Vapor phase measurement experimental conditions

Henry s Law is obeyed with organic pollutants of low solubility provided the pressures are not high or temperatures too low - conditions under which one might expect deviations from ideal behavior. Experimental values for Henry s Law constant may be obtained by equilibrating a pollutant between the solvent and vapor phase and measuring its concentration in those two phases. Providing the solubility is low (PA< 0.1) Henry s Law constant can be calculated from the equilibrium vapor pressure (PA) and solubility (S) ... 

Vapor and liquid phases coexist in virtually all areas of petroleum production operations, including reservoirs, wellbores, surface-production units, and gas-processing plants. Knowledge of fluid properties and phase behavior is required to calculate the fluid in place, fluid recovery by primary depletion, and fluid recovery by enhanced oil recovery techniques such as gas cycling, hydrocarbon solvent injection, and C02 displacement. Because of the complex nature of petroleum reservoir fluids and the often complicated phase behavior observed at elevated temperature and pressure conditions, the fluid properties and phase behavior historically have been measured experimentally. The complex nature of the fluids arises because of the supercritical components which are dissolved in the mixture of paraffinic, naphthenic, and... 

Through careful consideration of the inner shape of the cell, effusion orifice, and surface area of the metallic sample, near-equilibrium conditions are attained between the condensed phases and the vapor phase while the orifice continuously samples the vapor by effusion. The distribution of the effusing vapor is defined by the shape of the orifice, and typically only a small solid angle of the distribution is selected to form a molecule beam that is analyzed with a mass spectrometer. A critical, but often overlooked, issue is correctly defining the thermodynamic system that is actually measured [7,8]. In a Knudsen cell, the boundary of the thermodynamic system is the inner surface of the cell, and thus the alloy sample, cell material, and vapor are all part of the equilibrium state being measured (alloy + cell material + vapor). All additional components and phases introduced by the container need to be included in the subsequent analysis and in the use of the measured data (the same is true for all experimental thermodynamic measurements made in the past and to be made in the future). In addition to components and phases, the temperature and chemical composition of the system need to be determined. Temperature is a particularly critical measurement in thermodynamics and will be discussed in detail. 

The information in Table V provides general comparisons but does not show details of the deviations at various temperatures and pressures. By studying the experimental and predicted K values on log K vs. log P plots at several temperatures, details of the deviations for each component at various conditions can be observed. Several examples of this type of comparison are shown in Figures 7-11. Knowing the percent deviation between the predicted and experimental K values does not provide a quantitative measure of errors in the predicted vapor-to-liquid ratio and the saturation pressure-properties which are important in reservoir-engineering calculations. The best indication of the accuracy of a K-value prediction method for reservoir fluids would be a detailed comparison of component K values as well as fractions of the fluid in the vapor and liquid phases and the saturation pressure. The latter comparisons are... 

Example 4.1. Thermodynamic properties of isobutane were measured at subcritical temperatures from 70°F (294.29°K) to 250°F (394.26°K) over a pressure range of 10 psia (68.95 kPa) to 3000 psia (20.68 MPa) by Sage and Lacey. Figure 4.1 is a log-log graph of pressure (psia) versus molal volume (fP/lbmole) of the experimental two-phase envelope (saturated liquid and saturated vapor) using the tabulated critical conditions from Appendix I to close the curve. Shown also is an experimental isotherm for 190°F (360.93°K). Calculate and plot 190°F isotherms for the R-K equation of state and for the ideal gas law and compare them to the experimental data. 

In theory it is possible to nucleate bubbles either in the bulk phase or at solid surfaces as a result of statistical density fluctuations. In practice, the theoretical and measured fracture pressures of pure liquids are far in excess of those corresponding to the superheats or supersaturations for vapor or gas bubble nucleation experimentally observed in engineering systems (F2, F7, Kl). On the other hand, conditions for homogeneous nucleation become favorable at extremely high superheats in the presence of ionizing radiation (G4, G5). The latter observation led to the introduction of the liquid-hydrogen bubble chamber. A simple explanation of this phenomenon is that the... 

More pertinent, however, is the consideration introduced above relating to the vapor saturation conditions applicable to experimental measurements of contact angles. Such a measurement involves a liquid drop resting on a solid surface and forming a three-phase line of contact. But in the immediate vicinity of the contact line, the adsorbed film on the solid surface must be exposed to vapor which is saturated [2]. Hence, the insensitivity of the contact angles in the experiments reported by Fox and Zisman [33] to the saturation conditions of the bulk vapor is to be expected. The results therefore, are not conclusive evidence for negligible values of the film pressures. 

Although the method proposed here is based on idealized models of two-phase flow, it does provide a means for estimating more realistic vapor fractions. Further research is necessary in order to fully understand the conditions under which the technique can be applied. It is obvious that exact measurements on vapor fractions are necessary in order to check the reliability and the accuracy of the proposed method. Experimental work is continuing with motion picture studies on two-phase flow during cool-dowm. This will provide further information on the mechanisms of two-phase flow as well as the two-phase fluid velocities. 

This brief survey shows that there are many options for measuring phase equilibria in reacting systems, which allow to carry out such studies for a wide range of systems and conditions. The main limitation for experimental investigations of reactive vapor-liquid equilibria is related to the velocity of the reaction itself if phase equilibrium measurements of solutions are needed, which are not in chemical equilibrium, the reaction must be considerably slower than the characteristic time constant of the phase equilibrium experiment. Apparatus are available, where that time constant is distinctly below one minute. For systems with reactions too fast to be studied in such apparatuses, it should in many cases be possible to treat the reaction as an equilibrium reaction, so that the information on the phase equilibrium in mixtures, which are not chemically equilibrated is not needed. 

Qu et al. [2] found evidence of two kinds of unsteady flow boiling for 21 parallel microchannels measuring 231 x 713 xm. They observed in their parallel microchannel array either a global fluctuation of the whole two-phase zone for all the microchannels (Fig. 1) or chaotic fluctuations of the two-phase zone (Fig. 2) over-pressure in one microchannel and under-pressure in another. The individual microchannel mass flow rate was not controlled. Hetsroni et al. [3] created an experimental setup to study liquid-gas and liquid-vapor flow in parallel triangular microchannels with diameters of 103 to 161 p.m. They used a fast video camera coupled with a microscope through a Pyrex plate to record the flow patterns. They showed the influence of the injection method (plenum shape) and found evidence for the same inlet conditions. 

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