Fuel Cell Stack Shutdown Thermal Mass Insulation
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Solution Overview
Problem
Cyclic use of solid polymer electrolyte fuel cell stacks, involving frequent shutdown and restart, leads to issues with water distribution and accumulation, which can cause reactant blockage, freezing damage, and reduced conductivity, necessitating improved methods for water management during shutdown.
Innovation Solution
Maintaining a temperature difference across the fuel cell stack during shutdown by using a thermal mass and insulation to concentrate water in selected flow fields, ensuring adequate conductivity while preventing freezing, through controlled cooling and thermal gradients.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the fuel cell stack is shutdown and allowed to cool without thermal management, then the cooling process is simple and fast, but water accumulates in the cells and may freeze causing permanent damage
Solution Approach 1:
The patent applies preliminary action by pre-positioning a thermal mass (such as a metal block or heat storage material) in thermal contact with the fuel cell stack before shutdown occurs. This thermal mass is prepared in advance to provide controlled cooling and prevent water freezing during subsequent shutdown periods, eliminating the need for active thermal management systems during storage.
Solution Approach 2:
The patent uses a thermal mass as an intermediary between the fuel cell stack and the ambient environment. This intermediary component mediates the heat transfer process, providing controlled cooling that prevents water freezing while avoiding the complexity of active thermal management systems. The thermal mass absorbs and releases heat as needed during the shutdown period.
2Reliability
If water is removed from the membrane electrolyte during shutdown, then freezing damage is prevented, but the conductivity of the membrane electrolyte is substantially reduced
Solution Approach 1:
The patent applies local quality by creating a temperature gradient across the fuel cell stack during shutdown, with different regions experiencing different temperatures. The thermal mass maintains certain regions warmer to prevent water freezing, while other regions can cool down to facilitate water removal. This spatial variation in temperature allows simultaneous water management and conductivity preservation in different locations of the stack.
Solution Approach 2:
The patent changes the temperature parameter during shutdown by introducing a thermal mass that controls the cooling rate. By adjusting the temperature profile through the thermal mass, the patent optimizes water distribution - allowing sufficient water to remain in the membrane electrolyte for conductivity while preventing excessive water accumulation that would cause freezing damage.
3Speed
If rapid cooling is applied during shutdown, then the shutdown process is fast and efficient, but water distribution becomes undesirable and may lead to cell damage
Solution Approach 1:
The patent applies dynamics by making the cooling rate adjustable and adaptive during shutdown. The thermal mass provides a controlled, dynamic cooling process that can be optimized based on operating conditions. Rather than fixed rapid or slow cooling, the system dynamically adjusts heat transfer to achieve desirable water distribution while maintaining fast shutdown performance.
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 achieves a desirable water distribution, maintaining membrane conductivity and preventing freezing damage, thereby enhancing the performance and durability of the fuel cell stack during storage and restart.
Implementation Method 1
maintaining a temperature difference across the fuel cell stack during shutdown by using a thermal mass and insulation
Implementation Method 2
water is transferred from the membrane electrode assemblies to one of the anode and cathode flow fields of the fuel cells during shutdown
Data Source
AI summary
Improved water distribution can be obtained within the cells of a fuel cell series stack by maintaining a suitable temperature difference between the cathode and anode sides of each cell in the stack during shutdown. This can be accomplished by thermally insulating the “hot” end and sides of the stack and by providing a thermal mass adjacent to the “hot” end.