Rotating discharge rate

Rotary V lve Feeders. Devices known as rotary valve feeders are commonly used for circular or square configured outlets. These are particularly useful when discharging materials to a pneumatic conveying system where a seal is required to prevent air flow through the hopper outlet. The discharge rate is set by the speed of rotation of the vanes or pockets of the valve. 

The impeller discharge rate can be increased at the same power consumption by increasing impeller diameter and decreasing rotational speed and peripheral velocity so that N D is a constant (Eq. 18-4)]. Flow goes up, velocity head and peripheral velocity go down, but impeller torque Tq goes up. At the same torque, N D is constant, P and Q <=< Dl. Therefore, increasing impeller diameter at... 

The discharge rate of solid particles is usually controlled by the size of the orifice or the aperture at the base of the hopper, though sometimes screw feeders or rotating table feeders may be incorporated to encourage an even flowrate. 

The screw rotation analysis leads to the model equation for the extruder discharge rate. There are now two screw-rotation-driven velocities, and and a pressure-driven velocity, Pp that affect the rate. and transport the polymer fluid at right angles to one another. In order to calculate the net flow from screw rotation It Is necessary to resolve the two screw-rotation-driven velocities into one velocity, Vpi, that can be used to calculate the screw rotation-driven flow down the screw parallel to the screw axis (or centerline) as discussed in Chapter 1 and as depicted in Fig. 7.14. The resolved velocity will then be integrated over the screw channel area normal to the axis of the screw. 

As indicated by Eig. 7.37 and Table 7.7 and as expected, the increase in melt temperature for a PC resin was always higher for the barrel rotation case as compared to screw rotation. If a very high die pressure was needed and the rate is reduced to 10 % of the rotational rate (T) = 0.9), the difference between discharge temperatures for the rotation cases was predicted at about 18 °C. In other terms, the temperature increase (47°C) for screw rotation was about 72% of the temperature increase (65 °C) for barrel rotation. The discharge temperature difference for the two rotation cases decreases to about 4 °C fora low die pressure case where the rate is 90% of the rotational flow rate (T) = 0.1). For this case, the melt temperature increase (6 °C) for screw rotation was about 60% of the temperature increase (10 °C) for barrel rotation. 

After the screw modification, the 148 kg/h rate was obtained at a screw speed of about 69 rpm with an extrudate temperature of 223 °C. Thus, the specific rate increased from 1.63 kg/(h rpm) before the modification to 2.14 kg/(h-rpm) after the modification, a specific rate increase of about 30%. At a screw speed of 69 rpm, the rotationai flow rate was calculated at 173 kg/h now the extruder was operating at about 86% of the rotational flow rate. The calculated axial pressure gradient required to maintain the flow of the extruder at the reported flow rate showed that pressures in the screw never decreased to zero, indicating that the channels were full as shown in Fig. 11.21. No adverse effects were experienced with the reduced discharge temperature (8 °C lower), no unmelted material was observed in the extrudate, and no gel showers occurred after the modification. A summary of the extrusion performance before and after the modification is shown in Table 11.5. 

Pumps are of two main classes centrifugal and the others. These others mostly have positive displacement action in which the discharge rate is largely independent of the pressure against which they work. Centrifugal pumps have rotating elements that impart... 

The impeller discharge rate can be increased at the same power consumption by increasing impeller diameter and decreasing rotational speed and peripheral velocity so that is a constant (Eq. 

---