Water Vapor Phase Research Articles

Experimental Setup for Studying Thermosolutal Convection in Moist Air

The paper is concerned with designing an experimental scheme for studying convection of moist air under conditions closely approximating the atmospheric conditions. Detailed numerical estimates, necessary conditions and dimensionless gas-dynamic parameters characteristic of the problem of dry and moist air convection are presented and analyzed. The distinctive features of convection of dry and wet air at constant pressure caused by changes in the concentration of water vapor as a result of its evaporation (condensation) are discussed. The effect of water vapor concentration on the convective instability of moist air is analyzed in the context of solutal convection, characterized by the Rayleigh concentration number. The obtained numerical estimates are used to demonstrate the possibility of differentiating and comparing between the processes of convective heat and mass transfer in humid and dry air under laboratory conditions. In future, this will allow researchers to obtain experimental data on the influence of the water-vapor phase transition on the intensity of convective motion in moist air. The structure and detailed technical characteristics of the constructed experimental setup designed for studying convection in moist air in the temperature range from 10 to 30 C are described.

Observation of the Chemical Structure of Water up to the Critical Point by Raman Spectroscopic Analysis of Fluid Inclusions.

Raman spectra were obtained simultaneously from the liquid and vapor phases of pure water trapped at the critical density (322 kg·m-3) within synthetic inclusions in quartz. As these inclusions are heated up to the critical temperature (373.946 °C), the liquid phase decreases in density and the maximum of the Raman OH-stretching band increases in wavenumber. Conversely, as the vapor phase increases in density, the maximum of the Raman OH-stretching band decreases in wavenumber. The Raman bands of the liquid and vapor phases converge to a single band at the critical point of water, where the fluid exists as a single phase. A comparison of the band centroids for the vapor and liquid phases of water indicates respective increases and decreases in the amount of hydrogen bonding in these phases as a function of increasing and decreasing density. These effects were further quantified by peak-fitting the Raman OH-stretching peak with five Gaussian components. All the Gaussian components of the liquid phase decrease in amplitude with increasing temperature with the exception of the double donor-single acceptor (H2O)4 cluster, which increases in amplitude and becomes the most intense component at temperatures above 300 °C. The Raman spectra of the vapor phase are dominated by the free OH component at temperatures below 300 °C, but, above this temperature, the double donor-single acceptor (H2O)4 cluster is again the most intense band. The results indicate that a significant quantity of water clusters is present in both liquid and vapor water at high temperatures and that supercritical water can be considered as a mixture of small water clusters [(H2O)n, n = 1-4] dominated by the double donor-single acceptor (H2O)4 cluster.

Hygrothermal performance of vernacular stone in a desert climate

Remote desert communities are often the most vulnerable to temperature extremes, as lack of access to reliable electricity prevents the use of active cooling or heating. Hence, there is a need to investigate how the building envelope itself can be used to passively regulate indoor environments. Readily available vernacular building materials in such areas are thought to aid in not only attenuating temperature swings but also moisture regulation, which improves comfort in a dry climate. Thus, the aim of this research is to investigate the hygrothermal properties of three different stone types commonly used as building materials in the Western Desert of Egypt: sandstone, limestone and, uniquely, Karshif, a rock rich in sodium chloride. The materials’ thermal conductivity, moisture sorption and buffering, water vapour resistance, porosity distribution and phase composition are experimentally investigated. Our results show that the local perception of limestone buildings having poor indoor comfort, despite the material’s superior thermal conductivity and specific heat capacity is only explainable through the relative superiority of sandstone and Karshif in moisture buffering. Vernacular materials need to be tested in environmental conditions representative of their local climate, rather than standardised conditions, as the latter may paint an incorrect picture of performance which, in the case of Karshif, led to partial dissolution under relative humidity of greater than 80%. However, testing under typical desert conditions demonstrates that both Karshif and sandstone are viable building materials that exhibit excellent moisture regulation behaviour. Since building materials in desert conditions may have to withstand atypical weather extremes, including rain, local materials need to be utilised within carefully designed wall assemblies or treated wall sections and, in the case of Karshif, not used in areas where relative humidity regularly reaches 80%. These findings are an important contribution in validating the performance of vernacular stone, and more widely, in demonstrating the importance of selecting appropriate testing conditions.

Two-Stream Numerical Simulation of a New Type Drum Dryer

In recent years, the new type of tumble waste dryer has been promoted and developed. Heat generation through phase transition is an environmental, friendly and efficient heat transfer drying method. In order to know under what conditions the water vapor has higher heat transfer efficiency in the semi-circular cylinder and more sufficient liquid phase transition, and under what conditions the quantity of heat transferred can be exactly controlled, we carried out relevant work. Based on the analysis of two-phase heat transfer of rotating body, a three-dimension model of garbage dryer is established. Then, the commercial CFD software ANSYS Fluent is used to simulate the two-phase flow in the semi-circular cylinder, and the simulation calculation is carried out. Finally, the theoretical calculation results are verified by experiments. Calculated by the simulation results analysis: according to the industrial use of setting conditions, simulation calculation results can achieve convergence, namely water vapor through the pipe wall heat conduction. Finally condense into liquid water, and to ensure that the liquid cavity in the body has a higher volume fraction, water vapor phase change rate is of more than 90%, the Nusselt number of the heat transfer surface is 60 to 300.

Numerical investigation of the effect of the shape of the nozzle on the flash boiling phenomenon

In this paper analysis of influence of the nozzle shape on the flash boiling phenomena is presented. The mixture model was applied to account for two-phase flow through the nozzle. The ZwartGerber-B lamri model was used to describe the dynamics of the water-vapor phase change process, with the relationship linking the saturation pressure and temperature of the fluid. The effect of the shape of the nozzle on the mass flow rate of the two-phase mixture was numerically investigated by considering thestepwise and conical geometry of its divergent part. At first analysis of the influence of grid size as well as the ways of turbulence and near wall region modelling on the mass flow rate of two-phase mixture were studied for the diameter of nozzle neck of 0.42 mm. Predictions were found independent onthese factors. Then simulations were carried out for three nozzle neck diameters (i.e., 0.62, 0.72 and 0.82 mm) and for several pressures (i.e., from 5 to 7 bar) and undercoolings (i.e., from 1 to 50 K)of water at the inlet. The shape of divergent part of the nozzle was found to not have effect on the mass flow rate of flashing water flowing through nozzle.

Development of a new Geant4-DNA electron elastic scattering model for liquid-phase water using the ELSEPA code

This paper presents the calculation of new elastic scattering cross sections for the simulation of electron interactions in liquid water. The calculations are based on the “ELastic Scattering of Electrons and Positrons by neutral Atoms” code, which adopts a Dirac partial wave analysis. A Muffin-tin potential was used in order to account for the liquid-phase of water, and the optical parameters of the correlation-polarization and the inelastic absorption potentials were optimized against vapour-phase water data. The differential and total elastic scattering cross sections calculated in the present work show a global agreement with the experimental data. The impact of these elastic scattering cross sections on the transport of electrons in liquid water was evaluated by track-structure simulations of range, dose-point-kernel, microdosimetric spectra, and ionization clustering using the Geant4-DNA simulation toolkit. The results are compared against those obtained with the elastic scattering models already available in Geant4-DNA and are discussed.

Research on cavitation involved in ultrasonic-assisted abrasive waterjet machining

The cavitation characteristics involved in ultrasonic-assisted abrasive waterjet were analyzed in the present study. The fluid field corresponding to ultrasonic-assisted AWJ was investigated through utilizing computational fluid dynamics. A cavitation model was adopted to simulate the mass transfer between water liquid and vapor phases. The evolution of cavitation during the impacting process and the effects of vibration parameters on cavitating characteristics were investigated. Moreover, a set of experiments were performed to evaluate the effects of ultrasonic-induced cavitation on erosion and material removal of ceramics. The results indicated that the evolution of cavitation had dependency on the fluid pressure and turbulence at impacted zone, and the synergetic erosion of microjets and accelerated particles induced by collapsing cavitation bubbles can evidently enhance the material removal. The material removal rate was improved by 82% at most under ultrasonic vibration.

Stability of vapor phase water electrolysis cell with anion exchange membrane

The production of renewable hydrogen gas with a vapor-fed solar hydrogen generator is an appealing strategy. In such all solid-state standalone device no liquid electrolyte is required. The use of an anion exchange membrane separating cathode and anode compartments is particularly advantageous and its performance matches the performance of liquid phase electrolysis. In this work, a vapor-fed water electrolyzer was investigated comprising a poly(vinyl alcohol) anion exchange membrane impregnated with 4M KOH solution and Ni-based catalysts. The performance was evaluated over time periods of hours to days. The vapor fed device showed similar initial activity as an electrolysis setup with the same electrodes immersed in 1M KOH liquid electrolyte. To sustain a current density of 10 mA/cm², it was observed that the required potential initially increased but eventually reached a steady state at ca. 1.9 V. From a D2O isotope labelling experiment of the vapor phase, it was noticed that the system initially consumed H2O absorbed in the membrane to produce H2. After this water of the membrane was consumed, water to be split is taken from the vapor phase and water mass transfer limitation starts occurring. Once water mass transfer and splitting reactions are matched, a steady state potential is reached. The results of this work are encouraging and pave the way to efficient stable operation of vapor-fed solar hydrogen generators.

A novel scheme for predicting the behaviors of liquid and vapor phases of water using the ideal gas theory

The ideal gas equation of state is the simplest equation of state for estimating the values of temperature, pressure and volume. This equation of state has a simple structure based on its simple theory. Hence, it has an explicit relation between these variables. In addition, calculating other thermodynamic properties (such as, internal energy, enthalpy and specific heats) is very simple for ideal gases. In this study, the ideal gas theory has been applicable for the liquid and vapor phases of water. To this aim, the temperature and molar volume have been modified as functions of the fluid molecular compressibility. In the presented method, effects of the temperature and volume on the non-ideality of the behaviors are considered, separately. Comparing the predicted values with the real data shows at least R-squared value equal to 0.98.

Mechanisms of low-temperature vapor-gas streams formation from sulfide mine waste

This paper presents experimental data that revealed the potential for chemical element transport by low-temperature vapor-gas streams. The study was conducted on sulfide waste heap sites located in the Kemerovo region, Russia. Condensates of vapor-gas streams were collected and analyzed in the air above the waste heaps and during laboratory experiments using samplers specially designed for this purpose. The gas streams from a waste heaps are complex mixtures consisting of water vapor, sulfur- and selenium-containing compounds (sulfur dioxide SO2, dimethyl sulfide C2H6S, carbon disulfide CS2, dimethyl disulfide C2H6S2, dimethyl selenide C2H6Se, and dimethyl diselenide C2H6Se2), elemental sulfur (S6, S7, and S8) and various chemical elements, including rock-forming elements (Ca, Mg, Na, K, Si, Fe, Al, and Mn), metals (Cu, Zn, Pb, Ni, and Sn), and metalloids (As, Te, and Sb). The main sources of chemical elements in the gas streams are unstable secondary minerals associated with crystalline hydrates: gypsum CaSO4 × 0.5H2O, sideronatrite Na2Fe(SO4)2(OH) × 3H2O, serpierite CaCu3Zn(SO4)2(OH)6 × 3H2O, and copiapite (Mg,Zn,Fe2+Fe3+)4(SO4)6(OH)2 × 20H2O that formed during the oxidation of sulfide minerals. Some of the elements come from pore waters that are acidic, highly mineralized solutions. The mechanism of element migration from the pore waters is as follow: the water vapor phase transports elements in the form of aqueous ions, but complexed species (such as MeSO4(aq), MeCl(aq), Me(OH)+, etc.) remain in the salt residue. A significant contribution to the processes of transformation and transport of elements is made by biochemical methylation reactions, which occur in the presence of bacteria producers of methyl groups and are accompanied by the formation of volatile compounds of arsenic, selenium, sulfur, and tellurium.

Vapor-gap membranes for highly selective osmotically driven desalination

In this study, we demonstrate nanostructured osmosis membranes that employ vapor-phase water transport to simultaneously achieve high rejection of solutes and a high permeability. The membranes consist of a hydrophobic, thermally conductive silica nanoparticle (SiNP) layer with tunable thickness supported by a hydrophilic track-etched membrane. The membrane permeability for water vapor is 1–2 orders of magnitude higher than hydrophobic microporous membranes used for osmotic distillation. This permeability is only mildly lower (~ 3 times) than the equivalent water permeability of typical forward osmosis (FO) membranes. We also demonstrate the high selectivity of the SiNP membrane via urea permeation tests, where this membrane exhibits a 2–3 orders of magnitude lower urea permeability coefficient than a thin-film composite (TFC) FO membrane. Further measurements and theoretical analysis using the dusty-gas model suggest that membranes with a smaller SiNP layer thickness are capable of having comparable water fluxes to TFC FO membranes while maintaining higher selectivity. Our work demonstrates that thin, hydrophobic nanostructured membranes composed of thermally conductive materials have a great potential to significantly extend the applications of osmosis-driven processes to treat challenging water sources.

Water vapor passing through asphalt mixtures under different relative humidity differentials

Water vapor diffusion in a newly constructed asphalt pavement consists of water vapor accumulating toward the asphalt layer (Phase I) and water vapor passing through the asphalt layer (Phase II). The water vapor diffusion in Phase I under different relative humidity (RH) differentials has been investigated and can be found elsewhere in literature. However, it remains unclear whether the RH differential would affect the diffusion flux and diffusivity of the water vapor passing through the asphalt layer in Phase II. This study investigated the Phase II water vapor diffusion in asphalt mixtures under a variety of RH differentials. Experimental setups were designed and assembled for the Phase II water vapor diffusion experiments. Distilled water, saturated MgCl2 solution, saturated NaBr solution, and saturated KCl solution were stored in containers to provide the RH level of 100%, 36.5%, 62%, and 87%, respectively, under the asphalt mixture specimens that were sealed on top of these containers. The experimental setups were conditioned in environmental chambers to maintain a constant test temperature of 20 ± 0.5 °C and specific RH levels to establish the RH differentials between the air above and below the asphalt mixture specimen. The weight loss of the experimental setup was monitored three times a day using a high-precision scale.A linear relationship was identified between the RH differential and the diffusion flux of the water vapor in Phase II diffusion, which demonstrated that the Phase II water vapor diffusion followed Fick’s first law of diffusion. The calculated water vapor diffusivities in Phase II diffusion were significantly larger than those in Phase I diffusion and were independent of the variation of the RH differential between the air above and below the asphalt mixture specimen.

Determining Water Vapour Phase Equilibrium Coefficients at Different Temperatures for Gas Wells

In the course of gas production from reservoirs across the world, salt precipitation from the reservoir water is observed to an increasing extent as recovery progresses. This phenomenon, likewise, occurs during the injection of dry gas into porous aquifers. Salt deposits can form in the production string, in the perforation zone as well as in the area of the reservoir surrounding the well [1]. A better understanding of salt precipitation phenomena along with the conditions under which this takes place is needed for a better productivity control [2]. Simulating the process and taking actions as necessary may reduce or even eliminate the necessity for down-hole fresh water washes and, in turn, minimize the overall production losses. Input for this simulation are also the Water-Vapour Phase Equilibrium Coefficients. This article presents a methodology on how to obtain these coefficients for different temperatures using commercial simulators.

Adsorption isotope effects of water on mesoporous silica and alumina with implications for the land-vegetation-atmosphere system

Soil water dynamics within a vadose (unsaturated) zone is a key component in the hydrologic cycle, especially in arid regions. In applying the Craig-Gordon evaporation model to obtain isotopic compositions of soil water and the evaporated vapor in land-surface models (LSMs), it has been assumed that the equilibrium isotope fractionation factors between soil water and water vapor, α(2H) and α(18O), are identical to those between liquid and vapor of bulk water. Isotope effects in water condensation arise from intermolecular hydrogen bonding in the condensed phase and the appearance of hindered rotation/translation. Hydrogen bonding between water molecules and pore surface hydroxyl groups influences adsorption isotope effects. To test whether equilibrium fractionation factors between soil water and water vapor are identical to those between liquid and vapor of bulk water and to evaluate the influence of pore size and chemical composition upon adsorption isotope effects, we extended our previous experiments of a mesoporous silica (15 nm) to two other mesoporous materials, a silica (6 nm) and an alumina (5.8 nm). Our results demonstrated that α(2H) and α(18O) between adsorbed water and water vapor are 1.057 and 1.0086 for silica (6 nm) and 1.041 and 1.0063 for alumina (5.8 nm), respectively, at saturation pressure (po), which are smaller than 1.075 and 1.0089, respectively, between liquid and vapor phases of free water at 30 °C and that the differences exaggerate at low water contents. However, the profiles of α values with relative pressures (p/po) for these three materials differ due to the differences in chemical compositions and pore sizes. Empirical formula relating α(2H) and α(18O) values to the proportions of filled pores (f) are developed for potential applications to natural soils. Our results from triple oxygen isotope analyses demonstrated that the isotope fractionation does not follow a canonical law. For the silica (15 nm), fractionation exponents (17θ) are 0.5361 ± 0.0018 and 0.5389 ± 0.0016 at p/po = 0.72 and 0.77, respectively. For the silica (6 nm), 17θ values are 0.5330 ± 0.0011 at p/po = 0.65 and 0.5278 ± 0.0010 at p/po = 0.81. For the alumina (5.8 nm), 17θ value is 0.5316 ± 0.0015 at p/po = 0.78. These values are greater than or equal to that of liquid-vapor equilibrium of bulk water (0.529 ± 0.001).

The adsorption and desorption of water from a carbonaceous deposit layer on the surface of stainless steel representing spent AGR nuclear fuel cladding

ABSTRACT Spent fuel discharged from advanced gas-cooled reactor power stations carries a deposit of carbon firmly attached to the cladding surface. The fuel route involves contact with water, for cooling and transport. Long-term storage potentially includes dry storage, however, the carry-over of water entrained within the carbon deposit needs to be considered regarding the storage environment. Drying of the fuel is possible, but little is known concerning the drying characteristics of such deposits. This work reports preparation of a laboratory simulant of a carbon deposit on a fuel pin surface and measurement of its adsorption and desorption properties regarding liquid and vapour phase water. This work found that water vapour equilibration is rapid and reversible. Liquid water uptake is appreciable (up to 5.7 times the mass of carbon) and most (up to 88%) is removed on standing for 12 h. Heating removes little more. The implications for spent fuel management are discussed.

Evaluation of a human skin surface temperature for the protective clothing – Skin system based on the protective clothing–skin imitating material results

Experimental studies used for evaluation of quality of the fire-fighters protective clothing are based on irradiation of the clothing sample by an external pulse of a given duration. The other side of the clothing sample is in contact with a material imitating the human skin, which has properties different than these of the skin. Therefore the problem considered in this paper was: what conditions should be satisfied to convert the experimental results, carried out on the stand with a skin-imitating material, to the case of the real human skin with different properties for which the experiments are not made? This will allow for better evaluation of the clothing protecting properties and estimation of the possible burns. Due to multilayer structure of the protective clothing and skin as well as complex phenomena involved in energy transfer through them the problem is very complicated. Therefore at the first attempt to solve the problem a simplified two-layer, clothing-skin system irradiated from external heat source was considered in the present paper. Temperature variation in the system was initially determined using the in-house 1D numerical code accounting for heat conduction in the skin and clothing, non-grey thermal radiation absorption, scattering and emission together with the water vapour diffusion and phase transformations of bound water to the gaseous phase in the protective clothing. Then the analytical model for temperature variation in the considered system was proposed and solved using the Laplace transform approach. In the latter model water vapour diffusion with its phase transformations were excluded and radiation emission was neglected. The analytical model allowed for deriving a formula which can be applied for converting the skin surface temperature obtained from the experiments carried out using the skin-imitating material to the material having skin properties. In order to verify the range of validity of the formula the analytical predictions were compared to the results of numerical simulations of temperature in the protective clothing-skin system considering cases in which different phenomena were included. For the majority of the cases studied good matching between analytical and numerical results was obtained for time corresponding to the heating and cooling processes of the protective clothing-skin system.

Electron emission from water molecule in collisions with fast highly charged C, O and Si-ions and scaling law

SynopsisDouble differential cross sections (DDCS) of vapor phase water molecules by similar velocity C6+, O8+ and Si13+ ion impact have been measured by the electron spectroscopy technique. The total ionization cross sections (TCS) were obtained by numerical integration of the DDCS results. All the existing data have been plotted after scaling. Gradual deviation of the TCS from the first Born predicted qp 2–scaling has been observed.

Liquid-phase tuning of porous PVDF-TrFE film on flexible substrate for energy harvesting

Emerging wearable and implantable biomedical energy harvesting devices demand efficient power conversion, flexible structures, and lightweight construction. This paper presents Polyvinylidene fluoride-trifluoroethylene (PVDF-TrFE) micro-porous structures, which can be tuned to specific mechanical flexibilities and optimized for piezoelectric power conversion. Specifically, the water vapor phase separation method was developed to control microstructure formation, pore diameter, porosity, and mechanical flexibility. Furthermore, we investigated the effects of the piezoelectric layer to supporting layer Young's modulus ratio, through using both analytical calculation and experimentation. Both structure flexibility and stress-induced voltage were considered in the analyses. Specification of electromechanical coupling efficiency, made possible by carefully designed three-dimensional porous structures, was shown to increase the power output by five-fold relative to uncoupled structures. Therefore, flexible PVDF-TrFE films with tunable microstructures, paired with substrates of different rigidities, provide highly efficient designs of compact piezoelectric energy generating devices.

The Optimization of PEM Fuel Cell Performance Using the CFD Method Combined with Experimental Validation

: The polymer electrolyte membrane fuel cell (PEMFC) possesses many advantages for both automotive and stationary application, including high energy efficiency, low operating temperature, zero emission, and so on. Aside from the fact that great improvement should be made on its key materials, i.e., the ORR electrocatalysts and proton exchange membrane, it is believed that the PEM fuel cell performance is greatly affected by the operating temperature, gas inlet humidity as well as the flow pattern, and so on [1,2]. Thus, in this work, a 3D steady state model is established to investigate detailedly the effects of the flow pattern (co-flow and counter-flow), the anode and cathode gas inlet relative humidity (RH) on the cell performance. The governing equations of the 3D model result from careful analysis on the electro-chemical reactions, current conservation, membrane proton migration, membrane water transport and water-vapor phase transition. The membrane water transport takes into accounts the electro-osmatic drag and water back diffusion, and the conservation of momentum, species and energy is applied to all components of the PEM fuel cell. Experimental validation is also performed and fits very well with the simulation. Figure 1 shows the current density distribution for different flow patterns: (a), co-flow and (b), counter-flow. The corresponding achievement will offer an efficient guide on the design and performance optimization of PEMFC. Acknowledgements This work was supported in part by National Natural Science Foundation of China (Grant No. 21373135 and 21533005) and Science Foundation of Ministry of Education of China ( Grant No. 413064). References K. Dannenberg, P. Ekdunge, G. Lindbergh, Mathematical model of the PEMFC, Journal of Applied Electrochemistry, 2000, 30: 1377-1387. S.H. Ge, B.L. Yi, A mathematical model for PEMFC in different flow modes, Journal of power sources, 2003, 124: 1-11. Figure 1

Assessment of hydrothermal performance by thermophysical characterization of a crimped glass wool building insulation

There is a need for experimental determination of thermophysical properties to bridge the gap between theoretically prediction and performance of insulating materials in buildings. This investigation concerns the study of hydrothermal performance of glass wool, a widely used insulation on the world market. It has been shown the low sensitivity of glass wool to water vapor, low hygroscopicity, and low permeability. On the other hand, the liquid permeability of glass wool is important. Obviously, the presence of liquid is generally accidental and should be prevented by good workmanship. Thermal characterization (conductivity and diffusivity) by hot disk, a transient technique, has been determined as a function of water. The effect of vapor phase water on thermal properties is not significant. Thermal conductivity increases by a factor 2 when liquid water is present in the insulation. It is shown that the hot disk method is useful to determine thermal characterization of insulation materials. Variations of thermal conductivity with water content have been explained from hydric characterization.