The Super Air Knife Vs. a Homemade Drilled Pipe Solution

A drilled pipe has been used for many years to blow compressed air across a span for cleaning, cooling, and drying.  They are a simple tool that was created from spare parts and many holes.  The cost to make this type of product is not expensive, but to use this product in your application is very expensive.  Similarly, an incandescent lightbulb is inexpensive to purchase, but it will cost you much more in electricity than a LED light bulb.  Since 1983, EXAIR has been innovating safe and efficient products to be used in compressed air systems.  In this blog, I will compare the drilled pipe with the Super Air Knife.

Even though you can find the components relatively easily to design your own drilled pipe, this blow-off design is very costly and stressful to your compressed air system.  Typically, the holes along the pipe are in a row next to each other.  As the airstream leaves from each hole, it will hit the airstream from the one next to it.  This will cause turbulent air flows which has inconsistent forces and loud noises.  Also, with turbulent air flows, the ability to entrain the surrounding ambient air is very small.  We call this the amplification ratio.  The higher the amplification ratio, the more efficient the blow-off device is.  For a drilled pipe, the amplification ratio is near 3:1 (3 parts ambient air to 1 part compressed air).

A colleague, Brian Bergmann, wrote a blog about the amplification ratio of the EXAIR Super Air Knife.  (Read it HERE.)  This blog demonstrates how EXAIR was able to engineer an efficient way to blow air across a span.  The unique design of the Super Air Knife creates an amplification ratio of 40:1 which is the highest in the market.   Unlike the drilled pipe, the gap opening runs along the entire knife for precise blowing.  This engineered gap allows for laminar air flow which has a low noise level, a consistent blowing force, and maximum amplification ratio.  With these benefits, the Super Air Knife can reduce the amount of compressed air required, which will save you money and save your compressed air system.

In comparing the drilled pipe to the Super Air Knife, I will relate both products in a simple cooling application.   Thermodynamics expresses the basics of cooling with an air temperature and an air mass.  Since both products are represented in the same application, the air temperature will be the same.   Thus, the comparison will be with the amount of air mass.  In this example, the customer did some calculations, and they needed 450 Lbs. of air to cool the product to the desired temperature.  At standard conditions, air has a density of 0.0749 lbs/ft3.  To convert to a volume of air, we will divide the weight by the density:

450 lbs. / (0.0749 lbs./ft3) = 6,008 ft3 of air

To meet this requirement, reference Table 1 below.  It shows the volume of air required by your compressed air system to meet this demand.  As you can see, your compressor has to work 13X harder to cool the same product when using a drilled pipe.  Just like the LED light bulbs, the Super Air Knife has more efficiency, more innovation, and uses less compressed air.  In turn, the Super Air Knife will save you a lot of money in electrical costs.  If you would like to see how much the Super Air Knife can save compared to the drilled pipe, we have that information in this blog.  (Read it HERE.)  For my reference, it will reduce the stress of your compressed air system.

if you would like to compare any of your current blow-off devices with an innovative EXAIR product, you can contact an Application Engineer.  We can do an Efficiency Lab to shine an LED light on saving energy and money with your compressed air.

John Ball
Application Engineer
Email: johnball@exair.com
Twitter: @EXAIR_jb

Fluidics, Boundary Layers, And Engineered Compressed Air Products

Fluidics is an interesting discipline of physics.  Air, in particular, can be made to behave quite peculiarly by flowing it across a solid surface.  Consider the EXAIR Standard and Full Flow Air Knives:

Compressed air flows through the inlet (1) to the Full Flow (left) or Standard (right) Air Knife, into the internal plenum. It then discharges through a thin gap (2), adhering to the Coanda profile (3) which directs it down the face of the Air Knife. The precision engineered & finished surfaces serve to optimize the entrainment of air (4) from the surrounding environment.

If you’ve ever used a leaf blower, or rolled down the car window while traveling at highway speed, you’re familiar with the power of a high velocity air flow.  Now consider that the Coanda effect can cause such a drastic redirection of this kind of air flow, and that’s a prime example of just how interesting the science of fluidics can be.

EXAIR Air Amplifiers, Air Wipes, and Super Air Nozzles also employ the Coanda effect to entrain air, and the Super Air Knife employs similar precision engineered surfaces to optimize entrainment, resulting in a 40:1 amplification ratio:

EXAIR Intelligent Compressed Air Products such as (left to right) the Air Wipe, Super Air Knife, Super Air Nozzle, and Air Amplifier are engineered to entrain enormous amounts of air from the surrounding environment.

As fascinating as all that is, the entrainment of air that these products employ contributes to another principle of fluidics: the creation of a boundary layer.  In addition to the Coanda effect causing the fluid to follow the path of the surface it’s flowing past, the flow is also affected in direct proportion to its velocity, and inversely by its viscosity, in the formation of a boundary layer.

High velocity, low viscosity fluids (like air) are prone to develop a more laminar boundary layer, as depicted on the left.

This laminar, lower velocity boundary layer travels with the primary air stream as it discharges from the EXAIR products shown above.  In addition to amplifying the total developed flow, it also serves to attenuate the sound level of the higher velocity primary air stream.  This makes EXAIR Intelligent Compressed Air Products not only as efficient as possible in regard to their use of compressed air, but as quiet as possible as well.

If you’d like to find out more about how the science behind our products can improve your air consumption, give me a call.

Video Blog: Which EXAIR Air Knife Is Right For You?

The following short video explains the differences between the 3 styles of Air Knives offered by EXAIR – The Super, Standard and Full-Flow. All of these Models are IN STOCK, ready to ship, with orders received by 3:00 PM Eastern.

If you need additional assistance choosing your EXAIR Air Knife, please contact an application engineer at 800-903-9247.

Justin Nicholl
Application Engineer
justinnicholl@exair.com
@EXAIR_JN

 

 

Super Air Knife Provides Tension with Fine Adjustment for a Lightweight Plastic Film

A company had a small converting machine that was winding a plastic film onto a roll. The width of the plastic film was only 3” across, and the amount of tension required for a consistent roll was small. The maximum amount of tension without damaging the plastic film was 16 ounces of force.  In converting media onto rolls, it is very important to control the tension on the web to reduce defects like wrinkles, out-of-round rolls, or stretching.

They explained the setup that they were trying. They had a 4” manifold with two 2” wide “duck-foot” nozzles attached.  They sent a hand drawing to better describe what they were using. (See below).  The issue that they were seeing was too much variation in the blowing force being applied to the film.  To get near the correct blowing force, they had to start at an air pressure of about 18 PSIG.  As they ran the process, the operator would have to adjust the pressure continuously to evenly roll the film onto the core.  The process was out of control, and they wondered if EXAIR had a better way to evenly exert this force.

Dual Flat Nozzle Manifold
Dual Flat Nozzle Manifold

In analyzing the drawing and their setup, I noticed a couple of things that could cause the variations. I modified his drawing to better explain the situation (Reference below).  As compressed air leaves the two flat nozzles, the center section will overlap.  This overlap will cause turbulence in the air flow pattern.  In order to get an even distribution of forces across the width of the product, turbulence cannot exist.  Turbulence is a mixing pattern where the velocity is not linear; thus, causing high and low pressure points on the target.  The other thing that I noticed was the low air pressure that they could not go above.  This limited the precision of the incremental forces.  Because of the fixed openings of the two nozzles, they had to have a ceiling with the air pressure at 18 PSIG for 16 ounces of force.  If they had to “bump” the force level, the change was difficult to hit exactly.  If we divided the 16 ounces of force between 0 – 18 PSIG, we would get roughly 0.9 ounce of force per PSIG.  You lose the accuracy to make fine adjustments.

Overlap of air flow pattern
Overlap of air flow pattern

I recommended our model 110003, 3” Super Air Knife and a model 110303 Shim Set. The Super Air Knife blows compressed air across the entire length.  Without any overlap, the flow is laminar, and the velocity profile is moving in the same direction.  Thus, an even force across the entire 3 inches.  The Shim Set comes with additional shim thicknesses of 0.001”, 0.003”, and 0.004” thick (the standard thickness of 0.002” is installed in the Super Air Knife). In working with such a precise force requirement, they needed additional options for more control.  They could change the shims as a coarse adjustment and adjust their pressure regulator as a fine adjustment.  This combination gave them the best results to accurately dial in the correct force and not damage the material.  With the maximum requirement of 16 ounces across 3 inches of film, they were able to change the shim to the 0.004” thickness.  For the model 110003 Super Air Knife, it put them at a maximum pressure of 86 PSIG, not 18 PSIG.  Thus the increment was now 0 – 86 PSIG for 16 ounces of force, or 0.19 ounces per PSIG.  There was much more resolution to make smaller changes to the force levels thus optimizing their adjustment range.

Super Air Knife with Shim Set
Super Air Knife with Shim Set

In replacing the competitor’s product with a Super Air Knife, our customer had all the necessary control to wrap rolls of film without issue. The setup with the nozzles on a manifold design resulted in turbulence, which was noisy and produced inconsistent results.  It also restricted their adjustment resolution in changing forces, as they do not use shims.  If you would like to exert a greater degree of precision blowing with products like the Super Air Knife, please contact us. We would be happy to discuss your application and help you meet such goals.

John Ball
Application Engineer
Email: johnball@exair.com
Twitter: @EXAIR_jb