Thermal and Water Management

Water is generated at the cathode reaction and must be removed from the fuel cell to prevent blockage of reaction sites. In the case of PEM fuel cell, proper humidification of the membrane is necessary to improve proton transfer (and efficiency), so commonly exhaust gas water is recycled to inlet air and hydrogen streams to carry water to the membrane. Thus, water management is very important in PEM fuel cells. The water management system in PEM fuel cells will contain a humidification system for both air and hydrogen streams. 

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FCS water management is the key factor for an efficient and reliable operation of a PEMFC stack. Membrane hydration control and water balance for a durable operation of FCS are the main objectives of this sub-system, whose design and control issues, strictly connected to thermal management but also to reactant subsystem components, are discussed in Sect. 4.5. The possibility of interactions between the wet and warm cathode outlet stream and the components of thermal and water management sub-systems is also discussed. 

The key parameters to be controlled in this sub-system are air mass flow rate and pressure. Therefore, this section is focused on the characteristics of devices capable to realize useful pressure and flow rate of the oxidant feed (blowers and compressors), postponing the discussion about the integration of air supply system with the other FCS sub-systems to the successive three sections, which are dedicated to thermal and water management strategies and to overall system performance optimization. 

A representative scheme of a low pressure FCS plant for automotive application is shown in Fig. 4.9. The reactant supply sub-systems could directly interact with thermal and water management sub-systems, by means of a simultaneous transfer of heat and mass into the humidifier devices, which should be inserted at the entrance of the stack for both reactants. Thermal sub-system includes an internal coolant circuit that is essentially constituted by a liquid pump, a radiator necessary to reject the stack waste heat, and a liquid reservoir. Other minor but equally important components are the de-ionizer filters, thermostat, and valves. 

While different developers are addressing improvements in individual components and subsystems in automotive fuel cell propulsion systems (e.g., cells, stacks, fuel processors, balance-of-plant components), we are using modeling and analysis to address issues of thermal and water management, design-point and part-load operation, and component-, system-, and vehicle-level eificiencies and fuel economies. Such analyses are essential for effective system integration. 

Research, develop, assemble, and test a 50 kW net polymer electrolyte membrane (PEM) fuel cell stack system comprised of a PEM fuel cell stack and the supporting gas, thermal, and water management subsystems. The PEM fuel cell stack system will be capable of integration with at least one of the fuel processors currently under development by Hydrogen Burner Technology (HBT) and Arthur D. Little, Inc. 

The PEM fuel cell stack system consists of the fuel cell stack and supporting gas, thermal and water management systems as shown in Figure 1. Overall system performance depends on the careful integration of these subsystems. The system developed under this contract was designed to accept reformed gasoline from a fuel processor. Development of the fuel processor was not part of this program. 

In addition, Yu et al. [59] proposed a water and thermal management model of a Ballard fuel cell stack which takes a set of gas input conditions and stack parameters such as channel geometry, heat transfer coefficients, and operating current. The model can be used to optimize the stack thermal and water management. Chen et al. [60] investigated numerically the flow distribution in a stack, and concluded... 

Weber AZ, Newman J (2006) Coupled thermal and water management in polymer electrol5Te fuel cells. J Electrochem Soc 153 A2205-A2214... 

As noted, PFSA-based polymer electrol34e membranes used in current PEMFCs require thermal and water management systems to cmitrol temperature and keep the membrane humidified. These extra components increase the weight and volume of... 

Direct hydrogen PEFC systems require extensive thermal and water management to ensure that the PEFC stack operates under the desired design conditions (Figure 3-10). Key components are... 

Modularity and scalability Delicate thermal and water management... 

Traditionally, fuel cells have been too big and expensive for smaller devices. Micro fuel cell faces lot of challenges, which researchers are trying to overcome. The performance of micro fuel cells should approach or exceed that of its macro counter part for it to be attractive. Micro fuel cell technologies, should preferably be self sustaining in its operation and shall be self regulating without the need for complex plumbing for fluid circulation for thermal and water management for it to be compact and autonomous. 

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