Fan Unit Surge Control via Recirculation Passage
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Solution Overview
Problem
Existing breathing assistance systems face challenges with flow instability and pressure fluctuations during exhalation, leading to noise and vibration issues due to impeller stall or surge, which affect the delivery of consistent pressurized gases to patients.
Innovation Solution
Incorporating a recirculation passage in the fan unit that allows the gases stream to be recirculated to the input of the impeller opposite to the main flow direction, combined with a wedge member that directs airflow to reduce turbulence and maintain airflow stability, and an adjustable impeller design to manage pressure and flow rates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional blower design is used, then the device is simple in structure, but flow instability and pressure fluctuations occur during exhalation causing noise and vibration
Solution Approach 1:
The blower is divided into distinct functional sections: an impeller section for gas compression, a diffuser section for pressure recovery, and a recirculation passage for flow management. This segmentation allows each component to be optimized for its specific function while working together to eliminate flow instability and pressure fluctuations during exhalation.
Solution Approach 2:
A recirculation passage is introduced as an intermediary element between the impeller and diffuser. This passage mediates the gas flow by providing an alternative path that prevents direct conflict between the impeller's compressive action and the diffuser's pressure recovery, thereby eliminating noise and vibration caused by flow instability.
2Stress or pressure
If the blower operates at high pressure, then pressurized gases are delivered effectively, but impeller stall or surge occurs causing noise and vibration
Solution Approach 1:
The recirculation passage creates a feedback mechanism where a portion of the high-pressure gas flow is redirected back toward the impeller inlet. This feedback loop prevents the impeller from stalling or surging by maintaining smoother, more stable flow conditions, thereby eliminating noise and vibration while preserving high pressure delivery capability.
Solution Approach 2:
The recirculation passage acts as an intermediary that buffers the interaction between the high-pressure gas stream and the impeller. By providing a controlled path for flow recirculation, it prevents direct conflict that would cause stall or surge, thus eliminating harmful noise and vibration while maintaining effective pressurized gas delivery.
3Stability of the object's composition
If the diffuser and volute channel have a sharp angular transition, then the structure is simple, but turbulence increases reducing airflow stability
Solution Approach 1:
The transition between the diffuser and volute channel is designed with a curved, spherical geometry rather than a sharp angular joint. This curvature eliminates abrupt flow separation and reduces turbulence, thereby improving airflow stability. The curved transition smoothly guides the gas flow from the diffuser into the volute channel, preventing the instability that would result from a sharp angle.
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 prevents impeller stall and surge, maintaining stable airflow and pressure delivery, reducing noise and vibration, and extending the useful operating range of the blower unit.
Implementation Method 1
a recirculation passage in the fan unit that allows the gases stream to be recirculated to the input of the impeller opposite to the main flow direction
Implementation Method 2
a wedge member that directs airflow to reduce turbulence and maintain airflow stability
Implementation Method 3
an impeller located within the casing adapted for connection to a motor to drive rotation of the impeller about an axis when in use
Data Source
AI summary
A fan unit that forms part of a gases supply unit used as part of a breathing assistance system for providing heated gases to a user. The fan has an impeller surrounded by an upwardly sloped surface to facilitate improved airflow performance under surge conditions.