Diffuser Collar Geometry for Axial Fan Recirculation Control
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Solution Overview
Problem
HVAC system axial fans experience efficiency losses and increased sound levels due to outflow recirculation caused by the larger duct diameter compared to the impeller, leading to reduced performance and noise issues.
Innovation Solution
The implementation of a diffuser collar with a variable diameter and concentrically arranged vane diffusers to radially expand the outflow from the axial fan, reducing recirculation and enhancing static efficiency, while also decreasing sound levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the duct diameter is larger than the impeller diameter, then the axial fan can move more air, but outflow recirculation occurs causing efficiency losses and increased sound levels
Solution Approach 1:
A diffuser collar is introduced as an intermediary component between the impeller and the duct. The diffuser collar has a diameter that is larger than the impeller diameter but smaller than or equal to the duct diameter, serving as a transition element that prevents recirculation while maintaining high airflow capacity.
2Productivity
If the duct diameter is larger than the impeller diameter, then the axial fan can move more air, but outflow recirculation causes increased sound levels
Solution Approach 1:
The diffuser collar acts as a mediator that eliminates the recirculation zone responsible for noise generation, while the large duct diameter is maintained to preserve high airflow volume and productivity.
3Loss of energy
If a diffuser collar is added to control outflow expansion, then static efficiency improves by 5-10%, but device complexity increases
Solution Approach 1:
The fan assembly is segmented into distinct functional zones: the impeller region, the diffuser collar region, and the duct region. This segmentation allows each component to be optimized independently, with the diffuser collar specifically designed to control expansion and maximize efficiency.
Solution Approach 2:
The diffuser collar is positioned locally at the impeller outlet where the expansion control is most critical. The collar has a specific diameter relationship (larger than impeller, smaller than or equal to duct) that creates optimal local flow conditions to prevent recirculation and maximize efficiency.
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 solution results in a 5-10% improvement in static efficiency and reduced sound levels by optimizing the expansion of the outflow, allowing for increased airflow without increasing fan speed.
Implementation Method 1
modifying the expansion rate of the outflow can improve the efficiency of the axial fan by, for example, increasing pressure rise through diffusion of the outflow
Data Source
AI summary
A fan assembly and a method of assembling a diffuser collar in the fan assembly are disclosed. The fan assembly includes an impeller including a plurality of blades. The impeller has an impeller diameter. A duct is configured to receive an outflow provided by the impeller. The duct has a duct exit diameter that is larger than the impeller diameter. The fan assembly further includes a diffuser collar extending from the impeller toward a duct exit. The diffuser collar is configured and arranged to radially expand the outflow provided by the impeller. The diffuser collar has a first diameter at a first edge disposed a first distance from the impeller. A contour extends from the first edge toward a second edge having a second diameter. The second edge is disposed a second distance from the impeller. The first distance is smaller than the second distance, the first diameter is smaller than the second diameter, and the first and second diameters are smaller than the duct exit diameter.