Fuel Cell System with Liquid-Cooled Stack

3 Fuel Cell System with Liquid-Cooled Stack 

Liquid-cooled stacks have higher volumetric power density and they are preferred when the output power is around 5 kW or higher. The resulting fuel 

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Therefore, a fuel cell system with an air-cooled stack will have an electrical efficiency of around 45% (0.95 x 0.55 x 0.95 x 0.90), and a fuel cell system with a liquid-cooled stack will have an electrical efficiency of around 42% (0.95 X 0.55 X 0.90 x 0.90). 

The air supply module provides air for the fuel cell system, mainly for the cathode reaction. For air-cooled stacks with combined reaction and cooling air, the ASM is simply the fans. For air-cooled stacks with separate reaction and cooling air, the ASM consists of the fans for the reaction air and an air blower or an air compressor for the cooling air. For liquid-cooled stacks, the ASM provides the reaction air using an air blower or an air compressor. Since the ASM for liquid-cooled stacks is more complex than for air-cooled stacks, the following discussion will be about the ASM for liquid-cooled stacks. 

During the start-up of a fuel cell system, the batteries provide all the power needs only for a few seconds. Afterward, the fuel cell stack begins supplying some power, and the output power from the batteries reduces correspondingly. With time, the stack supplies more and more power and the batteries supply less and less power, and finally, all the power is supplied by the stack. The duration of the load-sharing process by the stack and the battery depends on the discharging capacity of the batteries, the output voltage setup of the DC-DC converter, and how fast the stack can reach its nominal power output. For an air-cooled stack, the stack can reach the nominal power output in about 1 minute. For a liquid-cooled stack, the stack can reach the nominal power output in less than 5-10 minutes. But this does not necessarily mean that the load will be fully powered by an air-cooled stack within 1 minute, because the... 

Considering that simplicity is an important criterion in aviation, air cooling of the fuel cell system seems to be an appropriate solution. Despite benefits such as the availability of the coolant, its dual function and light weight, issues with varying parameters such as pressure, density and temperature must be addressed. The absolute pressure at an altitude of 10,000 m MSL is approximately 260 mbar, and the air density is 0.21 kg/m. Liquid cooling can be realized in a closed loop, which makes it independent of altitude. If the coolant exit temperature of the stack is controlled at 165 °C and if air is supplied to the stack at 20 °C, the volume flow must be two... 

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