Papers by sukanya saengket
The flow problems considered in previous chapters are concerned with homogeneous fluids, either s... more The flow problems considered in previous chapters are concerned with homogeneous fluids, either single phases or suspensions of fine particles whose settling velocities are sufficiently low for the solids to be completely suspended in the fluid. Consideration is now given to the far more complex problem of the flow of multiphase systems in which the composition of the mixture may vary over the cross-section of the pipe or channel; furthermore, the components may be moving at different velocities to give rise to the phenomenon of "slip" between the phases. Multiphase flow is important in many areas of chemical and process engineering and the behaviour of the material will depend on the properties of the components, the flowrates and the geometry of the system. In general, the complexity of the flow is so great that design methods depend very much on an analysis of the behaviour of such systems in practice and, only to a limited extent, on theoretical predictions. Some of the more important systems to be considered are: Mixtures of liquids with gas or vapour. Liquids mixed with solid particles ("hydraulic transport"). Gases carrying solid particles wholly or partly in suspension ("pneumatic transport"). Multiphase systems containing solids, liquids and gases. Mixed materials may be transported horizontally, vertically, or at an inclination to the horizontal in pipes and, in the case of liquid-solid mixtures, in open channels. Although there is some degree of common behaviour between the various systems, the range of physical properties is so great that each different type of system must be considered separately. Liquids may have densities up to three orders of magnitude greater than gases but they do not exhibit any significant compressibility. Liquids themselves can range from simple Newtonian liquids such as water, to non-Newtonian fluids with very high apparent viscosities. These very large variations in density and viscosity are responsible for the large differences in behaviour of solid-gas and solid-liquid mixtures which must, in practice, be considered separately. For, all multiphase flow systems, however, it is important to understand the nature of the interactions between the phases and how these influence the flow patterns — the ways in which the phases are distributed over the cross-section of the pipe or duct. In design it is necessary to be able to predict pressure drop which, usually, depends not only on the flow pattern, but also on the relative velocity of the phases; this slip velocity will influence the holdup , the fraction of the pipe volume which is occupied by a particular phase. It is important to note that, in the flow of a
Uploads
Papers by sukanya saengket