Fuel Cell Air Compressor Hub Venting for Axial Force Balance
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Solution Overview
Problem
Turbomachines used to supply air to fuel cell systems face inefficiencies due to high axial forces and significant power losses in large axial bearings, as well as cooling air requirements that divert resources away from the fuel cell process, reducing overall efficiency and increasing complexity.
Innovation Solution
The turbomachine design features a hub section with air channels that balance axial forces on the compressor wheel, reducing power losses and cooling air needs, while using air ducts to cool bearings and the electric motor, and incorporating an internally ventilated axial bearing disk to recover energy by increasing air pressure before the turbine wheel.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the maximum speed of the electric motor is limited to between 100,000 and 125,000 rpm for control and strength reasons, then the system is more reliable and easier to control, but the achievable compressor outlet pressure decreases and requires comparatively large outer diameters of the compressor wheel
Solution Approach 1:
The patent introduces a new dimension by forming air ducts in the hub section that connect the compressor inlet to the rear side of the compressor wheel, creating a pressure balancing system. This allows pressure equalization in the axial direction, enabling the use of lower motor speeds while maintaining required outlet pressures through the additional pressure management dimension.
2Stress or pressure
If compressor wheels with comparatively large outer diameters are used to achieve required pressures at limited speeds, then the required compressor outlet pressure is achieved, but large axial forces act on the compressor wheel requiring correspondingly large axial bearings
Solution Approach 1:
The patent applies the counterweight principle by introducing air pressure from the compressor inlet through hub air ducts to the rear side of the compressor wheel. This creates a counteracting pressure force that balances the axial thrust force generated by compression, effectively reducing the net axial load on the bearings.
3Strength
If large axial bearings are used to support the high axial forces, then the mechanical strength is sufficient, but the power loss increases significantly with the axial bearings accounting for 2/3 share of total bearing losses
Solution Approach 1:
By balancing the axial forces through pressure equalization in the hub air ducts, the required axial bearing size is reduced. Smaller bearings with lower friction surfaces result in significantly reduced power losses, addressing the energy efficiency problem while maintaining sufficient mechanical support.
4Reliability
If foil air bearings are used to keep the system oil-free, then the fuel cell system remains contamination-free, but air friction losses occur requiring additional cooling air that reduces overall system efficiency
Solution Approach 1:
The axial force balance reduces the load on foil air bearings, allowing them to operate with smaller clearance and lower friction. This reduces the cooling air requirement, thereby improving overall system efficiency while maintaining the oil-free operation necessary for fuel cell contamination prevention.
5Temperature
If additional air is diverted for cooling the bearings, then the bearing temperature is controlled, but the diverted air volume is no longer available for the fuel cell process reducing turbomachine efficiency
Solution Approach 1:
By reducing axial bearing sizes through force balancing, the cooling air requirement is minimized. This allows more air to remain available for the fuel cell process, improving overall productivity and efficiency while still maintaining adequate bearing temperature control.
6Temperature
If additional lines and cooling systems are provided to supply cooling air to the turbomachine, then the bearing cooling requirement is met, but the device complexity increases
Solution Approach 1:
The axial force balancing reduces bearing size and cooling requirements, simplifying the cooling system. The same hub air ducts that balance axial forces also serve as cooling air passages, eliminating the need for separate cooling lines and reducing overall system complexity.
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 design enhances turbomachine efficiency by minimizing power losses, reducing cooling air requirements, and improving robustness against external accelerations, while also recovering energy through optimized air pressure management.
Implementation Method 1
at least one air duct is formed in the hub section, via which air duct a compressor inlet is connected to an annular space on the side of the compressor wheel facing away from the compressor inlet, so that essentially the same air pressure is present on both sides of the compressor wheel. Consequently, axial forces act on the compressor wheel that completely or almost completely cancel each other out.
Implementation Method 2
The air supplied via the at least one additional air duct can be used to cool the at least one bearing. The air supplied via the at least one additional air duct is also routed via an annular gap between the shaft and a winding of the electric motor surrounding the shaft, which allows the air supplied via the at least one additional air duct to be used to cool the electric motor.
Data Source
Figure 1
Figure 2
AI summary
The invention relates to a turbomachine (1) for supplying air to a fuel cell system, comprising at least one compressor wheel (3) conjointly connected to a shaft (2), and an electric motor (4) for driving the shaft (2), the compressor wheel (3) being connected via a hub portion (5) to a preferably hollow-cylinder-shaped shaft portion (6) of the shaft (2). According to the invention, at least one air channel (7, 8) is formed in the hub portion (5), by means of which air channel a compressor inlet (9) is connected to an annular space (10) on the side of the compressor wheel (3) facing away from the compressor inlet (9) such that substantially the same air pressure is present on both sides of the compressor wheel (3). The invention further relates to a method for operating a turbomachine (1).