Thermal Flow Meter Protrusion for Pulsation Accuracy
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Solution Overview
Problem
Existing thermal flow meters face challenges in maintaining high measurement accuracy, especially in the presence of contaminants like dust and oil, and in accurately measuring air flow rates during intake pulsation and backward flows, due to the design limitations of previous solutions which fail to effectively rectify the measurement target fluid and reduce the impact of particles or contaminants on the sensing portion.
Innovation Solution
A thermal flow meter design featuring a bypass passage with a protrusion having an orifice surface and a recovery surface, where the heat transfer surface of the air flow sensing portion is exposed, with the orifice surface approaching the support body along the flow direction and the recovery surface returning to the wall surface, effectively guiding contaminants away from the sensing area and improving measurement accuracy during pulsation and backward flows.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an orifice is formed on the wall surface of the bypass passage to rectify the measurement target fluid, then measurement accuracy is improved, but particles or contaminants may be adhered to the sensing portion
Solution Approach 1:
The protrusion is divided into multiple functional surfaces: an orifice surface for rectifying the flow, a peak surface for contaminant deflection, and a recovery surface for flow restoration. This segmentation allows each surface to perform its specific function independently, resolving the contradiction between measurement accuracy and contaminant protection.
Solution Approach 2:
The protrusion acts as an intermediary structure between the orifice and the sensing portion. It intercepts and deflects contaminants before they reach the sensing portion, while still allowing the measurement target fluid to be rectified for accurate measurement.
2Measurement precision
If the air flow sensing portion is exposed to measure heat transfer with the measurement target gas, then flow rate measurement capability is improved, but the sensing portion is vulnerable to particle impact and contamination
Solution Approach 1:
The protrusion creates different flow conditions at different locations: the orifice surface rectifies flow for accurate measurement, the peak surface deflects contaminants, and the recovery surface restores flow. This local differentiation protects the sensing portion while maintaining measurement capability.
3Object-affected harmful factors
If a base is arranged with inclination to hide the sensing portion, then contaminant impact is reduced, but measurement accuracy of pulsation and backward flow is degraded
Solution Approach 1:
The protrusion design with its specific geometry (orifice surface, peak surface, and recovery surface) dynamically adapts to different flow directions. It effectively deflects contaminants during normal flow while maintaining accurate measurement capability during pulsation and backward flow conditions.
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 proposed design enhances measurement accuracy by reducing the impact of contaminants and improving the detection of air flow rates during pulsation and backward flows, leading to a more reliable and precise thermal flow meter operation.
Implementation Method 1
a flow rate of the gas is measured by performing heat transfer between the air flow sensing portion and the gas as a measurement target
Data Source
AI summary
To improve measurement accuracy of a thermal flow meter. The present invention provides a thermal flow meter, in which a protrusion 356 having an orifice surface 503 and a recovery surface 505 is provided on a wall surface 501 of a bypass passage, an intersection line 506 between the orifice surface 503 and the wall surface 501 is arranged in an upstream side from an upstream side end 401 of a circuit package 400, an intersection line 507 between the recovery surface 505 and the wall surface 501 is arranged in a downstream side from a downstream side end 402 of the circuit package 400, and an apex 504 of the protrusion 356 is arranged in a downstream side from a heat transfer surface of an air flow sensing portion 602 and in an upstream side from the downstream side end 402 of the circuit package 400.