Dew Point Curve Research Articles

The isothermal van’t Hoff equation for phase equilibria—A forgotten relation?

The extended van’t Hoff equations for dilute mixtures relate the differences of initial slopes of phase boundary curves to the phase transition enthalpy or volume of the solvent. While the isobaric van’t Hoff equation is frequently used in mixture thermodynamics, its isothermal counterpart has received much less attention. We show that the isothermal van’t Hoff equation can be used to interpolate dew point curves in isothermal phase diagrams or to create a model-free consistency test for experimental phase equilibrium data. Furthermore, an expression for the initial curvature of phase boundary curves is derived.

Measurement and prediction of dew point curves of natural gas mixtures

Dew point measurements for six synthetic natural gas (SNG) mixtures were performed using a custom made chilled mirror apparatus. The experimental data cover a temperature-range from 253 to 285K and a pressure-range from 3 to 105bar. The recently developed UMR-PRU model was revised and applied to these experimental data as well as to other dew point data for synthetic and two real natural gas mixtures reported in the literature. The results of the UMR-PRU model were compared to those obtained by the Peng–Robinson equation of state coupled with the classical van der Waals one fluid mixing rules using either zero interaction parameters or temperature dependent ones utilized in a predictive version of the PR EoS, the so-called PPR78 EoS.

Characterization of a Superheated Fuel Jet in a Crossflow

An experiment was conducted to characterize a superheated fuel jet (Jet-A) injected into an unheated crossflow of air. The liquid phase of the fuel jet was characterized with high speed imaging and phase Doppler interferometry. The transition from a shear-atomized to a flash-atomized spray at a fuel temperature of 513 K (465°F) was observed at an ambient pressure of 1 atm, which is consistent with the bubble and dew point curves predicted for JP-8. The explosive breakup that was seen in the flash-atomized spray produced submicron droplets with a high radial momentum. This unique behavior makes superheated fuels an attractive design feature for fuel preparation devices that can employ flash boiling to enhance fuel atomization and mixing in a compact volume.

Refrigeration cycle design for refrigerant mixtures by molecular simulation

We describe a molecular simulation methodology to calculate the properties of a vapor-compression refrigeration cycle and its Coefficient of Performance, in the case when the refrigerant is a mixture. The methodology requires only a molecular force-field model for each refrigerant pure component and, for improved accuracy, an expression for the vapor pressure of each pure component as a function of temperature. Both may be constructed by means of theoretical approaches in combination with minimal amounts of experimental data, and the latter may also be estimated by empirical formulae with reasonable accuracy. The approach involves a combination of several available molecular-level computer simulation techniques for the individual processes of the cycle. This work extends our earlier study to cases when the refrigerant is a pure fluid. The mixture refrigerant simulations entail the calculation of bubble- and dew-point curves for the refrigerant mixtures, and we propose a new approach for dew-point calculations via molecular simulation. We compare results for a test case with those obtained from the Equation-of-State model used in the standard REFPROP software and with experimental data for a commercially available refrigerant mixture of R32 (CH2F2) and R143a (CH2FCF3).

Prediction of Double Retrograde Vaporization by Hybrid Global-Local Optimization Using Fuzzy Clustering Means

Retrograde vaporization calculation is a hard problem, which possesses several solutions and demands a robust algorithm. In the present work, we solved the double retrograde vaporization problem by hybrid global-local optimization. In fact, we propose a new methodology that involves fuzzy clustering means together with Luus-Jaakola and Nelder-Mead algorithms. We applied the proposed methodology to solve the double retrograde vaporization problem for binary systems of methane + n-butane. For this mixture, the dew point curve exhibits an S-shape at temperatures slightly below the critical temperature of the more volatile component. This binary mixture was modeled using the original Peng-Robinson equation of state and the classical one-fluid van der Waals mixing rule.

Dew-Point Curves of Natural Gas. Measurement and Modeling

To achieve a reliable method to calculate the hydrocarbon dew point for natural gases in transmission, samples of natural gas were taken at the inlet of the Magreb-Europe pipeline in Spain. The composition up to the C12 fraction of each natural gas sample was determined by gas chromatography, and the dew-point curve was measured using a chilled mirror dew-point analyzer. In this work, we present the experimental measurements of dew points for six samples of natural gas between 1.1 × 105 Pa and 78.4 × 105 Pa in the temperature range from 235.2 to 277.9 K. The experimental results obtained were analyzed in terms of a predictive excess function−equation of state (EF-EOS) method based on the zeroth-approximation of Guggenheim's reticular model. Because the EF-EOS model uses a group contribution model, the availability of every binary experimental data corresponding to every binary interaction in the mixture is not necessary. Considering this and the good results obtained in previous studies, we concluded that...

( p, Vm, T) and phase equilibrium measurements for a natural gas-like mixture using an automated isochoric apparatus

We have developed an automatic apparatus for measuring phase equilibrium and ( p, V m, T) properties of gas mixtures in our laboratory. Based upon the isochoric method, the apparatus can operate at temperatures ranging from 100 K to 500 K at pressures up to 35 MPa, and yield absolute results in fully automated operation. Temperature measurements are accurate to 0.01 K and pressure measurements are accurate to 0.002 MPa. The isochoric method utilizes pressure versus temperature measurements along an isomole (near isochore) and detects phase boundaries by locating the change in the slope of the isomoles. We also have developed a strategy that allows us, when using the above isochoric method together with a second apparatus capable of isothermal density measurements, to collect derived densities that are competitive in accuracy with those of the densimeter, but with a procedure and design that is easy to automate. We present data on a natural gas-like mixture. The experimental data indicate that prediction of the dew point curve with current equations of state is unreliable.

Application of Exponential Decay Distribution of C6+ Cut for Lean Natural Gas Phase Envelope

The main goal of this paper is to generate a complete phase envelope for natural gases based on a exponential decay distribution for C 6+ . Using this technique, a single dew point measurement provides enough information to generate an accurate phase envelope. Using the single dew point measurement, appropriate distribution for C 6+ is determined. The distribution will contain normal alkanes ranging from nC 6 H 14 to nC 17 H 36 . Once the distribution is determined, a complete phase envelope containing the bubble point curve, dew point curve, retrograde curve, and hydrate curve can be generated. We have verified that the exponential decay or logarithmic distribution of hexane plus will improve the accuracy of PHLC (Potential Hydrocarbon Liquid Contenet) prediction by using a hexane plus molecular weight to match a single dew point. This approach enables the generation of full and accurate phase envelopes. This technique may be applied with any EoS of state so long as proper binary interaction coefficients are employed.

Condensation in gas transmission pipelines.

Several pressure and temperature reductions occur along gas transmission lines. Since the pressure and temperature conditions of the natural gas in the pipeline are often close to the dew point curve, liquid dropout can occur. Injection of hydrogen into the natural gas will change the phase envelope and thus the liquid dropout. This condensation of the heavy hydrocarbons requires continuous operational attention and a positive effect of hydrogen may affect the decision to introduce hydrogen. In this paper we report on calculations of the amount of condensate in a natural gas and in this natural gas mixed with 16.7% hydrogen. These calculations have been performed at conditions prevailing in gas transport lines. The results will be used to discuss the difference in liquid dropout in a natural gas and in a mixture with hydrogen at pressure reduction stations, at crossings under waterways, at side-branching, and at separators in the pipelines.

High pressure solid–fluid and vapour–liquid equilibria in model hyperbaric fluids: the system methane + tetracosane + triacontane

Bubble-point curves, dew-point curves and solid + fluid/fluid boundary curves of methane + tetracosane + triacontane were determined according to the synthetic method in the temperature range 320–475 K and at pressures up to 200 MPa. Two series of quasi-binary systems of constant methane mole fraction with mixtures of tetracosane and triacontane with composition varying between pure tetracosane and pure triacontane were studied. One quasi-binary system with methane mole fraction 0.975 showed dew-point behaviour, the other quasi-binary system with methane mole fraction 0.900 showed bubble-point behaviour. A gradual isothermal substitution of tetracosane by triacontane at constant mole fraction methane increases the bubble-point pressure and the dew-point pressure, while the liquidus temperature at constant pressure passes through a minimum. Similar behaviour was found by Flöter et al. [E. Flöter, B. Hollanders, Th.W. de Loos, J. de Swaan Arons, Fluid Phase Equilib. 143 (1998) 185–203] in the system methane + docosane + tetracosane.

The CO2–H2O system: IV. Empirical, isothermal equations for representing vapor-liquid equilibria at 110–350 °C,P≤ 150 MPa

Empirical formulae are presented for calculating vapor-liquid equilibria (VLE) in the CO 2 -H 2 O system at 10 temperatures between 110 and 350 °C. At each temperature, separate functions are used to represent the bubble- and dew-point boundary curves that: originate at the saturation vapor pressure of water (P sat; H₂O ) at X CO₂ = 0; diverge with increasing pressure up to ~P(X max CO₂ ) where ∂P/∂X CO₂ = +∞ along the dew-point curve; then converge with increasing pressure above P(X max CO₂ ). At temperatures below 265 °C and pressures > P(X max CO₂ ), the compositions of coexisting liquid and vapor [X CO₂ L(V) and X CO₂ V(L) ] do not converge completely with increasing pressure due to the absence of critical behavior. Thus, relatively simple functions suffice to accurately represent VLE at those temperatures. In contrast, at T > 265 °C, X CO₂ L(V) and X CO₂ L(V) converge rapidly as P approaches P c (the critical pressure in the CO 2 -H 2 O system at a given temperature between 265 and 374 °C and P ≤ 215 MPa). For those temperatures, therefore, more complex VLE formulae are required to achieve close representation of phase relations. For dew-point equations, this includes adding an exponential “correction term” to ensure that ∂P/∂X CO₂ = 0 at the critical points indicated by corresponding bubble-point functions. Stable liquid-vapor coexistence in mixed-volatile systems requires ƒ L i = ƒ V I (isofugacity conditions) for all “i” (volatile components) in the two fluid phases. Thus, the equations presented in this paper specify numerous P-T-X conditions where ƒ L H₂O = ƒ V H₂O and ƒ L CO₂ = ƒ V CO₂ in the CO 2 -H 2 O system. These results have important applications in the ongoing effort to develop a more rigorous thermodynamic model for CO 2 -H 2 O fluids at geologically relevant temperatures and pressures.

Thermodynamic Analysis of the Phenomenon of Double Retrograde Vaporization

The phenomenon of double retrograde vaporization (DRV) is explained on the basis of infinite-dilution critical phenomena. It is shown that the peculiar double-domed or inverse “S” shaped dew point curve distinctive of DRV arises from the conflicting requirements at infinite-dilute versus critical conditions. The argument is general and takes into account both classical and nonclassical behavior. The transitions from subcritical temperatures through double retrograde behavior to normal retrograde condensation at higher temperatures are also explained on the basis of infinite-dilution critical anomalies. The criterion for the existence of DRV is given based on the volumetric properties of the two phases in equilibrium.

Thermodynamic Properties of Synthetic Natural Gases. 5. Dew Point Curves of Synthetic Natural Gases and Their Mixtures with Water and with Water and Methanol: Measurement and Correlation

Dew points for two synthetic natural gas (SNG) mixtures between 1.2 × 105 and 81.8 × 105 Pa in the temperature range from 213.6 to 261.4 K, four SNG + water mixtures between 1.1 × 105 and 41.0 × 105 Pa and temperatures from 244.7 to 288.1 K, and four SNG + water + methanol mixtures between 1.1 × 105 and 20.7 × 105 Pa and temperatures from 247.6 to 288.6 K were experimentally determined. The experimental results obtained on the multicomponent systems were analyzed in terms of a predictive excess function−equation of state (EF−EOS) method, which reproduced experimental dew point temperature data with absolute average deviation (AAD) between 0.9 and 3.1 K for the dry systems, from 0.0 to 1.6 K for the systems with water, and from 0.0 to 3.0 K for the systems with water and methanol. The experimental results obtained for synthetic natural gas (SNG) + water mixtures at pressure values higher than 5 × 105 Pa were also compared to a predictive equation of state (EOS) model. It reproduced experimental dew point temperature data within AAD between 1.8 and 5.3 K.

03/02207 Thermodynamic properties of synthetic natural gases. Part 3. Dew point curves of synthetic natural gases and their mixtures with water. Measurement and correlation.: Avila, S. et al. Energy & Fuels, 2003, 17, (2), 338–343

03/02207 Thermodynamic properties of synthetic natural gases. Part 3. Dew point curves of synthetic natural gases and their mixtures with water. Measurement and correlation.: Avila, S. et al. Energy & Fuels, 2003, 17, (2), 338–343

Double retrograde vaporization in a multi-component system: ethane+orange peel oil

Among the various peculiar infinite-dilute near-critical phase behavior phenomena, one can mention “double retrograde vaporization” (DRV). This phenomenon is characterized by displaying two “domes” on the retrograde dew point curve, instead of the single-domed dew point curve in the familiar “single” retrograde condensation. This behavior had previously been observed in binary systems. This study shows that DRV also occurs in systems composed of a larger number of components. This is in line with a previous suggestion that the phenomenon of DRV is general. Experiments were carried out on the multi-component system ethane+orange peel oil, indicating quadruple-valued dew points at certain concentrations. Bubble point, dew point and critical point temperatures and pressures are presented for five different compositions ranging from 97.8 to 99.9 mass percent ethane. The data range within temperatures and pressures of 285–363 K and 3–7 MPa, respectively. The shapes and trends of DRV of the multi-component system ethane+orange peel oil are compared with those of the binary system ethane+limonene.

High pressure phase behavior of the system ethane+orange peel oil

High-pressure vapor–liquid equilibria of ethane+orange peel oil was determined experimentally by a synthetic method. No liquid–liquid immiscibility was observed in this system. Bubble and dew points were measured at ethane mass fractions ranging from 0.1 to 0.9988 and within temperature and pressure ranges of 282–363 K and 1–10 MPa, respectively. Critical points were also determined experimentally for ethane mass fractions of 0.75–0.9988. At very high ethane concentrations, the experimental results showed double retrograde vaporization behavior, in which the dew point curve has a double-domed shape. In this limited region, increasing the pressure at fixed concentration results in triple- or quadruple-valued dew points. The bubble and dew point data of this work were also compared with those of ethane+lemon peel oil and ethane+limonene, indicating an almost perfect match between all three systems. Even the double retrograde behavior of the orange oil system showed good agreement with that of ethane+limonene, even though the oil is composed of numerous components. The experimental data were correlated with the Stryjek–Vera modified version of the Peng–Robinson equation of state using the Mathias–Klotz–Prausnitz mixing rule with two binary interaction parameters. The results showed fairly good agreement with the data.

Simulation of double retrograde vaporization using the Peng–Robinson equation of state

Double retrograde vaporization is a phenomenon characterized by an unexpected retrograde dew point curve at compositions approaching nearly the pure volatile component (component A) and at temperatures very close to the critical temperature of the more volatile component ( Tc A). On the p– x– y diagram, instead of the single-domed dew point curve in the familiar “single” retrograde vaporization, double retrograde vaporization shows two “domes” at temperatures above but close to Tc A. At temperatures below but close to Tc A, the dew point curve has an “S”-shape. This results respectively in quadruple- or triple-valued dew points at a specific composition. In this work, the phenomenon of double retrograde vaporization has been simulated using a cubic equation of state. Both the “double-dome” and the “S”-shape curves for the binary systems (ethane+linalool) and (ethane+ d-limonene) were successfully modelled, even without the use of binary interaction parameters. Results are also obtained by optimizing interaction parameters using experimental bubble point data. Even though double retrograde vaporization has rarely been observed in literature, we believe that it is the normal behaviour that always occurs in binary mixtures in which the two components differ largely enough in molecular symmetry to produce a very steep dew point curve. To further verify this generality, simulations were performed on a number of binary mixtures of different families. Double retrograde vaporization was estimated in every system with a steep dew point curve.

Thermodynamic Properties of Synthetic Natural Gases. Part 3. Dew Point Curves of Synthetic Natural Gases and Their Mixtures with Water. Measurement and Correlation

Experimental measurements of dew points for eight synthetic natural gases (SNG) + water mixtures were carried out between (1.2 and 99.3) × 105 Pa in the temperature range from 226.4 to 287.6 K. The experimental results were analyzed in terms of both an equation of state model and an excess function-equation of state method, which reproduced the experimental data within AAD from 1.4 to 4.1 K and from 0.6 to 4.3 K, respectively.

Thermodynamic Properties of Synthetic Natural Gases. 1. Dew-Point Curves of Synthetic Natural Gases and Their Mixtures with Water and Methanol. Measurement and Correlation

Experimental measurements of dew points for five synthetic natural gas (SNG) mixtures between 1.9 × 105 and 106.0 × 105 Pa in the temperature range from 195.5 to 277.3 K and nine SNG + water + methanol mixtures between 1.4 × 105 and 73.1 × 105 Pa and at temperatures from 237.3 to 288.2 K were determined. The experimental results obtained on the multicomponent systems were analyzed in terms of an equation of state chemical reticular method, which reproduced experimental dew-point temperature data within an absolute average deviation between 0.8 and 3.7 K for the dry systems and from 0.5 to 1.9 K for the systems with water and methanol.

Thermodynamic properties of synthetic natural gases: Part 4. Dew point curves of synthetic natural gases and their mixtures with water: measurement and correlation

Experimental measurements of dew points for five synthetic natural gases (SNG)+water mixtures were carried out between 2.1×10 5 and 73.2×10 5 Pa in the temperature range from 224.3 to 270.2 K. The experimental results were analysed in terms of both an equation of state (EOS) model and an excess function–EOS method, which reproduced the experimental data with an AAD from 2.1 to 3.4 K and from 1.9 to 3.0 K, respectively.