Centrifugal Blower Scroll Casing Radius Variation

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Solution Overview

Problem

Conventional centrifugal blowers produce undesirable noise due to abrupt changes in air passage width and static pressure between blades, which can be mitigated by enlarging the scroll radius at the start portion but results in increased air re-circulation and reduced blowing pressure.

Innovation Solution

A centrifugal blower design with a scroll casing that has a varying scroll radius, where the maximum radius is closer to one axial wall than the other, maintaining a constant maximum radius from the motor-side scroll start to the finish portion, and a minimum radius that increases in a logarithmic spiral shape from the suction port-side scroll start to the finish portion, reducing static pressure fluctuations and noise.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-affected harmful factors

If the scroll radius is enlarged at the scroll start portion to increase the width of the air passage, then noise is reduced by avoiding abrupt reduction in air passage width, but air re-circulation increases and blowing pressure decreases

Engineering Contradiction:

ImprovenoiseVSAvoidblowing pressure

Core Design Contradiction:

Object-affected harmful factorsVSProductivity

Solution Approach 1:

The scroll radius is differentiated into two distinct characteristics: a first scroll radius at the scroll start portion and a second scroll radius at the scroll finish portion. The first scroll radius is smaller than the second scroll radius, creating local variation in air passage width. This local quality differentiation allows the air passage to have appropriate width at different locations, preventing both abrupt reductions (which cause noise) and excessive expansion (which causes re-circulation), thereby resolving the contradiction between noise reduction and blowing pressure maintenance.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The air passage width is designed to dynamically vary along the scroll path rather than remaining constant or changing abruptly. The transition from the first scroll radius to the second scroll radius creates a gradual, controlled expansion that adapts to the flow conditions at different positions, optimizing both noise characteristics and blowing pressure performance.

Inventive Principle:

Principle #15Dynamics

2Volume of moving object

If the width of the air passage is abruptly reduced from the scroll finish portion toward the scroll start portion, then the structure is compact, but static pressure between blades becomes abruptly higher and noise increases

Engineering Contradiction:

Improveblower sizeVSAvoidnoise

Core Design Contradiction:

Volume of moving objectVSObject-affected harmful factors

Solution Approach 1:

The air passage is designed with different width characteristics at different locations: narrower at the scroll start portion and wider at the scroll finish portion. This local quality variation prevents abrupt pressure changes while maintaining a relatively compact overall structure, resolving the contradiction between compactness and noise reduction.

Inventive Principle:

Principle #3Local quality

3Productivity

If the cross-sectional area of the air passage is increased from the scroll start side toward the scroll finish side, then stagnation or contraction of air flow is reduced and flow amount increases, but the structure becomes more complex

Engineering Contradiction:

Improveflow amountVSAvoidscroll casing structure

Core Design Contradiction:

ProductivityVSDevice complexity

Solution Approach 1:

The scroll radius parameter is systematically varied along the scroll path, with the first scroll radius at the start portion being smaller than the second scroll radius at the finish portion. This parameter change creates a gradual expansion of the air passage that optimizes flow characteristics while maintaining structural simplicity through a straightforward radial expansion design.

Inventive Principle:

Principle #35Parameter changes

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 levels and maintains sufficient blowing pressure by minimizing static pressure fluctuations and increasing the cross-sectional area of the air passage, thereby reducing air re-circulation and enhancing blowing properties.

Implementation Method 1

a centrifugal multi-blade fan is provided in a central portion of a scroll casing. The scroll casing includes an air passage in which air blows radially outward due to rotational motion of the centrifugal multi-blade fan

Methodology Applied

Scientific EffectCentrifugal force: Centrifugal Force

Implementation Method 2

the width of the air passage increases from the scroll start toward the scroll finish side of the scroll casing. Since a cross sectional area of the air passage increases from the scroll start side toward the scroll finish side of the scroll casing, occurrence of stagnation or contraction of air flow in the air passage is reduced

Methodology Applied

Scientific EffectFluid dynamics:

Data Source

PatentUS7972110B2Centrifugal blower

Publication Date: 2011.07.05 DENSO CORP

AI summary

A centrifugal blower having a fan including a blade. A scroll casing houses the fan and has a first axial wall portion, a second axial wall portion, and a side wall extending between the first and second axial wall portions. The scroll casing includes a suction port in the first axial wall portion. The scroll casing also defines a scroll start portion and a scroll finish portion. The scroll casing has a scroll radius measured transverse to the rotation axis that changes from the scroll start portion to the scroll finish portion. Also, a maximum radius of the scroll radius is closer to the second axial wall portion than the first axial wall portion.