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

EXAIR Flat Air Nozzles: Powerful, Quiet, Safe and Adjustable

Are you tired of your current compressed air being so loud? Well then, we have a solution for you; EXAIR’s Flat Super Air Nozzles. The patented design of the 1” and 2” Flat Super Air Nozzles makes it great for applications that require a powerful but precise flat stream of air. The Flat Super Air Nozzles work much like our Super Air Knives, the main difference being that the Flat Super Air Nozzles provides a more forceful stream of air. The design of the Flat Super Air Nozzles also provides a greatly reduced sound level.

2″ Flat Super Air Nozzle

EXAIR’s Flat Super Air Nozzles are safe, reliable, and efficient. The nozzles are specifically designed in a way to prevent dead head pressure as stated in OSHA Standard 1910.242(b). The directive stats that compressed air used for cleaning purposes can not exceed a dead-end pressure of 30 psig. If a dead-end pressure were to exceed that pressure then there is potential for an air embolism to form. EXAIR has designed our Flat Super Air Nozzles so that they cannot be dead-ended; this allows you to run at a typical 80-100 psig from your compressed air system.

Various Applications of Flat Super Air Nozzles

EXAIR Flat Super Air Nozzles are designed to also be quiet while operating at those higher pressures. When operating at 80 psig the 2” Flat Super Air Nozzle is going to have a sound level of 77 dBA were as the 1” Flat Super Air Nozzle when operated at 80 psig is going to have a sound level of 75 dBA. The higher the pressure the more air is going to flow through the nozzle; the more air flowing though the nozzle the louder it is going to be.

2″ Flat Super Air Nozzle

EXAIR’s High Power Flat Super Air Nozzles are designed for those tougher applications where you need more force, and will operate at slightly louder levels. The HP series Flat Super Air Nozzles have a thicker shim in them that allows for more air to escape out the end delivering a high force. The High powered 2” Flat Super Air Nozzle when operated at 80 psig has a sound level of 83 dBA where the 1” is only 82 dBA.

All of EXAIR’s flat Super Air Nozzles are designed with an internal patented shim which allows for adjusting the total volume of airflow and force that the nozzle produces. These shims are available in different thicknesses and aid in keeping noise levels down, provide gross adjustment of airflow and the flexibility for achieving a successful application. 

If you have any questions or want more information on EXAIR’s Flat Super Air Nozzles or any of our 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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Know What to Look For – Are Your Compressed Air Guns OSHA Safe?

One of the easiest ways to find out if your compressed air guns are safe for operation is by looking at the nozzle.  First, take your current compressed air gun and disconnect it from the compressed air line.  Second, look directly into the end of the nozzle where the air comes out.  If you can see the inside of the nozzle, then your air gun or blow-off device is unsafe.  Nine out of ten compressed air guns are considered to be dangerous.  In this blog, I will go through the dangers and violations of compressed air guns and nozzles that are very common in the market place.

Occupational Safety and Health Administration, OSHA, is an organization that enforces standards for safe and healthy working environments.  They have training, outreach programs, and educational assistance for manufacturing plant.  But, they will also enforce these standards with heavy fines for violations.  The two most common violations with compressed air guns and nozzles are 29CFR 1910.242(b) for dead-end pressure/chip shielding and 29CFR 1910.65(a) for maximum allowable noise exposure.  If you are unfortunate in receiving an audit, the OSHA agent will target your compressed air guns and blow-off devices.

Unsafe Nozzle

Here is the first example of a nozzle that I would like to discuss.  As you can see, there is only one opening where the air can come out from the nozzle.  Other types of nozzles that would fall into this category will include copper pipes, extensions, or worn nozzles.  They are dangerous as the compressed air cannot escape if it is blocked by your skin.  An air embolism could occur within the body which can cause bodily harm or death.  If operated above 30 PSIG (2 bar), these nozzles would violate the OSHA 29CFR 1910.242(b) for dead-end pressure.  This is a hazard which can be avoided by using EXAIR Super Air Nozzles and Safety Air Guns.  The nozzles are designed to utilize fins to allow air to escape and not penetrate your skin.  With EXAIR products, you will not violate this standard even if you go above the 30 PSIG (2 bar).

Safety Air Gun

To counteract the dead-end pressure violation, some nozzle manufacturers created a hole through the side of the nozzle (Reference photo below).  This will allow for the compressed air to escape, but, now the issue is noise level.  With an “open” section in the nozzle, the compressed air is very turbulent and very loud.  They state that 70% to 80% of all hearing loss within a manufacturing plant is caused by compressed air.  For this, OSHA 29CFR 1910.65(a) was created to show the maximum allowable noise exposure.  This chart shows the time and noise limits before requiring hearing protection.  The EXAIR Super Air Nozzles are designed to have laminar flow which is very quiet.  With our typical Safety Air Gun, model 1210, the sound level is only 74 dBA; well under the noise exposure limit for 8 hours.

Unsafe Air Gun

Hearing loss is the best known, but not the only, ill effect of harmful noise exposure. It can also cause physical and psychological stress, impair concentration, and contribute to workplace accidents or injuries.

Why do I bring these points up?  Because safety is everyone’s responsibility.  The National Institute for Occupational Safety and Health, NIOSH, has an overview of how to handle hazards in the workplace.  They call it the Hierarchy of Controls (click).  This is a means to best protect workers from dangers.  The most effective way is by eliminating the hazard or substituting the hazard.  The least effective way is with Personal Protective Equipment, or PPE.  For your unsafe compressed air nozzles and guns, EXAIR can help by substituting the hazardous air gun and nozzle with an engineered solution designed with safety in mind.

In my opening statement, I explained a quick and easy method to determine if your compressed air guns are dangerous.  To keep your company compliant and safe, EXAIR offers a variety of different types of nozzles and Safety Air Guns to best fit your requirement.  If you find that you are using hazardous blowing equipment, you can contact an Application Engineer to find a safe and effective alternative.

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