Coandă Profiles & Effect

Here at EXAIR, Coandă is a household name that can be heard on any given day multiple times throughout the day. The Coandă effect is fairly easy to visualize with a ligthweight ball and some high velocity airflow. Take the video below for example. This 2″ Super Air Amplifier on a stand powered at 40 psig at the inlet easily lifts this hollow plastic ball and then suspends the ball due to the Coandă effect.

If you were able to see the airflow, you would see it impacting the surface of the sphere at all different points then following the profile of the sphere until it colides with itself and is forced to separate off the surface. The turbulent flow on the top is creating a downward pressure as well. The science behind this was all found and showcased by Henri Coandă. He showcased this with a propulsion device which used a domed hood with airflow to follow the curvature of the dome then exit off the sharp edge or where the separate air streams began to recombine causing a turbulent / low pressure area depending on the angle.

This stream of air following a surface begins to pull in all surrounding and impacted air molecules from around the stream which is called entrainment. This is a key factor for EXAIR products and one reason the Coandă profiles are a key characteristic to obtaining the peak performance and efficiency out of a compressed air product.

As the high velocity air stream exits the EXAIR model 1100 Super Air Nozzle the ambient air is entrained around the fins and angled surfaces of the nozzle.

Many EXAIR products utilize the Coandă principle to improve their efficiencies and performance. Below you can see the EXAIR product families containing Coandă profiles within their design which increases the ambient air entrainment resulting in an amplified air blowoff.

Super Air Wipes, Super Air Knives, Super Air Nozzles and Super Air Amplifiers use the Coanda principle to become some of the most efficient compressed air blowoff products available.

If you would like to discuss how the Coandă profile and EXAIR Intelligent Compressed Air Products® can help your process, please give us a call.

Brian Farno
Application Engineer
BrianFarno@EXAIR.com
@EXAIR_BF

The Theory of the Vortex Tube

There are many theories regarding the dynamics of a vortex tube and how it works. Many a graduate student has studied them as part of their research requirements.

VT_air2

The Vortex Tube was invented by accident in 1928, by George Ranque, a French physics student. He was performing experiments on on a vortex-type pump that he had developed and noticed that warm air exhausted from one end and cold air from the other! Ranque quickly stopped work on the pump, and started a company to take advantage of the commercial possibilities for this odd little device that produced both hot and cold air, using only compressed air, with no moving parts. The company was not successful, and the vortex tube was forgotten until 1945 when Rudolph Hilsch, a German physicist, published a widely read paper on the device.

A vortex tube uses compressed air as a power source, has no moving parts, and produces hot air from one end and cold air from the other. The volume and temperature of the two air streams is adjustable with a valve built into the hot air exhaust.  Temperatures as low as -50°F (-46°C) and as high as 260°F (127°C) are possible.

Here is one widely accepted explanation of the physics and the phenomenon of the vortex tube.VT

Compressed air is supplied to vortex tube and passes through nozzles that are tangent to to an internal counterbore (1). As the air passes through it is set into a spiraling vortex motion (2) at up to 1,000,000 rpm. The spinning stream of air flows down the hot tube in the form of a spinning shell, like a tornado (in red). The control valve (4) at the end allows some of the warmed air to escape (6) and what does not escape reverses direction and heads back down the tube as a second vortex (in blue) inside of the low pressure area of the larger warm air vortex. The inner vortex loses heat and exits the through the other end of as cold air (5).

It is thought that that both the hot and cold air streams rotate in the same direction at the same angular velocity, even though they are travelling in opposite directions. A particle of air in the inner stream completes one rotation in the same amount of time that an air particle in the outer stream. The principle of conservation of angular momentum would say that the rotational speed of the inner inner vortex should increase because the angular momentum of a rotating particle (L) is equal to the radius of rotation (r) times its mass (m) times its velocity (v).  L = r•m•v.  When an air particle moves from the outer stream to the inner stream, both its radius (r) and velocity (v) decrease, resulting in a lower angular momentum. To maintain an energy balance for the system, the energy that is lost from the inner stream is taken in by the outer stream as heat. Therefore, the outer vortex becomes warm and the inner vortex is cooled.

At EXAIR, we have harnessed the cooling power of the vortex tube, and it can be found and utilized in such products as Spot Coolers, Cabinet Coolers, and the Vortex Tube themselves.

Harnessing the cooling power of the vortex tube 

If you have questions about Vortex Tubes, or would like to talk about any of the EXAIR Intelligent Compressed Air® Products, feel free to contact EXAIR and myself or any of our Application Engineers can help you determine the best solution.

Brian Bergmann
Application Engineer
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