An experimental investigation of a water desalination unit using different microparticle-coated absorber plate: yield, thermal, economic, and environmental assessments

Investigations on a solar humidification dehumidification desalination system equipped with various packing materials and multi-stage bubble column dehumidifier

This work presents the theoretical and experimental investigation of a solar-powered humidification dehumidification desalination (HDD) system with different humidifier packing materials and a two-stage bubble column dehumidifier (BCD). Naturally available coconut shells (CS) and coconut shells with drilled holes (CSH) on the surface to improve water permeability were used as packing materials in the humidifier, and their performance was compared with that of commercial-type pall ring (PR) and raschig ring (RR) packings. An in-house developed numerical model of the HDD system in conjunction with a flat plate solar water collector was used in this study. Steady-state experimental results showed that CSH packing exhibited the highest volumetric mass transfer coefficient (0.00852 kg/s), resulting in maximum humidifier efficiency (96%) and freshwater yield (2.16 kg/hr), followed by PR (0.00841 kg/s, 94%, and 2.137 kg/hr), CS (0.00831 kg/s, 90%, and 2.127 kg/hr), and RR (0.0081 kg/s, 81%, and 2.087 kg/hr) at feedwater mass flow rate of 1.5 kg/min and humidifier inlet temperature of 75 [Formula: see text]. Furthermore, transient outdoor test results showed that using a two-stage configuration in a BCD increased the daily average effectiveness to 0.93, as against 0.79 for a single-stage BCD. Employing CSH instead of PR and RR packings in the humidifier reduced freshwater costs by 6.2% and 7.6%, respectively.

Advanced design techniques in passive and active tubular solar stills: a review

Clean water production using green energy supply plays a significant role in the globe's health and economic development. In recent years, so much importance is given on developing the advanced designs of solar stills to improvise the productivity of conventional solar stills. Tubular solar stills (TSSs) are one of the emerging areas to improve clean water productivity. This paper's main aim is detailed review of passive and active tubular solar still design specifications and highlighting the specific merit of each design. The common tube materials in passive and active TSS are glass, stainless Steel 304, vinyl chloride, flexi glass, poly carbonate, and poly ethylene with variation in thickness from 0.07 to 2.5 mm. Diameter of the tube varied from 50 to 280 mm in both the cases. Also, the monetary analysis of TSS is discussed, and the average price of water for passive and active tubular solar still is $0.022 and $0.027 per liter of water. Future perspectives also included in the conclusion section for the possible design and material improvements one can do to enhance the performance of the TSS for the benefit of researches. The excellent cover material for TSS is polythene film when compared to the vinyl chloride sheet. TSS with PCM, wick materials, and corrugated absorber enhance productivity during night time. Multi-effect tubular stills performed 28.70% better in comparison to single-effect stills, and TSSs with horizontal axis are 19.12% more productive than vertical axis tubular stills.

Historic review and recent progress in internal design modification in solar stills

Solar still, which uses solar renewable energy sources, especially solar energy, to produce pure water, is a promising technology as it is abundantly available and eco-friendly. Researchers have innovated in internal and external designs to enhance distillate productivity in solar desalination systems. The present review paper discusses the major internal modifications done in history and recent past to enhance the distillate output. Six sub-sections have been developed concerning historic internal modifications that discuss types of basin liners, water depth, stones, dyes, phase change materials, and weirs. It has been found that among all the historic internal modifications, phase change materials were the most effective with distillate yield enhancement of up to 80%. The limitation in distillate yield made the researchers to perform further modifications to enhance the productivity, and hence, recent internal designs have also been discussed. Recent internal modifications have six sub-sections: fins, wicks, nanofluids, nanostructures, dynamic modifications, and natural materials. Among the recent, dynamic modifications were the most efficient with productivity enhancement of up to 300%, with a maximum cumulative yield of 8.78 kg/m2/day for the rotating wick solar still compared to CSS which gave only 2.21 kg/m2/day. Such a kind of review work has not been performed till date, which covers all the internal design modifications in one paper exhaustively. Furthermore, gaps have been identified, and future perspectives have been presented in the conclusion section. It has been observed that nanostructures, nanoparticles, and dynamic modifications are the most promising internal modifications in recent times that can boost distillate productivity to a greater degree.

Exploring the photo-thermal conversion behavior and extinction coefficient of activated carbon nanofluids for direct absorption solar collector applications

This work aims to explore the optical and thermal conversion characteristics of activated carbon-solar glycol nanofluids with various volume fractions namely 0.2, 0.4, and 0.6%, respectively. Kigelia africana leaves were synthesized into porous activated carbon nanomaterials by using the high-temperature sintering process and the pyrolysis process in a muffle furnace. The experimental investigation was carried out with different nanofluid concentrations by using the solar simulator. Nanofluids were heated with the assistance of a solar simulator test system and the convection/conduction heat loss was decreased by using the glass as an insulating material around the test section. Prepared nanofluid with 0.6 vol% activated carbon augmented the thermal conductivity by 14.36% at 60°C. The maximum temperature difference of 10°C was attained at 0.6% volume concentrations of nanofluid as compared with base fluid (solar glycol). In addition, maximum receiver efficiency of 94.51% was attained at 0.6% volume fractions of activated carbon-based nanofluid compared with solar glycol thru a light radiation time of 600 s. Moreover, activated carbon-based nanofluid exhibited significantly higher absorption efficiency as the majority of the radiation was absorbed by the nanofluid. It is concluded that activated carbon-based nanofluids could be a suitable low-cost highly stable material for developing working fluid for direct absorbance solar collector-based applications.

Optimization of thermal efficiency on solar parabolic collectors using phase change materials - experimental and numerical study

Solar energy is a one-of-a-kind renewable energy source that has many uses, and in the thermal applications, it is receiving more attention and is becoming more feasible. The present work presents numerical and experimental studies to investigate the performance of a parabolic trough solar concentrator (PTC) integrated with a thermal energy storage system. A new receiver design is built that stores thermal energy using phase change material (PCM). A concentric absorber tube with two different kinds of PCM - MgCl₂·6H₂O and erythritol (filling the annular-space of absorber tube) - were used to construct a PTC, and its thermal performance and thermal efficiency were investigated under two different HTF flow rates of 0.005 kg/s and 0.033 kg/s. Solar energy is transformed into heat, which is then used to store in the PCM before being discharged to cold water, which is the final heat transfer fluid in the receiver's inner pipe. The simultaneous studies of the PTC with and without PCM are investigated. A commercial Mat Lab's operating model through an imperialist competitive algorithm of the entire PTC system is presented, and the numerical results were compared to the experimental results, which were carried out with and without PCM in PTC. With the PCM in PTC (0.005 kg/s and 0.033kg/s), the HTF exhibited gain in peak temperatures of 11°C (erythritol) and 9°C (MgCl2·6H2O) at 0.05 kg/s, whereas the peak temperatures further increase to 14°C (erythritol) and 12°C (MgCl2·6H2O) respectively at 0.033 kg/s, as compared to HTF without PCM. Average thermal efficiency of PTC with HTF flow rate of 0.033 kg/s was highest with usage of erythritol (40.6%), among all the cases. The experimental and predicted thermal efficiency performance indices for different flow rates and PCM are found to be with a deviation of around ± 1.9%, demonstrating the accuracy of the developed numerical model.

A comparative study of hemispherical solar stills with various modifications to obtain modified and inexpensive still models

The present study aims to obtain the best modification of the hemispherical solar distillers that achieves the highest productivity with the lower inexpensive. To achieve this goal, this paper dealt with conducting a comparative study, operating performance analysis and an economic study of two different modifications, and comparing them with the reference distiller in order to obtain the best adjustments that achieve the highest productivity at the lowest cost. In the first modification, CuO nanoparticles with three different concentrations (0.1, 0.2, and 0.3%) were added to the basin water, to increase the intensity of absorbed solar energy, improve the thermal properties of basin fluid, and then increase the rate of vapor generation inside the distillation basin. In the second modification, water film glass cooling technology with three different flow rates (1.5, 2, and 2.5 L/h) was utilized to increase the water vapor condensation rate. In this experimental study, three hemispherical distillers were fabricated and tested under the same climate conditions at a 1-cm basin fluid depth, namely, conventional hemispherical solar still (CHSS), hemispherical solar still with glass cover cooling (HSS-C), and hemispherical solar still with CuO-water-based nanofluid (HSS-N). The experimental results presented that the average daily accumulative yield of CHSS is 3.85 L/m²/day, while the daily accumulative yield of HSS-N increases to 5.75, 6.40, and 6.80 L/m²/day with improvement 49.3, 66.2, and 76.6% at volume fraction 0.1, 0.2, and 0.3%, respectively. Also, the daily accumulative yield of HSS-C increases to 4.9, 5.35, and 5.7 L/m²/day with improvements of 27.3, 39, and 48% at water film flow rates of 1.5, 2, and 2.5 L/h, respectively. The cost of distilled water produced from CHSS is 0.0106 $/L, while the utilization of HSS-C (2.5 L/h) and HSS-N (0.3%) reduces the cost of distilled water to 0.0072 and 0.0066 $/L, respectively. Based on accumulative yield and economic analyzes, it is recommended that the modified HSS-N (0.3% volume fraction) be utilized to achieve the highest accumulative yield and the lowest price of the produced distilled water.

Energy and exergy efficiency analysis of solar still incorporated with copper plate and phosphate pellets as energy storage material

In this work, a new attempt was made to study the behavior of the conventional solar still (CSS) by adding a black-painted copper plate and phosphate pellets. Therefore, the performance of the three solar stills has been studied and compared. The first is the CSS, and the second is the modified solar still (MSS). The MSS performance was tested using black-coated copper plate (measuring 49 × 49 cm and 0.2 cm thick) with and without phosphate pellets and compared to the CSS in the similar climatic conditions. The results showed that the combination of black coated copper plate and the inclusion of phosphate pellets improved the evaporation rate and daily productivity. During the experiments, yields using black coated copper plate without and with phosphate pellets were 14.96% and 29.53% greater than the CSS. The effectiveness of the CSS, MSS with copper metal plate (MSS-CP), and MSS with copper metal plate with phosphate pellets (MSS-CP and PP) are around 30.23, 35.3, and 41.44%, respectively.

Secondary transmission of SARS-CoV-2 through wastewater: Concerns and tactics for treatment to effectively control the pandemic

The SARS-CoV-2 virus has spread globally and has severely impacted public health and the economy. Hand hygiene, social distancing, and the usage of personal protective equipment are considered the most vital tools in controlling the primary transmission of the virus. Converging evidence indicated the presence of SARS-CoV-2 in wastewater and its persistence over several days, which may create secondary transmission of the virus via waterborne and wastewater pathways. Although, researchers have started focusing on this mode of virus transmission, limited knowledge and societal unawareness of the transmission through wastewater may lead to significant increases in the number of positive cases. To emphasize the severe issue of virus transmission through wastewater and create societal awareness, we present a state of the art critical review on transmission of SARS-CoV-2 in wastewater and the potential remedial strategies to effectively control the viral spread and safeguard society. For low-income countries with high population densities, it is suggested to identify the virus in large scale municipal wastewater plants before following up with one-to-one testing for effective control of the secondary transmission. Ultrafiltration is an effective method for wastewater treatment and usually more than 4 logs of virus removal are achieved while safeguarding good protein permeability. Decentralized wastewater treatment facilities using solar-assisted disinfestation methods are most economical and can be effectively used in hospitals, isolation wards, and medical centers for reducing the risk of transmission from high local concentration sites, especially in tropical countries with abundant solar energy. Disinfection with chlorine, sodium hypochlorite, benzalkonium chloride, and peracetic acid have shown potential in terms of virucidal properties. Biological wastewater treatment using micro-algae will be highly effective in removal of virus and can be incorporated into membrane bio-reaction to achieve excellent virus removal rate. Though promising results have been shown by initial research for inactivation of SARS-CoV-2 in wastewater using physical, chemical and biological based treatment methods, there is a pressing need for extensive investigation of COVID-19 specific disinfectants with appropriate concentrations, their environmental implications, and regular monitoring of transmission. Effective wastewater treatment methods with high virus removal capacity and low treatment costs should be selected to control the virus spread and safeguard society from this deadly virus.