A centrifugal spin on a 500-year-old air compressor design • Hacker News Board

Re: A centrifugal spin on a 500-year-old air compressor design

#41

Post by extrapickles » Thu, May 06, 2021, 10:07 PM UTC

dusted wrote: post #27

hinkley wrote: post #5

Earlier quoted context omitted.

I didn't realize that air compression hardware has to deal with water removal but apparently it does. One article I found is suggesting that air at 7 bar can hold about 1/3 as much water. What confused me is that the a wing stall (low pressure above a wing) causes cloud formation, due to vapor condensing out of the air. But 7 bar is ~7 times as much air per cubic centimeter, so that's 14% as much space containing 33%…

When you compress air, the moisture falls out, the amount that falls out depends on pressure and temperature. pretty much all normal compressors simply have a, I don't know the right english word, but.. a valve at the bottom and once in a while (like, once a year or less, depending how much you use it) you take the pressure mostly off the compressor and open this, then the water is blown out.

Fancy air compression systems (eg: not consumer) will have a drain valve that automatically opens when the pressure falls from turning system off for night/weekend/other maintenance so people don't forget to drain it.

Its also not just water that is collected at the bottom of the air tank, compressor oil also collects. Oil can also be deliberately added by either as a byproduct of compressor design or from separate equipment, into the airstream help lubricate and protect equipment from the moisture, reducing the need to remove the moisture through other means.

Re: A centrifugal spin on a 500-year-old air compressor design

#42

Post by DannyBee » Thu, May 06, 2021, 10:14 PM UTC

hinkley wrote: post #5

teuobk wrote: post #2

Interesting. A few questions that come to mind: 1. What is the dew point of the compressed air? Many applications using compressed air require very dry air so as to avoid corrosion issues (e.g., air tools) as well as problems related to heating of water vapor (e.g., tires). For small applications, the dew point is reduced using simple traps, silica gel beads, or molecular sieves, but for even-drier air or larger appl…

I didn't realize that air compression hardware has to deal with water removal but apparently it does. One article I found is suggesting that air at 7 bar can hold about 1/3 as much water. What confused me is that the a wing stall (low pressure above a wing) causes cloud formation, due to vapor condensing out of the air. But 7 bar is ~7 times as much air per cubic centimeter, so that's 14% as much space containing 33%…

Most industrial compressors (IE rotary screw, scroll, rotary vane, etc) have aftercoolers, because the temperature of compression is pretty high. The aftercooler causes most of the water to condense out.

So what you lose is efficiency, because it will take compressing more intake air to get the same yield of compressed air at a certain pressure/dewpoint.

(this is why you often see a lot of wet storage tanks for air - leaving it in the tank lets a lot of the intake air water condense at the bottom)

Aftercoolers remove a ton of of the water, and so you often get an 20 degree approach temperature.

Removing more than that requires some form of air dryer.

Re: A centrifugal spin on a 500-year-old air compressor design

#43

Post by aj7 » Thu, May 06, 2021, 10:15 PM UTC

extrapickles wrote: post #41

dusted wrote: post #27

Earlier quoted context omitted.

When you compress air, the moisture falls out, the amount that falls out depends on pressure and temperature. pretty much all normal compressors simply have a, I don't know the right english word, but.. a valve at the bottom and once in a while (like, once a year or less, depending how much you use it) you take the pressure mostly off the compressor and open this, then the water is blown out.

Fancy air compression systems (eg: not consumer) will have a drain valve that automatically opens when the pressure falls from turning system off for night/weekend/other maintenance so people don't forget to drain it. Its also not just water that is collected at the bottom of the air tank, compressor oil also collects. Oil can also be deliberately added by either as a byproduct of compressor design or from separate e…

About the only thing practical thing that valve does is perhaps lengthen the time fir the tank to rust out. Any serious industrial installation winds up with a refrigerated water removal unit.

Re: A centrifugal spin on a 500-year-old air compressor design

#44

Post by pacaro » Thu, May 06, 2021, 10:16 PM UTC

owenversteeg wrote: post #37

From the diagram, this seems like it wouldn't be terribly hard to DIY: you can take an off the shelf heat exchanger and a fan, then all you'd need is the centrifuge part and tubing for the pressurized gas. Would there be any special considerations in DIYing this that I'm overlooking? The only part that I can see being tricky is the centrifuge mechanism and sealing the bottom of that to a compressed air tube... not qu…

Building a DIY centrifuge is a great way to become a Darwin award candidate.

Re: A centrifugal spin on a 500-year-old air compressor design

#45

Post by metalman » Thu, May 06, 2021, 10:25 PM UTC

Very interesting machine. The target market is for food and other processes that require food grade ingredients or just very clean air. If they can get cleaner air with less power and maintanance then its a go. And the initial model is slated to be 10 to 20 hp ,so the size of a big deepfreez,hundreds of pounds. 100% duty cycle,air and water filtration,clean outs,drains,etc,all has to be assumed to fit into an industrial environment.

Re: A centrifugal spin on a 500-year-old air compressor design

#46

Post by londons_explore » Thu, May 06, 2021, 10:28 PM UTC

lttlrck wrote: post #35

londons_explore wrote: post #28

Air compressors need not be noisy. Your fridge at home likely has a cylinder air compressor in it, pumping gas up to 30 bar (400 psi) and it only makes a quiet humming. The trick is that air compressor is attached to a big vibration damping weight, mounted on big springs, which are mounted into an oil filled heavy steel box, which is itself mounted onto rubber feet.

Isn't the difference that a refrigerator is a closed system whereas many industrial/workshop air compressors are open and must maintain relatively high pressure due to a "controlled leak"? I am certainly no expert but they don't seem the same to me?

Cut a pipe on the back of a fridge and it'll run open circuit just fine. Doesn't make it appreciably louder. (beware, some fridge gasses are illegal to vent to the atmosphere, and others are pretty explosive)

Re: A centrifugal spin on a 500-year-old air compressor design

#47

Post by mnouquet » Thu, May 06, 2021, 10:31 PM UTC

londons_explore wrote: post #28

Air compressors need not be noisy. Your fridge at home likely has a cylinder air compressor in it, pumping gas up to 30 bar (400 psi) and it only makes a quiet humming. The trick is that air compressor is attached to a big vibration damping weight, mounted on big springs, which are mounted into an oil filled heavy steel box, which is itself mounted onto rubber feet.

> The trick is that air compressor is attached to a big vibration damping weight, mounted on big springs, which are mounted into an oil filled heavy steel box, which is itself mounted onto rubber feet

So easy... If it was that easy, it would have already been done, but...

1) compressor are maybe 100lb of solid cast steel

2) owners need to fix mechanical wear, not simply "replace the whole thing" - head gasket fails, gauges fails, hose leak (think thermal expansion / contraction), oil need to be changed, etc.

3) refrigerator system are sealed, air compressor need to pull air from the outside (ie. it can be DIRTY), which means lot of the noise actually come from the intake

Re: A centrifugal spin on a 500-year-old air compressor design

#48

Post by mnouquet » Thu, May 06, 2021, 10:34 PM UTC

londons_explore wrote: post #46

lttlrck wrote: post #35

Earlier quoted context omitted.

Isn't the difference that a refrigerator is a closed system whereas many industrial/workshop air compressors are open and must maintain relatively high pressure due to a "controlled leak"? I am certainly no expert but they don't seem the same to me?

Cut a pipe on the back of a fridge and it'll run open circuit just fine. Doesn't make it appreciably louder. (beware, some fridge gasses are illegal to vent to the atmosphere, and others are pretty explosive)

> Cut a pipe on the back of a fridge and it'll run open circuit just fine

Try to run a plasma cutter, or a 1" impact wrench out of a fridge compressor...

Re: A centrifugal spin on a 500-year-old air compressor design

#49

Post by TheSpiceIsLife » Thu, May 06, 2021, 11:04 PM UTC

dusted wrote: post #27

hinkley wrote: post #5

Earlier quoted context omitted.

I didn't realize that air compression hardware has to deal with water removal but apparently it does. One article I found is suggesting that air at 7 bar can hold about 1/3 as much water. What confused me is that the a wing stall (low pressure above a wing) causes cloud formation, due to vapor condensing out of the air. But 7 bar is ~7 times as much air per cubic centimeter, so that's 14% as much space containing 33%…

When you compress air, the moisture falls out, the amount that falls out depends on pressure and temperature. pretty much all normal compressors simply have a, I don't know the right english word, but.. a valve at the bottom and once in a while (like, once a year or less, depending how much you use it) you take the pressure mostly off the compressor and open this, then the water is blown out.

Ours are on a timer to blow off a small amount of air at a few low spots in the system every five minutes, even though having a refrigeratant type demudifier.

One of the devices stopped working between services and the bottom reciever tank half filled with water.

Edit: they're call bleed valves

Re: A centrifugal spin on a 500-year-old air compressor design

#50

Post by TheSpiceIsLife » Thu, May 06, 2021, 11:07 PM UTC

aj7 wrote: post #43

extrapickles wrote: post #41

Earlier quoted context omitted.

Fancy air compression systems (eg: not consumer) will have a drain valve that automatically opens when the pressure falls from turning system off for night/weekend/other maintenance so people don't forget to drain it. Its also not just water that is collected at the bottom of the air tank, compressor oil also collects. Oil can also be deliberately added by either as a byproduct of compressor design or from separate e…

About the only thing practical thing that valve does is perhaps lengthen the time fir the tank to rust out. Any serious industrial installation winds up with a refrigerated water removal unit.

Any serious industrial installation will have multiple mitigation approaches.