John Satherley

An extended scaled equation for the temperature dependence of the surface tension of pure compounds inferred from an analysis of experimental data

Abstract We have made a literature survey and performed a critical analysis of the available experimental surface tension data for the most volatile compounds in petroleum fluids: nitrogen, methane, ethane, propane, i-butane, n-butane, n-pentane, n-hexane, n-heptane and n-octane. Including the selected data with those for oxygen, xenon, krypton and those obtained recently for 16 partially halogenated hydrocarbons (refrigerants), we propose the following extended scaled equation to represent the surface tension of these substances: σ=kT c N A V c 2/3 (4.35+4.14ω)t 1.26 (1+0.19t 0.5 −0.25t) where t1−T/Tc is reduced temperature, k, NA, Vc, and ω are the Boltzmann constant, Avogadro number, the critical volume and the acentric factor, respectively. This equation, which only differs slightly from that proposed by Schmidt et al. [J.W. Schmidt, E. Carrillo-Nava, M.R. Moldover, Fluid Phase Equilibria 122 (1996) 187–206] for refrigerants, yields values for σ within 3.5% of the experimental values for all these compounds. Available data for other compounds (refrigerants) are in agreement with this relation; in the light of that we also examine some compounds (carbon dioxide and argon) for which there exist conflicting datasets.

The electrical conductivity of some hydrous and anhydrous molten silicates as a function of temperature and pressure

Abstract Electrical conductivity of the following molten silicate systems (in mol%): 60SiO 2 -40Na 2 O; 65SiO 2 -35Na 2 O; 75SiO 2 -25Na 2 O; 78SiO 2 -22Na 2 O; 72SiO 2 -24Na 2 O-4CaO; 66SiO 2 -19Na 2 O-15H 2 O; and an anhydrous and hydrous (4 wt% H 2 O) Mt. Erebus lava, have been measured as a function of temperature (to 1000°C) and pressure (to 1.3 kbar). The anhydrous soda-rich melts have a positive pressure coefficient of conductivity to ~200 bars and beyond this pressure the pressure coefficient is small and negative. Addition of water lowers the conductivity and gives rise to a negative pressure coefficient at the highest temperatures. The conductivity of hydrous Mt. Erebus lava passed through a maximum with increasing temperature at constant pressure. These phenomena are interpreted in terms of explanations of similar phenomena found in molten salt and aqueous electrolyte solutions.

The measurement of ultralow interfacial tension by video digital techniques

Abstract A video image processor is used to extend the range of interfacial tension measurement using the inflection plane method of pendant drops to the ultralow tension region. The success of the technique relies on the choice of drop geometry. Drops containing a neck are unsuitable since this introduces an inherent instability which is accentuated at ultralow interfacial tension. However, pendant drops without an equator but still having an inflection plane have been found to be stable and suitable for the present study. These drops have the magnitude of the shape parameter, β, more negative than 1.3. The drop shape can be controlled by the choice of capillary tip diameter. Interfacial tension results for the two-phase system: n-hepatane:propan-1-ol:water are reported as the system approaches the consulate point. Results into the micro-Newton per meter range have been obtained.

The effect of industrial biocides on sulphate-reducing bacteria under high pressure

Abstract This study was undertaken to determine the influence of temperature (20, 37, and 50°C) and pressure (1, 100 and 200 atm) on a strain of sulphate-reducing bacteria (SRB), isolated from an oil reservoir in Alaska. The effect of different concentrations (100, 200 and 500 ppm) of biocides isothiazolone (ITZ) and formaldehyde (FA) on planktonic population of SRB was tested in order to determine the efficacy of biocides under these conditions. The highest bacterial growth rate was 0.26±0.03 h −1 at 37°C under pressure of 100 atm. Statistical evaluation showed that although both temperature and pressure had exerted an effect on bacteria by significantly increasing their growth rate; temperature rather than pressure had greater influence on bacterial proliferation. The effectiveness of both FA and ITZ in controlling planktonic populations of SRB was comparable except at 37°C/200 atm, under which conditions FA proved to be more potent. The effectiveness of both biocides decreased with an increase in cell number, as observed at 37°C/100 atm.

Effective potential approach to bulk thermodynamic properties and surface tension of molecular fluids II. Binary mixtures of n-alkanes and miscible gas

Abstract A representation of alkanes and alkane/gas mixtures is proposed in terms of simple fluids interacting through pairwise square well potentials parameterised by the range of attractive forces. Using the model, vapour–liquid equilibria and interfacial tension (IFT) are studied both for pure alkane fluids (C4, C5, C6, C8, C10 and C14) and their high pressure binary mixtures formed with methane, nitrogen or carbon dioxide. Potential parameters for the isolated components are first determined from the critical parameters, Pitzer’s acentric factor and one surface tension datum at a chosen temperature. Cross-term interactions between species are obtained from modified Lorentz–Berthelot rules which provide good fits to the vapour–liquid coexistence densities as functions of mixture composition. At a general state point, the interfacial tension is predicted using generalised van der Waals (gvdW) theory, which is a mean field free energy density functional theory. This semiempirical procedure typically produces very satisfactory agreement with experimental interfacial tension data.

The liquid–liquid coexistence curve and the interfacial tension of the methanol–n-hexane system

At atmospheric pressure, the bulk density and liquid–liquid coexistence curve for the binary system of methanol and n-hexane have been measured as a function of temperature in the range 293–308 K. Comparison with the most reliable of the sparse literature data shows good agreement. A video image processor designed for automatic digital measurement has been used to determine the interfacial tension by the pendant drop technique. Results into the 0.01 mN m −1 range have been readily obtained. The coexistence envelope has been analysed in terms of near critical extended scaling theory using non-asymptotic Wegner corrections to indirectly determine the upper critical solution temperature at 309.5 K, in excellent agreement with contemporary work. Of the possible order parameters considered (mole, mass and volume fraction), the volume fraction difference proved the most satisfactory, yielding a critical exponent consistent with 3D Ising universality. Simple scaling relations for the interfacial tension are inadequate for reduced temperatures beyond 10 −2 .

Generalised van der Waals theory of fluids. Vapour-liquid equilibria in simple binary mixtures

Abstract By accounting for both short and long range correlation effects to the lowest nontrivial order in density, a correction to the mean field approximation is developed within the generalised van der Waals free energy density functional theory. For bulk fluids the theory yields an analytic pressure explicit equation of state (up to a simple one-dimensional quadrature) that remains cubic in the density (or volume). The encouraging results obtained for pure simple fluids are largely found to carry over to the mixture case. In particular, the vapour-liquid coexistence regime of the phase diagram for a binary mixture has been verified by comparison with statistical mechanical simulation results as well as predictions of the song-Mason-Ihm and Peng-Robinson equations of state, and experimental observations. The importance of normalising for shifts in theoretical determinations of the critical surface is discussed.

The effect of P/N/A distribution on the parachors of petroleum fractions

Abstract This study has investigated the influence of varying the ratio of paraffin, naphthene and aromatic (P/N/A) components in narrow, wide and real petroleum fractions on the parachors of the fractions. Surface tension and density measurements have been made on synthetic hydrocarbon mixtures simulating real SC8, SC10, SC13 groups, their mixtures and a kerosene sample covering the range SC4–SC14 in order to determine their experimental parachors. Two methods to compute the parachors of fractions are proposed based on the equation of Broseta, the correlations of Riazi and Al-Sahhaf and the pseudocompound approach of Daubert. The first, denoted method I, is given by P a ( cut )= [0.85−0.19ω( cut )]T c 12/11 ( cut ) P c 9/11 ( cut ) and the second, denoted method II, by P a ( cut )=z P P a ( P )+z A P a ( A )+z N P a ( N ) where Pa is the parachor of the cut, ω the acentric factor, P, N and A the P/N/A components, zP/N/A the mole fractions of the P/N/A components and the other terms have their usual meaning. Both of these methods were found to compute the parachors of mixtures representing the SC8, SC10 and SC13 groups, mixtures of these groups and the kerosene sample with an absolute deviation of 2%. Comparison of the experimental parachors with calculated ones show that the parachor of a petroleum fraction depends not only on its molecular weight but also on the ratio of the P/N/A components. It was also found that the parachor of each of the families of P, N and A components could be expressed as a linear function of molecular weight leading to the following expression for a mixture containing P, N and A components P a ( cut )=(z P A P +z N A N +z A A A ) MW +(z P B P +z N B N +z A B A ) where the A and B terms were those found in the linear regression fit for each family. The approach proposed gives quantitatively better results than methods such as that of Fawcett, where the P/N/A distribution is not taken into account in the computation of petroleum fraction parachors.

THE USE OF FAST FRAME VIDEO FOR THE STUDY OF BUBBLE-GROWTH

The kinetics of bubble evolution have received considerable attention in various contexts [l-5]. The process of bubble nucleation electrolytically [6,71, from dissolved gas solutions [8,9], or by the boiling of liquids [l,lO] has been studied in depth as a consequence of its industrial importance. The overall behaviour of bubbles at interfaces may also depend strongly on the process of bubble growth and the closely linked process of bubble detachment, since bubbles that are long-time resident at a potential nucleation site on a gas evolving surface prevent the occurrence of further nucleation events. We show that a fast frame video system may be used to study the growth stage of bubble evolution at surfaces. It should be noted that the filming of bubbles growing either electrolytically or non-electrolytically [6,7] is not a new concept, but the extension of the technique to record the growth cycles of several successive bubbles from their point of nucleation is relatively unexplored. It is expected that a video system may be used to study the nucleation and growth/detachment stages in the same experiment, and thus to determine directly the rate limiting process in bubble evolution. In these experiments, the bubble filming technique has been used to study the radii of either electrolytically or non-electrolytically generated bubbles as a function of time. In some cases it was possible to resolve the points of nucleation and detachment for the bubbles and to