Thermal Flow Sensor with Isolated Physical Property Detection
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Solution Overview
Problem
Conventional flow rate measuring devices face challenges in accurately measuring flow rates due to changes in physical properties of fluids, leading to reduced measurement accuracy and inability to correct for errors within specific detection ranges.
Innovation Solution
A flow rate measuring device with a physical property detection unit and flow rate correction unit, where the physical property detection unit is isolated from the flow rate detection unit, allowing for individual control of flow rates and accurate correction of flow rate measurements based on calculated physical properties, reducing turbulence and stagnation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a thermal flow rate measuring device is used to measure flow rate based on temperature distribution changes, then flow rate measurement is achieved, but output characteristics change when physical properties of the fluid change
Solution Approach 1:
The device is divided into two independent detection units: a flow rate detection unit with thermopiles arranged upstream and downstream of a heater, and a physical property detection unit with thermopiles arranged perpendicular to the flow direction. This segmentation allows each unit to independently detect its respective parameter without mutual interference, enabling separate optimization for flow rate measurement and physical property detection.
Solution Approach 2:
The physical property detection unit acts as an intermediary that measures fluid physical properties (thermal conductivity, specific heat, density) and provides correction data to compensate for their influence on the flow rate detection unit's output characteristics. This intermediary measurement enables the system to adapt to different fluid types and maintain measurement accuracy.
2Measurement precision
If physical property detection is added to correct for fluid property changes, then measurement accuracy improves, but device complexity increases
Solution Approach 1:
Both the flow rate detection unit and physical property detection unit share common components: the same heater structure and the same thermopile array is used for both detection purposes. The thermopiles are arranged to serve dual functions - detecting temperature differences for flow rate measurement and detecting thermal properties for physical property measurement. This merging reduces component count and simplifies the overall device structure.
Solution Approach 2:
The thermopile array and heater combination serves multiple functions: it detects both flow rate (through upstream-downstream temperature difference) and physical properties (through perpendicular temperature distribution). This multi-functionality eliminates the need for separate sensors, reducing device complexity while maintaining measurement precision.
3Measurement precision
If thermopiles are disposed upstream and downstream of the heater for flow rate detection, then flow rate measurement is enabled, but turbulence and stagnation occur affecting detection precision
Solution Approach 1:
The thermopiles are positioned at specific locations relative to the heater - upstream and downstream along the flow direction - to create localized temperature difference detection zones. This local quality arrangement ensures that the thermopiles measure temperature differences caused by fluid flow without being affected by turbulence or stagnation that may occur in other regions of the flow path.
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 device achieves high accuracy in measuring flow rates by minimizing the impact of physical property changes on output characteristics, ensuring accurate flow rate corrections and enhanced detection precision.
Implementation Method 1
a heating unit configured to heat the fluid to be measured
Implementation Method 2
a temperature detection unit configured to detect a temperature of the fluid to be measured
Implementation Method 3
a thermal flow rate measuring device that measures the flow rate of the fluid to be measured, based on a change of a temperature distribution in the flow path
Implementation Method 4
a thermal flow rate measuring device that measures the flow rate of the fluid to be measured, based on a change of a temperature distribution in the flow path
Data Source
Figure 1(a)~1(b)
Figure 2
Figure 3(a)~3(b)
AI summary
A flow rate measuring device (1) includes: a flow rate sensor (8); a physical property sensor (7) having a micro heater and a thermopile; and a sub-flow path portion (3) having a physical property detecting flow path (32) in which the physical property sensor (7) is disposed. The micro heater and the thermopile are disposed side by side in a direction orthogonal to a flow direction of a fluid to be measured, and the flow rate sensor (8) is disposed at a position except for the physical property detecting flow path (32).