Calculate the oxygen flow rate in ml/min needed at an individual cell of a PEM f

Question

Calculate the oxygen flow rate in ml/min needed at an individual cell of a PEM fuel cell stack and the rate of water vapor formation in ml/min in order to produce an electric current of 10 A. Use a formula derived from Faraday’s laws for the determination of the substance change. Then determine the theoretically needed volumetric air flow for the entire stack on the assumption that the usable oxygen portion in air is 20%. Consider the number of cells of the stack. Perform the calculation at standard conditions (0 oC, 1.01325 bar). The molecular standard volume is Vm = 22.4 L/mol; the Faraday constant F = 9.648 x 104 C/mol.

Explanation / Answer

using First Faraday's Law

m = ECE . I . t

second Law of electrochemical value of ECE is ECE = M / z .F

by equating we get

m / t .I = M / z . F

and n = m / M = t.I / z . F

n = I / F . z

O2 + 4 H+ + 4 e- ----> 2 H2 O

nO2 = 10 / 4 X 9.648 X 104

= 2.59 X 10-5 mol/sec

VO2 = 2.59 X 10-5 X 22.4 X 1000 X 60

VO2 = 34.82 ml/min

Vair = 34.82 X 10 X ( 1 / 0.2 )

Vair = 1741 ml/min

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