Question: Fuel cells are used in spacecraft for generating power and heat. The cell produces electric power by the reaction between liquid hydrogen and liquid oxygen:
2H2 + O2 → 2H2O
Design a ratio controller to maintain the flows of liquid hydrogen and oxygen into the cell in the exact stoichiometric ratio (both hydrogen and oxygen are valuable in space, so we cannot supply either in excess). Calculate the design flows of hydrogen and oxygen required to produce 0.5 kg/h of water, and give the design ratio of oxygen to hydrogen flow. Sketch a ratio control scheme that
will manipulate the flow of oxygen to maintain the exact stoichiometric ratio between the two flows. You may assume that the signals from the flow transmitters are linear with the mass flow rates. Calculate reasonable ranges for the flow transmitters and the ratio in terms of the transmitter signals.