Static mixers pressure drop

AP, = static mixer pressure drop in turbulent flow, psi... 

P0 = Np = Power number, dimensionless, Equation 5-19 Ppew = Plate coil width, one plate, ft Ap = Pressure drop, psi AP0 = Pressure drop for open pipe, psi AP, = Static mixer pressure drop in turbulent flow, psi Q = Flow rate or pumping capacity from impeller, cu l t/sec, or Ls/1... 

Design guidehnes for static mixers for this application are not available in the literature and therefore need to be developed through experimentation. Fundamental concepts of gas-liquid contacting in static mixers, discussed in Chapter 7, can be used to select an appropriate mixer type. Since no hterature data are available for the specific fluids at process conditions, it is advised to conduct pilot plant tests at scale at actual pressures to quantify the effect of mixer pressure drop on mass transfer rate and to develop scale-up criteria. 

Pressure drop in static mixers depends very strongly on geometric arrangement of the inserts. It is simply defined in relation to the pressure drop AP in an empty tube given by Darcy s equation ... 

Static mixers are typically less effective in turbulent flow than an open tube when the comparison is made on the basis of constant pressure drop or capital cost. Whether laminar or turbulent, design correlations are generally lacking or else are vendor-proprietary and are rarely been subject to peer review. 

Reactors with a packed bed of catalyst are identical to those for gas-liquid reactions filled with inert packing. Trickle-bed reactors are probably the most commonly used reactors with a fixed bed of catalyst. A draft-tube reactor (loop reactor) can contain a catalytic packing (see Fig. 5.4-9) inside the central tube. Stmctured catalysts similar to structural packings in distillation and absorption columns or in static mixers, which are characterized by a low pressure drop, can also be inserted into the draft tube. Recently, a monolithic reactor (Fig. 5.4-11) has been developed, which is an alternative to the trickle-bed reactor. The monolith catalyst has the shape of a block with straight narrow channels on the walls of which catalytic species are deposited. The already extremely low pressure drop by friction is compensated by gravity forces. Consequently, the pressure in the gas phase is constant over the whole height of the reactor. If needed, the gas can be recirculated internally without the necessity of using an external pump. 

Likewise, the Increased pressure drop associated with some thin-channel systems, turbulence promoters, and static mixers must be weighed against the increased flux obtained. 

The fact that dissolved ozone is produced brings a very important advantage to subsequent ozone applications mass transfer from the gas to liquid phase is not required. Efficient mixing (e. g. with static mixers) of the ozone-rich pure water stream with the (waste-)water stream to be treated, though, is required. During this in-situ ozone production, the liquid ozone concentration (cL) can easily reach the solubility level (cr ), depending on the pressure (P) and temperature (T) in the cell. Oversaturation of the feed-water will immediately occur, when the pressure drops. Due to this potential degassing, vent ozone gas destruction is also required for this system. 

By computing the pressure drop in the static mixer and the pressure drop in the granulating head and adding this to the exergy requirements of the compressor, it is possible to compute the exergy input of the alternative scheme, and compare this with the regular extruder (Figure 11.7). 

From an efficiency point of view, the new setup is advantageous. As the pressure drop across the static mixer is approximately 25 MPa (for diameter 0.5 m ... 

Pressure drop across static mixer for different diameters. 

Attempts to use these kinds of devices on low-viscosity materials showed that the flows did not twist and curl in quite that same fashion. In the low-viscosity region, pressure drop is a key factor. The second type of static mixer gets pressure drop through controlled channels, different types of static elements, as well as random placement of baffles, blades, orifices, or other devices inside the pipeline. 

For instance, with the Hi-Mixer (161), 6Q/6 = 4n. A factor of 5 is easy to obtain for m with respect to an empty tube, at the expense of a corresponding increase in pressure-drop. A comparison between the existing types of static mixers (162) shows that most of them have an equivalent effectiveness. The case of Sulzer-Mixers has been especially studied (163), including use with gases (164). 

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