Filled length

Identihcation of the microorganisms from any positive units and investigation of any contamination events observed during media fills Length of time media were stored in holding tank prior to hltration Length of time taken to hll all containers... 

With the preceding assumption, the instantaneous flow rate Q(t), at given constant inlet pressure, Pq, and instantaneous fill length, Z(t) at time, t, is given by (see Example 3.4 or Table 12.2) ... 

Table 13.2. Influence of extrusion parameters on the filled length.

The large variations in viscosity during reactive extrusion can lead to process instabilities as a result of competition between die effects and pressure build-up abilities of the screws. In general, two stable working points can be distinguished - one at low conversion with a short, fully filled length, and one at high conversion with a... 

An increase in die resistance demands for a larger pressure build-up in the extruder, which leads to a longer fully filled length. 

An increase of the screw rotation rate at constant throughput increases the back-flow and therefore decreases the filled length. 

An increase of throughput increases the die pressure and decreases the back-flow, both leading to an increase of the filled length. 

An increase in viscosity both increases the die pressure and the pressure buildup abilities of the extruder. In the simplified case of an iso-viscous process, the filled length remains constant. In reactive extrusion, where the material is generally far from iso-viscous, the filled length may increase or decrease, depending on the viscosity changes along the screw. 

Hydrodynamic considerations lead to the contention that there are two stable operating points in reactive extrusion - one with a large, fully filled length and a high conversion, and one with a small, fully filled length and a low conversion. Severe... 

The influence of different capillary diameters and filling length were studied as were different kinds of optical observation methods. We found a pronounced decrease of the LCST cloud point temperature of this blend of PMMA/SAN with increasing pressure (3). 

The other cases, which describe situations where the capillary is not completely filled and/or where the meniscus on one side is not present, follow from (9.22) by adjusting the relevant capillary pressure term and using the filled length z instead of the real length L. Note that case 6 of Fig. 9.9 obeys Eq. (9.2). 

When inside a slot or a tube there is a filled length behind a bulk meniscus that connects to a thin-film in a partly-filled length, the slot half-width or tube radius, R sets the thin-film... 

If, for instance, for the simplified case that the extruder is filled with an isoviscous liquid, the resistance of the die is doubled, the pressure in front of the die will also double because the output remains constant. However, the leakage flow is not influenced by the die pressure, so that the pressure gradient in the extruder remains constant. Ergo, the completely filled length increases as indicated in Fig. 2.11. 

Table 2.1 Influence of Extrusion Parameters on the Filled Length...

As a consequence the fully filled length before the die in axial direction is... 

Z is the filled length in the channel direetion. The axial filled length Lf can easily be obtained from... 

When an extruder is working under steady-state conditions several factors can influence the process. The primary parameters that in principle can be controlled externally are the screw speed, the throughput, the barrel temperature, and the die resistance. All other parameters are influenced by the changes in the primary variables, e.g., filled length, heat transfer, and pressure gradient, or are predetermined, e.g., screw geometry or material properties. 

Additionally, expressions for the fully filled length, the kinetics and the heat transfer are needed to complete the model. The fully filled length is determined by the leakage flows, the viscosity profile of the reacting material and the die pressure the expressions for leakage flows and pressure buildup are derived in Chapter 2. The viscosity expressions can be found in Chapter 4, using the kinetics of an addition polymerization with gel effect, as given in Chapter 3. For the heat transfer coefficient one of the expressions from Chapter 6 can be used. 

Figure 7.6 Influence of fully filled length on the conversion and molecular weight for the extruder polymerization of w-BMA (+ experiments, — model).

All simulations above were performed with an open die, i.e., a die pressure equal to zero. The die pressure has a major influence on the reaction process because it influences the fully filled length and therefore the residence time. Figure 7.11 shows this influence. Two simulations are given, the zero... 

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