DEF Sensor Housing With Porous Membrane Micro-Bubble Mitigation
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Solution Overview
Problem
Existing diesel exhaust fluid (DEF) sensors are adversely affected by micro-bubbles, which adhere to sensor surfaces and disrupt readings due to their low buoyancy and attachment to vertical and horizontal surfaces, despite venting mechanisms that allow larger bubbles to escape.
Innovation Solution
A housing assembly with a porous membrane and air accumulation volume is used to prevent micro-bubbles from entering the sensing volume, while allowing DEF fluid to flow through, and a vent system directs air away from the sensor to minimize interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If venting apertures are provided in sensor enclosures to allow trapped air to escape, then larger bubbles can be removed from the enclosure, but micro-bubbles are driven into the enclosures through the same apertures and adhere to sensor surfaces
Solution Approach 1:
A hydrophobic coating is applied to the internal surfaces of the sensor enclosure, including the reflector and sensor faces. This coating acts as an intermediary that prevents micro-bubbles from adhering to these surfaces while still allowing the venting apertures to function for larger bubble removal. The hydrophobic property creates a surface that micro-bubbles cannot stick to, thus eliminating the harmful effect of micro-bubble adhesion without compromising the venting function.
Solution Approach 2:
A porous membrane is introduced as a new component in the enclosure structure. This porous material allows for selective passage of fluids and gases while providing a surface treatment that prevents micro-bubble adhesion. The porous structure combined with hydrophobic coating creates a barrier that micro-bubbles cannot penetrate or stick to, while still permitting necessary fluid exchange and larger bubble escape.
2Productivity
If large venting apertures are used to allow air to escape easily, then trapped air can be removed effectively, but micro-bubbles are drawn into the enclosures through these large openings
Solution Approach 1:
The hydrophobic coating serves as a protective intermediary layer on all internal surfaces. This coating allows the large venting apertures to maintain their high productivity for air removal while simultaneously preventing micro-bubbles from adhering to surfaces or being drawn into the enclosure through the same apertures. The coating transforms the surface properties without altering the aperture size or shape.
Solution Approach 2:
The surface energy parameter of the internal enclosure surfaces is changed by applying a hydrophobic coating. This parameter change causes micro-bubbles to repel from the surfaces rather than adhere to them. The large apertures maintain their original dimensions for efficient air removal, while the modified surface parameter prevents micro-bubble ingress and adhesion.
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 solution effectively mitigates micro-bubble attachment, ensuring accurate and reliable DEF sensor readings by isolating the sensing volumes and preventing air bubbles from interfering with sensor operations.
Implementation Method 1
At least one porous membrane is assembled between the fluid port and the housing, the at least one porous membrane covering the first and second fluid apertures
Implementation Method 2
The first sensing volume comprises a vertically-oriented waveguide and is fluidly coupled to an exterior of the housing through the first fluid aperture
Implementation Method 3
These larger bubbles have higher buoyancy and typically rise easily in the liquid
Data Source
AI summary
A housing assembly for a fluid sensor assembly includes a housing having a first and second sensing volumes. A fluid port attached to the housing has a porous membrane covering first and second fluid apertures. The first sensing volume included a vertically-oriented waveguide and is fluidly coupled to an exterior of the housing through the first fluid aperture, where the first aperture port has an area smaller than an area of a cross-section of the waveguide. The second sensing volume is coupled to the exterior of the housing through the second fluid aperture, the second fluid aperture having an area larger than a cross-section of the second sensing volume. While the first sensing volume and the second sensing volume are both in fluid communication with an exterior of the housing, the fluid port and porous membrane internally isolate the first sensing volume from the second sensing volume.