Bonus HW Assignment - ChE205
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University of Notre Dame *
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Course
221
Subject
Industrial Engineering
Date
Dec 6, 2023
Type
Pages
4
Uploaded by AdmiralStarDolphin25
Bonus HW Assignment: Katie Huang HW 5, Problem 2 (5.35) & HW 4, Problem 3 (4.87) HW 5, Problem 2 (5.35) My team did not get full points on Homework 5, Problem 2 mostly due to our wrong calculations. Errors were made in the beginning of the calculation, and it carried on throughout the problem, causing our team to lose points. Specifically, the air required to dilute was carried out incorrectly, as we forgot to use the flammability percentage correctly (divided instead of multiplied; equation was not set up properly). Also, when calculating the ratio of flow rates, using the wrong number from the diluted air hurt our calculation for the ratio and the mole percentage of pentane. We struggled with the problem due to not being able to use the information presented in the problem statement, as well as neglecting useful information like STP and flammability percentages to carry out our calculations. The original solution is attached below. For the new homework solution to this problem, I utilized the information presented in the problem statement. In comparison to the original solution, I used the flammability limit from the problem of 2.3% and 4.03% to calculate diluted air, which I did not do in the original. Also, I used STP conditions to help me solve part c so I can use the density to help calculate the ratio easier (the ratio used cubic meters). I also considered using the ideal gas law without STP again, which would work I believe, if I just had used the correct units and masses. I would explain this concept to the student by emphasizing using information given in the problem and using that to start your problem solving. Also, since this is a combustion problem, don
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t forget to utilize the air composition and molar ratios to your advantage. Since the gas is in an ideal state, one can either use the ideal gas law or other STP calculations to solve
for the requested information (such as flow rates of hydrocarbons). The information listed can greatly help when dealing with combustion. From this process, I learned that I need to need thoroughly and use the information given in the problem statement whenever possible, if it applies, of course. I also need to make sure I am applying the constraints into my problem solving (like the flammability limit) because that will greatly change my air molar flow rate calculations. Overall, I need to take the problem slowly and one step at a time, so I don
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t skip over any pertinent information. Attached below is the new solution.
HW 4, Problem 3 (4.87) For this problem, like previous, my team did not score a full mark because of our calculations. In this case, we made a calculation error will trying to calculate the total molar flow rate of oxygen, so we can calculate the molar flow rate of air required for the fuel feed. We did not use a correct approach; we did a mole balance to find total molar flow rate of oxygen instead of using the stoichiometric relationships for the carbon monoxide and hydrogen gas equations. I think we used mole balance to try find the oxygen molar flow rate, but we got certain information messed up. For example, the mole balance was set up incorrectly. We set the mole fraction of hydrogen gas to nitrogen gas; we did not pay close enough attention to what was going in and out because a diagram was not drawn. The original solution is attached below. For the new solution, I re-did the power equation graph in excel by using the power function. The graph was not wrong, so I added it along with the new power graph, as it showed x, a, b, and R. However, in the new solution, I drew a diagram, so I knew what was going in and out. I also wrote my stoichiometric equations for carbon monoxide and hydrogen gas reacting with oxygen separately. Using the information from the graph, I figured out my mole fractions for stream 1. Then, I was able to find the total molar flow rate of oxygen by using the stoichiometric relationships of carbon monoxide and hydrogen gas; I added the moles reacting from each equation to figure out the total molar flow rate of oxygen. Finally, I used the excess air information to calculate the molar flow rate required for a fuel feed rate of 175 kmol/h in this problem. Another solution could be using mole balances. I think if we were to set up the correct mole balances in the original solution and draw a process flow diagram, we may have gotten the correct answer. I would explain this to other students by telling them to use the necessary information from the data and information given from the problem statement to begin your calculations. Since this is a classic combustion problem, I would advise the student to see if they could write any known/implied equations (since it is combustion, it has oxygen involved) and use the stoichiometric relationships to solve for unknown mole balances/molar flow rates. Also, I would tell them to always remember that excess air means 100% + excess air percentage given when using it in a calculation to find a specific molar flow rate of air required. I would tell them that remember to always
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draw the process flow diagram, no matter how simple the problem seems so they can keep track of composition. Once again, like the previous problem, I learned how to take the problem slower and take more information into consideration. I made sure I drew a picture to help me visualize and use the necessary information given in the problem statement regarding carbon monoxide, hydrogen gas, and nitrogen gas to figure out the molar compositions and flow rates. Attached below is the new solution.