Evaporative Fuel Cell Cooling for High-Load Aircraft Heat Rejection
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Solution Overview
Problem
Existing cooling systems for fuel cells in vehicles, particularly in aircraft, face challenges in efficiently removing waste heat during high load conditions without increasing drag or adding unnecessary weight and bulk, especially during take-off and climb.
Innovation Solution
A coolant circuit with an evaporative cooling device that uses a thermally conductive conduit and a working fluid to evaporatively cool the coolant, combined with a vacuum pump and evacuation system to manage pressure, allowing for efficient heat removal without increasing drag by varying coolant flow through the evaporative cooling device based on load conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If an air-cooled heat exchanger is positioned in the ambient airflow path to remove waste heat during high load conditions, then the waste heat dissipation capability is improved, but the drag experienced by the aircraft increases
Solution Approach 1:
The cooling system is divided into multiple independent circuits: a primary coolant circuit that circulates through the fuel cell, a secondary evaporative cooling circuit that activates during high load conditions, and a tertiary ram air cooling circuit. This segmentation allows the system to engage only the necessary cooling level for current operating conditions, avoiding continuous drag from large heat exchangers.
Solution Approach 2:
The system dynamically adjusts cooling capacity by varying coolant flow rates through the evaporative cooling device based on load conditions. During high load events, the coolant flow rate increases to maximize evaporative cooling effectiveness. During normal operation, the flow rate decreases or stops, eliminating unnecessary drag while maintaining adequate cooling capacity when needed.
2Temperature
If the volume of the air-cooled heat exchanger is increased to accommodate high load cooling requirements, then the waste heat dissipation capability during take-off and climb is improved, but the weight and bulk of the aircraft increases
Solution Approach 1:
The evaporative cooling device is integrated within the existing coolant circuit infrastructure, with the thermally conductive conduit and evaporation chamber nested within the fuel cell assembly structure. The coolant passageway is defined within existing structural components, eliminating the need for separate, bulky heat exchanger housings and reducing overall system weight.
Solution Approach 2:
The system changes the cooling mechanism from passive conduction through solid heat exchanger surfaces to active evaporation of working fluid. This parameter change allows for high cooling capacity with minimal mass, as the latent heat of vaporization provides intense cooling without requiring large thermal mass or extensive surface area.
3Temperature
If ambient air is directed through the aircraft to cool the fuel cell, then the cooling effectiveness is improved, but the energy efficiency of the vehicle decreases due to increased drag
Solution Approach 1:
The evaporative cooling device utilizes the coolant itself as the working fluid, which circulates through the fuel cell and absorbs heat directly at the source. The system self-regulates by allowing the coolant temperature and flow rate to naturally dictate the cooling demand, eliminating the need for separate fans or pumps that would consume additional energy.
Solution Approach 2:
The system exploits the phase transition of the working fluid from liquid to vapor during evaporation. This phase change absorbs large amounts of latent heat from the coolant, providing highly effective cooling without requiring mechanical work or external energy input, thereby maintaining vehicle energy efficiency.
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
Effectively removes waste heat from fuel cells during high load events while minimizing drag and weight, enhancing energy efficiency by utilizing latent heat transfer and phase change materials.
Implementation Method 1
the evaporative cooling device is configured to evaporatively cool the coolant flowing through the coolant channel by promoting evaporation of the working fluid from the outer surface of the thermally conductive conduit
Implementation Method 2
enhancing energy efficiency by utilizing latent heat transfer and phase change materials
Implementation Method 3
The outer surface of the thermally conductive conduit is exposed to an environment within the evaporation chamber
Implementation Method 4
combined with a vacuum pump and evacuation system to manage pressure
Data Source
AI summary
A cooling system for a fuel cell onboard a vehicle includes a coolant circuit and an evaporative cooling device including an evaporation chamber and a thermally conductive conduit extending through the evaporation chamber. The coolant circuit is configured to circulate a coolant through the coolant circuit and through a portion of the fuel cell. The thermally conductive conduit has an inner surface that at least partially defines a coolant channel in fluid communication with the coolant circuit and an opposite outer surface exposed to an environment within the evaporation chamber. When a working fluid is applied to the outer surface of the thermally conductive conduit within the evaporation chamber. the evaporative cooling device is configured to evaporatively cool the coolant flowing through the coolant channel by promoting evaporation of the working fluid from the outer surface of the thermally conductive conduit.