Constant Vapor Pressure Research Articles

Application of sorption tests to estimate selected properties of alluvial soils in Żuławy Elbląskie

Application of sorption tests to estimate selected properties of alluvial soils in Żuławy Elbląskie The specific surface area and hence the sorption or desorption moisture at constant water vapour pressure will increase with increasing content of humus and clay fraction in soils. Adopting such an assumption, preliminary experimental studies were performed to assess the possibility of using sorption/desorption tests to determine some features of alluvial soils from Żuławy such as cation exchange capacity CEC and the specific external surface area Se. Results of the sorption tests were compared with the analyses of the same soil properties determined with standard methods to evaluate the usefulness of the former. Preliminary studies showed a high similarity in the determination of CEC and Se with both methods. Confirmed usefulness of sorption/desorption methods for determination of the specific surface area of mineral soil particles and particularly for analyses of cation exchange capacity would bring a significant simplification of studies and a possibility of their dissemination due to the ease of such analyses. Determination of the specific surface area with the sorption and desorption method does not require sophisticated equipment and laborious and costly preliminary procedures. Dissemination of this method and recognition it as a reference one would, however, need further studies on various soil types.

Transfer of tritium in concrete coated with hydrophobic paints

An experimental study on tritium (T) transfer in porous concrete for the tertiary T safety containment is performed to investigate (i) how fast HTO penetrates through concrete walls, (ii) how well concrete walls contaminated with water-soluble T are decontaminated by a solution-in-water technique, and (iii) how well hydrophobic paint coating works as a protecting film against HTO migrating through concrete walls. The experiment is comparatively carried out using disks of cement paste which W(water)/C(cement) weight ratio is 0.6:1 with or without hydrophobic paints, and mortar disks which W/C/sand ratio is 0.6:1:2 with or without the paints. The hydrophobic paints tested in the present study are an epoxy polymer resin paint and an acrylic-silicon polymer resin one. After T exposure during specified time under a constant HTO vapor pressure in an acrylic box, the amount of water-soluble HTO on/in the disks is determined using a technique of H 2O dissolution during specified time. The results obtained here are summarized as follows: (1) HTO penetration in porous concrete can be correlated in terms of the effective diffusivity. (2) Its value in porous cement without coating is 1.2 × 10 −11 m 2/s at 25 °C. (3) HTO penetrates only through pores in cement, and there is no path for HTO transfer in non-porous sand. (4) Rates of sorption and dissolution of HTO in disks of cement and mortar coated with the epoxy resin paint are correlated in terms of the effective diffusivity through the paint film which value is D T = 1.0 × 10 −16 m 2/s. The rate-determining step is diffusion through the paint. (5) The epoxy resin paint works more effectively as an anti-HTO diffusion coating. (6) Another acrylic-silicon resin paint does not work well as anti-HTO diffusion coating. This may be because the hydrophobic property of the silicon resin paint is deteriorated with elongating the contact time with H 2O vapor or liquid. (7) The HTO uptake inside the epoxy paint is greater than that of the silicon one. (8) The permeation reduction factor (PRF) of HTO for the epoxy paint at steady-state is expected large, if HTO vapor only contributes to diffusion. However, when concrete surfaces coated with the epoxy paint are under wet conditions, the PRF value becomes smaller. All those results can be used to estimate the effect of HTO soaking in concrete walls in case of accidental T release in a fusion reactor room and to decontaminate wastes of tritiated concrete.

An Oral-Controlled Release Drug Delivery System for Liquid and Semisolid Drug Formulations

A novel oral drug delivery system for the controlled release of liquid drugs, drug solutions, and semisolid drug preparations is presented that is utilizing the constant vapor pressure of liquefied gas. The system is equipped with a capillary as an element determining the drug delivery rate and contains a liquefied propellant with a suitable boiling point below human body temperature. In the dissolution studies, polyacrylate gels of different viscosities containing paracetamol as model drug were used. Zero-order release kinetics was obtained. The release rates were dependent on the gel viscosity. Besides, by gel viscosity, the drug release rates could also be modified by changing the propellant type and the capillary parameters such as length or diameter. Accordingly, the new system enables a wide range of drug delivery kinetics which can be modified in a case-by-case basis in order to match the desired drug delivery characteristics.

Effects of sulphur and tin disulphide vapour treatments of Cu2ZnSnS(Se)4 absorber materials for monograin solar cells

The aim of this study was to find a heat-treatment procedure for monograin powders using a controllable reactive gas phase to improve the CZTS(Se) crystal surface for effectively working p-n junctions. The influence of an isothermal treatment in S and SnS2 vapour on the parameters of monograin layer solar cells is depending on the CZTS(Se) initial composition. The efficiencies of solar cells improve continuously with increasing temperatures of the absorber materials’ post-annealing from 823 to 973K under constant sulphur vapour pressure of 100 Torr. The highest values of Jsc= 18.4 mA/cm2 and Voc= 720 mV were obtained for a device made from CZTS powder annealed at 1013K in SnS2 vapour.

Photocatalytic mineralization of volatile organic compounds over commercial titanium(IV) oxide modified with rhodium(III) ion under visible light irradiation and correlation between physical properties and photocatalytic activity

Rhodium(III) ion (Rh 3+)-modified TiO 2 (Rh 3+/TiO 2) samples having various physical properties and structures (anatase and rutile) were prepared using commercially available TiO 2 samples. Thus-prepared Rh 3+/TiO 2 samples were used for degradation of acetaldehyde or mineralization of acetone with a constant vapor pressure under irradiation of visible light and correlations between the photocatalytic activities and physical properties were investigated. Rhodium(III) ion on the surface of TiO 2 worked as an inorganic photosensitizer and the Rh 3+/TiO 2 samples showed a kind of volcano-like tendency against specific surface area of TiO 2, indicating that the balance of surface area and crystallinity of TiO 2 is important in an Rh 3+/TiO 2 photocatalyst. The latter reaction system was found to be a simple and convenient method to evaluate the activity of a photocatalyst in a short time. The role of Rh 3+ as a catalyst for multi-electron reduction of oxygen is discussed on the basis of results obtained for Rh 3+-modified rutile-type TiO 2 samples.

Kinetics of water and alcohol vapors adsorption on natural zeolite

AbstractAlcohols are important high volatility industrial chemicals, and when present in low concentrations require highly selective separation techniques. This paper investigates the kinetics of the adsorption of water, methanol, and butanol vapors on natural clinoptilolite based on experimental data obtained from laboratory‐scale equipment under constant saturated vapor pressure conditions at ambient temperature. In order to determine the corresponding mass transfer and diffusion coefficients of the adsorbed components in the zeolite particles, the kinetic curves have been investigated using two simple models—the linear driving force model (LDFM) as well as the particle diffusion model. The equilibrium and the kinetic parameters can also be determined from the experimental values of the statistical moments of the kinetic curves. Two main results have been obtained from this study. At the experimental conditions, the overall rates of adsorption of both methanol and water vapors are nearly equal, and they are of the same order of magnitude to the macro‐(meso)‐pore and intracrystalline diffusion rates predicted for the biporous clinoptilolite structure. In contrast, the diffusion of butanol vapors is much slower in the zeolite particles and particle crystals, where the intracrystalline mass transfer resistance plays a dominant role, even for the largest particles studied. The simple LDFM predictions exhibit very good correlation to the experimental data for all adsorptive components and particle sizes, despite the biporous zeolite structure. This model can be used to provide an acceptable and quick interpretation of adsorption rate curves, even at nonlinear equilibrium conditions. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd.

Constant vapour pressure evaporation from a fragrance emulsion—effect of surfactant content in the liquid crystal

AbstractThe evaporation paths for constant fragrance vapour pressure were calculated in a model emulsion system of water, surfactant, and linalool.It was found that the water content of the liquid crystal had a moderate effect on the time during which the fragrance vapour pressure was constant; significantly less of a consequence than the fraction of surfactant in the oil phase in equilibrium with the aqueous and liquid crystal phases.The results will serve as a guidance for the formulation of optimal fragrance emulsions for the mass market.

Further Study of the Effect of Water Vapor on Slider Air Bearing

It has been proved that water vapor in moist air contributes to slider air-bearing pressure in a totally different way from dry air. It is a very good first order approximation to take a constant water vapor pressure inside and outside the interface. The simulated slider flying height and attitude in moist air are different from that in dry air and the higher the relative humidity the bigger the difference. This work is a further study of the effect of water vapor on slider air bearing. In this paper, the effect of slider air-bearing pressure on the saturated water vapor pressure is explained. The adsorbed water film thickness on slider and disk surfaces as a function of relative humidity at different temperatures is calculated. The effects of slider air-bearing pressure, temperature, slider-disk spacing, and relative humidity on the water vapor pressure in slider-disk interface are studied. An empirical equation is developed for the calculation of accurate water vapor pressure distribution in slider-disk interface.

The Spreading of Inkjet‐Printed Droplets with Varying Polymer Molar Mass on a Dry Solid Substrate

AbstractAn experimental study on the spreading of inkjet printed droplets of a polystyrene/toluene solution with varied molar masses on solid dry surfaces is presented. The polymer's number‐averaged molar mass was varied between 1.5 and 545 kDa, which also caused a variation in the viscosity from 0.6 to 1.7 mPa · s. The results were compared with theoretical models for droplet spreading and were found to fit with an error between 2 and 20% with the predictions. Furthermore, the in‐flight evaporation of the free‐falling droplet was investigated for polystyrene/toluene solutions that have a constant vapor pressure by printing from a systematically increased height.magnified image

Constant vapor pressure emulsions evaporation: Linalool/water stabilized by Laureth 4

Evaporation paths were calculated in the title system using the relevant part of its published phase diagram and the assumption of equilibrium between vapor and liquids. The vapor pressure of linalool was reduced while the emulsion resided in the two-phase region but remained constant within the three-phase range. The duration of the time for constant vapor pressure depended on the relative humidity (RH) to a surprising degree.

Chemical preparation and thermal behavior of neodymium cyclotriphosphate pentahydrate NdP 3O 9·5H 2O: A study by Controlled Rate Thermal Analysis (CRTA)

A new neodymium cyclotriphosphate pentahydrate powder, NdP 3O 9·5H 2O, has been prepared using a classical chemistry method and characterized by X-ray diffraction and infrared spectroscopy techniques. The IR spectrum shows the characteristic bands of cyclotriphosphates as the triplet in the range 1055–1007–917 cm −1. The thermal behavior of the titled compound was also carried out using conventional thermal analysis techniques (TG and DSC) under air atmosphere and Controlled transformation Rate Thermal Analysis (CRTA) technique under constant water vapour pressure of 5 hPa. It was shown that thermal treatment in air, with linear heating rate of 10 K min −1, favourites the structure breakdown as soon as the release of water molecules starts. In this case an amorphous compound is obtained, which then crystallizes at 1073 K and gives the polyphosphate Nd(PO 3) 3. However, by CRTA technique at P H 2 O = 5 hPa , the water molecules are eliminated with a lower rate which permits to save the initial structure up to an advanced dehydration step. The breakdown of the initial structure is immediately followed by the crystallization of the anhydrous polyphosphate Nd(PO 3) 3 phase in the temperature range 455 K < T < 793 K.

Water Vapor Diffusion through Wheat Straw Residue

Accurate prediction of evaporative water loss from dryland agricultural soils requires knowledge of diffusive resistance. Our objective was to experimentally determine the effective vapor diffusion coefficients and the diffusive resistances for water vapor through wheat (Triticum aestivum L.) residue layers. A laboratory diffusion chamber was designed to investigate the effects of wheat residue type (straw vs. chaff), residue amount (2, 4, 8, and 12 Mg ha−1), and residue orientation (horizontal vs. vertical straw) on vapor diffusion. The diffusion chamber consisted of two well‐stirred chambers separated by a residue layer. In one chamber, a constant saturated water vapor pressure was maintained, while in the other chamber, vapor pressure increased with time due to the diffusion of vapor through the residue layer. Vapor pressure was measured with a humidity sensor. The diffusion equation was used to obtain the effective diffusion coefficient from the measured data by inverse modeling. Results showed that for both straw and chaff residue, increasing the quantity of residue did not necessarily decrease the effective diffusion coefficient but did increase the diffusive resistance. For the same quantity of residue, chaff had a lower effective diffusion coefficient than straw, but the diffusive resistances were similar. The diffusive resistances were in the order of 800 to 3700 s m−1 for 2 to 12 Mg ha−1 residue treatments. The factor affecting the diffusive resistance the most was the thickness of the residue layer: the thicker the residue layer, the larger the diffusive resistance.

Constant vapour pressure evaporation from a fragrance emulsion—effect of solubility of surfactant in the fragrance compound

AbstractThe algebraic system to extract information from phase diagrams was used to establish some of the conditions for an emulsion to evaporate under constant vapour pressure. The model system for the calculations was an emulsion characterized by virtually no solubility in water by either the surfactant or the fragrance and the same condition for the water in the oil. The surfactant and the fragrance, on the other hand, were assumed to be mutually completely soluble and this solution was presupposed to be close to ideal. The results showed a surprisingly strong dependence of the times for evaporation under constant vapour pressure on the surfactant concentration in the oil phase, at which the two‐phase equilibrium between the aqueous and the oil phases is replaced by a three‐phase equilibrium: aqueous phase, oil phase and liquid crystal phase. The lower this concentration, the more extended the times for evaporation under constant vapour pressure. Copyright © 2008 John Wiley &amp; Sons, Ltd.

The interaction of the theophylline metastable phase with water vapor

The conditions of hydration of the stable and metastable theophylline phases were determined. Two-phase metastable phase/monohydrate and stable phase/monohydrate equilibrium pressures were measured at 25, 30, and 35°C. The metastable phase began to react with water vapor at lower relative humidities than the stable phase. Processes that occurred with the metastable and stable theophylline phases over various water pressure ranges were considered. The metastable phase exhibited an unusual behavior at 25°C and relative humidity 47%. At constant water vapor pressure and temperature, theophylline was initially hydrated and then lost water and again became anhydrous. Two consecutive processes occurred in the system, the formation of theophylline monohydrate from the metastable phase and its decomposition to the stable phase. The ratio between the rates of these processes determined the content of the monohydrate at the given time moment.

Apparent latent heat of evaporation from clothing: attenuation and “heat pipe” effects

Investigating claims that a clothed person's mass loss does not always represent their evaporative heat loss (EVAP), a thermal manikin study was performed measuring heat balance components in more detail than human studies would permit. Using clothing with different levels of vapor permeability and measuring heat losses from skin controlled at 34 degrees C in ambient temperatures of 10, 20, and 34 degrees C with constant vapor pressure (1 kPa), additional heat losses from wet skin compared with dry skin were analyzed. EVAP based on mass loss (E(mass)) measurement and direct measurement of the extra heat loss by the manikin due to wet skin (E(app)) were compared. A clear discrepancy was observed. E(mass) overestimated E(app) in warm environments, and both under and overestimations were observed in cool environments, depending on the clothing vapor permeability. At 34 degrees C, apparent latent heat (lambda(app)) of pure evaporative cooling was lower than the physical value (lambda; 2,430 J/g) and reduced with increasing vapor resistance up to 45%. At lower temperatures, lambda(app) increases due to additional skin heat loss via evaporation of moisture that condenses inside the clothing, analogous to a heat pipe. For impermeable clothing, lambda(app) even exceeds lambda by four times that value at 10 degrees C. These findings demonstrate that the traditional way of calculating evaporative heat loss of a clothed person can lead to substantial errors, especially for clothing with low permeability, which can be positive or negative, depending on the climate and clothing type. The model presented explains human subject data on EVAP that previously seemed contradictive.

Synthesis of industrial scale NaY zeolite membranes and ethanol permeating performance in pervaporation and vapor permeation up to 130 °C and 570 kPa

NaY zeolite tubular membranes in an industrial scale of 80 cm long were synthesized on monolayer and asymmetric porous supports. The quality of synthesized membranes were evaluated by pervaporation (PV) experiments in 80 cm long at 75 °C in a mixture of water (10 wt.%)/ethanol (90 wt.%), resulting in higher permeation fluxes of 5.1 kg m −2 h −1 in the monolayer type membrane and of 9.1–10.1 kg m −2 h −1 in the asymmetric-type membranes, respectively. The uniformity with small performance fluctuation in longitudinal direction of the membranes were observed by PV for 10–12 cm long samples at 50 °C in a mixture of methanol (10 wt.%)/MTBE (90 wt.%). The ethanol single component permeation experiments in PV and vapor permeation (VP) up to 130 °C and 570 kPa were performed to determine the relations between the ethanol flux and the ethanol pressure difference across the membrane which is represented by permeance (Π, mol m −2 s −1 Pa −1) for estimate of potential of ethanol extraction through the present NaY zeolite membranes applying feasible studies. Results indicate that (1) the permeation fluxes are linearly proportional to the driving force of vapor pressure for each sample in VP and PV. The permeances through an asymmetric support type membrane were rather constant of 0.6–1.2 × 10 −7 mol m −2 s −1 Pa −1 in the wide temperature range of 90–130 °C in PV and VP, indicating that the ethanol permeances have weak temperature dependency with the feed at the saturated vapor pressure. The results of superheating VP experiments showed that ethanol permeation fluxes are increased with increasing of the degree of superheating at a given constant feed vapor pressure. The ethanol permeances are increased with increasing of temperature at a given feed vapor pressure. The superheating VP could be a feasible process in industry.

Humidity parameters from temperature: test of a simple methodology for European conditions

AbstractAtmospheric water content is important for local and regional climate, and for chemical processes of soluble and solute species in the atmosphere. Further, vapour pressure deficit (D) is one of the key controls on the opening of stomata in plants and is thus an important force for evapotransporation, plant respiration and biomass production and for the uptake of harmful pollutants such as ozone through the stomata.Most meteorological stations typically measure both temperature and relative humidity (RH). However, even if recorded at finer time resolution, it is usually the daily or often monthly means of RH which are published in climate reports. Unfortunately, such data cannot be used to obtain the changes in RH or vapour pressure deficit over the day, as this depends strongly on the diurnal temperature variation during the day and not upon the mean temperature.Although RH typically changes significantly over the day, the ambient vapour pressure is often remarkably constant. Here a simple method to estimate diurnal vapour pressure is evaluated, based upon an assumed constant vapour pressure, and that recorded minimum temperatures approximate dew‐point temperatures. With a knowledge of only temperature, we will show that day to day estimates of vapour pressure, humidity and especially D, can be made with reasonable accuracy. This methodology is tested using meteorological data from 32 sites covering a range of locations in Europe. Such a simple methodology may be used to extract approximate diurnal curves of vapour pressures from published meteorological data which contains only minimum temperatures for each day, or where humidity data are not available. Copyright © 2007 Royal Meteorological Society

A new methodology of studying the dynamics of water sorption/desorption under real operating conditions of adsorption heat pumps: Modelling of coupled heat and mass transfer in a single adsorbent grain

A new experimental methodology of studying the kinetics of water vapour sorption/desorption under operating conditions typical for isobaric stages of adsorption heat pumps has been proposed and tested experimentally in [Yu.I. Aristov, B. Dawoud, I.S. Glaznev, A. Elyas, A new methodology to study the kinetics of water vapour sorption/desorption under real operating conditions of adsorption heat pumps: 1. Experiment, Int. J. Heat Mass Transfer, submitted for publication]. Here, we analysed results obtained in [Yu et al., submitted for publication] by mathematical modelling of the coupled heat and mass transfer in a single adsorbent grain which is in thermal contact with a metal plate subjected to a fast temperature jump/drop (at constant vapour pressure). The dynamic behaviour turns out to be closely linked with equilibrium properties of the adsorbent, in particular, with the initial/final temperatures and with the shape of the segment of water sorption isobar (convex or concave) between these temperatures.

Constant vapor pressure evaporation from emulsions

The evaporation from three phases in equilibrium in a three-component emulsion was investigated. The calculations considered the fact that the composition of three phases and that of the vapor is determined by the system per se, leaving only the gross composition of the emulsion to be varied. The total composition was established for one scenario, the evaporation taking place with no change in the composition of the emulsion. The relative amounts of the three phases to satisfy this condition were calculated using two methods, and the complexity of the methods was compared.

Evaporation from a Limonene Emulsion

A publication to honor the legacy of Per Ekwall, the Finnish colloid chemist, whose research was on the forefront for several decades in the area of colloidal association structures. In the article an algebraic method was applied to obtain information about the conditions during evaporation of the volatile compounds in a system of limonene, water and Laureth 4 (a commercial tetraoxyethylene dodecyl ether). The evaporation path was calculated using published information about the phase diagram of the system and about the vapor pressures of the components at selected compositions. In the calculations intervals between steps were made proportional to the difference between the excess vapor pressure of water at the selected level of relative humidity and its full vapor pressure at zero relative humidity. This calculation method inherently gave linear time dependence of the remaining water in the emulsion because of its constant vapor pressure. The calculations also revealed the amount of limonene to be close to linearly dependent on time. The reason for this latter result was found in the features of the phase diagram; in turn caused by the limonene oil phase being a W/O microemulsion with moderate vapor pressure variation with composition.