Thermal Flow Meter Drainage Passage for Water Separation
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Solution Overview
Problem
Thermal flow meters face challenges in maintaining measurement accuracy when water enters the bypass passage, leading to discharge of both water and measurement target gas, resulting in reduced accuracy and potential damage to the flow rate detection circuit.
Innovation Solution
A thermal flow meter design incorporating a bypass passage with an inlet and outlet port, an air flow sensing portion for heat transfer, and a drainage passage to separate water from the measurement target gas, ensuring accurate flow rate measurement while preventing damage to the circuit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a through hole is provided to directly connect the inside and the outside of the bypass passage, then water discharge function is improved, but measurement target gas is also discharged and measurement accuracy deteriorates
Solution Approach 1:
The drainage passage is segmented into multiple sections: a first passage connecting the inlet port area to the outside, and a second passage connecting the outlet port area to the outside. This segmentation allows water to be discharged through the first passage while measurement target gas is returned through the second passage, resolving the contradiction between water discharge function and measurement accuracy.
Solution Approach 2:
The harmful element (water) is extracted from the bypass passage through the drainage passage equipped with a water separator. The water separator specifically removes water from the measurement target gas, allowing only the gas to be returned to the main passage. This extraction approach maintains measurement accuracy while providing effective water discharge capability.
2Reliability
If water remains inside the bypass passage, then discharge function is not needed, but measurement accuracy deteriorates and flow rate detection circuit may be damaged
Solution Approach 1:
A water separator is introduced as an intermediary component in the drainage passage. This water separator acts as a mediator that separates water from the measurement target gas, allowing water to be discharged while protecting the flow rate detection circuit from water damage. The intermediary component resolves the contradiction by providing protection without significantly increasing overall device complexity.
3Reliability
If measurement target gas is discharged to the outside, then water discharge is achieved, but the state is not preferable for maintaining measurement accuracy
Solution Approach 1:
The drainage system is divided into separate pathways: a first drainage passage for water discharge and a second drainage passage for measurement target gas return. This segmentation ensures that water is discharged while measurement target gas is returned to the main passage, preventing gas loss and maintaining measurement accuracy.
Solution Approach 2:
Different sections of the drainage passage are designed with different functions: the first passage near the inlet port is optimized for water discharge, while the second passage near the outlet port is optimized for gas return. This local differentiation of quality and function allows simultaneous achievement of water discharge and gas retention for accurate measurement.
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 enables high-accuracy flow rate measurement and prevents damage to the flow rate detection circuit by effectively discharging water without losing measurement target gas, maintaining measurement precision and reliability.
Implementation Method 1
a flow rate detection circuit for measuring a flow rate of the measurement target gas flowing through the main passage by performing heat transfer with the measurement target gas flowing through the bypass passage
Data Source
AI summary
Provided is a thermal flow meter through which a measurement with high accuracy and has a discharge function. In a thermal flow meter 300 of the invention, a part of a measurement target gas 30 flowing through the main passage 124 flows into a bypass passage. A drainage passage 3528 is provided in the bypass passage to communicate a bypass passage 4232 on the inlet port (between the inlet port 350 and the measurement surface 430 serving as the air flow sensing portion) and a bypass passage 4234 on the outlet port (between the measurement surface 430 serving as the air flow sensing portion and the outlet port 352). The drainage passage 3528 includes a through hole 3512. The through hole 3512 includes an inlet port 3542 which penetrates a wall surface 4212 forming the bypass passage 4232 on the inlet port and is opened in the bypass passage 4232 on the inlet port, and an outlet port 3544 which is opened in a rear surface 4213 of the wall surface. Water 3552 flowing into the bypass passage is guided to the through hole 3512, and guided to the bypass passage 4234 on the outlet port through the drainage passage 3528, and discharged to the main passage 124. Therefore, an influence of the water flowing into a measuring portion can be reduced, and the measurement accuracy can be improved.