Entrainment: What is it?

By definition, entrainment is a form of the verb, entrain, which is fluid that is swept along into an existing moving flow.   Whenever there is a discussion about fluid dynamics, the Bernoulli’s equation generally comes up.  This equation is unique as it relates flow energy with kinetic energy and potential energy.  The formula was mainly linked to incompressible fluids, but under certain conditions, it can be significant for gas flows as well.  I would like to discuss how EXAIR uses the Bernoulli’s equation for entrainment to maximize efficiency within your compressed air system.

This relationship between pressure as compared to flow and velocity came to be known as the Bernoulli’s principle.  “In fluid dynamics, Bernoulli’s principle states that an increase in the speed of fluid occurs simultaneously with a decrease in static pressure or a decrease in the fluids potential energy”1. Bernoulli realized that the sum of kinetic energy, flow energy, and potential energy is a constant during steady flow.  He wrote the equation like this:

Equation 1:

P/r + V2/2 + gz = constant

P – Pressure

r – density

V – velocity

g – gravitational constant

z – height difference

 

Not to get too technical, but you can see the relationship between the velocity squared and the pressure from the equation above.  Being that this relationship is a constant along the streamline; when the velocity increases; the pressure has to come down.  An example of this is an airplane wing.  When the air velocity increases over the top of the wing, the pressure becomes less.  Thus, lift is created and the airplane flies.

Since we know the criteria to apply the Bernoulli’s equation with compressed air, let’s look at some EXAIR products.  Blowing compressed air to cool, clean, and dry, EXAIR can do it very efficiently as we use the Bernoulli’s principle to entrain the surrounding air.  Remember from the equation above, as the velocity increases, the pressure has to decrease.  When the pressure decreases, the surrounding air will move toward the low pressure.  That low pressure will sweep the ambient air into the air stream; called entrainment.

Compressed air is expensive, but the ambient air is free.  The more ambient air we can entrain, the more efficient the blowing device is.  As an example, we engineer the Super Air Knife to maximize this phenomenon to give an amplification ratio of 40:1. So, for every 1 part of compressed air, the Super Air Knife will bring into the air streamline 40 parts of ambient “free” air.  This makes the Super Air Knife one of the most efficient blowing devices on the market.  By adding mass to the flow stream, it will reduce the compressed air usage, saving you money, and allow for better cooling and a stronger blowing force.  For a drilled pipe, the amplification ratio is generally only two to three times.

We use this principle for many of our products like the Air Amplifiers, Safety Air Guns, Air Nozzles, Air Knives, and Gen4 Static Eliminators. Daniel Bernoulli was able to find a relationship between velocities and pressures, and EXAIR was able to use this to create efficient, safe, and effective compressed air products.  To find out how you can use this advantage to save compressed air in your processes, you can contact an Application Engineer at EXAIR.  We will be happy to help you.

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

 

  1. Wikipedia https://en.wikipedia.org/wiki/Bernoulli%27s_principle

EXAIR’s Gen4 Power Supplies, the Foundation of Gen4 Static Eliminators

In the fall and winter seasons, the air becomes much drier. You may be familiar with the unpleasant shock you get from the door knob after walking across a carpeted surface. While this type of shock doesn’t generally cause any sort of problems, in many industrial processes this static electricity can cause a wide range of issues. These may manifest as nuisance shocks to an operator – similar to the door knob example, but it can also cause problems with the finish quality of coatings and paint. It will make ink jetted codes unreadable, cause blemishes in printing processes, and short out sensors being relied upon for counts and quality inspections…just to name a few. 

The reason that you experience static shocks more frequently during winter is due to the relative humidity. At colder temperatures air does not hold as much water as it does when it’s warm, and since water conducts electricity, higher humidity keeps static at lower levels. Even though you’re heating your house to a similar temperature, the air that is being drawn into your home and heated is still the dry cold air containing less moisture.

So how do we tackle this static problem that’s running rampant in your processes? EXAIR has a wide range of Static Eliminators available to ship same-day from stock. Each of which is designed to handle different types of applications. At the heart of these Static Eliminators is the EXAIR Power Supply. Available with either 2 or 4 ports, the Gen4 Power Supply is suitable for use with either 115V or 230V via the selector switch on the back. A 6’ modular power cord and lighted power switch are included. The modular cable protects sensitive electronics against electromagnetic interference while easing connections and routing. An integrated fuse (spare fuse is also included) on the primary protects against voltage spikes.

Model 7960 Gen4 Power Supply (top) has two ports; Model 7961 (bottom) has four, depending on how many Static Eliminators you wish to operate from the same Power Supply

Two shielded cables are included with both styles of Power Supply. A standard 3-prong outlet for North American customers, and another that allows you to install your own plug to accommodate any style of electrical outlet. The integrated ground connection on the high voltage side allows for complete connection using just the bayonet connector. A grounding post on the front-face of the Power Supply is available for bonding of the Power Supply to machine frames. Shunting circuitry designed into the Power Supply protects the user against any short circuit on the secondary side.

The Power Supply includes an integrated flange for easy mounting in any orientation. Rugged and durable stainless steel connections are present at the high voltage side vs the plastic connectors of the competition. This facilitates the integrated ground and shockless design of all of our Static Eliminator products. The Power Supply is both RoHS and CE compliant, as well as UR Listed.

Here at EXAIR we’ve helped customers in a wide range of industries solve their static issues within their processes. If you would like to discuss the best option for dealing with your static, give us a call. An Application Engineer is ready on the other line to help diagnose your issue and make a suitable recommendation.

Tyler Daniel
Application Engineer
E-mail: TylerDaniel@EXAIR.com
Twitter: @EXAIR_TD

Bifurcation Of Air – The Wonders of Science That Is The Vortex Tube

EXAIR has provided the benefits of vortex tube technology to the industrial world since 1983. Prior to that, French scientist George Ranque wrote about his discovery in 1928 calling it the tube tourbillion. But it wasn’t until German physicist Rudolf Hilsch’s research paper in 1945 on the wirbelrorhr or whirling tube, that the vortex tube entered the minds of commercial engineers. Nearly 60 years later, EXAIR is a leading provider for cooling products utilizing vortex tube technology.

More than 2,000 BTU/hr in the palm of your hand!

EXAIR Vortex Tubes produce a cold air stream down to -50° F and are a low cost, reliable, maintenance-free (there are no moving parts!) solution to a variety of spot cooling applications. These applications span a wide variety of industries and include cooling of electronic controls, soldered parts, machining operations, heat seals, environmental chambers, and gas samples. We’re always finding compelling new cooling opportunities for the vortex tubes.

How a Vortex Tube Works

So how does it produce the cooling stream? Compressed air is plumbed into the side port of the Vortex Tube where it is ejected tangentially into the internal chamber where the generator is located. The air begins flowing around the generator and spinning up to 1 million RPM toward the hot end (right side in the animation above) of the tube, where some hot air escapes through a control valve. Still spinning, the remaining air is forced back through the middle of the outer vortex. Through a process of conservation of angular momentum, the inner stream loses some kinetic energy in the form of HEAT to the outer stream and exits the vortex tube as COLD air on the other side.

The adjustable control valve adjusts what’s known as the cold fraction. Opening the valve reduces the cold air temperature and also the cold airflow volume. One can achieve the maximum refrigeration (an optimum combination of temperature and volume of flow) around an 80% cold fraction. EXAIR publishes performance charts in our catalog and online to help you dial into the right setting for your application, and you can always contact a real, live, Application Engineer to walk you through it.

EXAIR manufactures its vortex tubes of stainless steel for resistance to corrosion and oxidation. They come in small, medium and large sizes that consume from 2 to 150 SCFM and offer from 135 to 10,200 BTU/hr cooling capacity. Each size can generate several different flow rates, dictated by a small but key part called the generator. That generator can be changed out to increase or decrease the flow rate.

While operation and setup of an EXAIR Vortex Tube are easy, its performance will begin to  decrease with back pressure on the cold or hot air exhaust of over 3 PSIG. This is a key  when delivering the cold or hot airflow through tubes or pipes. They must be sized to minimize or eliminate back pressure.

The Vortex Tube is integrated into a variety of EXAIR products for specific applications, like the Adjustable Spot Cooler, the Mini Cooler, the Cold Gun Aircoolant System and our family of Cabinet Cooler Systems.

If you would like to discuss your next cooling application, please contact an Application Engineer directly and let our team lead you to the most efficient solution on the market.

Brian Farno
Application Engineer
BrianFarno@EXAIR.com
@EXAIR_BF

Heavy Duty Line Vacs Within a Machining Facility

An overseas automotive company was using six machines that milled, stamped, and punched aluminum parts.  The machining center used two machines for stamping, and the piece of aluminum was 10mm X 10mm.  The second operation used two machines to punch out a 2mm diameter by 40mm rod. The last operation was milling the edges of the surface to a specific dimension.  The curly swarf that was being produced was around 5mm in diameter by 40mm in length.

Currently they had mechanical conveyors that would dump the scrap material into bins.  The operators would move the full bins to a central dumping area for recycling about 20 meters (66 feet) away.  They used shovels to move the scrap from the bins to a larger container.  This part of the operation took time and was ergonomically unsafe with lifting and twisting.   They were making about 300grams per minute, and with a 24-hour operation, that was a lot of material.  They contacted EXAIR to see if we could help them.

To move the aluminum scrap from the machines to the recycle container, they had to travel 20 meters (66 feet) horizontally, and 3 meters (10 feet) vertically above the floor.  For this distance and the size of the aluminum pieces, I recommended the EXAIR model 152200; 2” Heavy Duty Line Vac Kit.  The through opening for the 2” Line Vac was 44mm (1.75”) in order to move the material through.  This Line Vac is made from a hardened steel construction which is very resistant to wear.  It is also designed for higher vacuum levels to convey materials at a faster rate and longer distances.

The Line Vac is operated with only compressed air to generate a Venturi vacuum, and they are very compact and easy-to-use.  The vacuum generator does not have any motors or moving parts to wear, and the inline design makes it simple to attach a hose to the vacuum and exhaust side.  The kit includes a Filter Separator, Regulator and a bracket for cleaning, controlling and mounting.  They did have to add a hopper to each mechanical conveyor to collect the scrap.  Now, the Line Vac is connected to the hopper with a hose, and the scrap material would travel to the recycle container 20 meters (66 feet) away.

               The EXAIR Air Operated Conveyors, or Line Vacs™, are great tools for conveying items in a “scoop and shovel” type of applications.  If your company manually moves a product from point A to point B, you can contact an EXAIR Application Engineer to see if an Air Operated Conveyor could improve your process.  For this overseas customer above, the model 152200 Heavy Duty Line Vac Kit improved their operation and removed the ergonomic hazard for their operators.

 

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

 

Photo: Milling operation by gefrorene_wand  Pixabay License