Ostwald's Law Research Articles

Substantiation of analytical dependences for hydraulic calculation of high-viscosity oil transportation

One of the development priorities in oil and gas industry is to maintain gas and oil pipeline networks and develop pipeline-connected gas and oil fields of the Arctic zone of the Russian Federation, a promising region the resource potential of which will not only meet a significant portion of internal and external demand for various types of raw materials and primary energy carriers, but will also bring great economic benefits to subsoil users and the state. The mineral and raw material centers of the Nadym-Purskiy and Pur-Tazovskskiy oil and gas bearing areas are among the most attractive regions of the Arctic zone. It is necessary to develop a scientifically substantiated approach to improve the methods of oil transportation from the field to the existing pipelines. As it is known, the task of increasing the efficiency of pipeline transportation of high-viscosity oil is inseparably connected with solving problems in the field of thermal and hydraulic calculation of pipeline system. The article presents the substantiation of dependencies for hydraulic calculation of pipelines transporting high-viscosity oil exhibiting complex rheological properties. Based on the laws of hydraulics for non-Newtonian fluids, the formulas for calculating head losses for fluids obeying Ostwald's law are proposed, their relationship to the classical equations of hydraulics is shown. The theoretical substantiation of looping installation for increasing the efficiency of pipeline transportation of high-viscosity oil taking into account the received dependences for power fluid is considered.

Flow Measurement and Instrumentation

Crude oil flow in the pipelines is a source of major problems with heavy substance deposits on the wall surfaces. This situation can lead to lines blocking. Therefore, it is mandatory to have information concerning the flow. For this purpose the rheological properties of the crude oil are needed in order to propose adapted solutions. This paper deals with the study of the rheological properties of Algerian crude oil at different temperatures as well as its flow in pipe. The experimental results obtained with a modern rheometer can be used to predict the crude oil transport characteristics. The crude oil rheogram shows a non-Newtonian behavior which can be described by the Ostwald law. The shear stresses computations obtained from an analytical model and the MPTT model are compared and give the friction factor distribution across the pipe section. The obtained results are presented and discussed.

Determination of friction factor of Algerian crude oil during flow in pipe-lines

Crude oil flow in the pipelines is a source of major problems with heavy substance deposits on the wall surfaces. This situation can lead to lines blocking. Therefore, it is mandatory to have information concerning the flow. For this purpose the rheological properties of the crude oil are needed in order to propose adapted solutions. This paper deals with the study of the rheological properties of Algerian crude oil at different temperatures as well as its flow in pipe. The experimental results obtained with a modern rheometer can be used to predict the crude oil transport characteristics. The crude oil rheogram shows a non-Newtonian behavior which can be described by the Ostwald law. The shear stresses computations obtained from an analytical model and the MPTT model are compared and give the friction factor distribution across the pipe section. The obtained results are presented and discussed.

Rheological Behavior of Smectite Dispersions: The Influence of Suspension Concentration and Exchangeable Cation

The mechanical behaviors of smectite materials in water are very sensitive to many parameters, such as concentration, particle size and morphology, exchangeable cation nature, and chemical environment (pH, ionic strength). The literature usually provides general rules for sodium and calcium bentonites. However, it appears that the quantitative results present a large range of values. This study has established the relationships between the smectite nature (mineralogy, morphology, reactivity) and its rheological behavior according to the exchangeable cation. To develop a complete rheological study, we need 800 g of montmorillonite purified and saturated with or . Huge production necessitates optimized process with accurate control of the powder quality and the chemical environment. Smectite particles have been extracted from a natural bentonite and then saturated with sodium or calcium. Then, each sample was characterized with classical methods like X-ray diffractometry (XRD), and laser granulometry but also cutting-edge technologies like scanning transmission electron microscopy on wet samples (Wet STEM). The Na-smectite dispersion contains a lot of small units whereas the Ca-smectite dispersion contains a few large units. Rheological study consists in flow curves obtained with a high-resolution rheometer. Logarithmic representation of the rheograms permits detecting a yield stress, it separates solid and fluid behavior. The rheological datas (viscosity, consistency, and yield stress) allow defining the limits depending on the concentration and on the saturation state. A Newtonian law could be applied to around 4% for Na- and Ca-smectites. Seaward of these concentrations, the dispersions are shear thinning and modelled by Ostwald law. Finally a yield stress appears at 6% for Na-smectite and 11% for Ca-smectite, the flow curves could be modelled by Hershel-Bukley law. Results are in accordance with the bibliography.

Fermat–Ostwald Principle

Fermat's principle of least time and Ostwald's law of intermediate stages are postulates concerning the physical processes that deal with light and heat energy flows, respectively. A comparative analysis of these processes shows that there is a close analogy between them. This suggests that the principle of least time can be applied to phase transitions of first kind concerned Ostwald's law. This supposition has been proven using the Maxwell-Boltzmann distribution law and an assumed correlation between two parameters of solids (heat conductivity and activation energy of molecules). Thus, a modification of Fermat's principle is obtained, which can be named Fermat-Ostwald principle.

Cross-Nucleation between ROY Polymorphs

Cross-nucleation between polymorphs is a newly discovered phenomenon important for understanding and controlling crystal polymorphism. It contradicts Ostwald's law of stages and other theories of crystallization in polymorphic systems. We studied the phenomenon in the spontaneous and seeded melt crystallization of 5-methyl-2-[(2-nitrophenyl)amino]-3-thiophenecarbonitrile (ROY), currently the most polymorphic system of known structures. We observed extensive and sometimes selective cross-nucleation between ROY polymorphs. Certain polymorphs could not nucleate without the aid of others. The new polymorph was found to be more or less thermodynamically stable than the initial one but to always grow faster than or as fast as the initial one. The temperature and surface characteristics of the seed crystals affected the occurrence of cross-nucleation. Our results show that the pathway of crystallization in polymorphic systems is not determined solely by the initial nucleation, but also by cross-nucleation between polymorphs and the different growth rates of polymorphs. This study identified a new metastable polymorph of ROY, the 10th of the family.

Polymorphism and Thermodynamic Stability of Zn7Sb2O12

The composition Zn2.33Sb0.67O4 (or Zn7Sb2O12) exists in two polymorphic forms. The thermodynamically stable, low‐temperature orthorhombic β form transforms to the high‐temperature cubic α‐polymorph with a spinel structure at 1225°±25°C. The transformation is fully reversible but slower in the α→β direction and therefore, it is easy to preserve the high‐temperature α‐polymorph to lower temperatures where it is kinetically stable but thermodynamically metastable. It is also possible to synthesize the α‐polymorph directly at low temperatures, e.g., 900°C. This synthesis, of a phase that is thermodynamically stable only at high temperatures, but which has sufficient kinetic stability to exist metastably at low temperatures, represents an example of Ostwald's law of successive reactions in which the first phase to crystallize from a reaction mixture is not necessarily the equilibrium phase of lowest free energy. The crystal structure of the α‐polymorph has been confirmed by Rietveld refinement of X‐ray powder diffraction data to be an inverse spinel, (Zn)[Sb2/3Zn4/3]O4, in which octahedral sites contain a disordered, random mixture of Zn and Sb and tetrahedral sites are fully occupied by Zn.

Effect of thickeners and sweeteners on the release of blended aroma compounds in fat-free stirred yoghurt during shear conditions

Abstract The present study was conducted on aromatised fat-free stirred yoghurts and dealt with the influence of some thickeners and sweeteners on aroma compounds release and rheology. Thickeners (starch, pectin, locust bean gum and guar) and sweeteners (fructose, fructo-oligosaccahrides, aspartame and acesulfame) were added and mixed together in fruit preparations, which were then introduced in yoghurt. Different concentrations of thickeners and sweeteners were used in the fruit preparations and were obtained with an experimental design. The headspace composition was assessed by solid-phase microextraction during shear conditions in a closed vessel. Rheological properties of yoghurts were determined to obtain the flow behaviour index n and the consistency index K with the Ostwald law. The presence of pectin in yoghurts, tended to reduce the concentration of aroma compounds in the headspace of the samples. We observed also a significant decrease of aroma compounds in the headspace of yoghurt in the presence of starch. In the case of locust bean gum, a significant increase of flavour release was observed. Sweeteners and guar appeared to have no effect. We concluded that rheological parameters did not explain the difference on aroma release and it seemed that during shear conditions, the composition of fruit preparations showed a major role on aroma release. The influence of aroma compounds characteristics on the flavour release was observed, but experiments must be performed to highlight this observation.

Wall shear rate in the Taylor–Couette–Poiseuille flow at low axial Reynolds number

An experimental investigation was done by the use of visual observations and the electrochemical technique in order to study the appearance of hydrodynamic instabilities at low Re axg in the gap between two coaxial cylinders, with radius ratio R r/ R s=0.615 and aspect ratio L/ e=24. A motor drove the inner cylinder and the outer cylinder was fixed. A Newtonian fluid (Emkarox HV45) and two non-Newtonian fluids (aqueous solutions of guar and CMC) have been used. The analysis of the evolution of the size of the Taylor vortices is carried out for Re axg<4.0. For Re axg<2 we showed that the vortices underwent a contraction phase up to Ta g≈80, and a stretching phase for Ta g>80. For higher Re axg, the contraction phase vanished and the vortices progressively stretched with increasing Ta g. A dimensionless representation was also proposed for wall friction generalized to non-Newtonian fluids following the Ostwald law.

Polymorphism in 2,4,6-trinitrotoluene crystallized from solution.

An examination has been made of the role of solvent type in the definition of the polymorphic nature of 2,4,6-trinitrotoluene precipitated from solution. A combination of calorimetric and structural techniques including in situ crystallization studies using synchrotron radiation has shown that the variations in polymorphic form following precipitation from solution do not arise specifically from any stereospecific guidance that the nature of the solvent might impose on the structural form. Rather the differences are linked to the variations in solubility and hence supersaturation which might build up prior to nucleation and growth and to the isolation of the metastable orthorhombic phase from the solvent. The final conclusion is that the changes fit well with Ostwald's Law of Stages with the orthorhombic form always precipitating initially followed by its conversion to the stable monoclinic form. The previously observed tendency for some solvents to yield one or the other form then becomes attributable to kinetics in solution rather than structural control. It can be associated with the solubility of the material in the solvent used and the role of this factor in a solvent-mediated phase transformation. On this basis rules can be formulated for the isolation of the metastable forms of this and similarly related polymorphic systems.

Etude de la validite de la loi de Fick pour le transfer de matiere dans un fluide viscoelastique

An experimental study has been realized in a viscoelastic fluid to know if the Fick's law can be applied. This study also permitted to give some precisions about the differencies observed between the mass transfer measurements and the theorie results from the Ostwald's law.

Calcite Aragonite Problem: ABSTRACT

The fundamental stability relations of calcite and aragonite are considered in the light of: (a) calorimetric data, (b) solubility measurements, (c) direct studies of phase changes. New data of Crawford and Fyfe suggest slightly lower pressures for aragonite formation than have been formerly proposed. The difference in free energies of calcite and aragonite are small, and the effect on stability of grain size, non-hydrostatic stress, and impurities are evaluated and may be as large as ^DgrG°. Consideration of precipitation reactions involving nucleation and growth indicates that there need be no direct relationship between fundamental stability and the order of appearance of possible phases. Ostwald's law of stages implies an inverse correlation. Data on the effects of temperature and solution composition indicate that the form of calcium carbonate precipitated may frequently reflect favorable kinetics of aragonite nucleation enhanced by calcite growth inhibition. A basic problem in carbonate sedimentation involves the rate at which metastable aragonite undergoes transformation to calcite. Data on this reaction in the dry state are compared with similar processes in nitrates. It is suggested from study of single crystals that the dry process is essentially zero order, but a combination of structure and habit sensitivity may lead to other apparent rate laws. Nucleation normally takes place in the prism zone and proceeds via a linear boundary migration parallel to the c axis. A lack of reactivity of (001) also appears in aqueous reactions. In general, dry rates must be of no significance at the temperatures normally encountered in diagenesis unless deformation is extensive. In aqueous solution the problem is more complex. The rate is a function of volume, pH, PCO2, salt catalysis (general) and salt inhibition (specific), and organic protection as in some fossil aragonite, and aggregate fabric (as in fossils). It is suggested that the formation of calcite from aragonite in aqueous solutions involves homogeneous nucleation and that this is the slow rate step and is controlled by some function involving Ca++ and/or HCO3- activities. Specific inhibition appears to involve inhibition of growth and several explanations are possible, but the size of the inhibiting cation appears to be critical. End_of_Article - Last_Page 526------------

IX.—On the Relationship between Concentration and Electrolytic Conductivity in Concentrated Aqueous Solutions

Although great advances have been made during the last thirty years in our knowledge of dilute solutions, there has been no corresponding advance in respect of concentrated solutions. This is primarily due to the fact that hitherto no simple and general relationship has been discovered between the conductivity and the concentration of concentrated solutions of electrolytes. Ostwald's law of dilution holds only for dilute solutions of weak electrolytes, and the formulæ of Rudolphi and Van T'Hoff are applicable only to dilute solutions of good electrolytes. It seems therefore important to inquire whether the difficulty may not be to some extent overcome by an alteration in the mode of representing the facts.

VI. Experimental proof of Van't Hoff's constant, of Arrhenius's generalization, and of Ostwald's law of dilution in very dilute solutions

(1895). VI. Experimental proof of Van't Hoff's constant, of Arrhenius's generalization, and of Ostwald's law of dilution in very dilute solutions. The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science: Vol. 40, No. 242, pp. 119-144.