Cross-Flow Fan Blow-Out Path Narrowing to Reduce Noise and Backflow
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Solution Overview
Problem
In cross-flow fans used in air conditioners, the blown air tends to flow predominantly towards one wall portion, leading to reduced flow rates along the adjacent wall portion, noise, and potential backflow due to pressure losses, especially during high-load operations or when filters clog, causing air to reverse flow upstream.
Innovation Solution
The cross-flow fan design incorporates a blow-out path with a narrowed portion whose cross-sectional area decreases from a rectangular to a trapezoidal shape, with the distance between the first and second wall portions decreasing from upstream to downstream, and inclined surfaces that are recessed, to gradually contract the airflow and maintain flow rates along the entire path.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the blow-out path has a constant cross-sectional area, then the housing structure is simple, but the airflow becomes uneven causing noise and surging
Solution Approach 1:
The patent applies local quality by creating a narrowed portion with trapezoidal cross-section in the blow-out path, where the cross-sectional area gradually decreases from upstream to downstream. This localized geometric modification creates different flow characteristics in different regions of the blow-out path, ensuring uniform airflow distribution and preventing separation from the second wall portion, thereby reducing noise and surging without complicating the overall housing structure.
2Speed
If the cross-sectional area of the blow-out path is reduced, then the airflow velocity increases, but the pressure loss increases causing backflow
Solution Approach 1:
The patent employs curvature by designing the narrowed portion with a trapezoidal cross-section that gradually transitions from rectangular upstream to trapezoidal downstream. This gradual geometric transition with curved surfaces prevents sudden flow contraction, reducing flow separation and pressure loss while maintaining increased airflow velocity throughout the blow-out path.
3Speed
If the blow-out path is wide, then the airflow has low velocity, but the flow rate distribution becomes uneven causing air separation
Solution Approach 1:
The patent applies parameter changes by systematically varying the cross-sectional area of the blow-out path from upstream to downstream through the narrowed portion with trapezoidal geometry. This controlled parameter change (cross-sectional area reduction) increases airflow velocity while the gradual transition maintains flow attachment to all wall portions, ensuring uniform flow distribution and preventing air separation.
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
This design reduces noise and backflow by ensuring consistent airflow distribution and preventing air separation from the second wall portion, even during high-load operations, by gradually contracting the airflow and maintaining flow rates along the entire blow-out path.
Implementation Method 1
the blow-out path (F) has a narrowed portion (70) whose cross-sectional area decreases as its cross-sectional shape changes from a rectangular shape to a trapezoidal shape from an upstream side toward a downstream side
Data Source
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AI summary
Disclosed is a cross-flow fan (30) including a fan rotor (31) and a housing (32). The cross-flow fan (30) has a blow-out path (F) defined by first and second extension wall portions (36b) and (37b), and two sidewalls (38). The first extension wall portion (36b) continuously extends from a tongue portion (36a) of the housing (32) to the blow-out port (32b). The second extension wall portion (37b) faces the first extension wall portion (36b). The two sidewalls (38) are respectively provided at axial ends of the fan rotor (31). The two sidewalls (38) are formed such that the blow-out path (F) has a narrowed portion (70) whose cross-sectional area decreases as its cross-sectional shape changes from a rectangular shape to a trapezoidal shape from an upstream side toward a downstream side thereof, the trapezoidal shape having a portion near the second extension wall portion (37b) smaller in width than a portion near the first extension wall portion (36b).