Fuel Cell Cooling Valve Switching for Lighter Heat Rejection
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Solution Overview
Problem
Fuel cell systems face challenges in efficiently managing heat rejection, particularly in aviation settings, leading to larger and heavier heat exchangers and coolant volumes, which increase drag and aircraft size, and evaporative cooling systems face inefficiencies due to limited water evaporation and low air pressure issues.
Innovation Solution
A cooling sub-system with a multi-outlet valve arrangement and controller that switches between closed-loop and open-vented modes based on heat duty balance, allowing the coolant HEX to be sized for average conditions, reducing the need for a large HEX and coolant volume.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a HEX with large heat transfer area is provided to reject heat from coolant in Hot Day MTOW conditions, then cooling performance is sufficient, but the HEX becomes heavy, expensive and generates substantial drag
Solution Approach 1:
The patent applies dynamics by making the cooling system configuration changeable through a valve network that can switch between closed-loop and open-vented modes. The HEX size is optimized for average conditions rather than peak hot day conditions, and the valve network dynamically adjusts the cooling configuration based on real-time operating conditions. This allows the system to use a smaller HEX for normal operations while providing adequate cooling capacity when needed by switching to open-vented mode with direct coolant exhaust.
2Temperature
If a HEX with large heat transfer area is provided to reject heat from coolant in Hot Day MTOW conditions, then cooling performance is sufficient, but drag increases
Solution Approach 1:
The system dynamically adjusts between closed-loop and open-vented configurations using a valve network. For normal operations, a smaller HEX is used reducing drag. During hot day MTOW conditions, the system switches to open-vented mode where coolant is directly exhausted without requiring a large HEX, thereby minimizing drag while maintaining adequate cooling performance.
3Temperature
If large volumes of coolant are used to provide sufficient cooling, then cooling capacity is sufficient, but the coolant occupies more space and increases aircraft mass
Solution Approach 1:
The patent employs dynamic configuration switching between closed-loop and open-vented modes. In open-vented mode, the system does not require large coolant volumes to be circulated through a large HEX, as heat is rejected through direct exhaust. This reduces the coolant volume needed while maintaining sufficient cooling capacity during high-power operations.
4Temperature
If evaporative cooling is used to cool the FC stack, then cooling is achieved through water evaporation, but the amount of water that can be evaporated is capped based on water saturation point of air
Solution Approach 1:
The patent changes the operating parameters of the cooling system by switching between closed-loop and open-vented modes. In open-vented mode, the system bypasses the evaporation limitation by directly exhausting coolant to atmosphere, allowing heat rejection without being constrained by air saturation points. This enables effective cooling even when evaporation capacity is reached.
5Quantity of substance
If low air pressure is used to maximize water evaporation, then evaporation efficiency improves, but reaction rates within the FC decrease negatively impacting efficiency and performance
Solution Approach 1:
The system dynamically changes operating parameters by switching between closed-loop and open-vented configurations. This allows the system to achieve effective cooling without creating low air pressure conditions that would harm FC reaction rates. The valve network enables heat rejection through direct exhaust rather than relying on pressure-reduced evaporation, maintaining both cooling effectiveness and FC 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 configuration enables efficient heat management with a smaller, lighter coolant HEX, improving aircraft efficiency and reducing environmental impact while maintaining performance across varying power and ambient conditions.
Implementation Method 1
a coolant HEX; a coolant exhaust... to remove heat from the coolant
Implementation Method 2
the HEX acting as a radiator that rejects the heat to atmosphere
Implementation Method 3
cooling of the FC stack is achieved through transfer of heat energy from the FC stack to the water to effect evaporation
Implementation Method 4
The water vapour contained in the FC stack outlet is then condensed to separate out the water
Data Source
Figure 1
Figure 2
AI summary
A system (1) comprises a fuel cell stack (100), a coolant fluid tank (305), a heat-exchanger (320), an exhaust (325), a controller (395) and a valve (315) having an inlet (316) and first and second outlets (317, 318). Coolant fluid is conveyed from the tank to the stack on a feed line (340) and from the stack to the inlet on a discharge line (345). The controller controls the valve such that coolant fluid exits either at the first outlet, such that coolant fluid passes back to the tank on a recycle line (330) via the heat-exchanger, or at the second outlet, such that coolant fluid passes to the exhaust and leaves the system. The controller is arranged to select the first or second outlet according to the heat duty required across the stack and that achievable across the heat-exchanger. The gravimetric power density of the system is higher than that of an equivalent system which implements only closed-loop cooling.