Thermal Management and Meredith Effect Implementation for a Fuel Cell System in Aviation Application

The introduction of fuel cell systems in new power generation systems in the aeronautical field brings with it the need to increase the power density of these systems. To address the resulting increased criticality of thermal management, it is necessary to consider the correct cooling method, without it excessively affecting the net useful electrical power generated. Furthermore, since large amounts of heat must be dissipated, if this is correctly managed with a suitable radiator and an adequate air duct, the extracted heat can be exploited to generate additional thrust and thus compensate for part of the aerodynamic drag caused by the radiator itself. This effect is known as the Meredith Effect. This work fits into this context with the aim of creating, in the GT-Suite simulation environment, a model of a PEM fuel cell system, the related balance of plant with particular attention to the thermal system, and a radiator to be inserted into a duct to exploit the thrust generation caused by the Meredith Effect. To optimize the latter, the geometries of the air intake and the divergent and convergent ducts have been defined. Finally, the performance of the entire system was evaluated for different flight phases (take-off, climb, cruise, descent) and compared with the targets of an autogyro aircraft. A stack of 375 cells was then developed, with an active surface area of 250 mm2 and fueled by air and pure hydrogen, capable of generating 128 kW of electrical power and 130 kW of heat during take-off, with a voltage per single cell of 0.62 V at 80 °C. The cooling system for this application was supposed to involve the evaporation of the coolant inside the stack and its subsequent condensation in the radiator. This would have made it possible to exploit the latent heat of evaporation of the coolant to extract large amounts of heat from the stack, reducing the required flow rates and therefore the power loads. However, due to some problems with the software used, it was not possible to make this system effective, but its strengths and weaknesses were nevertheless reported. In addition, various cooling circuit configurations were evaluated, highlighting the advantages and disadvantages of each, and different radiator designs were studied, including an aluminum tube-fin radiator with triangular fins and flat tubes, with three fluid passages inside, and with a compactness of 778. Subsequently, this radiator was considered within a duct whose air intake was sized for the cruise phase, while the divergent and convergent sections were defined according to streamline geometry with the aim of reducing pressure losses and aerodynamic drag as much as possible. In conclusion, various flight conditions were simulated at different speeds and altitudes to assess the Meredith Effect.