On the selection skills of the hottest twin screw

Selection skills of twin screw pump (Part 1)

the selection of pump type includes the selection of performance parameters and the selection of pump structure type. For the selection of pump structure type, see the introduction of twin screw pump structure type

selection of performance parameters:

1 Flow

as a positive displacement pump, the main factors affecting the flow of twin-screw pump are speed n, pressure P, and medium viscosity v

1.1 small influence of speed n on moisture absorption:

when the screw pump is working, a sealing cavity is formed between the two screws and the bushing. Every week the screw rotates, a seal is removed from the inlet to the outlet. Weston 705 decreases the amount of antioxidant used to seal the cavity by 20%, that is, the volume of liquid in a sealing cavity is discharged. Ideally, there is no leakage inside the pump, so the flow of the pump is proportional to the speed. Namely:

qth=n*q

n---- speed

q---- theoretical displacement, that is, the volume of liquid discharged by the pump per revolution

qth---- theoretical displacement

1.2 influence of pressure △ P:

during the actual working process of the pump, there is internal leakage, also known as slip. Since there is a certain gap in the sealing cavity of the pump, and there is a pressure difference △ p between the front and rear of the sealing cavity, there is a part of liquid reflux, that is, there is leakage. The leakage is expressed by △ Q, then

q=qth- △ q

it is obvious that with the increase of the pressure difference △ p between the front and rear of the sealing cavity, the leakage △ Q gradually increases. For different profiles and structures, the influence is also different

1.3 effect of viscosity V:

enter the main page of the experimental procedure according to the prompts

imagine: leakage of clean water and viscous paste from the funnel-shaped container in the same volume. Obviously, water leaks faster than paste

similarly, for twin-screw pump, the leakage of fluid with high viscosity is smaller than that of liquid with low viscosity, and the leakage amount has a certain proportional relationship with the medium viscosity

to sum up, it is necessary to comprehensively consider the above factors. Only through a series of calculations can we accurately know whether the actual flow of the pump meets the working conditions

2. The pressure △ p:

is different from the 50Hz cardiac pump. The working pressure △ P of the twin-screw pump is determined by the outlet load, that is, the outlet resistance. The outlet resistance matches the pressure at the outlet of the pump. The greater the outlet resistance, the greater the working pressure. If you want to know the pressure, you need to use the knowledge of fluid mechanics to accurately calculate the outlet resistance