Tag: calculations

Tools Of The Trade: The Rotameter

Published on by Brian FarnoLeave a comment
EXAIR’s Free Efficiency Lab

One of the free services we offer to customers here at EXAIR is our Efficiency Lab. In case you are not familiar here is a brief synopsis. Speak with an Application Engineer about your existing compressed air blowoff/point of use product and that you would like to know how much air it consumes. Fill out the brief survey and send the product you use in to our facility. Let us perform tests on calibrated test equipment to determine the force, flow, and noise level. We will then issue you a report that states what the EXAIR model would best be suited (if applicable) as well as how much compressed air you will be able to save. Order the recommendation and start saving money.

To do these evaluations, we have to have calibrated equipment that is reliable and capable of handling vast range of products we may receive in. For this, we could use a Digital Flowmeter, in some cases that is what has to be done due to large flow rates. For the majority of these though we go old school. We utilize a piece of equipment called a rotameter.

A rotameter pairs nicely with a calibrated pressure gauge as well.
The float can be seen with graduated marks for readings. The taper of the chamber is not easily seen with the naked eye.

This is a device that is designed to measure the flow rate of a fluid within a closed tube. The inside diameter of the tube is varied which causes the float within the meter to raise or lower.  They are calibrated for a specific gas at a given pressure and temperature, most are calibrated for atmospheric conditions, 14.7 psi (1.014 Bar). The meter must be mounted vertically and this is not always best suited for industrial environments.

When testing products the compressed air within the meter is pressurized which means we have to correct the reading for the given pressure, if the temperature is outside of the calibration temp then we must also perform that correction. We do this using a table provided by the manufacturer of the meter or by using the calculations shown to get exact values that may be in between the pressures in the table.

Pressure Correction Table

 

This will allow us to then multiply the Correction Factor by the meter reading and calculate our corrected flow for the point of use device at a given operating pressure and temperature.

Temperature correction table

Knowing where the values that are measured and calculated come from add validity to the reports and understanding all of the variables that go into reading like this helps to better validate the cost savings that can be seen.

In a pinch, for a field estimation, we can also use these Correction Factors and determine an approximate consumption rate of a device that has been measured at a pressure such as our cataloged 80 psig (5.5 Bar). This can often be done on the fly to help determine the flowrates currently on a system. This can be helpful when troubleshooting, giving estimated simple ROIs, and help justify results and reasons for future purchases of engineered solutions.

If you want to discuss the Efficiency Lab or any of the math behind our calculations, contact any Application Engineer, we can all help out.

Brian Farno
Application Engineer
BrianFarno@EXAIR.com
@EXAIR_BF

OSHA 29 CFR 1910.95 (a) – It’s a Noise Exposure Standard, Not Just a Confusing Number

Published on by Brian FarnoLeave a comment

Strings of numbers and characters can often appear daunting.  For instance, if I wrote in binary code it would be a string of ones and zeros.  (01000101 01101110 01100111 01101001 01101110 01100101 01100101 01110010 01101001 01101110 01100111 00100000 01101001 01110011 00100000 01000001 01010111 01000101 01010011 01001111 01001101 01000101.) That can look like gibberish and cause concern if unknown or it can make sense to programmers and people familiar with binary code.

Other alphanumeric strings may cause some concern for industry professionals.  Take, for instance, OSHA standards. The OSHA standard 29 CFR 1910.95 (a) may be unfamiliar to some, and thus concerning. Many Environmental Health and Safety Engineers will recognize this code.  It is an OSHA standard that revolves around the amount of time an employee is permitted to be exposed to specific sound levels. These sound levels are all based on the weighted sound level of the noise the operators are exposed to. To better understand how the octave and frequency of the sound play into this, there is a chart provided below.

Equivalent A-Weighted Sound Level Chart – (1)

The weighted sound level is the level at which a Digital Sound Level Meter will read the current level of noise within an environment. This scale is then used to move further into the OSHA directive that we focus on helping companies meet to best provide safe environments for their employees to work in.

If you notice, the lowest weighted sound level is 90 dBA, this is also the lowest-rated noise level that OSHA speaks of in 1910.95(b)(2). It has been shown that noise levels over this level for extended periods will result in permanent hearing loss. The standard then goes on to discuss the duration an employee can be exposed to noise levels even with the use of personal protective equipment as well as even impulsive or impact noise.  The table of permissible time limits is shown below.

Permissible Noise Exposures (2)

As you can see from the table above provided by OSHA, any noise level that an operator is exposed to for eight hours cannot exceed 90 dBA. Noises within an industrial environment can also be variable throughout the day. For instance, the operator stands outside of a sheet metal press and the concussive strike on the press gives off a 90 dBA strike for every stroke of the press. This would not be a continuous noise level. Maybe the operator is operating a CNC machine that is cutting a nest of parts and uses a handheld blowgun to remove debris and coolant from the parts before taking them from their fixture. This blowgun is not used continuously and therefore would not be rated as such for the exposure time. A time study would be conducted on the average length of time the operator is utilizing this gun along with the level of noise it produces during use. OSHA then gives a calculation to use to appropriately combine the sound level while the gun is being used and when it is not in use. That equation is written out below.

Mixed Environment Exposure Fraction
C1/T1+C2/T2+… = ____
Total Exposure Fraction
Cn/Tn = ____

Where:
C1 = Duration of time for a specified noise level
T1 = Total time of exposure permitted at that level
Cn = Total time of exposure at a specified noise level
Tn = Total exposure time permitted at that level

Should the summation of the fractions for different exposures be greater than the Total Exposure fraction, the summation value should be used. As mentioned above, a time study on exposure to noise levels will be needed to obtain the information needed for this type of study. Once the study is done the process can proceed to the next level within the OSHA standard which is a hearing conservation program.

I would like to interject a small side-step at this point. Rather than rolling straight into the implementation of PPE which is proven to be the lowest reliable factor of protection by the CDC and NIOSH. If any of these noise levels being generated are due to the use of compressed air points of use, EXAIR can potentially lower the noise of these point of use applications. In the events, open blowoffs or “band-aid” fixes are in place to keep processes running, and Engineered Solutions can easily be implemented that will reduce the noise level produced by this operation. Whether it is on the handheld Safety Air Gun in the hands of a CNC operator, or if it is a part/scrap ejector that is blowing the sheet metal press out after every strike, we have products that have proven time over time using an Engineered Solution will save air, reduce noise levels, and still get the job done.

If you would like to discuss OSHA directives revolving around compressed air, share with us a recent citation you received from an inspector for this standard, or just discuss compressed air usage in general, contact us.

Brian Farno
Application Engineer
BrianFarno@EXAIR.com
@EXAIR_BF

 

1 – Equivalent A-Weighted Sound Level Chart – Retrieved from OSHA.Gov – https://www.osha.gov/pls/oshaweb/owadisp.show_document?p_id=9735&p_table=standards

2 – Permissible Noise Exposures – Retrieved from OSHA.Gov – https://www.osha.gov/pls/oshaweb/owadisp.show_document?p_id=9735&p_table=standards

 

Calculating CFM of Air Needed for Cooling

Published on by Russ BowmanLeave a comment

It’s easy to know that EXAIR’s Vortex Tubes can be used to cool down parts and other items, but did you know that our other engineered compressed air products can be used to cool down these same things? It’s the same process as cooling down hot food by blowing on it. And we can use the physical properties of any material – whether it’s the massive billets of steel in the photo up top, or the bowl of soup to the right, to calculate the amount of air flow required to change a certain mass of the material from one temperature to another.

For any material, there’s a certain amount of energy required to cause a certain temperature change of a certain mass of the material. This property is called Specific Heat (Cp), and it’s commonly expressed in Joules per gram per degree Celsius (J/g°C), or Btu’s per pound (mass) per degree Fahrenheit. (Btu/lbm°F). The Specific Heat of the material allows us to calculate the amount of heat that has to be removed to cool it from its starting to its desired temperature, using a standard heat transfer equation:

q = mCp ΔT, where:

  • q is the amount of energy it’ll take to cause the temperature change.
  • m is the mass of the material that you want to change the temperature of.
  • Cp is the Specific Heat we talked about above.
  • ΔT is the starting temperature, minus the desired temperature.

Once we know the amount of heat to be removed, we can then apply units of time, and calculate the rate of cooling you’ll need to achieve in order to get the material to the temperature you want, in the time that you want. Let’s work through an example, using a piece of steel weighing 50lbs that needs to be cooled from 300 °F to 200°F:

q = m * Cp * ΔT, where:

  • m = 50lbm
  • Cp = 0.117 Btu/lbm°F
  • ΔT = 300°F – 200°F = 100°F
  • q = 50lbm * 0.117 Btu/lbm°F * 100°F = 585 Btu of energy (heat) to be transferred

Now, let’s say we have two minutes to cool this piece of steel:

585 Btu/2 minutes X 60 minutes/hr = 17,550 Btu/hr

That’s the rate of cooling required for this application. Now, we can use another equation that’s commonly used in the HVAC industry to determine the amount of room temperature (70°F) air flow that’ll remove that amount of heat. It’s called the cooling power formula:

Q̇ = 1.0746 * ΔT * ṁ, where:

  • Q̇ is the rate of heat transfer
  • 1.0746 is a constant
  • ΔT is the difference between the desired temperature and the air temperature
  • ṁ is the flowrate of air in cubic feet per minute

Since “Q̇” is the unknown value, we have to get to use a little algebra and rearrange the equation:

ṁ = Q̇/(1.0746 * ΔT), where:

  • Q̇ = 17,550 Btu/hr
  • 1.0746 = 1.0746 (remember, it’s a constant)
  • ΔT = 100°F – 70°F = 30°F
  • 17,550 Btu/hr/(1.0746 * 30°F) = 544.4 cubic feet per minute

Now, this assumes that equilibrium will be reached (i.e. all of the heat than CAN be transferred to the air flowing past the steel WILL be transferred), but that’s not going to happen. Depending on the geometry of the material to be cooled, there are ways to maximize the contact time between the material and the cooling medium. For example, constructing a tunnel over a section of a conveyor so the airflow can blow in the opposite direction that the material is traveling. Even then, though, it’s unlikely you’ll reach equilibrium, so we’ll apply a service factor, and say our airflow is going to be 30% efficient in cooling the steel (which is really quite high) so we’ll need:

544.4 CFM/0.3 = 1,815 CFM

EXAIR Air Amplifiers are an excellent option for providing this kind of cooling flow. They’re compact, quiet, and efficient. Using the following table, we see that a 3″ Adjustable Air Amplifier supplied at 80psig has a total developed flow rate (Air Volume at Outlet) of 774 SCFM:

So, three of them will generate a total cooling flow of 2,322 SCFM, and that’s not counting the air entrained in the immediate discharge (Air Volume at 6″). That’s even more than we THINK we need…but that can be adjusted and/or regulated.

Another thing I like about the Adjustable Air Amplifiers for an application like this is that they’re, well, adjustable (it’s right there in the name). Turning the exhaust plug in or out will decrease or increase the air flow – this is how you can make gross adjustments to the air flow. A Pressure Regulator in the supply line then allows for precise ‘tweaks’ so you can dial in the performance to the level you need, without using any more compressed air than you have to.

With sixteen distinct models to choose from, EXAIR Air Amplifiers are a quick and easy way to provide a tremendous amount of cooling air flow from a compact, lightweight product.

If you have any questions about using compressed air for cooling, give me a call.

Russ Bowman, CCASS

Application Engineer
Visit us on the Web
Follow me on Twitter
Like us on Facebook

Webinar by EXAIR: Use This, Not That – Four Common Ways to Save Compressed Air in Your Plant

Published on by Tyler DanielLeave a comment

UThisThat_LIVEOD_600x150

Not much in life is free anymore. So, make sure and take advantage of EXAIR’s upcoming FREE webinar at 2:00 PM ET on 10/17/2019. Not only are we providing it for free, but in this webinar we’ll be discussing how you can save money by reducing your compressed air consumption. Something for free, that will help save you money? Almost unheard of these days!!! Hosted by one of our highly-trained Application Engineers, Jordan Shouse, you’ll learn about four common ways that you can easily save air in your facility.

Compressed air is often referred to as the fourth utility in industry. When used improperly, compressed air is extremely expensive. Homemade devices such as open-ended and drilled pipes, inefficient air nozzles, leaks, etc. all contribute to increased energy costs. In addition to being wasteful, these devices are not safe and compliant with OSHA standards and regulations. By using an Intelligent Compressed Air Product, you’ll be both saving money and creating a safer environment for your operators.

In this webinar, you’ll gain an understanding of the places in your facility that are wasting the most compressed air. We’ll educate you on the various engineered solutions available from EXAIR to help eliminate unnecessary compressed air usage. You’ll gain the knowledge necessary to determine the best solution based on the application, sound level, compressed air usage, and compliance with OSHA safety requirements. You’ll also learn about the various solutions available to help understand and optimize your compressed air system. You can’t begin implementing a plan to reduce air consumption until you fully understand the usage in your own facility and processes. EXAIR’s line of Optimization products are ideal to help you gain a baseline measurement and begin implementing new products and processes that’ll only help add to your bottom line.

UThisThat_OD_552x368

After the conclusion of the webinar will be a brief Q&A session where you can ask any questions you have about any of the topics covered. Unable to attend the webinar live? Don’t let that stop you from registering! Afterwards, each registrant will receive a link via e-mail where they’ll be able to access the full webinar at any time. Make sure and take advantage of this opportunity to gain some knowledge about the usage of your compressed air. You’ll be glad you did!

Tyler Daniel
Application Engineer
E-mail: TylerDaniel@EXAIR.com
Twitter: @EXAIR_TD