Screw pumps performance

McKelvey, J. M., U. Naire, and F. Haupt, Flow Gear Pumps and Screw Pumps Perform in Polymer-Processing Applications, Chem. Eng., V. 83, No. 20, 1976. 

M. L. Booy, Influence of Oblique Channel Ends on Screw Pump Performance, Polym. Eng. Sci., 7, 5-16 (1967). 

An oil with a 32.6° API gravity at 60°F is to be transferred from a storage tank to a process unit that is 10 ft above the tank, at a rate of 200 gpm. The piping system contains 200 ft of 3 in. sch 40 pipe, 25 90° screwed elbows, six stub-in tees used as elbows, two lift check valves, and four standard globe valves. From the pump performance curves in Appendix H, select the best pump to do this job. Specify the pump size, motor speed, impeller diameter, operating head and efficiency and the horsepower of the motor required to drive the pump. 

Screw pumps [Fig. 7.12(g)] are suited for example to high viscosity polymers and dirty liquids at capacities up to 2000 gpm and pressures of 200 atm at speeds up to 3000 rpm. They are compact, quiet, and efficient. Figure 7.4(d) shows typical performance data. 

Figure 7.19. Some rotary positive displacement compressors, (a) A two-lobe blower, (b) Performance of a two-lobe blower (Rools-Connersville Co.), (c) A screw pump with one power and two idle rotors (Kristal and Annett, 1940). (d) Performance of 3.5" screw pump handling oils at 1150 rpm against 325 psig (Kristal and Annett, 1940). (e) Principle of the liquid ring seal compressor (Nash Engineering Co.). (0 A sliding vane blower (Beaeh-Russ Co.).

In this section we derive a simple mathematical model for the single screw pump. In such a model, we seek relationships between performance and operating variables with the geometrical variables as parameters. 

We have seen how the screw extruder pump is synthesized from a simple building block of two parallel plates in relative motion. We have also seen how the analysis of the screw extruder leads in first approximation back to the shallow channel parallel plate model. We carried out the analysis for isothermal flow of a Newtonian fluid, reaching a model (Eq. 6.3-27) that is satisfactory for gaining a deeper insight into the pressurization and flow mechanisms in the screw extruder, and also for first-order approximations of the pumping performance of screw extruders. 

Screw conveyors, 76,79,80 sizing calculation, 80 sizing data, 79 types of screws, 80 Screw pumps, 134, 141 performance, 148 Segmentation behavior, 305-307 equipment, 319 equipment sketches, 320,338 Segregated flow, 560 volume ratio to CSTR, 561 volume ratio to maximum mixedness, 560... 

This particular fermentation is performed in 1+00 liter batches. Tangential flow filtration was carried out with a Pe licon cassette (Millipore Corp.). The filtration area was 25 ft using a 100,000 molecular weight cut off ultrafiltration membrane. The inlet pressure was maintained at 1+0 psig while the outlet pressure was 25 psig and recirculation rates of the cell suspension were 3 5 GPM tangential to the upstream membrane surface. Pumping of the cell suspension was performed with a Moyno screw pump. 

Non-Newtonian characteristics, notably shear-dependent viscosity and yield stress, strongly influence the choice of a suitable pump and its performance. While no deflnite quantitative information is available on this subject, general features of a range of pumps commonly used in industry are briefly described here. In particular, consideration is given to positive-displacement, centrifugal, and screw pumps. 

Melt pumps are most appropriate when the screw and die characteristics combine to give a relatively poor pumping performance by the total system. This can happen when die pressures are low but more often occurs when they are extremely high (5,000-8,000 psi), or when the melt viscosity is extremely low. When pumps are used to increase the production rate by reducing the extruder head pressure without a corresponding increase in the screw speed, the extrudate solids content often is increased. The result is an inferior product. This problem often necessitates additional filtration, which serves only to increase pressure and may counteract many of the benfits expected from the pump, as well as increasing the financial investment even further. 

Plasticator A very important component in a melting process is the plasticator with its usual specialty designed screw and barrel used that is used in different machines (extruders, injection molding, blow molding, etc.). If the proper screw design is not used products may not meet or maximize their performance and meet their cost requirements. The hard steel shaft screws have helical flights, which rotates within a barrel to mechanically process and advance (pump) the plastic. There are general purposes and dedicated screws used. The type of screw used is dependent on the plastic material to be processed. 

The new commercial process was based on the lab process and has the target performance shown in Table 9.2. To achieve this performance, an 80 mm diameter extruder with an L/D ratio of 28 was specified. The extruder was built with a 100 kW motor and a gear box such that the maximum speed of the screw was 117 rpm. A gear pump was positioned downstream of the extruder such that the extruder only needed to generate 6 MPa of pressure at all rates. 

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