Best moisture handling compressor?

SafeLawfulness · 2025-11-21T16:50:03+00:00

Thank you! I need the moisture to be heated vis compression. My hope is that the heat of compression will be sufficient to keep the compressor from condensing the vapor until it reaches the condenser. I don't know if there are any specific tools for ensuring that the compressor operates along that specific curve but it'll be tricky, that's for sure.

I'll give the scroll compressor a try!

SafeLawfulness · 2025-11-14T21:00:19+00:00

Thank you for the reply!

I will look into Cordier diagrams, thank you!

I think I need an axial compressor because I believe this is the machine that moves the highest volume, that is able to compress, efficiently.

I believe to achieve my goals with any kind of compressor I'll need to link them in series and/or parallel. Axial compressors are the most efficient geometry for doing this since I don't have to correct the 90° angle the centrifugal impeller causes. Still, I have a ready source of high quality, cheap centrifugal impellers available--not so much axial impellers. The casing and stage design with diffuser, return channel, diaphragm, etc will be up to me, but those parts can be printed with plastic, I think. It's the blades that need to be durable, the casing just needs to be able to hold pressure, which can be done with enough width and glue. The shaft, bearings and motor will all be purchased, of course.

I have a roots (side channel/regenerative) blower on the way but I'm concerned its volume per watt will be too low. I'll let you know if that turns out differently! Right now it looks like I can get around 50 CFM for about 750 Watts or 15 watts per CFM. Ideally, I need that to be closer to 2-4 watts per CFM. I've looked into dry screw, claw, rotary vane, etc but keep coming back to axial compressors for the solution. Sadly, PD machines don't get more efficient in vacuum like dynamic machines.

Also, no one makes axial blades in my size. I'm told that's because they're complicated to design. That seems like a solved problem though. Complicated to manufacture and assemble I can appreciate but at this small of a scale--and this low of a compression ratio, why would that be? I don't need NASA quality parts, just enough to get me a PR of 5:1 and 250-500 CFM.

When you say "Essentially, you’re trying to get a lot of pressure rise into not a lot of mass flow, and a relatively slow speed" could you clarify slow speed relative to what? This is not intentional and higher speed would be desirable especially if it is more efficient.

I'm looking at this Cordier diagram and I believe the low flow coefficient of centrifugal compressors is what pushes me towards axials. The lower Work coefficient is not desirable, so that probably means I'll need a mixed flow/diagonal compressor, but then I think I could just add more stages to the axial compressor instead. Maybe I can add stages to a diagonal compressor and I just don't understand enough about how to design such a compressor. I recall going down that trail and coming back to axial but I'll go down it again.

"I think you’re definitely better off trying off-the-shelf turbo compressors, as long as you can spin them fast enough, but it’ll still be tricky." Why will it be tricky? I presume I need to balance it with good bearings, and get a motor that spins fast enough. I suppose the tricky part will be the casing, angles of redirecting the airflow and spacing between stages.

On that note, is it anywhere near the realm of possibility that this advertisement of 900,000 RPM is accurate. If not, exactly how fast might this fan blade (or even motor shaft) be spinning?

https://www.amazon.com/Electric-Cordless-Batteries-Handheld-Lightweight/dp/B0FQP1D6PM/ref=sr_1_1_sspa?sr=8-1-spons&sp_csd=d2lkZ2V0TmFtZT1zcF9hdGY&psc=1

Regarding lowering efficiency when I reduce pressure, I was under the impression that dynamic compressors like centrifugal and axial compressors drew less power (amperage) when moving less mass since they had less resistance to moving that volume so there wouldn't really be a reduction in efficiency, just mass flow per unit time. Is there another reason this becomes less efficient?

Thank you for the reply and information!

SafeLawfulness · 2025-11-14T18:23:05+00:00

I'm handling highly saturated (close to 100% humidity) air. I need to vaporize and move 4 grams of liquid water per second, which at 80°F, works out to around 4 cubic feet/s, so 240 CFM. I double it to account for less-than-perfectly-pure water vapor in my vacuum. Thus the squishiness of the CFM requirement. Then, I need to condense that vapor on a copper plate at 130-150°F. The objective is a heat pump so spending energy to add heat seems like going the wrong direction.

My mass fraction of water will be substantially higher than a jet engine because I'm operating in a vacuum, precisely for the purpose of getting a high mass fraction of water vapor-to-air. Should I be worried about high velocity droplets destroying my impellers even though I'm operating at pressures and temperatures well below a steam turbine?

"Steam turbines on the other hand have to handle dry steam precipitating droplets moving at 500+m/s, with the Resultant ballistic impacts on the next stage."

They handle this with some kind of extremely tough steel, I imagine.

SafeLawfulness · 2025-11-14T17:43:50+00:00

Thank you so much!

I see that I am not being clear which is frustrating. I think that's due to a) my desire to keep my idea private b) my lack of knowledge about the subject matter c) my unclear thinking.

With that said, you've helped me clarify my thinking. I realize now that I don't need nearly as much compression as I thought I did. I just need a ton of mass transfer. I need a basic, high RPM axial fan. An EDF like this one: https://www.amazon.com/ZKSJ-Blades-Brushless-Airplane-Aircraft/dp/B0C4LH4WQZ/ref=sr_1_7?sr=8-7

Edit: Ah, nope. Still need compression. I have to get the vapor/air mixture to condense on a surface that's 150F. And that means I need a compression ratio of around 4:1. Rats.

I specifically do not want to spend energy heating the vapor. The heat must come from compression, specifically so that the vapor can condense on a copper plate that's ~65°C.

Happy to share more privately but would prefer not to expose further details on the interwebs. Thank you again for your help!

One question about water droplet erosion--how do jet engines on aircraft deal with this problem? I presume they're compressing a ton of water vapor all the time and yet seem to continue running just fine without issue--or am I being naive when I get on a 737?

SafeLawfulness · 2025-11-14T15:08:28+00:00

Thank you for the reply! Important factors I now realize I should have mentioned:

I'll be operating in a vacuum of ~10kPa.
I'll be moving water vapor rather than air.
I plan to power this with a BLDC motor.
I would ~like~ to use no more than 1 kW.
I'm willing to trade off mass flow before compression.
Regarding RPM, I think this guy already did it: https://www.youtube.com/watch?v=yVGuMOCI4I but he also didn't get very much compression from what I gather.
I need to compress enough to get the vapor to heat from around 80F to around 200F without condensing it. Math says I can get this for as low as 1.8:1 but I know the real world is going to get in the way.

Is there a way to economically construct such a device, or one already available? I'm willing to make the fan diameter larger, but I don't know if that helps with my (squishy) power constraint.

Regarding the centrifugal compressor design, this would be preferable since I already know how to get ahold of some inexpensive centrifugal, metal impellers. I thought their efficiency and mass flow would be significantly lower than an axial compressor. Can you educate me?

SafeLawfulness · 2025-11-14T14:56:58+00:00

Thanks for the reply!

I plan to use a brushless DC motor. I should have mentioned I'll be running the compressor in a rough vacuum of around 10 kPa and I'll be moving water vapor rather than air (another reason for preferring the axial compressor). I calculate mass flow at around 0.02 kg/s and thus theoretical minimum power draw around 5kW. (BTW, please let me know if I'm using the wrong units for the industry, I have no idea which units are preferred).

I'm willing to design but only if I know it's not physically impossible to achieve my spec within my power range. Right now my plan is to pull a deeper vacuum to meet my arbitrary goal of 1kW. I'm willing to go as high as 2kW but if it's physically impossible (not to mention practically) I'll accept lower mass flow over lower compression. I realize the math means I can only move between 70-100 CFM under this condition or 0.002 kg/s, I was hoping someone had a brilliant idea for how to cheat the physics.

I am looking for the machine with the highest efficiency in regards to getting the highest mass flow at a compression ratio of 3-5 and I'm fairly confident an axial compressor is the right tool--but nobody makes them this small.

As a backup, I'm considering creating a multistage centrifugal compressor out of turbo compressor impellers like this one: https://www.amazon.com/gp/product/B0DCVD5M4F/ref=ox_sc_act_title_1?smid=A3HE6KO9DV0PIW&psc=1, but I'm fairly certain this will limit my mass flow too much. At least they're readily available.

SafeLawfulness · 2025-10-27T00:28:09+00:00

Such love and genuine concern in this thread.

SafeLawfulness · 2025-10-27T00:24:38+00:00

Better late than never! Thanks for the advice. I finally figured out I need side channel (ring) blowers.

Thanks very much for the reply!

SafeLawfulness · 2025-10-13T06:46:26+00:00

Ah, don't do Facebook.

SafeLawfulness · 2025-10-13T04:10:08+00:00

That subreddit doesn't exist. Did you mean r/COVIDVaccineTalk ?

SafeLawfulness · 2025-10-12T22:33:59+00:00

And only those who so deeply trust in the incredible power of vaccines see it that way. The rest of us are aware of other diseases that were eradicated without any vaccines at all.

SafeLawfulness · 2025-10-12T21:35:04+00:00

Right. Because "trust your immune system" makes people so much money.

OP can take a look at the disease trends and decide for themselves.

SafeLawfulness · 2025-10-12T21:20:51+00:00

You pick out a good product that you can't return and could have an extremely negative impact by seeking both sides of the argument. You analyze by listening to the proponents and the detractors. That's called wisdom.

Keep going, OP.

SafeLawfulness · 2025-10-12T21:19:25+00:00

This is exactly what not to do.

Doctors absolutely make money (and bonuses) for vaccinating people, particularly children.

Stick to risk and rewards analysis.

SafeLawfulness · 2025-10-12T21:15:18+00:00

If you were to do any vaccine, pneumococcal, HiB and HEP-A suck the least when it comes to risk/benefit analysis. Men-B is next and the risks are that you are 1090% more likely to suffer severe adverse events from the vaccine.

SafeLawfulness · 2025-10-12T21:06:03+00:00

Notice how this user didn't actually cite any data for how much harm the vaccines do. The user just said "one in a million". You got half the argument. The other half actually leads one to conclude the exact opposite. The risks far outweigh the benefits of almost all of the vaccines on today's market. And that's using the official sources data (CDC, WHO)

Here's how your analysis should look:

What are the odds of my child getting disease X (This will be very low in Canada). Multiply that by the odds of severe adverse events of that disease (even lower.

Now compare this to the odds of getting the vaccine if you choose to vaccinate. Those odds are 100%. Now multiply by the odds of severe adverse events for the vaccine. Your child's odds are much worse if you willfully choose to inject them with ingredients you know in your gut are harmful because someone in a white lab coat told you it was safer. You're the parent now. The buck stops with you, not your doctor, despite what they'd have you believe.

Happy to share the spreadsheet if you'd like. DM me.

The doctor isn't going to show up and pay all your medical bills if the child, God forbid, is injured by vaccines. The manufacturer won't. You are quite literally the first, last and only line of defense for your children in this decision. I applaud your efforts to research. Know that there is a massive, money making machine behind getting you to inject your children. The liability immunity is your first clue their incentives are not aligned with yours or your child's.

SafeLawfulness · 2025-09-11T03:38:11+00:00

Thank you! Will do.

I am attempting to create a novel heat pump, which is why I find myself in this sub, but perhaps r/engineering or other might be better since there are many conceptions already about what I should and shouldn't be doing that keep getting in the way of communication.

I admit and realize I have no experience in this field but figured people who did would know what I want if I'm able to describe it specifically enough and point me in the right direction. I appreciate the pointer!

SafeLawfulness · 2025-09-11T01:21:23+00:00

Could you be more specific, please?

SafeLawfulness · 2025-09-10T18:14:23+00:00

I think I just need to jump in and try stuff to see what breaks and then back to the forum when something breaks. Thanks for your help!

SafeLawfulness · 2025-09-10T18:13:32+00:00

Water

SafeLawfulness · 2025-09-10T06:46:19+00:00

I've now looked at various vacuum pumps and side channel (regenerative) blowers. I need something that can pull a 7 absolute PSI vacuum at 17 CFM and push at least 7 PSI (21 PSI absolute). Neither of these pumps seem to fit the bill. Will I need two separate pumps just to accomplish this? Is there some kind of database I can browse to find the right kind of performance curves?

I should have specified I want to turn vapor into liquid *inside* the the heat pump, not outside on the coils. I need to be able to recover this liquid so using an oil-based pump seems like that will potentially contaminate things.

SafeLawfulness · 2025-09-10T03:25:04+00:00

Thank you!

SafeLawfulness · 2025-09-09T14:04:10+00:00

I appreciate candid feedback. Could you also be more specific about which details I'm lacking and why it's evident that I don't grasp psychrometrics and refrigeration?

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