Fuel Cell Humidity Control via High Frequency Resistance Feedback
Solution Overview
Problem
Fuel cells face challenges in controlling relative humidity, leading to performance limitations and potential damage from liquid water formation, especially when exposed to freezing conditions, due to difficulties in measuring and managing the humidity of gaseous reactant streams.
Innovation Solution
A model is developed to predict and maintain a desired relative humidity profile within the fuel cell stack by monitoring operating characteristics and using high frequency resistance in a closed-loop feedback system to adjust parameters such as temperature, stoichiometric quantity, and pressure drop, ensuring the membrane-electrode-assembly remains within an optimal humidified state.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the fuel cell is operated with MEAs humidified greater than 100% to prevent drying, then the MEA is protected from damage and drying, but liquid water forms that impedes gas diffusion and limits fuel cell performance
Solution Approach 1:
The patent changes the operating parameter from humidified greater than 100% to a controlled humidity range of 40-80%, optimizing the balance between MEA protection and performance by maintaining sufficient humidity without excessive water formation
Solution Approach 2:
The patent implements feedback control by measuring the actual humidity of the cathode reactant gas and using this measurement to adjust the humidification process, ensuring optimal humidity levels are maintained while preventing liquid water formation that would impede gas diffusion
2Reliability
If the fuel cell is operated with MEAs humidified greater than 100% to prevent drying, then the MEA is protected from damage, but liquid water acts as a flow blockage causing even higher fuel cell relative humidity and unstable performance
Solution Approach 1:
The patent changes the humidity parameter from uncontrolled supersaturation to a controlled range of 40-80%, preventing the positive feedback loop where liquid water blocks flow and causes even higher humidity, thereby maintaining stable performance
Solution Approach 2:
The patent uses feedback control to continuously monitor and adjust humidity levels, preventing the runaway effect where initial water formation leads to blocked flow and progressively higher humidity that destabilizes performance
3Reliability
If the fuel cell is operated with MEAs humidified greater than 100% to prevent drying, then the MEA is protected from damage, but liquid water formation causes significant damage when the fuel cell is shut down and exposed to freezing conditions
Solution Approach 1:
The patent changes the operating humidity parameter to a controlled range of 40-80% rather than humidified greater than 100%, eliminating the liquid water that would freeze and expand during shutdown, thereby preventing mechanical damage while still protecting the MEA through proper humidification control
Solution Approach 2:
The patent applies preliminary anti-action by controlling humidity during operation to prevent liquid water formation in the first place, thereby preemptively protecting against the harmful effect of freezing damage during shutdown rather than allowing water to form and then causing damage
4Reliability
If a water vapor transfer device is used to humidify the cathode reactant gas, then the cathode reactant gas is humidified to prevent MEA drying, but the operation of the WVT is difficult to characterize and the exact humidity is difficult to ascertain
Solution Approach 1:
The patent implements feedback control by measuring the actual humidity of the cathode reactant gas and using this measurement to adjust the humidification process, enabling precise control and accurate knowledge of the humidity level while still achieving the goal of preventing MEA drying
Solution Approach 2:
The patent replaces the difficult-to-characterize mechanical WVT operation with a measurement-based control approach, substituting direct mechanical humidification control with feedback from humidity measurements, thereby achieving precise and characterizable humidification
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
This approach allows for improved fuel cell performance by preventing liquid water formation, maintaining optimal humidity, and preventing damage from freezing, thereby enhancing operational stability and efficiency.
Implementation Method 1
Additionally, a high frequency resistance of the fuel cell can be used as a measure that is indicative of the humidity of the MEA within the fuel cell
Implementation Method 2
the inventors have developed a model of the relative humidity in a fuel cell as a function of the reaction progress within the fuel cell
Implementation Method 3
a water vapor transfer device (WVT) is utilized to humidify the cathode reactant gas prior to entering into the fuel cell
Implementation Method 4
the formation of liquid water impedes the diffusion of gas to the MEAs, thereby limiting their performance
Data Source
AI summary
A model uses various operating characteristics of a fuel cell to predict the relative humidity profile that is occurring within the fuel cell as a function of the reaction progress. The model is used to predict the relative humidity profile that will occur in response to changes to one or more of the operating characteristics of the fuel cell. A high frequency resistance of the fuel cell can also be used as a measure that is indicative of the humidity within the fuel cell. The model and/or the high frequency resistance can be used in a closed-loop feedback system to control the operation of the fuel cell to maintain the humidification of the MEA and fuel cells within a desired range to achieve a desired fuel cell performance.