Science Buddies: "Ask an Expert"

Hi,

My son is in 5th Grade, but he is doing the 7th grade project, "Fuel Cells - Fueling the Future." He has built the fuel cell, and ran all the test. Now he is trying to analyze the data, and it is just not coming out. Here is the data from the different test.

Eletrolysis Test 1
using the battery pack (hold two "AA" that came with the fuel cell)

Water Level - Oml
Value of Resistor - .5 Ohms

Resistor Current - 10 seconds = .49
30 seconds = .48
1 minute = .47
1.5 minutes = .45
Average Current = .47

Voltage - 10 seconds = 1.72
30 seconds = 1.73
1 minute = 1.73
1.5 minutes = 1.73
Average Voltage = 1.73

Time of Electrolysis = 2:14 minutes (134 in seconds)

Creating Energy Test 1
using the fuel cell to run the motor that came with the fuel cell kit

Resistor Current by Fuel Cell - 0 seconds = .38
2 minutes = .40
5 minutes = .39
8 minutes = .38
Average Current by FC = .39

Voltage by Fuel Cell - 0 seconds = .75
2 minutes = .78
5 minutes = .77
8 minutes = .75
Average Voltage by FC = .76

Time of Creating Energy = 12:48 (768 in seconds)

Formulas

POWER - Use this formula using the Electrolysis Data

Power = Average Current x Average Voltage
P= .47 x 1.73
P = .81 (Watts)

Energy - Using Electrolysis Data

Energy = Power x Time
E = .81 x 134
E = 108.54 (watt-seconds or joules)

Input Energy - Using Data from Electrolysis

Input Energy = Average Input Current x Average Input Voltage x Time to Electrolyze
IE = .47 x 1.73 x 134
IE = 108.95

***********Next Formula Uses Data From Creating Energy or Fuel Cell Data************

Output Energy

Output Energy = Average Current by Fuel Cell x Average Voltage by Fuel Cell x Run Time of the motor in seconds

OE = .39 x .76 x 768
OE = 227.64

Calculate Efficiency

Efficiency = Output Engergy divided by Input Energy
Efficiency = 227.64 divided by 108.95
Efficiency = 2.09

Now the question would be is the percentage 20.9%. If yes, then what could have gone wrong? From all his research the efficiency of a fuel cell is 50-70 percent.

Please help. If you can think of anything that he could have done wrong.
***I just seen that the fuel cell we ordered is not the fuel cell recommended for this project. Should it still work the same? Below is the fuel cell that was recommended and the one we purchased (the one we purchased was what the company recommended)**

The one Recommended - http://www.fuelcellstore.com/en/pc/show ... rd=7235009
The one we purchased - http://www.fuelcellstore.com/en/pc/view ... roduct=911

Please Help - Is this why the numbers are not coming out correct? Is there anything he can do?

Let's see if I can help here.

I'm not familiar with this experiment, but I have read the instructions, looked at the specifications for the fuel cell kit you purchased, and looked over the data you reported.

You have calculated the efficiency to be 209%. Based on the data you provided that is correct - but not possible. The energy required to produce the gas must be greater than the energy consumed running the motor. It appears you have recorded an incorrect voltage or current somewhere along the line either while in the electrolysis or energy production phases of the experiment. From what you have told me I can't figure out just where or what kind of mistake was made, but I have some suggestions on where to look.

How did you measure the current through the resistor during electrolysis and through the motor during energy production? Did you measure it directly with the multi-meter current function or by using the voltage drop across the resistor? I suspect this might the be source of your problem. I think you may have mixed up one of the voltage measurements. You might have used the voltage drop across the resistor instead of the voltage drop across the fuel cell to calculate electrolysis power, or perhaps there was an error calculating the current going through the resistor. As you did not provide that data, I cannot be sure.

I suggest you check into these ideas to see if you can find your error.

Good luck.

Dear Ed Neu,

Thank you for responding. I let my son read the post yesterday after school and it prompted him to read the instructions again. He has already done this many times, but this time he looked only at the Electrolysis and Creating Energy sections. In the Creating Energy section he found that he forgot to divided the results of the resistance or current over the fuel cell with the original resistor reading (.5 ohms) from the beginning of each test. Once he divided the average resistance current by .5 and recalculated the Output Energy formula he ended up with a more accurate percentage for each test. Next, he averaged the efficiency percentage of all five test and ended up with a fuel cell efficiency of 39.16%. This is not the 50-70% he was expecting, but it was much better than he was getting and the fuel cell we purchase was the wrong one for this experiment. Some of the individual fuel cell efficiency percent totals were in the mid 40's.

He is happy with his results, even though they proved his hypothesis wrong. His hypothesis was that a standard internal combustion engine (ICE) is more efficient than a fuel cell, because we have had over a hundred years to perfect the ICE's. According to his research ICE's efficiency is about 33%, and according to the Doctor who designed this experiment an ICE's efficiency is way below 40%.

Anyway, thanks again!