At the end of Naval Nuclear Power School, students who’ve just spent two years learning how to boil water must pass a comprehensive examination board before they’re released into the fleet as real live “Navy Nucs.” One popular question at these boards (in 1987 anyway) was to describe, in detail, the path a drop of seawater takes to become reactor coolant (a warship at sea must be self-reliant, and that includes making our own pure water.) A correct answer would prove the student’s knowledge of various piping systems, the steam distilling and water purification processes, reactor coolant chemistry maintenance, and, if you were lucky, a deep dive into the Six Factor Formula which mathematically defines the six events* that affect the probability of neutron multiplication, and hence, the sustainability of nuclear fission in the reactor core:
In that same vein, for today’s EXAIR blog, I thought I’d trace a Standard Cubic Foot (SCF) of air from the compressor room, through a typical industrial compressed air system, to its point of use. First, let’s define what that is: Imagine a cubic foot of air in front of you. If the atmospheric pressure is 14.5psia (average for sea level elevation), the ambient temperature is 68°F, and relative humidity is 0%, then that’s one Standard Cubic Foot of air. Now, let’s say this air is in an ideal compressor room – ‘ideal’ meaning those atmospheric conditions apply – and follow its path to an EXAIR Super Air Knife:
- Filter, Part 1 (intake): When the air compressor draws our SCF in, it passes through filtration media to remove impurities like dust, oil, and moisture. It’s important to remember that this filter is there to PROTECT THE COMPRESSOR from those contaminants, not to provide any measure of cleanliness to the compressed air itself.
- Compression: This is where our SCF gets compressed by reciprocal or rotating elements imparting energy to it, and it now occupies considerably less space than it did in the atmosphere. This also raises the temperature. When all the molecules that comprise our SCF get closer together, they run into each other more often, and that increased friction makes them hotter. Which can be bad, unless we do something about it.
- After cooler: Hot compressed air can cause unsafe surface temperatures and can damage gaskets, seals, or other components in the downstream system. Cooling our SCF down is the first thing we want to do after compressing it.
- Filter, Part 2 (discharge): While the Intake Filter takes care of impurities that could have damaged the compressor, the compressor itself can add some back into our SCF – like oil, wear particulate from meshing gears or seals on moving parts, etc. You’ll want to remove those as well, before letting them go any further in the system. Contaminants like that can really do a number on the operation and effectiveness of some types of dryers.
- Dryer: While the intake filter removes some finite amount of moisture from our SCF before compression, the compression cycle increases the moisture concentration of it. Dryers come in different types and configurations, each with their own pros & cons, and certain types are more suitable for certain situations. Here’s a link to a blog on the subject by Jordan Shouse that’s both informative and entertaining!
- Primary Storage: Once our SCF gets cooled, cleaned, and dried, it can take a little break if it’s not needed right away, in a receiver tank. Such a tank, like EXAIR’s Model 9500-60 60 Gallon Receiver Tank (right), near the compressor discharge, serves several purposes:
- It maintains header pressure during any load transients that happen too quickly for the compressor to keep up in real time.
- It provides further moisture removal, as any water that condenses in this receiver can be drained from a valve on the bottom.
- It also allows the compressed air to cool further.
- Distribution Header Piping: This is the “highway,” if you will, that our SCF travels to where it’ll be used. It’s not alone, either – there are sometimes hundreds, if not thousands, of other SCF’s passing through every minute. And if it’s not appropriately sized, there’ll be problems akin to traffic jams on crowded roads. The appropriate size and layout of the header piping will be determined by a number of factors – here’s a link to a blog with more details on that.
- Airdrops: These are the branches from the distribution header that lead to the various points of use in the facility. Our SCF will take whichever one it gets directed to…in this case, the aforementioned EXAIR Super Air Knife. The proper size of the drop piping or hose will be determined by the compressed air consumption of the load(s) serviced by the drop, and its length from the header. In the case of our EXAIR Super Air Knife that our SCF is heading towards, the recommended in feed pipe sizes are listed in the Installation/Maintenance Guide:
- Filter, Part 3 (point of use): Good engineering practice calls for point-of-use filtration. Our SCF has already been through two filters, I know, but it’s also potentially picked up some more contamination along the way. Rust from the inside walls of iron pipes is the most common culprit. The EXAIR Super Air Knife that our SCF is heading towards needs its supply to be filtered for particulate to a level of 10 microns or less. EXAIR Automatic Drain Filter Separators have 5-micron particulate elements, and centrifugal elements that ‘spin’ out any remaining moisture. Depending on the needs of the application, we also have Oil Removal Filters with coalescing elements for oil/oil vapor. They also provide additional particulate filtration to 0.03 microns.
- Regulator: It’s taken a good deal of effort and expense to get our SCF to this point, so it only makes sense to use it as efficiently as possible. A Pressure Regulator allows us to precisely ‘dial in’ the supply pressure so that we don’t use it (or any of the other SCF’s that it’s traveling with) any more than needed.
- Shutoff valve: Years ago, I talked to an engineer at a company that was using one of our Super Air Knives to blow off parts that were passed in front of it by a robot. The robot’s arm turned & rotated the part in the air curtain to ensure it got completely blown off. This only took a couple of seconds, as the operators had ‘tweaked’ the arm movement to do it as quickly as possible. However, there were about 15 seconds between parts…and the Super Air Knife WAS BLOWING THAT WHOLE TIME. Since they’d already told me how great their automation techs were at programming the robot, I suggested that they go one more step and install a Solenoid Valve in the supply line to the Super Air Knife and use the robot’s logic to open it right before the robot got there, and close it right after the robot left. Step Four of our Six Steps To Optimizing Your Compressed Air System is to “turn off the compressed air when it’s not in use,” and by doing so, they reduced the compressed air consumption of this one Super Air Knife by about 80%. THAT’S optimized. If you don’t have existing logic to do this, our EFC Electronic Flow Control will do it for you.
- The Super Air Knife: At long last, our SCF is ready to fulfill its purpose, and the Super Air Knife will help it do so in the most efficient way possible. It uses that SCF of air, along with all the others that pass through, to entrain a WHOLE BUNCH of SCF’s from the surrounding environment. The amplification ratio for EXAIR Super Air Knives is 40:1, making them the most efficient compressed air-blowing products on the market.
It’s been a LONG time since I’ve used the Six Factor Formula for the neutron life cycle in nuclear fission (and honestly, I haven’t missed it all that much), but every day, I use formulas and figures related to:
- Compressed air storage
- Return on investment for engineered compressed air products
- Adding sound levels from multiple devices
- Heat transfer
- Sizing a Cabinet Cooler System
Just to name a few. If you’d like to “math something out,” (just not the Six Factor Formula, please), give me a call.
Russ Bowman, CCASS
Application Engineer
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