Stable Vapor Research Articles

Nanocomposite Hydrogel Engineered Janus Membrane for Membrane Distillation with Robust Fouling, Wetting, and Scaling Resistance.

Membrane distillation (MD) is considered to be rather promising for high-salinity wastewater reclamation. However, its practical viability is seriously challenged by membrane wetting, fouling, and scaling issues arising from the complex components of hypersaline wastewater. It remains extremely difficult to overcome all three challenges at the same time. Herein, a nanocomposite hydrogel engineered Janus membrane has been facilely constructed for desired wetting/fouling/scaling-free properties, where a cellulose nanocrystal (CNC) composite hydrogel layer is formed in situ atop a microporous hydrophobic polytetrafluoroethylene (PTFE) substrate intermediated by an adhesive layer. By the synergies of the elevated membrane liquid entry pressure, inhibited surfactant diffusion, and highly hydratable surface imparted by the hydrogel/CNC (HC) layer, the resultant HC-PTFE membrane exhibits robust resistance to surfactant-induced wetting and oil fouling during 120 h of MD operation. Meanwhile, owing to the dense and hydroxyl-abundant surface, it is capable of mitigating gypsum scaling and scaling-induced wetting, resulting in a high normalized flux and low distillate conductivity at a concentration factor of 5.2. Importantly, the HC-PTFE membrane enables direct desalination of real hypersaline wastewater containing broad-spectrum foulants with stable vapor flux and robust salt rejection (99.90%) during long-term operation, demonstrating its great potential for wastewater management in industrial scenarios.

Biomimetic hydrophilic CuO-nanocluster/nanofibrous thin-film skeleton/hydrophilic CuO-nanocluster architecture membrane for efficient and stable solar water evaporation

Developing exquisitely structured light-absorbing materials could be a feasible approach to enhance solar evaporation performance. Herein, a CuO-nanocluster/PVDF-HFP nanofibrous thin-film skeleton/CuO-nanocluster (CPC) architecture membrane was developed via electrospinning, heating, and hydrothermal techniques. The CPC membrane architecture is similar to the triple-layer mesophyll/vein/mesophyll in a natural leaf, whereby mesophyll performs photosynthesis for plant growth and the vein acts as a support skeleton. Similarly, CPC mimicking a leaf structure possesses: (1) upper and lower hydrophilic CuO-nanoclusters to absorb sunlight, promote water supply, and prevent salt crystallization during the evaporation process; and (2) a middle nanofibrous thin-film membrane that acts as a supportive layer. The resulting CPC membrane exhibited an evaporation rate of 1.21 kg m−2 h−1 and 1.06 kg m−2 h−1 for 3.5 wt% saline water and actual industry dye wastewater, respectively. Meanwhile, the CPC membrane was applied in the cycle, continuous, and outdoor evaporation tests. In addition, the CPC membrane displayed impressive mechanical strength and flexibility, making it suitable for the long-term use in practical applications. These findings demonstrate the excellent performance of the CPC membrane for solar water evaporation and should inspire further research on developing dedicated architecture membranes for use in fields such as catalysis, sensing, energy, and other applications.

Novel solar evaporator with closely-stacked reverse U-shaped hydrogel tubes for long-term stable evaporation with excellent salt resistance

Novel solar evaporator with closely-stacked reverse U-shaped hydrogel tubes for long-term stable evaporation with excellent salt resistance

Study of the VAC of the EPCTT process with varying electrode parameters

Nowadays the treatment of machine parts, instruments is one of the actual topics in the modern world. One of the modern processing method is chemical-thermal treatment of parts, in which there is an increase of hardness in the surface part to increase wear resistance, while the core of the part remains in a ductile state for resistance to shock loading. The solution to this problem could be the electrolytic plasma chemical-thermal treatment of the parts. This method has a number of advantages over traditional methods, such as costeffectiveness and speed of processing. In the present work the influence of changes in technological parameters on the volt-ampere characteristics of electrolyte-plasma chemical-thermal treatment unit is presented. A solution of soda ash (Na₂CO₃), urea (CH₄N₂O) in distilled water was used as an electrolyte. According to the results of the study current-voltage diagrams were plotted by varying the diameter of the anode (D=90; 110;130 mm) and the distance between the electrodes (L=50;70; 90 mm). According to the analysis, in the voltage range of 180-220 V, with anode diameter D=110 mm and electrode spacing D=70 mm, a more stable vapor-gas envelope is formed. It was found that by changing the anode diameter, respectively the ratio of active and passive electrodes we can significantly influence the formation of stable vapor gas shell and establishment of the optimum mode of treatment of parts.

Polyester fiber bundle-based solar evaporator manufactured by dyeing for efficient desalination and zero liquid discharge

Interfacial solar desalination is a promising technology to address global freshwater scarcity. However, low evaporation rates, complex manufacturing processes, and poor salt resistance have hindered the practical application of solar evaporators. In this study, a three-dimensional (3D) solar evaporator named DB-PFB was developed by dyeing industrial dispersion black (DB) onto polyester fiber bundle (PFB). Vertical channels in the PFB rapidly transport water from the bottom to the top through the wicking effect. This, together with hydrophobic polyester fibers, prevents salt accumulation, ensures stable desalination performance and achieves zero liquid discharge. The 3D DB-PFB can utilize ambient energy and has a stable evaporation rate of about 2.60 kg m–2h−1 for desalination of 20 wt% brine at 1-solar intensity. Continuous evaporation allows the collection of salt crystals and dye wastes in the distillation tank. Long-term indoor and outdoor desalination experiments (about 150 h each) have proven the durability of the DB-PFB. 1 m2 DB-PFB can produce approximately 18 kg of freshwater per day from 20 wt% brine, meeting the daily drinking water needs of six adults. This efficient, easy-to-manufacture, and salt-resistant solar evaporator offers a feasible solution to alleviate global freshwater scarcity.

Thermal and electrical conductive 2D CuO evaporator for all-day steam generation

Solar energy-driven water evaporation is an effective way to obtain clean water through seawater desalination. Due to the day and night cycle, all-day steam generation is an urgent project. Here, 2D evaporators with effective heat management were designed and constructed by facile folding, in which superhydrophilic CuO coatings with honeycomb-like pores were in situ deposited on brass plates via electroplating and heat oxidation. In the daytime, the 2D evaporator has excellent photothermal performance due to the appropriate pore structure, light absorption, and water supply. The evaporation rate reaches 1.4 kg m−2 h−1, and the energy conversion efficiency of 93.5% under 1 sun in 3.5% artificial seawater for ten cycles. Except forsolar-driven water evaporation, some heat converts into electricity due to the temperature difference between the two surfaces of the high thermal conductive 2D evaporator. At night, steam is generated through the flexible photoelectric transition. The evaporation rate is 5.8 kg m−2 h−1 at an input voltage of 6 V. The stable evaporation performance of this evaporation system and the advantages of all-day steam generation show considerable prospects. It may be widely used in pure water production in the future.

A hierarchical salt-rejection strategy for sustainable and high-efficiency solar-driven desalination

Solar steam generation (SSG) is widely regarded as one of the most sustainable technologies for seawater desalination. However, salt fouling severely compromises the evaporation performance and lifetime of evaporators, limiting their practical applications. Herein, we propose a hierarchical salt-rejection (HSR) strategy to prevent salt precipitation during long-term evaporation while maintaining a rapid evaporation rate, even in high-salinity brine. The salt diffusion process is segmented into three steps—insulation, branching diffusion, and arterial transport—that significantly enhance the salt-resistance properties of the evaporator. Moreover, the HSR strategy overcomes the tradeoff between salt resistance and evaporation rate. Consequently, a high evaporation rate of 2.84 ​kg ​m−2 ​h−1, stable evaporation for 7 days cyclic tests in 20 ​wt% NaCl solution, and continuous operation for 170 ​h in natural seawater under 1 sun illumination were achieved. Compared with control evaporators, the HSR evaporator exhibited a >54% enhancement in total water evaporation mass during 24 ​h continuous evaporation in 20 ​wt% salt water. Furthermore, a water collection device equipped with the HSR evaporator realized a high water purification rate (1.1 ​kg ​m−2 ​h−1), highlighting its potential for agricultural applications.

Self‐Assembled Nanofibrous Hydrogels with Tunable Porous Network for Highly Efficient Solar Desalination in Strong Brine

AbstractHydrogel‐based solar evaporators (HSEs) emerged as energy‐efficient designs for water purification due to the reduced vaporization enthalpy in the hydrated polymeric network. However, it remains challenging for HSEs to achieve stable performance in desalination, partly due to the tradeoff between desired evaporation dynamics and salt tolerance. Here, composite hydrogels with tunable self‐assembled nanofiber networks are exploited for the engineering of solar evaporators with both high evaporation performance and resistance to salt accumulation. The nanofibrous hydrogel solar evaporators (NHSEs) present an intrinsic open network with high porosity, above 90%, enabling continuous water channels for efficient mass transfer. Theoretical modeling captures the complex nexus between microstructures and evaporation performance by coupling water transfer, thermal conduction, and vaporization enthalpy during evaporation. The mechanistic understanding and engineering tuning of the composites lead to an optimum configuration of NHSEs, which demonstrate a stable evaporation rate of 2.85 kg m−2 h−1 during continuous desalination in 20% brine. The outstanding performance of NHSEs and the underlying design principles may facilitate further development of practical desalination systems.

Janus membrane with enhanced interfacial activation for solar evaporation

Low solar spectrum coverage, high evaporation enthalpy, and undesired salt deposition severely limited the solar-driven interfacial evaporation technology for further sewage purification and seawater desalination. To overcome these problems, we designed an amphiphilic Janus-structured polyaniline (PANI)/ZrC/cellulose acetate (CA) (J-PZCA) membrane. Firstly, the interfacial interaction between PANI and ZrC enhances the photoabsorption and photothermal conversion efficiency. Secondly, low thermal conductivity reduces the heat lost at the interface. Most importantly, ZrC could facilitate interfacial activation, which weakens the intermolecular forces of water by affecting the hydrogen bond. Under 1 solar irradiation (1 sun), the composite membrane exhibits a high evaporation rate of 1.31 kg m−2 h−1 and an excellent efficiency of 79.4%. In addition, the sewage purification and seawater desalination experiments reveal a remarkable purification capability of J-PZCA membrane. Especially for the treatment of high-concentration salt solution, it realizes a long-term stable evaporation performance due to the excellent salt deposition resistance. Therefore, the J-PZCA membrane constructed in this study provides a new perspective for the design of efficient interfacial evaporation devices.

Peanut shell-derived photothermal absorber for solar desalination

The development of efficient photothermal materials for solar steam generation (SSG) is important achieving high evaporation rates and efficiencies. Among various materials, biomass-derived photothermal absorbers (PTAs) can convert solar light into heat for solar desalination. This study pioneers the utilization of peanut shell as a renewable resource in solar desalination. Peanut shells, an agricultural waste with meso- and micropores, were utilized as an evaporator for interfacial solar steam generation (ISSG). Although peanut shells are an excellent source of protein, fat, and fiber, they are usually discarded after consumption. In this work, waste peanut shells were carbonized at 600 °C and 1000 °C to prepare carbonized peanut shell powder (CPS). Furthermore, the prepared CPS was coated onto polyvinyl alcohol (PVA) sponges for solar evaporation. The CPS-derived PTAs were hydrophilized with sodium alginate (SA) and cross-linked by using CaCl2 to obtain PVA@SA–CPS evaporators for solar desalination. In the seawater desalination experiment, PVA@SA–CPS–1000 exhibited a stable evaporation rate that lasted for up to 14 cycles. It presented an evaporation rate of 2.16 kg m−2 h−1 with an efficiency of 90.4 % under 1 sun illumination. Sustainability, cost-effectiveness, low greenhouse emissions, and easy adoptability are the other features of CPS utilized for desalination and water treatment.

Stable isotope compositions and vapor sources of precipitation in the Yellow River Delta, China.

To uncover the vapor source, formation mechanism, and the influence of meteorological factors on precipitation in the saline land of the Yellow River Delta, I employed stable isotopes of precipitation, especially for δ17O and 17O-excess, along with the Hybrid Single Particle Lagrangian Integrated Trajectory Model (HYSPLIT), to analyze the isotopic variation characteristics of precipitation and water vapor sources at different temporal scales and precipitation intensities [(<5, 5-10, 10-25, 25-50, >50 mm·d-1)] from May to October in Dongying, located in the Yellow River Delta. There were wide ranges of isotopes in the daily precipitation data between May and October, with smaller ranges and enriched average values during the dry season. The slope between δ'18O and δ'17O was the minimum of 0.5211 when precipitation intensity was below 5 mm·d-1, indicating the potential influence of evaporation from the moisture source site on precipitation. The maximum value was 0.5268 when precipitation intensity was between 10 mm·d-1 and 25 mm·d-1. For precipitation intensities below 50 mm·d-1 with four different intensities, δ2H, δ18O and δ17O decreased with the increase of precipitation. During the dry season, 17O-excess exhibited a positive relationship with temperature, suggesting the influence of continental circulating water vapor on precipitation. Conversely, in the wet season, 17O-excess displayed a negative relationship with relative humidity (RH), indicating less influence of evaporation. Analysis of air mass back trajectories using the HYSPLIT model indicated that precipitation during the dry season was primarily influenced by the continental monsoon, while precipitation during the wet season was affected by both oceanic and continental monsoons. In conclusion, precipitation in the Yellow River Delta is influenced by the evaporation of various water vapor sources, local meteorological factors, and atmospheric water vapor sources, resulting in different isotopic signatures across different scales. The fin-dings would provide a scientific basis for the allocation of scarce water resources in the Yellow River Delta.

Oriented porous hydrogel with excellent anti-salt and antibacterial properties for high-performance interfacial solar steam generation

In recent years, solar interfacial evaporation has drawn substantial attention in wastewater and seawater treatment, but it still requires intensive development in high-performance evaporators, particularly simultaneous with high anti-salt and antibacterial abilities to supply freshwater. In this work, a directionally channeled evaporator with excellent resistance to salt crystallization and microbial was designed and synthesized by using silver nanoparticles (AgNPs) / polydopamine (PDA) hydrogel via a simple freeze-dried method. The novel structure was proposed to enhance convection and accelerate water transport that prevents salt crystallization. PDA and AgNPs were deposited to achieve superb optical absorption, photothermal conversion and anti-biofouling ability. Therefore, the evaporation rate of the AgNPs-PDA hydrogel achieved 1.70 kg m−2 h−1 with a light-to-heat conversion efficiency of 90.3 %. Based on the efficient evaporation ability and especially structure of the AgNPs-PDA hydrogel, the evaporator presented a tolerance to high salt water and the stable evaporation performance of actual seawater evaporation during long-time application. Simultaneously, the addition of AgNPs endowed the AgNPs-PDA hydrogel evaporator with excellent antibacterial ability. Thus, these favorable properties endowed the special AgNPs-PDA hydrogel evaporator a great potential for obtaining efficient evaporation and simultaneously solving the fouling problem, especially to waterborne pathogens and salt crystallization in tanglesome applications.

Moisture‐Thermal Stable, Superhydrophilic Alumina‐Based Ceramics Fabricated by a Selective Laser Sintering 3D Printing Strategy for Solar Steam Generation

AbstractThe solar‐driven interface evaporation is one of the most promising technologies for desalination and wastewater purification. However, in the ebb and flow of the tide, water absorbed in the hydrophilic evaporator bottom would significantly change, leading to the shape deformation of the system and further failure of solar steam generation. Here it is reported that the moisture‐thermal stable and superhydrophilic alumina‐based ceramics can be fabricated by a selective laser sintering (SLS) 3D printing strategy. The printed alumina‐based ceramics possess superhydrophilicity. Along the side surface of the printed sample, a 5 µL water droplet can be fast absorbed in 14 ms. Most importantly, they can maintain stable and high evaporation efficiency even after being dried out for ten times, demonstrating the excellent physical resistance to continuous moisture‐thermal transition. Finally, the “I‐shaped” evaporators are printed with salt‐resistant ability, which can maintain a steady high evaporation efficiency in seawater and 20 wt% brine for long‐term steam generation process. The moisture‐thermal stable alumina‐based ceramics prepared in this work will provide inspiration for stable solar steam generation materials, and expand the development of 3D printing functional materials.

Superhydrophilic Interconnected Biomass-Based Absorbers Toward High-Speed Evaporation for Solar Steam Generation.

Taking abundant and sustainable solar energy as the only energy source, solar-powered interface evaporation has been regarded as a promising method to alleviate the pressure of freshwater shortage. However, the uptake of clean water from brine is constantly accompanied by evaporation of water and condensation of vapor, which inevitably generates salt solid, preventing further continuous and stable evaporation. The most direct method is to fabricate a photothermal material with salt self-resistance by using the reflux of salt ions. Here, a superhydrophilic interconnected biomass carbon absorber (SBCA) is prepared by freeze-drying and carbonization, realizing strong liquid pumping, and self-blocking salt. In combination with superior broadband light absorption (94.91%), high porosity (95.9%), superhydrophilicity, and excellent thermal localization, an evaporation device with excellent evaporation rate (2.45kg m-2 h-1 under 1kW m-2) is successfully proposed. In the meantime, the porous skeleton and rapid water transport can enhance the diffusion of salt ions and slow down the rate of salt deposition. As a result, no salt deposition is found on the SBCA surface after continuous irradiation at 1kW m-2 for 15 h. The design can provide a convenient and low-cost efficient strategy for solar steam generators to address clean water acquisition.

Strain gauge measurements of an oscillating heat pipe from startup to stable operation

Oscillating heat pipe (OHP) devices offer high heat flow (Q) and low thermal resistance (Rth) capabilities with convenient form factors for applications in spacecraft and terrestrial thermal management. Though prior measurements have used intrusive strain measurements in a single OHP turn to study the complex thermal-fluid mechanisms of OHP operation, minimally-intrusive external strain measurements on the casing of a multi-turn OHP have not been previously reported. Here, we affix strain gauges to the exterior casing of an ammonia filled flat plate OHP and use strain measurements to quantify the frequency response of ammonia vapor pressure fluctuations over a broad Q range. For all Q, the Fourier transformed strain signals referenced to the Q=0 W background are well-described by a low-pass filter fitting function with a low-frequency amplitude a and characteristic “knee” frequency c. In all cases, a increases with increasing Q due to the enhanced vapor pressure fluctuations at larger thermal loads. In the startup regime of Q<10W, we observe large temporal deviations in the strain response, large Rth>0.1K/W, and c values that increase with increasing Q. In the stable operating regime for Q near 100W, we observe a stable frequency response, a minimum value of Rth=0.02K/W, and Q-independent c values that saturate near 10Hz. Our strain gauge findings are consistent with a mechanism of intermittent boiling near startup followed by stable vapor plug/liquid slug motion at higher Q. Thus, our measurements show that externally placed and minimally invasive strain gauges canprovide diagnostic capabilities and additional insight into operation in both the startup and stable regimes for multi-turn, lightweight OHP devices used in aerospace and terrestrial thermal management applications.

Anomalous stable hydrogen-oxygen isotope characteristics and water vapor sources of autumn precipitation in the Weihe River basin, Northwest China.

The extreme changes in autumn rain have significant impacts on the ecological environment of Weihe River basin. Based on 117 autumn rain samples and corresponding meteorological data from 2015 to 2021 at Yangling located in the middle of Weihe River basin, we investigated the stable hydrogen and oxygen isotope composition and water vapor sources of precipitation. The results showed that, (1) extreme changes in autumn rainfall in the study area occurred frequently in recent years, which could be divided into extreme-high autumn precipitation year (HAP, 2021), general autumn precipitation year (GAP, 2015-2017, 2019-2020) and extreme-low autumn precipitation year (LAP, 2018) based on the autumn rain index (ARI); (2) the stable isotopes of different types of precipitation differed significantly, with a pattern of LAP>GAP>HAP for both δ2H and δ18O values. the variations of d-excess values and the slopes and intercepts of the meteoric water lines of autumn rain showed opposite trends. The main factor controlling autumn rain anomaly was not the local meteorological parameters, but the El Nino-Southern Oscillation and the Indian Ocean dipole events, which could explain 99% and 93% of the autumn rain isotopic variations, respectively. These coupling phenomena affected water vapor transport intensity of the marine air mass to the northwest inland, which determined autumn rainfall amount and the stable hydrogen-oxygen isotope composition. Our results would be helpful for improving the understanding of autumn rain anomalies in West China, and provide basic data and theoretical support for regional hydrological model building, would thereby better serve water resources management and disaster prevention and reduction.

A numerical study of saturated pool film boiling over a sphere

A detailed numerical investigation of saturated pool film boiling over a sphere is presented in this work. The CLSVOF method was used for capturing the dynamic interface. Computations were performed to study the effect of dimensionless sphere diameter (D/λ0), the dimensionless wall superheat (Jav) and the external gravity field on the interface evolution and the associated heat transfer characteristics. The simulations were performed for D/λ0 varying in the range of 0.5-5.0, while Jav varies in the range of 6.36-19.07 for both normal and reduced gravity field. Under the normal gravity conditions, a periodic vapour bubble ebullition cycle is observed for D/λ0=0.5 and 1.0, whereas a stable vapour column is observed to develop for D/λ0=5.0. The vapour film thickness decreases as the D/λ0 increases for a constant Jav under normal gravity conditions. Furthermore, under the normal gravity conditions, vapour generation is observed to be asymmetrical in the thin vapour film for D/λ0=5.0. For D/λ0=0.5 and 1.0, vapour bubbles are released further downstream of the heated sphere as the dimensionless wall superheat increases under normal gravity. When compared to the normal gravity conditions, the interface evolution pattern changes significantly at low gravity. The space–time averaged Nusselt number is used to quantify the heat transfer in the present work. A Fast Fourier Transform (FFT) analysis of the temporal evolution of the space averaged Nusselt number reveals a complex interplay between different forces for saturated pool film boiling over a sphere for various flow and geometrical conditions.

Plant-inspired multi-environmentally adaptive, flexible, and washable solar steam generation fabric

Interfacial solar water evaporation has been widely fabricated for water treatment owing to its great promise in harvesting fresh water with clean energy in need for carbon neural target. However, developing an evaporator with recyclability under severe contamination and adaptability for various complex aqueous environments, remains challenging. Herein, inspired by mangrove forest growing in salty shoals, an adaptive tree-like evaporator (ATE) was fabricated by rolling cotton threads and punched (pin-holed) carbon nanotube (CNT) film into modified photothermal bundles and further weaving them into root-leaf like structure, enabling uncoated cotton bundles as dense roots for extracting and transporting water and coated part as leaves with open holes for evaporation. Such a facile ATE showed stable water evaporation rate, and an excellent salt-self-cleaning performance. Importantly, the ATE was also available to extract and evaporate wastewater from some severe environments, such as mud, sand, emulsion and dye solution. The ATEs were scalable, and particularly proved to be flexible and robust for washing and reusing, with evaporation performance almost unchanged after 100 cycles. This work has demonstrated a prototype for an efficient, adaptive and scalable fabric evaporator for solar-driven wastewater treatment, opening the possibility to solve provisional freshwater supply in poverty-stricken or polluted areas.

Magnetic field induced the assembling of Photothermal evaporator for efficient solar‐driven desalination

AbstractSolar‐driven interfacial evaporation is a sustainable and economical technology for freshwater generation. Structural design of photothermal material is an effective strategy to improve the evaporation performance but is usually bothered by complicated processes and non‐adjustability. Herein, magnetic nanoparticles assembled photothermal evaporator was developed, which showed an adjustable spinal array surface under uniform magnetic field induction. By regulating position in the magnetic field, the desirable surface structures could be uniform at relatively low load density of magnetic nanoparticles to improve light absorption via multiple reflections. Magnetic field induced evaporator could accelerate evaporation to over 1.39 kg m−2 h−1 under 1‐sun illumination, which was 2.8 times that of natural evaporation. After coated by carbon layer, magnetic nanoparticles could overcome the oxidation to realize stable evaporation in long‐term desalination. The facile strategy to optimize the surface structure via magnetic field is appropriate for various fields with special requirements on surface structure.image

Electrostatic self-assembly cellulose nanofibers/MXene/nickel chains for highly stable and efficient seawater evaporation and purification

Electrostatic self-assembly cellulose nanofibers/MXene/nickel chains for highly stable and efficient seawater evaporation and purification