Orifice blending

Flow Nozzles. A flow nozzle is a constriction having an eUiptical or nearly eUiptical inlet section that blends into a cylindrical throat section as shown in Figure 8. Nozzle pressure differential is normally measured between taps located 1 pipe diameter upstream and 0.5 pipe diameters downstream of the nozzle inlet face. A nozzle has the approximate discharge coefficient of an equivalent venturi and the pressure drop of an equivalent orifice plate although venturi nozzles, which add a diffuser cone to proprietary nozzle shapes, are available to provide better pressure recovery. 

Figure 10.14. Some kinds of in-line mixers and blenders, (a) Mixing and blending with a recirculating pump, (b) Injector mixer with a helical baffle, (c) Several perforated plates (orifices) supported on a rod. (d) Several perforated plates flanged in. (e) Hellical mixing elements with alternating directions (Kenics Corp.). (f) Showing progressive striations of the flow channels with Kenics mixing elements.

In orifice blending, the viscosity increases as the solution passes through the orifice as shown on Figure 2. The viscosity loss upon filtration is small in this case, indicating that this high shear field device is required for the dispersion of xanthan gum. 

The heart of this drying system is a rotary-valved pulse combustor. Referring to Fig. 7.81, combustion air (1) is pumped at low pressure into the pulse combustor s outer shell and flows through an unidirectional air valve (2) into a tuned combustion chamber [ Helmholtz Resonator (3)] where fuel (4) is added. The air valve closes. The fuel-air mixture is ignited by a pilot (5) and explodes, creating hot air which is pressurized to approx. 0.2 bar above combustion air fan pressure. The hot gas exits the chamber through a pipe (6) towards the atomizer area (7). Just above the atomizer, quench air (8) is blended in to achieve the desired process temperature. The orifice releases the liquid... 

For Hifax PP/EPDM blends, a general purpose screw is recommended. The clamping pressure increases with part size. The nozzle should be as short as possible with orifice larger than usual. All tools should be vented trapped air may cause localized burning, surface sinks and voids. Keeping the moving half of the mold cooler than the stationary part aids demolding. 

The melt index test measures the rate of extrusion of a thermoplastic material through an orifice of specific length and diameter under prescribed conditions of temperature and pressure. This test is primarily used as a means of measuring the uniformity of the flow rate of the material. In this study, the melt flow index (MFI) value increased from 1.35 to 1.69 g/10 min with increase in EMA content from 0 to 10% in the PMMA/EMA blends (Table 5.3). This may be due to the reduction in cohesive strength as well as the plasticizing effect of EMA in PMMA/EMA blends. However, further addition of EMA content above 10% by weight shows no more increase in MFI. 

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