Laminar Flow Compared to Turbulent Flow

turbulent vs laminar

Fluid mechanics is the field that studies the properties of fluids in various states.  There are two main areas; fluid statics and fluid dynamics.  Fluid dynamics studies the forces on a fluid, either as a liquid or a gas, during motion.  Osborne Reynolds, an Irish innovator, popularized this dynamic with a dimensionless number, Re. This number determines the state in which the fluid is moving; either laminar flow, transitional flow, or turbulent flow.  Equation 1 below shows the relationship between the inertial forces of the fluid as compared to the viscous forces.

Equation 1:  Re = V * Dh/u

Re – Reynolds Number (no dimensions)

V – Velocity (feet/sec or meters/sec)

Dh – hydraulic diameter (feet or meters)

u – Kinematic Viscosity (feet^2/sec or meter^2/sec)

The value of Re will mark the region in which the fluid (liquid or gas) is moving.  If the Reynolds number, Re, is below 2300, then it is considered to be laminar (streamline and predictable).  If Re is greater than 4000, then it is considered to be turbulent (chaotic and violent).  The area between these two numbers is the transitional area where you can have eddy currents and some non-linear velocities.  To better show the differences between each state, I have a picture below that shows water flowing from a drain pipe into a channel.  The water is loud and disorderly; traveling in different directions, even upstream.  With the high velocity of water coming out of the drain pipe, the inertial forces are greater than the viscous forces of the water.  This indicates turbulent flow with a Reynolds number larger than 4000.  As the water flows into the mouth of the river, the waves transform from a disorderly mess into a more uniform stream.  This is the transitional region.  A bit further downstream, the stream becomes calm and quiet, flowing in the same direction.  This is laminar flow.  Air is also a fluid, and it will behave in a similar way depending on the Reynolds number.

Turbulent to Laminar Water

Why is this important to know?  In certain applications, one state may be better suited than the other.  For mixing, suspension and heat transfer; turbulent flows are better.  But, when it comes to effective blowing, lower pressure drops and reduced noise levels; laminar flows are better.  In many compressed air applications, the laminar region is the best method to generate a strong force efficiently and quietly.  EXAIR offers a large line of products, including the Super Air Knives, Super Air Amplifiers and Super Air Nozzles that utilizes that laminar flow for compressed air applications.  If you would like to discuss further how laminar flows could benefit your process, an EXAIR Application Engineer will be happy to help you.

John Ball
Application Engineer
Email: johnball@exair.com

Twitter: @EXAIR_jb

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

Air Nozzles and Air Jets: An Overview

One of the simplest solutions to lower your air consumption and noise level when it comes to compressed air is to switch your open tubes or pipes and liquid nozzles which are being used for air applications to an engineered compressed air nozzle. EXAIR’s Engineered Air Nozzles and Jets provide a simple solution for a wide variety blow off and compressed air applications and can solve a multitude of process problems efficiently. These applications can include simple blow offs, cooling, part ejection, and much more.

Super Air Nozzles:
Super Air Nozzles are one of the more versatile of all of EXAIR’s Engineered Air Nozzles. They come in many different sizes from a tiny size of M4 threads and 13 millimeters long to the largest with  1-1/4 NPT threads which has a 2″ hex and is almost 5″ long. These are usually used for standard blow off applications that replace open pipes to reduce your air consumption and noise. The force values vary from 2 ounces to 23 pounds of force. 

Another variation of the Super Air Nozzles is the Flat Super Air Nozzles; these nozzles create a small flat curtain of air at a high force to provide a wider blow off area for smaller NPT sized nozzles. The 1” and 2” Flat Super Air Nozzle also have replaceable shims that allow you to adjust the force coming out of the nozzle by increasing the amount of air that is used.   

EXAIR Air Nozzles

Back Blow Air Nozzles:
Back Blow Air Nozzles are designed in a way that blows that makes it easy to blow out the inside of pipes. The Back Blow Air Nozzles have holes around the outside diameter pointed back that creates a cone of air around the air inlet port. This makes it easy to dislodge clogs in pipes that you don’t want going back into the machine and for blowing out liquid and debris from the inside. They are also commonly used with EXAIR’s Chip Shield as to prevent any particles from flying back and hitting the user. Back Blow Air Nozzles come in three sizes: M4, ¼”, and 1” and can be used on inside diameters ranging from ¼” to 16”. 

EXAIR Back Blow Air Nozzles

Super Air Nozzle Clusters:
Super Air Nozzle Clusters use a number of the ¼” Super Air Nozzles to create one nozzle that has a wider cone and larger force. Clusters are usually used in wide area blow off but can also be used for part cooling and part reject as they do supply a wider area of force. Super Air Nozzle Clusters are sized by the number of nozzles in the cluster; the three sizes that we offer are 4-nozzle cluster (3/8” NPT inlet), 7-nozzle cluster (1/2” NPT inlet), and the 12-nozzle cluster (1” NPT inlet). 

EXAIR Super Air Nozzle Cluster

Air Jets:
Air Jets amplify the total volume of air into a high velocity stream of air. This makes it very useful for blowing off/drying applications and cooling applications due to the higher volume of air flowing through the unit. Air Jets come in two variations which are the High Velocity Air Jet and the Adjustable Air Jets. The High Velocity Air Jet uses a 0.015” shim that allows the air to escape the unit at a high velocity laminar flow to entrain the surrounding ambient air; this can be adjusted down using the shim kit which includes a 0.006” and 0.009” shims. The Adjustable Air Jet allows the user to easily adjust the air gap using the micrometer gap indicator. 

EXAIR Air Jets

If you have any questions about compressed air systems or want more information on any of EXAIR’s products, give us a call, we have a team of Application Engineers ready to answer your questions and recommend a solution for your applications.

Cody Biehle
Application Engineer
EXAIR Corporation
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Keep Your Pneumatics “Healthy” and “Running Like a Brand New Car”

Compressed air systems are used in facilities to operate pneumatic systems, and these systems are vital for industries.  So, it is important to keep them running.  The system can be segregated into three different sections; the supply side, the demand side, and the distribution system.  I like to represent these sections as parts of a car.  The supply side will be the engine; the distribution system will be the transmission; and, the demand side will be the tires.  I will go through each section to help give tips on how to improve the “health” of your pneumatic system.

From the supply side, it will include the air compressor, after-cooler, dryer, and receiver tank that produce and treat the compressed air.  They are generally found in a compressor room somewhere in the corner of the plant.  The air compressor, like the engine of your car, produces the pneumatic power for your plant, and needs to have maintenance to keep it working optimally.  The oil needs to be changed, the filters have to be replaced, and maintenance checks have to be performed.  I wrote a blog that covers most of these items, “Compressed Air System Maintenance”.

To connect the supply side to the demand side, a distribution system is required.  Distribution systems are pipes which carry compressed air from the air compressor to the pneumatic devices.  Just like the transmission on the car, the power is transferred from the air compressor to your pneumatic products.

Maintenance is generally overlooked in this area.  Transmissions have oil which can be detected if it is leaking, but since air is a gas, it is hard to tell if you have leaks.  Energy is lost from your pneumatic “engine” for every leak that you have.  So, it is important to find and fix them.  A study was conducted within manufacturing plants about compressed air leaks.  They found that for plants without a leak detection program, up to 30% of their compressed air is lost due to leaks.  This will be equivalent to running on only 6 cylinders in a V-8 engine.

EXAIR offers the Ultrasonic Leak Detector to find those pesky leaks.  It makes the inaudible “hiss”; audible.  It can detect leaks as far as 20 feet (6m) away with the parabola attachment, and can find the exact location of the leak to be fixed with the tube attachment.

Another area for discussion with the distribution system is contamination like rust, oil, water, and debris.  Compressed air filters should be used to clean the compressed air that supplies your pneumatic products. They can remove the debris for your pneumatic products to have a long life.  You can read about the EXAIR compressed air filters here, “Preventative Maintenance for EXAIR Filters”.

The third section is the demand side.  So, you have an engine that makes the power, the transmission to transfer that power, and the tires to use that power safely and efficiently.  Many managers miss the importance of the demand side within their pneumatic system.  If you are using blow-off devices like open pipes, coolant lines, copper tubes, or drilled pipe; it will be like running your car on flat tires.  It is very unsafe as well as reducing gas mileage.  To improve safety and efficiency, EXAIR has a line of Super Air Nozzles and Super Air Knives.  Not only will it increase your “gas mileage” to save you money, but they also will keep your operators safe.

In this analogy, you can have a high-performance engine and a durable transmission, but if your tires are bald, flat, or cracked; you cannot use your car safely and efficiently.  The same thing with your compressed air system.  You have to optimize your blow-off devices to get the most from your pneumatic system.  EXAIR is a leader in engineered blow-off devices for efficiency and safety.  So, if you want to improve the “health” of your pneumatic system, you should begin at how you are using your compressed air on the demand side.  EXAIR has Application Engineers that will be happy to help you in trying to keep your pneumatic system running like a “brand new car”.

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

 

Photo: Ford Mustang Roadster by openclipart-VectorsPixabay License