Greetings!

Has anyone ever heard of a fluidic diode?! I am wondering what it is and what it looks like. Apparently, fluid can flow easily in one direction but not the other.

Any information would be greatfully received. Thanks.

It's commonly called a check valve. I've handled them in sizes ranging from 0.5" diameter to 24" diameter (a friend of mine has been inside one that was 60" diameter). They are generally of two basic designs, swing and lift. A swing check valve has a disk on a pivot that is "swung" open by a differential pressure across the disk. A lift check valve looks like a globe valve with no stem. The disk is "lifted" by differential pressure. Sometimes the disk is spring loaded to increase the differential pressure required to open it. There are also a number of less common check valve types.

Crane Technical Paper 410 (a classic) has some small, cartoonish, schematic drawings in it.

Thanks for the info. Alton. We had thought of the check valve, but this fluidic diode has no mechanical parts to it. (Otherwise, it would be called a check valve!!!). Similar to the way an electrical diode has no mechanical parts. Also, I think these diodes can be smaller than 0.5".

Thank you for the response anyway.

Hi, Suzanne.

Well, literally, I heard about them but not more than that. Cannot give references. If I remember right, some Russian invented them, and references could be in Russian. Probably, many others invented them, too, the idea is obvious enough, so it is worth trying a search engine in English.

Suppose, you have a tube with a diaphragm in it, well, just like a wall across the tube with a hole in the center. Then, the hydraulic resistance is the same in both directions due to the symmetry. Deform the diaphragm by moving the center to one side along the tube axis, so that it is shaped like a cone with a hole. Then, the resistance in one direction is greater than in the other. Now, the crucial step is to put many such diaphragms into a tube. In that case the difference in the hydraulic resistance coefficients in different directions may be quite high, and not only because of the local resistances added but also because when the fluid flows in the direction in which the cross-section area diminishes it forms a jet with the diameter close to the diameter of the hole and such a jet passes through the following holes relatively easy. When moving into another direction, the diameter of the jet is substantially less than the diameter of the hole, and if the geometry is properly chosen then, due to instability of the flow in diverging channels, it expands, and the next diaphragm will again add to the resistance.

Well, for those who have experience and intuitive understanding of fluid behaviour this is quite simple, qualitatively, but it is difficult to explain in short. If you want some understanding, try a search engine on flow in converging and diverging channels, sudden expansions, and Borda mouthpiece.

Certainly, using the idea, many geometries can be used for obtaining this diode. If I remember right, one of the simplest and quite efficient is just a plane channel with a number of flat plates mounted at one wall at an angle to it. From the picture I recollect the number of plates was at least ten, the angle was about \pi/4, the length was such that they blocked 75% of the cross-section, and the axial spacing was about 25% of the channel width. However, I do not remember whether it was a drawing with proper dimensions or just a sketch illustrating the idea.

I do remember that the difference in resistances was huge, but cannot give values.

Practical applications are numerous and obvious. Valves for piston pumps, for example.

Hope this helps.

Sergei

(1). Section 5.2 Diodes, Edited by Arthur Conway, "A Guide to Fluidics", published by MacDonald, London 1971. (2). .....Vortex diode,....The device is in its high-resistance state when fluid flows in through the tangential port, (***vortex or flow separation***) , with the flow in other direction, the device is in its low-resistance state- a vortex is not formed. (**** no flow separation****).....First reported in 1935,....three types commonly used,....pressure ratios up to 50:1,....pressure ratios up to 180:1,..... (3). (***** something like flying an airplane forward vs flying backward, ****non-separated flow vs separated flow****). .....no moving parts.....

Suzanne

A fluidic diode is like a cyclone in reverse, except there is no hopper. It consists of a thin or squat cylidrical body with a tangential port and an axial port. When fluid enters through the axial port it exits the tangential port and there is low resistance. If the flow is reversed so that the fluid enters the tangential port (swirl is induced) and there is a resistance to the flow exiting the axial port.

These devices and be combined to give fluidic circuits resulting in amplifers etc. Much development was carried out in the nuclear industries, where these devices are employed in glovebox systems. A good contact is my colleague Dr. John Tippetts at Sheffield University, UK.

Regards

Alan Rose

ROSE Consulting Engineers