Thermal Conductivity Sensor With Diffusion-Calmed Gas Flow
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Solution Overview
Problem
Conventional sensors for detecting properties of fluid media, such as hydrogen fraction in fuel cell exhausts, face challenges due to high gas flow velocities and water droplets, which distort measurement signals and reduce sensitivity and accuracy.
Innovation Solution
A sensor design that includes a heatable measurement membrane, a branch element acting as a Venturi nozzle to reduce flow velocity and prevent droplet entry, and multiple diaphragms to calm fluid flow and ensure diffusion-based delivery to the sensor element, thereby minimizing convective distortion and enhancing measurement precision.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a thin membrane sensor element is used to measure thermal conductivity, then measurement sensitivity is improved, but convection of exhaust gas past the membrane distorts the measurement signal
Solution Approach 1:
A flow-calming element with porous structure is introduced as an intermediary between the exhaust gas flow and the sensor element. This mediator allows gas molecules to pass through while calming the convective flow, enabling the thin membrane sensor to operate without convective distortion while maintaining its high measurement sensitivity
Solution Approach 2:
The harmful convective motion is extracted and separated from the measurement process by directing the gas flow through the porous flow-calming element before it reaches the sensor, isolating the sensor from direct exposure to high-velocity convective flow
2Loss of time
If the sensor is placed directly in the exhaust tract to detect hydrogen concentration, then response time is improved, but water droplets and high flow velocities distort the measurements
Solution Approach 1:
A porous flow-calming element is used to filter and calm the exhaust gas flow. The porous structure allows gas molecules to pass through rapidly (maintaining short response time) while blocking water droplets and reducing convective velocity, preventing measurement distortion
Solution Approach 2:
The exhaust gas flow is pre-treated by passing through the flow-calming element before reaching the sensor. This preliminary action removes water droplets and reduces flow velocity in advance, protecting the sensor from harmful effects while maintaining rapid response
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 achieves improved sensitivity, measuring range, response time, and selectivity by reducing convective flow and ensuring that the fluid medium reaches the sensor element mainly by diffusion, thus minimizing signal errors and maintaining measurement accuracy even in high-flow environments.
Implementation Method 1
sensor element which is designed for detecting a thermal conductivity of the fluid medium
Implementation Method 2
a branch element which defines an interior space and is designed to branch off a part of the fluid medium from the measurement chamber into the interior space
Implementation Method 3
the fluid medium reaches the sensor element substantially by means of diffusion
Data Source
AI summary
A sensor for detecting at least one property of a fluid medium in a measurement chamber, in particular for detecting a H2 fraction in a measurement gas. The sensor includes at least one sensor element which is designed to detect a thermal conductivity of the fluid medium and for outputting a measurement signal. The sensor further includes a branch element, which defines an interior space, the branch element being designed to branch off a part of the fluid medium from the measurement chamber into the interior space, and at least one diaphragm. The sensor element is fluidically connected to the interior space using the diaphragm.