Secondary Inlet Bell and Flow Grid for Centrifugal Fan Noise Reduction
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Solution Overview
Problem
Centrifugal fans and compressors in HVACR systems produce significant noise due to periodic airflow interactions with rotating blades, leading to audible tones that are not effectively mitigated by existing technologies.
Innovation Solution
The integration of a secondary inlet bell and a flow grid that synergistically reduce sound levels by minimizing airflow turbulence and variation, with the secondary inlet bell directing air into the primary inlet bell and the flow grid guiding air to promote laminar flow, thereby reducing the magnitude of tones produced.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a single inlet bell is used, then the structure is simple, but the sound levels and tones produced by the centrifugal fan or compressor are significant
Solution Approach 1:
The inlet bell is divided into two separate components: a primary inlet bell that directs air into the fan wheel inlet, and a secondary inlet bell that directs air into the primary inlet bell. This segmentation allows each component to be optimized for specific flow characteristics, reducing turbulence and noise while maintaining structural manageability
Solution Approach 2:
The secondary inlet bell acts as an intermediary component between the external environment and the primary inlet bell. It conditions the airflow before it enters the primary inlet bell, smoothing out turbulence and variations that would otherwise generate noise and unwanted tones
2Object-affected harmful factors
If airflow is allowed to move freely into the fan wheel, then the flow path is short, but the airflow turbulence interacts with rotating blades to produce audible tones
Solution Approach 1:
The secondary inlet bell performs preliminary action by conditioning the airflow before it reaches the primary inlet bell and fan wheel. It pre-smooths the airflow, eliminating turbulence and variations upstream, so that when air enters the fan wheel, it does so in a more uniform manner, reducing the generation of audible tones
Solution Approach 2:
The flow grid and secondary inlet bell together form an intermediary system that mediates between the external airflow and the fan wheel inlet. This intermediary structure controls and conditions the airflow, preventing direct turbulent interaction with the rotating blades that would produce audible tones
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The combination of the secondary inlet bell and flow grid significantly reduces noise levels, achieving a greater sound reduction than either component alone, effectively minimizing the largest tones produced by centrifugal fans and compressors.
Implementation Method 1
The flow grid guides the air such that it has a more laminar flow when the air enters the fan wheel
Implementation Method 2
The secondary inlet bell directs the air into the primary inlet bell... minimizing the distance that the air must flow from outside the centrifugal fan assembly to one or more blades of the fan wheel
Data Source
AI summary
A centrifugal fan assembly including fan wheel, a primary inlet bell, a secondary inlet bell, and a flow grid. The primary inlet bell and secondary inlet bell direct air into an inlet of the fan wheel of the centrifugal fan. Also disclosed is a sound reduction assembly for reducing the sound produced by a centrifugal fan or centrifugal compressor. A method of directing air flowing into a centrifugal fan or a centrifugal compressor is also disclosed.