Contents Fluid flow

Compressible fluid flow occurs between the two extremes of isothermal and adiabatic conditions. For adiabatic flow the temperature decreases (normally) for decreases in pressure, and the condition is represented by p V (k) = constant. Adiabatic flow is often assumed in short and well-insulated pipe, supporting the assumption that no heat is transferred to or from the pipe contents, except for the small heat generated by fricdon during flow. Isothermal pVa = constant temperature, and is the mechanism usually (not always) assumed for most process piping design. This is in reality close to actual conditions for many process and utility service applications. 

In general, the temperature 0S at the axis is not known, and the heat transfer coefficient is related to the temperature difference between the walls and the bulk fluid. The bulk temperature of the fluid is defined as the ratio of the heat content to the heat capacity of the fluid flowing at any section. Thus the bulk temperature 9S is given by ... 

The coupled precipitation kinetics-fluid flow model was applied to the distribution of Si02 content and K2O content of the hydrothermally altered andesite in the Hishikari Au-Ag mine area, south Kyushu, Japan by Shikazono et al. (2002). This will be described in section 1.4.6. 

Further error is introduced if reactions distinct from those for which data is available affect the chemistry of a natural fluid. Consider as an example the problem of predicting the silica content of a fluid flowing through a quartz sand aquifer. There is little benefit in modeling the reaction rate for quartz if the more reactive minerals (such as clays and zeolites) in the aquifer control the silica concentration. 

Exploration for unconformity-related deposits is based firstly on Proterozoic red-bed basins overlying basement complexes and source regions characterized by high U contents. Given this criteria alone, there are nearly 200 basins that would qualify. Graphitic metasedimentary units within the basement complex are desirable, but not necessary, as exemplified by the Nabarlek deposit in the Northern Territory, Australia (Polite et al. 2004). Repeated brittle reactivations of ductile structures, normally from far field tectonic events, that may offset the basal unconformity and were foci for fluid flow are required. 

Recall our short discussion in Section 18.5 where we learned that turbulence is kind of an analytical trick introduced into the theory of fluid flow to separate the large-scale motion called advection from the small-scale fluctuations called turbulence. Since the turbulent velocities are deviations from the mean, their average size is zero, but not their kinetic energy. The kinetic energy is proportional to the mean value of the squared turbulent velocities, Mt2urb, that is, of the variance of the turbulent velocity (see Box 18.2). The square root of this quantity (the standard deviation of the turbulent velocities) has the dimension of a velocity. Thus, we can express the turbulent kinetic energy content of a fluid by a quantity with the dimension of a velocity. In the boundary layer theory, which is used to describe wind-induced turbulence, this quantity is called friction velocity and denoted by u. In contrast, in river hydraulics turbulence is mainly caused by the friction at the... 

Other factors indicated m the data of Tables 1 and 2 include Pour Point—defined as the lowest temperature at which the material will pour and a function of the composition of the oil in terms of waxiness and bitumen content Salt Content—which is not confined to sodium chloride, but usually is interpreted in terms of NaCl Salt is undesirable because of the tendency to obstruct fluid flow, to accumulate as an undesirable constituent of residual oils and asphalts, and a tendency of certain salt compounds to decompose when heated, causing corrosion of refining equipment Metals Content—heavy metals, such as vanadium, nickel, and iron, tend to accumulate in the heavier gas oil and residuum fractions where the metals may interfere with refining operations, particularly by poisoning catalysts. The heavy metals also contribute to the formation of deposits on heated surfaces in furnaces and boiler fireboxes, leading to permanent failure of equrpment, interference with heat-transfer efficiency, and increased maintenance. 

Most laboratory experiments demonstrating the utility of EO transport of organic compounds were conducted with kaolinite as the model clay-rich soil medium. Shapiro et al. (1989) used EO to transport phenol in kaolinite. Bruell et al. (1992) have shown that TCE can be transported down a slurry column by electroosmotic fluid flow, and more recently, Ho et al. (1995) demonstrated electroosmotic movement of p-nitrophenol in kaolinite. Kaolinite is a pure clay mineral, which has a very low cation exchange capacity and is generally a minor component of the silicate clay mineral fraction present in most natural soils. It is not, therefore, representative of most natural soil types, particularly those which are common in the midwestem United States. The clay content can impact the optimization and effectiveness of electroosmosis in field-scale applications, as has recently been discussed by Chen et al. (1999). 

Dead time is also called transportation lag, because it is the time required for fresh heat transfer fluid to displace the contents of the exchanger and its associated piping. The dead time is the worst enemy of control, because until it has expired, a change in the heat transfer fluid flow (or temperature) will not even begin to have an observable effect. For a heat exchanger, the dead time is usually between 1 and 30 seconds. When the equipment is correctly designed, the dead time is much less than the time constant. 

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