Tools Of The Trade: The Rotameter

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

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

 

 

Advantages of Thermal Mass or Thermal Dispersion Flow Measurement

EXAIR’s Digital Flow Meter offers an easy way to measure, monitor and record compressed air consumption. The Digital display shows the current amount of compressed air flow, allowing for tracking to identify costly leaks and/or inefficient air users.

dfm

How exactly does the Digital Flow Meter work?  The unit falls under the category of Thermal Mass or Thermal Dispersion type flow meters.  Below shows the backside of a unit.

IMG_7387

Thermal mass flow meters have the advantage of using a simple method of measuring flow without causing a significant pressure drop. The EXAIR units have (2) probes that are inserted through the pipe wall and into the air flow.  Each of the probes has a resistance temperature detector (RTD.) One of the probes measures the temperature of the air flow.  The other probe is heated to maintain a preset temperature difference from the temperature measured by the first probe.  The faster the air flow, the more heat that is required to keep the second probe at the prescribed temperature.  From Heat Transfer principles, the heat energy input required to maintain the preset temperature is based on the mass velocity of the air.  Using basic physical properties for compressed air, the volumetric rate can be determined (SCFM), and displayed.

It is important to note that the compressed air should be filtered to remove oils, and dried to remove water, as these liquids have different physical properties from air, and will cause erroneous readings.

Advantages

  • Easy to install – No cutting or welding required
  • Summing Remote Display and Data Logger available
  • Sensitive at low flows
  • Rugged, reliable and no moving parts
  • No calibration or set-up required
  • Models from 1/2″ to 4″ schedule 40 iron pipe in stock
  • Short lead time for sizes up to 6″ Schedule 40 iron pipe
  • Available for size 3/4″ to 4″ copper pipe
  • New Wireless Capability

If you have any questions about the Digital Flow Meter 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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Air Amplifiers – What is an Amplification Ratio?

On Friday my colleague, Russ, blogged about the Super Air Amplifier (see that BLOG here, including a video demo)  In discussing the Air Amplifiers, the topic of amplification was mentioned. Today, I’d like to expand a bit further the amplification aspect of the Air Amplifier performance.

As the name of the device implies, the compressed air used by the Air Amplifier is added to, and thus ‘amplified’, the total output flow of the unit. Depending on the size and type of Air Amplifier, the amplification ratio starts at 12:1 and goes up to 25:1, with the ratio being the output flow to the compressed air usage.

AirAmplifiers.jpg
Super Air Amplifier and Adjustable Air Amplifier

EXAIR offers (2) types- the Super Air Amplifier and the Adjustable Air Amplifier.  The Super Air Amplifier uses a patented shim technology to maintain a precise gap, which controls the compressed air flow and expansion through the unit.  As the expanded air flows along the Coanda profile, a low pressure area is created at the center which induces a high volume flow of surrounding air into the primary air-stream.  The combined flow of primary and surrounding air exhausts from the Air Amplifier in a high volume, high velocity flow.  The larger diameter units have a greater cross sectional area with larger low pressure areas, resulting in greater amplification ratios.

The Below table shows the amplification ratios.

SuperAirAmplifierPerformance

The Adjustable Air Amplifier does not use a shim, but rather has an infinitely adjustable gap, allowing for fine adjustment of performance.  Force and flow is changed by turning the exhaust end to adjust the gap, and is then locked into place. The method of the amplification is the same as for the Super Air Amplifier, and the amplification ratios are similar and shown below.

AdjustableAirAmplifierPerformance

The Super Air Amplifiers and Adjustable Air Amplifiers are ideal for use in applications and processes that require cooling, drying and/or cleaning of parts, or the ventilation of confined areas or weld smoke or the exhausting of tank fumes.

If you have questions regarding the Air Amplifier, or would like to talk about any EXAIR Intelligent Compressed Air® Product, feel free to contact EXAIR and myself or one 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