Thermal Flowmeter Sensor Segmented End Face Design
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Solution Overview
Problem
Conventional thermal flowmeters face limitations in measuring high flow velocities of liquids due to saturation of the characteristic curve, leading to reduced sensitivity and a limited measuring range, especially when dealing with liquids that have higher thermal conductivity compared to gases.
Innovation Solution
A thermal flowmeter with a sensor design featuring a divided end face into segments, including an inclined first segment and a central segment with a surface normal vector angle of at least 5° relative to the longitudinal axis, and a downstream segment, which creates a thicker thermal boundary layer and reduces heat dissipation, allowing for extended measuring range and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If conventional thermal flow meters with flat end faces are used, then the sensor structure is simple, but the measuring range is limited due to quick saturation of the characteristic curve at high flow velocities
Solution Approach 1:
The end face of the sensor is divided into multiple segments (first side segment, middle segment, second side segment) with different geometric configurations. The first and second side segments have inclined surfaces forming angles of 5-15 degrees with the longitudinal axis, while the middle segment has a surface perpendicular to the longitudinal axis. This segmentation allows different regions to serve different functions in extending the measuring range.
Solution Approach 2:
Different segments of the end face are given different local geometric properties. The inclined side segments create specific flow patterns and thermal boundary layer characteristics, while the perpendicular middle segment provides a reference surface. This local differentiation optimizes heat transfer characteristics across the entire end face for extended measuring range.
2Volume of moving object
If the sensor elements are closely spaced to improve compactness, then the device size is reduced, but crosstalk between the active sensor element and temperature-measuring sensor element occurs at low speeds
Solution Approach 1:
The sensor elements are divided into functionally distinct segments: an active sensor element for heat input and a passive sensor element for temperature measurement. The segmented end face geometry with inclined surfaces creates thermal boundary layers that prevent direct thermal coupling between closely spaced sensor elements, eliminating crosstalk while maintaining compact dimensions.
3Reliability
If cylindrical sensor caps are used to provide thermal insulation, then crosstalk is prevented, but the characteristic curve reaches saturation quickly at higher flow rates
Solution Approach 1:
The sensor elements are equipped with cylindrical sensor caps that provide thermal insulation. The inclined surfaces of the end face segments work in conjunction with the cylindrical geometry to control flow patterns and thermal boundary layer development, extending the measuring range while maintaining thermal insulation properties.
Solution Approach 2:
The end face is given non-uniform local geometry with inclined side segments and a perpendicular middle segment. This local geometric variation creates optimized flow patterns that delay saturation of the characteristic curve, allowing the cylindrical sensor caps to provide thermal insulation without limiting the measuring range.
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 sensor design extends the measuring range and stability by reducing heat input requirements and delaying power saturation to higher flow velocities, providing more accurate and reliable measurements across a broader range of flow speeds.
Implementation Method 1
This principle is based on the cooling of a heated resistance thermometer, hereinafter also referred to as the heating and measuring or active sensor element, from which heat is extracted by the flowing medium
Implementation Method 2
heat is extracted by the flowing medium. The extracted energy is compensated for by increasing the electrical heating current
Implementation Method 3
a first temperature sensing element and at least one second temperature sensing element, which preferably comprise resistance thermometers
Data Source
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AI summary
The invention relates to a thermal flow rate measurement device for determining and/or monitoring a thermal mass flow of a measurement medium through a measurement tube, comprising a sensor having a first heatable resistance thermometer and at least one second heatable resistance thermometer, wherein the sensor has a longitudinal axis (A) and an end face (3), which is divided into at least two segments (3a-3c) arranged next to each other, wherein a surface normal vector of at least one first segment encloses an angle (a) of at least 5° with the longitudinal axis (A) of the sensor. The invention further relates to the use of a thermal flow rate measurement device.