Agitation flow number

Flow number, agitation, 290 limiting values, 293 Flowsheets... 

Fig. 13. Spatial distributions of bubble size in three vessels agitated by different impellers a classical Rushton turbine (DT), a hydrofoil impeller (A315) manufactured by Lightnin, and a Pitched Blade Impeller (PBT). The gas flow numbers in these simulations are in the range 0.01-0.02. These simulation results have been obtained by using GHOST Reproduced with permission from Bakker (1992).

Agitation impellers act as caseless pumps. Measured pumping capacities for various impellers have been used to develop correlations of the flow number (Nq = Q/ND ), as a function of Nrj and system geometry. Figure 10.8 presents such a correlation for a 4BP and Figure 10.9 presents a pumping correlation for the HE-3. 

FLOW NUMBER. A turbine or propeller agitator is, in essence, a pump impeller operating without a casing and with undirected inlet and output flows. The governing relations for turbines are similar to those for centrifugal pumps discussed in Chap. 8. Consider the flat-bladed turbine impeller shown in Fig. 9.8. The nomenclature is the same as in Fig. 8.11 2 is Ihe velocity of the blade tips V 2 and F 2 are the actual tangential and radial velocities of the liquid leaving the blade tips, respectively and V 2 is the total liquid velocity at the same point. 

For axial-flow impellers such as pitched-blade turbines or marine propellers, q is the discharge rate in a vertical direction as measured immediately below the impeller. The flow number Nq may be considered constant. For the design of baffled agitated vessels the following values are recommended ... 

Flow number, q(nDl Nq, at gas redispersion point Re Agitator Reynolds number, nDlp/p for non-newtonian fluid,... 

Level of cleanliness required Type and amount of organic contaminant Type, size, composition and amount of particulate contaminant Co-solvent requirements Type of parts to be cleaned (e.g., size, complexity, porosity, loading density, pressure sensitivity) Production capacity Breadth of application Temperature, pressure, separator efficiency, cycle time Temperature, pressure, co-solvents Flow rate, agitation, filtration Type, quantity, emission control and recycle considerations Dimensions, fixturing and flow pattern within cleaning vessel process control strategy Parts per cycle and cycles per work period Number of different processes that must be performed by the system... 

An agitator acts like a centrifugal ptimp impeller without a casing and gives a flow at a certain pressure head. This circulation rate Q in m /s from the edge of the impeller is the flow rate perpendicular to the impeller discharge area. Fluid velocities have been measured in mixers and have been used to calculate the circulation rates. Data for baffled vessels have been correlated using the dimensionless flow number Nq (Ul). 

This chapter reviews the various types of impellers, die flow patterns generated by diese agitators, correlation of die dimensionless parameters (i.e., Reynolds number, Froude number, and Power number), scale-up of mixers, heat transfer coefficients of jacketed agitated vessels, and die time required for heating or cooling diese vessels. 

For example, if a worker turns on a stirrer in a reactor, he or she may use a local or control room indicator to verify that current is flowing to the agitator motor. Errors may arise at several points in the input process. At the sensory stage, there may be so many sources of information that the worker may be unable to scan em all in the time available. This can be a particular problem when a large number of alarms occur following a major process disturbance. 

Power is defined for a well-agitated vessel with a mechanical stirrer then read power number for turbulent flow from Figure 6.6, Chapter 6 ... 

Fig. 1. Relationships between agitation intensity and transfer rates at constant gas flow [after Gal-Or and Walatka (G9)]. At increased gas flow, the holdup fraction is increased mainly by an increase in the number of bubbles produced.

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