by joe » Thu Apr 07, 2005 10:19 pm
To calculate the efficiency do this math
1. First make the following measurements carefully and simultaneously:
>>Collect the hydrogen produced with a test tube: The test tube should be initially filled with water (by submerging it) and positioned over the negative electrode, with the open end submerged and the closed end pointing upwards (such that the tube is completely filled with water at the start of the experiment). Run the experiment until the water level inside the test tube matches the water surface level. At this point the pressure of the hydrogen will equal ambient pressure. Stop the experiment when this level is reached.
>>Measure the current I in amps: Do this by placing an ammeter in the electrolysis circuit - have someone read the meter during the experiment to get a good idea of the average current. Make sure you express the result in amps, which may require conversion from milliamps.
>>Time the entire experiment with a stopwatch in seconds. (This may be a large number).
>>Measure the ambient (room) temperature in Celsius degrees.
2. Calculate the volume of hydrogen produced at ambient pressure in cubic meters: Measure the dimensions of the test tube, and the length of the tube above water. Make sure you answer is expressed in cubic meters. For example, if you initially calculate the volume in cubic centimeters, divide your answer by 1 million.
3. Now calculate the theoretical (maximum) volume of the hydrogen produced, also in cubic meters, from the other data for the current and the time, using "Faraday's First Law":
Vtheoretical = (R I T t) / (F p z),
where R=8.314 Joule/(mol Kelvin), I = current in amps, T is the temperature in Kelvins (273 + Celsius temperature), t = time in seconds, F = Faraday's constant = 96485 Coulombs per mol, p = ambient pressure = about 1 x 105 pascals (one pascal = 1 Joule/meter3), z = number of "excess" electrons = 2 (for hydrogen, H2), 4 (if you're measuring oxygen production instead).
4. Finally, calculate the efficiency by comparing the volume produced to the theoretical maximum volume:
Efficiency (in %) = 100 x Vproduced / Vtheoretical .
5. Discuss the possible sources of inefficiencies/errors, such as
-Failure to capture hydrogen and oxygen at once.
-Energy lost to heat.
-Various measurement errors.
-Note weather of not the water was distilled , filtered or straight from the tap. For puprose of comparable results, it'd be good if we could get a standardized method of water purification.
-electrolyte (personally i'd rather we didnt use any so that the gases and fuel line is clean as possible)