Efficiency during Pressure Generation

Efficiency during pressure generation is just as important as the back-pressure length for the design of a pressure build-up zone. By efficiency we mean the relationship between the pressure energy that is stored in the flow at the end of the pressure build-up zone and the energy that is introduced into the pressure build-up zone. 

The efficiency during pressure generation can be calculated from Eqs. 7.2 and 7.5 with a few transformations. 

A numerical example is used in the following to illustrate this  

The size of the machine and the throughput (and often the revolution speed as well) are determined by other factors, so the pressure build-up zone should be optimized by selecting the pitch and gap [2]. 

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The optimum efficiency during pressure generation is generally achieved at A 0.5. In this case, three times the length in relation to the left-hand element is required to generate the pressure. The back-pressure rises fast as the throughput per revolution increases. At A = 0.8, the back-pressure is already 9 times as long as the left-hand element. 

Figure 7.9 Efficiency of a triple-flighted screw during pressure generation in relation to the kinematic parameter of flow A...

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