Vapor Density Research Articles

New modified PC-SAFT pure component parameters for accurate VLE and critical phenomena description

The theory of Perturbed Chain Statistical Associating Fluid (PC-SAFT) is largely applied in many industrial fields. It requires three parameters: the segment number (m), the hard-core segment diameter (σ), and the segment-segment interaction energy parameter (ε/k) for every pure non-associating fluid. By convention, they are determined by fitting vapor pressure and liquid density data. However, the shortage behind these parameters adopted by their respective authors is that they give excessive values of critical temperatures and critical pressures, which are crucial to forecasting vapor-liquid critical pressure and composition of the mixture at high pressures and temperatures.In this paper, a new approach is proposed to evaluate PC-SAFT parameters of different substances from diverse chemical families. Good fits of saturation pressure and vapor densities values of 94 pure substances are obtained, with an overall AARD of 0.89% and 1.50% respectively.The proposed method requires as input the critical pressure (Pc), the critical temperature (Tc), and the acentric factor (ω). By using these parameters, PC-SAFT estimates with accuracy the critical properties of pure compounds as well as the successful prediction of vapor-liquid equilibria for many non-associating binary systems at critical regions including mixtures containing ammonia, comparing with other literature values. But the limitation of this method is reflected in underestimated liquid densities.

New Helmholtz Equation of State for HFO-1234ze(E) with Comprehensive Assessment

Two issues of energy and environment cannot be separated in energy utilization systems. Using the working fluids in the thermal systems has to be highly attained due to these fluids may affect to the energy efficiency, global warming, and ozone depletion. Trans-1,3,3,3-tetrafluoropropene (HFO-1234ze(E)) was developed to address the issue. This fluid can replace the use of R-134a which is available in commercial market. Reliable thermodynamic equation of state (EOS) for HFO-1234ze(E) plays important role on optimization and design of refrigeration and thermal power systems.Helmholtz EOS is used as base of mathematical model because it is able to easily derive all thermodynamic properties and reliable to represent for a wide range of fluid phase. A new EOS was developed with a genetic algorithm combined with regression. The EOS represents thermodynamic properties of HFO-1234ze(E) with average absolute deviation (AAD) of 0.043% for the ideal gas isobaric specific heat, 0.084% for the liquid density, 0.39% for the vapor density, 0.096% for the vapor pressure, 0.11% and 1.0% for the saturated liquid and vapor densities. The caloric properties can be represented within AAD of 13%, 1.5%, and 5.4% for the isochoric, isobaric, and saturated specific heats, respectively, and the ADD of the speed of sound is 0.12% for liquid phase and 0.063% for vapor phase. The EOS also has proper behavior of the second and third virial coefficients and has proper extrapolation trend for the caloric and PVT properties. The EOS can be applied for temperature up to 600 K and pressure up to 100 MPa.

Vapor-liquid equilibrium, liquid density and excess enthalpy of the carbon dioxide+acetone mixture: Experimental measurements and correlations

ABSTRACT New vapor-liquid equilibrium data of the CO2+acetone mixture were determined from vapor pressure measurements using a static and synthetic method from (283.15 to 383.15) K and a composition range from (4 to 85) % in CO2 mole fraction. The fugacity coefficients approach with the Soave-Redlich-Kwong equation of state was used to calculate the composition of the phases and the binary interaction parameter. The average relative deviation between the experimental and calculated pressure values was 0.14 % and the maximum deviation was 5.0 %. Carbon dioxide shows total miscibility and good solubility in acetone in the conditions studied. The liquid density of the mixture was measured with a vibrating-tube densimeter from (283.15 to 353.15) K, at sufficient pressure to guarantee the liquid state, and a composition range from (6 to 82) % in CO2 mole fraction. The liquid density values calculated by the equation of state with the Peneloux correction were compared with the experimental values and agreement was good with a maximum deviation of 7 % and an average deviation of 0.7 %. The excess molar enthalpies were measured by a flow-calorimetric technique at (283.30 and 298.30) K and pressures from (9.00 to 14.00) MPa. Finally, the experimental data on vapor pressure, density, and excess molar enthalpy were fitted using empirical equations, and the first two were compared with data reported in the literature. Average deviations were between (0.07 and 30) % in the vapor-liquid equilibrium, and between (0.51 and 8.8) % in the density.

Simplified surface heat source distribution for GMAW process simulation based on the EDACC principle

A simplified surface heat source for gas metal arc welding (GMAW) process simulation based on the principle of evaporation determined arc cathode coupling (EDACC) is presented. It allows for a simple implementation in any GMAW weld pool simulation and is dependent on the width of the arc, as well as the weld pool surface temperature, but it can also be applied with the temperature and iron vapor density of the plasma instead of the width of the arc, if available. While it is considered separately from the droplets, it gives the heat flux as well as the current density distribution onto the weld pool surface, which are in general not axis-symmetric. The heat source distribution is normalized and multiplied to the value of any total heat and total current and it allows to calibrate for the maximum weld pool surface temperature. For the ionization and evaporation, only iron atoms are considered, and the shielding gas is assumed as argon. The result is given in graphical form as well as in the form of easy to implement functions for a reasonable range.

Multi-sensor study of precipitable water vapor and atmospheric profiling from microwave radiometer, GNSS/MET, radiosonde, and ECMWF reanalysis in Beijing

We compare the precipitable water vapor (PWV) determined using a domestic ground-based microwave radiometer (MWR PWV) with PWV measurements from radiosondes (RS PWV), the Global Navigation Satellite System (GNSS PWV), and reanalysis from the European Centre for Medium-Range Weather Forecasts (ECMWF) (EC PWV). The MWR PWV is affected by precipitation, and thus it differs greatly from the other three observations. The correlation coefficient between the MWR PWV and RS PWV (EC PWV) is 0.934 (0.933), and the root mean square error (RMSE) is 17.19 mm (16.05 mm), whereas the correlation coefficient between the GNSS PWV and RS PWV (EC PWV) is 0.989 (0.986), and the RMSE is 17.04 mm (15.83 mm). The scatter distributions of the MWR PWV and the other observations show a systematic deviation that is negatively correlated with the surface air temperature. After polynomial fitting and corrections are applied, the correlation coefficients between the MWR PWV and the RS PWV and EC PWV increase to 0.993 and 0.99, and the RMSEs decrease to 14.13 and 15.86 mm, respectively. The temperature and water vapor density profiles are retrieved from the bright temperature and can reflect the quality of the bright temperature. Because the PWV retrieved from the ground-based MWR has a linear relationship with the brightness temperature, the accuracy of the PWV can be analyzed in terms of the quality of the brightness temperature. We found that the differences in the temperature profile below 2000 m are smaller, whereas those in the water vapor density profile below 2000 m show the largest difference. This finding reflects the differences in the brightness temperature, which may be the cause of the inaccurate PWV observations.

Upward Transport of Trichloroethylene Vapour in a Dry Soil Column

Experimental and modelling studies were performed to assess the predictability of gas phase transport models based on the Fickian-type diffusion expression and dusty-gas model (DGM) equations for the upward transport of trichloroethylene (TCE) vapour at low vapour source densities in a dry soil column. The TCE vapour concentrations measured upstream in the column were only 6% and 15.7% of the TCE saturated vapour concentration (i.e., TCE vapour densities of 0.031 and 0.08 g/L, respectively) when TCE liquid existed in the upstream cavity as a vapour source. A good fit between the model-predicted profile of the downstream TCE vapour concentration and the observed data can only be attained by using a tortuosity value that is 0.2–0.3 times of that computed by the Millington and Quirk’s (1961) empirical equation. This result revealed that diffusion dominates over advection for the aforementioned transport conditions. Furthermore, the differences between the concentration evolution profiles away from the source predicted by the Fickian and DGM-based models present a reverse trend depending on whether the downstream boundary is covered (impermeable) or uncovered (opened to the air). The results revealed that the predicted upward transport of dense vapour at low source densities with a covered downstream boundary predicted by the two models differed considerably. • Trichloroethylene (TCE) vapour was <20% saturated in the experimental soil column containing the TCE liquid. • The fitted effective molecular diffusion coefficient was less than the estimated coefficient by the usual method. • A Fickian-type diffusion model may under- or over-predict vapour concentrations for upward transport of dense vapour.

Simulation of the outflow of steam from a high-pressure volume into a closed external region

A numerical simulation of the process of unsteady outflow of steam (steam-water mixture) from a volume under high pressure into a closed region with rigid boundaries is carried out. The calculations used a thermodynamically equilibrium homogeneous model of a vapor-liquid medium. At small and large (up to 0.15 s) times, spatial distributions of pressure, mass vapor content, density and temperature were obtained and analyzed.

Properties of Vacuum Arcs Generated by Switching RMF Contacts at Different Ignition Positions

The influence of initiation behavior of the drawn arc on the arc motion, on arc characteristics during the active phase, as well as on the post-arc parameters, was studied. The study was focused on arc dynamics, determination of the anode surface temperature after current interruption, and diagnostics of metal vapor density after current zero crossing. Different optical diagnostics, namely high-speed camera video enhanced by narrow-band optical filters, near infrared spectroscopy, and optical absorption spectroscopy was applied. The initiation behavior of the drawn arc had a clear influence on arc parameters. Higher local electrode temperature occurs in case of the electrodes with ignition point near the outer electrode boundary. This further causes an enhanced density of chromium vapor, even in cases with lower arc duration. The results of this study are important for design development of switching RMF contacts for future green energy applications.

Resolving the discrepancy between theoretical and experimental polarization of hyperpolarized 129Xe using numerical simulations and in situ optical spectroscopy

For emerging biomedical applications of hyperpolarized xenon, the ability to obtain reliably high nuclear spin polarization levels is paramount. Yet, experimental nuclear spin polarization levels of xenon are highly variable and, more than often than not, well below what theory predicts. Despite rigorous and well-studied theoretical models for hyperpolarization and continuous-flow spin-exchange optical pumping (SEOP), there remains a substantial discrepancy between the theoretical and experimental polarization of 129Xe; inexplicably, seemingly similar experimental parameters can yield very different polarization values. In this paper, the validity of the assumptions typically made about the thermodynamic state of the Rb vapor inside the optical pumping cell and the gas dynamics are investigated through finite element analysis simulations of realistic optical pumping cell models, while in situ optical and nuclear magnetic resonance spectroscopy measurements are used to validate the results of the simulations. Our results show that shorter xenon gas residence times and lower Rb vapor densities than those predicted by empirical saturated vapor pressure curves, along with incorrect SEOP parameters, are the primary cause of the discrepancy between theoretical and experimental polarization values reported in the literature.

Characteristics of Heat Transfer During Cooling Down Process in a Single Cargo Tank of LNG Carrier

A deep understanding of heat transfer characteristics is essential in evaluating risk and putting forward any option for the Liquefied Natural Gas (LNG) tank cooling down process. A novel Computational Fluid Dynamics (CFD) model was built to perform the flow and heat transfer simulation of the process. The predicted results agreed well with the test data from a prototype LNG tank. Then the heat transfer characteristics of the process were analysed. It was found that the vapour temperature and density were linearly varying and became stable after 2.3 hours. A sudden pressure drop risk was identified during the process, which will cause the inwards collapse risk of the invar membrane. Then the proposals to prevent the risks of the inwards collapsing membrane are presented. The heat transfer characteristics of the vapour and different membrane layers were analysed in detail, and if the suggested option was to be implemented this could save about 39% of LNG consumed.

Molecular Complexity of Working Fluids Dedicated to Organic Rankine Cycle (ORC)

Organic Rankine Cycle (ORC) power plants are the most well-known and mature technology used to converting low and medium-temperature heat into electricity, especially from waste heat and renewable energy sources (including geothermal and solar thermal). Despite the level of development of ORC systems available on the market, there are still many aspects in the context of improving those units – constructing economically profitable low power unit, improving efficiency, selection an appropriate working fluid, etc. This paper analyzes 17 workings fluids dedicated to ORC system and discusses an existence of low stability region in their dense vapors and its influence on some peculiarities in behaviors of selected isentropic and dry fluids. The analysis shows relation between the retrograde phenomena in the flow of ORC fluids and mechanical and thermodynamic stability parameters.

Application of Hazop, Lopa and Sil to an Alkylation Unit in a Refinery: a Case Study

In a refinery, an alkylation unit is a process for producing gasoline range material (alkylate) from olefins such as propylene, isobutene, butylene, and pentene. In the alkylation process, light hydrocarbons from the Fluid Catalytic Cracking Unit (FCC) react in presence of a catalyst (hydrofluoric acid or sulphuric acid), to form a mixture of heavier hydrocarbons. After the reaction, the alkylate meets the specification as high octane gasoline. Important safety considerations in this process are related to the catalyst. For example, if hydrofluoric acid (HF) is used, its high vapour pressure, making it easily vaporized if a leak occurs in the units. HF can travel a significant distance as a dense vapour. Even though a small concentration of HF is used in the reaction, it is still enough to cause human and environmental problems, since it is a very corrosive and toxic inorganic acid. The objective of this study was to evaluate the hazards in the alkylation unit at a refinery located in Latin America, applying HAZOP, LOPA, and SIL methodologies. This study is based on the assumption that the process operates according to the conditions intended in its design, thus the risk and operability problems are unlikely to occur. The HAZOP (Hazard and Operability Study) analysis covered 13 sections of the alkylation process. Hazardous scenarios were categorized as: related to safety, environmental, and financial; each topic was also risk ranked to assess the strength of existing safeguards. The causes of hazardous scenarios were identified including human error, equipment failure, and external events. The severity of deviations was evaluated without any protection or safeguards. From all the deviations that were analysed, 24 scenarios were identified as significant risk and of high risk. These scenarios were then analysed by LOPA (Layer of Protection analysis) and SIL (Safety Integrity Level) methodologies, to identify the layers of protection that mitigate the hazardous scenarios found in the HAZOP analysis, as well as assigning a PFD (probability of failure on demand) value on each safeguard. Based on this, recommendations are provided, to mitigate the consequences or improve the operational capab

Oxidation of Dibenzothiophene in Water Vapor and Argon at Increased Pressure

This article presents the results of study of dibenzothiophene (DBT, the fuel equivalence ratio $$\varphi = 0.94$$ –1.01) oxidation in a medium of dense water vapor or argon at uniform heating (1 K/min) to 853 K of a tubular reactor made of stainless steel. The oxidation of DBT was found to proceed by the mechanisms of heterogeneous and homogeneous reactions. From the dynamics of the temperature of the reaction mixtures it follows that self-ignition of DBT in an environment of water vapor and argon occurs at 532 K. A Pt-Rh/Pt thermocouple introduced into the center of the reaction volume was found to have a catalytic effect on DBT oxidation. The results of mass spectrometry analysis of gas products show that the degree of carbon burnout exceeds 95% mol. The interaction of stainless steel and H $$_{2}$$ SO $$_{4}$$ formed in the DBT oxidation in water vapor causes steel corrosion, which is suppressed due to neutralization of the acid by calcium carbonate. The composition of the corrosion products was determined by the X-ray diffraction and energy-dispersive analysis methods.

Competition of Concentration Narrowing and Power Broadening of a Dark Resonance in a Ladder System of Rubidium Atoms: Specificities of Its Occurrence in Thin Spectroscopic Cells

The effect of electromagnetically induced transparency (EIT) in a three-level ladder system 5S1/2‒5P3/2 –5D5/2 of Rb atoms is investigated. The effect of spectral narrowing of a dark resonance (DR) as a function of atomic vapor density and thickness L of a spectroscopic cell containing Rb vapor is demonstrated. Thickness L was varied in the range of 390 nm to 4 mm, while atomic density N was increased up to ~1016 cm–3; in the process, high-intensity coupling radiation and weak probe radiation were used. The strongest effect, namely, a 22-fold spectral narrowing of the DR, was achieved in a cell of thickness L = 4 mm. The effect of spectral narrowing was decreasing with decrease in thickness L: a 2.4-fold spectral narrowing of the DR was observed at L = 2 μm. Spectral narrowing was nearly absent at L = 0.8 μm, and spectral broadening of the DR was observed with further decrease in the cell thickness down to L = 0.4 μm. A close to 100% DR contrast was achieved in nearly all cases at moderate atomic densities and high intensities of the coupling radiation. An interpretation of the effect of spectral narrowing and broadening of the DR is proposed.

Modelling acid gas mixtures of polar aprotic solvents and CO2 with the Cubic Plus Association equation of state

The Cubic Plus Association (CPA) equation of state and the Soave–Redlich–Kwong (SRK) equation of state coupled to Mathias–Copeman and volume correction parameters were used to correlate the vapor pressures and densities of pure polar aprotic solvents (PAS). It is shown that the CPA model (with 2B scheme) performed better than CPA (with inert scheme), SRK and its modifications in all cases for vapor pressure and densities. The performance of two mixing rules, namely the van der Waals one–fluid (vdW1f) and the Huron–Vidal (HV) mixing rules, is evaluated for these models on correlating the bubble–point pressures of CO2 + PAS mixtures. The CPA–HV model performs best at several temperatures, with the global average absolute deviations equal to 7.2 % for CPA–HV, 8.1 % for CPA–vdW1f and 8.7 % for SRK–HV. No improvements were found in the performance of the CPA–vdW1f when the solvation between CO2 and PAS was accounted for regression of bubble–point pressures.

Model for photothermal ionization and molecular recombination during pulsed ablation of polyethylene

The surface erosion of polyethylene is studied under conditions characteristic of extremely high-rate heating expected in laser-driven and high energy density experiments. A coupled model for photoionization and volumetric photothermal degradation of polyethylene is developed that includes finite rate chemistry and molecular recombination of radicals. First, the model is used to explore the evolution of radicals and hydrocarbons during isochoric heating, for which it is found that polyethylene is not in chemical equilibrium for rates &amp;gt;108K/s. Then, the model is used to explore the cooperativity between photoionization and photothermal ionization during one-dimensional ablation from a pulsed heating source, accounting for coupled energy deposition, thermokinetics, thermochemistry, hydrodynamics, mechanics, and thermal conduction in the ALEGRA multi-physics code. The ablation depth per energy pulse is found to agree with an analytical model for instantaneous energy deposition and absent molecular recombination or photoionization. Otherwise, molecular recombination of radicals reduces the depth of ablation per pulse, owing to thermal stabilization on forming branched molecules. Radical formation through photoionization can be compensated for by recombination, but it accelerates ablation at high enough photoionization rates. Finally, the influence of molecular recombination on the ablation depth is found to decrease for long pulses, owing to decreased recombination reaction rates at lower vapor densities near the ablated surface. These and other findings highlight competition between the processes of scission, recombination, and photoionization during pulsed ablation of polyethylene.

Nanostructured Alkali-Metal Vapor Cells

Atom-light interactions in nano-scale systems hold great promise for novel technologies based on integrated emitters and optical modes. We present the design architecture, construction method, and characterization of an all-glass alkali-metal vapor cell with nanometer-scale internal structure. Our cell has a glue-free design which allows versatile optical access, in particular with high numerical aperture optics, and incorporates a compact integrated heating system in the form of an external deposited ITO layer. By performing spectroscopy in different illumination and detection schemes, we investigate atomic densities and velocity distributions in various nanoscopic landscapes. We apply a two-photon excitation scheme to atoms confined in one dimension within our cells, achieving resonance line-widths more than an order of magnitude smaller than the Doppler width. We also demonstrate sub-Doppler line-widths for atoms confined in two dimensions to micron-sized channels. Furthermore, we illustrate control over vapor density within our cells through nano-scale confinement alone, which could offer a scalable route towards room-temperature devices with single atoms within an interaction volume. Our design offers a robust platform for miniaturized devices that could easily be combined with integrated photonic circuits.

On Correlations between Fields of Temperature, Small Gas Impurities, and Wind in the Surface Layer of the Atmosphere

In a number of studies, including our studies performed at the Institute of Atmospheric Physics, Russian Academy of Sciences, stable correlations have been found between scalar fields of the surface layer (fields of temperature and concentrations of small gas impurities—ozone and water vapor), as well as correlations between these scalars and wind speed. This article shows that the correlations of scalars can be understood on the basis of the hypothesis of similarity of surfaces with equal concentrations of impurities and isothermal surfaces, and that temperature maps explain, at a qualitative level, the correlations of temperature and speed. The unique low-inertia devices developed for pulsed measurements of the density of ozone and water vapor are described. Experiments with synchronous registration of temperature, humidity, and ozone, which showed a high correlation of the above scalar fields, and experiments with the vertically multipoint synchronous registration of temperature, which made it possible to construct maps of sections of isothermal surfaces with a vertical plane along the wind direction, are considered.

A semi-analytical model of heat transfer and pressure drop in annular flow regime for flow boiling in a horizontal microtube at uniform heat flux

A semi-analytical model for predicting heat transfer and pressure drop in annular flow regime for saturated flow boiling in a horizontal microtube at a uniform heat flux has been developed based on a one-dimensional separated flow model. More than 600 two-phase heat transfer, 498 two-phase pressure drop, and 153 void fraction experimental data points for annular flow regime were collected from the literature to validate the present model. The collected data were recorded for various working fluids, R134a, R1234ze, R236fa, R410a, R113, and CO2, for round macro- and microsingle horizontal tubes with an inner diameter range of 0.244 mm ≤ Dh ≤ 3.1 mm, a heated length to diameter ratio of 90 ≤ Lh/Dh ≤ 2000, a saturation temperature range of –10 ≤ Tsat ≤ +50 °C, and liquid to vapor density ratios in the range 6.4 ≤ ρf/ρg ≤ 188. The model was tested for laminar and turbulent flow boiling conditions corresponding to an equivalent Reynolds number, 1900 ≤ Reeq ≤ 48 000, and confinement number, 0.27 ≤ Cconf ≤ 3.4. Under the annular flow regime, the present model predicted the collected data of the heat transfer, pressure drop, and void fraction with mean absolute errors (MAE) of 18.14%, 23.02%, and 3.22%, respectively.

Demonstration of the 1.53-µm coherent DIAL for simultaneous profiling of water vapor density and wind speed.

The 1.53-µm coherent differential absorption lidar (DIAL) is demonstrated for the simultaneous profiling of water vapor (H2O) density and wind speed. The optical setup is fiber-based. The wavelength locking circuit can achieve precise locking of 13.0 MHz by the combination of the line center locking to the hydrogen cyanide (HCN) absorption line and offset locking to the H2O absorption wavelength. The measurable range for the simultaneous profiling is up to 1.2 km. The DIAL-measured H2O density is compared with the one measured by an in-situ sensor. Qualitative good agreement is shown with the random error of 0.56 g/m3.