Eddy turbulence

Different processes like eddy turbulence, bottom current, stagnation of flows, and storm-water events can be simulated, using either laminar or turbulent flow model for simulation. All processes are displayed in real-time graphical mode (history, contour graph, surface, etc.) you can also record them to data files. Thanks to innovative sparse matrix technology, calculation process is fast and stable a large number of layers in vertical and horizontal directions can be used, as well as a small time step. You can hunt for these on the Web. 

HOTMAC/RAPTAD requires very extensive meteorological and terrain data input. The program user s guide and diagnostics are inadequate. HOTMAC does not model multiple scale eddy turbulence and does not provide for dispersion of gases that are denser-than air. It must be tailored to reflect the climatic characteristics of specific sites. 

The daughter bubble size is thus limited by two constraints. The capillary pressure constraint states that if the dynamic pressure of the turbulent eddy Pc v x exceeds the capillary pressure aijd", the fluid particle is deformed and finally breaks up resulting in a minimum breakage fraction /vm, (or bubble size dj min) [69]. d denotes the diameter of the smaller daughter size (or two times the minimum radius of curvature). When breakage occurs, the d3mamic pressure induced by the eddy turbulence kinetic energy satisfy the criterion ... 

This model has several limitations. The film model assumes that mass transfer is controlled by the liquid-phase film, which is often not the case because the interface characteristics can be the limiting factor (Linek et al., 2005a). The liquid film thickness and diffusivity may not be constant over the bubble surface or swarm of bubbles. Experiments also indicate that mass transfer does not have a linear dependence on diffusivity. Azbel (1981) indicates that others have shown that turbulence can have such a significant effect on mass transfer such that eddy turbulence becomes the controlling mechanism in which diffusivity does not play a role. In most instances, however, eddy turbulence and diffusivity combine to play a significant role in mass transfer (Azbel, 1981). 

The border diffusion layer model was introduced as an amendment to the film model to present a more realistic description. It accounts for an undefined film thickness, turbulence effects, and the role of molecular diffusion. When the flow is turbulent, the flow around the bubble is split into four sections the main turbulent stream, the turbulent boundary layer, the viscous sublayer, and the diffusion sublayer. Eddy turbulence accounts for mass transfer in the main turbulent stream and the turbulent boundary layer. The viscous sublayer limits eddy turbulence effects so that the flow is laminar and mass transfer is controlled by both molecular diffusion and eddy turbulence. Microscale eddy turbulence is assumed to be dominant in the viscous sublayer. Mass transfer in the diffusion sublayer is controlled almost completely by molecular diffusion (Azbel, 1981). 

Current research falls into one of two schools of thought Calderbank s slip velocity model and Lamont and Scott s eddy turbulence model (Linek et al., 2004 Linek et al., 2005b). Even though both models are penetration-type models, they make very different assumptions. The slip velocity model assumes different behavior for small and large bubbles. It also assumes a significant difference between average velocities for the two phases. The slip velocity and the surface mobility control mass transfer and, in terms of penetration theory, surface renewal. 

The eddy turbulence model, or simply eddy model, assumes that the small-scale eddies control surface renewal and, subsequently, mass transfer. This model acknowledges a scale dependence. Macroscale movements, those represented by the Reynolds number. Re, are assumed to have a small impact on surface renewal, where the Reynolds number is defined as... 

The power dissipation influence on the liquid-phase mass transfer coefficient (/cl) is highly debated in STRs, especially at higher power densities. The slip velocity model and eddy turbulence model have been used to explain mass transfer, but they come to different conclusions with respect to power. The slip velocity model predicts a decrease in mass transfer with increasing power dissipation while the eddy turbulence model predicts an increase. Linek et al. (2004) postulate that the main reason for the confusion stems from the miscalculation of They investigated different measurement methods and models used by others and concluded that the slip velocity models were underestimating and, hence,... 

There is a dearth of data regarding actual injection profiles for every type of column chromatography. Dependence of the instrument variance on the mobile-phase flow velocity has been studied in liquid chromatography [32]. Probably in part because of the onset of eddy turbulence at various... 

Unlike the diffusion in catalyst pellets, molecular as well as eddy (turbulent) diffusion causes the mass dispersion in fixed-beds. The effective molecular diffusivity may be obtained by simply multiplying the gas molecular diffusivity by the factor s/k, where the tortuosity factor k is often taken as 1.5. The theory on eddy diffusivity is not well established. Therefore, the effective diffusivities are often correlated in the following form ... 

In general, the dispersion of a gas flowing in a packol bed is considered to be a result of two main mechanisms molecular diffusion and eddy (turbulent) diffusion. At low Reynolds number (J g<1) the dispersion is controlled by the molecular difhision. At Reo>10, fte turbulent dif sion is a dominant factor. Since all industrial packings operate at rather great values of Rea, the molecular diffusion is not of importance for the aaial mbdng in the phase. 

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