Plug flow conveying

The air velocity w is between 3 and 10 m s , whereas the ratio of product velocity V to air velocity w is smaller than 0.5. The product mass flow can be a hundred times larger than the air mass flow. 

The required power for the vacuum generator can roughly (incompressible) calculated with Eq. (17.5). 

The energy requirements for dense phase conveying are comparable with dilute phase because although the required air flow rate is much lower a larger pressure difference is required. The ratio is proportional. 

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For reasons of completeness, results for the determination of the process function for plug flow conveying shall be stated briefly as well. Since in this case a two phase flow with high particle concentrations is regarded the options to... 

As seen in Section 17.2.1. the total pressure difference during powder conveying depends on the amount of material in the conveying hne. Basically at vacuum conveying three different types of conditions can be described (Figure 17.5) dilute phase, dense phase and plug flow conveying [4]. 

Chapters 13 and 14 deal primarily with small deviations from plug flow. There are two models for this the dispersion model and the tanks-in-series model. Use the one that is comfortable for you. They are roughly equivalent. These models apply to turbulent flow in pipes, laminar flow in very long tubes, flow in packed beds, shaft kilns, long channels, screw conveyers, etc. 

A. Levy, Two-fluid approach for plug flow simulations in horizontal pneumatic conveying, Powder Technol. 112 (2000) 263-272. 

Incremental models track the local conditions of the gas and particles through the dryer, mainly in one dimension. They are especially suit le for cocurrent and countercurrent dryers, e.g., flash (pneumatic conveying) and rotary dryers. The air conditions are usually treated as uniform across the cross-section and dependent only on axial position. This method can also be used to determine local conditions (e.g., temperature) where a simpler model has been used to find the overall drying rate. A two- or three-dimensional grid can also be used, e.g., modeling vertical and horizontal variations in a band dryer or plug-flow fluidized bed. 

The model is effective and appropriate for dryers where both solids and gas are approximately in axial plug flow, such as pneumatic conveying and cascading rotary dryers. However, it runs into difficulties where there is recirculation or radial flow. 

For pneumatic conveying all the particles are evenly dispersed in the gas. This makes contacting ideal or close to ideal. The plug flow model is thus well suited for the dilute transport reactors, but has also been used for the denser fast fluidization regime neglecting gradients in the solids distribution. For first order reactions the model can be written as ... 

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