Laminar Flow and Digital Flowmeters: An Explanation On How To Achieve Laminar Flow

When I see turbulent flow vs. laminar flow I vaguely remember my fluid dynamics class at the University of Cincinnati.  A lot of times when one thinks about the flow of a liquid or compressed gas within a pipe they want to believe that it is always going to be laminar flow. This, however, is not true and there is quite a bit of science that goes into this.  Rather than me start with Reynolds number and go through flow within pipes I have found this amazing video from a Mechanical Engineering Professor in California. Luckily for us, they bookmarked some of the major sections. Watch from around the 12:00 mark until around the 20:00 mark. This is the good stuff.

The difference between entrance flow, turbulent flow and laminar flow is shown ideally at around the 20:00 mark.  This length of piping that is required in order to achieve laminar flow is one of the main reasons our Digital Flowmeters are required to be installed within a rigid straight section of pipe that has no fittings or bends for 30 diameters in length of the pipe upstream with 5 diameters of pipe in length downstream.

This is so the meter is able to measure the flow of compressed air at the most accurate location due to the fully developed laminar flow. As long as the pipe is straight and does not change diameter, temperature, or have fittings within it then the mass, velocity, Q value all stay the same.  The only variable that will change is the pressure over the length of the pipe when it is given a considerable length.

Another great visualization of laminar vs. turbulent flow, check out this great video.

 

If you would like to discuss the laminar and turbulent flow please contact an Application Engineer.

Brian Farno
Application Engineer
BrianFarno@EXAIR.com
@EXAIR_BF

1 -Fluid Mechanics: Viscous Flow in Pipes, Laminar Pipe Flow Characteristics (16 of 34) – CPPMechEngTutorials – https://www.youtube.com/watch?v=rQcZIcEa960

2 – Why Laminar Flow is AWESOME – Smarter Every Day 208 – SmarterEveryDay – https://www.youtube.com/watch?v=y7Hyc3MRKno

 

 

Traffic And Fluid Dynamics

Traffic

Earlier this morning I heard that a high speed chase that started in Michigan ended near Cincinnati, Ohio. My first thought was that, due to traffic, the chase became a jam.  Depending on the time of day, it’s IMPOSSIBLE to go anywhere, no matter how much you want it to happen (a circumstance many of us experience).

Similarly, when there is inadequate sizing of a compressed air line, no amount of desire is going to deliver the air where it needs to be.  Imagine every air molecule in the pipe is a car on the road.  When demand spikes and all those air molecules need to go to the same place, they have to have sufficient space to do so, just like vehicles on the road need enough lanes to prevent backup.  When the demand for compressed air reaches the maximum flow rate of the pipe, this is called saturation.  When the demand for compressed air exceeds this saturation point, end use items such as air nozzles or air tools are going to be starved for air.  The air might get there, but it will be late, and the earlier air molecules will be long spent, leading to underperformance of the item.

Unfortunately for those of us who fight traffic daily, fluid flow mechanics don’t apply to traffic flow.  But, fortunately for those of us who use compressed air as a utility, compressed air IS bound by fluid mechanics.  So, if we can quantify the compressed air demand in a system, we can design the system with enough capacity and volume capability to perform as needed.

EXAIR Application Engineers are well versed in helping our customers determine line sizes and providing support for our products on their systems.  If you need help with an EXAIR product and how it integrates into your compressed air system, contact an Application Engineer.

If only we could call city engineers to help with traffic…

Lee Evans
Application Engineer
LeeEvans@EXAIR
@EXAIR_LE