Remember seven points of knowledge, select screw compressor in minutes
For how to choose screw air compressor, is a headache for users, choose the equipment skills.
(1) screw type should be chosen appropriately: under a certain speed of common air compressor after the impeller pressure coefficient smaller to only t, while the impeller diameter is larger, and its efficiency is higher; and the forward impeller is on the contrary.
(2) the choice of air compressor transmission mode is divided into a variety of: such as transmission mode is A, D, F three, the air compressor speed and motor speed is the same; and B, C, E three are variable speed, design can flexibly choose air compressor speed. In general, A is widely used in small air compressors, which is directly connected with motors. For large air compressors, and sometimes the belt drive is uncomfortable, most of them are driven by D and F transmission. The protection and cooling of motors and bearings should be taken into consideration in the case of high temperature and dusty conditions.
(3) the size of spiral case: the spiral case should be as small as possible. For the high specific speed air compressor, the shortened volute shape can be adopted, and the standard worm shape is generally selected for the low specific speed air compressor. In order to reduce the volute size, the outlet speed of volute is larger than the inlet speed of air compressor, and the outlet diffuser is used to increase the static pressure.
(4) the selection of screw outlet angle: screw outlet angle is one of the main geometric parameters which should be selected in the design. In order to facilitate the application, we classify the screw as follows: strong back bending screw (water pump), back curved circular screw, back bending screw, rear bent wing screw, radial outlet screw, radial straight screw, front bending screw, strong front bending screw (multi blade). Table 1 shows the approximate range of the screw outlet angle of the screw type in the screw air compressor.
(5) the selection of screw number: in the screw air compressor, increasing the number of screw impeller can improve the theoretical pressure of the impeller, because it can reduce the influence of relative vortex (that is to increase the value of K). However, the increase of the number of screws will increase the friction loss of the impeller passage, which will reduce the actual pressure of the air compressor and increase the energy consumption. Therefore, for each impeller, there is an optimum number of screws. How many screws should be determined, depending on the designer's experience. According to the present situation of application in China, the selection range of screw number is recommended in table 2.
(6) the total pressure coefficient is selected T: Design of screw compressor, the actual pressure is always given in advance. Then need to select the total pressure coefficient is t, the total pressure coefficient of roughly range refer to table 3.
(7) the main geometric dimensions of the inlet and outlet of the centrifugal impeller are determined: the impeller is the only element that the air compressor transfers to the energy of the gas, so its design has a great influence on the air compressor; whether the main structure of the impeller can be correctly determined plays a key role in the performance parameters of the air compressor. It contains the key technology of screw air compressor design -- screw design. The key link of screw design is how to determine the screw outlet angle beta 2A.
It's important to note that..:
Screw compressor impeller design must also take into account the specific speed and screw type there is a certain relationship, so in determining the screw outlet angle at the same time, we must consider the impact of three kinds of screw type on the pressure, radial size and efficiency. It has laid a solid foundation for the determination of other main geometric dimensions of the screw air compressor, thus playing a key role in the performance of the screw compressor.
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