Another busy week has gone by and I have not had a lot of time to experiment but I did manage to do a few things with the Ranque-Hilsch Vortex Tube experimental setup I built last week. As I mentioned this setup is not intended to actually create a hot and cold flow separation but rather to try and figure out what is going on inside the tube. Specifically I am interested in how the counter flow starts at the cone valve and determine how much influence the cone valve shape has on the counter flow. With that in mind I did a few computer simulations using SolidWorks and FloXpress. SolidWorks is a parametric CAD system and FloXpress is a fluid dynamics flow simulation add on to SolidWorks. Because it's a free add on to SolidWorks and not the full version there are limitations to what it can do but the results were interesting. Check out the cool picture below!
|Vortex Tube Computer Flow Simulation|
The picture above is a side view of a vortex tube that I modeled in SolidWorks. The blue spaghetti wrapped around the inside is the calculated vortex airflow going around the inside of the tube. The air is entering in the upper right and flowing round and round slowly making it's way to the left side where the hot end cone valve is located. If you are not sure what I am talking about click on the Ranque-Hilsch Vortex Tube Wikipedia link and read about what a vortex tube is!
A close look at the above picture shows that there is a counter flow down the middle of the tube that is headed to the right side of the picture. This would be the cold air, or air that is being cooled. Below is another picture from a better angle of the simulation and a video of not only the computer simulation in action but also experimental tests to image the airflow! Using lasers!!
As promised below is another view of the computer simulation. You can see where the start of the counter flow starting back down the middle of the tube toward the Cold Air Hole. Click on the picture for a better view. I stopped the simulation before the tube filled up with all the blue lines to see the flow clearer. As I mentioned a full animation of both views of this simulation are included in the video at the end of this post.
|Ranque-Hilsch Vortex Tube Simulation|
One of the first things that I noticed about the simulation is the counter flow is rotating the same direction as the primary flow is rotating against the I.D. of the tube. This was news to me because most of the pictures that I have seen on line show it going in the opposite direction. One thing I should mention here is the free version of FloXpress that I am using only allows for one input 'port' and one output 'port'. In other words I can't simulate the gas squirting in from multiple jets and I can't have both the hot end and the cold ends of the tube open. What I did to run the simulation was make the Cold Air Hole the output and the hot end was closed off but much longer than necessary. Making the hot end long gave the air a place to go (down into the hot end) but not actually flow out the hot end. This is as close as I can get to the real world with the software that I have.
If you didn't read my fist post about this experiment HERE you should at least have a look at THIS picture of the setup. It is a clear plastic tube with a movable cone valve on one end, a cold air hole on the other. There are two air inlets at a tangent to the tube inner diameter connected to 2 small variable speed diaphragm pumps. The difference between the picture and the setup this time is I am using only one green 10mw laser with a lens in front of it to make the beam into a fan. The fan is spread into a vertical plane that bisects the tube from the cold air hole end. I used a laser because it illuminates the flow of air and smoke in the tube. Here is a video of the tube running with a the green laser and also the animated computer simulations.
What I noticed with this experiment is the flow that I see in the tube appears to match the computer simulation! Yeah! Also it takes a lot of airflow to build up a counter flow that actually escapes out the cold air hole. Without a lot of airflow the counter flow is drawn back into the primary vortex along the inner wall of the tube. I think that there are two area for improvement of the tube design. The first would be to optimize the cone valve shape to generate a strong counter flow. The second improvement would be to arrange the geometry near the cold air plate and the gas entry points to facilitate the exit of the counter flow gas. Those two things will be what I work on next.
If you have any questions please send me an email at firstname.lastname@example.org and/or leave a comment here on the blog!