Thermal Conductivity Sensor Branching for Wet High-Flow Gas
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Solution Overview
Problem
Existing hydrogen sensors in fuel cell vehicles face challenges in accurately measuring thermal conductivity due to high gas flow velocities and water droplets in the exhaust stream, which distort measurement signals.
Innovation Solution
A sensor design featuring a branching element, such as a Venturi nozzle, that diverts a portion of the fluid medium into an interior space, reducing flow velocity and using apertures to ensure the medium reaches the sensor primarily by diffusion, minimizing convective components and preventing large droplets from reaching the sensor element.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a thermal conductivity sensor element is used in high-velocity exhaust gas flow, then the sensor can detect hydrogen content in the exhaust stream, but convection of the gas past the membrane distorts the measurement signal
Solution Approach 1:
A baffle plate is introduced as an intermediary element between the exhaust gas flow and the sensor membrane. The baffle plate intercepts the high-velocity convective flow, causing the gas to follow a longer, more tortuous path around it before reaching the membrane. This converts direct high-speed convection into slower, more diffuse transport near the membrane surface, reducing convective distortion of the thermal conductivity measurement while still allowing hydrogen detection.
2Measurement precision
If the sensor is placed directly in the exhaust stream to capture hydrogen content, then real-time detection is achieved, but water droplets in the exhaust stream distort the measurement
Solution Approach 1:
The harmful water droplets are extracted or removed from the measurement path by the baffle plate geometry. As the exhaust gas flows past the baffle plate, larger water droplets are separated from the gas stream due to inertial effects and impinge on the baffle plate surface or are redirected away from the sensor membrane. This allows the sensor to detect hydrogen content in the gas phase without interference from liquid water droplets that would otherwise condense on the heated membrane and distort thermal conductivity readings.
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 design significantly reduces measurement errors by ensuring minimal convective flow and exclusion of large droplets, maintaining accurate thermal conductivity measurements with minimal signal deviation of less than 5%, suitable for high-flow environments like fuel cell vehicle exhausts.
Implementation Method 1
Conductive traces of a sensor circuit with at least one heating element are applied to the measuring surface
Implementation Method 2
The sensor element is designed to detect a thermal conductivity of the fluid medium
Implementation Method 3
The aperture is designed such that the fluid medium reaches the sensor element primarily by diffusion
Implementation Method 4
Along this flow path, the convective flow is calmed by one or more apertures
Implementation Method 5
A branching element, such as a Venturi nozzle, that diverts a portion of the fluid medium into an interior space, reducing flow velocity
Data Source
Figure 1
AI summary
The invention relates to a sensor (10) for detecting at least one property of a fluid medium (12) in a measurement chamber (14), in particular for detecting a H2 fraction in a measurement gas (16). The sensor (10) comprises at least one sensor element (22) which is designed to detect a thermal conductivity of the fluid medium (12) and for outputting a measurement signal. The sensor (10) further comprises a branch element (28), which defines an interior space (30), the branch element (28) being designed to branch off a part of the fluid medium (12) from the measurement chamber (14) into the interior space (20), and at least one diaphragm (52, 56, 64). The sensor element (22) is fluidically connected to the interior space (30) by means of the diaphragm (52, 56, 64).