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Unformatted text preview: University of California, Davis Department of Chemical Engineering & Materials Science ECH 157 - Fall 2011 Answers to Projects Frequently Asked Questions Questions about the fuel cell model: 1. The term n r H 2 that appears in the stack temperature equation represents the number of moles of H 2 consumed due to the reaction per unit time (it is essentially the reaction rate). It is a function of the load current, and its dependency on I can be easily deduced by inspecting the mass balance equation for H 2 ; specifically n r H 2 = 2 K r I . 2. The outlet molar ow rate for each species is not constant, but a function of the partial pressure (think of the ideal gas law). Again, the relationship can be deduced from the mass balance equations. For example, q out H 2 = K H 2 p H 2 (check the units to convince yourself of the result). 3. The inlet molar ow rates for H 2 and O 2 are specified in Table 1, but the inlet molar ow rate for H 2 O is not given because it is zero, since the feed contains no water, and water is only...
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- Fall '08