Challenges and Opportunities for Solar Evaporation

Emerging solar desalination by interfacial evaporation shows great potential in response to global water scarcity because of its high solar-to-vapor efficiency, low environmental impact, and off-grid capability. However, solute accumulation at the heating interface has severely impacted the performance and long-term stability of current solar evaporation systems. Here, a self-regenerating solar evaporator featuring excellent antifouling properties using a rationally designed artificial channel-array in a natural wood substrate is reported. Upon solar evaporation, salt concentration gradients are formed between the millimeter-sized drilled channels (with a low salt concentration) and the microsized natural wood channels (with a high salt concentration) due to their different hydraulic conductivities. The concentration gradients allow spontaneous interchannel salt exchange through the 1-2 µm pits, leading to the dilution of salt in the microsized wood channels. The drilled channels with high hydraulic conductivities thus function as salt-rejection pathways, which can rapidly exchange the salt with the bulk solution, enabling the real-time self-regeneration of the evaporator. Compared to other salt-rejection designs, the solar evaporator exhibits the highest efficiency (≈75%) in a highly concentrated salt solution (20 wt% NaCl) under 1 sun irradiation, as well as long-term stability (over 100 h of continuous operation).

A High-Performance Self-Regenerating Solar Evaporator for Continuous Water Desalination

Solar-enabled steam generation has attracted increasing interest in recent years because of its potential applications in power generation, desalination, and wastewater treatment, among others. Recent studies have reported many strategies for promoting the efficiency of steam generation by employing absorbers based on carbon materials or plasmonic metal nanoparticles with well-defined pores. In this work, we report that natural wood can be utilized as an ideal solar absorber after a simple flame treatment. With ultrahigh solar absorbance (∼99%), low thermal conductivity (0.33 W m-1 K-1), and good hydrophilicity, the flame-treated wood can localize the solar heating at the evaporation surface and enable a solar-thermal efficiency of ∼72% under a solar intensity of 1 kW m-2, and it thus represents a renewable, scalable, low-cost, and robust material for solar steam applications.

Robust and Low-Cost Flame-Treated Wood for High-Performance Solar Steam Generation

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Experimental Methods for Engineers

Progress and Expectation of Atmospheric Water Harvesting

Most of the desalination systems are energy intensive, which consume high grade energy like gas, electricity, oil and fossil fuels These processes lead to carbon footprints, which causes depletion of ozone layer as well as health hazards on mankind It is also lead to global warming which is the burning topic and becomes threat to life sustainability The potential of harnessing solar energy is most efficient and effective for heat to heat conversion The thermal desalination is a low temperature application processes with one time investment for life time water production up to 10 to 15 years In this paper, various solar thermal desalination methods such as direct and indirect methods have been discussed The indirect methods are preferable for medium and large scale desalination systems, whereas the direct methods employing the solar stills are more suitable for small scale systems The performance of the low cost solar stills can be improved with simple modification by using various locally available materials These low cost stills can be easily and economically fabricated for meeting daily need of the fresh drinking water These low cost solar stills are sufficient for the small households and communities living in islands, coastal areas It can also be uses for distillation of brackish water for the population residing near river banks Such a system also suitable for the fluoride affected area to remove fluoride from the water The low cost solar stills are sufficient for removal of arsenic, mercury, cadmium, coliform, virus and bacteria

Water desalination system using solar heat: A review

Water generation from atmospheric air by using composite desiccant material through fixed focus concentrating solar thermal power

An experimental investigation of an evacuated tube solar air collector coupled to a latent thermal energy store for generating hot air when no solar radiation is incident was undertaken. Acetamide was used as a phase change material (PCM). The latent thermal energy store was integrated with the manifold of the solar collector and water was used as the working fluid transferring solar gain to the air being heated. The maximum measured temperature differential between the heated air and the ambient air was 37°C and 20.2°C during conditions of incident and non-incident solar radiation, respectively. This occurred using a circular fin configuration at a flow rate of 0.018 kg s−1. The efficiency at low (0.018 kg s−1) air flow rates was 0.05–0.50 times less as compared to high (0.035 kg s−1) air flow rates. This system has advantages over systems using sensible storage as it can be used after sunset due to better heat storing capacity of the PCM.

Experimental analysis of thermal performance of evacuated tube solar air collector with phase change material for sunshine and off-sunshine hours

Experimental investigation of solar powered water production from atmospheric air by using composite desiccant material “CaCl2/saw wood”

In this article, the regeneration and adsorption of different desiccants such as silica gel, activated alumina, and activated charcoal for producing dry air is proposed. The air needed for regeneration was heated in an evacuated tube solar collector with a surface area of 4.44 m2. The desiccants were regenerated at temperatures in the range of 54.3–68.3°C. The regeneration performance was greatly affected by the regeneration temperature but depended on the initial moisture content, temperature of the desiccants, and flow rate of regeneration air. Comparison of the performances showed that at high hot air flow rate the regeneration time and adsorption time were shorter for these desiccants than that at low flow rate. Silica gel was observed to perform better at high as well as low flow rates for regeneration and adsorption than activated alumina and activated charcoal.

Avadhesh Yadav

Papers

Water desalination system using solar heat: A review

Water generation from atmospheric air by using composite desiccant material through fixed focus concentrating solar thermal power

Experimental analysis of thermal performance of evacuated tube solar air collector with phase change material for sunshine and off-sunshine hours

Experimental investigation of solar powered water production from atmospheric air by using composite desiccant material “CaCl2/saw wood”

Experimental Comparison of Various Solid Desiccants for Regeneration by Evacuated Solar Air Collector and Air Dehumidification