Vapor Density Research Articles

Dependence of vapor bubble collapse in hot tetradecane on its pressure

Specific features of the phenomenon of vapor bubble collapse in hot tetradecane (with a temperature of 663 K) are considered for various values of pressures in the liquid in the range from 13 to 100 bar. At the beginning of the collapse, the vapor in the bubble is in the state of saturation with a pressure of 10.3 bar, and with the initial radius of the bubble to equal 500 µm. It is shown that, at a liquid pressure lower than 13 bar, a nearly-uniform vapor compression is realized in the bubble, whereas at higher pressure values, compression is realized by means of radially converging isentropic waves (at 14–18 bar) and shock waves (starting from 19 bar). The degrees of vapor compression, estimated from the vapor pressure, density and temperature at the boundary of a small central region of the bubble of 0.25-µm radius, are compared with the degrees of vapor compression realized when a similar vapor bubble collapses in cold acetone at a temperature of 273 K (as in known experiments on acoustic cavitation of deuterated acetone). It is found that the degrees of compression comparable with those achieved in the case of acetone at a pressure of 15 bar, equal to the amplitude of the acoustic action exercised in the mentioned experiments, are achieved in the case of tetradecane at a pressure of 70 bar. In the latter case, the maximum rate of bubble collapse in tetradecane is 10 times lower than that in acetone (110 m/s versus 1100 m/s).

Vapor pressure, density, and speed of sound of the R134a-R227ea refrigerants in the vapor phase

The pressure on the dew line and density of the gas-phase 69.2 wt.% R134a / 30.8wt.% R227ea refrigerant were investigated using a constant volume piezometer in the temperature range from 293 to 373 K and at pressures from 0.45 to 3.1 MPa. The speed of sound of the 70.1 wt.% R134a / 29.9 wt.% R227ea mixture (323-373 K, 1.2-1.5 MPa) was also measured using an ultrasonic interferometer. The measurement errors of the temperature, pressure, density, and speed of sound were ±20 mK, ±4 kPa, ± (0.15–0.25)%, and ± (0.2–0.3)%, respectively. Approximation dependences of the studied properties were obtained and their errors were estimated. The obtained results were compared with the calculations using the REFPROP program.

Vapor Pressures, Densities, and PC-SAFT Parameters for 11 Bio-compounds

One major sustainable development goal is to produce chemicals and fuels from renewable resources, such as biomass, rather than from fossil fuels. A key part of this development is data on the properties of chemicals that appear in this bio-based supply chain. Many of the chemicals have yet to be studied thoroughly, and data on their properties is lacking. Here, we present new experimental data on the properties of 11 bio-compounds, along with PC-SAFT parameters for modeling their properties. The measured data includes vapor pressures, compressed densities, and refractive indexes. The 11 bio-compounds are tetrahydrofuran, 2-pentanone, furfural, 2-methoxy-4-methylphenol, 2-methylfuran, dihydrolevoglucosenone, cyclopentyl methyl ether, 2-sec-butylphenol, levoglucosenone, γ-valerolactone, and 2,6-dimethoxyphenol.

Validity of Assuming Equilibrium Between Liquid Water and Vapor for Simulating Evaporation

AbstractThe standard assumption used in evaporation theory that at any location in a soil water vapor density is equal to the value in thermodynamic equilibrium with the liquid water has recently been questioned. This paper defines precise criteria for nonequilibrium to occur during evaporation in soils. In doing so a physically based model of the pore transfer coefficient critical to quantifying the degree of nonequilibrium is developed. The likelihood of departure from the equilibrium assumption for various soil textures and temperature conditions, including the extreme case of surface fire, is presented. Furthermore the pore transfer coefficient is incorporated into steady‐state nonequilibrium simulations of evaporation from a coarse sand under field conditions and compared with the corresponding equilibrium simulation. Outside of the narrow subsurface evaporation zone there were no significant differences between the nonequilibrium and equilibrium simulations. Since nonequilibrium effects were most likely to be seen with the coarse sand abandoning the standard assumption in future work is unnecessary, and all previous work based on it need not be questioned.

Transport phenomena in the Knudsen layer near an evaporating surface.

Using the combination of the kinetic theory of gases (KTG), Boltzmann transport equation (BTE), and molecular dynamics (MD) simulations, we study the transport phenomena in the Knudsen layer near a planar evaporating surface. The MD simulation is first used to validate the assumption regarding the anisotropic velocity distribution of vapor molecules in the Knudsen layer. Based on this assumption, we use the KTG to formulate the temperature and density of vapor at the evaporating surface as a function of the evaporation rate and the mass accommodation coefficient (MAC), and we use these vapor properties as the boundary conditions to find the solution to the BTE for the anisotropic vapor flow in the Knudsen layer. From the study of the evaporation into a vacuum, we show the ratio of the macroscopic speed of vapor to the most probable thermal speed of vapor molecules in the flow direction will always reach the maximum value of sqrt[1.5] at the vacuum boundary. The BTE solutions predict that the maximum evaporation flux from a liquid surface at a given temperature depends on both the MAC and the distance between the evaporating surface and the vacuum boundary. From the study of the evaporation and condensation between two parallel plates, we show the BTE solutions give good predictions of transport phenomena in both the anisotropic vapor flow within the Knudsen layer and the isotropic flow out of the Knudsen layer. All the predictions from the BTE are verified by the MD simulation results.

Thermophysical Properties of the Lennard-Jones Fluid: Database and Data Assessment.

Literature data on the thermophysical properties of the Lennard-Jones fluid, which were sampled with molecular dynamics and Monte Carlo simulations, were reviewed and assessed. The literature data were complemented by simulation data from the present work that were taken in regions in which previously only sparse data were available. Data on homogeneous state points (for given temperature T and density ρ: pressure p, thermal expansion coefficient α, isothermal compressibility β, thermal pressure coefficient γ, internal energy u, isochoric heat capacity cv, isobaric heat capacity cp, Grüneisen parameter Γ, Joule-Thomson coefficient μJT, speed of sound w, Helmholtz energy a, and chemical potential) were considered, as well as data on the vapor-liquid equilibrium (for given T: vapor pressure ps, saturated liquid and vapor densities ρ' and ρ″, respectively, enthalpy of vaporization Δhv, and as well as surface tension γ). The entire set of available data, which contains about 35 000 data points, was digitalized and included in a database, which is made available in the Supporting Information of this paper. Different consistency tests were applied to assess the accuracy and precision of the data. The data on homogeneous states were evaluated pointwise using data from their respective vicinity and equations of state. Approximately 10% of all homogeneous bulk data were discarded as outliers. The vapor-liquid equilibrium data were assessed by tests based on the compressibility factor, the Clausius-Clapeyron equation, and by an outlier test. Seven particularly reliable vapor-liquid equilibrium data sets were identified. The mutual agreement of these data sets is approximately ±1% for the vapor pressure, ±0.2% for the saturated liquid density, ±1% for the saturated vapor density, and ±0.75% for the enthalpy of vaporization-excluding the region close to the critical point.

Effect of instantaneous change of surface temperature and density on an unsteady liquid–vapour front in a porous medium

This article presents a comprehensive analysis of time dependent condensation model embedded in a porous medium with variations in liquid–vapour densities. Both similarity and asymptotic solutions for the unsteady liquid–vapour phase change front are obtained with the manifestation of various pertinent parameters. The obtained results are compared which congregate well as depicted clearly in graphs. Results indicate that with different diffusivity and contrast ratios, the similarity front parameter is found to be gradually declining with variation in a density ratio. We have shown for the condensation process, the ratio of sensible to latent heat is independent of time and is equal to the half of the Stefan number of the liquid phase.

Experimental Evaluation of an Automotive Heat Pump System with R1234yf as an Alternative to R134a

In this study, performance characteristics of an automotive heat pump (AHP) system using R1234yf and R134a were investigated. Compressor speeds, air temperature and air flow velocity significantly influence the system performance parameters. Therefore, the effect of compressor speeds, air flow velocities and temperatures on the system performance characteristics were evaluated under various test conditions. Optimum experimental conditions were arranged to determine the performances of the AHP system. As a result, the heating performance of R1234yf is lower than R134a. The heating performance of AHP systems gets higher as air flow velocities drop. While the air flow velocities raised up from 1.2 to 4.5 m s−1, the heat capacity was decreased by 15%. Change in air velocities plays more role on the performance characteristics than the change in ambient temperature at low air flow velocities. Comparing the suction and discharge pressures of both the R134a and R1234yf, R1234yf is higher because of its vapour densities. Finally, R1234yf can be used in AHP systems for both cooling and heating applications.

Effects of Water Vapor Addition on the Flame Structure and Soot Formation in a Laminar Ethanol/air Coflow Flame

ABSTRACT Ethanol is a promising alternative fuel to gasoline engines; however, the problem of particulate matter (PM) emissions still exists when ethanol is applied to gasoline direct injection (GDI) engines, especially under high load. Water injection is proved to be an effective way to reduce the PM emissions and engine knocking, simultaneously. In this work, a numerical calculation was carried out in an ethanol/air coflow diffusion flame to investigate the effects of water vapor addition on the flame structure and soot formation. A complete step-by-step decoupling method was proposed to numerically isolate the dilution, density, transport, thermal, radiative and chemical effects of water vapor by introducing several virtual species. Results show that the temperature distribution of the flame is mainly affected by the dilution effect and thermal effect of water vapor, followed by radiative effect and chemical effect. The mole fraction of OH radical increases because of the enhancement of the reaction H2O + H <=> OH + H2 and O + H2O <=> OH + OH, while the conversion of CO to CO2 is promoted through the reaction CO + OH <=> CO2 + H, due to the chemical effect. Soot volume fraction is also reduced, where the dilution and chemical effects play the most important roles. Hydrogen-abstraction-carbon-addition (HACA) surface growth and OH oxidation are the processes controlling the soot mass addition and consumption, respectively. HACA rate is mainly affected by the dilution and chemical effects. However, chemical effect has little influence on the OH oxidation rate, since the collision probability of OH with soot particles remains almost unchanged as a result of the increase of OH concentration and the decrease of soot volume fraction under the chemical effect.

Remote N2O gas sensing by enhanced 910-m propagation of THz pulses.

We modified our 910-m long path THz system to increase the signal-to-noise ratio (S/N) with a nanostructure plasmonic THz transmitter (Tx) chip and a seven-mirror array reflector with 1 m diameter. When the THz pulse propagates the 910-m distance in the atmosphere, the S/N is up to 1170:1, which made the THz pulse measurable at a high water vapor density (WVD) of up to 25.2 g/m3. The time shift of the THz pulse according to the WVD measured for each meteorological season was matched well with the theoretical result. Due to the modified long-distance THz system, we were able to measure for the first time the resonances of N2O gas, which is located 455 m away from the Tx and receiver (Rx) chips and contained in a 1.5-m diameter rubber balloon under atmospheric pressure. Seven resonances can be detected except for one overlay of resonant frequency by water vapor.

Prediction of vapor pressure and density for nonaqueous solutions of the ionic liquid 1-ethyl-3-methylimidazolium ethyl sulfate using PC-SAFT equation of state

The experimental data on density and vapor pressure for nonaqueous solution of ionic liquids are important not only for the design and optimization of chemical processes, but also from the theoretical perspective to predict physical properties and modeling under different conditions. In this study, the vapor pressure for nonaqueous solutions of the ionic liquid, 1-ethyl-3-methylimidazolium ethyl sulfate [EMIM][ES] in some polar organic solvents, i.e. 1-propanol, ethanol and methanol, in dilute region of the ionic liquid concentration were measured by the use of isopiestic method at 298.15 K. In this regard, the Perturbed Chain Statistical Association Fluid equation of state (PC-SAFT) is used for prediction of the vapor pressure and density of the investigated systems. The obtained results from the PC-SAFT equation of state provide reliable and accurate predictions with the absolute average deviations (AAD), 0.01 and 0.084 for density and for vapor pressure , respectively.

Modeling moisture and heat transfer during superheated steam wood drying considering potential evaporation interface migration

In the present study, a mathematical model with a moving evaporation interface was constructed to quantitatively assess the mechanisms of moisture and heat transfer during superheated steam wood drying. In this model, the unsaturated Darcy flow of free water was considered as Fick diffusion. By modeling the interface evaporation rate and volume evaporation rate, the model (1) characterized the moving water evaporation interface; (2) quantified the dynamic alterations of wet/dry regions; and (3) predicted the change regularity of real-time temperature, moisture content, interface evaporation rate, volume evaporation rate, vapor density, and relative humidity at specific locations during the wood drying. Compared with the superheated steam drying experiments using camphorwood (Cinnamomum camphora (L.) Presl) and teak (Tectona grandis L.f) specimens in different sizes, it was suggested that the developed model was able to accurately predict their drying processes, and the parameters calculated from the model contributed to the optimization of a superheated steam drying technique for teak.

Effect of Ethyl Octanoate and Ethyl Oleate on the Properties of Gasoline Fuel Mixture

The objective of this study was to evaluate the application of esters as gasoline additives based on physicochemical characterization analyzes. Reid vapor pressure, density, distillation curves, and rheological profile of pure gasoline and its mixture with esters (ethyl octanoate and ethyl oleate) at different concentrations (0, 2.5, 5, 15%) were analyzed. Heat of combustion, corrosiveness, and octane number (MON—motor octane number, RON—research octane number) of the mixtures were also evaluated. The results showed that the Reid vapor pressure, distillation curve, and corrosiveness of the mixtures were within the values required by the legislation. In relation to the rheological study, the Oswald de Waele model best fits the experimental values of the ester + gasoline systems. The density of the gasoline mixtures with esters increased with increasing ester concentration in the mixture. The heat of combustion of the gasoline mixtures decreased with an increase in the ester concentration in gasoline. The octane indices MON and RON were better when ethyl octanoate was added to gasoline.

A NEW SETUP FOR THE STUDY OF ADSORPTION/DESORPTION PROCESSES AND NANOPARTICLES FORMATION IN POROUS ALUMINA

We present a setup devoted to the study of adsorption and desorption processes of alkali atoms after deposition on a 300 nm thick porous alumina substrate in an Ultra High Vacuum chamber. Rubidium atoms, delivered by a dispenser source, enter the 20-30 nm diameter pores, diffuse in and stick to their walls. A 1 W power laser is used in order to induce detachment and take the atoms back in the vapor phase in a very tight confinement region. The desorbed atoms coming out the sample can be monitored via both a resonant optical detection and an electronic amplifier after ionization. The desorbing laser is also able to promote the formation of Rubidium nanoparticles, as the high Rb vapor density in the pores favors aggregation around nucleation point defects. In this way, the apparatus allows for the study of the fundamental processes related to atom – surface interactions in presence of light as well as of several promising application to nanomaterials.

Operational behavior and heat transfer in a thermosiphon desorber at sub-atmospheric pressure. Part I: The model

The thermosiphon desorber or bubble pump is advantageous in absorption cooling devices, since the processes of refrigerant desorption and solution pumping is combined in one hermetical unit. This supersedes the necessity of a mechanical solution pump. In the application with NH3/H2O the thermosiphon desorber typically operates at a pressure of around 15 bar with a liquid vapor density ratio in the range of 102, which is in a well-known regime of two phase flow. Nevertheless, for the application of thermosiphon desorbers in H2O/LiBr absorption chillers, which are commonly operated at a pressure below 0.1 bar with the liquid vapor density ratio in the range of 104, there is a lack of heat transfer correlations for two-phase flow.First attempts to fill this gap of flow boiling heat transfer correlations in the thermosiphon desorber at sub-atmospheric pressures is presented in this paper. A model is formed by solving simultaneously the mass, energy, and momentum equations. The well-known correlations for predicting single-phase and two-phase flow heat transfer coefficient and frictional pressure drop have been reviewed to find a possibility for applying them to the thermosiphon desorber. The mass flow rate and heat transfer behavior with the different flow length of the riser tube and with changing the pressure has been theoretically studied in the model. For verification, the model has been compared to experimental data using pure water. This will be presented in the second part of the paper.

Experimental study for flame base drag and burning efficiency of spilled crude oil during in-situ burning on water

In-situ burning (ISB) has been proven to be a practical way to clean oil on water. The burning behavior of spilled oil is strongly influenced by wind. The flame characteristics of flame base drag and burning efficiency affected by wind speed have been studied through a series of experiments in this study. The wind speeds varied from 0.5 m/s to 2.0 m/s and the inside diameters of the oil pools made from quartz glass were 40 mm, 90mm and 140mm. The variation of fuel vapor density was considered in the dimensionless model for predicting flame base drag length. The proposed formula was shown to correlate with the data of different pool diameters and wind speeds non-dimensionally by Froude number, fuel-air density ratio and the dimensionless heat release rate. The study helped to better understand the fire behavior under wind conditions, and most importantly the developed model would help guide better assessment of the burning in ISB operation.

Heterogeneous–homogeneous oxidation of pyrrole in water vapor at elevated pressure

The paper presents research results of the pyrrole oxidation in stoichiometric, rich, and lean mixtures of C4H4NH/O2 (ρPy = 0.15 mol/dm3, ρO2 = 0.61−0.91 mol/dm3), diluted with argon and water vapor (xD = 46−62%mol), at the uniform heating (1 K/min) of a tubular reactor made of stainless steel. It was revealed that pyrrole oxidation proceeds through the heterogeneous and homogeneous oxidation mechanisms. The contribution of heterogeneous oxidation increases with the accumulation of corrosion products on the reactor wall and a decrease in the density of water vapor. Based on the time dependences of the temperature of the reaction mixtures, it was revealed that in the presence of corrosion products, the ignition temperature of pyrrole in argon medium is about 50 K below than that in water vapor (varies within the range 608−619 K). From the results of mass spectrometric analysis, it follows that pyrrole oxidation occurs mainly through the formation of NH3. Along with N2 and NH3, N2O was detected in volatile oxidation products. It is shown that the increase in water vapor density inhibits pyrrole oxidation. The degree of nitrogen removal from the pyrrole in the form of N2 is changed from 9.9 to 90.1%mol. The composition and morphology of corrosion products are determined by X-ray diffraction analysis and scanning electron microscopy.

Influence of climatic conditions on evaporation in soil samples

Evaporation rates can be successfully modelled for soil–atmosphere interaction problems by means of a convective vapour flux at the soil surface equal to the product of a driving force (difference between the vapour density at the soil surface and that of the surroundings) and a mass transfer coefficient characterising the resistance of a boundary layer where the transfers take place. While the vapour density at the soil surface can be deduced from solving the coupled heat and moisture transfer equations for the soil below the surface, the determination of the mass transfer coefficients under varying weather conditions is rarely investigated. Laboratory-scale drying tests are performed on a compacted silt specimen, focusing on the influence of atmospheric conditions (relative humidity and wind speed) on the evaporation kinetics and the mass transfer coefficient. Two experimental techniques are used and compared: a drying chamber with relative humidity controlled through saline solutions and a convective microdryer. New insights are given into the prediction of mass transfer coefficients from mass transfer theories. Finally, the results highlight the necessity of testing specimens that are large enough to define relevant mass transfer coefficients for geotechnical applications.

A simple finite element model to study the effect of plasma plume expansion on the nanosecond pulsed laser ablation of aluminum

In this paper, a simple model was proposed using finite element analysis (FEA) with a commercial FEA software ABAQUS to simulate the two-dimensional (2-D) laser heat transfer in an aluminum material. Without relying on the conventional hydrodynamic model, the proposed model not only predicts the evolutions of the temperature field and ablation profiles in the target material, but also provides an estimation on the evolutions of electron density, plasma temperature, and plasma absorption coefficient. The assumptions used in the model include the local thermal equilibrium and additional assumptions regarding the average plasma temperature and vapor density. The assumptions allowed the laser heat transfer equation to be solved together with the Saha–Eggert equation and conservation equations of matter and charge. When compared to the existing hydrodynamic models, the proposed model solves a less number of nonlinear equations and hence is computationally more efficient. The proposed FE model was employed to study the plasma-shielding effect on PLA produced by a 193 nm Excimer laser and a 266 nm Nd:YAG laser. The predictions of ablation depths, electron density, and plasma temperature agree well with the experimental data. Moreover, effects of the laser intensity and the average plasma temperature on the efficiency of the plasma shielding during PLA were also investigated and discussed in this study.

The effect of Cu nanoparticles on the characteristics of vapor–liquid interface of argon at various saturated temperatures by molecular dynamic simulation

In this study, the effect of copper nanoparticles on the interface properties of liquid–vapor argon is investigated by molecular dynamics simulation. Stoddard Ford potential function has been utilized to estimate the interactions of argon–argon and argon–copper particles. Simulation is done in the nanoscale computational domain to phase change of vapor to liquid at different saturated temperatures. Density values and surface tension for different cutoff radii are obtained. It is demonstrated that in the $$r_{\text{c}} = 4\sigma$$ calculated values are acceptable. Simulation results show that nanoparticles change the interface properties of liquid–vapor argon. With addition of nanoparticles, liquid density decreases and vapor density increases. Nanoparticles displace density distribution and cause fluctuations in the density profile. Also, surface tension increases with increase in nanoparticle concentration.