Fluid system

Before the phase change, however, there has been the possibility of a considerable relaxation of order. When molecules rotate on their axes extra configurational complexions arise. An angular coordinate 

A liquid, then, would appear to be a lattice so mobile imder shear that it exists only as a time average. It might perhaps be likened to a flight of birds attempting to keep formation in a gale. They are 

That order and mobility are by no means very closely correlated is evident from the existence of glasses, which represent highly supercooled liquids. They are hard and brittle, but possess no definite crystalline structure. The randomness of the molecular arrangement is about the same as that in liquids, but they are not necessarily entirely devoid of certain kinds of order, as is suggested by the characteristic conchoidal fracture which is often shown. 

In a perfect gas the expansive force originates in the tendency to assume a state of greater entropy, and dUjdV is zero. In rubber the contractile force originates in what is essentially the same way, namely in the tendency of the molecules to pass to a state of higher entropy. In the two cases there is the same law of temperature variation. Gas pressure on the one hand and contractile force on the other both increase in direct proportion to the absolute temperature. 

Now since P for a given elongation is found experimentally to vary directly as T, dUjdl cannot contribute in any important way. In other cases, of course, there is no reason why internal energy changes accompanying the distortion should not be the major factors in causing the appearance of the contractile force. Here the temperature dependence would become quite different. 

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The principle of operation of the hydraulic reciprocating pump is similar to the beam pump, with a piston-like sub-surface pump action. The energy to drive the pump, however, is delivered through a hydraulic medium, the power fluid, commonly oil or water. The power fluid drives a downhole hydraulic motor which in turn drives the pump. A separate surface pump delivers the hydraulic power. The power fluid system can be of the closed loop or of the open type. In the latter case, the power fluids are mixed with the produced fluid stream. The performance of the hydraulic pump is primarily monitored by measuring the discharge pressures of both surface and sub-surface pumps. 

Thermal Properties and Temperature related Behavior of Rock/fluid Systems... 

We discuss classical non-ideal liquids before treating solids. The strongly interacting fluid systems of interest are hard spheres characterized by their harsh repulsions, atoms and molecules with dispersion interactions responsible for the liquid-vapour transitions of the rare gases, ionic systems including strong and weak electrolytes, simple and not quite so simple polar fluids like water. The solid phase systems discussed are ferroniagnets and alloys. 

A2.5.3 ANALYTIC TREATMENT OF CRITICAL PHENOMENA IN FLUID SYSTEMS. THE VAN DER WAALS EQUATION... 

Figure A2.5.11. Typical pressure-temperature phase diagrams for a two-component fluid system. The fiill curves are vapour pressure lines for the pure fluids, ending at critical points. The dotted curves are critical lines, while the dashed curves are tliree-phase lines. The dashed horizontal lines are not part of the phase diagram, but indicate constant-pressure paths for the T, x) diagrams in figure A2.5.12. All but the type VI diagrams are predicted by the van der Waals equation for binary mixtures. Adapted from figures in [3].

A third exponent y, usually called the susceptibility exponent from its application to the magnetic susceptibility x in magnetic systems, governs what m pure-fluid systems is the isothennal compressibility k, and what in mixtures is the osmotic compressibility, and detennines how fast these quantities diverge as the critical point is approached (i.e. as > 1). 

Nearly all experimental eoexistenee eurves, whether from liquid-gas equilibrium, liquid mixtures, order-disorder in alloys, or in ferromagnetie materials, are far from parabolie, and more nearly eubie, even far below the eritieal temperature. This was known for fluid systems, at least to some experimentalists, more than one hundred years ago. Versehaflfelt (1900), from a eareflil analysis of data (pressure-volume and densities) on isopentane, eoneluded that the best fit was with p = 0.34 and 8 = 4.26, far from the elassieal values. Van Laar apparently rejeeted this eonelusion, believing that, at least very elose to the eritieal temperature, the eoexistenee eurve must beeome parabolie. Even earlier, van der Waals, who had derived a elassieal theory of eapillarity with a surfaee-tension exponent of 3/2, found (1893)... 

The exponents apply not only to solid systems (e.g. order-disorder phenomena and simple magnetic systems), but also to fluid systems, regardless of the number of components. (As we have seen in section A2.5.6.4 it is necessary in multicomponent systems to choose carefully the variable to which the exponent is appropriate.)... 

If these assumptions are satisfied then the ideas developed earlier about the mean free path can be used to provide qualitative but useful estimates of the transport properties of a dilute gas. While many varied and complicated processes can take place in fluid systems, such as turbulent flow, pattern fonnation, and so on, the principles on which these flows are analysed are remarkably simple. The description of both simple and complicated flows m fluids is based on five hydrodynamic equations, die Navier-Stokes equations. These equations, in trim, are based upon the mechanical laws of conservation of particles, momentum and energy in a fluid, together with a set of phenomenological equations, such as Fourier s law of themial conduction and Newton s law of fluid friction. When these phenomenological laws are used in combination with the conservation equations, one obtains the Navier-Stokes equations. Our goal here is to derive the phenomenological laws from elementary mean free path considerations, and to obtain estimates of the associated transport coefficients. Flere we will consider themial conduction and viscous flow as examples. 

Measurement by Electromagnetic Effects. The magnetic flow meter is a device that measures the potential developed when an electrically conductive flow moves through an imposed magnetic field. The voltage developed is proportional to the volumetric flow rate of the fluid and the magnetic field strength. The process fluid sees only an empty pipe so that the device has a very low pressure drop. The device is useful for the measurement of slurries and other fluid systems where an accumulation of another phase could interfere with flow measurement by other devices. The meter must be installed in a section of pipe that is much less conductive than the fluid. This limits its appHcabiHty in many industrial situations. 

Siace 1980 over 1000 patents have been issued for drilling fluid systems and materials ia the United States alone. A 1994 listing of products from 117 supphers offers ca 3000 trade names (6). This array of trade name products actually represents less than 100 separate chemical types that may be purchased iadividuaHy or as a blend. Moreover, some of these materials are for completion and workover fluids. These differ from drilling fluids ia that completion fluids are used after the well has been drilled and prior to the initia tion of production whereas workover fluids are used duting remedial work on older wells. 

Slurry Pipelines. Finely divided soHds can be transported in pipelines as slurries, using water or another stable Hquid as the suspending medium. Flow characteristics of slurries in pipelines depend on the state of subdivision of the soHds and their distribution within the fluid system. 

A number of theoretical models have been proposed to describe the phase behavior of polymer—supercritical fluid systems, eg, the SAET and LEHB equations of state, and mean-field lattice gas models (67—69). Many examples of polymer—supercritical fluid systems are discussed ia the Hterature (1,3). 

Gas AntisolventRecrystallizations. A limitation to the RESS process can be the low solubihty in the supercritical fluid. This is especially evident in polymer—supercritical fluid systems. In a novel process, sometimes termed gas antisolvent (GAS), a compressed fluid such as CO2 can be rapidly added to a solution of a crystalline soHd dissolved in an organic solvent (114). Carbon dioxide and most organic solvents exhibit full miscibility, whereas in this case the soHd solutes had limited solubihty in CO2. Thus, CO2 acts as an antisolvent to precipitate soHd crystals. Using C02 s adjustable solvent strength, the particle size and size distribution of final crystals may be finely controlled. Examples of GAS studies include the formation of monodisperse particles (<1 fiva) of a difficult-to-comminute explosive (114) recrystallization of -carotene and acetaminophen (86) salt nucleation and growth in supercritical water (115) and a study of the molecular thermodynamics of the GAS crystallization process (21). 

Equations 54 and 58 through 60 are equivalent forms of the fundamental property relation apphcable to changes between equihbtium states in any homogeneous fluid system, either open or closed. Equation 58 shows that ff is a function of 5" and P. Similarly, Pi is a function of T and C, and G is a function of T and P The choice of which equation to use in a particular apphcation is dictated by convenience. Elowever, the Gibbs energy, G, is of particular importance because of its unique functional relation to T, P, and the the variables of primary interest in chemical technology. Thus, by equation 60,... 

Photochromic compounds that can be thermally faded have also been used in engineering studies to visuali2e flows in dynamic fluid systems (44,45). 

The definitions of enthalpy, H, Helmholtz free energy. A, and Gibbs free energy, G, also give equivalent forms of the fundamental relation (3) which apply to changes between equiUbrium states in any homogeneous fluid system ... 

Cussler, Diffusion Mass Transfer in Fluid Systems, Cambridge, 1984. 

Close-Clearance Stirrers For some pseiidoplastic fluid systems stagnant fluid may be found next to the -essel walls in parts remote from propeller or turbine impellers. In such cases, an anchor impeller maybe used (Fig, 18-6), The fluid flow is principally circular or helical (see Fig, 18-7) in the direction of rotation of the anchor. Whether substantial axial or radial fluid motion also occurs depends on the fluid iscosity and the design of the upper blade-supporting spokes. Anchor agitators are used particularly to obtain irnpro ed heat transfer in high-consistency fluids,... 

When the problem is to disrupt Ughtly bonded clusters or agglomerates, a new aspect of fine grinding enters. This may be iUustrated by the breakdown of pigments to incorporate them in liquid vehicles in the making of paints, and the disruption of biological cells to release soluble produces. Purees, food pastes, pulps, and the like are processed by this type of mill. Dispersion is also associated with the formation of emulsions which are basically two-fluid systems. Syrups, sauces, milk, ointments, creams, lotions, and asphalt and water-paint emulsions are in this categoiy. 

In the selection of materials of construction for a particular fluid system, it is important first to take into consideration the characteristics... 

In the absence of factual corrosion information for a particular set of fluid conditions, a reasonably good selection would be possible from data based on the resistance of materials to a very simifar environment. These data, however, should be used with some reservations. Good practice calls for applying such data for preliminary screening. Materials selected thereby would reqmre further study in the fluid system under consideration. 

A criterion for the namre of flow, either laminar or mrbulent flow in fluid systems is the value of the Reynolds number. This number, Rg is defined by the equation... 

Steam traeing is the most eommon type of industrial pipe traeing. In 1960, over 95 pereent of industrial traeing systems were steam traeed. By 1995, improvements in eleetrie heating teehnology inereased the eleetrie share to 30 to 40 pereent, but steam traeing is still the most eommon system. Fluid systems other than steam are rather uneommon and aeeount for less than 5% of traeing systems. 

Like thermal systems, it is eonvenient to eonsider fluid systems as being analogous to eleetrieal systems. There is one important differenee however, and this is that the relationship between pressure and flow-rate for a liquid under turbulent flow eondi-tions is nonlinear. In order to represent sueh systems using linear differential equations it beeomes neeessary to linearize the system equations. 

The information assembled for the selected node includes descriptions of the hardware and physical parameters of the operating mode. For example, the information for a fluid system must include physical parameters, such as flow, pressure, temperature, temperature gradients, density, and... 

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