Engineering project
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EASC211project2.docxUNIVERSITY OF NEW HAVEN
TAGLIATELA COLLEGE OF ENGINEERING
EASC2211 Introduction to Modeling of Engineering Systems Spring 2018
TO: EASC2211 Students
FROM: Jinsong Yu, EASC Instructor
RE: Project 2 – Recommendation for a Fuel Cell Model
Date:
The development department of a fuel cell company is working on a small fuel cell that will be used in home applications. Data has been obtained on the performance of the latest prototype. You are asked to use the performance data to derive a model that can be used to predict the voltage delivered by the fuel cell at different current loads. The work should be summarized in a technical memo, due May 2nd 2018. It should be submitted on BB via Turn-It-In.
The form of the model should be similar to that used in class to model batteries, a constant voltage source (VS) in series with an internal resistance (RS). This model will be used by the Applications Department to determine the ability of the fuel cell to operate various home appliances. Engineers in that department will analyze circuit models that incorporate various loads with your model representing the source. Your recommendation is also needed for the maximum current draw that should be used with this system. Base the maximum current recommendation on the current for which the actual voltage is 6% or more below the prediction.
The data for the fuel cell are shown in Table 1 and Figure 1. Obviously the relationship between terminal voltage and current is not linear, but it should be possible to develop a linear model that is adequate to represent the low current region and a different linear model for to predict behavior in the medium current region. At high current loads the voltage begins to drop more rapidly as the fuel cell reaches its limit.
In particular, you will need to develop 2 separate models and recommend the maximum current draw:
· Model for low current region, VS-low, RS-low
Figure1
· Model for medium current region, VS-med, RS-med
· Identify the maximum current draw above which the fuel cell should not be used Imax.
Sketch a circuit diagram to show the source model (constant voltage source with series resistor) and generic load. Using simple relationships, such as KVL, KCL and Ohm’s law, you can establish a linear model to relate terminal voltage to current drawn from the fuel cell. Use regression techniques with data in each region to obtain the constants VS and RS to best fit the data in each region. You will need to exercise judgment in deciding the cut-off point between the low and medium regions. The regions should overlap by one data point – that is the low and medium region will both include one data point at the boundary between the regions. One strategy for judging the best cut-off points is to use a measure of the error across the full data set, such as the average absolute value of difference between the predicted and actual data points or the sum of the squares of this error. Determine the value of your overall measurement using different cut-off points and select the best choice based on the minimum error measurement. Note also that the maximum usable current should be as high as possible, so you will need to balance accuracy of the model with useful range in your work. For example, a very accurate model that limits the fuel cell to usage below 10 amps would not be a good result.
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Table 1 |
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Fuel Cell PEM-15 Performance Data |
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|
Current |
Voltage |
Current |
Voltage |
Current |
Voltage |
|
Amps |
Volts |
Amps |
Volts |
Amps |
Volts |
|
0.0 |
14.2 |
8.0 |
10.9 |
22.0 |
6.88 |
|
0.2 |
14.0 |
10.0 |
10.2 |
24.0 |
6.76 |
|
0.5 |
13.8 |
12.0 |
10.0 |
26.0 |
6.27 |
|
1.0 |
13.3 |
14.0 |
9.4 |
28.0 |
4.65 |
|
2.0 |
12.7 |
16.0 |
8.8 |
30.0 |
3.91 |
|
4.0 |
11.8 |
18.0 |
8.3 |
|
|
|
6.0 |
11.0 |
20.0 |
8.0 |
|
|
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Experimental data for single cell unit of PEM-15 measuring terminal voltage under varying loads. Note that the data here is organized into 3 sets for convenience in the table. This should not be used as a grouping of the data for modeling purposes. |
Report your results to Dr. Robin Hood, Director of Applications Department, in a technical memo, no longer than 3 pages. Note that Dr. Hood has a strong background in fuel cells, so she understands the details of fuel cells, but you will need to explain how your model can be used to predict voltage from current without needing to consider the reactions and ion transport within the fuel cell. Include a paragraph discussing this. The memo should include a presentation of your results along with a discussion of how you selected the regions for each model with summary tables and figures include in the memo to justify your choices. Do not include all data in your report, but select values to show in small tables and figures to make your case. For example, you may show a table with the average error (e.g., absolute value) between experiment and model for each region, rather than the error for every point. Attach 1 or 2 sheets from your workbook to show all the results, including comparisons between the experimental data and the model predictions.
