Three important structural parameters of screw air compressor
The three important structural parameters of the screw air compressor are: addendum speed and speed, rotor diameter and length-to-diameter ratio, and internal volume ratio, which will be explained in detail below.
Parameter 1: Addendum speed and rotational speed The rotor addendum peripheral speed is an important factor affecting the size, component, power and transmission method of the screw air compressor. It is customary to use the value of the peripheral speed of the addendum of the male rotor to characterize it. Obviously, increasing the addendum speed will improve the weight and shape of the air compressor. In addition, after increasing the speed of the addendum, the relative leakage of gas passing through the gaps of the air compressor will be reduced, and at the same time, the volumetric power and adiabatic power of the air compressor will be improved. At the same time, it causes the loss of gas activity in the suction and exhaust ports and the volume between the teeth, the loss of rotor friction and blowing, and the corresponding increase in the oil hitting loss of the fuel injection machine, resulting in a reduction in adiabatic power. Theoretically speaking, only at a certain optimum addendum speed, the total loss is very small, and the power of the time-space compressor reaches the highest value. In fact, the specific value of the optimal addendum speed is affected by many factors, which are related to the rotor profile, operation method, pressure difference, pressure ratio, displacement, gas properties, clearance and other factors. In addition, the machine structure, the roughness of the gas active surface, etc. also have an impact on the optimal addendum speed value. Therefore, it is often within a certain scale.
Parameter two: rotor diameter and aspect ratio Rotor diameter is an important parameter related to the serialization of screw air compressors and the standardization and generalization of parts. The principle of determining the serialization of the rotor diameter is: within the range of the optimum addendum speed, use as few rotor diameter specifications as possible to satisfy the widest possible displacement range. The aspect ratio refers to the ratio of the length of the working section of the rotor to the diameter of the male rotor. Since the displacement of the screw air compressor is proportional to the square of the rotor diameter, the displacement values of adjacent series of rotor diameters are quite different, especially when the rotor diameter is large. For this reason, under each rotor diameter, multiple length-to-diameter ratios are usually selected to change the range of exhaust volume, so that the exhaust volume of adjacent series of rotor diameters is staggered.
Parameter 3: Internal volume ratio In the design of screw air compressors, although it is more convenient to use the internal pressure ratio to indicate the operating conditions of the air compressor, the internal pressure ratio is generally not regarded as the basic design parameter of the air compressor. When describing screw refrigeration air compressors and screw process air compressors, the internal volume ratio is generally used instead of the internal pressure ratio. This is because the internal volume ratio is a fixed structural parameter of the air compressor, which depends on the inherent orientation of the suction and exhaust ports of the air compressor itself, and the internal pressure ratio is also related to the properties of the compressed gas. As long as the compressed medium is always the same gas, such as in a screw air compressor, the internal pressure ratio can be used as the planning parameter of the air compressor.
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