I am trying to simulate a single cell recirculating anode (open end anode) PEMFC using Ansys Fluent Fuel cell module.
It is recommended by Ansys to keep "mass-flow inlet" for anode & cathode inlet boundaries, and "pressure-outlet" for anode & cathode outlet boundaries.
Could i use any other boundary condition for inlet or outlet?
You could use either mass flow or pressure for either, it just gets more complicated away from their recommended setup, since that's mass flow controllers are the inlet controls and backpressure is set after the outlet.
For research-sized cells (5-50 cm2), typical operation is at high flows (e.g. 0.25-0.5 slpm H2, 0.5-1.0 slpm O2 or air), so typical pressure drop works out to around 5 psi at the inlet to around 0.5 psi at the outlet. If you're adding backpressure, it's just additive to the pressure (e.g. 30 psi backpressure will have ~35 psi inlet, ~30 psi outlet at high flows).
You could go stoichiometric flows, (e.g. 1.2/1.5 stoichiometric flows H2/O2 or H2/Air), but high flows are considered more representative of large stacks, where stoichiometries and pressure will be much higher for most of the MEA. If you wanted to figure mass transport out, you could subtract the stoichiometric amount of gases used at whatever current density operation you're modeling.
Thank you @Benjamin Britton. I would like to get clarification for few practical questions about PEMFC's.
1. Is it mandatory to control the back pressure in PEMFC?
2. Probably in industrial applications, mass flow rate of reactants has to be changed based on the power requirements. In such case, should we have to employ a back pressure controller to maintain the optimum back pressure at the cathode & anode outlets?
1. It's not mandatory - zero backpressure is very typically reported, but that's essentially uncontrolled. If you do have backpressure, it is important to control it - From a practical standpoint, you want to minimize pressure variations to reduce fatigue, especially as membranes get more brittle with radical attack. Most or all industrial models use a compressor + backpressure to some degree. Anode backpressure is 'free' (compressed H2 tank), but O2-side pressure makes much more of a difference, especially with thin membranes (these give a shallower ohmic-region slope - I've seen current densities past 10 A/cm^2 with backpressure). I wouldn't go past +2 bar gauge (3 bar absolute pressure) - DOE test protocols use +0.5 to +1.5 bar, so that's my guess for the range industry uses.
2. Yes, flows change with current density, so you do need a backpressure controller. Small devices tend to use 'dead-end mode,' AKA constant hydrogen pressure with no real flux, but large devices tend to use some sort of a circulation system.
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