PEM Fuel Cell Stack Thermal Regulation Using External Two-Phase Cooling
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Solution Overview
Problem
High temperature PEM fuel cell stacks face challenges in maintaining uniform temperature, as existing cooling systems complicate design, increase risk of leaks, and require complex seals due to the use of specialized heat transfer fluids, which can be hazardous and increase the risk of internal shorting.
Innovation Solution
A novel cooling system using thermal-masses with integrated fluidic-circuits that maintain a two-phase flow of working-fluids, allowing for efficient heat transfer through sensible and latent heat exchange, eliminating the need for internal cooling elements and simplifying bipolar plate design.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If specialized heat transfer fluids (e.g., Dowtherm, Fluorinert) are used for thermal regulation, then the stack can operate at high temperatures (120-200°C), but sealing reliability deteriorates due to material compatibility issues and fluid leakage
Solution Approach 1:
The patent changes the working fluid from specialized high-temperature fluids (Dowtherm, Fluorinert) to water or water-organic mixtures. This parameter change resolves the sealing reliability issue while maintaining thermal regulation capability, as water-based fluids are compatible with standard sealing materials and do not exhibit problematic wetting/wicking behavior.
Solution Approach 2:
The patent utilizes phase change (vaporization) of water as the working fluid to enhance heat transfer efficiency. The phase transition occurs in the heat exchanger where liquid water vaporizes, absorbing latent heat, and the vapor is then condensed back to liquid. This phase change mechanism provides superior cooling capacity compared to single-phase fluids, effectively managing the high temperature operation without requiring specialized fluids that compromise sealing reliability.
2Temperature
If internal coolant paths are routed through the bipolar plates, then thermal regulation is achieved, but device complexity increases due to the need to seal three species (reactants and coolant)
Solution Approach 1:
The patent separates the thermal regulation function from the reactant flow paths by implementing external coolant circulation. The bipolar plates maintain their primary function of housing reactant channels, while a separate external cooling system with independently sealed coolant loops manages thermal regulation. This segmentation eliminates the need to seal three species simultaneously, reducing sealing complexity from three separate sealing requirements to independent single-species sealing systems.
Solution Approach 2:
The patent introduces external heat exchangers as intermediary components that couple the fuel cell stack to the coolant circulation system. These heat exchangers act as mediators, transferring thermal energy between the stack and coolant without requiring direct integration of coolant paths into the bipolar plates. This intermediary approach simplifies the sealing architecture by decoupling the reactant and coolant systems.
3Loss of energy
If phase change cooling is implemented inside the stack, then cooling efficiency is improved, but device complexity increases due to high internal pressure requirements
Solution Approach 1:
The patent moves the phase change process from the internal dimension (inside the stack) to the external dimension (in external heat exchangers). The coolant undergoes phase change in separate cooling loops outside the stack, allowing the stack itself to operate at its optimal temperature and pressure conditions without being subjected to the high pressures required for internal vaporization. This dimensional relocation preserves cooling efficiency while eliminating pressure containment complexity.
4Loss of energy
If conductive particles are entrained in the coolant flow, then heat transfer is enhanced, but reliability deteriorates due to internal shorting risk
Solution Approach 1:
The patent employs disposable or easily replaceable filters in the external coolant circulation system to remove conductive particles from the water-based coolant. These filters are positioned in the coolant lines between the stack and heat exchangers, capturing any particles that may have shed from stack components. By using simple, maintainable filtration rather than complex preventive designs, the system maintains heat transfer efficiency while eliminating internal shorting risk, accepting the need for periodic filter maintenance as a trade-off.
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 system provides high-capacity heat removal, reduces system complexity and weight, minimizes parasitic power loss, and prevents leaks, while maintaining consistent stack temperature.
Implementation Method 1
heat transfer through sensible and latent heat exchange
Implementation Method 2
heat transfer through sensible and latent heat exchange
Implementation Method 3
heat transfer through vaporization of the water could provide an advantage because of the efficiency of cooling associated with the phase change
Implementation Method 4
The flow is routed from the thermal-mass to a heat exchanger where vapor is condensed to liquid and where the temperature of the working-fluid may decrease
Data Source
AI summary
The present invention provides fuel cell stacks comprising effective means to maintain the fuel cell stacks at a constant temperature using plates mated to at least one face of the stack and in contact with the edges of the repeat and non-repeat layers while making use of the phase change of working-fluids such as water or water-organic species mixtures for heat transfer. Also provided are processes for maintaining said fuel cell stacks at a constant temperature by adjusting the flow rate and pressure of the cooling fluid so that both liquid and vapor are present at the same time.