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Sunday, May 8, 2011

Another Long Week and Little Time to Play

I had huge plans for this last week related to the experiments that I want to do with high voltage and my Schlieren photography setup. Unfortunately for various reasons I didn't have time to do much. One reason for my lack of "experiment time" is I have not won the lottery and am unable to have all the 'normal' things taken care of by an army of personal assistants. I did add "build robotic servant" to my list of things to do but that is for another day.

What I am writing about this week is a continuation of lasts weeks post. You can re-red that post HERE just because it was so interesting! Just in case you didn't read it and don't want to let me explain a bit what I am doing. I have a high voltage power supply that I am connecting to two electrodes. The high voltage wire is connected to one electrode made from a stainless steel sewing needle. The other electrode is a small 'banana'  electrode that is movable. It's movable so I can raise it up and change the gap between the two electrodes. This whole setup is sitting in front of the parabolic mirror that I use to make beautiful and interesting Schlieren videos ;-) Below is a picture of the setup.

High Voltage Electrode Schlieren Setup
Do you notice something strange about the above picture? If you know me well you won't think anything is strange because you know that I can't spell! I noticed the error after I made the picture and I'm too lazy busy to fix it. The picture is pretty self explanatory if you read the explanation I wrote above. What isn't so obvious is why I'm doing this. Continue reading to find out and don't miss the exciting and entertaining video!

If you are a regular reader of my blog you have probably guessed that I am interested in high voltage especially after reading about the "lifter" experiments that I did recently HERE. After playing around with the lifter and the Schlieren setup I thought it might be fun to just record what happens to the air surrounding high voltage electrodes. My thinking is that the shape and relative sizes of the electrodes changes how the sir is flowing as described in the Biefeld-Brown effect (click HERE for a link to the Biefeld-Brown effect).

One of the problems I have been having while trying to look into this is getting the high voltage that I need / want. After blowing up transistors, my Fluke meter and shocking the pee pee out of myself a few times I have decided to just buy a high voltage supply. Until I get one these experiments are limited to the power supply that I built and wrote about HERE. Now onto what I want to write about...
One of the interesting things that I saw while messing around was there is a significant airflow coming off the high voltage sewing needle but not coming off the point of it. The airflow is coming off about 3mm before the tip as shown below:
High Voltage Sewing Needle Electrode
This is a picture that I posted last week but I added a couple of annotations. What you can see is airflow coming off before the point of the needle. I'm guessing that is because as the needle gets thinner and tapers down  to a point and the charge is moving toward the tip, the charge / surface area is getting larger as the needle gets thinner. At some point along the length of the needle the 'charge density' gets so high that is flies off the needle. Not such a scientific explanation but then again I'm only guessing.
Another interesting thing that I noticed while moving the electrode up toward the needle is the region where the air is flowing off the needle moves. I can make it come off rather high on the needle by moving the lower ground electrode closer to the needle point. As the ground electrode is moved closer the air stream comes closer to the point of the needle and eventually arcs to the ground electrode. Also the airflow goes away completely if I leave it alone for some time. Moving the electrode up again and drawing an arc causes the airflow to start again. My guess as to why this is happening is because if I draw an arc it's creating a lot of ions and charged air particles, ozone and other gases. All this energized air is allowing a flow off the needle as I mentioned above. After awhile the flow alone is not enough to sustain itself at the voltage that I am using and it does off. You can see this happening in the video at the end of this post.
The airflow created by an arc itself isn't all that interesting but it is neat looking. The flow is very different than the flow that is created by just having the electrodes close but not arcing. Here are a couple of pictures of what I am talking about.

High Voltage Airflow From An Arc
Above is a screen shot from the video showing an arc and the surrounding airflow going out and up. It's clear that this is hot air being driven out by the arcing and flowing up because it's hot ;-)

High Voltage Airflow After Arcing
The picture above shows the air flowing away from the needle and also clearly air flowing down toward the larger ground electrode. This is the airflow that I am interested in. In the video you can see a ring of air moving off the needle and air moving down toward the larger ground electrode. There is also a pronounced stream of air moving from the tip of the needle to the lower electrode at times. It's a bit difficult to see in the video because of the compression. From moving the electrode around in the experiment it's easy to find a place where this effect is optimized. I believe there is an optimum electrode shape and distance for a given voltage to maximize this effect.
As always if you have any questions leave a comment of send me an email at and I'll be happy to answer or discuss anything you like ;-) I'm planning on getting a better and more reliable, safer high voltage source and I'll continue to mess with this at that time.
Enjoy the video!

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