At present, many enterprises use centrifugal fans as boiler induced draft fans during production. However, due to the influence of various factors, the fan impeller is prone to unstable operation. The appearance of this phenomenon not only affects the performance of the fan, but also increases the number of fans. energy consumption.
1)Reasons for the unstable operation of centrifugal fan impeller
Generally, it can affect the stability of the impeller operation, which is mostly related to the wear of the impeller and the structural defects of various parts of the fan. Here we mainly introduce the unstable operation of the impeller caused by the structural defects of each part. As for the reasons for the wear of the impeller of the centrifugal fan, in the previous article The editor has already made a detailed introduction, so I won’t repeat it here. The reasons for the unstable operation of the impeller caused by the structural defects of various parts of the fan are as follows:
1. Structural defects of current collectors
The working principle of the collector is to improve the efficiency of the impeller and the overall performance of the centrifugal fan by evenly feeding the airflow into the inlet section of the impeller. There are many types of collectors, and the commonly used collector is a conical arc. The airflow of the collector is relatively stable in one shift, but the boundary layer separation phenomenon is prone to occur from the throat of the collector to the inlet of the impeller, which makes the operation of the impeller unstable, increases the loss of the centrifugal fan, and leads to low fan efficiency.
2. Structural defects of the volute
The volute is an important part of the impeller of the centrifugal fan, which can improve the efficiency of the fan by guiding the flow and expanding the pressure. The airflow at the inlet of the volute is affected by the asymmetric flow of the volute, resulting in uneven distribution, which will directly block the outlet of the impeller, thereby causing the impeller to periodically accelerate or decelerate, thereby reducing the working efficiency of the centrifugal fan and reducing the size of the fan. The working range affects the smooth operation of the impeller.
3. Motor structural defects
Some equipment using centrifugal fans has a small internal space. In order to save space, a built-in motor is used. The length and head inclination of this motor affect the performance and noise of the fan to a certain extent. If the shape of the built-in motor is designed Improper, such as the narrowing of the flow channel at the inlet of the impeller, will make the de-flow area at the front disc larger, resulting in flow loss inside the impeller, resulting in increased noise and reduced fan performance.
4. Blade shape defect
The shape defect of the blade is also one of the reasons for the unstable operation of the centrifugal fan impeller. The flow of air flow in different areas of the blade is very different. In the middle and rear discs of the impeller, the flow mode of the air flow is mainly radial flow. If the blade shape is unreasonably designed, the flow pattern of the air flow will change, which will cause the impeller to run erratically.
2)the solution to the unstable operation of the centrifugal fan impeller
For the unstable operation of the impeller caused by the structural defects of each component, the solution is naturally to optimize the structure of each component to make it more in line with the operation mode of the impeller to ensure its normal operation. The specific optimization method is as follows:
1. Optimize the structure of the current collector
When designing the structure of the collector, it should be ensured that it conforms to the flow of the airflow near the impeller, and at the same time, the smooth operation of the airflow in the collector should be ensured. For the conical arc current collector, the efficiency of the centrifugal fan can be improved by reducing the taper and increasing the radius of the throat to ensure the smooth operation of the impeller.
2. Optimize the volute structure
In the optimal design of the volute of the centrifugal fan, the influence of the width of the volute on the flow field must be taken into account, and the width of the volute must be reasonably designed to reduce the influence on the flow field, and at the same time, ensure that the inlet air flow is as symmetrical as possible when entering the volute , so as to ensure the smooth operation of the impeller.
3. Optimize the shape of the motor
There is a positive correlation between the axial length of the motor and the displacement rate of the airflow. Therefore, when designing the built-in motor, the influence of the shape of the motor on the flow inside the impeller should be fully considered, the width of the flow channel should be increased as much as possible, and the length of the motor shaft should be reduced, thereby reducing the front The size of the disc off-flow area improves the stability of the impeller and ensures the performance of the fan.
4. Optimize the blade shape
Usually, when designing and optimizing the blade, it focuses on the structural optimization of the blade outlet installation angle and the structural optimization of the blade height, but ignores the optimization of the blade shape. Generally, by optimizing the shape of the blade, the air supply volume of the blade and the width of the effective channel can be increased to a certain extent, so that the efficiency of the centrifugal fan can be improved, thereby ensuring the smooth operation of the impeller.
