a novel-designed ISS, with some modifications.
Based on the study and similar study results, it is strongly recommended that fin, PCM, and wick be incorporated in ISSs. It is also suggested to consider fin design and wick material modification for further enhancement of the surface area. The ultimate task is the large-scale production and sustainable commercialization of potable forms of ISS for solar desalination. ISS has the capability to produce distilled water under dynamic conditions. This feature will be of greater value in large-scale production with less space occupancy. More relatively, Sasikumar et al. (2020) experimentally investigated the passive ISS with a PV panel basin under various flow rates of 4.68, 7.56, and 10.08 kg/h1. The results exhibited corresponding energy and exergy as follows: 36.06, 25.56, 16.95%, and 2.97, 1.91, and 1.01%, for flow rates of 4.68, 7.56, and 10.08 kg/h, respectively; hence the increase in flow rate decreased the SS performance. However, PV performance notably increases with an increase in the flow rate. It was predicted to be 8.05, 8.81, 9.44, 11.43, 20.8, 22.17, 19.38, 20.58, and 21.16% for energy and exergy values of PV panels, respectively. Insulation and foreign matter deposits on the PV panel greatly affect PV panel performance. A flat plate solar collector was installed and the insulation removed to reduce the PV panel temperature. Jobrane et al. (2022) proposed ISS with a PV panel, but PV is located out of the still. Feed water was flown on the back side of the PV panel to extract heat, and it was sent into the ISS. The results revealed that distilled water yield per day was 4.03 L/m2 at the average solar intensity of 380 W/m2, compared with CSS, which is a 32% higher yield. However, the big issue that was found was salt and undissolved matter deposited on the PV panel. Typically, the hybrid system does not shorten the issues against productivity because, practically, the hybrid system faces some difficulties; hence, researchers are focused on heat transfer enhancement and condensation upgradation strategies by using sensible and latent heat storage material, coating, nanoparticles, and some modifications on the passive SS. Sathyamurthy et al. (2016) theoretically analyzed the ISS with a baffle plate and investigated the effect of Mf relative to water temperature, internal heat transfer coefficient, and absorber basin temperature. The results revealed productivity was increased at a low Mf, at a minimum of 0.0833 kg/min and attaining a 57.14% increased yield against the maximum flow rate of 0.4166 kg/min. Notably, the water temperature for the minimum flow rate was 62°C compared with the higher flow rate, which was nearly twice. In addition, the authors presented a Ravi-Harris-Nagarajan (RHN) model for calculating the average water temperature inside the SS. In a similar vein, El-Agouz et al. (2015) evaluated the ISS performance theoretically under continuous flow. Three models including ISS, ISS with makeup water, and ISS without makeup water were compared with CSS on yield and performance. The results showed that with makeup water, ISS displayed maximum productivity by achieving 52.7% higher productivity compared with CSS. Ahmed et al. (2021) used an ISS with a black cotton wick under continuous flow. A freshwater yield of about 3.21 L/m2 day was achieved, against the SS without wick, and it was 21.13% higher. Overall the proposed modification increased the efficiency and cost by 139.12 and 57.86% against without wick.
Suraparaju & Natarajan (2021a, 2021b) used Luffa acutangula fibers (ridge gourd fiber) as a porous medium for augmenting the fresh water generation from the single-slope SS. Initially, the characteristics of the Luffa acutangula fibers were studied and the number of these fibers on SS were varied from 10 to 25 to study the evaporation of water from the basin surface. The characterization results revealed that the Luffa acutangula fibers have a porosity of 6.7% and a capillary rise of 72 mN/m. Similarly, the capillary rise made by the fluid through the porous medium was found to be 5.8 mm/h, which is higher compared with other fabric materials in the literature as these were the most critical parameters in improving the evaporation of water through the fiber. The experimental results revealed that the increased number of fibers in contact with the water surface improved the absorption of water, while the evaporation rate was reduced. The outperformed Luffa acutangula fibers were found as 15, which produced a higher yield of about 25.23% than the CSS. A significant improvement was obtained on the fresh water yield of about 22.69, 22.04, 17.45, and 12.27 from SS using 16, 14, 13 and 10 Luffa acutangula fibers on the water surface. With improved fresh water yield, the thermal efficiency of the SS improved significantly. It was furthermore concluded that the cost of fresh water produced per liter was 22.5% lowered in the case of natural porous medium in the absorber as compared with the CSS, which simultaneously reduced the payback period.
The simultaneous enhancement on evaporation and condensation of an SS using the cover cooling technique and hollow fins filled with paraffin wax as thermal energy storage was experimentally analyzed by Suraparaju & Natarajan (2022). Along with the thermal energy storage technique, a novel pond fiber was added in the basin to improve the evaporation rate. The cover cooling technique was executed by adding long sisal fibers, which carry the water from the dripping water arrangement for augmented condensation rates. It was reported that the use of hollow fins with PCM, cover cooling, and pond fibers on the SS improved the temperature of the water by 12% and reduced the temperature of glass by 30%, thereby improving the evaporation and condensation rate compared to the CSS. The fresh water produced from the SS using the proposed technique was augmented by about 126%, which is higher compared with the SS without energy storing material. The economic analysis results revealed that the cost per liter of fresh water generated and the payback period of the proposed design on the SS decreased by about 38.5 and 49.3%, respectively, which is lower compared with the CSS.
Eco-friendly and low-cost materials were introduced as energy storing materials in the SS for improving the evaporation rate compared with the CSS, and were experimentally analyzed by Natarajan et al. (2022). Moreover, another way to gain higher fresh water output was through cover cooling, which was achieved using straw from bamboo, stem of banana leaf, and rice straw. The energy storing materials employed in the basin of SS were sawdust, rice husk, and molasses powder. The experimental results revealed that the use of sawdust as a thermal energy storage material showed a remarkable improvement in the freshwater generation by about 34.81% based on thermal evaporation compared to the CSS. Moreover, using rice straw over the cover improved the rate of condensation by about 51.88% than the CSS. The simultaneous effect of cover cooling using rice straw and evaporation technique with sawdust as thermal energy storage was that the freshwater generation was augmented by 62.88% compared to CSS. Using the proposed technique on cover cooling and thermal evaporation, the payback period and cost per liter of fresh water were reduced.
The inadequate efficiency of SSs poses a significant impediment to their widespread and effective adoption worldwide and these were carried out by incorporating porous materials. The influence of pond fiber in single-slope SS was experimentally analyzed by Suraparaju et al. (2021). The number of dried pond fibers was varied from 3 to 20. It was reported that the optimal number of pond fiber on the basin was found to be 5 as the increase in number of pond fibers on the SS reduced evaporation while absorption was enhanced due to the higher level of porosity. The optimal use of 5 pond fibers improved the thermal efficiency and daily production of fresh water by 29.67 and 29.66%, respectively, compared with the CSS. According to the economic analysis results, the cost per liter of freshwater produced from the SS equipped with naturally dried pond fiber as a porous medium was 30.76% less than that of CSSs. Similarly, the payback period from the SS using the proposed modification was 91 days whereas, using CSS, the payback period was 115 days.
Therefore, based on several studies, it can be concluded that increase in surface area and porosity in the absorber basin are the key to improving the evaporation and condensation of passive SS. At the same time, selectivity of material and area of occupancy is crucial. After conducting an extensive literature review on ISSs, it became evident that the research landscape has primarily focused on steady-state and open-loop water flow systems. However, there is a noticeable scarcity of studies that explore the application of continuous flow with makeup water under dynamic flow rate conditions. In the present study, this was achieved by a bio-wick material facilitated to claim sustainable and economic benefits. Because of the continuous flow condition, this study concentrates on improving the rate of evaporation. For that staggered fin arrangement and jute cloth were incorporated into the ISS. This study aims to bridge this research gap and promises to offer valuable insights for future large-scale SS operations. This paper centers around the experimentation with an innovative ISS design that incorporates bio-jute cloth within a dynamic flow environment. Several modifications have been introduced in the ISS experimental setup to enhance its performance, as follows:
Combining vertical and horizontal fins to increase the surface area and partially restrict water flow.
Implementing a common rail split supply to ensure water availability across the entire still area.
Incorporating bio-jute cloth as a wick material to further increase the surface area and improve water retention.
Employing a compact design to reduce space requirements.
The primary objective of this study was to enhance the evaporative and condensation efficiency of the ISS under dynamic flow conditions by leveraging fin configurations and the modified jute cloth as a wick material. By doing so, this research contributes to the development of more efficient and effective SS systems that hold promise for practical applications in large-scale operations.
MATERIAL AND METHODS
Proposed experimental system design and construction
Novel-designed ISS.
The previous more related and consistent study ensures that near the location's latitude is often the optimal angle for achieving maximum equipment effect. Based on the local latitude, the SS tilt angle was fixed at 45.9°. The SS was made up of mild steel with a thickness of 3 mm. The absorber fin basin was made up of mild steel plate and coated with black paint. A transmitting cover with a thickness of 3 mm made of glass with a transparency of 88% was used. Vertically six fins were located at a relative distance from each fin of 50 mm, length of 700 mm, thickness of 2 mm, and height from the absorber plate of 10 mm, which was the same to the depth of the still. The horizontal fin was built horizontally in the length of 45 mm with an equal distance of 70 mm. Each vertical fin adapted nine horizontal fins, which are displayed in Figure 1. A modified jute cloth in the shape of a fishnet was placed between the fins, with the dimensions of 700 mm length, 50 mm width, and 3 mm thickness.
Photographs of the experimental setup.
Jute bio-wick has the potential to be an eco-friendly, low cost, widely available, and renewable and sustainable wick material for SS applications. Jute cloth is inherently porous; due to its natural fiber composition and weaving structure, it can contribute to moisture absorption. It has a hydrophilic affinity to water, meaning it can absorb and retain moisture; therefore, it was a known natural fiber energy storage medium with water suitable for the present continuous flow feed water condition. Jute cloth is suitable for use in this conceptual way of thermal energy storage. Hopefully, this will reduce the thermal loss of the ISS during the continuous flow. The thermo-physical properties of jute cloth are provided in Table 1.
Thermo-physical properties of jute cloth
| S.no | Properties | Values |
|---|---|---|
| 1 | Type of fiber | Coarse |
| 2 | Nominal thickness | 0.898 |
| 3 | Density (kg/m2) | 0.310 |
| 4 | Specific heat capacity (kJ/kg K) | 1.287 |
| 5 | Thermal conductivity (W/m K) @ dry condition | 0.05 ≈ 0.055 |
| 6 | Absorption at 65% of relative humidity and T = 20°C | 13% |
| S.no | Properties | Values |
|---|---|---|
| 1 | Type of fiber | Coarse |
| 2 | Nominal thickness | 0.898 |
| 3 | Density (kg/m2) | 0.310 |
| 4 | Specific heat capacity (kJ/kg K) | 1.287 |
| 5 | Thermal conductivity (W/m K) @ dry condition | 0.05 ≈ 0.055 |
| 6 | Absorption at 65% of relative humidity and T = 20°C | 13% |
Uncertainty analysis
Experimental uncertainty, often referred to as measurement uncertainty, is an essential concept in scientific research and experimentation. It represents the doubt or lack of exactness associated with any measurement, observation, or experimental result. Understanding and quantifying uncertainty is crucial because it helps researchers assess the reliability and credibility of their data. Random errors are unpredictable and can result from various factors, such as fluctuations in environmental conditions (e.g., temperature, humidity), operator skill, or inherent variability in the phenomenon being measured. They can be minimized through multiple measurements and statistical analysis. The uncertainty that occurred during the experiments were based on the temperature, solar radiation, wind velocity, and distillate collection measurement. The uncertainty from each piece of equipment used in the experiments is listed in Table 2 along with the range and accuracy of the instrument.
Accuracies and errors for used measuring instruments
| S. No | Instrument | Range | Accuracy | % of error |
|---|---|---|---|---|
| 1 | Thermocouple (RTD (PT-100 type) | 0–120°C | ±1 °C | 0.3 |
| 2 | Solar power meter (TES132) | 0–2,000 W/m2 | ±10 W/m2 | 2 |
| 3 | Anemometer (AM4836) | 0–10 m/s | ±0.1 m/s | 5 |
| 4 | Measuring jar | 0–1,000 mL | ±10 mL | 5 |
| S. No | Instrument | Range | Accuracy | % of error |
|---|---|---|---|---|
| 1 | Thermocouple (RTD (PT-100 type) | 0–120°C | ±1 °C | 0.3 |
| 2 | Solar power meter (TES132) | 0–2,000 W/m2 | ±10 W/m2 | 2 |
| 3 | Anemometer (AM4836) | 0–10 m/s | ±0.1 m/s | 5 |
| 4 | Measuring jar | 0–1,000 mL | ±10 mL | 5 |
Process variables description
The feed water supply was varied at different Mfs such as 0.285, 0.635, 0.8, and 1 kg/min. Hot water from the still was collected at a separate thermal insulation tank and reutilized continuously. The head was constantly controlled in the tank and the flow rate was varied using flow control valves. A K-type thermocouple connected digital indicator was used to measure the absorber fin, water inlet, outlet, transmitting inner and outer cover, and atmospheric temperature. Hourly variations of the solar intensity, atmosphere, absorber fin, water, and glass cover temperatures of the fabricated SS at respective flow rates are displayed, and their effect on water yield are discussed in the following. In addition, the performances of the novel-designed still with jute cloth and without jute cloth under a dynamic flow rate are compared.
Climate description
Hourly difference in ambient parameters: (a) solar radiation, (b) ambient temperature, (c) wind velocity, and (d) relative humidity during the experiments.
Hourly difference in ambient parameters: (a) solar radiation, (b) ambient temperature, (c) wind velocity, and (d) relative humidity during the experiments.
RESULT AND DISCUSSION
Effect of dynamic flow on the absorber, water, and glass temperature
Hourly difference in the temperatures of the absorber, water, and glass in the experiments without wick at different flow rates.
Hourly difference in the temperatures of the absorber, water, and glass in the experiments without wick at different flow rates.
Impact of wick on the absorber, water, and glass temperatures during dynamic flow
Hourly difference in the temperatures of the absorber, water, and glass in the experiments with wicks and different flow rates of water.
Hourly difference in the temperatures of the absorber, water, and glass in the experiments with wicks and different flow rates of water.
Figures 4 and 5 show the contrasting behavior of absorber, water, and glass during the presence and absence of jute cloth at various Mfs. The absorber and water temperatures are increased at all hours and all Mf with jute cloth. It is critical to denote here in both cases, glass temperature does not produce a significant temperature difference. Moreover, they have positive effects during the increase in Mf and the presence of wick conditions, which is a sign of effective condensation. The potential of jute cloth to increase evaporation and condensation simultaneously is noted. Maximum absorber and water temperatures are 68 and 62°C, respectively, at midday and Mf of 0.285 kg/min during the absence of jute cloth experimentation.
Average temperatures of the absorber, water, and glass from the ISS without and with the wick material at different Mfs of water.
Average temperatures of the absorber, water, and glass from the ISS without and with the wick material at different Mfs of water.
Effect of dynamic flow on the hourly changes along with cumulative water yield
(a) Hourly changes along with (b) cumulative water yield in the without wick experimentation.
(a) Hourly changes along with (b) cumulative water yield in the without wick experimentation.
Impact of wick on hourly changes and cumulative water yield during dynamic flow
(a) Hourly changes along with (b) cumulative water yield in the experiments with wick.
(a) Hourly changes along with (b) cumulative water yield in the experiments with wick.
Jute cloth reduces the distance between the evaporation surface and the glass cover; it simultaneously supports evaporation and condensation because of the greenhouse effect. This effect happens by a buffer layer formation in the hot jute cloth, which means one thick layer has an almost constant temperature and does not participate much in the various transfers; consequently, this layer promotes one thin layer for rapid evaporation (Sharon et al. 2020). The phenomenon can be elucidated as a thermal energy storage capability. From Figure 7(b), it can be concluded that the maximum cumulative yield during the presence of wick experimentation at various Mfs until 18:00 pm of the day has the value of 4.1 kg/m2; it was 1.6 kg/m2 more against without jute cloth experimentation at 0.285 kg/min Mf. For 0.625, 0.8, and 1 kg/min Mfs, it was 0.8, 1.1, and 1.2 kg/m2 higher against the absence of jute cloth experimentation. This clearly illustrates that jute cloth usage increases clean water production along with an increase in Mf. This meticulously points out that in the presence of a wick the cumulative water yield of 2.5 kg/m2 at 0.635 kg/min Mf is very close to that in the absence of a wick, with a cumulative yield of 2.3 kg/m2 during 0.285 kg/min Mf. In the previous case, the temperature started to decline rapidly during the afternoon hours (14:00–16:00 pm of the day), but the presence of jute cloth has a greater impact on still performance and clean water yield due to the soaking up by the jute cloth of the water creating stores of moisture and thermal energy in the peak hours, which are liberated during the sunset period, increasing the yield simultaneously (Table 3).
ECONOMIC ANALYSIS
The estimation of economic measure is based on local materials and services in Tamil Nadu, India. The cost per liter relative to the life span of the ISS is listed in Table 4, in Indian rupees as well as US dollar currencies (1 Indian rupee = 0.012 dollars). The life span of a device is approximately considered as 10 years. Jute cloth is frequently replaceable, but its cost is negligible due to its wider local availability. Moreover, the average operating days of the device are considered as 290 days per year. Based on the economic analysis clean water production with and without jute cloth costs 0.5, 103 and 0.326 USD/L and is lower than without jute cloth, the main reason being jute cloth is cheaper yet increases the production of clean water annually.
Comparison between major findings of the current study with some related results of other researchers
| Current study | Ahmed et al. (2021) | Modi & Modi (2019) | Taamneh et al. (2020) | Murugavel & Srithar (2011) | Sharshir et al. (2020) | Alshqirate et al. (2023) | Kabeel et al. (2018a, 2018b) | |
|---|---|---|---|---|---|---|---|---|
| Place/season | India/summer | KSA/Winter | India/summer | India/summer | India/summer | Egypt/summer | Jordan/summer | India/summer |
| Type of SS | ISS with staggered fin (0.75 × 0.35 × 0.1) | ISS (0.9 m2) | Single-slope double-basin SS (0.5 m × 0.5 m × 0.1 m) | ISS @ stepped absorber (1,810 × 920 × 150 mm). | ISS (1 × 0.75 × 0.157 m) | Stepped double slope SS (0.5 m2) | Equilateral pyramid SS (1 m × 1 m × 0.1 m) | Single-slope SS (1 m × 0.5 m) |
| Wick material | Jute cloth | Black cotton wick | Small pile of jute cloth and cotton cloth | No wick | Water coral fleece material | Linen wicks | Palmately leaves | Jute wick-wrapped sand |
| Flow condition | Dynamic flow (0.285, 0.635, 0.8, and 1 kg/min) | Continuous flow (8 L of water) | 0.01 m and 0.02 m water depth | Mf (4.68 kg/h) | 5 mm depth (7.5 kg) | Steady-state depth (1 cm) | Water depth (3 cm) | Maintain constant head condition |
| Clean water yield | 4.1 kg/m2 day | 3.21 L/m2 day | 0.91 L/m2 day | 2.65 L/m2 day | 4.28 L/day | 3.81 L/m2 day | 5.16 L/m2 | 5.9 kg/m2 |
| Current study | Ahmed et al. (2021) | Modi & Modi (2019) | Taamneh et al. (2020) | Murugavel & Srithar (2011) | Sharshir et al. (2020) | Alshqirate et al. (2023) | Kabeel et al. (2018a, 2018b) | |
|---|---|---|---|---|---|---|---|---|
| Place/season | India/summer | KSA/Winter | India/summer | India/summer | India/summer | Egypt/summer | Jordan/summer | India/summer |
| Type of SS | ISS with staggered fin (0.75 × 0.35 × 0.1) | ISS (0.9 m2) | Single-slope double-basin SS (0.5 m × 0.5 m × 0.1 m) | ISS @ stepped absorber (1,810 × 920 × 150 mm). | ISS (1 × 0.75 × 0.157 m) | Stepped double slope SS (0.5 m2) | Equilateral pyramid SS (1 m × 1 m × 0.1 m) | Single-slope SS (1 m × 0.5 m) |
| Wick material | Jute cloth | Black cotton wick | Small pile of jute cloth and cotton cloth | No wick | Water coral fleece material | Linen wicks | Palmately leaves | Jute wick-wrapped sand |
| Flow condition | Dynamic flow (0.285, 0.635, 0.8, and 1 kg/min) | Continuous flow (8 L of water) | 0.01 m and 0.02 m water depth | Mf (4.68 kg/h) | 5 mm depth (7.5 kg) | Steady-state depth (1 cm) | Water depth (3 cm) | Maintain constant head condition |
| Clean water yield | 4.1 kg/m2 day | 3.21 L/m2 day | 0.91 L/m2 day | 2.65 L/m2 day | 4.28 L/day | 3.81 L/m2 day | 5.16 L/m2 | 5.9 kg/m2 |
Economic analysis estimation of ISS with Jute cloth
| Components | Indian cost value (₹/m2) | US ($/m2) |
|---|---|---|
| Still basin | 1,572.00 | 18.86 |
| Steel frame | 620.00 | 7.44 |
| Glass cover (4 mm) | 520.00 | 6.24 |
| Jute cloth | 25.00 | 0.30 |
| Black paint | 250.00 | 3.00 |
| Reflective foam insulation and so on | 1,200.00 | 14.00 |
| Capital cost | 4,187.00 | 50.23 |
| Salvage value | 628.05 | 7.54 |
| Annual first cost | 569.44 | 6.83 |
| Annual operating and maintenance cost (AO & M) | 85.15 | 1.02 |
| Annual salvage value | 47.73 | 0.57 |
| Total annual cost | 606.82 | 7.28 |
| Yield | 4.1 L/m2 | 4.1 L/m2 |
| Annual yield (Consider 290 days) | 1,189 | 1,189 |
| Cost per Liter | 0.5103 | 0.0061 |
| Components | Indian cost value (₹/m2) | US ($/m2) |
|---|---|---|
| Still basin | 1,572.00 | 18.86 |
| Steel frame | 620.00 | 7.44 |
| Glass cover (4 mm) | 520.00 | 6.24 |
| Jute cloth | 25.00 | 0.30 |
| Black paint | 250.00 | 3.00 |
| Reflective foam insulation and so on | 1,200.00 | 14.00 |
| Capital cost | 4,187.00 | 50.23 |
| Salvage value | 628.05 | 7.54 |
| Annual first cost | 569.44 | 6.83 |
| Annual operating and maintenance cost (AO & M) | 85.15 | 1.02 |
| Annual salvage value | 47.73 | 0.57 |
| Total annual cost | 606.82 | 7.28 |
| Yield | 4.1 L/m2 | 4.1 L/m2 |
| Annual yield (Consider 290 days) | 1,189 | 1,189 |
| Cost per Liter | 0.5103 | 0.0061 |
CONCLUSION
The present experimental investigation was carried out on a newly developed, novel-designed compact high surface area ISS under dynamic flow in the months of March and April 2023 to examine the bio-wick (jute cloth) impact on performance and yield under various Mfs.
First, the newly designed compact ISS works successfully and attains a maximum water and absorber temperature of up to 65 and 70°C at 0.285 kg/min Mf. Specific fin arrangements and common rail split passages substantially support performance behavior.
Normally increase in Mf reduces the still performance; however, the usage of jute cloth overcomes this issue, and sucks the positive impact of a higher Mf, which has a higher heat transfer coefficient.
An Mf of 0.285 kg/min is secure for the maximum water temperature reach and clean water yield of 70°C and 4.1 kg/m2, respectively, along with jute cloth; it was 1.6 kg/m2 more against without jute cloth.
Specifically, during sunset hours the presence of jute cloth has more impact on still performance and clean water yield due to the soaking up by the jute cloth of water stores and thermal energy in the peak hours, which are liberated during the sunset period, increasing the yield.
The study meticulously points out that cumulative water yield of 2.5 kg/m2 at 0.635 kg/min Mf in the presence of a jute cloth is very close to the absence of a wick cumulative yield of 2.3 kg/m2 during 0.285 kg/min Mf. From these results, the authors would like to conclude higher Mf is preferable for increasing the still performance and clean water yield. The whole study highlights the fully renewable passive SS to keep on implementation for, to attain renewable and sustainable desalination. This study fully correlates with the Sustainable Development Goals (SDGs) of the UN such as Clean Water and Sanitation (SDG: 6), Affordable and Clean Energy (SDG: 7), Responsible Consumption and Production (SDG: 12), and Climate Action (SDG: 13) due to clean water production from renewable energy and resources.
Introducing high conductive nanoparticles with feed water (nanofluid) is highly recommended to enhance the evaporation rate in the ISS. Studying scaling and fouling is crucial for long-term operation. Salt deposition and the life span of wick material may be a concern; however, the use of jute cloth is widely available at a cheaper cost; therefore, it overcomes the above issue and supports industrialisation. Moreover, during the time of experimentation, jute cloth was found to be in good condition even after 8 days of experimentation. It was meticulously found during the experimentation that increasing Mf increases heat transfer; however, in that specific application of desalination, maintaining the temperatures of the absorber and water is crucial. It was the main reason for limiting the rise of the Mf. The current study of jute cloth significantly supports the Mf rising; however, it is strongly recommended that further investigation relative to continuous flow conditions, especially with dynamic conditions, be undertaken.
FUTURE SCOPE
The future scope of inclined SSs with jute cloth and extended surfaces holds immense potential in revolutionizing water desalination technologies and addressing pressing global challenges related to water scarcity and sustainable development. By combining the traditional ISS design with innovative extended surfaces made from jute cloth, this approach offers several advantages and opens up new avenues for applications in various regions worldwide. The integration of jute cloth extended surfaces into inclined SSs opens up opportunities for further research and innovation. Future studies could focus on optimizing the design and configuration of extended surfaces to maximize water evaporation rates and collection efficiency. Additionally, research into advanced materials and coatings for extended surfaces could enhance their durability and performance in harsh environmental conditions.
AUTHOR CONTRIBUTION
Conceptualization, methodology, resources, formal analysis, writing – original draft preparation, review and editing, supervision, and investigation were carried out by Pitchaiah Sudalaimuthu and Ravishankar Sathyamurthy.
DATA AVAILABILITY STATEMENT
All relevant data are included in the paper or its Supplementary Information.
CONFLICT OF INTEREST
The authors declare there is no conflict.
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