Control system for a sealed coolant flow field fuel cell power plant having a water reservoir
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Solution Overview
Problem
Fuel cell power plants face challenges in maintaining optimal relative humidity of reactant streams, leading to issues such as flooding, drying of the proton exchange membrane, and potential combustion risks due to inadequate control of water content and humidity levels.
Innovation Solution
A control system that includes a water reservoir and relative-humidity sensors and controllers to manage water movement between the reservoir and reactant streams, ensuring optimal humidity levels by adjusting flow rates, pressures, and coolant temperatures based on power output, thereby maintaining relative humidity above 1.00 during high power demands and below 1.00 during low power output.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the relative humidity of the reactant stream is increased to prevent PEM drying, then moisture transfer to the reactant stream is improved, but water accumulation as liquid occurs causing flooding
Solution Approach 1:
A hydrophobic porous layer is introduced as an intermediary between the PEM and the reactant stream. This layer acts as a mediator that releases moisture to the reactant stream while preventing liquid water accumulation, thus resolving the contradiction between maintaining PEM moisture and preventing flooding.
Solution Approach 2:
A hydrophobic porous layer with specific pore structure is used to control moisture transport. The porous structure allows vapor phase moisture transfer to maintain PEM hydration while the hydrophobic nature prevents liquid water penetration, solving the flooding issue while maintaining reliability.
2Object-generated harmful factors
If the relative humidity of the reactant stream is decreased to prevent flooding, then liquid water accumulation is reduced, but moisture within the PEM evaporates causing drying
Solution Approach 1:
The hydrophobic porous layer serves as a protective intermediary that supplies moisture to the reactant stream independently of its relative humidity setting. This allows the system to operate at lower relative humidity to prevent flooding while the layer continuously provides moisture to prevent PEM drying.
Solution Approach 2:
The system changes the moisture delivery mechanism from direct reactant stream humidity control to a controlled release from the hydrophobic porous layer. This parameter change allows decoupling of flooding prevention from PEM moisture maintenance, enabling operation at lower relative humidity without causing PEM drying.
3Temperature
If a sealed coolant flow field is used to remove heat, then thermal exchange efficiency is improved, but control of reactant stream humidity becomes more difficult
Solution Approach 1:
The hydrophobic porous layer acts as an intermediary moisture management system that operates independently of the sealed coolant flow field. This separates the thermal management function (coolant flow field) from the humidity control function (porous layer), simplifying overall system control while maintaining both heat removal efficiency and humidity control.
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 solution effectively maintains optimal relative humidity, preventing flooding and membrane drying, enhancing fuel cell performance, reducing parasitic power demand, and allowing for higher coolant exit temperatures, which decreases cooling demands and radiator size requirements.
Implementation Method 1
water in the form of water vapor moves from the water reservoir into the reactant stream
Implementation Method 2
water generated at the cathode catalyst during operation of the cell will accumulate as a liquid instead of evaporating into the reactant stream
Implementation Method 3
a coolant system that directs a coolant fluid through a sealed coolant flow field in thermal exchange with the MEA to remove heat generated during operation of the fuel cells
Data Source
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AI summary
The system (10) controls at least one of a pressure of the reactant streams (16A, 16B) within at least one of an anode flow field (28) and a cathode flow field (36), a flow rate of the reactant streams (16A, 16B) flowing through the anode and/or cathode flow fields (26, 28), a temperature of a coolant fluid passing through a sealed coolant flow field (44), and a flow rate of the coolant fluid; so that water (14) moves from a water reservoir (18A, 18B) into the reactant stream (16A, 16B) whenever power generated by the fuel cell (20) is between about 80% and about 100% of a maximum fuel cell power output, and so that water (14) moves from the reactant stream (16A, 16B) into the water reservoir (18A, 18B) whenever fuel cell power is less than about 75% of the maximum power output.