## 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.

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

## Efficiency Lab Provides Specific Benefits

This weekend, myself and many others are going to be participating in an event held all over the country, the Go Ruck Light event.  This test of toughness (mental and physical) is put on by former military personnel and it is based around one of the things they do a lot of at the beginning of their military training.   This is a 7 to 10 mile event that will take up to 4 hours to complete.   It is not like a race or any other obstacle event that we have ever done.   This is an event where the leader, or Cadre, will lead you through the miles and many physical exercises along the way all while carrying a 20 lb weight in a ruck sack on your back.   This not only tests individuals but it also requires the entire group to work as a team to ensure everyone finishes and everyone is together.

While I feel that I am under-prepared for this event physically, my mind is prepared to find out just how much I really can do and it will be at the end of the test that I realize the benefits.

Not many of the tasks I am responsible for at EXAIR require that kind of physical toughness and some of them require the mental toughness. But one instance I am always prepared for is the customer that calls and thinks they have the weirdest application and that there is nothing to solve it.   We actually have this experience quite a bit and it helps make what we do more interesting and fun.  With our diverse background and extensive knowledge, chances are we have experienced the application or we have seen something that is very close.  This helps us to be specific when recommending a solution.

EXAIR feels that the best solutions can also provide information on air and dollar savings as well.  The best savings information can be provided if our customers are willing to provide us details about their current application, and there is no better way to provide us the details than to take advantage of our Efficiency Lab. It is a free service letting you to send in a sample of your current blowoff product (typically homemade nozzles, open tube or pipe, snap together coolant hose, etc.), in return we will test it for you with our calibrated equipment and provide you a detailed report on air volume, force and noise. Then you will know the specific benefits of your recommended solution.

The fact is, we go into every conversation with the mentality of only providing solutions.  If we can’t provide it, we will try to direct you to someone that can.

Brian Farno
Application Engineer Manager
BrianFarno@EXAIR.com
@EXAIR_BF