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A lot of new work on supercritical fluids is the ability of calculate properties for those. normally we don't access to those conditions, so it is tricky to measure, but there is always new work on correlations capable of explaining the anomalies present on near critical and supercritical fluids. On the viscosity front, there is this new framework named Entropy Scaling, that postulates that scaled viscosity ≈ f(residual entropy)^(2/3). There is also new work on calculation of interfacial tensions from pure equations of state,that are relevant because you could have a two phase liquid-liquid mix and you want to transport something from one liquid phase to another.
Also, as the article says, over the critical point, there is no surface tension, because there is only one phase. (do not take this phrase literally, because that only happens in a pure compound, as soon as you have a mixture, the surface tension will depend on all elements of the mixture) Furthermore, some fluid mixtures present something called UCST (upper critical solution temperatures) and LCST (lower critical solution temperatures). imagine if you lower the temperature of and oil-water mixture and suddenly they start to mix. and if you keep lowering the temperature, they unmix again!, and of course, not every fluid presents those properties, but we need to understand those who do. and specially, calculate those points. Few if any industrial thermodynamic calculators can do this, because you require fourth order accurate derivatives (can this be solved with automatic differentiation like what they do with neural networks?, of course, but you need a differentiation-ready equation of state) On more macro properties, supercritical cycles are useful. you can start from a liquid and end with a gas without boiling, if you pressurize your liquid over the critical pressure (isothermically) then lower the temperature (isobarically) and finally releasing pressure (isothermically). one advantage of doing that is that you don't produce bubbles or any kinetic artifacts that are present during a normal phase transition. |