The Decibel

The decibel is a unit of measurement that relates the ratio of a physical value to another value and is expressed on a logarithmic scale.  The common symbol for decibel is dB.  The decibel is used as a measure for many parameters in science and engineering such as acoustics (sound), electronics (power levels) and control theory.

The decibel originates from methods used to express performance and loss in telegraph and telephone circuits.  The term ‘bel’ was coined in honor of Alexander Graham Bell, and the decibel, being 1/10th of a bel was established.

For most of us, the decibel is the familiar term relating to how loud a sound is.

With sound, the sound pressure is typically what is measured and is the local pressure deviation from the base or equilibrium atmospheric pressure, caused by a sound wave. In air, the sound pressure can be measured by a standard microphone, and is measured in pascals (Pa.)

To get to the common decibel reading we are familiar with, a little mathematics comes into play.

Capture

  • where Lp is the Sound Level in dB, prms is the measured sound pressure, and pref is the standard sound reference pressure of 20 micropascals.
  • The prms is what is measured by a microphone

Below are some representative sounds and the decibel rating – Note that sounds that are above 85 dB can cause hearing issues, and proper protection should be taken.Decibel Scale Still Photo

Some other interesting blogs about sound for you take a look at-

Measuring and Adding Sounds

Sound Power Level and Sound Pressure

Super Air Knife Math – When 72  + 72 = 75

If you would like to talk about sound or any of the EXAIR Intelligent Compressed Air® Products, feel free to contact EXAIR and myself or one of our Application Engineers can help you determine the best solution.

Brian Bergmann
Application Engineer

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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

EXAIR Air Nozzle Provides Non-Marring Solution For Rotary Die Cutting

Die Cutting is a highly efficient means to produce large volumes of uniquely shaped parts while creating a low volume of wasted materials. There are several different ways to produce die cut parts with one of the more common being Rotary Die Cutting. A Rotary Die Cutter typically incorporates the material passing between a roller die cutter and a heavy roller anvil to cut the specific shape  then passes the material down a conveyor or feed line while retrieving the waste material in another collection device.

I recently worked with a customer who was starting to see a large volume of scrap in their vinyl and rubber parts die cutting process as the die cut parts themselves were getting stuck onto the rolling die cutter and weren’t getting grabbed by the conveyor rollers. To try and get the parts to eject from the cutter they installed a few 1/4″ open copper tube air lines running across the roller but were concerned with amount of air they were wasting and the high pitch noise levels of close to 100 dBA. They were also seeing some damage to the parts they were able to get loosened from the die as some of the parts would make contact with the pipe, causing a “blemish” on the part, ultimately failing inspection.

I recommend the customer use our Model # 1100-PEEK Super Air Nozzle. The Model # 1100 consumes only 14 SCFM of compressed air (at 80 PSIG), much less than a 1/4″ open pipe, tested at close to 140 SCFM @ 80 PSIG. This nozzle produces a low sound level of only 74 dBA falling well within the allowable noise exposure levels set forth by OSHA. In addition, the PEEK plastic construction provides a non-marring solution in the event one of the parts did make contact with the nozzle.

1100-peek
1100-specs Model # 1100-PEEK Super Air Nozzle with Performance Specs

EXAIR offers a large selection of engineered air nozzles with varying airflow patterns, force, sound levels and materials of construction to meet a wide variety of application requirements. With help selecting the best solution or to discuss your particular application, please give us a call.

Justin Nicholl
Application Engineer
justinnicholl@exair.com
@EXAIR_JN

One Super Air Wipe doing the job of 3 Generic Air Wipes

Today, I had the opportunity to the work with a customer, who produces soft seals for the window and door industry. The soft seals are created through a multi-step process, where drying is critical for the overall quality of the product. After the extrusion of PPE (polyphenyl ethers) material, the seal is run through a water bath.  The next step is for the extruded PPE to be dried using compressed air.  After drying, a glue is applied to join the PPE soft seal to an aluminum frame.  If the PPE was not dry from the water bath, the glue would not bond the aluminum and soft seal together.

 

The customer wanted to replace their current compressed air drying system. The current system utilized (3) ceramic air wipes to dry off the PPE seal before the gluing process. He was relatively new to the company or the particular line, so he did not have all the history for the production line during our conversation. We were both wondering why three consecutive air wipes were used when one air wipe should be getting the job done, but we never could figure it out regardless. I pointed out that one EXAIR Super Air Wipe will clean off a variety cross sections in one pass. The old air wipes used 7.6 SCFM of compressed air for each air wipe or a total air flow of 22.8 SCFM to dry the rubber seal. Also, the old air wipes created 80 dB of noise. A correctly sized 1/2″ EXAIR Super Air Wipe would lower that noise to 75 dBA and lower the total air consumption to 13.9 SCFM.

AirWipe

By replacing three inferior ceramic wire dryers with one EXAIR model 2400 Super Air Wipe, the customer was able to get the job done better, reduce his noise level and save compressed air. EXAIR has the broadest line of problem solving compressed air products, if you have a problem area or an application you think we may be able to solve, please let us know. We are happy to assist.

Dave Woerner
Application Engineer
Davewoerner@EXAIR.com
@EXAIR_DW