Tag: noise level

What’s So Great About Air Entrainment?

Published on by Russ BowmanLeave a comment

Air entrainment is the phenomenon that occurs when air (or any gas) under pressure is released from a device in such a way that a low pressure is generated in the immediate area of the air (or gas) discharge.  Air (or gas) from the surrounding environment is then pulled (or entrained) into the discharged air stream, increasing its volumetric flow rate.  EXAIR Corporation has been engineering & manufacturing compressed air products to take maximum advantage of this phenomena since 1983…and we’ve gotten better & better at it over the past 36 years.

Obviously, the first thing that’s so great about air entrainment is…free air flow.  Every cubic foot that’s entrained means that’s a cubic foot that your compressor didn’t have to spend energy compressing.  Considering the EXAIR Super Air Knife’s entrainment ratio of 40:1, that makes for a VERY efficient use of your compressed air.

Another thing that’s so great about air entrainment is…it’s quiet.  As you can see from the graphic at the top of this blog, the Super Air Knife entrains air (the lighter, curved blue arrows) into the primary compressed air stream (the darker, straight blue arrows) from above and below.  The outer layers of the total developed flow are lower in velocity, and serve as a sound-attenuating boundary layer.  The sound level of a Super Air Knife (any length…here’s why) is only 69dBA.  That means if you’re talking with someone and a Super Air Knife is running right next to you, you can still use your “inside voice” and continue your conversation, unaffected by the sound of the air flow.

I always thought it would be helpful to have more than just a graphic with blue arrows to show the effect & magnitude of air entrainment.  A while back, I accidentally stumbled across a stunning visual depiction of just that, using a Super Air Knife.  I had the pleasure of talking with a caller about how effective a Super Air Knife might be in blowing light gauge paperboard pieces.  So I set one up in the EXAIR Demo Room, blowing straight upwards, and tossed paper plates into the air flow.  It worked just as expected, until one of the paper plates got a little closer to the Super Air Knife than I had planned:

As you can see, the tremendous amount of air flow being entrained…from both sides…was sufficient to pull in lightweight objects and ‘stick’ them to the surface that the entrained air was being drawn past.  While it doesn’t empirically prove the 40:1 ratio, it indisputably demonstrates that an awful lot of air is moving there.

If you’re looking for a quiet, efficient, and OSHA compliant solution for cleaning, blow off, drying, cooling…anything you need an even, consistent curtain of air flow for – look no further than the EXAIR Super Air Knife.  If you’d like to discuss a particular application and/or product selection, give me a call.

Russ Bowman
Application Engineer
EXAIR Corporation
Visit us on the Web
Follow me on Twitter
Like us on Facebook

EXAIR Digital Sound Level Meters Measure Noise Exposure Levels

Published on by Jordan T ShouseLeave a comment
slm-newlabel
Digital Sound Meter

EXAIR offers the model 9104 Digital Sound Level Meter.  It is an easy to use instrument for measuring and monitoring the sound level pressures in and around equipment and other manufacturing processes.

Sound meters convert the movement of a thin membrane due to the pressure waves of sound into an electric signal that is processed and turned into a readable output, typically in dBA.  The dBA scale is the weighted scale that most closely matches the human ear in terms of the sounds and frequencies that can be detected.

Noise induced hearing loss can be a significant problem for many workers in manufacturing and mining. To protect workers in the workplace from suffering hearing loss OSHA has set limits to the time of exposure based on the sound level.  The information in the OSHA Standard 29 CFR – 1910.95(a) is summarized below.

OSHA Noise Level

The EXAIR Digital Sound Level Meter is an accurate and responsive instrument that measures the decibel level of the sound and displays the result on the large optionally back-lit LCD display. There is an “F/S” option to provide measurement in either ‘slow’ or ‘fast’ modes for stable or quickly varying noises. The ‘Max Hold’ function will capture and hold the maximum sound level, and update if a louder sound occurs.

Certification of accuracy and calibration traceable to NIST (National Institute of Standards and Technology) is included.

If you have questions about the Digital Sound Level Meter, or would like to talk about any of the quiet 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.

Jordan Shouse
Application Engineer
Send me an email
Find us on the Web 
Like us on Facebook
Twitter: @EXAIR_JS

 

What is Sound and Interesting Facts About Sound

Published on by Leave a comment

In physics, sound is a wave of pressure. It occurs in a medium, which can be a solid, liquid or gas. Sound cannot travel through a vacuum, such as in space. The wave of pressure reaches our ears and causes the ear drum to vibrate, which then goes through a complex process to ultimately be perceived as audible sound.

There are several characteristics of sound waves that can be measured and help define the sound. A sound wave can be visualized as a repeating sinusoidal wave (see below), and can be described by these properties – frequency and wavelength, amplitude, and speed.

Sound Wave
Sound Wave
  • Frequency is the number of cycles in 1 second, and is measured in Hertz (Hz)
  • Wavelength is the distance over which 1 cycle occurs, and for audible sound is  between 17 m and 17 mm long
  • Amplitude is the measure of its change over a single period, and normally a measure of sound loudness
  • Speed is the distance traveled per unit time

The speed of sound in air can be found using the equation:  a = Sqrt (γ•R•T)

where for air:
γ = ratio of specific heats = 1.4,
R = gas constant = 286 m²/s²/K
T = absolute temperature in °K (273.15 + °C)

At room temperature, 22°C (71.6°F), the speed of sound is 343.8 m/s (760 mph)

Some interesting facts about sound:

  • Sounds generally travels faster in solids and liquids than in gases.
  • You can estimate the distance from a lightning strike by counting the seconds that pass between seeing the lightning flash and hearing the thunder.  Take this duration an divide by 5 to get the distance away, in miles.
  • Humans normally hear sound frequencies between 20 Hz and 20,000 Hz.
  • Sound waves above 20,000 Hz are known as ultrasound, and sound waves below 20 Hz are known as infrasound.
  • Sound travel through water close to 4 times faster then through air.
  • The sound of a cracking whip occurs because the speed of the tip has exceeded the speed of sound.

Sound that is too loud can be a problem. The Occupational Safety and Health Administration (OSHA) has set limits on the noise exposure that an employee can be subjected. Exceeding these values can cause permanent damage to your ears and cause noise induced hearing loss. So, knowing and reducing the sound levels within a manufacturing operation is important.

OSHA Chart

EXAIR has many products that can help reduce the sound levels in your processes.  With products such Air Knives, Air Wipes, Air Amplifiers, Air Nozzles and Jets, and Safety Air Guns, strong, quiet and efficient blowoff, drying, and cooling can be performed.

Quiet Products

If you have questions about sound and keeping your sound levels in check or any of the 15 different EXAIR Intelligent Compressed Air® Product lines, feel free to contact EXAIR and myself or any of our Application Engineers can help you determine the best solution.

Brian Bergmann
Application Engineer
Send me an email
Find us on the Web 
Like us on Facebook
Twitter: @EXAIR_BB

Understanding Decibels & Why OSHA Pays Attention to Your Noise Exposure

Published on by John BallLeave a comment

In the simplest of metric terms, a decibel is one-tenth of a bel.  But, historically, bel was a unit created to honor Alexander Graham Bell who invented the telephone.  In the early days with telephone wires, they noticed that the signal strength would decay over a long distance.  In order to determine power requirements to connect people for communications, they determined that they could use the ratio of power levels.  As a start, it had to be based on a minimum amount of power required for a person to hear on the telephone.  They found that the signal power level to generate an angular frequency of 5000 radians per second would be that minimum value as determined by an average number of people.  They used this mark as a reference point in the ratio of power levels.  Because of the large variations in values, they simplified the equation on a base-10 log scale and dividing the bel unit by 10.  Thus, creating the measurement of decibel.

Today, this same method is used to measure sound.  Like frequency waves that travel through the telephone wires, pressure waves travel through the air as sound.  This sound pressure is what our ears can detect as loudness, and it has a pressure unit of Pascals (Pa).  As an example, a small sound pressure would be like a whisper while a large sound pressure would be like a jet engine.  This is very important to know as high sound pressures, or loudness, can permanently damage our ears.

With sound pressures, we can determine the Sound Pressure Level (SPL) which is measured in decibels (dB).  Similar to the equation for the telephone power signals above, the SPL also uses a ratio of sound pressures in a base-10 logarithmic scale.  For a minimum reference point, an average human can just start to hear a sound pressure at 0.00002 Pa.  So, the equation for measuring sound levels will use this minimum reference point as shown in Equation 1.

Equation 1:

L = 20 * Log10 (p/pref)

where:

L – Sound Pressure Level, dB

p – Sound pressure, Pa

pref – reference sound pressure, 0.00002 Pa

Why is this important to know the decibels?  OSHA created a chart in 29CFR-1910.95(a) that shows the different noise levels with exposure times.  This chart was created to protect the operators from hearing loss in work environments.  If the noise level exceeds the limit, then the operators will have to wear Personal Protection Equipment (PPE), or suffer hearing damage.  EXAIR offers a Sound Level Meter, model 9104, to measure sound levels in decibels.  It comes calibrated to accurately measure the sound to determine if you have a safe work environment.

Sound Level Meter

There is a term that is used when it comes to loud noises, NIHL.  This stands for Noise Induced Hearing Loss.  Once hearing is damaged, it will not come back.  To keep your operators safe and reduce NIHL, EXAIR offers many different types of blow-off products that are designed to decrease noise to a safe level.  So, here’s to Alexander Graham Bell for creating the telephone which can be used to contact EXAIR if you have any questions.

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

 

Photo of Telephone by Alexas_Fotos.  CC0 Create Commons