Mixed Flow Fan Assembly with Ambient Air Induction and Straightening Vanes
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Solution Overview
Problem
Mixed flow fan assemblies face inefficiencies due to primary exhaust recirculation and noise issues, as well as reduced static efficiency caused by radial and tangential velocity components and noise generation.
Innovation Solution
The design incorporates ambient air induction through a multi-purpose port and aperture to cool the motor and maintain pressure, provides openings to balance low pressure regions, uses airfoil impeller blades with a single-thickness trailing edge to reduce noise, and includes full-length straightening vanes to redirect airflow, enhancing static efficiency and reducing noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the fan operates with primary exhaust flow only, then the exhaust gas/air flow is maintained, but static efficiency is reduced due to radial and tangential velocity components
Solution Approach 1:
The patent introduces a third dimension to the flow by adding axial velocity component through ambient air induction. The straightening vanes redirect the radial and tangential velocity components into an axial direction, combining with the existing axial flow from the impeller. This multi-dimensional flow approach increases volumetric flow rate and improves static efficiency by converting kinetic energy more effectively.
Solution Approach 2:
The patent uses straightening vanes as intermediary elements between the impeller outlet and the discharge nozzle. These vanes mediate the flow transition by redirecting the radial and tangential velocity components into the axial direction, thereby improving flow efficiency and reducing energy loss without requiring changes to the impeller or discharge geometry.
2Productivity
If the fan operates at high velocity to increase volumetric flow rate, then productivity increases, but noise output increases
Solution Approach 1:
The patent changes the flow direction from radial/tangential to axial using straightening vanes, which reduces the velocity components that generate noise. By redirecting flow along the axis rather than radially outward, the high-velocity flow is contained within a more controlled path, reducing turbulence and noise generation while maintaining volumetric flow rate.
Solution Approach 2:
The patent modifies the flow parameters by changing the velocity vector direction from radial/tangential to axial. This parameter change reduces the kinetic energy components that generate noise while maintaining the volumetric flow rate through the addition of ambient air flow, thereby achieving quieter operation at equivalent productivity.
3Reliability
If the motor enclosure is sealed to protect from exhaust contamination, then reliability improves, but cooling efficiency decreases
Solution Approach 1:
The patent segments the motor enclosure from the exhaust plenum using a seal wall, creating distinct zones that prevent exhaust contamination while allowing independent flow paths. The multi-purpose port provides a separate cooling air intake path, segmenting the cooling function from the exhaust flow. This segmentation enables both motor protection and effective cooling by maintaining separate airflow paths.
Solution Approach 2:
The patent introduces ambient air as an intermediary cooling medium that flows through the multi-purpose port and cools the motor and VFD without contacting the exhaust flow. This intermediary air path allows the motor enclosure to remain sealed against exhaust contamination while still achieving effective cooling through the ambient air stream.
4Productivity
If ambient air is induced through openings in the base to balance low pressure, then recirculation is minimized, but device complexity increases
Solution Approach 1:
The patent makes the base openings serve multiple functions: they induce ambient air to balance low pressure regions, prevent exhaust recirculation, and can serve as structural mounting points. The multi-purpose port in the housing serves both as a cooling air intake and as a structural element. By making these features multi-functional, the patent reduces the need for separate components and minimizes overall device complexity while achieving the desired flow control.
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 modifications increase static efficiency by minimizing recirculation, enhancing volumetric flow rate, and reducing operational noise, resulting in improved performance and energy efficiency.
Implementation Method 1
Fresh ambient air is induced through the opening(s) by the venturi effect of the primary exhaust exiting the fan wheel shroud
Implementation Method 2
Impeller blades are designed with airfoil profiles, with an overlap of substrate at the trailing edge creating a single-thickness trailing edge
Data Source
AI summary
A mixed flow fan assembly uses induced reverse ambient air flow through the in-line motor enclosure for motor cooling, motor segregation from primary exhaust contamination, and augmentation of volumetric flow rate. Induced ambient airflow through openings in and/or around the base of the fan housing balances low pressure around the fan wheel and the inlet cone to inhibit primary exhaust recirculation and increase volumetric flow rate. Straightening vanes downstream of the fan wheel are used to axially reorient radial and tangential velocity components of primary effluent flow. Airfoil impeller blades have a scalloped and/or perforated single-thickness trailing edge to attenuate fan noise.