Experimenting With Plasma Actuators Inside Hollow Pipes

Plasma actuators are electromagnetic devices that generate wall bounded jet stream. They do so by ionizing and accelerating the air around them.

Before we dive into the crucs of it, here’s a video of the actuator taken at run time.

So How Do Plasma Actuators Work?

A plasma Actuator consists of an electric circuit in which an insulator is sandwiched between a pair of electrodes. This layer, also called as a dielectric layer (made up of a dielectric medium), inhibits current to flow from one electrode to another. One of these electrodes is encapsulated with a Kapton tape, while the other (inner electrode) is exposed to air from one side.

When sufficiently large amounts of AC voltage (order of 7 kV) at high frequencies (order of 20 kHz) are supplied across this setup, the air molecules in contact with the exposed electrode ionize. This creates a region of plasma around the edges of the exposed electrode. The ionized air molecules get attracted to the unexposed electrode by the virtue of the electric field around them. This accelerates the ionized air molecules in the direction of the unexposed electrode, which is axially offset. The dielectric medium inhibits both current as well as air to flow across it, hence the ionized air flows axially through the pipe, imparting kinetic energy to the non-ionized air molecules in the way. This effectively creates a draft inside the pipe without using any moving parts.

Ionized air molecules release energy which in this context is called Corona Discharge. This can be seen in the video provided above.

Experimental Setup

The experimental set up consists of the following

• Wooden Base
• Acryclic Pipe
• Copper Electrodes
• Hight Voltage Transformer
• Kapton Tape
• Hot Wire Annemometer

The Transformer

The PVM 500 is a reliable Plasma Driver that supplies high AC voltages at high frequencies. This reliable and flexible Plasma Driver powers conventional resistive loads such as plasma devices with internal electrodes, or Jacob’s ladders, voltage multipliers, arc generators, neon tubing and other similar devices that do not require resonant operation.

Observations

In the experiments conducted, voltage and frequency were gradually increased accross their range while keeping the other constant. The draft velocities were measured using a hot wire annemometer and tabulated.

Results

Above images show before and after the plasma actuator was switched on. Corona Discharge could also be observed inside the pipe if you have taken a look at the video above.

As can be inferred from the line plot above. The air velocity increases in a concave-down fashion with increase in frequency when the AC frequency is constant.

The air velocities generated weren’t as high so as to even contend to replace traditional devices such as fans and blowers. Especially considering the voltages applied and that such voltages can’t be generated by ordinary transformers.

Nonetheless, extended research on Plasma Actuators and Electrostatic Fluid Accelerators could very well mean such devices could become more efficient so as to replace conventional devices like fans, blowers or even Jet Engines!