Electrical conductivity of flames (OT?)

I don't know the Physics, but a probe into a flame apparently behaves as a rectifier. ...Jim Thompson

Similar to the effects of a heated cathode in a triode tube? The metal rod is, I'd guess, much hotter than the nozzle so more free electrons leading to a rectification effect.

If you download the pdf of the patent and look at fig 1. it shows the direction of the diode... from the probe to the grounded nozzle. I also get the impression that it works fairly fast (a second or less.) which hardly seems like enough time for the probe to heat up. If one assumes that all the current is carried by the electrons in the plasma, then you see more current when the electrons are moving in the same direction as the mass flow in the flame.... maybe that is important?

I don't see how the relative areas matter though.

George H.

you?ll see he talks about different areas being important. But no other explanation. Anyone have an idea of what?s going on?

Thanks George H.

If he lightly sands off the oxide coating on the rod, it will work again for six to 12 months. The rod gets an insulating layer formed by the combustion products in the flame. Think dust, etc.

I have the same issue on my gas water heater and that is how I get around it.

tm

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Yup, he cleaned the rod and it's working again. It looks like a yearly cleaning of the rod is now recommended maintenance.

George H.

Water heaters would almost certainly use a thermopile, and be powered by the flame, no external power supply needed. Usually, when the thermopiles fail, they have internal shorts or opens, and have to be replaced.

Jon

Brilliant!

I was recently called out to repair a gas boiler system, ostensibly with a failed flame-conducting sensor. It turned out that the sensor worked from live to earth and someone had reversed the live and neutral at the supply meter tails a few days before. Every electrical appliance in the house was live when it was switched off.

Simple. Think of a vacuum tube, where a heated element emits electrons that are collected elsewhere. Collection areas are different and so capability, control, etc vary - and according to relative bias.

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ows

this also mentions area

something kinda related is ion sensing ignition, biasing the spark plug gap to 80V and looking at the current right after the spark things like misfires, peak pressure position and knocking can be detected

-Lasse

I ralize my answer here is off topic for your question but others may be interested.

It is my understanding that years ago Japan had a major fire throughout a city, so some engineers took the opportunity to use the blocks and blocks of fire to make some measurmeents. They beamed through the flames and smoke and obtained REAL data regarding the conductivity over a spectrum of an actual fire.

Don't know where that data resides, but it does represent some incredible information. Anybody know where it is?

This is an automatic control that needs to instantly detect ignition of the gas. A thermocouple would take too much time to heat up. In that time, the whole system gets filled with the perfect air-gas mix. Then you get a "Joerg super-phuut".

tm

Why would the field strength be different for different applied polarity? The field depends on the applied voltage and the electrode geometry.

The field strength at the same electrode is the same, but the end that would be emitting electrons changes. It is much harder to emit atoms with a positive charge than electrons, so only the negative end matters.

Back when I was in high school I read about a flame loud speaker. I built one using a propane torch and two pieces of carbon from dry cells. It actually worked! Not very loud but it worked. I entered it in the science fair. It didn't occur to me to use the torch for one of the electrodes. I've still got the brackets for holding the torch somewhere.

ws

I think he is confusing that with a rectum-fryer.

Tom