Thermal Flow Meter Bypass Stage for Contaminant Protection
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Solution Overview
Problem
The air flow sensing portion in thermal flow meters is exposed and prone to contamination by substances like oil mist or carbon, leading to a decrease in measurement accuracy due to changes in heat capacity.
Innovation Solution
The air flow sensing portion is mounted on a support surface within the bypass passage, where it is surrounded by a stage with an inner portion protruding more than the outer portion, effectively blocking contaminants and preventing them from adhering to the sensing surface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the air flow sensing portion is arranged in an exposed state inside the bypass passage, then the flow rate measurement can be performed, but contaminants such as oil mist or carbon are adhered to the air flow sensing portion, degrading the heat capacity and reducing measurement accuracy
Solution Approach 1:
A protective cover is introduced as an intermediary component between the contaminants in the bypass passage and the air flow sensing portion. The cover allows the sensing portion to remain exposed for measurement while physically blocking contaminants from adhering to it, thus resolving the contradiction between measurement accessibility and contamination protection
Solution Approach 2:
The protective cover is designed to prevent contaminant adhesion before it can affect the air flow sensing portion. By establishing this protective barrier in advance, the measurement accuracy is maintained without requiring post-contamination cleaning or replacement operations
2Object-affected harmful factors
If the air flow sensing portion is covered to protect it from contaminants, then contaminant adhesion is prevented, but the heat transfer between the sensing portion and the measurement target gas is hindered, reducing measurement accuracy
Solution Approach 1:
The protective cover is designed with selective permeability - it provides complete protection against contaminant adhesion while maintaining sufficient heat transfer capability for accurate measurement. The cover's material and structure are optimized to allow thermal energy passage while blocking physical contaminant particles
Solution Approach 2:
The protective cover serves as a mediator that reconciles two opposing requirements: it blocks contaminants from reaching the sensing portion while simultaneously allowing heat transfer to occur. This intermediary structure enables both protection and measurement functionality to coexist
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 configuration enhances the measurement accuracy of the thermal flow meter by preventing contaminants from affecting the heat transfer process, thus maintaining high precision in gas flow rate measurements.
Implementation Method 1
an air flow sensing portion for measuring a flow rate of the measurement target gas by performing heat transfer with a measurement target gas flowing through the bypass passage through a heat transfer surface
Data Source
AI summary
In order to provide a thermal flow meter capable of preventing adherence of contaminants to an air flow sensing portion, the thermal flow meter (300) of the invention includes a bypass passage for flowing a measurement target gas (30) received from a main passage (124) and an air flow sensing portion (602) for measuring a flow rate of the measurement target gas (30) by performing heat transfer with the measurement target gas (30) flowing through the bypass passage through a heat transfer surface (437). The air flow sensing portion (602) is provided to be exposed to an exposed surface (402) arranged along a flow direction of the measurement target gas (30) inside the bypass passage is embedded, the mount support surface (402) has a stage (407) formed to surround a periphery of the air flow sensing portion (602), and an inner portion surrounded by the stage protrudes more than an outer portion of the stage.