# What is the most efficient way to ionize air?

I have a project to convert wind energy directly to electrical energy with no moving parts. The wind will enter a reducing tunnel for concentration, then go through an unobstructing de-humidifier, then through a multi-plate sandwich type electrode setup like that of a capacitor where the voltage would be very high to ionize the air passing through.

This ionized air molecule would then pass through a magnetic field to generate electricity. A fraction of the electricity would be used to ionize the incoming stream again. I realize that the less the spacing between the capacitor plates, and the greater the voltage, the better the ionization. I was wondering what would be optimal plate spacing and voltage for dry air at STP, if a cylindrical plate arrangement would be better than rectangular, etc. Other advise also appreciated.

• I think dimensions of your setup and a picture of the electrode setup would be helpful because the flow characteristics at the beginning and through the electrodes would (I think) greatly affect your power output. Is the project just proof of concept or do you have power targets that you have to meet? Personally, this method of electricity generation seems wonky, but the data will reveal all! Commented Apr 26, 2017 at 20:10
• en.wikipedia.org/wiki/Magnetohydrodynamic_generator
– ARi
Commented Apr 29, 2017 at 15:22

It will depend on the degree of ionization you require, as well as the pressure of the air passing through the ionization region. Your gas will not likely be at STP if the air is moving through a reducing tunnel.

Ionization and breakdown (the common name for the process of forming a plasma by ionization) occurs more easily at lower pressures (so a quickly moving flow will be easier to break down) and can be initiated by DC voltage, RF, microwave, laser power, or sufficient heat. In terms of efficiency, microwave frequency power will cause breakdown at lower power levels than RF or DC, but the equipment is in general more expensive. It can also be a complex engineering problem to deliver sufficient microwave power in the right configuration.

DC discharges are less efficiently generated but are relatively simple: apply 3 kV across a 1 mm gap and you should be near the threshold of breakdown. You can get very high temperature gas this way, but your anode and cathode will get ablated.

The more strongly your gas is ionized, the more power will get generated by passing through the magnetic field.

In general you're going to spend a lot of power ionizing the air. For large flow rates, you will require thousands of watts. You will likely recapture a very small portion of it from running it through a magnetic field. I think it is important to realize you will need to pump more electrical power into the system than you will capture from it.

The wikipedia page for Paschen's law, which shows the curve of applied electric field to pressure required to break down a gas (for DC), is a good starting point: https://en.wikipedia.org/wiki/Paschen%27s_law

If you're interested in reading more, I recommend "Gas Discharge Physics" (back in print!) by Yuri Raizer. Sanborn Brown also has a good book, likely in most large university libraries, "High Frequency Gas Discharge Breakdown," which is pretty readable.

• @ Phyllis diller : Wonderful answer, I would just throw in OAUGD (one atmosphere uniform glow discharge) so the OP can could have an easy way to ionize air if there is only the option of ionizing air at one atmosphere. Also Tesla coils are an efficient way to ionize air, all the laws of AC discharges of course apply here. Commented Apr 27, 2017 at 2:32