A fuel cell stack has a rated power output of 250 kW if the

A fuel cell stack has a rated power output of 250 kW. if the fuel cell has a thermal efficincy of 45% and the fuel is hydrogen, estimate the air flow rate required to provide the necessary oxygon? the reaction inside the fuel cell can be takes as

2H₂ + O₂ = H₂O

assume heating value of hydrogen as 120 MJ/kg

Solution

Power output, OP= 250kW

Thermal efficiency, n = .45

Let energy or power input of the cell be IP

Therefore, n = OP/IP

So, IP=OP/n =250/.45 = 555.56kW

Heating value of Hydrogen is 120 MJ/kg

So, amount of Hydrogen required, m= 555.56/120000 = 0.00463 kg/s

From the chemical equation, 4 kg H requires 32 kg O

So, 0.00463 kg/s H requires (32*0.00463)/4 = 0.037 kg/s O

Now, 100 kg of air contains 23.3 kg of O

Hence, 0.037 kg/s O is contained in 0.037*100/23.3 = 0.159 kg/s air

Therefore, mass flow rate of air is 0.159 kg/s.