What is the effect of using an inlet bell with internal guide vanes on a centrifugal fan?

Using an inlet bell with internal guide vanes on a centrifugal fan primarily serves to decrease air swirl. The design of the inlet bell and the presence of guide vanes are specifically intended to streamline the airflow entering the fan. By guiding the air into a more uniform and straightened flow, the internal vanes reduce turbulence and disorder, which effectively lessens any swirling motion of the incoming air.

This enhancement in airflow direction helps improve the overall performance of the fan by ensuring that the air enters the rotating wheel more efficiently, which can lead to increased pressure and improved fan efficiency. The reduction of air swirl allows for smoother operation and can help minimize the possibilities of flow separation, which is critical for maintaining the fan's performance characteristics.

In contrast, while the introduction of guide vanes does modify the velocity and pressure characteristics of the air flowing into the fan, the primary effect emphasized by the use of an inlet bell with vanes is the control and reduction of swirling tendencies within the airflow.