Surge in Explosion-Proof Centrifugal Fans

Surge in Explosion-Proof Centrifugal Fans

Should an explosion-proof centrifugal fan operate in an unstable state, significant fluctuations in flow rate, total pressure, and current may occur. As air flows back and forth, the fan and ductwork undergo intense vibration, resulting in substantially increased noise levels. This unstable operational state is termed surge. Following a surge event, damage may occur to the fan and associated pipework, compromising the safety of both the fan and the entire system. Formation of Surge: The qv-p performance curve of an explosion-proof centrifugal fan. By reducing the fan flow via throttling, the operating point shifts from point A to point D. When the operating point reaches D, the pressure within the fan's discharge duct cannot decrease to the pressure at point D. Instead, the pressure at point D remains higher than that at point D, remaining nearly identical to the original pressure at point A. Furthermore, as gas within the discharge duct flows back towards the fan, it inhibits operation. Consequently, the operating point naturally shifts to point B, where the fan delivers zero flow. As air within the fan outlet duct flows back towards the fan, the dynamic pressure within the duct rapidly decreases to supply air externally. Once the pressure within the outlet duct falls below the pressure at point B, the fan resumes air supply, shifting the operating point to point E. The explosion-proof centrifugal fan within the piping system must operate via point D; therefore, the fan's operating point must be returned to point D. Consequently, the aforementioned process repeats cyclically: EADBE. When the frequency of this cycle matches the oscillation frequency of the explosion-proof centrifugal fan's ventilation system, resonance and surging occur within the fan. When the operating point of the explosion-proof centrifugal fan occasionally resides at point A, full-length rotational flow occurs. Slight turbulence in the low-flow direction causes the fan's total pressure to plummet to point D. Subsequently, air within the fan's outlet duct reverses direction instantaneously, returning the operating point to point A. Subsequent process A. When the frequency of this reciprocating pulsation aligns with the system's oscillation frequency, surges occur. Such surges near the breakpoint of the performance curve are typically termed boundary period surges. Periodic surges at the boundary generate substantial, intense vibrations. When partial expanded rotational discharges cause surges, the vibration amplitude and intensity are significantly milder than the former. In summary, the following conditions are required for wind turbines to generate surges: The performance curve of explosion-proof centrifugal fans qyA exhibits an upward-rightward inclination. When operating under unstable conditions, the ductwork system possesses sufficient capacity to form a flexible air pressure system with the fan. Resonance occurs when the frequency of the explosion-proof centrifugal fan's full operating cycle synchronises with the system's air vibration frequency. Both separation and surging manifest within the unstable region to the left of the peak on the 4v-p performance curve. Thus, vortex shedding is closely related to surging. However, separation and surging exhibit fundamental differences. Separation occurs within the unstable region to the left of the peak on the 9v-p performance curve. Surging occurs exclusively in the upper-right portion of the 4v-p performance curve. Vortex generation depends solely on the structural characteristics of the impeller itself and the airflow, being independent of the volume and shape of the ductwork system. When a explosion-proof centrifugal fan experiences rotational flow, it is generally difficult for operators to detect, thus having negligible impact on the fan's normal operation. The entire explosion-proof centrifugal fan can continue functioning under conditions of rotational flow, flow supply, specific pressure generation, and specific power consumption. However, the situation differs entirely when the fan experiences a rapid surge during operation. Following a surge, the fan's flow rate, total pressure, and output may exhibit pulsations or significant fluctuations. Concurrently, pronounced noise occurs, occasionally accompanied by high-decibel levels. Vibrations during surges can become severe, potentially damaging both the fan and the ductwork system. Consequently, under rapid acceleration conditions, the explosion-proof centrifugal fan cannot sustain operation. Naturally, the fan need not accelerate rapidly within the upper portion of the 4v-p performance curve, but it must nonetheless satisfy the aforementioned conditions.