The above setup is used to show the dependency of current and EHD thrust upon the type of gas in which it flows. Since the ion flow is governed by the electric field shape and momentum exchange, it follows that thrust should depend on the electric field, density of the gas, its ion mobility.
Dry air is mainly composed as follows (Permittivity ordered):
|Element trace||Percentage in air||Density @ 273°K 1 atm.||Permittivity @ 293°K 1 atm.|
|Helium||0.000524 %||0.1785 g/L||1.0000688|
|Neon||0.00182 %||0.9000 g/L||1.00013|
|Hydrogen||0.01 %||0.0899 g/L||1.00026|
|Oxygen||20.946 %||1.429 g/L||1.00052|
|Argon||0.934 %||1.7824 g/L||1.00055|
|Nitrogen||78.084 %||1.2506 g/L||1.00058|
|Krypton||0.000114 %||3.750 g/L||1.00077|
|Carbon Dioxide||0.03 %||1.977 g/L||1.00098|
The experiment was setup as follows:
A basic triangular EHD cell of air gap 40 mm, side length 150 mm is set up in an enclosed glass container, with normal air at atmospheric pressure. A pipe goes in this enclosure which may fill up the whole volume with any required gas type. Helium was used for the first experiment. Helium is the lowest density gas after Hydrogen, and has the lowest dielectric constant of all gases present in air. For obvious reasons this setup was not done with Hydrogen (and please do not try it!!).
Test 1 - Helium
A 30 kV supply is connected to the thruster and switched on, in normal air. The thruster immediately goes up, and held floating in air by three strings. The Helium valve is then opened, expelling air from a lower vent in the container, thus replacing the air with Helium, from top to bottom, still at atmospheric pressure. As this happens, the thruster looses its thrust, until it lands down and is totally inactive. Corona glow around the top wire becomes visible and the normal hissing sound dies out.
Current goes up to 5 times that of normal air. With the enclosure still full of Helium, the voltage was then increased until the thruster floated up again. This happened at about 40 kV, but at about 7 times the total power consumption of what would be required to float in air.
Test 2 - Carbon Dioxide
A 30 kV supply is connected to the thruster and switched on, in normal air. The thruster immediately goes up, and held floating in air by three strings. The Carbon dioxide valve is then opened, expelling air from an upper vent in the container, thus replacing the air with carbon dioxide, from bottom to top, still at atmospheric pressure. As this happens, the thrust is unchanged and current consumption remains constant.
Test 3 - Nitrogen
A variable 30 kV max. power supply is connected to the thruster and switched on, in normal air. The voltage is increased from zero until the thruster has enough thrust to hover in air, held from escaping up by three strings. The Nitrogen valve is then opened, expelling air from an upper vent in the container, thus replacing the air with the heavier Nitrogen gas, from bottom to top, still at atmospheric pressure. As this happens, the thruster gains thrust, and in fact the supply voltage could be decreased while the thruster still hovers in Nitrogen. These are the results with positive emitter:
In AIR at RTP: Lift off occurs at 21 kV, 0.7 mA - 14 Watts
In Nitrogen at RTP: Lift off occurs at 18 kV, 0.45 mA - 8.1 Watts
Thrust ratio at same power level: 175% - almost twice as much!
Since Nitrogen makes up 78% of normal air, one could say that the majority of the EHD thrust in air with positive corona is due to its Nitrogen content.
Also, it is possible for a thruster to carry its own Nitrogen 'fuel' supply in order to achieve better efficiency.
On negative polarity I got:
In air - lift off at 21.4 kV, 1 mA = 21 Watts
In Nitrogen - lift off at 24 kV, 0.9 mA = 21.6Watts
This shows that Nitrogen ions are not the main thrusting ions when emitter is negative.
Conclusions from these experiment