System Modelling
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[pic 1]System ModellingAssignment, Question 1ByKevin Gan Kwan YewDepartment of Chemical EngineeringSchool of EngineeringThe University of Birmingham18th January 2018Table of ContentsContentsTable of Contents 2Abstract 31.0 Introduction 41.1 Solid oxide fuel cells 41.2 Interconnects 41.3 Chromium Vaporization 41.4 Aim and Objectives 52.0 Theory 52.1 Ficks second law 52.2 Boundary conditions 82.3 Parameters 83.0 Discussion 94.0 Methods 105.0 Conclusion 106.0 References 10AbstractChromium is now widely used commercially as part of the steel used as interconnects. This is because the oxidation of chromium produces a layer of chromium oxide scale that has a protective function. However the oxidation causes the chromium to deplete over time . The oxidation also increases the electrical resistance of the interconnects. By modifying the Deal-Grove model given, and using the flux obtained throughout, a new model could be obtained where the optimum oxide growth as well as the chromium depletion could be found. Using the model an equation based on the growth of oxide over time could be found which is Furthermore by using Fick’s second law and differential equations as well as forward,backward and central differences, a relationship of dc/dt was obtained.[pic 2]Introduction1.1 Solid oxide fuel cellsSolid oxide fuel cells (SOFC) are electrochemical devices that generate electricity in the most efficient way using various fuel cells such as methane, hydrogen and even natural gas without any combustion or mechanical processes. (SOFC) also generates high quality byproduct heat while also generating very low amount of pollutants which shows the importance of SOFC in the past and also the future. (W.Z.ZhuS.C.Deevi ,2003)[pic 3][pic 4]1.2 InterconnectsThe importance of solid oxide fuel cells (SOFC) has brought many modifications to further improve it where an interconnect component is installed which can be seen in figure 1. The interconnect is a critical component in any SOFC as the role of interconnect as it operates in both oxidizing and reducing atmosphere where it: (Joelle C.W Mah,2016)
Prevents the fuel electrode material from contacting with oxidizing atmosphere of the oxidant electrode side.Connects the cathode and anode to provide electrical connectionActs as a barrier in between the air electron material and the reducing environment of the fuel electrode1.3 Chromium VaporizationAlmost all metals undergo oxidation when it is exposed to oxygen in air. Negative oxygen ions which forms penetrates into the metal causing a growth of oxide surface. When the oxide layer grows the rate of electron transfer decreases. An example of oxidation can be seen in the equation below where chromium is oxidized [pic 5][pic 6]