Cataldo has found all rigidly rotating self-gravitating perfect fluid solutions in 2+1 dimensions with a negative cosmological constant Λ, for a density that is specified a priori as a function of a certain radial coordinate. We rewrite these solutions in standard polar-radial coordinates, for an arbitrary barotropic equation of state p(ρ). For any given equation of state, we find the twoparameter family of solutions with a regular centre and finite total mass M and angular momentum J (rigidly rotating stars). For analytic equations of state, the solution is analytic except at the surface, but including at the centre. Defining the dimensionless spin J := √ −Λ J, there is precisely one solution for each ( J, M ) in the region | J| − 1 < M < | J|, which consists of parts of the point particle region M < −| J| and overspinning regions | J| > |M |. In an adjacent compact part of the black hole region | J| < M (whose extent depends on the equation of state), there are precisely two solutions for each ( J, M ). Hence exterior solutions exist in all three classes of BTZ solution (black hole, point particle and overspinning), but not all possible values of ( J, M ) can be realised as stars.Regardless of the values of J and M , the causal structure of all stars for all equations of state is that of anti-de Sitter space, without horizons or closed timelike curves.
Kinetic Hydrate Inhibitors (KHIs) are one of the two types of Low Dose Hydrate Inhibitors (LDHIs) which are more and more used for gas hydrate control in the oil and gas industry, offering significant CAPEX advantages over traditional thermodynamic inhibitors (e.g. methanol, glycols). As KHIs are traditionally considered "nucleation inhibitors", their lab evaluation is generally undertaken by measurement of an "induction" or "hold" time before hydrates start effectively to form. However, as nucleation is stochastic by nature, obtaining repeatable/transferrable data is often highly problematic and timeconsuming, making robust evaluation difficult. A new crystal growth inhibition (CGI) approach has been recently published which showed that KHIs induce a number of highly repeatable, well-defined hydrate crystal growth inhibition regions as a function of subcooling, ranging from "complete" inhibition, through severely to moderately reduced growth rates, ultimately to final rapid/catastrophic growth as subcooling increases. Delineation of these regions provides much more reliable and rapid means to evaluate the relative performance of KHIs under simulated worst case scenario conditions. Nine commercial KHIs have been provided by vendors for one gas/condensate field development in the Middle-East. The screening of these nine KHIs with the CGI method highlighted great variations in their ability to inhibit crystal growth. Furthermore, the ability of some KHIs to completely or severely inhibit hydrate growth even when modest fractions of hydrate (>1% of converted water) are present strongly demonstrates that commercial KHIs can act very differently and that this test method allows to identify "robust" additives compatible with real operating conditions.
TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractReplacement of the traditional thermodynamic hydrate inhibitors (methanol and glycols) in wet gas applications is more and more highly desirable for cost savings and for Health, Safety & Environment (HSE) considerations. This seems achievable by using alternative Kinetic Hydrate Inhibitors (KHI). KHIs are able to delay hydrate formation for the time needed to transport the effluents in hydrate region conditions. The KHI efficiency is generally based both on the subcooling that can be matched by the inhibitor and on the hydrate formation time delay that the inhibitor can provide. Within the frame of various Field Development studies carried out since 1990, we have had the opportunity to evaluate the performance of several KHIs. These evaluations have been conducted on two hydrate loop facilities with a service pressure of respectively 80 bara and 165 bara. Thanks to these two pilots, we have been able to observe and to quantify the influence of various parameters on the KHI efficiency. Among these parameters, two of them have proved to be of importance: the presence of other inhibitors, such as corrosion inhibitors (CI), and the operating pressure. Their strong influence is illustrated in this paper through the results obtained in three different case studies. The practical conclusion is that KHIs selected in "routine" lab tests may be not efficient in the field and that appropriate selection tests are required.
TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractReplacement of the traditional thermodynamic hydrate inhibitors (methanol and glycols) in wet gas applications is more and more highly desirable for cost savings and for Health, Safety & Environment (HSE) considerations. This seems achievable by using alternative Kinetic Hydrate Inhibitors (KHI). KHIs are able to delay hydrate formation for the time needed to transport the effluents in hydrate region conditions. The KHI efficiency is generally based both on the subcooling that can be matched by the inhibitor and on the hydrate formation time delay that the inhibitor can provide. Within the frame of various Field Development studies carried out since 1990, we have had the opportunity to evaluate the performance of several KHIs. These evaluations have been conducted on two hydrate loop facilities with a service pressure of respectively 80 bara and 165 bara. Thanks to these two pilots, we have been able to observe and to quantify the influence of various parameters on the KHI efficiency. Among these parameters, two of them have proved to be of importance: the presence of other inhibitors, such as corrosion inhibitors (CI), and the operating pressure. Their strong influence is illustrated in this paper through the results obtained in three different case studies. The practical conclusion is that KHIs selected in "routine" lab tests may be not efficient in the field and that appropriate selection tests are required.
We carry out numerical simulations of the gravitational collapse of a rotating perfect fluid with the ultrarelativistic equation of state P = κρ, in axisymmetry in 2 + 1 spacetime dimensions with Λ < 0. We show that for κ 0.42, the critical phenomena are type I and the critical solution is stationary. The picture for κ 0.43 is more delicate: for small angular momenta, we find type II phenomena and the critical solution is quasistationary, contracting adiabatically. The spin-to-mass ratio of the critical solution increases as it contracts, and hence so does that of the black hole created at the end as we fine-tune to the black-hole threshold. Forming extremal black holes is avoided because the contraction of the critical solution smoothly ends as extremality is approached.
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