LH2 Thermal Pumping With Gas Accumulators for Fuel Cell Pressure
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional fossil fuel-powered aircraft engines emit significant CO2 and non-CO2 greenhouse gases, and the storage of liquid hydrogen for hydrogen fuel cells poses a challenge due to the weight and pressure requirements for aircraft applications.
Innovation Solution
A liquid hydrogen storage system comprising a primary tank for ambient pressure storage and small, high-pressure gas accumulator tanks with a thermal pumping system to raise the pressure of hydrogen gas for fuel cell feed, utilizing a cooling and heating interface to maintain a consistent 5-10 bar pressure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If liquid hydrogen is stored in lightweight composite cryogenic storage dewar structures at close to ambient pressure, then the mass fraction of hydrogen is improved (up to 40%), but the pressure is insufficient for direct fuel cell operation which requires 5-10 bar gas pressure
Solution Approach 1:
The hydrogen storage system is divided into two separate tanks: a primary lightweight composite dewar for ambient pressure storage and a secondary high-pressure accumulator tank for fuel cell feed. This segmentation allows each tank to be optimized for its specific function, resolving the contradiction between weight and pressure requirements.
Solution Approach 2:
A thermal pumping system acts as an intermediary mechanism between the primary and secondary tanks. This system uses thermal expansion and contraction of liquid hydrogen to automatically transfer and pressurize hydrogen without requiring heavy mechanical compressors, thereby maintaining the weight advantage while achieving the required pressure.
2Stress or pressure
If LH2 storage tanks are designed to operate at 5-10 bar pressure, then the pressure requirement for fuel cell operation is met, but the tank weight increases by 2-3 times compared to ambient pressure tanks
Solution Approach 1:
The system separates the high-pressure function into a small secondary accumulator tank that only needs to hold enough hydrogen for immediate fuel cell operation, rather than the entire hydrogen supply. This segmentation allows the high-pressure tank to remain lightweight while still meeting pressure requirements.
Solution Approach 2:
The thermal pumping system uses the natural thermal properties of liquid hydrogen (expansion when heated, contraction when cooled) to automatically pressurize and transfer hydrogen to the accumulator tank without external energy input or heavy mechanical equipment, enabling the system to serve itself.
3Device complexity
If a single GAT is used for thermal pumping, then the system complexity is reduced, but the hydrogen supply to the fuel cell is interrupted during the cooling and heating cycles
Solution Approach 1:
The single GAT is divided into multiple parallel GATs (typically two or three) that operate in sequence. While one GAT is being cooled and filled with liquid hydrogen, another GAT is being heated and delivering pressurized hydrogen to the fuel cell. This segmentation of the thermal pumping function ensures continuous supply.
Solution Approach 2:
The multiple GATs operate in a periodic cycle where each alternates between cooling/filling and heating/discharging phases. This periodic operation of multiple units creates a continuous flow of pressurized hydrogen to the fuel cell, eliminating interruptions while maintaining relatively simple individual GAT designs.
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 system achieves a superior mass fraction and uninterrupted hydrogen supply to fuel cells, reducing the weight burden and thermal rejection requirements of aircraft systems while minimizing emissions.
Implementation Method 1
Cooling the GAT lowers the temperature within the GAT and creates a vacuum in the GAT
Implementation Method 2
Heating the GAT increases the pressure in the tank due both to evaporation of the LH2 into H2 gas and thermodynamic gas pressure
Implementation Method 3
Heating the GAT increases the pressure in the tank
Implementation Method 4
An increased pressure, typically 5-10 bar, is achieved and maintained by a thermal pumping scheme utilizing heat flow within the GAT
Data Source
AI summary
A liquid hydrogen (LH2) fuel storage system for a fuel cell-powered vehicle, and method includes a main LH2 storage fuel tank configured for close to ambient pressure storage of LH2, and one or more gas accumulator tanks (GATs) smaller than the main LH2 storage fuel tank and configured for elevated pressure storage of LH2 and for feeding pressurized LH2 to the fuel cell, wherein the one or more GATs each have a cooling interface configured to cool the GAT employing LH2 from the main LH2 storage fuel tank, and a heating interface configured to heat contents of the GAT with warm working fluid from the fuel cell-powered vehicle whereby to raise pressure of the LH2 in the GAT to a working pressure for feeding the LH2 to the fuel cell.