What is Laminar Flow and Turbulent Flow?

Super Air Knife

Fluid mechanics is the field that studies the properties of fluids in various states.  There are two 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 or turbulent flow.  Equation 1 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 viscosity of the water.  This indicates turbulent flow with a Reynolds number larger than 4000.  As the water flows into the mouth of the river after the channel, 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 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

Laminar vs. Turbulent Flow

Laminar flow is an fundamental component of compressed air efficiency. Believe it or not, laminar flow is controlled exclusively by the airline used in a compressed air system. To fully understand the effects of laminar flow in a compressed air system, we need to explain exactly what it is.

Fluids & gases are unique in their ability to travel. Unlike solid molecules that remain stationary whose molecules tend to join others of the same kind; fluid molecules aren’t so picky. Fluid molecules, such as gases and liquids, partner with different molecules and are difficult to stop.

Laminar flow describes the ease with which these fluids travel; good laminar flow describes fluid travelling as straight as possible. On the contrary, when fluid is not travelling straight, the result is turbulent flow.

PVDF Super Air Knife
Laminar Flow

Turbulent air flow results in an inefficient compressed air system. This may not seem like a major concern; yet, it has huge impacts on compressor efficiency. Fluid molecules bounce and circle within their path, causing huge energy wastage. In compressed air systems, this turbulent airflow results in a pressure drop. How do you avoid this from happening? It all comes down to compressed air system design.

Flow type
Laminar vs. Turbulent Flow

The design and material of the air pipe, as well as the positioning of elbows and joints, has a direct connection to laminar flow and pressure drop. To avoid high energy consumption of your compressed air system, reducing pressure drop is key.

If your system is experiencing high pressure drop, your compressor has to work overtime to provide the needed air pressure. When your compressor works overtime, it not only increases your maintenance costs, but also your energy bills.

To discuss your application and how an EXAIR Intelligent Compressed Air Product can help your process, feel free to contact EXAIR and myself or one of our Application Engineers can help you determine the best solution.

Jordan Shouse
Application Engineer
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Twitter: @EXAIR_JS

EXAIR’s Super Air Knife: The Benefits of Laminar Airflow

SSPlumbingKitpr_cheese-559x

When a wide, even, laminar flow is necessary there isn’t a better option available on the market than EXAIR’s Super Air Knife. We’ve been manufacturing Air Knives for over 35 years, with the Super Air Knife making its first appearance back in 1997. Since then, the Super Air Knife has undergone a few enhancements over the years as we’re constantly trying to not only introduce new products but also improve on the ones we have. We’ve added new materials, longer single piece knives, as well as additional accessories. But, by and large, the basic design has remained the same. As the saying goes: “If it ain’t broke, don’t fix it!”.

What really sets EXAIR’s Super Air Knife above the competition is the ability to maintain a consistent laminar flow across the full length of the knife compared to similar compressed air operated knives. This is even more evident when compared against blower operated knives or fans. A fan “slaps” the air, resulting in a turbulent airflow where the airflow particles are irregular and will interfere with each other. A laminar airflow, by contrast, will maintain smooth paths that will never interfere with one another.

turbulent vs laminar
A representation of a turbulent flow on top, and laminar flow on bottom

The effectiveness of a laminar airflow vs turbulent airflow is particularly evident in the case of a cooling application. The chart below shows the time to cool computers to ambient temperatures for an automotive electronics manufacturer. They used a total of (32) 6” axial fans, (16) across the top and (16) across the bottom as the computers traveled along a conveyor. The computers needed to be cooled down before they could begin the testing process. By replacing the fans with just (3) Model 110012 Super Air Knives at a pressure of just 40 psig, the fans were cooled from 194°F down to 81° in just 90 seconds. The fans, even after 300 seconds still couldn’t remove enough heat to allow them to test.

air-knife-cooling
While the fans no doubt made for large volume air movement, the laminar flow of the Super Air Knife resulted in a much faster heat transfer rate.

Utilizing a laminar airflow is also critical when the airflow is being used to carry static eliminating ions further to the surface. Static charges can be both positive or negative. In order to eliminate them, we need to deliver an ion of the opposite charge to neutralize it. Since opposite charges attract, having a product that produces a laminar airflow to carry the ions makes the net effect much more effective. As you can see from the graphic above showing a turbulent airflow pattern vs a laminar one, a turbulent airflow is going to cause these ions to come into contact with one another. This neutralizes them before they’re even delivered to the surface needing to be treated. With a product such as the Super Ion Air Knife, we’re using a laminar airflow pattern to deliver the positive and negative ions. Since the flow is laminar, the total quantity of ions that we’re able to deliver to the surface of the material is greater. This allows the charge to be neutralized quickly, rather than having to sit and “dwell” under the ionized airflow.

With lengths from 3”-108” and (4) four different materials all available from stock, EXAIR has the right Super Air Knife for your application. In addition to shipping from stock, it’ll also come backed up by our unconditional 30-day guarantee. Test one out for yourself to see just how effective the Super Air Knife is on a wide variety of cooling, cleaning, or drying applications.

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

What is Laminar Flow and Turbulent Flow?

Fluid mechanics is the field that studies the properties of fluids in various states.  There are two areas, fluid statics and fluid dynamics.  Fluid dynamics studies the forces in a fluid, either as a liquid or a gas, during motion.  Osborne Reynolds, an Irish innovator, popularized this dynamic with a dimensionless number, Reyonlds number. This number can indicate the different states that the fluid is moving; either in laminar flow or turbulent flow.  The equation below shows the relationship between the inertial forces of the fluid as compared to the viscous forces.  Reynolds number, Re, can be calculated by Equation 1:

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 the fluid is considered to be turbulent (chaotic and violent).  The area between these two numbers is called the transitional area where you can have small 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 in the channel is loud and disorderly; traveling in different directions, even upstream.  With the high speed coming from the drain pipe, the inertial forces are greater than the viscous forces of the water.  The Reynolds number is larger than 4000 which indicates turbulent flow.  As the water travels into the mouth of the river after the channel, 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 the laminar flow region where Re is less than 2300.  Air, like the water in the picture, is also a fluid, and it will behave exactly in the same way depending on the Reynolds number.

Turbulent to Laminar Flows

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

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