(Daily Question) Coal-to-Oil and Olefins Forum, April 24, 2018
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3.jpg Participation: Prize of 5 Wealth； Correct answer: Reward of 10 wealth points ； Note: This post is valid for 48 hours. Question: (DMTO) Olefin separation unit: What factors are related to the critical speeds of turbines and compressors? The critical speed of the rotor is influenced by factors such as the bearing span, the weight of the coupling, as well as the structure and stiffness of the shaft, the loads acting on the shaft and their distribution along it, and the type of supports, all of which determine the natural vibration frequencies of the rotor. Note: The answers will be announced automatically in two days!
The rotors of high-speed rotating machinery such as centrifugal compressors, steam turbines, and blowers cannot achieve perfect balance due to factors related to material, manufacturing, and assembly; there is always an eccentricity e between their center of mass and the axis. When rotating at high speeds, the unbalanced mass within the rotor generates periodic disturbing forces and torques due to the eccentricity e. When the frequency of these disturbing forces and torques acting on the rotor is equal to or close to the rotor’s natural vibration frequency, the machine experiences intense vibrations; this phenomenon is known as resonance. The speed at which the machine resonates is referred to as the critical speed.
The rotors of high-speed rotating machinery such as centrifugal compressors, steam turbines, and blowers cannot achieve perfect balance due to factors related to material, manufacturing, and assembly; there is always an eccentricity e between their center of mass and the axis. When rotating at high speeds, the unbalanced mass within the rotor generates periodic disturbing forces and torques due to the eccentricity e. When the frequency of these disturbing forces and torques acting on the rotor is equal to or close to the rotor’s natural vibration frequency, the machine experiences intense vibrations; this phenomenon is known as resonance. The speed at which the machine resonates is referred to as the critical speed.
The critical speed is related to factors such as the elasticity and mass distribution of the rotor
The critical speed of the rotor is related to factors such as the bearing span, the weight of the coupling, the structure and stiffness of the shaft, the loads on the shaft and their distribution along it, and the type of supports.
The critical speed is related to factors such as the shaft’s structure and thickness, the mass and position of the impeller, and the way the shaft is supported
The critical speed of the rotor is influenced by factors such as the bearing span, the weight of the coupling, as well as the structure and stiffness of the shaft, the loads acting on the shaft and their distribution along it, and the type of supports, all of which determine the natural vibration frequencies of the rotor.
What factors are related to the critical speed of turbines and compressors? Answer: The value of the critical speed depends on factors such as the structure and thickness of the shaft, the mass and position of the impeller, and the way in which the shaft is supported.
It is related to the rotor’s material, geometry, size, structural form, support conditions, and operating environment.
The critical speed is the speed at which the rotor experiences severe vibration; it is a type of problem that has been well studied in rotor dynamics. In a rotating system, the centers of mass of various segments of the rotor cannot lie exactly on the axis of rotation. Therefore, as the rotor rotates, lateral disturbances occur, and at certain speeds these disturbances can cause severe vibrations in the system. The speed at which this happens is known as the critical speed. To ensure the proper operation of the system or to prevent it from being damaged due to vibration, the operating speed of the rotor in the rotating system should, as much as possible, be kept away from the critical speed; if this cannot be achieved, special vibration prevention measures must be taken. The critical speed is the same as the natural frequency of lateral vibration when the rotor is not rotating; in other words, the critical speed is related to factors such as the rotor’s elasticity and mass distribution. For a discrete rotating system with a finite number of concentrated masses, the number of critical speeds equals the number of concentrated masses ； For an elastically rotating system with a continuous mass distribution, there are infinitely many critical speeds.
The critical speed of the rotor is related to factors such as the bearing span, the weight of the coupling, the structure and stiffness of the shaft, the loads on the shaft and their distribution along it, and the type of supports.