Condensation Of Na Research Articles

Liquid evaporation from nanochannel in the presence of non-condensable gas by direct simulation Monte Carlo

Liquid-vapor phase change in the form of evaporation and with the confinement of nanostructures is of vast importance in many engineering applications. The direct simulation Monte Carlo (DSMC) approach was employed to simulate the liquid evaporation from two-dimensional nanochannels in the presence of non-condensable (NC) gases. The thermodynamic properties of vapor and NC gas flow fields as well as the evaporation rate of liquid were calculated. Factors such as channel opening ratio, meniscus receding depth and the NC gas density were examined to reveal their impacts on the liquid evaporation rates. The results showed that the gas mixture flow field transforms to one-dimensional away from the channel exit. The overall vapor pressure drop can be divided into that across the liquid–vapor interface, that within the channel, outside the channel, as well as that caused by the binary diffusion. The effect of NC gas on the evaporation rate was found to be the most outstanding with pinned meniscus and with a wide channel opening, in which case the normalized evaporation rate drops to 0.43. Moreover, the Maxwell-Stefan equation could capture the evaporation data with modified diffusion lengths. For receded meniscus (250 nm deep) and small opening ratio (0.417), the effective diffusion length was as large as 1.6 times that in the one-dimensional case.

Key factors affecting the performance of the multi-stream heat exchanger for CO2 condensation

The multi-stream heat exchanger (MS-HEX) is an important equipment in CO2 capture processes, especially for CO2 condensation. By now, little attention has been paid to thoroughly investigating its performance. To provide insights for optimizing the design and operation of the MS-HEX, this paper evaluated the impacts of some key factors, such as the flow arrangement and the content of non-condensable (NC) gases, on the performances of the MS-HEX, including the exit vapor fraction, the pressure drop, the heat transfer coefficient (HTC), and the sub-cooling degree. A 3D CFD model was developed and validated. Based on simulations, it was found that the flow arrangement can clearly affect the performance of the MS-HEX, and there existed an optimal one, which can give the highest sub-cooling degree. Moreover, increasing the volume fraction of NC gases can lead to a decrease of the HTC and the sub-cooling degree; and Ar showed the biggest impact, followed by O2 and N2. For instance, compared to condensing a stream containing 5 vol % N2, condensing a stream containing 5 vol % Ar led to a lower HTC and a lower sub-cooling degree, which can be up to 27.3% and 4 K, respectively.

Vapor condensation induced by fast-moving liquid film in the presence of noncondensable gas molecules

In this study, vapor condensation phenomena at the surface of a fast-moving planar liquid film in a gas mixture (vapor and noncondensable (NC) gas), aimed to imitate a cavitation bubble collapse, were simulated to investigate the evaporation and condensation coefficients of vapor molecules based on the Enskog–Vlasov equation. These coefficients indicate the evaporation and condensation rates of vapor molecules, and they were incorporated into the kinetic boundary condition (KBC) for the vapor/gas–liquid interface. We employed the Enskog–Vlasov direct simulation Monte Carlo method to simulate the condensation phenomena. Based on the results, we confirmed that the obtained coefficients decreased with an increase in the liquid temperature and NC gas content at the condensing interface. Additionally, the coefficients had the same values as those in the equilibrium state, even for such a moving system. Notably, the nonequilibrium effect on condensation phenomenon discussed in the field of cavitation bubble dynamics, whereby vapor molecules fail to condense when the liquid velocity is significantly high, could not be confirmed in this simulation. Furthermore, we conducted an analysis based on the Boltzmann equation using the direct simulation Monte Carlo method to verify the obtained coefficients.

Effect of substrate charge density on the adsorption of intrinsically disordered protein amyloid β40: a molecular dynamics study.

The inhibitory effect of negatively charged gold nanoparticles (AuNPs) on amyloidogenic protein fibrillation has been established from experiments and computer simulations. Here, we investigate the effect of the charge density (σ) of gold (Au) surfaces on the adsorption of the intrinsically disordered amyloid β40 (Aβ40) monomer using molecular dynamics (MD) simulations. On the basis of the binding free energy, some key residues (ARG5, LYS16, LYS28, LEU17-ALA21, ILE31-VAL38) were found to be responsible for preventing the β-sheet formation, which is known to be a precursor for fibrillation. Until a critical charge density (σc) of -0.167 e nm-2, the key residues remained adsorbed on the Au slab. A saturation in the number of condensed counterions (Na+) on Aβ40 was also observed at σc. Beyond σc, the condensation of Na+ occurs only on the Au slab, leading to competition between positively charged key residues and condensed ions. This competition was found to be responsible for the lack of adsorption of the key residues, leading to β-sheet formation for σ > -0.167 e nm-2. This study suggests that if the key residues are not adsorbed, then β-sheet formation is observed, which can then lead to the development of proto-fibrils and subsequently fibrillation. Therefore the surface should have an optimal charge density to be an effective inhibitor of fibrillation.

Modeling the Process and Properties of Ash Formation during Pulverized Biomass Combustion

The present work mainly developed a mathematical model based on the plug flow model and coarse fly ash particles’ fragmentation model to describe the behavior and evolution of ash formation and the influence of the biomass feeding rate and flue gas cooling rate on ash properties, which is validated by literature data. The model considers homogeneous nucleation of alkali vapors, heterogeneous condensation of vapors on newly formed particles and fly ash particles, and collision-coagulation between aerosol particles, which is also applied to numerically study and analyze the ash formation characteristics in the cases of practical boiler pulverized fuel combustion and SO2 sulfation. The results show that the mathematical model can reasonably describe the ash formation and the influence of the biomass feeding rate and the flue gas cooling rate on the mass PSDs of PM10 and its elements. The initial nucleation temperature and initial nucleation particle size increase with the biomass feeding rate, which is of great importance to the cooling rate on the initial nucleation number concentration and the initial nucleation particle size. Elements Na, K, and Cl are mainly concentrated in PM1, but rarely distributed in PM1–10. The condensation of Na, K, and Cl on coarse particles increases with the biomass feeding rate and decreases with the cooling rate. The ash characteristics obtained from the experiment condition with an ultra-high flue gas cooling rate and minimum biomass selected may have a large deviation from that of practical biomass combustion, and the sulfated reaction may reduce Cl corrosion rather than ash deposition.

Molecular dynamics simulation of evaporation coefficient of vapor molecules during steady net evaporation in binary mixture system

In this study, an evaporation coefficient representing the evaporation rate of vapor molecules was calculated in a vapor–gas binary mixture and non-equilibrium system using molecular dynamics simulation. The non-equilibrium herein refers to a state in which the net evaporation of vapor molecules occurs, and the calculation system is composed of vapor molecules and non-condensable (NC) gas molecules. The evaporation coefficient in the non-equilibrium state was demonstrated to have almost the same value as that in the equilibrium state. The number density of NC gas molecules around the gas–liquid interface, which is related to the probability that vapor molecules are prevented from evaporating owing to molecular collisions, is shown to be independent of the system state. This makes the evaporation coefficient the same regardless of whether the system is in equilibrium or non-equilibrium. In contrast, the evaporation coefficient decreased as the molar fraction of the NC gas molecules increased. The increase in the molar fraction causes a higher number density of NC gas molecules around the gas–liquid interface, leading to an increase in the number of molecular collisions, which prevents vapor molecules from evaporating. Moreover, it was clarified that the change in the interface structure caused by the presence of NC gas molecules affects the velocity distribution of evaporation vapor molecules.

Mean-field kinetic theory analysis of vapor flow between evaporating and condensing interfaces in the presence of non-condensable gas molecules

To investigate the vapor kinetic boundary condition (which is the boundary condition for the Boltzmann equation) in the presence of a non-condensable (NC) gas at a non-equilibrium liquid interface, we performed numerical simulations of non-equilibrium vapor (condensable gas) and NC gas mixture flows. The Enskog–Vlasov direct simulation Monte Carlo method (EVDSMC method) was utilized for this two-surface problem to obtain the evaporation and condensation coefficients, which represent the vapor–molecule evaporation and condensation rates, respectively. These coefficients are incorporated in the kinetic boundary condition. The simulation results showed that the evaporation and condensation coefficients decrease with increasing numbers of NC-gas molecules at the liquid interface with the same tendency. To investigate the validity of these coefficients, we also utilized the obtained evaporation and condensation coefficients for Boltzmann equation analysis. Hence, we concluded that these coefficients simply depend on the NC-gas number density at the liquid interface if the liquid temperature is constant. Thus, they are independent of the non-equilibrium or equilibrium state, and therefore, the coefficient values obtained for the equilibrium state can be used in the analysis of a non-equilibrium state. This finding will aid future predictions of non-equilibrium vapor flows with NC gas.

Experimental study on enhancement characteristics of steam/nitrogen condensation inside horizontal multi-start helical channels

Abstract The aim of this study was to reveal the internal mechanism of enhanced condensation heat transfer, by experimentally performing steam condensation with higher inlet velocity in the horizontal multi-start helical channels (HMSHCs), and investigating the influences of pressure of steam, mass flowrate of cooling water, and mass fraction of noncondensable (NC) gas on steam condensation performance. Taking steam condensation in horizontal circular condensation channel (HCCC) as a reference, the condensation heat transfer coefficients (CHTCs), the outlet condensate mass flowrates (CMFRs), and the total steam condensation pressure drops (SCPDs) were compared and discussed, respectively. The results indicated that NC gas had a strong inhibitory effect on steam condensation, and average condensation characteristics decreased with the increase in NC gas fraction for lower Rem. But for higher Rem, the gas–liquid interfacial shearing stress can likely weaken the negative effect of NC gas. In addition, increasing the cooling water flowrate can entirety promote steam condensation. The comparison results indicated that steam condensation performance of HMSHC is better than that of HCCC under same experimental conditions. For the specific experimental scope, the average CHTCs and the outlet CMFRs in HMSHC are approximately 2.35 and 1.25 times of that inside HCCC, respectively, while the overall SCPDs in HMSHC are about 1.16 times of that inside HCCC. After introducing the performance evaluation factor, the calculation results revealed that the performance evaluation factor h PEC {h}_{\text{PEC}} of the average CHTCs in HMSHC is approximately 2.02, and the performance evaluation factor m PEC {{m}}_{\text{PEC}} of the outlet CMFRs in HMSHC is approximately 1.08. The two evaluating values are reasonable.

An improved model based on real gas state equation and fog formation for condensation heat and mass transfer

In order to predict the condensation heat transfer coefficient precisely, this work aimed at proposing a generalized model with a wide scope of parameters applicability, namely, we presented an improved model that can predict the condensation characteristics which based on heat and mass transfer analogy with consideration of gas compressibility factor, fog formation factor, film waviness factor, suction factor and eddy diffusion factor. The improved model is suitable for those conditions: low pressure condensation at plate-shape and curved-shape surface with natural/forced convection, high pressure condensation at curved shape surface with natural convection. The improved model shows good applicability with the scope of the pressure is up to 2 MPa and the non-condensable (NC) gas mass fraction up to 90%. Six experimental databases (including 436 data) were chosen to validate this model. More than 97% of the results predicted by the improved model were within ±30% bands.

Novel Model for the Release and Condensation of Inorganics for a Pressurized Fluidized-Bed Gasification Process: Effects of Gasification Temperature.

A model is established to investigate the release and condensation of inorganics for a wood steam/oxygen-blown fluidized-bed gasification process. In the established model, fates of major elements (C, H, O, N, S, and Cl) and minor elements (Al, Ca, Fe, K, Mg, Mn, Na, P, Si, Ti, and Zn) are modeled separately. The composition of gaseous species involving major elements is predicted using Aspen Plus based on a semiempirical model. The release of minor elements and the condensation of inorganics are predicted using software SimuSage. The combination of Aspen Plus with SimuSage is achieved by manually inputting the stream parameters calculated from Aspen Plus into SimuSage. On the basis of this developed model, effects of gasification temperature on the condensation of Na-, K-, and Cl-containing species during gas cooling are studied. Results show that the process model established by combining Aspen Plus and SimuSage is valid and can be used to investigate the release of inorganics during gasification and condensation of inorganics during gas cooling. Under the investigated gasification conditions, regardless of the bed material, there are two temperature ranges within which no salt melt is formed during gas cooling. As the gasification temperature increases, the high-temperature range without salt melt formation becomes successively wider.

Analysis of Stagnant Non Condensable Gases Effects on Condensation Heat Transfer in a Vertical Tube

In a vertical condenser tube installed at the cold end of a non-vacuum separate type heat pipe, non condensable (NC) gases in the system is pushed by continuous vapor flowing from the hot end into the condenser tube at the cold end, gathering above condensate at the outlet of the condenser tube. Therefore, condensation heat transfer of vapor with the stagnant NC gases occurs in the condenser tube. It is necessary to comprehend the effects of stagnant NC gases on condensation heat transfer. A VOF method was adopted to analyze how stagnant NC gases affect condensation heat transfer, a mass fraction equation of NC gases was used to solve diffusion between NC gases and vapor, a Hertz-Knudsen-Schrage model was applied to deal with condensation rate of vapor on the surface of liquid film. Parameters, including volume fraction, velocity, pressure, mass fraction of NC gases and condensation heat transfer coefficients (HTC), were obtained. Results show that a lot of NC gases deposits in the condenser tube rear, leading a lot of vapor to condense at the condenser tube front. NC gases slightly affect condensation HTC of the tube front, and severely degrade condensation HTC of the tube rear. Furthermore, an increase in mass of NC gases causes a rise in pressure and velocity, improving condensation heat transfer.

Case study on the CO 2 release in horizontal falling film evaporator

The release of non-condensable (NC) gases, especially CO 2 in multiple-effect distiller (MED) for seawater desalination has been barely investigated and has very less publications available in it. NC gases which are carbon dioxide (CO 2), oxygen (O 2) and nitrogen (N 2) notably affect the heat transfer for condensation zone, energy consumption, the performance and material life span of the distillers. The understanding of CO 2 release in MED is very important knowledge for design and better operation of desalination distillers. The present paper describes a model of CO 2 release and the carbonate system in falling film horizontal tube-evaporators, physical properties of seawater and following correlations. The model was applied 5-effects MED, operating at top brine temperature (TBT) of 60–75 °C. The CO 2 release rates as well as depend on the salinity and top brine temperature of the inlet seawater and the specific CO 2 release decreased first to last effect.

Scaling of passive condenser system for separate effect testing

The passive containment cooling system (PCCS) of the simplified boiling water reactor (SBWR) is a passive condenser system designed to remove energy from the containment for long term cooling period after a postulated reactor accident. Depending on pressure condition and noncondensable (NC) gas fraction in drywell (DW) and suppression pool (SP), three different modes are possible in the PCCS operation namely the forced flow, cyclic venting and complete condensation modes. The prototype SBWR has total of six condenser units with each unit consisting of hundreds of condenser tubes. Simulation of such prototype system is very expensive and complex. Hence a scaling analysis is used in designing an experimental model for the prototype PCCS condenser system. The motive for scaling is to achieve a homologous relationship between an experiment and the prototype which it represents. A scaling method for separate effect test facility is first presented. The design of the scaled test facility for PCCS condenser is then given. Data from the test facility are presented and scaling approach to relate the scaled test facility data to prototype is discussed.

Effect of electrohydrodynamic (EHD) on condensation of R-134a in presence of non-condensable gas

Effects of applying EHD and non-condensable (NC) gas contents have been experimentally studied on inter-tubular condensation of refrigerant R-134a flow. Applying of electrical field enhances condensing heat transfer coefficient (CHTC), but presence of NC gas in condensing vapour reduces this coefficient. In competition of these two effective parameters on condensation, it can be observed that at higher concentration of NC gas, the effect of electrical field on enhancement of CHTC is greatly reduced. But at lower concentration of NC gas, the effect of electrical field is more considerable, due to thickness of heat transfer boundary layer.

CO 2 release in vertical tube falling film evaporators

The release of non-condensable (NC) gases, essentially carbon dioxide, oxygen and nitrogen, from the evaporating brine in desalination distillers notably affects the heat transfer for condensation, the energy consumption, the performance and the material life span of the distillers. A better knowledge of CO 2 release and of the interaction with the carbonate system in desalination distillers is very important for the design of the venting system and a stable distiller operation. Since CO 2 release and scale formation are closely related to the carbonate system of the brine, a better understanding of CO 2 release may contribute to the knowledge of scale formation in desalination distillers and improve scale prediction and prevention methods. A model has been developed for the prediction of the CO 2 release rates in falling film evaporators with vertical tubes. The theory of mass transfer coupled with chemical reaction kinetics (chemical desorption) was applied to the problem of CO 2 release. The mass transfer and the chemical reaction kinetics were studied for the conditions prevailing in falling film seawater evaporators. In addition to the CO 2 release rates the model allows for calculation of the HCO 3 −, CO 3 2−, CO 2, H +, and OH − concentrations in the carbonate system of the brine. The model was applied to a falling film evaporator at various operating conditions. The release rates of CO 2 along the flow path of the falling film were determined. The paper presents the main principles of the model and discusses the simulation results. The effects of process parameters and the seawater properties such as evaporation temperature, seawater salinity, and pH value on the CO 2 release rates are shown. Moreover, the paper discusses in which desorption regime (e.g. slow, fast, instantaneous) the CO 2 release process takes place and whether the mass transfer is enhanced by the chemical reactions.

Effect of noncondensable gas in a vertical tube condenser

An experimental study is performed to investigate the effects of noncondensable (NC) gas in the steam condensing system. A vertical condenser tube is submerged in a water pool where the heat from the condenser tube is removed by boiling heat transfer. The design of the test section is based on the passive condenser system in an advanced boiling water nuclear power reactor. Data are obtained for various process parameters, such as inlet steam flow rate, noncondensable gas concentration, and system pressure. Degradation of the condensing performance with increasing noncondensable gas is investigated. The condensation heat transfer coefficient and heat transfer rate decrease with noncondensable gas. The condensation heat transfer rate is enhanced by increasing the inlet steam flow rate and the pressure. The condensation heat transfer coefficient increases with the inlet steam flow rate, however, decreases with the system pressure. For the condenser submerged in a water pool with saturated condition, the strong primary pressure dependency is observed.

Origin of Na2SO4 blisters in sheet glass

Abstract The properties and origin of fine Na 2 SO 4 blisters have been studied experimentally. They are 0.1–1.0 mm in size and contain crystalline Na 2 SO 4 with a small amount of CaO and K 2 O. Most of them are formed in molten glass during decomposition of the batch mixture. The blisters are formed by condensation of Na 2 SO 4 from Na 2 O and SO 3 selectively absorbed into dolomite at an early stage of batch melting. They remain immiscibly in molten glass, after MgO and CaO in the dolomite have been dissolved into the glass.

Interaction of molecular beams of NaF with (100) surfaces of LiF

Abstract The interaction of molecular beams of NaCl with (100) surfaces of KCl is studied by measurements of the desorption fluxes of the monomers NaCl and KCl and the dimers Na 2 Cl 2 , NaKCl 2 , and K 2 Cl 2 and by static SIMS for crystal temperatures T from 619 to 866 K and for impinging sodium chloride fluxes from 1.3 × 10 10 to 5.8 × 10 14 molecules cm 2 · s. The results for undersaturation can be interpreted by an interplay of condensation and re-evaporation of Na + containing molecules and of bulk diffusion of Na + ions, respectively. From measurements of transient desorption fluxes the bulk diffusion coefficient of Na + in KCl D = 34.3( +121 −27 ) exp [ − (1.59 ± 0.10 eV) kT ] cm 2 s −1 with a corresponding jump energy E m = 0.34 eV is obtained. Determining the surface concentrations of K and Na by static SIMS the desorption fluxes can be interpreted in terms of activity coefficients. From these measurements and a rough model the ratio of the Na + K + exchange time with the terrace and the desorption time of the admolecules can be estimated. At supersaturation a solid solution layer grows on the surface with a surface composition changing continuously from KCl to NaCl with increasing thickness. The morphological development of the overlayers is studied by the electron microscopic decoration technique. At an intermediate stage multiple spirals corresponding to bunches of 2–9 screw dislocations are observed.