Pressure-Based Liquid Level Detection for Fuel Cell Stack Assembly
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Solution Overview
Problem
Existing liquid level detection systems for fuel cell power plants are inadequate during start-up and shut-down phases, as they rely on voltage-based measurements that are not available during these times, and mechanical sensors are prone to failure and inaccuracies, especially under frozen conditions.
Innovation Solution
A pressure-based liquid level detection system that uses a single conventional pressure sensor to measure fluid pressure in the fuel cell stack assembly, providing a signal indicative of liquid level and controlling liquid flow or level, even when there is no detectable voltage, and operates safely in frozen conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If voltage-based liquid level detection is used, then liquid level can be detected during steady-state operation, but it cannot detect liquid level during start-up and shut-down when voltage is not available
Solution Approach 1:
The patent introduces a pressure sensor as an intermediary measurement tool that indirectly detects liquid level by measuring pressure changes in the coolant system. This pressure-based detection serves as a mediator that works during all operational phases including start-up and shut-down when voltage-based direct detection fails.
Solution Approach 2:
The patent replaces the electrical voltage-based detection system with a pressure-based mechanical detection system. The pressure sensor measures pressure variations caused by liquid level changes, substituting the electrical measurement approach with a mechanical/physical approach that operates independently of system voltage.
2Measurement precision
If float type sensors are used, then liquid level can be measured, but the mechanical parts are subject to breakage and give false readings under frozen conditions
Solution Approach 1:
The patent replaces the mechanical float-type sensor system with a pressure sensor-based system. This substitution eliminates mechanical moving parts that are prone to breakage and freezing issues, using instead a pressure measurement approach that is more reliable under extreme conditions including frozen states.
Solution Approach 2:
The patent changes the measurement parameter from direct mechanical position (float height) to pressure variation. By monitoring pressure changes in the coolant system that correlate with liquid level, the system achieves measurement without the mechanical limitations of float-type sensors.
3Reliability
If conductivity sensors are used, then liquid presence can be detected, but external power sources are required increasing system complexity and weight
Solution Approach 1:
The patent replaces the electrical conductivity sensor system that requires external power with a pressure sensor system. This substitution eliminates the need for external batteries or wire taps, using instead pressure measurements that provide liquid presence detection without additional power requirements or system complexity.
Solution Approach 2:
The pressure sensor system utilizes the existing pressure variations in the coolant system itself to provide detection information. The system serves itself by using the natural pressure changes caused by liquid level variations, without requiring external power sources or additional active components.
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
Enables effective liquid level monitoring and control throughout the entire operating spectrum, including start-up, shut-down, and steady-state operations, ensuring proper thermal management and preventing issues like membrane dry-out and reactant blockage.
Implementation Method 1
uses a pressure sensor to measure fluid pressure in the fuel cell stack assembly
Data Source
AI summary
A fluid detection system and method for a fuel cell power plant is disclosed having a pressure sensor (61, 161) positioned in a fuel cell stack assembly (10) to measure pressure of fluid/liquid in a fluid/liquid flow path (40, 42, 44) therein and to provide a pressure-based signal (90, 63). The pressure-based signal (90, 63) is used to control a liquid management arrangement (53) at least during start-up and shut-down of the cell stack assembly (10) to regulate water level. The liquid management arrangement (53) may include means (50, 51) for controllably applying and releasing a vacuum to a water manifold (44, 54; 100) of the cell stack assembly (10) to regulate water flow and level therein. The pressure-based control of water level may extend across the entire operating range of the cell stack assembly (10), or may be complemented during steady state operation by voltage-based sensors (66, 166).