Fuel Cell End Plate Assembly with Flexible Backbone
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Solution Overview
Problem
Fuel cell stacks with high thermal capacity metallic pressure plates face challenges in quickly raising end cell temperatures during startup from subfreezing conditions, leading to water freezing and flooding, which retards reactant fluid flow and causes negative voltage, degrading performance and stability, especially in PEM electrolyte-based systems undergoing frequent start-stop cycles.
Innovation Solution
An integrated end plate assembly with a non-conductive, composite pressure plate and a flexible stainless steel backbone that redistributes clamping load and allows for expansion within operating limits, minimizing thermal mass and preventing excessive expansion, using a backbone-support plane and deflection plane configuration to act as a cantilevered beam for load follow-up.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If large, conductive metal pressure plates are used to provide load follow-up system, then the stack can accommodate expansion within operating dynamic limits, but the thermal capacity becomes excessively high causing slow heating of end cells during startup
Solution Approach 1:
The pressure plate is segmented into a rigid backbone portion and a flexible membrane portion. The backbone provides structural support and load distribution, while the membrane provides flexibility for expansion accommodation. This segmentation allows the pressure plate to have both mechanical stability for load control and low thermal mass for rapid heating.
Solution Approach 2:
The pressure plate uses composite construction with a rigid backbone (stainless steel or other rigid material) and a flexible membrane (elastomeric material or metal alloy with different properties). This composite structure combines the advantages of both materials: the rigid backbone provides structural integrity and load distribution, while the flexible membrane provides thermal responsiveness and expansion accommodation.
2Reliability
If heavy metallic pressure plates are used for load follow-up system, then constant minimum load can be applied to seal compression seals, but the weight and thermal mass increase significantly
Solution Approach 1:
The pressure plate is divided into a rigid backbone that provides structural support and load distribution, and a flexible membrane that provides sealing contact. This segmentation allows the use of lighter materials while maintaining both seal compression reliability and reduced weight.
Solution Approach 2:
The flexible membrane portion of the pressure plate acts as a thin film that can deform to accommodate stack expansion while maintaining constant contact pressure on the compression seals. This thin film structure significantly reduces weight and thermal mass compared to traditional solid metal pressure plates.
3Adaptability or versatility
If the pressure plate is made flexible to permit expansion, then the stack can accommodate dimensional changes, but the load distribution and sealing effectiveness may be compromised
Solution Approach 1:
The pressure plate is segmented into a rigid backbone and flexible membrane. The rigid backbone maintains structural integrity and load distribution capability, while the flexible membrane provides expansion accommodation. Each segment performs its specialized function optimally.
Solution Approach 2:
The rigid backbone and flexible membrane are merged into a single integrated pressure plate structure. This merging allows the structure to simultaneously provide both load distribution (through the rigid backbone) and expansion accommodation (through the flexible membrane) without requiring separate 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
This solution efficiently raises end cell temperatures, reduces thermal losses, and maintains stable operation by allowing limited expansion while preventing excessive load changes, thus enhancing the performance and long-term stability of the fuel cell stack.
Implementation Method 1
The backbone has adequate flexibility to permit expansion of the fuel cell stack within operating dynamic limits of the stack and the backbone has adequate flexural strength to prohibit expansion of the fuel cell stack beyond the operating dynamic limits of the stack
Implementation Method 2
The pressure plate is made of an electrically non-conductive, non-metallic composite material... This solution efficiently raises end cell temperatures, reduces thermal losses
Implementation Method 3
During such a 'bootstrap' start up, the fuel cells 14 that are in a central region of the stack 10 quickly rise in temperature compared to the end cells 16, 18 that are adjacent opposed ends of the stack 10. The end cells 16, 18 heat up more slowly because heat generated by the end cells 16, 18 is rapidly conducted into the large, conductive metallic pressure plates 20, 22.
Data Source
AI summary
A fuel cell stack (30) includes an integrated end plate assembly having a current collector (40) secured adjacent and end cell (36) of the stack, a pressure plate (42) secured adjacent the current collector (40), and a backbone (60) secured within a backbone-support plane (44) defined within the plate (42). Tie rod ends (62, 64, 66, 68) of the backbone (60) extend over a gap (84) defined between the backbone-support plane (44) and a deflection plane (50) defined within the pressure plate (42) so that the tie rod ends deflect within the gap (84) upon tightening of tie rods (78, 80). Deflection of the backbone enables the backbone (60) to permit limited expansion of the fuel cell stack (30) during operation, and the backbone (60) has adequate flexural strength to prohibit expansion of the stack (30) beyond operating dynamic limits of the stack (30).