By: Taksshiil Sharma
Abstract
The novel technique of ionic thrusters has been developing recently. The idea of using electricity instead of fuel in air travel seems to be the better idea as technology is advancing, though this technology isn’t being looked as at much for use on earth. Using a high voltage transformer of a million volts to ionize air molecules which go to the negative end of the ionic thruster, knocking other air molecules in the process, this causes air flow. Every part is either 3D printed or measured, and every electrical component, such as the voltage, is a constant for fair and efficient testing. Power output was measured by wind speed output, all wind was funneled into the same area. The following testing showed that as the ionic thruster’s size increased, wind speed and as a result power increased, even though my hypothesis was the opposite.
1) Introduction
The size of an ionic thruster is crucial to building a functioning medium for flight, which is generally used in space. They can be used on earth but that’s far less common, it’s because relative to their weight they’re far worse than traditional modes of thrusting air. Eventually, an electrical solution would be better for travel on earth, but that would require a lot of development, but evidence it can be made has been seen from MIT’s solid-state propulsion. For models that are used in space, such as ones used in rockets, studies in all metrics are numerous yet there are still too many challenges as this technology is new. For models made for earth, studies are far fewer, so the number of challenges grow a lot more. That’s why this research paper is made, to understand one factor of what could help develop this technology. I aim to study how the size affects the actual performance of ionic thruster, using a 3D model as the control, one scaled up by 30% and one scaled down by 30% to research
For the design I chose to use 3D printed parts for the experiment, 3D printing is vital as small changes can affect ionic thrusters a lot. The only factor that should be changed is the size and precision is important. Due to the fact metal 3D printed objects are harder to make, they would increase the main problem with ionic thrusters on earth, the weight being too much, and metal 3D printed parts are not required, I went with plastic 3D printed tubes. These need to conduct electricity, though, which can only be done by physically covering the plastic with a layer of metal, generally copper. This can be done by taking a thin layer of the metal and wrapping it
around the parts physically like using something such as copper tape, or electroplating. I chose the latter, to cover it in graphite I used a 99.9% purity graphite block along with an adhesive that’s both conductive and waterproof to cover the 3d printed set, then in a tub of water containing hydrated copper sulfate, then connected the negative end to the 3d printed object coated in graphene, and the positive end to a copper strip in the solution. This caused a layer of copper to be on top of the plastic, which allowed it to conduct electricity. The 3D printed parts are 3 tubes, which is used for the ionic thruster design which will be explained later, but that’s where all the air goes through.
To calculate power we measure the cross-sectional area of the tube by using πr², and measuring diameter, and dividing by 2 for radius, measure the speed of the wind passing through using a digital speed anemometer and keeping temperature constant in the same room for constant air pressure using a large room with an AC to keep temperature at 20°C and using a thermometer to confirm. Using E=Pt, KE=½mv² we can find the power by seeing mass of air passing through and its velocity. Mass of air passing through for 1 second can be measured using m=ρAv we can see P=½ρAv³, were ρ is the air pressure (in pascals), A is the cross-sectional area, and v is the velocity of air passing through. These values can be used to prove the bigger the ionic thruster, the smaller the power as they precisely calculate power for each size.
2) System description
The system uses spikes cut from a copper sheet measured 1.3cm² of area (1.3cm base, 2cm height) along with a 3d printed tube (with radius of 1.5cm) for each nozzle to prevent airflow in different directions velocity is not accounted for. The tube also acts as the negative end that the positive ions go to. The spikes are scaled up by and down by roughly 14% as the area of the ionic thruster is increased and decreased by 30%, not the circumference.
The design works by using a styrofoam surface carved as a base for the tube and a stick that holds up the spikes. The stick has many spikes attached to it, along with the negative end of a 1 million volt transformer to it while the tube is electroplated and has the positive end attached to it, this causes a distorted electric field, more concentrated around the spikes, causing ionization of surrounding air closer to the spikes as electrons are shot with high voltage, causing repulsion of surrounding electrons, causing ionization or in other words creating a positively charged ion. As the air particles are ionized closer to the spikes/positive end as electric field is more concentrated, they travel to the negative end as they have a positive charge, knocking air molecules in the process, in their direction of motion, which is towards the positive end.
A 12V battery is used on the DC transformer and a total of 7 copper spikes, also scaled up / down 30%, are used on Model 1 on each of the Ionic thrusters. The ionic thruster runs for 5 seconds before measuring the speed using a digital anemometer, as speed may not be constant
before 5 seconds. The experiment is repeated 3 times for each ionic thruster and the average value of speed is calculated, the tube area is calculated, and the air pressure is measured at 101000Pa using a barometer and the room temperature is measured to be 20°C, this is done to use NTP (normal temperature and pressure). All the values are then plugged into the formula given above (P=½ρAv³).
3) Experiment
First everything was tested to be fine, the voltage given to the transformer is 12V, then the experiment was carried out in 2 different ways, both ways not only lead to the same conclusion but the same values. Those were dependent on what constitutes a bigger ionic thruster, is it just the components, or also a 30% smaller or larger gap, but to the closest integer it made no difference so regardless, the values and conclusion hold true either way. The values given though, will be off the experiment done when all 3 models have the same gap
The experiment was carried out 3 times for each of the 3, as there was no difference in the process there was no measurable difference between all 3 of the times the experiment was done. The ionic thruster was switched on, to confirm it worked, the lights were switched off before measuring any results, there was a clear purple glow, caused by the ionized gases, this was to see if there was a glow from all 7 spikes to see if they worked and they did for all 3 ionic thrusters.
3.1) Results
After this the lights were turned back on, the wind emitted was measured. Contrary to my hypothesis the biggest ionic thruster not only had the most power output, but also the most speed, while obviously having the largest radius at 7m/s (7.2 to 1 Decimal place), the normal one had a speed of 5 m/s and so did the small one to the closest integer but the one with the original measurements was 5.3 m/s and the smallest one was 4.7 m/s.
Even though it’s not necessary for the conclusion, as both the velocity and the area are bigger as the size increased, while pressure is constant, we can plug in these values into the equation P=½ρAv³ to calculate power. As ρ 101325 Pa, A is πr², where r is 1.5cm for the original so area is 7 cm², the smaller version is 5 cm², and the bigger version is 9 cm². As standard unit is m², you divide the result by 10,000 to convert cm² to m². The power output for the original one is 190W, the smaller one is 120W and the bigger one is 330W to 2sf.
4) Conclusion
While some might say energy is generally lost more in a bigger system, evidence points to the opposite. My initial reasoning was the bigger gap, which is what I originally experimented with. When I made the gaps the same though, this was proven wrong as that didn’t change the result. The next possible explanation is that the smaller systems transferred electrons much slower as they were smaller, and their size was a limiting factor for the voltage. Another proof I had for this reason was that the bigger ionic thruster had a marginally brighter glow when the lights were off.
Overall, this proves, the bigger the ionic thruster, the more power it produces if every other factor is the same.
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