Conventional Evaporators Research Articles

Three-Dimensional Double-Layer Multi-Stage Thermal Management Fabric for Solar Desalination.

Water scarcity is a serious threat to the survival and development of mankind. Interfacial solar steam generation (ISSG) can alleviate the global freshwater shortage by converting sustainable solar power into thermal energy for desalination. ISSG possesses many advantages such as high photothermal efficiency, robust durability, and environmental friendliness. However, conventional evaporators suffered from huge heat losses in the evaporation process due to the lack of efficient thermal management. Herein, hydrophilic Tencel yarn is applied to fabricate a three-dimensional double-layer fabric evaporator (DLE) with efficient multi-stage thermal management. DLE enables multiple solar absorptions, promotes cold evaporation, and optimizes thermal management. The airflow was utilized after structure engineering for enhanced energy evaporation efficiency. The evaporation rate can reach 2.86 kg·m-2·h-1 under 1 sun (1 kW·m-2), and 6.26 kg·m-2·h-1 at a wind speed of 3 m·s-1. After a long duration of outdoor operation, the average daily evaporation rate remains stable at over 8.9 kg·m-2, and the removal rate of metal ions in seawater reaches 99%. Overall, DLE with efficient and durable three-dimensional multi-stage thermal management exhibits excellent practicality for solar desalination.

Superelastic Polymer Aerogel with Superamphiphilicity.

Elastic aerogels have become a research hot spot in both academia and industry recently. The reported elastic aerogels are all made of hard materials by controlling their shapes. Herein we report an elastic aerogel made of a polymer elastomer with entropy elasticity. In the aerogel, cross-linked carboxyl nitrile rubber nanoparticles with hydrophilicity are dispersed in hydrophobic derivative of styrene-maleic anhydride alternating copolymer, forming a very special micro-nano surface structure with hydrophilic protrusions and hydrophobic depressions on the aerogel wall; therefore, the aerogel is not only superelastic but also superamphiphilic. A leak-free phase-change composite was prepared using the aerogel and paraffin, which can maintain at phase change temperature of paraffin for a longer time than the traditional one. The aerogel is also extremely suitable for desalination evaporators in solar-driven interfacial evaporation technology due to its superamphiphilicity, superelasticity, and ability to absorb sunlight. Exceptional evaporation rate of 2.78 kg·m-2·h-1 and evaporation efficiency of 170% could be reached even without using expensive light-absorbing materials. The evaporation rate exceeds that of most evaporators with expensive light-absorbing materials, and the evaporation efficiency exceeds the theoretical limit of conventional 2D solar evaporators. Both the phase-change composite and the evaporator can be easily recovered because the novel superelastic aerogel reported in this work is also recyclable.

Quasi-waffle solar distiller for durable desalination of seawater.

Water purification via interfacial solar steam generation exhibits promising potential. However, salt crystallization on evaporators reduces solar absorption and obstructs water supply. To address it, a waffle-shaped solar evaporator (WSE) has been designed. WSE is fabricated via a zinc-assisted pyrolysis route, combining low-cost biomass carbon sources, recyclable zinc, and die-stamping process. This route enables cost-effective production without the need of sophisticated processing. As compared to conventional plane-shaped evaporators, WSE is featured by extra sidewalls for triggering the convection with the synergistic solute and thermal Marangoni effects. Consequently, WSE achieves spontaneous salt rejection and durable evaporation stability. It has demonstrated continuous operation for more than 60 days in brine without fouling.

Solar-driven abnormal evaporation of nanoconfined water.

Intrinsic water evaporation demands a high energy input, which limits the efficacy of conventional interfacial solar evaporators. Here, we propose a nanoconfinement strategy altering inherent properties of water for solar-driven water evaporation using a highly uniform composite of vertically aligned Janus carbon nanotubes (CNTs). The water evaporation from the CNT shows the unexpected diameter-dependent evaporation rate, increasing abnormally with decreasing nanochannel diameter. The evaporation rate of CNT10@AAO evaporator thermodynamically exceeds the theoretical limit (1.47 kg m-2 hour-1 under one sun). A hybrid experimental, theoretical, and molecular simulation approach provided fundamental evidence of different nanoconfined water properties. The decreased number of H-bonds and lower interaction energy barrier of water molecules within CNT and formed water clusters may be one of the reasons for the less evaporative energy activating rapid nanoconfined water vaporization.

Downward design of solar-driven interfacial evaporators: Beyond the limitation of vertical water delivery in conventional upward evaporators

Solar-driven interfacial evaporation (SIE) represents a promising approach for freshwater production that eliminates the need for fossil fuel inputs. One of the primary objectives of SIE is to achieve a high evaporation rate. To enhance SIE performance, it is advantageous to increase the height of the evaporators, as this expands the evaporating interface. However, many existing evaporators face limitations in water delivery due to the competition between gravity and capillary forces. In this study, we propose a downward design strategy that mitigates this competition, resulting in a larger evaporating interface and higher evaporation rate. Through our experimental setup, we achieved an impressive evaporation rate of 2.01 kg·m−2·h−1 using the downward evaporator, which is 46.7% higher than that of the upward evaporator. When applied to desalination, downward evaporators exhibit excellent anti-salt performance, owing to an ample water supply, thereby enabling prolonged operation without a decline in evaporation rate or observable salt precipitation, even under 2.0-sun illumination. Furthermore, we demonstrate that the downward design strategy allows water bodies, rather than air, to serve as the cold source for condensation, enabling the attainment of a higher temperature gradient and enhanced vapor condensation. We achieved a notable water harvesting rate of 0.76 kg·m−2·h−1 under 1.0-sun irradiation.

Two-stage evaporator for R744 heat pumps using greywater as heat source

Heat pumps are pinpointed as a key technology in decarbonizing buildings' heat supply, which is currently dominated by fossil-fuel based systems. To minimize the environmental impact of heat pumps over their lifetime, selecting natural working fluids (refrigerants) is the only viable long-term choice. Independent of the refrigerant, the efficiency of a heat pump is closely linked to temperature of the applied heat source, and to this end, wastewater is a promising candidate that is abundant in all urban environments. This experimental study investigates a novel two-stage, ejector-supported, brazed plate evaporator for its use in R744 (CO2) heat pumps with greywater as a heat source and compares it to more conventional evaporators. The work shows that splitting the evaporation process in two stages with an ejector in between allows reducing the evaporation pressure while the compressor suction pressure can be increased, in some cases significantly. Even if several possibilities for further optimization of the novel two-stage evaporator were identified, the results show heat pump efficiency improvements above 10% compared to an equivalent heat pump with a well-performing one-stage evaporator. Heat pump systems aiming at utilizing maximum temperature difference for the greywater should use a high pressure lift ejector.

Ion-Transfer Engineering via Janus Hydrogels Enables Ultrahigh Performance and Salt-Resistant Solar Desalination.

Emerging solar interfacial evaporation offers the most promising response to the severe freshwater crisis. However, the most challenging bottleneck is the conflict between resisting salt accumulation and maintaining high evaporation performance since conventional salt-resistant evaporators enhance water flow to remove salt, leading to tremendous heat loss. Herein, an ion-transfer engineering is proposed via a Janus ion-selective hydrogel that enables ion-electromigration salt removal, breaking the historical dependence on water convection, and significantly lowering the heat loss. The hydrogels drive cations downward and anions upward, away from the evaporation surfaces. An electrical potential is thus established inside the evaporator and salt in 15wt% brine is removed stably for seven days. A record-high evaporation rate of 6.86 kg m-2 h-1 in 15wt% brine, 2.5times the previously reported works, is achieved. With the from-scratch salt-resistant route, comprehensive water-thermal analysis, and record-high performance, this work holds great potential for the future salt-resistant evaporators.

Highly Efficient, Antibacterial, and Salt-Resistant Strategy Based on Carbon Black/Chitosan-Decorated Phase-Change Microcapsules for Solar-Powered Seawater Desalination.

Solar-powered interfacial evaporation has been recognized to be a promising and sustainable technology for seawater desalination, in view of the challenge of freshwater scarcity and fossil energy storage. Nevertheless, current cutting-edge interfacial evaporation systems mostly ignore the issues of intermittent solar irradiation and bacterial contamination. We have hereby developed a novel type of an interfacial evaporator equipped with carbon black (CB)/chitosan (CS)-decorated phase-change microcapsules as a multifunctional photothermal material for solar-powered seawater desalination, based on a highly efficient, antibacterial, and salt-resistant multipurpose strategy. In the developed microcapsules, an n-docosane phase-change material (PCM) core was engulfed in a TiO2 shell, followed by surface decorating a CB/CS nanocomposite layer. A high thermal energy-storage capacity of more than 140 J g-1 was achieved, thanks to tight sealing of n-docosane as a PCM core in the perfect core-shell structured microcapsules. Moreover, a rational combination of CS and CB nanoparticles not only contributes an extremely high solar absorption efficiency of 95.04% and good wettability to the as-synthesized microcapsules, but also imparts outstanding antibacterial and salt-resistant abilities to them. These innovative designs enable the developed evaporator to gain a high evaporation rate of 2.58 kg m-2 h-1, along with an evaporation efficiency higher than 90% for consecutive and stable evaporation of seawater under intermittent solar illumination. Compared to conventional evaporators without a PCM, there is an increase by 1.03 kg m-2 in the total water production of the develop evaporator under natural solar illumination for 8 h on a semicloudy day. The resultant evaporated water presents good vegetation compatibility to meet the requirement of crop growth for agricultural cultivation. This work provides a new pathway for designing and developing the high-performance interfacial evaporators with prominent antibacterial and salt-resistant abilities to produce purified water through solar-powered sustainable seawater desalination.

Wormlike Perovskite Oxide Coupled with Phase‐Change Material for All‐Weather Solar Evaporation and Thermal Storage Applications

Interfacial solar‐driven water evaporation has shown promising prospects in desalination technology. However, the lower photothermal conversion efficiency caused by the intermittent nature of sunlight and salt accumulation remains a significant challenge for continuous desalination. Herein, the hierarchical design of interfacial solar evaporation is reported, which realizes enhanced photothermal conversion, waste heat storage/release, and effective thermal management for continuous desalination. The solar evaporator is composed of worm‐like SrCoO3 perovskite oxide anchored on super hydrophilic polyurethane (PU) foam succeeded by in situ polymerization of conducting polypyrrole (SrCoO3@PPy). The energy storage system is introduced within polyurethane matrix by a paraffin block followed by a tongue‐and‐groove structure for convective water transportation, and a heat recovery unit largely reduces heat losses. The solar evaporator possesses excellent evaporation rates (2.13 kg m−2 h−1) along with 93% solar‐to‐vapor conversion efficiency under 1 kw m−2 solar irradiation owing to its minimum equivalent evaporation enthalpy and (0.85 kg m−2 h−1) under intermittent solar irradiation as compared to conventional solar evaporators. More importantly, state‐of‐the‐art experimental investigations validate waste heat recovery/release and the salt‐resistant capability of solar evaporators optimized by computational fluid dynamic simulation. This study breaks conventional solar interfacial evaporation's limitations and demonstrates stable desalination under intermittent sunlight.

MXene-decorated magnetic phase-change microcapsules for solar-driven continuous seawater desalination with easy salt accumulation elimination

Solar-driven interfacial evaporators provide a powerful means for rapid wastewater purification and seawater desalination. However, there is still an immense challenge in interfacial evaporators with efficient energy utilization and long-term evaporation stability due to intermittent solar illumination and salt accumulation. To address these issues, we developed a novel type of interfacial evaporator based on the microencapsulated n-tetracosane and n-eicosane as twin phase-change material (PCM) cores with a SiO2/Fe3O4 composite shell along with a surface-coated polypyrrole layer and surface-decorated MXene nanosheets. The resultant microcapsules act as both a solar absorber and a latent-heat storage material for sustainable evaporation of seawater. Benefiting from a rational combination of PCMs and solar absorbers, the evaporator based on the microcapsules achieved a high light absorption efficiency of 95.4 % together with evaporation rates of 2.04 and 4.11 kg·m−2·h−1 under 1.0-sun and 2.0-sun illumination, respectively. Owing to the photothermal energy released by the PCM cores, the developed evaporator exhibits a consecutive and stable evaporation behavior even without solar illumination. Compared to conventional evaporators without a PCM, there is an increase by 0.45 kg·m−2 in the yield of the distilled water obtained from the developed evaporator under 2.0-sun illumination and then in the dark environment. Based on magnetic Fe3O4 nanoparticles in the silica-matrix shell, the separability of the microcapsules from the accumulated salt crystals was improved through simple washing and magnetic separation. Through an innovative integration of magnetic phase-change microcapsules and solar absorbers, this study will provide a new idea and promising approach for the sustainable evaporation system design based on solar energy utilization for applications of seawater desalination and wastewater treatment.

Janus Biopolymer Sponge with Porous Structure Based on Water Hyacinth Petiole for Efficient Solar Steam Generation.

Solar-driven steam generation for desalination is a facile, sustainable, and energy-saving approach to produce clean freshwater. However, the complicated fabrication process, high cost, potential environmental impact, and salt crystallization of conventional evaporators limit their large-scale application. Herein, we present a sustainable Janus evaporator based on a biopolymer sponge from the water hyacinth petiole (WHP) for high-performance solar steam generation. The freeze-dried WHP maintained its original porous structure and aligned channels well, and therefore holds the capability for rapid water transport due to strong capillary action. The WHP coated with carbon nanotubes/ethyl cellulose paste on its surface (WHP-C) gains a good photothermal property, thus achieving an efficient solar steam generation with a rate of 1.50 kg m−2 h−1 under 1 sun irradiation. Moreover, the WHP-C after hydrophobic modification by fluorocarbon (WHP-CH) is endowed with high water repellency and exhibits good salt resistance during long-term solar desalination. Additionally, we demonstrate that a stable wet surface that enables efficient water supply and vapor escape is also significant to the successive desalination of a solar evaporator. Our work provides new insights into the high-value utilization of biomass waste, i.e., water hyacinth, and the development of sustainable interfacial solar evaporators for the environmentally friendly production of freshwater.

Emulsion‐templated synthesis of 3D evaporators for efficient solar steam generation

AbstractInterfacial solar steam generation holds great promise in water desalination thanks to its high energy efficiency by heating only the top layer of water for evaporation. While three‐dimensional (3D) evaporators have been proven to increase the evaporation rate by harnessing the energy from the surroundings, further development is still required in terms of convenient fabrication with potential scalability. Herein, we propose to overcome this challenge by using a high internal phase emulsion (HIPE) to template the synthesis of 3D hierarchically porous evaporators. The HIPE‐templated synthesis combined with a molding process can efficiently fabricate the desired 3D shape without wasting any materials and generate a hierarchically porous internal structure for continuous water supply. Engineering the overall shape and internal pores produces a 3D evaporator that can suppress conduction heat loss and efficiently collect thermal energy from its surroundings, boosting the evaporation rate to 2.82 kg/(m2 h) under 1‐sun illumination, which is significantly higher than conventional 2D evaporators. HIPE‐templating synthesis is an easy but effective way to produce various porous polymers, promising for a wide range of applications where easy production, excellent shape control, and potential scalability are critical.

Evaporator Performance for Water Refrigerant Adsorption Cooling System

Adsorption Cooling System gives an alternative to the commercial vapor compression refrigeration cycles due to their benefits of having a very environmentally friendly and promising energy-saving system. An adsorption cooling system consists of four main components which are thecondenser, evaporator, expansion valve, and adsorption bed for the system to effectively function. One of the factors that affect the efficiency of the system is the performance of the evaporator itself as the system operates at sub-atmospheric pressure and the performance is mediocre when using conventional evaporators. Due to the low-pressure condition, hydrostatic pressure may affect the saturated temperature of the water refrigerant in a flooded type evaporator. Therefore, in this study, the performance of the evaporator was investigated based on the water height variation. The highest heat transfer coefficient and evaporation heat transfer rate are achieved when the water is set at the heat exchanger tube diameter level. Furthermore, 0.1 kg of silica gel adsorbent is used to obtain the maximum of 250 W/kg of Specific Cooling Power when the heat transfer fluid is set to 20 ºC.

Hyperstable and compressible plant fibers/chitosan aerogel as portable solar evaporator

Solar interfacial evaporation is an effective zero-energy method for seawater desalination, and solar evaporator is the key component in this evaporation system. Despite a great deal of solar evaporators have been reported, the poor portability of large-scale evaporators as well as high costs and materials toxicity still restrict their applications. In this work, a portable solar evaporator was constructed with low-cost plant fibers from papermaking pulp, using a facile method in absence of any toxic cross-linkers and solvents. The evaporator exhibited excellent stability and flexibility, and endured tremendous and repeated compression over 100 times. A large-scale evaporator could be compressed to reduce storage space by 78%, which would be portable for individuals. The evaporator presented a high evaporation rate of 1.38 kg m-2h−1, and solar-to-vapour conversion efficiency of 84.27% under one sun irradiation. The portable solar evaporator was salt-rejecting, and worked well under harsh conditions of high salinity and different pH values. The entire material cost of this potable solar evaporator is approximately 1.75 U.S. dollar m−2, much lower than those of conventional solar evaporators. This study provides a new approach for preparing portable and cost-effective solar evaporator.

Improving marshmallow production technology by adding the fruit and vegetable paste obtained by low-temperature concentration

A formulation composition and a low-temperature technique have been devised for concentrating fruit and vegetable puree with the following component content: 20 % apple; 20 % pumpkin; 15 % beets; 15 % cranberries; 15 % hawthorn. The puree is concentrated in a rotary evaporator to a solids content of 50 % at a temperature of 50...56 °C under vacuum. The processing time was reduced to 1...2 min, which is several times less compared to conventional single-case pump vacuum evaporators (60...90 mins). Reducing the temperature influence of concentrating contributes to an increase in the organoleptic and physicochemical parameters of the resulting paste. To determine the effect of the contribution of each component to the structure of the paste, the structural and mechanical properties of the puree from each raw material and concentrated semi-finished products were investigated. The devised paste has an increased strength of the structure with a dynamic viscosity value of 394 Pa⋅s, which is 2.5 times more than that in the control sample. The devised blended fruit and vegetable paste has an increased content of physiologically functional ingredients and good organoleptic parameters, unlike control (apple paste). It was established that the partial replacement of apple puree in the formulation composition of marshmallow with 75 % of the devised multicomponent fruit and vegetable paste gives the product original properties. The dynamic viscosity value of the marshmallow in which 75 % of apple puree was replaced with the devised paste has increased, compared to the control sample (marshmallow without additives), from 408 Pa⋅s to 908 Pa⋅s. The color of the marshmallow mass where 75 % of apple puree were replaced is bright pink with a wavelength of 596.7 nm and a brightness of 62.3 %. The data reported here make it possible to improve the quality of original marshmallow products when adding fruit and vegetable semi-finished products whereby an increase in functional properties is provided

Evaporation rate far beyond the input solar energy limit enabled by introducing convective flow

Solar-driven interfacial evaporation for desalination is regarded as one of the most promising technologies to relieve global freshwater scarcity due to its high efficiency, sustainability and low cost. However, the evaporation rate, as one of the decisive factors of the throughput of evaporative water, has been severely restricted due to heat loss and insufficient vapor diffusion in the conventional evaporators. Herein, we demonstrate that a carbon nanotubes (CNTs) and airlaid paper-based 3D wavy evaporator not only facilitates the double-surface evaporation, but also can effectively diffuse the suspended vapor assisted by the convective flow, so as to reverse the heat loss and continuously harvest additional energy for efficient evaporation. An evaporation rate as high as 5.55 kg m−2h−1 is achieved under one sun illumination coupled with convective flow of 5 m s−1, well beyond 278% of the input solar energy limit, presuming 100% solar-to-vapor energy conversion. More importantly, the 3D wavy evaporator can consistently evaporate for 24 h in the natural environment, with the outdoor evaporation up to 53.72 kg m−2 and no salt deposition. Furthermore, theoretical simulations of convective flow velocity and distribution, as well as relative humidity distribution, are remarkably compatible with experimental results. The realization of such a high evaporation rate provides a new inspiration for designing the around-the-clock and high-throughput evaporation system that can be practically applied.

Suspended Membrane Evaporators Integrating Environmental and Solar Evaporation for Oily Wastewater Purification

Solar-driven evaporation is promising in oily wastewater treatment, in particular for emulsions, but conventional evaporators suffer from pore blocking by residual oil or contamination by volatile oil compounds in the condensed water. In the current research, we develop a suspended membrane evaporator integrating solar evaporation with oil-in-water emulsion separation. The heating and evaporating interface is separated from the rejecting interface to avoid oil escape and improve heat management. A temperature gradient forms on the membrane surface that can promote evaporation performance by combining both solar and environmental evaporation. Such an evaporator achieves a maximum evaporation rate of 1.645 kg/(m2·h) as well as an apparent evaporation efficiency of 111.9%. Moreover, the superhydrophilic and superoleophobic membrane shows excellent oil repellence and emulsion rejection, which can achieve an oil removal efficiency above 98.8% in oil-in-water emulsion separation, and high evaporation rate recovery in cycling tests. A scaled-up membrane evaporator array produces ∼8 kg/(m2·d) of clean water from oily wastewater in outdoor experiments, further demonstrating the strong purification performance of this evaporator in oily wastewater treatment.

Aligned Millineedle Arrays for Solar Power Seawater Desalination with Site-Specific Salt Formation.

As a sustainable and clean water production technology, solar thermal water evaporation has been extensively studied in the past few years. One challenge is that upon operation, salt would form on surface of the solar absorbers leading to inefficient water supply and light absorption and thus much reduced water vaporization rate. To address this problem, a simple solar evaporator based on an array of aligned millineedles for efficient solar water evaporation and controlled site-specific salt formation is demonstrated. The maximum solar evaporation rate achieved is 2.94kg m-2 h-1 under one Sun irradiation in brine of high salinity (25wt% NaCl), achieving energy conversion efficiency of 94.5% simultaneously. More importantly, the spontaneously site-specific salt formation on the tips of millineedles endows this solar evaporator with salt harvesting capacity. Rationally separating the clean water and salt from brine by condensation and gravity assistance, this tip-preferential crystallization solar evaporator is not affected by the salt clogging compared with conventional 2D solar evaporators. This study provides new insights on the design of solar evaporators and advances their applications in sustainable seawater desalination and wastewater management.

An Easy‐to‐Fabricate 2.5D Evaporator for Efficient Solar Desalination

AbstractSolar‐driven steam generation, whereby solar energy is harvested to purify water directly, is emerging as a promising approach to mitigate the worldwide water crisis. The scalable application of conventional 3D evaporators is hindered by their complex spatial geometries. A 2.5D structure is a spatial extension of a 2D structure with an addition of a third vertical dimension, achieving both the feasibility of 2D structure and the performance of 3D structure simultaneously. Here, an interconnected open‐pore 2.5D Cu/CuO foam‐based photothermal evaporator capable of achieving a high evaporation rate of 4.1 kg m−2 h−1 under one sun illumination by exposing one end of the planar structure to air is demonstrated. The micro‐sized open‐pore structure of Cu/CuO foam allows it to trap incident sunlight, and the densely distributed blade‐like CuO nanostructures effectively scatter sunlight inside pores simultaneously. The inherent hydrophilicity of CuO and capillarity forces from the porous structure of Cu foam continuously supply sufficient water. Moreover, the doubled working sides of Cu/CuO foam enlarge the exposure area enabling efficient vapor diffusion. The feasible fabrication process and the combined structural features of Cu/CuO foam offer new insight into the future development of solar‐driven evaporators in large‐scale applications with practical durability.

Microvessel‐Assisted Environmental Thermal Energy Extraction Enabling 24‐Hour Continuous Interfacial Vapor Generation

Interfacial solar evaporators have great potential for clean water production; however, their evaporation performance relies greatly on the solar illumination condition, which is restricted by daily sunshine time and climates. Here, a wood-based vapor generator in pyramid structure is fabricated to achieve efficient water evaporation under dark condition (0 kW m-2 ) through efficient extraction of environmental thermal energy. The microvessels of wood provide fast water transportation whereas the tailored pyramid surface structure enables efficient evaporative cooling for extracting energy from the environment. The method enables fast water evaporation without the need of solar heat input. We demonstrate a vapor generation rate of up to 2.15 kg m-2 h-1 under dark condition (0 kW m-2 ), which is even 1.4 times faster than the theoretical limit of conventional solar thermal evaporators working under 1 sun (1 kW m-2 ) illumination condition. During the 24-h continuous evaporation test, the evaporator presented a daily vapor generation rate of up to 50.8 kg m-2 day-1 and 60.7 kg m-2 day-1 on cloudy and sunny day, respectively, offering a novel approach for the development of 24-h full-time water evaporators for seawater desalination and wastewater treatment.