Surge is the periodic oscillation of the medium in fluid machinery and its pipelines; it is the mechanical vibration of the medium excited by the periodic intake and exhaust.
Surge is a periodic oscillation of the medium in fluid machinery and its pipelines, resulting from the mechanical vibration of the medium excited by the periodic intake and exhaust. In centrifugal air compressors, surge is one of the common faults during compressor operation and a further development of rotating stall. When the load on a centrifugal compressor decreases to a certain level, the compressed gas will form a separation mass on the non-working surface of the impeller, leading to a sharp increase in impact loss. This not only increases flow loss and reduces efficiency but also causes air to flow back from the pipeline network to the compressor, causing strong vibrations in the compressor body and resulting in a "surge" or "roaring" sound. This phenomenon is called "surge" in centrifugal compressors. The frequency and amplitude of the mechanical vibration caused by surge are closely related to the volume of the pipeline network. The larger the volume of the pipeline network, the lower the surge frequency and the larger the amplitude.
When a centrifugal compressor experiences surge, typical phenomena include:
1. The compressor's outlet pressure initially rises, then drops sharply, exhibiting periodic and significant fluctuations;
2. The compressor's flow rate drops sharply and fluctuates significantly; in severe cases, air may even flow back into the intake pipe.
3. The current and power meter readings of the motor driving the compressor are unstable and fluctuate significantly;
4. The machine generates strong vibrations and emits abnormal airflow noise.
Currently, there are three common methods for addressing surge:
1. Add a vent valve to the compressor to allow excess gas to escape.
2. Use a dual-rotor or triple-rotor compressor.
3. Use adjustable blades.
As I theoretically stated, the surge range can be found on the operating condition curve.
Main causes :
1. The evaporation pressure is too low, or the evaporation temperature is too low.
This could be caused by a low return water temperature, which leads to a rapid decrease in the guide vane opening, causing the compressor's outlet pressure and condensing pressure to become close, or by a blockage in the throttling device, resulting in insufficient liquid refrigerant in the evaporator to support the compressor's continuous output of high-pressure gaseous refrigerant to the condenser.
2. The condensing pressure is too high, or the condensing temperature is too high.
The cause of excessively high condensing temperatures may be that the cooling system is unable to properly remove heat from the high-pressure gaseous refrigerant in the condenser. Several factors can contribute to this, such as insufficient cooling water volume, blockages in the cooling water pipes, blockages or scale buildup on the inner and outer walls of the condenser's heat exchange copper tubes, and insufficient fan output to expel the heat from the cooling water into the atmosphere.
3. Compressor malfunction or problem with the mechanical transmission mechanism.
A compressor mainly consists of two parts: the motor and the mechanical compression mechanism. The motor is self-explanatory; a slow motor speed or three-phase imbalance can cause problems. The mechanical compression mechanism is prone to issues such as high-speed gear wear and malfunctions in the guide vane and connecting rod transmission mechanism, leading to jamming.
4. The throttling device cannot open normally, or the load is too low, causing the throttling valve to open too small.
The best explanation is that the high-pressure liquid refrigerant in the condenser cannot return to the evaporator in time through the throttling device, causing a large amount of refrigerant to accumulate in the condenser, which forces the condensing pressure to rise and eventually causes surge.
