Ruben's Tube | Standing Wave Flame

The first Ruben's Tube that I noticed was in a musical video called "Science vs Music". I'm sure many of you may have noticed the same. So, lets know something more about this amazing experiment in this Instructable.

A Rubens' tube, also known as a standing wave flame tube, is an antique physics apparatus for demonstrating acoustic standing waves in a tube. Invented by German physicist Heinrich Rubens.

Heinrich Rubens was a German physicist born in 1865. Though he worked with better remembered physicists such as Max Planck at the University of Berlin on some of the ground work for quantum physics, he is best known for his Flame tube, which was demonstrated in 1905. This original Rubens' tube was a four-meter section of pipe with approximately 100 holes of 2mm diameter spaced evenly along its length.

He put a sound source at one end of the tube and produced standing waves inside the tube. Now the pressure varied from hole to hole and showed pressure nodes and anti-nodes. It graphically shows the relationship between sound waves and sound pressure, as a primitive oscilloscope.

The Ruben´s tube can only show standing waves in inflammable gases. Today, it is just used only occasionally as a demonstration in physics education. Learn more about Ruben's Tube From the wiki page.

A length of pipe is perforated along the top and sealed at both ends, one seal is attached to a small speaker or frequency generator, the other to a supply of a flammable gas (propane tank).

The pipe is filled with the gas, and the gas leaking from the perforations is lit. If a suitable constant frequency is used, a standing wave can form within the tube. When the speaker is turned on, the standing wave will create points with oscillating (higher and lower) pressure and points with constant pressure (pressure nodes) along the tube. Where there is oscillating pressure due to the sound waves, less gas will escape from the perforations in the tube, and the flames will be lower at those points. At the pressure nodes, the flames are higher. At the end of the tube gas molecule velocity is zero and oscillating pressure is maximal, thus low flames are observed.

Again,

Since, the time averaged pressure is equal at all points of the tube, it is not simple to explain the different flame heights. The flame height is proportional to the gas flow. Based on Bernoulli's principle, the gas flow is proportional to the square root of the pressure difference between the inside and outside of the tube.

The flame height depends non-linearly on the local, time-dependent pressure. The time average of the flow is reduced at the points with oscillating pressure and thus flames are lower.

The main parts of this experiment are a Metal pipe with holes along its length, a Diaphragm at one end and a pressurized Gas at the other end.

Though it does not require a lot of things to make it, the tools and some materials that I used personally in this experiment are listed below.

TOOLS :

• Mini hacksaw
• Scissor
• Cutter
• Nail (0.5mm)
• Hammer
• Sand paper
• Lighter
• Pen
• Plier
• Ruler
• Nut & bolt

MATERIALS :

• Deo can (metal pipe)
• Plywood (2mm & 6mm)
• Balloon (elastic diaphragm)
• Cello tape & thread
• Teflon tape
• Double sided tape
• Plastic pipe (6mm & 2mm)
• Pipe joints (L-joint & I-joint)
• Pressure controller joint
• Wood glue (fevicol)
• Super glue
• Extra deo can (optional)

For the experiment there are four main parts that we will be making,

1. The Metal Pipe
2. The Diaphragm
3. The Gas Input System
4. The Stand

So, here we will be first making our Metal pipe. For the pipe you can use any kind of metal pipe of any thermal proof material. In my case I will instead use a empty Deodorant can for the same.

Now we need to make some holes along the top for our flames to lit. Here I marked 14 holes of 0.5mm diameter spaced evenly along 1/4 inch distance each.

For making I used my drawing compass to punch the holes and then I hammered the holes with 0.5mm Nail Pins. Thus it makes very tiny and perfect straight holes for my can.

Later,

I simply cut the bottom of the can with the help of my mini hacksaw. So, that later on we can fit our Diaphragm on this end. Then I removed the spraying pipe attached to it from the top and leave the hole as it is, so that we can use this end as our Gas Inlet system.

A Diaphragm is commonly constructed of a thin membrane or sheet of various materials. The mechanical vibrations to the Diaphragm varies air pressure of sound waves can be converted to some other type of signal or waves, like a Sine wave in our case.

So, now is the time for fitting the Diaphragm to the opening end of our can. In this case I used a Balloon as an elastic membrane, which will produce a vibration inside the can and hence we will notice sudden changes in our flame.

As shown in the pictures cut the balloon and bind it tightly to the end with extra thread protection so that no air leakage can occur.

Note: Remember to choose a material so that it can be heat resistive, as when the flames will lit the metal pipe gets heated & so membrane should not break away.

Here is the time for making the Gas input system. You can use any gas like propane tank, butane tank or any other flammable gas.

I made the Gas intake system with the help of 6mm aquarium pipes and plastic joints. I also used 2 L-joints, 2 I-joints and a pressure regulator valve for controlling the gas flow.

I used a I-joint and some Teflon tape and then I inserted in the opening of our Deodorant can, it easily fits in there. Use some super glue to permanently fix the joint so that no movement can happen and no gas leaks.

As shown in the pictures I cut 3 pieces of 6mm pipe and joined all the L-joints to the regulator end. Then I used another 2mm pipe with a I-joint and attached to the other end of the regulator. This pipe will be connected to the Lighter head.

A Lighter is a cheap and easily available tool that contains flammable gases and is suitable for our demonstration. I already mentioned using a butane or propane tank is much recommended.

This step is really simple I only used a small nut and bolt to fix the gas flow lever.

First I disassembled the Lighter and take out other non necessary parts. Then I fitted the nut through a piece of hard plastic and then super glued the assembly to the Lighter. And hence, when we lower our bolt it will push and hold our trigger lever so that a continuous gas flow may occur.

Now, install the 2mm pipe to the Lighter nozzle and connect to the regulator.

The base is made with Plywood of thickness 2mm and 6mm. I had a few scrap pieces of ply, though I used them to get a durable stand for my experiment.

Or, you can simply use pieces of cardboard to make the same. It will be much easier and cost effective too.

Here, I used a long piece of 6mm ply as the bottom plate. Then I took another two vertical pieces of 2mm ply and cut them in quarter circle in top, so that our metal pipe can easily rest in there. Also I used a 6mm stand for the pressure valve to sit on.

I used regular wood glue (fevicol) to fix them all and lastly, I coated the base with Varnish.

All our major parts are completed, now lets put them together in the base. For this I used double sided tape to fix the regulator, lighter and the can to the stand.

So, our mechanism is completed and we are ready to begin our experiment now.

Now I released the gas form the Lighter and lit the can, what I see is the flow of flame are too small due to a low pressure. Suddenly I noticed that gas was leaking from the nozzle of the lighter and at this flow we can not run our experiment.

So, I need to replace the lighter and use another source of gas. I knew a filled deodorant can contains alcochol as an ingredient, hence it is also flammable and that time I had the only choice available in my home.

Therefore I made a hole in my Deo can and connected to the regulator and now there is no gas leakage and the flames are higher than before. And I can now easily control the gas flow by turning the valve regulator. Also suddenly I got fire in my regulator too as it was fully open and gas leaked through the hole.

Therefore,

Now if you place a frequency generator or a speaker near the Diaphragm, you can see a change in pattern to the flame with the change in frequency. At the pressure nodes, the flames are higher and vice-versa.

Also if you tap the Diaphragm with your finger you will be able to see the same change instantly. Hence it is confirmed that the standing wave will create points with oscillating (higher and lower) pressure and points with constant pressure (pressure nodes) along the tube. Thus we will see the formation of nodes and anti-nodes among the flame.

The result is in front of you now. At the pressure nodes, the flames are higher. At the end of the tube gas molecule velocity is zero and oscillating pressure is maximal, thus low flames are observed. It is possible to determine the wavelength from the flame minimum and maximum by simply measuring with a ruler.

So,

If you find any difficulty or any suggestion you want to put, please comment it below.

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