Novel Combinative Structure of High-Performance Solar Steam Device derived from Areca Nut
Abstract
A novel combinative structure, consisting of lateral hydrophobic pontoon oAN and central hydrophilic evaporator iAN, was designed for high-performance solar steam device. Both oAM and the iAN were derived from areca nut (AN), through different thermal and surface chemical treatments. With inferior water absorption and evaporation efficiency, the pontoon oAN nevertheless provides footage for the entire device, in contrast, although being efficient in water adsorption and evaporation, iAN requires the supporting oAN to keep its buoyancy. We therefore combined advantages of oAN and iAn to assemble a solar steam device with long-term stability and high solar thermal efficiency of ∼82% under 1-sun illumination. The idea using combinative structure as efficient solar steam device can be further extended to other potential systems, therefore, this study provided foundation for future development of novel solar steam devices. importance.
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Introduction
Solar-driven water evaporation1-8 , which utilizes sunlight as a renewable energy source, is a promising approach to provide clean water with minimized environmental impact. Recently, an interfacial evaporation route using non submersible solar steam devices, has been proposed to improve heat localization at the liquid surface, which has successfully achieved high evaporation efficiency9-17. In this system, the confined thermal energy selectively heated up the water at the surface, thus minimizing heat loss to bulk water. Moreover, the surface temperature of the absorber is low due to effective evaporation, lowering radiation and convection heat losses at the absorber surface. With this scheme, solar-to-vapour conversion efficiencies can be as high as 90 this aspect, several natural materials, such as plants18-21 , green leaf of Scindapsus aureus22 and trees23, had been subjected to different surface treatments to result in interfacial evaporation systems for study.
In general, interfacial system can be classified into direct and indirect contact systems according to the relative position of the solar steam devices to the water surface. Direct contact configuration used self-floating hydrophobic absorbers derived from various materials, such as nanoparticles24,25 monolithic aerogel and foams6,26,27, which are all capable of converting light into heat to vaporize the adsorbed water. However, this direct contact system is generally inferior in vaporizing the water, e.g. porous polymer–coding inorganic sheets25 exhibited a solar thermal conversion efficiency of 63.6% under 1-sun irradiation. Aside from the self-floating means, films consisting of the absorber materials coating on light-weight and hydrophobic scaffolds, such as stainless steel (SS) mesh3 , polypropylene (PP) mesh28, gauze29, and carbon fabric30, were also reported. All these direct contact systems utilized hydrophobic absorbers, which have limited water vaporization routes and are therefore low in photo thermal conversion efficiency.
In contrast, indirect contact system involved a bilayered structure, with the top absorber layer absorbing the solar flux without contacting the bulk water and the bottom supporting layer offering stable support for the top solar steam devices. In general, the bottom layers referred to microporous structure with interconnected channels for efficient water supply, for which carbonized mushroom31 and basswood32were previously used as hydrophilic components containing microporous channels for facile water absorption and vaporization, These carbonized mushroom and basswood exhibited a high conversion efficiency of 78% and 75%, respectively, but their long-term stability needed to be justified as we consider that the water adsorbed by the hydrophilic supporting materials would overload and sink the whole device eventually. The longterm stability problem may be reasonably improved by using hydrophobic supporting system, instead. Previously, polypryrrole was used as the absorbent layer30on top of the supporting polypropylene (PP) membrane. This served as insulating layer minimizing the heat loss of the device to the bulk water, however, the reverse effect of the hydrophobic PP in preventing the water adsorption should just the conversion efficiency (58%) of the device.
Conclusion
In summary, we have introduced a novel solar steam device aAN, with lateral hydrophobic oAn as supporting pontoon and central hydrophilic iAN as evaporator, for highly efficient solar steam device. With the hydrophobic CB-coated CM outer layer, oAN acted as efficient supporting material, in contrast, owing to the natural vessel structure and hydrophilicity, the iAN formed an ideal water adsorption, transport and vaporization system for solar steam device. In our instance, the efficiency of aAN was calculated to be 82%, which is higher than those of oAN (11%), iAN (34%), CM-coated paper (52%) and wood (24%). Although the evaporation of seawater by aAN is lower than that of pure water system, the desalination process still maintained a high conversion efficiency of 76% and showed a high value of 72% after 5 experiment cycles. Importantly, we had demonstrated that AN, a low-cost material ($1.1 per kg), which can be easily obscured in the street corners of Asian cities, can be used to derive efficient solar steam device, through ingenious design idea using pontoon as separate supporting component. The idea of using pontoon as separate component of an efficient device can be extended to other existing or potential hydrophilic light absorbers, e.g. paper and wood.