Centrifugal Fan Scroll Geometry for Pressure Gain With Lower Noise
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Solution Overview
Problem
Conventional centrifugal fans with shifted clearance between the scroll casing and fan periphery in the blade rotation direction face challenges in efficiently increasing pressure in the scroll portion, leading to noise issues due to sudden pressure differences.
Innovation Solution
The centrifugal fan design incorporates a peripheral wall with a narrowed portion reducing distance from the inner end to the closest portion and an expanded portion increasing distance from the closest portion, gradually reducing and then increasing the distance between the peripheral wall and the outer peripheral portion, thereby securing air volume and increasing gas velocity to enhance pressure in the scroll portion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the position where the clearance between the scroll casing and the outer periphery of the fan is minimum is shifted from the tongue portion in the blade rotation direction, then the noise level is reduced, but the pressure increase in the scroll portion becomes inefficient
Solution Approach 1:
The peripheral wall is divided into three distinct portions with different geometric characteristics: a first portion with gradually decreasing distance, a second portion (narrowed portion) with minimum distance, and a third portion (expanded portion) with gradually increasing distance. Each portion serves a specific function in managing airflow and pressure distribution, allowing local optimization of both noise reduction and pressure increase efficiency.
Solution Approach 2:
The peripheral wall employs curved, spiral geometry forming a volute shape that smoothly guides airflow. The continuous curvature of the peripheral wall, particularly in the first and third portions, prevents sudden flow direction changes and reduces turbulence-induced noise while maintaining efficient pressure increase through gradual centrifugal force application.
2Stress or pressure
If the distance between the peripheral wall and the outer peripheral portion of the fan is continuously reduced, then the pressure in the scroll portion increases, but the air volume is reduced
Solution Approach 1:
The peripheral wall is segmented into three functional portions: the first portion gradually reduces distance to build pressure, the second portion (narrowed portion) achieves minimum distance for maximum pressure, and the third portion (expanded portion) increases distance to restore air volume. This segmentation allows the system to sequentially achieve both pressure increase and air volume maintenance.
Solution Approach 2:
The first portion of the peripheral wall preliminarily prepares the airflow by gradually reducing the distance before the airflow reaches the narrowed portion. This preliminary action ensures that when the airflow enters the minimum clearance zone, the pressure increase is optimized while preventing sudden flow disruption that would reduce air volume.
3Stress or pressure
If the gas passage between the tongue portion and the blades is suddenly narrowed, then the pressure difference increases, but the noise level increases
Solution Approach 1:
The peripheral wall employs continuous curved geometry that smoothly transitions the gas passage cross-section. The spiral volute shape of the peripheral wall creates gradual area changes rather than sudden narrowings, allowing pressure difference to build progressively without generating the turbulence and noise associated with abrupt geometric transitions.
Solution Approach 2:
The geometric parameters of the gas passage, particularly the cross-sectional area and distance between the peripheral wall and fan blades, are continuously varied along the flow direction. The distance parameter transitions smoothly from the first portion through the minimum at the second portion to the increased distance in the third portion, maintaining parameter continuity that prevents sudden pressure changes and noise generation.
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 effectively increases pressure in the scroll portion while reducing noise levels by managing air volume and velocity, addressing the inefficiencies and noise issues of previous designs.
Implementation Method 1
a fan (2) configured to be driven to rotate; a scroll casing (4) housing the fan (2)... the centrifugal direction... increasing the pressure thereof
Implementation Method 2
a narrowed portion (4d) at which the distance between the peripheral wall (4c) and the rotation shaft (RS) is reduced... as the gas of the secured volume passes through the closest portion (41c), the velocity of the gas is increased
Data Source
AI summary
A centrifugal fan includes a fan configured to be driven to rotate, and a scroll casing housing the fan. The scroll casing includes a peripheral wall having a volute shape having an inner end of a spiral thereof at a boundary with a tongue portion of the scroll casing. When a portion at the peripheral wall at which a distance between the peripheral wall and a rotation shaft of the fan is minimum is defined as a closest portion, the peripheral wall includes a narrowed portion at which the distance between the peripheral wall and the rotation shaft is reduced from the inner end toward the closest portion in a rotation direction of the fan, and an expanded portion that is formed between the narrowed portion and the closest portion and at which the distance between the peripheral wall and the rotation shaft is increased.