Decrease In Evaporation Rate Research Articles

Evaporation of a water droplet on composite materials Cu-SiC, Cu/G and alloy AlMg3: Modeling the wettability of a metal-matrix composite with MDS

Composite materials are widely used in technology. The choice of exact composite material depends on its purpose, functional properties, stability of parameters over time, and specific conditions of use. In this work, the wettability of various materials was studied. The materials used were processed in two ways: polishing and laser texturing with and without craters. The surface wettability using molecular dynamics methods was modeled when changing the concentration of the reinforcing component in the composite. The crystalline grain orientation and surface roughness of the Cu-SiC composite after texturing is different from Cu, which is important to consider when modeling the wettability. The sensitivity of the wettability of various materials to the surface temperature (Δθ0/ΔTw) was studied experimentally. The maximum sensitivity of the contact angle to temperature was found for the superhydrophobic surface. The minimum sensitivity was observed for polished AlMg3 surface. Power-law dependences of the evaporation rate of water droplet on the contact angle were obtained for various materials in the temperature range of 25–90 °С. As the droplet diameter increases, the influence of the wetting diameter on the evaporation rate decreases, while that of convection increases. The data obtained can be useful for the development of composite materials technologies and optimization of their functional properties.

Analysis of experimental and simulation data of evaporation‐driven isotopic fractionation in unsaturated porous media

AbstractStable water isotopologs can add valuable information to the understanding of evaporation processes. The identification of the evaporation front from isotopolog concentration depth profiles under very dry soil conditions is of particular interest. We compared two different models that describe isotopolog transport in a drying unsaturated porous medium: SiSPAT‐Isotope and DuMux. In DuMux, the medium can dry out completely whereas in SiSPAT‐Isotope, drying is limited to the residual water saturation. We evaluated the impact of residual water saturation on simulated isotopic concentration. For a low residual water saturation, both models simulated similar isotopolog concentrations. For high residual water saturation, SiSPAT‐Isotope simulated considerably lower concentrations than DuMux. This is attributed to the buffering of changes in isotopolog concentrations by the residual water in SiSPAT‐Isotope and an additional enrichment due to evaporation of residual water in DuMux. Additionally, we present a comparison between high‐frequency experimental data and model simulations. We found that diffusive transport processes in the laminar boundary layer and in the dried‐out surface soil layer need to be represented correctly to reproduce the observed downward movement of the evaporation front and the associated peak of isotopolog enrichment. Artificially increasing the boundary layer thickness to reproduce a decrease in evaporation rate leads to incorrect simulation of the location of the evaporation front and isotopolog concentration profile.

Mathematical modeling of concentration influence on evaporative convection in a bilayer system of binary mixtures

A problem of evaporative buoyancy-thermocapillary convection in a two-phase system of binary media is studied. Characteristics of a joint steady flow of evaporating fluid and gas in a narrow plane horizontal channel are analyzed on the example of aqueous ethanol solution and mixture of the nitrogen with the ethanol vapor. The influence of solutal effects related to changes in the ethanol concentration in the liquid mixture is scrutinized. New exact solution of thermosolutal convection equations is constructed in the framework of a two-sided model based on the Oberbeck–Boussinesque approximation. The model used implies the presence of the liquid–gas interface admitting evaporation where surface phenomena play a key role. The testing of problem statements is performed in order to determine feasible closing relations. A correct problem statement is proposed that provides acceptable accordance with known experimental data concerning both the working liquid properties and possible pattern of the bilayer flows. Non-linear character of dependence of evaporation rate on the concentration of the aqueous solution is established. The solution predicts the decrease in evaporation rate due to the diffusion resistance effect for some compositions of the liquid mixture, thereby it is shown the possibility of control of the heat exchange parameter by means of the choice of the working fluid compound. The results obtained can be useful under developing the experimental methods for exploration of the interfacial effects in multicomponent fluids.

SiO2@MXene-based fabric featuring low heat loss for high-efficiency solar-driven freshwater production

Interfacial solar-driven steam generation is a promising approach for addressing the global freshwater crisis. However, the lower evaporation rate owing to high heat-loss is still a primary obstacle to commercialization. Given the high transmittance to solar radiation and superior isolation to thermal radiation of SiO2 aerogel, herein we design a hanging SiO2@MXene-based fabric (SMF) evaporator for high-efficiency solar-driven freshwater production. Under light irradiation, the internal MXene-based fabric with high solar absorption can rapidly convert solar radiation into heat-energy, while the outermost transparent SiO2 aerogel with excellent thermal insulation performance can efficiently prevent the internal heat-quantity from escaping outward. As such, the solar-to-thermal is well confined within the MXene-based fabric, endowing SMF with low heat loss towards surroundings. An evaporation rate as high as 1.87 kg•m−2•h−1 along with heat-loss as low as 5.9% is achieved under 1-sun, superior to other prior evaporators. Better yet, neither a decrease in evaporation rate nor fouling on SMF is observed even when treating high-salinity brine. This work provides new insights into reducing heat loss to enhance evaporation rate during solar desalination.

Dependence on relative humidity in the formation of reactive oxygen species in water droplets

Water microdroplets (7 to 11 µm average diameter, depending on flow rate) are sprayed in a closed chamber at ambient temperature, whose relative humidity (RH) is controlled. The resulting concentration of ROS (reactive oxygen species) formed in the microdroplets, measured by the amount of hydrogen peroxide (H2O2), is determined by nuclear magnetic resonance (NMR) and by spectrofluorimetric assays after the droplets are collected. The results are found to agree closely with one another. In addition, hydrated hydroxyl radical cations (•OH-H3O+) are recorded from the droplets using mass spectrometry and superoxide radical anions (•O2-) and hydroxyl radicals (•OH) by electron paramagnetic resonance spectroscopy. As the RH varies from 15 to 95%, the concentration of H2O2 shows a marked rise by a factor of about 3.5 in going from 15 to 50%, then levels off. By replacing the H2O of the sprayed water with deuterium oxide (D2O) but keeping the gas surrounding droplets with H2O, mass spectrometric analysis of the hydrated hydroxyl radical cations demonstrates that the water in the air plays a dominant role in producing H2O2 and other ROS, which accounts for the variation with RH. As RH increases, the droplet evaporation rate decreases. These two facts help us understand why viruses in droplets both survive better at low RH values, as found in indoor air in the wintertime, and are disinfected more effectively at higher RH values, as found in indoor air in the summertime, thus explaining the recognized seasonality of airborne viral infections.

Directional drying of a colloidal dispersion: quantitative description with water potential measurements using water clusters in a poly(dimethylsiloxane) microfluidic chip.

We have developed a poly(dimethylsiloxane) (PDMS) microfluidic chip to study the directional drying of a colloidal dispersion confined in a channel. Our measurements on a dispersion of silica nanoparticles once again revealed the phenomenology commonly observed for such systems: the formation of a porous solid with linear growth in the channel at short times, slowing down at longer times as the evaporation rate decreases. The growth of the solid is also accompanied by mechanical stresses that are released by the delamination of the solid from the channel walls and the formation of cracks. In addition to these observations, we report original measurements using hydrophilic filler in the PDMS formulation used (Sylgard-184). When the PDMS matrix is in contact with water, water molecules pool around these hydrophilic sites, resulting in the formation of microscopic water clusters whose size depends on the water potential ψ. In our work, we have used these water clusters to estimate the water potential profile in the channel as the porous solid grows. Using a transport model that also takes into account solid delamination in the channel, we then linked these water potential measurements to the hydraulic permeability of the porous solid. These measurements finally enabled us to show that the slowdown in the evaporation rate is due to the invasion of the porous solid by air/water nanomenisci at a critical capillary pressure ψcap.

Distribution-according-to-work: Enhancing solar vapor generation of photothermal sponge by using cellulose-based water storage platform

Interfacial solar vapor generation (ISVG) has shown extraordinary promise in achieving high-efficiency water purification. However, the rapid water supply often leads to excessive water in the solar absorber, resulting in undesired heat loss and a decrease in evaporation rate. To tackle this issue, we developed a bio-based solar evaporator comprising cellulose-based water retention resin (CRR) and straw-derived photothermal sponge. CRR serves as an effective water storage platform with a high binding capacity for water molecules, preventing water from entering the absorber and reducing the water evaporation enthalpy. The water management of CRR confines the solar-to-vapor conversion to the interface between CRR and the photothermal sponge, thereby eliminating the adverse effects of excess water. Additionally, the ISVG process operates based on the principle of Distribution-according-to-work, meaning that the quantity of generated vapor depends on the evolution of the sponge structure. Optimal sponge configuration enables evaporation rates of 2.28 and 1.53 kg/m2/h under solar irradiation of 1.0 and 0.5 kW/m2, respectively. Additionally, the obtained evaporator is capable of producing 7.1 kg/m2/day of freshwater in outdoor experiment. This report proposes a novel approach to designing an ISVG device that incorporates effective water management strategy for achieving high-efficiency water purification in real-world scenarios.

Multi-Functional Janus Hollow Solar Evaporator Based on Copper Foam for Non-Contact High-Efficiency Solar Interfacial Distillation.

As a sustainable, clean, and friendly technology with a minimal carbon footprint when treating seawater or wastewater, interfacial solar vapor generation (ISVG) technology is a great alternative to traditional desalination and water purification methods (e.g., reverse osmosis and ultrafiltration). So far, it presents tremendous potential for applications in realizing desalination of seawater or brine, wastewater treatment, and so forth. However, the precipitated salt particles during conventional ISVG inevitably block the evaporator surface, resulting in the degradation of photothermal conversion and decrease of evaporation rate. Herein, a multi-functional non-contact Janus hollow evaporator based on copper foam was prepared, which was assembled by a hydrophobic light-to-heat conversion layer and a hydrophilic interfacial water evaporation layer as two separate parts. Accordingly, the precipitated salt in the ISVG system does not block the photothermal interface, increasing the stability of solar capture and reusability of the evaporator. Notably, the hollow structure of the evaporator has a local interfacial heating effect, endowing the evaporation system with a high seawater evaporation rate of 2.249 kg m-2 h-1. The evaporator is capable of stable operation for 10 h under 1 sun illumination even when evaporating concentrated brine (15 wt %). Moreover, the evaporation rate of water under one sun irradiation reached 2.284 kg m-2 h-1 and the solar-to-vapor efficiency reached 96.6%. Not only that, the evaporator was able to successfully purify wastewater containing dyes and heavy metal ions. The multi-functional Janus hollow interfacial solar evaporator will provide inspiration for upcoming research on the production of safety water.

A Lotus‐Petiole‐Inspired Hierarchical Design with Hydrophilic/Hydrophobic Management for Enhanced Solar Water Purification

AbstractSolar‐driven vapor generation offers an affordable and sustainable approach to solve global freshwater scarcity. Creating interfacial solar evaporators capable of increasing water production rates matching human water requirements is highly desirable but challenging due to the slow water transportation dynamics and unavoidable oil‐fouling. Herein, a bio‐inspired lotus‐petiole‐mimetic microstructured graphene/poly(N‐acryloyl glycinamide) solar evaporator with integrated hydrophilic and hydrophobic microregions is developed. Through accurate control of the supramolecular interactions, the optimized solar evaporator incorporating unique structural features and wettability shows high light harvesting, enhanced water activation, and reduced energy demand for water vaporization, enabling a groundbreaking comprehensive performance along evaporation rate up to 3.4 kg m−2 h−1 and energy conversion efficiency of ≈93% under one sun irradiation (1 kW m−2). Molecular dynamics simulations reveal that the abundant hydrogen bonding sites of the polymeric networks can thermodynamically modulate the escape behavior of water molecules. Notably, neither decrease in evaporation rate nor fouling on solar evaporators is observed during the prolonged purification process toward nano/submicrometer emulsions, oily brines, actual seawater, and domestic wastewater. This study provides distinctive insights into water evaporation behaviors at a molecular level and pioneers a rational strategy to design high‐yield freshwater‐generation systems for wastewater containing complex contaminants.

Lattice Boltzmann simulation of surface evaporation in porous media

In this study, the phase-change lattice Boltzmann method was used to simulate the evaporation phenomenon on the surface of a porous medium. A new wetting boundary scheme was proposed to consider the surface wettability. The effect of surface wettability on the evaporation in the porous medium was studied. It is found that when the porous medium is hydrophilic, the surface evaporation rate can be increased by reducing the contact angle of the porous media skeleton. However, as the contact angle of the skeleton decreases, the benefit of decreasing the contact angle to improve the evaporation rate decreases.

Better understanding of solar water evaporation systems using a biosourced foam and its modelling

• A water evaporation model is validated using a tannin foam. • Material’s light absorption, water diffusion and thickness are modelled. • Insufficient water transport to the surface decreases evaporation by 40%. • Insulating the exterior wall increases evaporation by 4%. • Hot and dry climates have the highest water evaporation potential. A two-dimensional axisymmetric finite element model of a solar evaporator based on a tannin foam has been developed using COMSOL Multiphysics. This model includes a set of boundary conditions and mass transfer within the porous structure. Experiments were conducted to validate the model as the parameters changed over time. Using the model, the effects of light absorption at the surface, water diffusion inside the material, and the thickness of the material and the insulating wall were investigated. We showed that a 38% decrease in evaporation rate was observed when water diffusion does not allow sufficient transport of water to the surface. In addition, an increase in light absorption from 0.8 to 0.9 increases the evaporation performance by 12% and insulation of the exterior does not yield significant changes. A final section of the article focuses on the temporal evolution of water evaporation in several locations around the world. We concluded that hot and dry climates have the highest evaporation potential. Among the cities studied, the highest theoretical evaporation for this biosourced foam was predicted for Dubai, 5342 kg·m −2 , followed by Cairo, 4723 kg·m −2 .

Honeycomb-structured fabric with enhanced photothermal management and site-specific salt crystallization enables sustainable solar steam generation

The emerging of solar-driven interfacial evaporation provides new opportunities to alleviate the shortage of fresh water resource. Nevertheless, in practical solar desalination, salt precipitation will lead to the decrease of evaporation rate due to reduced light absorption and blocked evaporation channels of evaporator. It still remains a challenge to eliminate salt accumulation and simultaneously maintain high-efficient evaporation. In this work, a solar evaporator was prepared based on reduced graphene oxide and chitosan coated honeycomb-structured fabric (rCHF). The rCHF showed a high light absorbance of 97.2% due to enhanced light trapping of the honeycomb structure and ultra-low thermal conductivity of 0.044 W m−1 K−1. Furthermore, the temperature gradient generated inside the honeycomb unit can induce the Marangoni effect, which led to the site-specific salt crystallization on rCHF in seawater evaporation. As a result, the rCHF realized an excellent solar evaporation rate of 2.02 kg m-2h−1 under one sun irradiation (1 kW m−2). The site-specific salt crystallization on the surface of rCHF ensured stable evaporation even in 20% brine, and the isolated salt can be removed by natural dissolution owing to the excellent hydrophilicity of rCHF. This work provides a new perspective for the design of solar evaporator for practical solar seawater desalination.

Droplet Evaporation on Hot Micro-Structured Superhydrophobic Surfaces: Analysis of Evaporation from Droplet Cap and Base Surfaces

In this study, evaporation of sessile water droplets on hot micro-structured superhydrophobic surfaces is experimentally and theoretically investigated. Water droplets of 4 µL are placed on micro-pillared silicon substrates with the substrate temperature heated up to 120°C. A comprehensive thermal circuit model is developed to analyze the effects of substrate roughness and substrate temperature on the sessile droplet evaporation. For the first time, two components of heat and mass transfer, i.e., one from the droplet cap surface and the other from the droplet base surface, during droplet evaporation are distinguished and systematically studied. As such, the evaporation heat transfer rates from both the droplet cap surface and the interstitial liquid-vapor interface between micropillars at the droplet base are calculated in various conditions. For droplet evaporation on the heated substrates in the range of 40°C – 80°C, the predicted droplet cap temperature matches well with the experimental results. During the constant contact radius mode of droplet evaporation, the decrease of evaporation rate from the droplet base contributes most to the continuously decreasing overall evaporation heat transfer rate, whereas the decrease of evaporation rate from the droplet cap surface is dominant in the constant contact angle mode. The influence of internal fluid flow is considered for droplet evaporation on substrates heated above 100°C, and an effective thermal conductivity is adopted as a correction factor to account for the effect of convection heat transfer inside the droplet. Temperature differences between the droplet base and the substrate base are estimated to be about 2°C, 5°C, 8°C, 13°C and 18°C for droplet evaporation on substrates heated at 40°C, 60°C, 80°C, 100°C, and 120°C, respectively, elucidating the delayed or depressed boiling of water droplets on a heated rough surface due to evaporative cooling.

Effect of Relative Humidity on the Thickness of Assembled Silica Colloidal Crystal Films.

In order for the colloidal crystal films to be better applied, the influence of relative humidity on the preparation of silica colloidal crystal (SCC) films was systematically studied to solve the problem of different thicknesses of SCC films prepared by different batches under the conditions with the same temperature, concentration of suspension and diameter of the particles. SCC films with 190 nm particles were prepared by static vertical deposition method under different humidity regulated by saturated salt solutions, and the thickness of the films was obtained by an interferometric method. The results showed that the increase in humidity would reduce the thickness of the prepared films, which was believed to be caused by the decrease in evaporation rate after the wetting film absorbs water vapor. A new formula for calculating film thickness was proposed and verified from a series of experiments. With the control of humidity, high-quality SCC films with controlled thickness can be repeatedly prepared.

Volatile organic compounds enhancing sulfuric acid-based ternary homogeneous nucleation: The important role of synergistic effect

Abstract New particle formation (NPF) is an important source of atmospheric aerosols. Sulfuric acid (SA) and water (W) are recognized as essential participating substances in the nucleation of the atmosphere. In addition, as one of the most common organic acids, oxalic acid (OA) can improve NPF when amine such as methylamine (MA) is present. However, exploring the properties of atmospheric particles made up of different components is challenging and the role of volatile organic compounds in SA–based ternary homogeneous nucleation is still lacking in research. In this work, the structures and energies of (SA)x(OA)y(MA)z(W)m (0 ≤ x, y, z ≤ 3, 0 ≤ m ≤ 1) are investigated. The results indicate that it is accessible for SA to form clusters with OA and MA molecules through hydrogen bonds and proton transfer interactions. The analysis of non–covalent interactions and proton transfer reveals that ternary nucleation systems have stronger hydrogen bonds and more proton transfers than binary systems to stabilize the clusters. In terms of the thermodynamic properties, the Gibbs free energies of the clusters will decrease as the addition of SA, OA or MA molecules indicating that the synergistic effect of these three substances may be of potential in forming the initial cluster and subsequent growth processes. Moreover, the evaporation rates of clusters show that the synergistic effect of ternary clusters leads to a decrease in evaporation rate which may promote atmospheric nucleation.

Pore-scale study of thermal fields during evaporation from drying porous surfaces

The drying of a porous surface and subsequent pore emptying resemble a sequence of drainage whereby pores are invaded according to their respective capillary size (large pores are invaded first). The emptying of pores modifies both the local evaporative fluxes and surface thermal fields adjacent to invaded pores. These local adjustments could result in a gradual decrease in evaporation rate and a potential increase in surface temperature thereby altering energy partitioning over the drying surface as described by the Pore-scale Coupled Energy Balance (PCEB) model of Aminzadeh and Or (2014). This study aims to observe and quantify these dynamic pore-scale mass and energy interactions to test key assumptions in the basis of the PCEB model and gain new insights into these important processes. We used a novel experimental system consisting of individual and clustered evaporating pores drilled into rough glass surfaces. Thermal fields around individual evaporating pores and their interactions were observed using highly resolved infrared imager under different radiative fluxes. Thermal observations and direct measurements of evaporative fluxes were in good agreement with predictions by the PCEB model. Drying of a glass beads surface was captured by optical and thermal imaging to provide links between pore emptying sequence and surface thermal adjustments. The results highlight the upscalability of pore-based representation of surface drying and the predictability of energy partitioning over drying porous surfaces.

Enhanced gas barrier and mechanical properties in organoclay reinforced multi-layer poly(amide-imide) nanocomposite film

Multifunctional single and triple-layer films exhibiting flexibility, enhanced modulus and gas barrier properties were developed using a soluble polyamide-imide (PAI) in dimethylacetamide (DMAc) with ammonium-modified montmorillonite (MMT, Cloisite 30B) mineral clay. The drying behavior and associated anisotropy development were determined real-time, using a newly developed real-time measurement system. Out-of-plane birefringence development takes place earlier for thinner neat samples caused primarily by increased depletion rate of solvent. Addition of organoclay content resulted in a decrease in evaporation rate of solvent due to planar orientation of well exfoliated nanoplatelets as shown by TEM images and WAXS. This is in agreement with the out-of-plane anisotropy development observed during drying. Beyond a critical solid wt%, out-of-plane birefringence started to increase earlier with organoclay addition. In the case of multi-layer organoclay reinforced PAI films, the drying behavior of each individual layer was tracked and a complementary drying model is proposed. Planar orientation of nanoplatelets resulted in high helium-barrier properties.

Numerical study of non-uniform magnetic fields effects on subcooled nanofluid flow boiling

The main goal of the present work is to investigating the effect of non-uniform axial magnetic field with positive and negative gradients on subcooled nanofluid flow boiling. Also, for better understanding the existing phenomena, single-phase convection has been studied in the first part. Control volume technique for discretizing the governing equations, SIMPLEC algorithm for pressure-velocity coupling, and SST k-ω model for turbulent flow have been used in this research, respectively. In the second part, a three dimensional two-fluid model is used to subcooled flow boiling and the available R-113 boiling experimental data are used to validate the results. The obtained results indicate that single-phase convection as well as subcooled flow boiling characteristics change not only by using nanofluid as a working fluid, but also by applying the non-uniform axial magnetic field. For the case of magnetic field with negative gradient, single-phase convection heat transfer rate increases. Also for the subcooled boiling flow, negative magnetic field gradient will lead to increase critical heat flux (CHF), due to the decrease in evaporation rate in the wall surface which is eventually responsible for wall dryout. As a result, a more safe operation condition of the industrial equipments can be achieved.

Nanofluid pendant droplet evaporation: Experiments and modeling

Nanofluids, stable colloidal suspensions of nanoparticles in a base fluid, have potential applications in the heat transfer, combustion and propulsion, manufacturing, and medical fields. Experiments were conducted to determine the evaporation rate of room temperature, millimeter-sized pendant droplets of ethanol laden with varying amounts (0–3% by weight) of 40–60nm aluminum nanoparticles (nAl). Time-resolved high-resolution droplet images were collected for the determination of early-time evaporation rate (D2/D02>0.75), shown to exhibit D-square law behavior, and surface tension. Results show an asymptotic decrease in droplet evaporation rate with increasing nAl loading. The evaporation rate decreases by approximately 15% at around 1–3% nAl loading relative to the evaporation rate of pure ethanol. Surface tension was observed to be unaffected by nAl loading up to 3% by weight. A model was developed to describe the evaporation of the nanofluid pendant droplets based on D-square law analysis for the gas domain and a description of the reduction in liquid fraction available for evaporation due to nanoparticle agglomerate packing near the evaporating droplet surface. Model predictions are in relatively good agreement with experiment, within a few percent of measured nanofluid evaporation rate.

A Rayleigh-Plesset based transport model for cryogenic fluid cavitating flow computations

The present article focuses on modeling issues to simulate cryogenic fluid cavitating flows. A revised cavitation model, in which the thermal effect is considered, is derivated and established based on Kubota model. Cavitating flow computations are conducted around an axisymmetric ogive and a 2D quarter caliber hydrofoil in liquid nitrogen implementing the revised model and Kubota model coupled with energy equation and dynamically updating the fluid physical properties, respecitively. The results show that the revised cavitation model can better describe the mass transport process in the cavitation process in cryogenic fluids. Compared with Kubota model, the revised model can reflect the observed “frosty” appearance within the cavity. The cavity length becomes shorter and it can capture the temperature and pressure depressions more consistently in the cavitating region, particularly at the rear of the cavity. The evaporation rate decreases, and while the magnitude of the condensation rate becomes larger because of the thermal effect terms in the revised model compared with the results obtained by the Kubota model.