Vapor Pressure Curve Research Articles

Graphical Interpretation of Wet Surface Evaporation Equations

AbstractPotential (wet surface) evaporation is the basis for many methods to estimate actual evaporation. Penman's (1948, https://doi.org/10.1098/rspa.1948.0037) combination of energy budget with mass and energy transfer equations can be depicted on temperature‐vapor pressure graphs. Key to this depiction is two straight lines on the graph representing constant enthalpy of the air at measurement height and at the surface skin, with the gap between the lines representing a combination of aerodynamic resistance variables and available energy. The equations on which Penman based his formula are easily solved numerically (without need for Penman's famous assumption) for T0w, the temperature the surface would have if it was saturated, keeping all other variables constant. Wet surface evaporation is proportional to the vapor pressure difference between the measurement height and the surface skin. Equilibrium evaporation, based on the slope of the vapor pressure curve at T0w, is also easily represented in the graph. The difference between the correct wet surface evaporation rate and Penman's approximation is immediately visible on the graphs. The different wet surface evaporation rates are compared using data from a tropical savanna in Australia. Implications for the classic two‐component interpretation of Penman's equation are discussed.

Method for prediction of vapor pressure for isotopes and isotope-containing gases

Stable isotopes of light elements, such as 13C, 18O and 15N are used as markers in medicine, pharmacy, biology and other sciences. The demand for isotopes is continuously rising. It will lead to the extension of existing production capacities in the next years and could trigger the development of corresponding processes and systems. The most important issue concerns the optimization of the isotopes production costs. It would be a key factor for the establishment and commoditization of isotope-based methods for everyday life and could improve the quality of health care worldwide. The most economical approach to industrial scale production of stable isotopes is the cryogenic distillation. This method uses the difference in substances’ vapor pressures for separation purposes. But only limited data on the vapor pressure curves of isotopes is currently available, which affects the development of new processes. A new method to predict vapor pressures for stable isotopes is described in the present work. The method is based on a combination of the theory of corresponding states with limited experimental data on the vapor pressure ratios of isotopes available in the literature. This method allows to generate parameters like the critical temperature and pressure for isotopes and isotope-containing gases. In the present work this method is applied to carbon monoxide based on the carbon isotopes.

Calculation of the thermodynamic properties of R448A and R449A in a saturation temperature range of 233.15 K to 343.15 K using molecular dynamics simulations

R448A, which is a quinary mixture and has a global warming potential (GWP) of 1390, and R449A, which is a quaternary mixture and has a GWP of 1282, have been recommended for commercial refrigeration systems to replace R404A, which has a GWP of 3943 as per EU Regulation No. 517/2014. The thermodynamic properties of R448A and R449A, such as vapor pressure, saturated density, and vapor-liquid coexistence curve with critical points were computed for temperatures ranging from 233.15 K to 343.15 K via molecular dynamics (MD) simulations. The computed vapor pressures of R448A and R449A closely match that of R404A. The MD simulations predict the saturated densities of R448A and R449A very well in the subcritical region. The computed critical points of the three blend refrigerants were compared with published data. The radial distribution functions (RDFs) show that intra-molecular and inter-molecular interactions occur in the vapor and liquid phases for R448A and R449A. The thermodynamic properties of R448A and R449A estimated in this work will be useful for analyzing the performance of commercial refrigeration systems operating with these new blend refrigerants.

Gas-controlled heat pipes in metrology: More than 30 years of technical and scientific progresses

Abstract Gas-Controlled Heat Pipes (GCHPs) are devices based on generating and maintaining, at millikelvin level, a thermodynamic liquid-vapour equilibrium of a fluid. For this reason, GCHPs have been studied for more than thirty years for research and applications in thermal metrology. Capabilities have been constantly improved and adapted by National Metrology Institutes (NMIs) and accredited laboratories. Activities include study of vapour pressure curves of pure elements and substances, thermometers’ non-uniqueness up to 960 °C, calibrations between −20 °C and 900 °C with millikelvin uncertainties, studies of innovative pressure controllers allowing regulation better than 10−6 from below 1000 Pa up to 400 kPa. GCHPs operating at different temperature ranges have also been connected to a common pressure line in the so-called “Temperature Amplifier” configuration. This review paper presents an almost complete report about the several models of GCHPs, materials and working fluids, techniques adopted in different temperature/pressure ranges. All involved NMIs using GCHP are here included, with detailed bibliography.

Vapor-liquid equilibrium of 3-ethoxy-1,2-propanediol + water/ethanol/diethyl ether/glycerol/1,2-propanediol at different pressures

The large availability of glycerol on the market and EU directives in the field of automotive fuels prompt Eni S.p.A to develop a technology for producing biofuels from glycerol. This work focuses on determining isobaric vapor-liquid equilibrium data at different pressures of binary systems constituted by 3-ethoxy-1,2-propanediol, an intermediate product, and some of the other compounds involved in the reactions: water, ethanol, 1,2-propanediol, diethyl ether and glycerol. Moreover, the vapor pressure curve of 3-ethoxy-1,2-propanediol was determined at different temperatures. Finally, different thermodynamic models (UNIFAC, UNIQUAC, NRTL and Wilson), were tested against the experimental data to analyze their possible use when designing separation processes of 3-ethoxy-1,2-propanediol.

Uncertainty assessment of potential evapotranspiration in arid areas, as estimated by the Penman-Monteith method

The Penman-Monteith (PM) method is the most widely used technique to estimate potential worldwide evapotranspiration. However, current research shows that there may be significant errors in the application of this method in arid areas, although questions remain as to the degree of this estimation error and how different surface conditions may affect the estimation error. To address these issues, we evaluated the uncertainty of the PM method under different underlying conditions in an arid area of Northwest China by analyzing data from 84 meteorological stations and various Moderate Resolution Imaging Spectroradiometer (MODIS) products, including land surface temperature and surface albedo. First, we found that when the PM method used air temperature to calculate the slope of the saturation vapor pressure curve, it significantly overestimated the potential evapotranspiration; the mean annual and July-August overestimation was 83.9 and 36.7 mm, respectively. Second, the PM method usually set the surface albedo to a fixed value, which led to the potential evapotranspiration being underestimated; the mean annual underestimation was 27.5 mm, while the overestimation for July to August was 5.3 mm. Third, the PM method significantly overestimated the potential evapotranspiration in the arid area. This difference in estimation was closely related to the underlying surface conditions. For the entire arid zone, the PM method overestimated the potential evapotranspiration by 33.7 mm per year, with an overestimation of 29.0 mm from July to August. The most significant overestimation was evident in the mountainous and plain nonvegetation areas, in which the annual mean overestimation reached 5% and 10%, respectively; during July, there was an estimation of 10% and 20%, respectively. Although the annual evapotranspiration of the plains with better vegetation coverage was slightly underestimated, overestimation still occurred in July and August, with a mean overestimation of approximately 5%. In order to estimate potential evapotranspiration in the arid zone, it is important that we identify a reasonable parameter with which to calibrate the PM formula, such as the slope of the saturation vapor pressure curve, and the surface albedo. We recommend that some parameters must be corrected when using PM in order to estimate potential evapotranspiration in arid regions.

A new thermogravimetric application for determination of vapour pressure curve corresponding to average boiling points of oil fractions with narrow boiling ranges

The average boiling point of oil fractions with narrow boiling ranges or pseudo-components is an important parameter in thermodynamic calculations in the fields of process design and environmental protection. The present work provides an experimental approach, involving a method based on the thermogravimetric analysis, for determination of the pressure dependence of average boiling points (or in other words for determination of “the vapour pressure curve corresponding to average boiling points”) of oil fractions with narrow boiling ranges, pre-prepared by distillation. This method can be used for determination of the atmospheric average boiling points (corresponding to atmospheric pressure) of thermally unstable fractions from the pressure dependence curves, obtained from the tests conducted at lower pressures. The method uses the principle of ASTM E1782 “Standard Test Method for Determining Vapor Pressure by Thermal Analysis”, where the material is vaporised at pre-determined pressure from a hermetically sealed capsule through a pinhole using a constant heating rate experiment. The accuracy of the method was evaluated on the basis of the average boiling point values of narrow boiling ranges fractions determined by rectification both at atmospheric pressure and in vacuum (determined as the arithmetic mean of the lower and upper temperature limits of the fraction). The pressure dependence curves of the average boiling points, formed here on the basis of average boiling points obtained in the pressure range from 5 kPa to atmospheric pressure, can be reliably described by the integrated Clausius-Clapeyron equation. To increase the accuracy in determining the atmospheric average boiling points of thermally unstable fractions, obtained in extrapolation from the Clausius-Clapeyron curve of the average boiling points in the tests conducted at lower pressures, a higher number of tests, on the basis of which to conduct the extrapolation, is desirable.

A PC-SAFT model for hydrocarbons V: Alcohol-hydrocarbon phase behavior with application to petroleum pseudo-components

Prediction of alcohol-hydrocarbon phase behavior within a SAFT equation of state is a well-studied topic in the recent literature. Most of these studies focus on the phase behavior of alcohols with n-alkanes, and have demonstrated the successful prediction of non-ideal phase behavior. If the same predictability is to be attained for mixtures of alcohols with aromatic species, there must be a systematic approach to allow for the aromatic cores to receive hydrogen bonds. In this work, we develop a new alcohol parameterization within the PC-SAFT equation of state which is shown to give accurate predictions of alcohol-hydrocarbon phase behavior with both saturated and aromatic hydrocarbons. A major application of alcohol-hydrocarbon phase behavior is the prediction of the phase behavior of alcohol-gasoline blends. In a refinery setting, gasoline will be described by a series of petroleum pseudo-components. In conjunction with the developed alcohol parameterization, we demonstrate the ability of the recently developed EMPETRO characterization scheme to predict the phase behavior of alcohols with petroleum pseudo-components. In a sister publication [Vella J. R. and Marshall B. D., Fuel, 2019] we apply this methodology to predict refinery blending properties of alcohol-gasoline blends such as Reid vapor pressure and ASTM D86 distillation curves.

Effects of fuels on flash boiling spray from a GDI hollow cone piezoelectric injector

Flash-boiling of fuel sprays can have a significant effect on spray formation and its characteristics due to bubble nucleation, growth, and phase change, producing explosive-like atomization and complex spray structures. In this work, experiments were conducted to study the spray of both pure substance fuels (pure isooctane, pure ethanol) and multicomponent fuels (50/50 mixture of isooctane and ethanol, commercial gasoline), under flash boiling conditions and non-flash boiling conditions. Under different temperature and ambient pressure, different superheated degrees can be achieved for the fuels. Pure substances have a single vapor pressure curve, while mixtures do not have a single boiling point at a given pressure, and a two-phase region exists for multicomponent fuel. Under the same conditions, ethanol has higher superheated degree compared to isooctane, but the heat of vaporization for ethanol is also much higher. This contributes to the fact that less boiling is observed in the ethanol spray with longer penetration in several cases. Mixture 50/50 shows a good average of isooctane and ethanol for spray penetration and spray front plume ratio analysis. Gasoline, due to its low initial boiling point and wide range of components, has the widest plume ratio distribution and smallest gradient, as well as complex peak penetration velocity distribution. The results also imply that adding low boiling point (preferably with low heat of vaporization as well) additive or component to high boiling point fuel can facilitate flash boiling, fuel vaporization and mixing.

The vapor pressure of liquid and solid water phases at conditions relevant to the atmosphere

In the atmosphere, water can be present in liquid and solid phases, but the vapor phase is generally predominant. Condensed phases of water occur under a wide range of conditions, ranging from polar mesospheric clouds at the lowest atmospheric temperatures and at low pressure to the much warmer tropospheric clouds. The temperature range at which ice or water clouds are observed spans from T = 100 to 300 K with pressures ranging from about 10−3 mbar to about 1 bar. Over this wide range, water is known to form several condensed phases, which can be separated into crystalline (hexagonal and stacking disordered ice) and noncrystalline phases (liquid and supercooled liquid water, amorphous solid water). We report on the vapor pressure of these water phases with a focus on metastable amorphous solid water and stacking disordered ice in the light of recent experimental findings and discuss possible implications for the atmosphere. We present evidence that supercooled liquid water and low density amorphous solid water do not belong to the same phase and therefore, no continuous vapor pressure curve can be given.

Physical properties of gasoline-ETBE-isobutanol (in comparison with ethanol) ternary blends and their impact on regulatory compliance

Many developed countries promote biofuels to fight against climate change. The blend of ethanol and ethyl tert-butyl ether (ETBE) with gasoline is a common way to increase the renewable energy content of fuel. The use of bio-isobutanol instead of or in addition to ethanol can help solve some problems of ethanol.Eighty five gasoline-isobutanol-ETBE blends (up to 100/100/30%v/v respectively) were tested. For each blend, the density, vapour pressure (RVP) and distillation curve were measured. The impact that the addition of isobutanol-ETBE blends has on gasoline standards was analysed and also compared with that caused by the addition of ethanol-ETBE blends.Some chemical data of these fuels and the densities measured allow us to identify some advantageous properties for isobutanol blends in terms of oxygen content, energy density, stoichiometry, renewable energy content, etc. The excess of RVP for isobutanol ternary blends is lower than that of ethanol blends, being advantageous in terms of evaporative emissions. Apart from the oxygen content limit, the most restrictive parameters for isobutanol ternary blends are the evaporated percentages at 100 °C and 70 °C, and the RVP. Nevertheless, the different performance of ethanol and isobutanol blends could help to meet fuel standards by using both bio-alcohols at once.

Design of heat-integrated columns: Industrial practice

Heat integration of distillation columns offers a significant potential to reduce energy costs and carbon footprint in process plants. The conceptual design for heat integration is straightforward: candidate columns may be identified simply by evaluation of the vapor pressure curves of their top and bottoms products. Once the energy and cost savings potential is estimated, the easy part is over and the real challenge for the designers begins. Successful implementation of heat integration will have a strong impact on the overall plant setup intensifying interactions between equipment design, plant layout, instrumentation, process control, and safety concept. In order to master this increased project complexity, the design team needs to begin to tackle these questions in early project stages and find sustainable solutions in the pre-basic engineering phase already.The paper outlines a useful methodology for the successful design of heat-integrated column systems. The guidelines provided help the practitioner to anticipate and solve typical problems, avoid pitfalls and find practical solutions resulting in cost-effective, reliable designs near the energy optimum. The methodology has been successfully applied in industrial practice and is demonstrated using a recent project as an example.

Spectroscopic Measurements of Methane Solid-Gas Equilibrium Clapeyron Curve between 40 and 77 K.

The infrared gas-phase absorption spectrum of methane was used to determine its Clapeyron solid-gas equilibrium curve in the 40-77 K temperature range. For comparative purposes and to obtain more reliable results, two different optical experimental setups were used. At higher temperatures (53-77 K), a single pass cryogenically cooled cell was coupled to a standard low-resolution Fourier transform infrared spectrometer. The second system was a state-of-the-art vertical-external-cavity surface-emitting laser tunable source operating at around 2.3 μm, combined with a 7 m path Herriott cell, to record methane absorption features down to 40 K. From the measurements, the vapor pressure curve ln( p/Pa) = -(1191.92 ± 8.92)/( T/K) + (22.49 ± 0.16) was derived in the range 40-77 K. This corresponds to a value of 9910 ± 75 J mol-1 for the sublimation enthalpy. The relation was validated down to 40 K, increasing our knowledge of the saturation pressure by 2 orders of magnitude. Data were compared with available pressure measurements from the literature, obtained by manometric or mass spectrometry techniques, and the sublimation enthalpy was compared with a thermodynamic approach based on heat capacity measurements in the solid and gas phases.

Vapour pressure data for 2-n-propylresorcinol, 4-ethylresorcinol and 4-hexylresorcinol near their normal boiling points measured by differential scanning calorimetry

Current study presents vapour pressure curves and from these derived normal boiling points and heats of vaporisations at normal boiling points for three alkylresorcinols: 2-n-propylresorcinol, 4-ethylresorcinol, 4-hexylresorcinol. Measurements were made near their boiling points, i.e. bracketing the normal boiling points. A differential scanning calorimeter (DSC) was used for measuring vapour pressure, by which the compound’s boiling point was determined at various selected pressures following the procedure recommended by the ASTM E1782 standard. The experiments were carried out using hermetically sealable pans, that had pinholes with diameter of 50 μm in the lids, and a heating rate of 5 K·min−1. Antoine equation constants were derived to describe vapour pressure behaviours in temperature ranges of the measurements, which were 480.5 K to 629.3 K for 4-ethylresorcinol, 470.5 K to 618.9 K for 2-n-propylresorcinol, and 517.8 K to 651.0 K for 4-hexylresorcinol. The normal boiling points were found to be (605.4 ± 0.4) K for 4-hexylresorcinol, (561.8 ± 0.5) K for 4-ethylresorcinol and (552.5 ± 0.5) K for 2-n-propylresorcinol. The heats of vaporisations at normal boiling points were calculated to be (65.8 ± 0.5, 60.9 ± 0.5 and 58.6 ± 0.4) kJ·mol−1 respectively. In addition some indicative lower accuracy vapour pressure data were measured for resorcinol and catechol at lower pressures (1.3–5.3) kPa (three data points), and for 4-hexylresorcinol at (1.95–7.89) kPa (5 data points).

Creating and Experimenting with a Low-Cost, Rugged System to Visually Demonstrate the Vapor Pressure of Liquids as a Function of Temperature

A creative apparatus for use in a hands-on laboratory experiment that allows the visualization of the vapor pressure as a function of temperature is described in this paper. Inspired by homemade barometers and using simple materials that are easily accessible for teaching laboratories, a low-cost system for the establishment of the vapor-pressure curve was constructed and applied in deionized water and in car-radiator-additive samples (based on ethane-1,2-diol) at different concentrations. The system constructed proved to be efficient, simple, and quite robust and is applicable in teaching activities for comparing and visualizing vapor-pressure curves of different liquids. It can also be used to estimate the molar enthalpy of water vaporization. The main advantages and drawbacks of the apparatus created, the results obtained for liquid samples, and the evaluation of the ruggedness of this experiment are described throughout the text. The establishment of this system is the result of a project developed by first-year-undergraduate students along with postgraduate students and professors from the Bachelor’s Program of Science and Technology, hosted by the Universidade Federal do ABC, as part of the innovative course the Experimental Basis of Natural Sciences, a practical course which seeks to build knowledge through experimentation.

Determination of the vapour pressure curves and vaporization enthalpies of hafnium alkoxides using thermogravimetric analysis.

In order to identify a volatile metallo-organic precursor for the deposition of hafnium oxide (HfO2) films for atomic layer deposition (ALD) applications, the evaporative properties of hafnium alkoxides (hafnium isopropoxide, hafnium n-propoxide and hafnium n-butoxide) were investigated using thermogravimetric analysis. These hafnium alkoxide samples were synthesized by the electrochemical method and characterized by Fourier transform infrared spectroscopy, nuclear magnetic resonance and inductively coupled plasma analysis techniques. The characterization results indicated that the products were 99.997% high-purity hafnium alkoxides and could meet the requirement of purity considering the usage of making HfO2 gate oxide by ALD. Synthesized samples were subjected to a simultaneous thermogravimetric–differential thermal analysis unit at 10 K min−1 in a dry nitrogen atmosphere flowing at 100 ml min−1. Benzoic acid was used to calculate a calibration constant, which could then be inserted into a modified Langmuir equation to calculate vapour pressure curves for hafnium isopropoxide and hafnium n-propoxide. Detailed vapour pressure data for the HfO2 precursor hafnium alkoxides were determined. The vapour pressure curve of hafnium isopropoxide was constructed within the first stage, and calculated to be lnp = 31.157 (±0.200)−13130.57 (±56.50)/T. Hafnium n-propoxide and hafnium n-butoxide were simultaneously undergoing evaporation and decomposition, thus making calculations invalid.

Compressed-liquid densities of the binary mixture dimethyl carbonate + heptane at three compositions

Compressed-liquid densities of the binary system dimethyl carbonate + heptane have been measured with a vibrating-tube densimeter over the temperature and pressure ranges of 270 K to 470 K, and 1 MPa to 50 MPa at three compositions of the mixture. The measurements are part of an effort to better understand the molecular interactions of polar/non-polar mixtures. These types of mixtures often exhibit very non-ideal behavior. By measuring the mixture at three compositions and over a large range of temperature and pressure, the non-ideality can be assessed. There are no high-pressure liquid density data for this binary system in the literature, thus data reported here could only be compared to literature data at atmospheric pressure to establish their quality. The majority of literature data agree well with the presented results which have a maximum expanded uncertainty of 1.63 kg·m−3 (for the composition with the greatest mole fraction of dimethyl carbonate). The non-ideality for the mixture, in the temperature, pressure and composition range of this study was found to be minimal. This is rationalized by considering the molecular sizes, shapes, and charge distributions of the pure components and the attractive parts of their intermolecular force fields as they are reflected in the temperature ranges of their vapor pressure curves.

Flash‐point prediction of fragrances or flavours accounting for non‐ideality of the liquid phase

AbstractThe flammability classifications of flavour and fragrance oils are determined from their flash‐point temperatures, which are of critical importance for safety and regulatory considerations. The reliable prediction of flash points for our products is a business need challenged by the sheer number of ingredients present in a typical formulation, ranging from dozens to hundreds of ingredients, and their chemical diversity. To assess the predictability of flash points for the complex mixtures relevant to our industry, we consider five model mixtures of 15 perfume and flavour raw materials, with a variety of chemical functionalities, and apply Le Chatelier('s rule together with vapour pressure curves from the Design Institute for Physical Properties (DIPPR) database and activity coefficients predicted from the Modified UNIFAC (Dortmund 1993) group contribution model. Flash‐point temperatures of the 15‐compound model mixtures were predicted with an accuracy of ±2°C, compared with experimental data, when taking into account the non‐ideality of the liquid phase.

Experimental study on low temperature desalination by flash evaporation in a novel compact chamber design

The production of potable water in dry areas nowadays is mainly done by the desalination of seawater. State of the art desalination plants usually are built with high production capacities and consume a lot of electrical energy or energy from primary resources such as oil. This causes difficulties in rural areas, where no infrastructure is available neither for the plants' energy supply nor the distribution of the produced potable water. To address this need, small, self-sustaining and locally operated desalination plants came into the focus of research. In this work, a novel flash evaporator design is proposed which can be driven either by solar power or by low temperature waste heat. It offers low operation costs as well as easy maintenance. The results of an experimental setup operated with water at a feed flow rate of up to 1600 l/h are presented. It is shown that the proof of concept regarding efficient evaporation as well as efficient gas-liquid separation is provided successfully. The experimental evaporation yield counts for 98% of the vapor content that is expected from the vapor pressure curve of water. Neither measurements of the electrical conductivity of the gained condensate, nor the analysis of the vapor flow by optical methods show significant droplet entrainment, so there are no concerns regarding the purity of the produced condensate for the use as drinking water.

Design of Heat-Integrated Columns: Industrial Practice

Heat integration of distillation columns offers a significant potential to reduce energy costs and carbon footprint in process plants. The conceptual design for heat integration is straightforward: candidate columns may be identified simply by evaluation of the vapor pressure curves of their top and bottoms products. Once the energy and cost savings potential is estimated, the easy part is over and the real fun for the designers begins. Successful implementation of heat integration will have a strong impact on the whole plant setup intensifying interactions between equipment design, plant layout, instrumentation, process control, and safety concept. In order to master this increased project complexity, the design team needs to begin to tackle these questions in early project stages and find sustainable solutions in the pre-basic engineering phase already.The paper outlines a useful methodology for the successful design of heat-integrated column systems. The guidelines provided help the practitioner to anticipate typical problems and pitfalls and to find practical solutions resulting in in cost-effective, reliable designs near the energy optimum. The methodology has been successfully applied in industrial practice and is demonstrated using a recent project as an example.