Problem 1 (20 points): Identify, write and label, the equations governing mass transport processes. Of the mass transport process(es), which mechanism(s) typically limit(s) the fuel cell performance at steady state, when equilibrium conditions are reached? For the limiting mechanism(s) and using the equation that models the phenomena, discuss what changes may be made to enhance the fuel cell performance. Justify each of your answers through writing brief statements! Problem 2 (20 points): Identify, write and label, the equations governing charge transport process(es). How do the charge transport process(es) equation(s) differ from those of mass transport? Of the charge transport process(es), which mechanism(s) typically dominate(s) the fuel cell performance at start-up, until equilibrium conditions are reached? For the dominate mechanism(s) and using the equation that models the phenomena, discuss what changes may be made to enhance the fuel cell performance. Justify each of your answers through writing brief statements! Problem 3 (20 points): Write the expressions for conductivity, electronic and ionic. Identify the expression for electronic conductivity and define each of the symbols for the expression. Where does electronic conductivity take place? Write the range of electron conductivities within those type(s) of materials. Identify the expression for ionic conductivity and define each of the symbols within expression. Where does ionic conductivity take place? Write the range of ionic conductivities within those type(s) of materials. Identify which conductivity range is larger, electronic or ionic, and discuss reason(s) for that conductivity range to be larger. In a fuel cell, is electron conductivity or ion conductivity the rate limiting process that determines steady state conditions? Justify each of your answers through writing brief statements! Problem 4 (20 points): Write a general expression and define each of the symbols within the expression that describes the total concentration losses in a fuel cell. Write a general expression and define each of the symbols within the expression that describes the total conductivity losses in a fuel cell. Justify your answers through writing brief statements! Problem 5 (20 points): For the high current region of the fuel cell, write an expression for the limiting current density of the fuel cell. How can the current density be increased? Estimate the order of magnitude improvement that may be expected for each of the possible ways of increasing the current density. Of the three major flow geometries: (a) parallel; (b) serpentine; (c) parallel serpentine; and (d) interdigitated, which typically increases the fuel cell performance the most? Does the selection of flow geometry affect current density? If so, explain your answer. Justify your answers through writing brief statements! Problem 1 (20 points): Identify, write and label, the equations governing mass transport processes. Of the mass transport process(es), which mechanism(s) typically limit(s) the fuel cell performance at steady state, when equilibrium conditions are reached? For the limiting mechanism(s) and using the equation that models the phenomena, discuss what changes may be made to enhance the fuel cell performance. Justify each of your answers through writing brief statements! Problem 2 (20 points): Identify, write and label, the equations governing charge transport process(es). How do the charge transport process(es) equation(s) differ from those of mass transport? Of the charge transport process(es), which mechanism(s) typically dominate(s) the fuel cell performance at start-up, until equilibrium conditions are reached? For the dominate mechanism(s) and using the equation that models the phenomena, discuss what changes may be made to enhance the fuel cell performance. Justify each of your answers through writing brief statements! Problem 3 (20 points): Write the expressions for conductivity, electronic and ionic. Identify the expression for electronic conductivity and define each of the symbols for the expression. Where does electronic conductivity take place? Write the range of electron conductivities within those type(s) of materials. Identify the expression for ionic conductivity and define each of the symbols within expression. Where does ionic conductivity take place? Write the range of ionic conductivities within those type(s) of materials. Identify which conductivity range is larger, electronic or ionic, and discuss reason(s) for that conductivity range to be larger. In a fuel cell, is electron conductivity or ion conductivity the rate limiting process that determines steady state conditions? Justify each of your answers through writing brief statements! Problem 4 (20 points): Write a general expression and define each of the symbols within the expression that describes the total concentration losses in a fuel cell. Write a general expression and define each of the symbols within the expression that describes the total conductivity losses in a fuel cell. Justify your answers through writing brief statements! Problem 5 (20 points): For the high current region of the fuel cell, write an expression for the limiting current density of the fuel cell. How can the current density be increased? Estimate the order of magnitude improvement that may be expected for each of the possible ways of increasing the current density. Of the three major flow geometries: (a) parallel; (b) serpentine; (c) parallel serpentine; and (d) interdigitated, which typically increases the fuel cell performance the most? Does the selection of flow geometry affect current density? If so, explain your answer. Justify your answers through writing brief statements
