【Q&A Question 030】May 20, 2016
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【Q&A Question 030】May 20, 2016: What is the critical speed of a centrifugal pump? The answer key will be available after responding; scoring is based on answering the key points. When the centrifuge reaches a certain speed, resonance occurs in its structure; this speed is known as the critical speed
When the frequency of variation of the periodically changing centrifugal force equals the natural frequency of the rotor, the compressor experiences severe vibration, known as \"resonance\". Therefore, the critical speed of a rotating machine can also be considered as the speed at which rotor resonance occurs during its operation
The speed at which the engine unit experiences severe vibration
The amplitude of the rotor in a circulating hydrogen compressor increases as the speed increases; it reaches its maximum value at a certain speed. Beyond this speed, the amplitude gradually decreases as the speed keeps rising, and remains stable within a certain range. The speed at which the rotor amplitude is at its maximum is known as the rotor’s critical speed.
The amplitude of the rotor increases as the rotational speed rises; it reaches its maximum value at a certain speed. Beyond this speed, the amplitude gradually decreases as the speed continues to increase, settling within a certain range. The speed at which the rotor amplitude is at its maximum is known as the rotor’s critical speed. This rotational speed is equal to the natural frequency of the rotor. As the speed increases further and approaches 2 times the natural frequency, the amplitude increases again. When the speed equals 2 times the natural frequency, it is referred to as the second-order critical speed; similarly, there are third-order and fourth-order critical speeds
The amplitude of the rotor increases as the rotational speed rises; it reaches its maximum value at a certain speed. Beyond this speed, the amplitude gradually decreases as the speed continues to increase, settling within a certain range. The speed at which the rotor amplitude is at its maximum is known as the rotor’s critical speed.
Within the critical speed range, the vibration levels of the unit increase, and it is necessary to pass through this area quickly.
The components of various parts of the turbine rotor are highly precise, and they are balanced during assembly. However, it is still not possible for the center of gravity of the turbine rotor to exactly coincide with the center of the shaft. Due to this discrepancy between the center of the shaft and the center of gravity of the rotor, centrifugal force is generated as the shaft rotates, and this is the main cause of turbine vibration and shaft bending. As the rotor rotates, its center of gravity moves along the axis line, and the direction of the centrifugal force also changes as it rotates. One vibration occurs each time the axis completes one full rotation, and the number of such forced vibrations per second is known as the frequency of the forced vibration. The rotor of a turbine is an elastic body with a certain natural frequency. Resonance occurs when the frequency of the forced vibrations of the rotor coincides with its natural vibration frequency – that is, when the frequency causing the forced vibrations is the same as or proportional to the rotor’s natural frequency. In such cases, the rotor’s vibrations become extremely intense; this rotational speed is known as the critical speed