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Abstract The desalination of water is a process wherein the brackish water is purified by removing the salts. With increasing demand for fresh water, there is a vast scope for development of sea water desalination process. A number of methods exist for the desalination process, but solar desalination method promises to save energy in today’s energy crunch scenario. A novel solar desalination setup is proposed here. It uses an elliptic hyperboloid concentrator and a helical receiver along with a multi-tray desalination unit to purify water in the most effective manner. The helical receiver proposed in the present work aims at the Dean Flow effect in order to enhance heat transfer in laminar flow. The effectiveness of this property with respect to various physical parameters has been observed and an optimum design has been suggested based on this. The elliptic hyperboloid concentrator is a special design for concentrating solar radiation because of it offers to operate at high efficiency without the requirement of tracking. A detailed ray-tracing code was developed to simulate the radiation incident on the concentrator and an accurate estimation of the optical efficiency was made based on this. The two systems were integrated in order to arrive at a maximum output level for the solar desalination system as a whole.

Abstract A combination of heat pump and humidification-dehumidification (HDH) process is a suitable choice to obtain fresh water for small-scale desalination applications, especially when the solar energy is used as the auxiliary heat source. In this paper, a novel two-stage solar assisted heat pump (SAHP) desalination system based on HDH, in which the humidifiers are connected in parallel, is proposed. A mathematic model is developed to improve the system performance by optimizing the operating parameters such as process air flow rate and cooling seawater flow rate, and it is also validated by the experimental results. Analysis results indicate that there exists an optimal process air flow rate in the desalination system, which does not vary with the hot seawater flow rate. However, it will be increased with the increase of cooling seawater flow rate. When the flow rates of process air and cooling seawater are 350 m3/h and 0.55 m3/h, respectively, the maximum fresh water yield is 17.94 kg/h. The corresponding gained-output-ratio (GOR) is 2.02. However, the system performance is constrained by a bottleneck: increasing dehumidifying capacity can result in a reduction in the performance of lower-temperature (LT) humidifier. Consequently, a modified system is then proposed to solve this bottleneck effectively. The maximum fresh water yield can be increased by 16.70% to 20.54 kg/h, and the corresponding maximum GOR is also increased by 18.05% to 2.42.

Abstract Phase effect of bismuth vanadate (BiVO4) nanostructured catalysts for the photoelectrochemical (PEC) solar water oxidation, removal of toxic organic pollutants from wastewater, and electrochemical storage were reported. The monoclinic (BV-M) and tetragonal (BV-T) crystal structured BiVO4 photocatalysts were synthesized using a facile hydrothermal route without the support of any template. The BV-T photoelectrode also exhibits lower charge transfer resistance compare to BV-M photoelectrode. The BV-T photoelectrode showed a remarkable photocurrent density (0.4249 mAcm−2) over BV-M photoelectrode (0.0702 mAcm−2), which is about 6 times greater than BV-M photoanode. Furthermore, BV-T sample showed 17 times superior electrochemical capacitance over BV-M sample at the scan rate of 10 mVs−1. The photocatalytic analysis has also shown that the BV-T photocatalyst revealed greater photocatalytic activity for the methyl orange under visible light, about 87.8% of the MO was degraded within 80 min.

Abstract A water desalination idea with high-efficiency was presented, which employed a vacuum tube type solar distiller to stuffy-thermal distillation and raw water preheating, and also utilized the hydrophobic α-Al2O3 ceramic membrane distillation (HCMD) modules and preheated raw water to membrane distillation (MD). In order to show the potential of HCMD to improve the photo-thermal conversion efficiency of the vacuum tube type solar distiller, this study explored the thermal performance and water desalination capacity of HCMD module driven by the recovered latent heat of the vacuum tube type solar distiller. The research results indicate that the membrane flux of HCMD had a significant positive exponential correlation with the raw water temperature (Tr). The convective heat transfer coefficient (h) of the hot side surface of hydrophobic α-Al2O3 ceramic membrane (HCM) was positively correlated with Tr and the concentration of raw water (C). The effects of Tr and cooling water temperature (Tc) on the thermal efficiency (η) of HCMD had an interaction. The theoretical maximum of η was close to 67.8%, and the variation range of η corresponding to the temperature range of preheated raw water by the solar distiller was 8.32–42.90%. The rejection rate of the HCM for all measured ions in the raw water was greater than 99.96%. This research was of great theoretical guiding significance for realizing the engineering application of the solar-thermal membrane coupling water desalination system.

Abstract Microencapsulated n-octadecane with titanium dioxide (TiO2) shell was prepared by a sol–gel method in a nonaqueous oil-in-water (o/w) emulsion using a green solvent as the dispersion medium. The morphology, chemical structure, and crystalloid phase of the resultant microcapsules were determined by scanning electronic microscope (SEM), Fourier transformation infrared spectroscope (FT-IR), and X-ray diffractometer (XRD), respectively. The differential scanning calorimeter (DSC) and the thermogravimetric analyzer (TGA) were used to investigate the thermal properties and thermal stabilities of the samples. The resulting microcapsules presented spherical shape with average size of 2–5 μm. The results of FT-IR and XRD showed that n-octadecane was well microencapsulated in TiO2 shell. DSC and TGA results indicated that the samples exhibited good performance of storing and releasing the latent heat during phase-change cycles and high thermal reliability. The microencapsulation process in this study is simple, high-efficiency, and environmentally friendly. The microencapsulated n-octadecane with TiO2 shell will be a potential candidate material for thermal energy storage applied in the fields of solar energy storage, building energy conservation, air-conditioning systems, and waste heat recovery.

Abstract This article presents the experiences learned using micro-hydro power at the village level. Site evaluation procedure, financing methods, turbine fabrication, and site construction are discussed. Micro-hydro power provides a decentralized energy source for several of the energy-intensive tasks of villagers. Low-head, small volume hydro potential is common in the Zairian countryside. Often a potential site also serves as the village water source, hence it is located near potential beneficiaries of the power. Over the past three decades, a religous NGO in the Ubangi and Mongala Subregions of northwest Zaire has been developing this small hydro potential as part of its technology transfer and village development program. Local materials and knowledge are used as much as possible in construction. Experiences gained constructing a 370 kW hydro-electric site, as well as building water wheels for water pumping has led to the construction of micro-hydro sites using locally made cross-flow turbines. Four water wheel sites and six micro-hydro sites have been built. The hydropower is used to mill flour and hull coffee. One site also generates 220 V electricity, and two others have 12 V generation planned.

Abstract Water-filling and air-releasing were used to design a natural vacuum solar desalination system. The system was tested in various weather conditions to determine the operational regularity and total performance evaluation indices at different flow rates and temperatures. Economic analysis was applied to calculate the cost of freshwater produced. Results showed that the system performed better under the constant flow rate input of 0.150 kg/s with a heat collection area of 18.0 m2. The efficiency and recovery ratios could reach 87.821 and 3.858%, respectively and these were 1.568 and 1.631 times the values before heat recovery. Moreover, the average freshwater yield could reach up to 6.018 kg/h. When seawater was added at a constant temperature while considering utilisation of waste heat at night, efficiency could reach 84.256% when the heat collection area was 14.4 m2 and this was 1.080 times that of 18.0 m2. The recovery ratio could reach 4.133% when the area was 18.0 m2 and this was 1.069 times that of 14.4 m2. After calculation, the cost of freshwater was about 0.0113 $/kg and this had certain advantages over other systems.

Abstract Solar water evaporation attracts much attention owing to its widespread applications, including in power generation, seawater desalination, wastewater treatment, and clean water production. A multilayer thin film with a physically combined structure has been designed to achieve multi-functionality. However, this film leads to a decline in the evaporation capacity because of the mutual influences of different layers. In this work, a compound film based on Au@TiO 2 core–shell nanoparticles was designed and fabricated for achieving highly efficient solar water evaporation. The effects on solar evaporation enhancement of different evaporation styles, nanoparticle films, and light intensities were determined by solar evaporation experiments. It was found that the core–shell nanoparticle film showed better solar evaporation enhancement than the suspension of Au@TiO 2 core–shell nanoparticles, films based on solely Au or TiO 2 nanoparticles, and multilayer thin films of Au and TiO 2 nanoparticles because of the formation of a core–shell nanostructure. The solar evaporation enhancement achieved by the Au@TiO 2 core–shell nanoparticle film could simplify the film structures, reduce costs, and expand their applicability.

Abstract A given temperature difference across the upper and the lower convective zone of a solar pond is commonly sought in thermoelectric power generation. Based on this consideration, this work is aimed at predicting the lengths of various zones of a solar pond to ensure a minimum temperature potential throughout the year between its upper and lower convective zones. For predicting the critical lengths of various zones of the solar pond, at first, the heat energy conservation-based model available in the literature is modified by accounting the effect of salinity and temperature on various thermal parameters. The model is satisfactorily-validated with similar model and experimental data reported in the literature. Thereafter, considering the requirement of a thermoelectric power generator ( TEG ) , an inverse problem is solved with the aid of a genetic algorithm-based optimization method to predict feasible lengths of various zones satisfying a minimum temperature potential across TEG considering suitable thermal resistances. The present results reveal improved pond dimensions achieving a better temperature profile at a lower total height than that available in the literature. Further, case studies of diverse meteorological conditions of India are carried out and it becomes apparent that, around the year, multiple combinations of convective and non-convective regions of the solar pond can ensure the required minimum (or more) temperature difference across relevant zones of the solar pond. Finally, the present study also reveals that the temperature of the upper convective zone is largely governed by the thickness of this zone, whereas, the thickness of the non-convective zone is largely responsible for the temperature within the storage zone. The present study provides a novel inverse methodology to predict and optimize the suitable dimensions of various regions of a salt-gradient solar pond to ensure a minimum temperature potential across the year for thermoelectric power generation.