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Name: Ryan T. H.
Status: student
Age: 18
Location: N/A
Country: N/A
Date: 2000-2001


Question:
I am a physics student working on a stirling engine. The method of heating it is by a small alcohol lamp. To find the efficeny and work out produced by the engine, we need to measure the temperature of the flame. We attempted to do this by using thermocouples attached to a multimeter, but they maxed out and melted. Any other ideas?


Replies:
Ryan,

If the flame melted the thermocouples slowly, if their maximum temperature is NEAR the flame temperature, you can use approximation. You must also have the ability to control the rate of flow of fuel.

Decrease the flow rate to perhaps half. Measure the temperature. Increase by a small amount, to maybe 60 percent of the full rate. Measure the temperature. Continue boosting by the same amount, measuring the temperature at each point. If you want more data, make smaller increases. Plot temperature as a function of fuel flow. If the graph is linear, do a linear fit. If curved, do a fit of whatever works. Extend the graph to the full fuel flow. Mind, this will only work if you can get data up to about 90 percent of the full flow. It is only an approximation, but it can be quick. If the graph is close to a straight line, the graph is fairly trustworthy.

If you can find a wire, perhaps steel, that will not melt in the flame, you may be able to use the fact that heat is lost from the wire over distance. You will need about a meter of wire, with one end connected to a thermocouple. You will also need something to hold both ends of the wire without starting a fire. Some parts of the wire will be as hot as the flame.

Place a point on the wire far from the thermocouple end in the flame. Let things balance out. Measure the temperature of the thermocouple. Carefully measure the distance from flame to thermocouple. Shift the flame (or wire) such that the flame is closer to the thermocouple. Measure temperature and distance. Repeat, taking as many data points as possible, small changes of distance. When the thermocouple gets very close to its maximum, quit. I do not know how close you will get. That depends on the situation. If you can get kind of close, graph temperature vs distance. Estimate from the graph what the temperature will be at distance zero, the thermocouple in the flame.

Dr. Ken Mellendorf
Illinois Central College


Hello,

You can find thermocouples that are suitable for high temperatures or you can use an IR camera. A company called Omega "WWW.OMEGA.COM" has ample information about thermocouples for your review.

AK
--

Ali Khounsary, Ph.D.
Advanced Photon Source
Argonne National Laboratory



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