Computational fluid dynamics 4781 Subject

Care is needed when modeling compressible gas flows, flows of vapor-liquid mixtures, slurry flows, and flows of non-Newtonian liquids. Some simulators use different pipe models for compressible flow. The prediction of pressure drop in multiphase flow is inexact at best and can be subject to very large errors if the extent of vaporization is unknown. In most of these cases, the simulation model should be replaced by a computational fluid dynamics (CFD) model of the important parts of the plant. 

This whole subject is part of what has come to be known as computational fluid dynamics (CFD). Many books and reviews are available, for example. Curl (1963), Hill (1976), Libby and Williams (1980), Brodkey (1975), Nauman and Buffham (1983), Villermaux (1985, 1991), Fox (1996), and Baldyga and Bourne (1999), The general use of CFD in most reactor design calculations is open to question in a number of practical situations. This is particularly true of organic synthesis/technology. 

Until this point we have considered only inelastic liquids in both the analytical and numerical treatments of polymer processing. The viscoelasticity of polymer melts sometimes plays a major role in the mechanics of processing behavior, and we take up this important issue in the next and subsequent chapters. Numerical problems are greatly compounded by the presence of fluid elasticity, but the overall approach is unchanged. We will return to the use of computational fluid dynamics with complex rheology after taking up the subject of viscoelasticity. 

Obtained using the commercial computational fluid dynamics (CFD) software, STAR-CD, Figure 11.2 shows the temperature distribution within the interconnect which is subject to the largest temperature gradient, 5 minutes after startup. 

The equation of state of a hard-sphere fluid has been the subject of considerable research, and far better approximate equations than Eq. (9.8-4) have been obtained. One such equation of state is found in Problem 9.64. Much additional research on gases and liquids has used the technique of molecular dynamics, in which solutions to the classical equations of motion for a system of several hundred particles are numerically simulated by a computer program. Energies, pressures, etc., are then calculated by averaging over the particles positions and velocities. As we would expect, the molecular dynamics calculations indicate that there is no gas-liquid condensation in the hard-sphere system. However, there is considerable evidence from these calculations that a gas-solid phase transition occurs. This result was originally somewhat surprising because of the absence of attractive forces. 

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