Heterogeneous Condensation Of Water Vapor Research Articles

Microscopic visualization of heterogeneous condensation of water vapor on hydrophilic and hydrophobic particles

Heterogeneous condensation of water vapor on particles is widely used in the fields of atmospheric cloud physics and industrial particulate abatement. Particles surface wettability plays a fundamental role in water vapor condensation, but a microscopic insight of the impact of particles surface wettability on vapor condensation is lacked. Therefore, the Environmental Scanning Electron Microscope (ESEM) is adopted to directly visualize vapor condensation on particles with different surface wettability at a microscopic scale. Firstly heterogeneous condensation of water vapor on the hydrophilic and hydrophobic particles is obtained by the ESEM. The results show that when water vapor condenses on the hydrophilic particles, a spherical cap-shaped embryo first appears and subsequently develops into a spherical droplet to finally wrap the single particle. While on the hydrophobic particles, a spherical cap-shaped embryo will first appear and continue to grow into a spherical droplet to finally detach from the particle. Then the wetting coefficient is introduced to characterize the wetting degree of the droplet on the particle. The wetting coefficient will increase with the decrease of the contact angle, so the wettability of water vapor on the hydrophilic particles is better than that on the hydrophobic particles. Meanwhile based on classical nucleation theory, the geometrical factor and the critical supersaturation will decrease when the contact angle decreases, making it easier for water vapor to condense on the hydrophilic particles. Finally the line tension is investigated to explain the condensation mechanism. On the hydrophilic particles, when the droplet has crossed the equatorial line of the particle, the positive line tension promotes the spreading movement of the droplet over the particle to form a wrapped spherical droplet. Therefore, there is a transition from a spherical cap-shaped embryo before crossing the equatorial line of the particle to a wrapped spherical droplet after crossing the equatorial line. While on the hydrophobic particles, the negative line tension suppresses the spreading movement of the droplet over the particle to form a detached spherical droplet. So there is a transition from a spherical cap-shaped embryo before crossing the equatorial line of the particle to a detached spherical droplet after crossing the equatorial line.

Enhanced mitigation of inhalable particles and fine particle-bound PAHs from a novel hazardous waste-power plant candidate

Emissions of the inhalable particle (dp < 10 μm, PM10) and their harmful compositions from combustion sources have high potential on health risk with nearly no regulation. This study investigates the particle size distribution (PSD), as well as the removal mechanism of PM10 and fine particle (FP)-bound polycyclic aromatic hydrocarbons (PAHs) from the flue gas of a hazardous waste thermal treatment system. It has ultralow regulated emission and becomes a candidate of power generation module. A series of the advanced scrubbers, cyclonic demister, and baghouse was equipped for multi-pollutant control. The moderate or intense low oxygen dilution (MILD) combustion effectively inhibited the PM2.5 generation by volumetric oxidation. Advanced scrubbers removed PM1, PM2.5, and PM10 by 85.24, 68.68, and 97.60%, respectively, which achieved by local supersaturation, heterogeneous condensation of water vapor, and the growth of fine PM. Moreover, the scrubbers effectively scavenged the course PM10 containing the high-molecular-weight PAH homologs onto the water phase but promoted the condensation and absorption of the lighter homologs onto the fine particle surface (dp ∼5.3 μm). The size window (dp = 0.3–1.0 μm) of the minimum efficiency reporting value of a BH filtration led to the peak of FP-PAH mass and BaP equivalent (BaPeq) toxicity at dp = 0.1–0.4 and 0.1–0.8 μm, respectively. Consequently, the synergy of MILD combustion and the SCB-CYC-BH system effectively inhibited the PM2.5, PM10, PM2.5-PAHs, and FP-PAH levels from a waste thermal treatment process and further mitigated the potential health risk.

Effect of CO2 on the heterogeneous condensation of water vapor on insoluble fine particles

Heterogeneous condensation preconditioning technology has generated broad interest in removing fine particles from coal-fired flue gas due to its economic and environmental advantages. Here, a flow cloud chamber was used to study the effect of 0%–90% CO2 concentrations on the growth performance of insoluble fine particles with different operational conditions. The results suggest that a higher CO2 concentration in the particle growth environment is detrimental to the fine particles growth. The higher the CO2 concentration, the worse the growth performance. The adverse effect of CO2 on the growth performance decreases with the increase of growth time and the increase of supersaturation caused by temperature, and does not change significantly with the increasing particle concentration.

Formation of Liquid Film in Heterogeneous Condensation of Water Vapor: Effects of Solid-Fluid Interaction and Sulfuric Acid Component.

Understanding the phenomenon of filmwise condensation on solid surfaces is vital for industrial processes such as air pollutant control and desalination. In this work, we study the formation of condensed liquid films via molecular dynamics simulations, and the effects of solid-fluid interactions and the sulfuric acid component are given major attention. Water is chosen as the fluid, while the solid-fluid interaction is modified to characterize different solid surfaces. The results show that as the solid-fluid interaction decreases, the solid surface transforms from a completely wetting surface to a partially wetting surface, and the film formation process shows significant differences. The condensed liquid on the completely wetting surface forms small liquid films, which merge to form a complete film covering the surface. With the enhancement of solid-fluid interaction, the condensation rate increases first and then remains virtually invariant, resulting in a film formation time that decreases first and then maintains constant. The condensed liquid on the partially wetting surfaces appears as nanodroplets, and the coalescence between nanodroplets leads to the formation of the liquid film. It is found that the stronger the solid-fluid interaction, the more the coalesced droplets tend to be pinned at nucleation sites, the easier it is to form a liquid film, and the shorter the time required for droplet merging. The sulfuric acid component accelerates liquid film formation on both completely wetting and partially wetting surfaces, but the effect of sulfuric acid is more significant on partially wetting surfaces. The 5% molar fraction of sulfuric acid reduces the nucleation time by 72% and increases the condensation rate by 137% under partial wetting, while the same amount of sulfuric acid only increases the nucleation rate by 6% on the completely wetting surface.

Heterogeneous condensation process observed by environmental scanning electron microscopy (ESEM): On smooth single aerosol particle

Heterogeneous condensation of water vapor on the aerosol particles is a very important phenomenon in natural and industrial processes such as the formation of cloud droplets, the measurement of aer...

Heterogeneous Condensation of Water Vapor on Fine SiO2 Particles in Two-Section Growth Tube

Vapor condensation on submicron particles is a promising pretechnique to remove fine particles. For effectively enhanced particle growth, the study of particle amplification by heterogeneous conden...

Heterogeneous Condensation on Fine Particles of Water Vapor in a Moderated Growth Tube

Abstract: A novel process of heterogeneous condensation of water vapor on fine particles was presented in this paper. In order to improve the performance of heterogeneous condensation of water vapor on fine particles, a moderated experimental scale growth tube was developed. The essential supersaturated environment was established by adding hot water into the cooled gas in the growth tube. The supersaturation profiles in the growth tube was described and the performance of particle enlargement in the original growth tube and in the moderated growth tube both were experimentally investigated. The results showed that the performance of particle enlargement could highly be improved by the moderated approach. A comparison between the performance of the original approach and the moderated approach was presented; also, the different growth mechanisms in different growth tube were elucidated.

Heterogeneous condensation of water vapor on particles at high concentration

Although heterogeneous condensation on fine particles is one of the most promising precondition technologies for particles abatement which has been proved by many works, little direct data were reported on the process of particles enlargement by vapor condensation. A direct measurement of enlarged particle size distribution in a lab scale growth tube by water vapor condensation is presented. Four parameters that affect the performance of the particle enlargement at high particle number by heterogeneous condensation were identified: supersaturation, particle size, residence time and particle wettability. The results show that particle enlargement exponentially increases with the increase of supersaturation. The particle size has a negative impact on particle growth ratio. The residence time is in favor of the particle enlargement which depends on the supersaturation level. Additionally, the residence time extension would weaken the vapor depletion on particle enlargement caused by particle number increase. Particle wettability may lead to different processes of particle enlargement. This work deeply revealed the process of vapor condensation on particles at high concentration by direct measurement.

Characteristics of Vapor Condensation on Coal-Fired Fine Particles

Heterogeneous condensation of water vapor on coal-fired fine particles was investigated in a growth tube. The influence of operating parameters and wetting agent addition on vapor condensation enlargement for three coal-fired fine particles from different power plants were tested. The results show that all the three coal-fired fine particles induce heterogeneous condensation and the process is favored by increasing the water temperature and residence time and decreasing particles initial number concentration; wetting agent addition highly facilitates the effect of vapor condensation on fine particles and the performance is increased with the increase of wetting agent addition. It is also found that excessive addition encourages the performance of final mean size of particles but discourages the performance of finer particles enlargement. With wetting agent addition, the mean diameter of fine particles can be enlarged above 3 μm while the mean diameter can only be enlarged above 2 μm without wetting agent ...

A role of aerosol particles in atmospheric ice nucleation

Considered is the process of ice nucleation in the atmosphere as a result of heterogeneous condensation of water vapor in surface inhomogeneities of aerosol particles and of subsequent heterogeneous crystallization of supercooled water accumulation. It is revealed that the size, structure, and composition of aerosol particles determine the thermal regime of crystallization.

Heterogeneous Condensation of Water Vapor on Nanoparticles in a Membrane-Based High-Flow Process Monitored by a NewIn SituMeasuring Cell

This article presents a membrane-based process to improve separation efficiency of airborne particles by heterogeneous condensation of water vapor. A plant was set up in laboratory scale to control the supersaturated state of water vapor in air accurately. Droplet growth due to heterogeneous condensation is investigated experimentally and supersaturation is calculated by solving the differential equations for heat and mass transfer in a laminar gas flow. The apparatus is based on a water condensation particle counter (WCPC). It operates with several growth tubes in parallel thereby allowing higher aerosol throughput. The increase of particle size based on heterogeneous condensation is detected by an in situ measuring system. Therefore a new measuring cell was operated with well-defined test aerosols differing in wetting abilities and initial nuclei size. First results of particle activation and condensational droplet growth are presented.Copyright 2015 American Association for Aerosol Research

Experimental study of fine particles removal in the desulfurated scrubbed flue gas

Droplets growth by heterogeneous condensation of water vapor as a preconditioning technique for the removal of fine particles from flue gas was investigated experimentally in a wet flue gas desulfurization (WFGD) system using spray scrubber as scrubber. The supersaturated vapor environment was achieved by adding water vapor into the particle growth region, which was above the liquid phase inlet in the desulfurization tower. Fine particles grow in size by vapor heterogeneous condensation with the particles acting as nucleation centers, and then the grown droplets are removed efficiently by a high-efficiency wire mesh demister. The results show that particle number concentration decreased significantly by application of heterogeneous condensation of water vapor in the WFGD system. The influence of initial particle number concentration, temperature of inlet flue gas and desulfurization solution, amount of steam added on the removal efficiency of fine particles is presented. The removal efficiency of fine particles decreased with increasing the initial particle concentration. Anyway, heterogeneous condensation in combination with a WFGD system is a highly efficient technique for the separation of fine particles from the desulfurized flue gas.

Removal of fine particles in wet flue gas desulfurization system by heterogeneous condensation

A novel process to remove fine particles with high efficiency by heterogeneous condensation in a wet flue gas desulfurization (WFGD) system is presented. A supersaturated vapor phase, necessary for condensational growth of fine particles, was achieved in the SO2 absorption zone and at the top of the wet FGD scrubber by adding steam in the gas inlet and above the scrubbing liquid inlet of the scrubber, respectively. The condensational grown droplets were then removed by the scrubbing liquid and a high-efficiency demister. The results show that the effectiveness of the WFGD system for removal of fine particles is related to the SO2 absorbent employed. When using CaCO3 and NH3·H2O to remove SO2 from flue gas, the fine particle removal efficiencies are lower than those for Na2CO3 and water, and the morphology and elemental composition of fine particles are changed. This effect can be attributed to the formation of aerosol particles in the limestone and ammonia-based FGD processes. The performance of the WFGD system for removal of fine particles can be significantly improved for both steam addition cases, for which the removal efficiency increases with increasing amount of added steam. A high liquid to gas ratio is beneficial for efficient removal of fine particles by heterogeneous condensation of water vapor.

Growth and motion of heterogeneous water droplets in laminar diffusion chambers: 2. High nanoparticle concentrations

The heterogeneous condensation of water vapor on nanoparticles and the growth of formed droplets are numerically studied under conditions of laminar diffusion chamber (LDC) of a new type with a hot porous wall. The main attention is focused on the growth of heterogeneous droplets in the gas flow at high number densities of nanoparticles exceeding 108 droplet/m3. Under these conditions, there is an interrelation between the growth of droplets and processes of heat and mass transfer in LDC due to vapor depletion and the release of latent heat of phase transition on growing droplets. The efficiency of the coverage of nanoparticles with water film is studied under LDC nonuniform conditions. It is shown that, at initial number densities of nanoparticles (Nd > 1011 droplet/m3), heterogeneous droplets do not grow to optically detected sizes.

Experimental investigation on removal of coal-fired fine particles by a condensation scrubber

The removal of coal-fired fine particles by heterogeneous condensation of water vapor in a scrubber was investigated. Supersaturated vapor phase necessary for the condensation growth of fine particles was achieved in the scrubbing zone as well as in the top of the scrubber by means of steam addition in the gas inlet and above the scrubbing liquid inlet, respectively. The condensation grown droplets were then removed by the scrubbing liquid and high-efficient demister. Influences of the steam addition amount, the temperature difference between the inlet gas and scrubbing liquid, and the liquid-to-gas ratio, etc. on removal efficiency were examined. The results show that with a steam addition amount of 0 .04 kg/ m STP 3 flue gas, number removal efficiencies of more than 60% and 70% can be attained for the two cases of steam addition, respectively. For the cases with steam addition in the gas inlet of scrubber, higher temperature difference between the inlet gas and scrubbing liquid enhances the removal of fine particles. Under the conditions of steam addition above the scrubbing liquid inlet, the removal efficiency decreases with increasing temperature difference. The removal efficiency can be effectively improved by increasing the liquid-to-gas ratio for both steam addition modes.

Inhibition of water condensation by a soluble salt nucleus

In heterogeneous condensation of water vapor on an insoluble solid surface, the presence of a soluble salt crystal has two effects. The first is the well-known effect as a nucleus for condensation at low supersaturation. We show that it also inhibits condensation around it by reducing the concentration of adsorbed molecules. This effect extends to macroscopic distances.