ICFM, SCFM, ACFM, CFM What does it all mean!

A common question we get asked is “What does SCFM mean?” Most people are aware of CFM but the “S” in front seems to be less known about! Well strap on your seat belt, we are about to go into a compressed air worm hole all about volumetric flow rates!

Here at EXAIR we rate all of our products air consumption in SCFM at a given supply pressure. CFM stands for Cubic Feet per Minute, but one definition will not satisfy the conditions that will be experienced in many applications by a number of variables  (altitude, temperature, pressure, etc.). Air by nature is a compressible fluid. The properties of this fluid are constantly changing due to the ambient conditions of the surrounding environment.

This makes it difficult to describe the volumetric flow rate of the compressed air. Imagine you have a cubic foot of air, at standard conditions (14.696 psia, 60°F, 0% Relative Humidity), right in front of you. Then, you take that same cubic foot, pressurize it to 100 psig and place it inside of a pipe. You still have one cubic foot, but it is taking up significantly less volume. You have probably heard the terms SCFMACFM, and ICFM when used to define the total capacity of a compressor system. Understanding these terms, and using them correctly, will allow you to properly size your system and understand your total compressed air consumption.

SCFM is used as a reference to the standard conditions for flow rate. This term is used to create an “apples to apples” comparison when discussing compressed air volume as the conditions will change. EXAIR publishes the consumption of all products in SCFM for this reason. You will always notice that an inlet pressure is specified as well. This allows us to say that, at standard conditions and at a given inlet pressure, the product will consume a given amount of compressed air. It would be nearly impossible, not to mention impractical, to publish the ACFM of any product due to the wide range of environmental conditions possible.

ACFM stands for Actual Cubic Feet per Minute. If the conditions in the environment are “standard”, then the ACFM and SCFM will be the same. In most cases, however, that is not the case. The formula for converting SCFM to ACFM is as follows:

ACFM = SCFM [Pstd / (Pact – Psat Φ)](Tact / Tstd)

Where:

ACFM = Actual Cubic Feet per Minute
SCFM = Standard Cubic Feet per Minute
Pstd = standard absolute air pressure (psia)
Pact = absolute pressure at the actual level (psia)
Psat = saturation pressure at the actual temperature (psi)
Φ = Actual relative humidity
Tact = Actual ambient air temperature (oR)
Tstd = Standard temperature (oR)

The last term that you’ll see floating around to describe compressed air flow is ICFM (Inlet Cubic Feet per Minute). This term describes the conditions at the inlet of the compressor, in front of the filter, dryer, blower, etc. Because several definitions for Standard Air exist, some compressor manufacturers have adopted this simpler unit of measure when sizing a compressor system. This volume is used to determine the impeller design, nozzle diameter, and casing size for the most efficient compressor system to be used. Because the ICFM is measured before the air has passed through the filter and other components, you must account for a pressure drop.

The inlet pressure is determined by taking the barometric pressure and subtracting a reasonable loss for the inlet air filter and piping. According to the Compressed Air Handbook by the Compressed Air and Gas Institute, a typical value for filter and piping loss is 0.3 psig. The need to determine inlet pressure becomes especially critical when considering applications in high-altitudes. A change in altitude of more than a few hundred feet can greatly reduce the overall capacity of the compressor. Because of this pressure loss, it is important to assess the consumption of your compressor system in ACFM. To convert ICFM to ACFM use the following formula:

ICFM = ACFM (Pact / Pf) (Tf / Tact)

Where:

ICFM = Inlet Cubic Feet Per Minute

P = Pressure after filter or inlet equipment (psia)

Tf = Temperature after filter or inlet equipment (°R)

If you’re looking into a new project utilizing EXAIR equipment and need help determining how much compressed air you’ll need, give us a call. An Application Engineer will be able to assess the application, determine the overall consumption, and help recommend a suitably sized air compressor.

Jordan Shouse
Application Engineer

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Why Dryers Are Needed in Compressed Air Systems

Air compressors are extremely proficient at compressing anything in the air they are intaking. With that air that is taken in, moisture is going to be present. The amount of moisture will all depend on where you are located geographically and the ambient conditions in the area. Here in Ohio, we experience all 4 seasons so the moisture content is higher in the air during the summer months, rather than the winter months. When this air is saturated with water vapor and the conditions are right, the air reaches a point it cannot hold any additional water vapor. This point is known as the dew point of the air and water vapor will begin to condense to form droplets.

When ambient air is compressed, heat is generated and the air increases in temperature. In most industrial compressed air systems, the air is then processed to an aftercooler, and that is where condensation begins to form. To remove the condensation, the air then goes into a separator which traps the liquid water. The air leaving the aftercooler is typically saturated at the temperature of the discharge, and any additional cooling that occurs as the air is transferred will cause more liquid to condense out of the air. To address this moisture, compressed air dryers are used.

It is critical to the quality of the system and components downstream that actions are taken to prevent this condensation in the air. Condensation is generally detrimental to any point of use application and or the piping that conveys the air. Rust and/or corrosion can occur anywhere in the piping, leading to scale and contamination of the compressed air and processes. When trying to dry products off using compressed air or using the air to atomize a liquid such as paint, adding in these contaminants and moisture will cost production losses.

There are several options when it comes to the type of dryer that one may consider installing on their compressed air supply side.

• Refrigerant Dryer – the most commonly used type, the air is cooled in an air-to-refrigerant heat exchanger.
• Regenerative-Desiccant Type – use a porous desiccant that adsorbs (adsorb means the moisture adheres to the desiccant, the desiccant does not change, and the moisture can then be driven off during a regeneration process).
• Deliquescent Type – use a hygroscopic desiccant medium that absorbs (as opposed to adsorbs) moisture. The desiccant is dissolved into the liquid that is drawn out. Desiccant is used up and needs to be replaced periodically.
• Heat of Compression Type – are regenerative desiccant dryers that use the heat generated during compression to accomplish the desiccant regeneration.
• Membrane Type– use special membranes that allow the water vapor to pass through faster than the dry air, reducing the amount of water vapor in the air stream.
The air should not be dried any more than is needed for the most stringent application, to reduce the costs associated with the drying process. A pressure dew point of 35°F to 38°F (1.7°C to 3.3°C) often is adequate for many industrial applications. Lower dew points result in higher operating costs.
If you have questions about compressed air systems and dryers or any of the 15 different EXAIR Intelligent Compressed Air® Product lines, feel free to contact EXAIR, and I or any of our Application Engineers can help you determine the best solution.

Brian Farno
Application Engineer
BrianFarno@EXAIR.com
@EXAIR_BF

Convective Heat Transfer: How Do We Use It?

Vortex Tubes have been studied for decades, close to a century. These phenoms of physics and the theory behind them have been discussed on this blog before. Many customers gravitate toward Vortex Tubes when needing parts and processes cooled. The fact of the matter is there is still more to be discussed on how to correctly select the which product may be needed in your application. The reason being, area, temperatures, and air flow volumes play a large role in choosing the best product for cooling. The tendency is to say, well I need to cool this down as far as possible so I need the coldest air possible which leads to the assumption that a Vortex Tube will be the right solution. That isn’t always the best option and we are going to discuss how to best determine which will be needed for your application. The first step, is to call, chat, or email an Application Engineer so that we can learn about your application and assist with the implementation of the Vortex Tube or other cooling product for you. You may also want to try and take some initial readings of temperatures. The temperatures that would help to determine how much cooling is going to be needed are listed below:
  • Part temperature
  • Part dimensions
  • Part material
  • Ambient environment temperature
  • Compressed air temperature
  • Compressed air line size
  • Amount of time desired to cool the part: Lastly desired temperature

With these bits of information, we use cooling equations to help determine what temperature and volume of air will best suit your needs to generate the cooling required. One of the equations we will sometimes use is the Forced or Assisted Convective Heat Transfer. Why do we use convective heat transfer rather than Natural Heat Transfer? Well, the air from EXAIR’s Intelligent Compressed Air Products® is always moving so it is a forced or assisted movement to the surface of the part. Thus, the need for Convective Heat Transfer.
Calculation of convection is shown below: q = hc A dT Where: q = Heat transferred per unit of time. (Watts, BTU/hr) A = Heat transfer area of the surface (m2 , ft2) hc= Convective heat transfer coefficient of the process (W/(m2°C), BTU/(ft2 h °F) dT = Temperature difference between the surface and the bulk fluid (compressed air in this case) (°C, °F)

The convective heat transfer coefficient for air flow is able to be approximated down to hc = 10.45 – v + 10 v1/2

Where: hc = Heat transfer coefficient (kCal/m2 h °C) v = relative speed between the surface of the object and the air (m/s)

This example is limited to velocities and there are different heat transfer methods, so this will give a ballpark calculation that will tell us if we have a shot at a providing a solution.  The chart below is also useful to see the Convective Heat Transfer, it can be a little tricky to read as the units for each axis are just enough to make you think of TRON light cycles. Rather than stare at this and try to find the hidden picture, contact an Application Engineer, we’ve got this figured out. convective_heat_transfer_chart

1 – Convective Heat Transfer Chart
Again, you don’t have to figure any of this out on your own. The first step to approach a cooling application is to reach out to an Application Engineer, we deal with these types of applications and equations regularly and can help you determine what the best approach is going to be.
Brian Farno Application Engineer BrianFarno@EXAIR.com @EXAIR_BF
1 – Engineering ToolBox, (2003). Convective Heat Transfer. [online] Available at: https://www.engineeringtoolbox.com/convective-heat-transfer-d_430.html [02/10/2021]

EXAIR Founder’s Day 2021

EXAIR celebrates Founder’s Day each year on February 22nd (or the closest working day) in order to commemorate the birthday of our founder, Roy Sweeney.  He founded the company in 1983 and drove EXAIR to become the strong, successful and innovative company that it has over the years.  Roy led EXAIR for 33 years.  Today would have been his 87th birthday.

We choose to make this day a celebration and a day to mark our ongoing commitment to the service of others in keeping with the values that Roy and his wife Jackie felt (and feel) very strongly about.  We continue to look outside our company, outside ourselves and outside our immediate surroundings to do what we can to improve the world around us.

This marks our 5th Founder’s Day.  Over the past four years, we have supported a total of 21 different charities with direct, substantial donations as part of our commitment to organizations that are making a difference right here in our area.  This year, we have chosen to further deepen our commitment by contributing to all 21 organizations that we have supported in past years:

  • Freestore Foodbank
    Supplies 33 million meals per year to those in need
    https://freestorefoodbank.org/
  • Lighthouse Youth and Family Services
    Supporting their Safe and Supported program for LGBTQ youth
    https://www.lys.org/safeandsupported/
  • DAV
    Supporting disabled American veterans and their families
    https://www.dav.org/
  • Arts Wave
    Funds and supports 100+ arts projects and organizations through impact-based grants
    https://www.artswave.org/
  • Cincinnati Works
    Partners with all willing and capable people living in poverty to assist them in advancing to economic self-sufficiency through employment
    https://cincinnatiworks.org/
  • Habitat for Humanity Greater Cincinnati
    Helps eliminate substandard housing locally and globally by building and renovating decent, affordable homes to sell to low-income first-time homebuyers.
    https://www.habitatcincinnati.org/
  • Matthew 25: Ministries
    Provides humanitarian aid and disaster relief along with partners in the Greater Cincinnati area, across the US and in more than 60 countries
    https://m25m.org/
  • SPCA Cincinnati
    Offers programs including animal adoptions, animal cruelty investigations, spaying and neutering shelter animals, companion animal and wildlife rescue
    https://spcacincinnati.org/
  • Tender Mercies
    Transforms the lives of homeless adults with mental illness by providing security, dignity, and community in a place they call home
    https://www.tendermerciesinc.org/
  • Bethany House
    Helps homeless and at-risk families with solutions to achieve housing stability and long-term self-sufficiency
    https://bethanyhouseservices.org/
  • Women’s Crisis Center
    Supporting victims of domestic violence, sexual assault and sexual abuse
    https://www.wccky.org/
  • Dragonfly Foundation
    Supporting pediatric cancer patients and their families
    www.dragonfly.org
  • Master Provisions
    Supporting those in need with food, clothing and other items in the Greater Cincinnati area and abroad through mission trips
    www.masterprovisons.org
  • Cincinnati Youth Collaborative
    Supporting vulnerable children and young adults to overcome obstacles and succeed in education, career, and life
    www.cycyouth.org
  • Ronald McDonald House of Greater Cincinnati
    Cincinnati’s Ronald McDonald House provides a home for critically ill children and their families while they get the life-saving medical care they need
    www.rmhcincinnati.org
  • Women Helping Women
    Prevents gender-based violence and provides evidence-based prevention and expert crisis intervention and support services for survivors of dating violence, sexual violence, domestic violence and stalking 
    www.womenhelpingwomen.org
  • Elementz
    Elementz is an urban oasis of hope and a catalyst of change for Cincinnati’s inner-city youth. This Urban Arts Center fosters talent, ignites potential and inspires possibilities.
    www.elementz.org
  • Special Olympics Ohio
    Special Olympics Ohio is part of the global inclusion movement using sports, health education, and leadership programs to empower people with intellectual disabilities. 
    www.sooh.org
  • Cincinnati Symphony Orchestra
    The CSO is situated in the heart of Cincinnati and is contributing at every level to serving our community and elevating Cincinnati’s vibrant cultural scene.
    www.cincinnatisymphony.org
  • MusiCorps
    MusiCorps is a conservatory-level music rehabilitation program that helps wounded warriors play music and recover their lives.
    www.musicorps.net

EXAIR also established an Employee Volunteer Program in 2018 that enables every full-time employee with at least 90 days of service to volunteer with organizations of their choice during the normal work week with full pay by EXAIR.  The COVID pandemic has impacted our ability to volunteer with outside organizations for nearly a year.  We look forward to better days when we can collectively work with organizations in our community to improve the lives of those in need.

So, as we celebrate Founder’s Day today, we wish Roy a happy birthday.  We miss having him here.  We remember what he did for all of us and for countless others.  And we pledge to continue his commitment to helping those who need it.

Happy Founder’s Day 2021 from everyone at EXAIR!

Bryan Peters
President
EXAIR Corporation