Dynamic Evaporation Research Articles

Comparing simulated and experimental molecular cluster distributions

Formation of secondary atmospheric aerosol particles starts with gas phase molecules forming small molecular clusters. High-resolution mass spectrometry enables the detection and chemical characterization of electrically charged clusters from the molecular scale upward, whereas the experimental detection of electrically neutral clusters, especially as a chemical composition measurement, down to 1 nm in diameter and beyond still remains challenging. In this work we simulated a set of both electrically neutral and charged small molecular clusters, consisting of sulfuric acid and ammonia molecules, with a dynamic collision and evaporation model. Collision frequencies between the clusters were calculated according to classical kinetics, and evaporation rates were derived from first principles quantum chemical calculations with no fitting parameters. We found a good agreement between the modeled steady-state concentrations of negative cluster ions and experimental results measured with the state-of-the-art Atmospheric Pressure interface Time-Of-Flight mass spectrometer (APi-TOF) in the CLOUD chamber experiments at CERN. The model can be used to interpret experimental results and give information on neutral clusters that cannot be directly measured.

Removing arsenic from anode slime by vacuum dynamic evaporation and vacuum dynamic flash reduction

In crude lead or copper electrorefining, the by-product anode slime is an important material of recycling precious metals. However, the existing methods for treating arsenic-rich anode slime are less than satisfactory not only for the removal effect of arsenic but also for the environment protection. Therefore, a new technology for treating arsenic-rich anode slime was proposed in this paper, namely the two-step process of vacuum dynamic evaporation (VDE) and vacuum dynamic flash reduction (VDFR). Through this two-step process, silver from the anode slime was left behind in distilland as the silver alloy, and the trivalent oxide of arsenic was evaporated in the distillate. The experimental results showed that the removal ratio of arsenic was 99.96%. Moreover, these vacuum technologies offer improvements in metallurgical and environmental performance.

Exceptional Superhydrophobicity and Low Velocity Impact Icephobicity of Acetone-Functionalized Carbon Nanotube Films

We present a simple method to produce carbon nanotube-based films with exceptional superhydrophobicity and impact icephobicity by depositing acetone-treated single-walled carbon nanotubes on glass substrates. This method is scalable and can be adopted for any substrate, both flexible and rigid. These films have indicated a high contact angle, in the vicinity of 170°, proved both by static and dynamic analysis processes. The dynamic evaporation studies indicated that a droplet deposited on the treated films evaporated in the constant contact angle mode for more than 80% of the total evaporation time, which is definitely a characteristic of superhydrophobic surfaces. Furthermore, the acetone-functionalized films showed a strong ability to mitigate ice accretion from supercooled water droplets (-8 °C), when the droplets were found to bounce off the films tilted at 30°. The untreated nanotube films did not indicate similar behavior, and the supercooled water droplets remained attached to the films' surfaces. Such studies could be the foundation of highly versatile technologies for both water and ice mitigation.

Encapsulated droplets with metered and removable oil shells by electrowetting and dielectrophoresis

A water-core and oil-shell encapsulated droplet exhibits several advantages including enhanced fluidic manipulation, reduced biofouling, decreased evaporation, and simplified device packaging. However, obtaining the encapsulated droplet with an adjustable water-to-oil volume ratio and a further removable oil shell is not possible by reported techniques using manual pipetting or droplet splitting. We report a parallel-plate device capable of generation, encapsulation, rinsing, and emersion of water and/or oil droplets to achieve three major aims. The first aim of our experiments was to form encapsulated droplets by merging electrowetting-driven water droplets and dielectrophoresis-actuated oil droplets whose volumes were precisely controlled. 25 nL water droplets and 2.5 nL non-volatile silicone oil droplets with various viscosities (10, 100, and 1000 cSt) were individually created from their reservoirs to form encapsulated droplets holding different water-to-oil volume ratios of 10:1 and 2:1. Secondly, the driving voltages, evaporation rates, and biofouling of the precise encapsulated droplets were measured. Compared with the bare and immersed droplets, we found the encapsulated droplets (oil shells with lower viscosities and larger volumes) were driven at a smaller voltage or for a wider velocity range. In the dynamic evaporation tests, at a temperature of 20 ± 1 °C and relative humidity of 45 ± 3%, 10 cSt 10:1 and 2:1 encapsulated droplets were moved at the velocity of 0.25 mm s(-1) for 22 and 35 min until losing 16.6 and 17.5% water, respectively, while bare droplets followed the driving signal for only 6 min when 11.4% water was lost. Evaporation was further diminished at the rate of 0.04% min(-1) for a carefully positioned stationary encapsulated droplet. Biofouling of 5 μg ml(-1) FITC-BSA solution was found to be eliminated by the encapsulated droplet from the fluorescent images. The third aim of our research was to remove the oil shell by dissolving it in an on-chip rinsing reservoir containing hexane. After emersion from the rinsing reservoir, the bare droplet was restored as hexane rapidly evaporated. Removal of the oil shell would not only increase the evaporation of the core droplet when necessary, but also enhance the signal-to-noise ratio in the following detection steps.

A vacuum assisted dynamic evaporation interface for two-dimensional normal phase/reverse phase liquid chromatography

A vacuum assisted dynamic solvent evaporation interface for coupling of two-dimensional normal phase/reverse phase liquid chromatography was developed and evaluated. A normal-phase liquid chromatographic (NPLC) column of a 250 mm × 4.6 mm I.D. 5 μm CN phase was used as the first dimension, and a reversed-phase liquid chromatographic (RPLC) column of 250 mm × 4.6 mm I.D. 5 μm C 18 phase was used as the second dimension. The eluent from the first dimension flowed into a fraction loop, and the solvent in the eluent was dynamically evaporated and removed by vacuum as it was entering the fraction loop of the interface. The non-evaporable analytes was retained and enriched in about 5–25 μL solution within the loop. Up to 1 mL/min of mobile phase from the first dimension can be evaporated and removed dynamically by the interface. The mobile phase from the second dimension then entered the loop, and dissolved the concentrated analytes retained inside the loop, and carried them onto the second dimension column for further separation. The operation conditions of the two dimensions were independent from each other, and both dimensions were operated at their optimal chromatographic conditions. We evaluated the interface by controlling the loop temperature in a water bath at normal temperature, and investigated the sample losses by using standard samples with different boiling points. It was found that the sample loss due to evaporation in the interface was negligible for non-volatile samples or for components with boiling point above 340 °C. The interface realizes fast solvent removal of mL volume of fraction and concentration of the fraction into tenth of μL volume, and injection of the concentrated fraction on the secondary column. The chromatographic performance of the two-dimensional LC system was enhanced without compromise of separation efficiency and selectivity on each dimension.

Microrods based on nanocubes of Prussian blue

Using a facile dynamic vacuum evaporation method, a novel microrod with diameters of ca. 1–2 μm and lengths of up to 80 μm has been constructed using uniform Prussian blue (PB) nanocubes as the building blocks. The PB nanocubes are arranged fairly orderly in the rod-like superstructures. The assembled architecture can be transformed from one-dimensional microrods to two-dimensional layers via a fish-bone-like structure by tuning the evaporation rate. The formation of the PB superstructures follows an oriented-attachment mechanism and this provides a simple approach to fabricate hierarchical nanostructures and self-assembled superstructures using nanosized building blocks. Magnetic studies indicate that the PB microrods have a Curie temperature ( T c) of 4.9 K and a coercivity of ca. 26 Oe at 1.8 K. The photoluminescence (PL) spectra of the PB microrods and the dispersed nanocubes show an UV emission band at 358 and 367 nm respectively, suggesting an interesting assembly effect.

Mercury isotope fractionation during liquid–vapor evaporation experiments

Liquid–vapor mercury isotope fractionation was investigated under equilibrium and dynamic conditions. Equilibrium evaporation experiments were performed in a closed glass system under atmospheric pressure between 0 and 22 °C, where vapor above the liquid was sampled at chemical equilibrium. Dynamic evaporation experiments were conducted in a closed glass system under 10 −5 bar vacuum conditions varying (1) the fraction of liquid Hg evaporated at 22 °C and (2) the temperature of evaporation (22–100 °C). Both, residual liquid and condensed vapor fractions were analyzed using stannous chloride CV-MC-ICP-MS. Equilibrium evaporation showed a constant liquid–vapor fractionation factor ( α 202/198) of 1.00086 ± 0.00022 (2SD, n = 6) within the 0–22 °C range. The 22 °C dynamic evaporations experiments displayed Rayleigh distillation fractionation behavior with liquid–vapor α 202/198 = 1.0067 ± 0.0011 (2SD), calculated from both residual and condensed vapor fractions. Our results confirm historical data (1920s) from Brönsted, Mulliken and coworkers on mercury isotopes separation using evaporation experiments, for which recalculated δ 202Hg′ showed a liquid–vapor α 202/198 of 1.0076 ± 0.0017 (2SD). This liquid–vapor α 202/198 is significantly different from the expected kinetic α 202/198 value ((202/198) 0.5 = 1.0101). A conceptual evaporation model of back condensation fluxes within a thin layer at the liquid–vapor interface was used to explain this discrepancy. The δ 202Hg′ of condensed vapor fractions in the 22–100 °C temperature range experiments showed a negative linear relationship with 10 6/ T 2, explained by increasing rates of exchange within the layer with the increase in temperature. Evaporation experiments also resulted in non-mass-dependent fractionation (NMF) of odd 199Hg and 201Hg isotopes, expressed as Δ 199Hg′ and Δ 201Hg′, the deviation in ‰ from the mass fractionation relationship with even isotopes. Liquid–vapor equilibrium yielded Δ 199Hg′/Δ 201Hg′ relationship of 2.0 ± 0.6 (2SE), which is statistically not different from the one predicted for the nuclear field shift effect (Δ 199Hg/Δ 201Hg ≈ 2.47). On the other hand, evaporation under dynamic conditions at 22 °C led to negative anomalies in the residual liquid fractions that are balanced by positive anomalies in condensed vapors with lower Δ 199Hg′/Δ 201Hg′ ratios of 1.2 ± 0.4 (2SD). This suggests that either magnetic isotope effects may have occurred without radical chemistry or an unknown NMF process on odd isotopes operated during liquid mercury evaporation.

A scheme for calculating soil moisture content by using routine weather data

Abstract. Soil moisture content is one of the most important parameters as input conditions in forecasting model systems of dust storm, but it can not be directly obtained from daily routine weather report. In this paper, a scheme is developed to calculate the surface soil moisture content in China by using both precipitation and evaporation. Precipitation is directly from routine weather report, while evaporation is indirectly calculated by using meteorological elements which are also from routine weather report. According to the formula by Penman, evaporation can be considered as a linear composition of dynamic evaporation and thermodynamic evaporation caused by radiation. First, an equation for calculating daily global radiation within China is given by using regression analysis and the data of global radiation and cloud cover from 116 meteorological stations in China. Then, an equation for calculating evaporation within China is given by using regression analysis and the data of cloud cover, air temperature, precipitation, relative humidity, and wind velocity from 701 meteorological stations. Finally, a scheme for calculating soil moisture content within China is established by using regression analysis and the soil moisture content, precipitation, and evaporation at 79 agro-meteorological stations. Validation results show that the forecasting accuracy of the Chinese dust numerical model can be improved by using this scheme.

Coupling dynamic blow down and pool evaporation model for LNG

Treating the dynamic effects of accidental discharges of liquefied natural gas (LNG) is important for realistic predictions of pool radius. Two phenomena have important influence on pool spread dynamics, time-varying discharge (blow down) and pool ignition. Time-varying discharge occurs because a punctured LNG tanker or storage tank drains with a decreasing liquid head and decreasing head-space pressure. Pool ignition increases the evaporation rate of a pool and consequently decreases the ultimate pool area. This paper describes an approach to treat these phenomena in a dynamic pool evaporation model. The pool evaporation model developed here has two separate regimes. Early in the spill, momentum forces dominate and the pool spreads independently of pool evaporation rate and the corresponding heat transfer rate. After the average pool depth drops below a minimum value, momentum forces are largely dissipated and the thin edges of the pool completely evaporate, so pool area is established by the heat transfer rate. The maximum extent of a burning pool is predicted to be significantly less than that of an unignited pool because the duration of the first regime is reduced by higher heat transfer rates. The maximum extent of an LNG pool is predicted to be larger upon accounting for blow down compared with using a constant average discharge rate. However, the maximum pool extent occurs only momentarily before retreating.

Numerical study of dynamic effects and evaporation of target material under irradiation of intense pulsed ion beam

Gaussian distribution models of voltage wave form of MID of TEMP Ⅱ accelerator and IPIB density near the MID focus region have been built according to the results of experiments. The energy deposited in the target were calculated by using Monte Carlo method based on these models. Then we use them as thermal sources in hydrodynamic equations, and simulate the evolution process of pressure transported in target based on different kinds of state equations of material. The pressure evolution profile of plasma generated by IPIB irradiated Al target with high enough beam energy density has also been calculated by combining the ideal gas model of plasma and HD equations.

The use of a thermogravimetric analyzer for the generation of primary analytical vapor standards of organophosphate pesticides

A thermogravimetric analyzer (TGA) was used for the generation of primary vapor standards of three organophosphate pesticides encompassing a wide range of vapor pressures. The technique combines a dynamic flow-through evaporation system with gravimetric analysis of weight loss from an analyte reservoir. Vapor reference standards may be produced in less than 1 h per compound, including purging the system between compounds. Vapor concentrations are gravimetrically monitored in real-time (1 Hz). Equilibration time was negligible, as the linear vaporization curves for the compounds were produced in real-time, and all had correlation coefficients ( R 2) greater than 0.99. For the current study, vapors were collected by sampling bags for transport. This sensitive (parts-per-million to parts-per-billion), fast (negligible equilibration time), robust (compounds with vapor pressures spanning five orders of magnitude), low consumption (μL), and extremely general technique may be used for the generation of countless vapors in a number of concentrations and quantities.

MRI investigation of the evaporation of embedded liquid droplets from porous surfaces under different drying regimes

A combination of in situ one-dimensional 1H magnetic resonance profiling and two-dimensional imaging has been applied to study the shape and subsequent dynamic evaporation behaviour of a single liquid droplet after impact onto a porous surface. Diethyl-malonate (DEM) droplets are initially embedded in the porous substrate by impingement, and are then evaporated over a period of several hours; the surface of the substrate being ventilated by a controlled airflow. The configuration is intended to mimic the behaviour of droplets evaporating into atmospheric flows. In order to evaluate the influence of the airflow at the surface of the porous medium, different experimental configurations were tested by varying the speed of the airflow stream above the porous surface. The method produces several types of data, including images of impinged droplets inside the porous substrate and their development with time during the evaporation episode, one-dimensional concentration profiles through the substrates, and corresponding estimates of the mass fraction of liquid remaining, evaporation rate and mass flux per unit area. The results obtained show that although liquid droplets tend to evaporate faster and present larger evaporation rates when exposed to a more efficient removal of vapour from the surface, the limiting effects of the porous medium are even more evident.

Modeling the number distributions of urban and regional aerosols: theoretical foundations

Recent studies suggest an association between particle number concentrations and adverse health effects in humans and laboratory animals. A photochemical model able to predict the particle number distribution and concentration will be very helpful to establish the association between emissions and air quality needed for developing rational emission control strategies. As the first step of the study, each term in the aerosol dynamic equation, namely condensation and evaporation, coagulation, gravitational settling, nucleation, advection, turbulent transport, emission, deposition and heterogeneous chemical reaction, is analyzed to estimate its influence on the overall number distributions under typical urban conditions.

Dynamics of a single bubble in a liquid in the presence of chemical reactions and interphase heat and mass exchange

The influence of inert and chemically reactive additives in the form of microdrops on the dynamics of a single bubble filled with an active gas mixture and collapsing under the action of a shock wave is considered. The development of a reaction during formation of the mixture is analyzed for instantaneous and dynamic evaporation of drops with allowance for various phases of their injection t inj . It is shown that in instantaneous evaporation, an increase in the fraction of gaseous argon in the H2+O2 system raises the final temperature of the system under cryogenic conditions, lowers it under ordinary conditions, and causes appreciable oscillations of the values of γ, heat release, and molecular weight. It is noted that there are values of t inj and D0 at which the final temperature of the mixture decreases practically to the initial temperature.

Simulation technique for dynamic evaporation processes

A new higher-order hyperbolic scheme is proposed. This scheme is applicable simultaneously to compressible and incompressible fluids. A sharp interface of two fluids is described by one grid throughout computation. The code is applied to laser-induced evaporation dynamics and vapor explosions. Among fundamental processes in vapor explosions, two important models are tested. One is the interaction of a shock wave with a liquid drop and subsequent break-up of a drop. Another one is the collapse of a bubble near a wall. Although the liquid jet appears, the mushroom structure is created inside a bubble and this combined structure deforms the wall surface only in a simple topological way without mushroom structure.

Dynamic evaporation behaviour of diketonate compounds of yttrium, copper and barium

The dynamic evaporations of Y(thd) 3, Cu(thd) 2 and Ba(thd) 2, where thd is 2,2,6,6-tetramethyl-3,5-heptane dionate, were studied using a microbalance technique. Our primary objective here was to investigate the evaporation stability of these compounds with respect to time. Our results showed that the evaporation rates of these compounds decreased inevitably with time due to the decrease in sample weight. The reasons for the decrease in evaporation rate with sample weight are: (i) the decrease in effective surface area with sample weight and (ii) the increase in diffusion distance in the region above the sample within the cell. Our results indicated that by preparing Cu(thd) 2 and Y(thd) 3 as pellets and then placing them level with the cell rim produces uniform evaporation rates. For Y(thd) 3, an additional decrease in evaporation rate occurred at high temperatures due to coalescence between particles and, hence, a decrease in surface area. The evaporation rate of Ba(thd) 2 decreased quite significantly with time. An empirical equation of the form n = n 0( T) + a exp(− bt) fitted our results quite well. There were some oligomers in the original sample, whose quantities seemed to decrease after thermal treatments. A species like Ba(thd) 2 · Hthd, may also exist which would make the Ba content in the original sample lower than in pure Ba(thd) 2.

An experiment on vaporization and microexplosion of emulsion fuel droplets on a hot surface

Changes in the composition during vaporization of oil and water emulsion fuel droplets levitated on a hot surface by the Leidenfrost phenomenon have been studied experimentally. Results show that there exists a strong mechanism of transporting microdroplets to the vaporizing droplet surface such that the component consisting of the microdroplets always vaporizes first. This phenomenon indicates that such effects as the differences in the boiling points and densities or phase equilibrium characteristics of the two constituents of emulsion fuels are secondary. Thus, the dynamic evaporation characteristics of microdroplets should be accounted for in predicting the occurrence of microexplosions in addition to considerations for the thermodynamic criteria of microexlosions such as the limit of superheat.

Dynamic evaporation control using optical transmission: E Furman, Vacuum, 32 (6), 1982, 367–368

Dynamic evaporation control using optical transmission: E Furman, Vacuum, 32 (6), 1982, 367–368

Dynamic evaporation control using optical transmission

A simple, reliable and low cost evaporation control method, based on optical transmission of a laser beam, is described. The method is suitable for metal evaporation in a relatively high-temperature environment.

The dynamic formation of quasi-static active region loops

A hydrodynamic model is used to analyse the formation of an active region coronal loop. After an impulse of energy that ‘lifts' part of a cool uniform plasma into the domain of radiative instability (T> 105 K) the atmosphere is allowed to relax dynamically to a new quasi-steady equilibrium. Although the radiative-hydrodynamic coupling leads to quite complex physical phenomena, the final state of the plasma shows excellent agreement with previous quasi-static loop calculation. The bearing of this analysis on the evolution of flare plasmas is then discussed. In particular, it is shown that the energy flux emanating from an excited coronal source leads to the ‘dynamic evaporation’ of cool transition-zone and chromospheric material. The analysis indicates, however, that an accurate description of the transition zone in solar flares requires considerably more sophistication than has hitherto been employed. Finally, a discussion is given of the uniqueness and stability of the quasi-static loop. It is concluded that, despite thermal instability, a quasi-static model should adequately describe the gross features of quiescent coronal loops.