Moisture visual indicator and relative humidity versus dew point.

[Luis H]

@Luis H : Table 551-D-2 predates modern correction factors.

I am not sure about that.

Thanks for all the links. I will have to take some time and look at them… And think about this. My thermodynamics is pretty rusty.

AFAIK, the calculator from Howell Labs is only good for relatively low pressure. I think it was only designed for a few hundred psi max. It was never intended for very high pressure air. I know the guy that wrote that program when he worked at Howell. He happens to sit in the office next to mine. I give him a hard time about it…

 

[lowviz]

Nice timing, caught me sitting at my laptop!

I'm intrigued by this: Air Dry Co. of America That device (notice the range of pressures) appears to work by fogging a mirror.

Dew Point and Frost Point are not the same. Is it possible that your table is a mix of dew and frost as in "whichever fogs the mirror first"?

It took me a bit to get my head around the fact that the frost point is HIGHER in temp than the dew point...

 

[Luis H]

Nice looking unit, but I don't think I can afford it... lol

 

[lowviz]

Ha!

Not what I meant. Is some device similar to that unit what generated 551-D-2? Maybe your friend knows...

This is getting crazy, but I'm learning a ton. My guess, bottom line is you change your dessicant when your 10% RH visual sensor "pinkies out".

 

[Luis H]

Yeah, I was just kidding.

The table says: “Data was calculated using Thunder Scientific Corp. software HumiCalc version 2.7.3.”

Thunder Scientific Corporation - Humidity Generation and Calibration Equipment

I don’t know when was it done.

The table does say: dewpoint/ frostpoint.

I have to think a bit about the properties of high pressure water. Ice melts under very high pressure. Water is the only substance that expands when it freezes and therefore very high pressure will melt it (like the pressure under ice skate creates a film of water). I don’t think that 3000 psi is really that high pressure to affect the freezing point of water very much, so many of those numbers are probably frostpoints.

I used to love thermodynamics in college, but I am embarrassed at how much I have forgotten. That being said, we didn’t really dealt with super high pressure air or high pressure moist air. The only psychrometric charts I have seen are for ambient pressure.


BTW, I was just reading the website from Thunder Scientific Corp. (software HumiCalc) and it sounds very promising. I may install it and the Cosa software and compare them.

 

[nadwidny]

@Luis H : Table 551-D-2 predates modern correction factors.

In all honesty, RH inputs in increments of 10% make this moot, but it would be nice to get an analytic solution to the moisture content of HP air using today's tools. I think that we are close.

Not only close but available and have been for decades. It all depends what you want to spend.

These are (last time I checked) around $2500.

Dew Point Meters for Industrial Measurements - Vaisala

The ones I work with in the lab are ~$9-13K

. SAI Inc.

 

[swamp diver]

Nothing can beat the eyeball humidity device in price and effectiveness but one must know its limitations such as switching the filters out at 10% RH if you want to pass the CSA Z275.2/180.1 -53 C moisture specification or the -65 F spec on the older CGA Grade E standard.

The Vaisala units are nice but require annual calibration of the dew point sensor last time I checked so depending on where you live that can get expensive with shipping and labor.

A much simpler answer if you have the money to spend is the Bauer Securus system which you can install as an add-on, but it does tie you into purchasing the proprietary Bauer Securus filters which are expensive. The system does work if only the OEM filters are used and will shut the compressor down in the -55 C to -58 C range. We've used the Securus system for over a decade now without issues as has the Canadian military on many of its hp compressors.
Breathing Air Systems - Cartridge Monitor, Securus, Retro Kit (SECURUS-KIT)
B-SECURUS

The Securus system has a very simple capacitance hygrometer in the final desiccant bed at the top of the filter and when the moisture level exceeds a certain threshold a yellow warning light shows up on the indicator box. At this point you have 3 to 5 hours left of filter life and then it turns red and the compressor shuts down.

No calibration is needed with this system because there is a new capacitance cell in every new cartridge. The aftermarket filter copies from LF do not work in the Bauer system. Attached is the patent from Heinz Bauer explaining its operation.

If you're in Europe or Asia L&W has their Puracon system which I have seen but never used. It appears to work as advertised.
L&W - Puracon Stationary PRO

 

[swamp diver]

BTW, I was just reading the website from Thunder Scientific Corp. (software HumiCalc) and it sounds very promising. I may install it and the Cosa software and compare them.

They both should give you the same answer but I'm not sure if the HumiCalc allows the choice of Greenspan enhancement factor. It's been a while since I used that one but I think they have Sonntag and Hyland and Wexler as options. If you call Thunder Scientific they will tell you which option is closest to the Greenspan enhancement factor.

 

[Guy Kuo]

Thanks to this thread, I was motivated to actually add a visual indicator to my setup....
For $100 total including shipping it was worth it even if I will never be breathing my Bauer JR's output.

By positioning the indicator proximal to my whip’s bleed and shutoff valves, I can protect the disc from exposture to atmospheric moisture between fillings. Both ends of the whip are sealed between uses and the air should remain dry in the whip.

 

[swamp diver]

I think you'll find that within a day the ambient moisture will leak in the line even with end plugs (moisture actually leaks through the thermoplastic hose wall) and the disc will turn pink, more so if you live in a high humidity environment. And you'll have to run it for at least an hour to get a true reading of the compressed air's moisture content once the disc turns pink.

After you've finished filling tanks I'd fill the line to 1800 psig and close the whip outlet valve and let the disc change to its final color assuming the PM valve on the other end in the Junior will hold pressure for a few hours.

Remember that the advertised Bauer filter service capacities are for usage at an ambient temperature of 50 F. In the summer at 80 F the service life is 0.43 which means if the service manual says the filter is good for 20 hours at 50 F you now only have 8 to 9 hours of processing capacity. The disc will change to pink very quickly in the summer if you are only running the stock P21 filter.