Nernst Equation is incorrect #63
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nRiccobo
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Aug 9, 2023
- added P_STD from scipy physical constants, which is 1 bar in Pascals - mods to calc_open_circuit_voltage() include updated p_cathode, split up partial pressures for hydrogen/oxygen according to Dalton's law. Issue NREL#63: Nernst equation was incorrect. This issue only became became apparent when adjusting cathode pressure. - changed E_cell calculation to use the correct partial pressures and replaced R+T with R*T. - Updated test_cell.py, test_stack.py, test_run_electrolyzer.py to account for the new model change. - Incomplete is test_run_lcoh.py. Need assistance to adjust lcoh_breakdown.
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After reviewing the code and discussing, the only bug exists in the General Nernst equation are the partial pressure calculations within the ln(). |
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While tracking issue #61, I saw a bug in the Nernst Equation in calc_open_circuit_voltage().
The partial pressures inside in the ln() component are backwards.
** See equation 8 of (1).
E = E_rev + (RT/nF) * ln((p_h2) * sqrt(p_o2))
The partial pressures of each gas is calculated by Dalton's Law, in equation 5, 6. p_h2 is the partial pressure of hydrogen and is found with p_cathode and p_h2o_sat because hydrogen exits at the cathode. The partial pressure of oxygen is found with p_anode - p_h2o_sat. The code currently has these two quantities flipped.
To Reproduce
See calc_open_circuit_voltage() in cell.py. Compare General Nernst Equation with equation 8 of the following reference.
(1) Vesa, Ruusskanen et al 2017. PEM Water Electrolyzer model for power hardware-in-the-loop. 10.1016/j.ijhydene.2017.03.046
Electrolyzer Version
0.1.0
System Information (please complete the following information):
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