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Air duster
24-04-2007, 03:56 AM
This is one of my ongoing ideas so I thought I would share it here. I have looked on the internet for similar ideas and found nothing close. So this is a 100% original idea as far as I know.

The idea.
(See diagram below)

Using extremely low temperature for drying a refrigerant charge. in a self contained loss less system. You could do the same thing using dry ice to cool a refrigerant tank, but that requires the out gassing of a lot of CO2 and it couldnít be operated continuously (well hard to operate continuously that is).

The moisture holding capability of a refrigerant goes down as temp goes down. The main reason I am posting this is another thread I seen

(URL clipped)
(Had to clip three URL's because of the 15 post rule for new people....)


Temperature ppm saturated level in liquid propane
-40C 3ppm
-30 5
-15 13
+6C 44
+15 75
+30 173
+45 360


That would mean that I could dry propane to 3PPM with that type of unit. If I go down to <-40C at around 0PSIG That is within refrigeration specs.

How good it would do on R134a, R22, and the others depends on the saturated water content of those refrigerants at low temp. I donít have that info on hand, and I canít find it on the web. If anyone has access to it and would like to post it, I would be very grateful.

If you send the refrigerant through a cycle that reaches that temperature it will percolate out the moisture in the form of ice in the cryo tank.

The basses of my project is an old vacuum flask designed for LOX that was in an old portable medical oxygen respirator.

(URL clipped)

Max operating of the flask in the original application is 30 PSIG at a real cold temp!!!!!! Original capacity was 3 pound of LOX.

If a person had access to a larger pressure rated vacuum flask you could hold a large amount of refrigerant standing in the unit while being dried.

I would like to get a hold of one of the LOX reservoirs/filling stations that went with the above unit.

(URL clipped)

That would be a good basses for a low temp project.

The intended normal operating pressure in my application is 0 PSIG. (around -42C for R290)

30PSIG relief valve will be left in place.

Cycle basics. The compressor pulls vapor off the top of the tank, and runs it though a compressor at high pressure to condense it. And it is dropped in pressure through a regulator and then a capillary tube which sticks into the cryotank. Some of the liquid will flash off as gas cooling the rest to -42C and depositing it in the tank.

The cryo regulator will regulate the pressure of the cryotank to about 0 PSIG. If the pressure is below 0 PSIG and the condenser is empty then the regulator will open up fully letting uncondensed gas back in to main tank. basically turning it into an open cycle. If the pressure increases it will hold up the refrigerant in the condenser and force some of it to liquefy before entering the cryotank and adding to the cooling effect. The cryo regulator is basically a normal externally equalized expansion valve with the sensor bulb cut off, which puts the valve reference point at 0 PSIG. The valve is set to zero, or close to zero superheat. Input is the output of the cycle condenser. eq port is hooked to the vapor space of the cryo tank. outlet is hooked to the input of the cap tube. The regulator will maintain the vapor space at 0 PSIG. the output pressure will be held higher than 0 PSIG provided by the cap tube restriction. the liquid refrigerant will not drop to full 0 PSIG (and reach lowest operating temp) until it leaves the cap tube end, which is in the cryo tank. That will reduce unwanted heat pickup from the surrounding atmosphere.

The heat exchanger at the intake/outlet of the cryotank will help supercool the refrigerant in the cap tube useing the heat uptake of the cold refrigerant gas/liquid mix leaving the tank to increase cycle efficiency.

The cycle evaporator is to warm the gas/liquid mix coming out of the tank to make sure that all the liquid evaporates before entering the cycle compressor.

When the cryo tank becomes full, the level will auto regulate by the fact that the liquid will start coming out the outlet (when the liquid level reaches the intake of the outlet port) which will vaporize in the evaporator and it will basically dump all the incoming liquid refrigerant back out of the tank that come in. When you see the evaporator icing up solid then the tank is full.

When you have the refrigerant in the tank you can let it set there and run while the moisture slowly percolates out of the liquid in the tank(and freezes into ice in the tank). The gas/liquid coming in through the cap tube will agitate the liquid in the tank to stop it from stagnating.

The trap is for purging any incondensable gas that gets into the system. It should have a sight glass in the column to monitor liquid level in the trap. To maximize purging efficiency. (To avoid purging liquefied refrigerant.)

The liquid pickup leg in the tank is for injecting the refrigerant back into the system, or storage bottle.
It goes through the evaporator which vaporizes the liquid at room temp so it can go through the injection compressor. The injection compressor brings the gas pressure back up to system pressure to reintroduce it back into the system. It can go straight in as gas. Or it can be run through the condenser to liquefy it before injection. Like when you want to put it into a tank and minimize tank heating from condensation.
When the job is done, and you have pumped the cryotank down, then you have to remove the moisture out of it after itís internal temperature comes above freezing. That is what the purge isolation valves are for. shut them off when you are done pumping down the system. After the tank warms up, purge the tank of water with dry nitrogen. or dry air. The water will go to the bottom of the tank that is why you use the liquid leg for the purge output.

The two compressor bypasses are used for capacity control. when you want to reduce the output of the compressor in a specific application. And it allows for easy restart of the compressor after loss of power. Shut off the purge isolation valve between the cycle evaporator and the cryotank. then open up the cycle bypass valve to eq the pressure across the cycle compressor for easy restart. Then close bypass valve and reopen the purge isolation valve once the cycle evaporator has pumped down to cyrotank operating pressure(to prevent pressure backlash into the cryotank and popping of the relief valve).
Same basic method with restarting the injection compressor.

The outer loop is for running the dry refrigerant through the injection system and back into the tank to dry out the injection system in case water get into some how.)

The two gauges on the condensers are for watching condensing pressure. If it goes too high, crack open the bypass for that system to allow the condenser to catch up.

The system could be strapped onto an operating refrigeration plant and pull refrigerant off the plant, dry it, and re-inject it. It could run until the refrigerant charge in the plant has been dried to satisfactory levels.

If you was building the system for just that type of operation, then you could simplify the cryo dryer system greatly. I will post a diagram of a basic system for that later.

Another idea. You could increase the efficiency of it by packing the tank with steel wool or something to increase the surface area for the ice to form on.

Does the system sound useful, or is it another one of my stupid ideas?

I have had the parts on hand, and have been intending to build it for a long while, if I can just get my lazy butt in gear.

PS, if decides to start making them and selling them in the thousands, for big $$$$ please remember to pass some of that green this way. I need the money!!!!!!!!!! :D

Good day!

Brian_UK
24-04-2007, 07:11 PM
Does the system sound useful, or is it another one of my stupid ideas?
I would have to ask, to whom would it be useful?

Not for site use and manufacturers do not produce 'wet' refrigerant.

But I may be wrong.....

The MG Pony
24-04-2007, 10:08 PM
Home hobbyists drying their refrigerants for use in home machines.

I was going to build a much simpler system that froze the water out of refrigerant my self. His idea isn't bad but way more complex then needs be IMO.

Air duster
24-04-2007, 10:36 PM
That is why i posted the idea here, to see what people say. :D


The benefits of the system over a normal replaceable dryer core is that the vacuum flask will entrap a lot more moisture for itís size than a solid dryer core. And it is easy to purge the dryer of all the trapped water when the job is done. (unlike a solid core dryer.) That means that you never have to change the active element in it.

Possible uses that come to mind for me are.....
Drying fuel grade refrigerants like butane and propane.

Drying recovered refrigerants and removing incondensables.

Drying heavily contaminated systems. where doing repeated (inline)dryer change outs would be hard. (Where you would normally put in an outside dryer loop with replaceable cores)

Being able to dry a large contaminated system without having to drain the system of refrigerant, isolate a section for putting in an inline dryer or having to start the large system up to move the refrigerant around to move it through an inline dryer. All you would have to do is, pull wet gas from one side and inject dry gas in the other side, and let the dryer run till the moisture indicator on the intake to the dryer indicates that the gas is dry coming out of the system.


All those without having too change out multiple dryer cores as they saturate.

Any place where a large capacity water entrapment device that easily purged of water whenever it becomes full can be used.

And it would pull the moisture level down to 3PPM no mater how full the dryer is of water. Which I think is better figures than solid core dryers. (I may be wrong on that. If anyone has the figures for reference then please post them.)

Air duster
24-04-2007, 10:55 PM
I was going to build a much simpler system that froze the water out of refrigerant my self. His idea isn't bad but way more complex then needs be IMO.

The reason it is so complicated is so that it can be utilized for many different applications without having to disassemble and reassemble it for every application. There is valves to isolate different section for different uses.

That way you can build it into a portable self contained cart with valves and gauges on the front that you can roll around to where ever you need it.

The MG Pony
25-04-2007, 01:58 AM
My system was aiming for the same design goals. but differant design from what you seem to be gunning for.

It had a single shell tube type cell that passed the refrigerant through and it would freze water to the bundle, and after the cycle compleats it by passes the shell tube and purges the water out. it could be put right after the oil seporater and use the gases being distilled out of the oil to combine 2 prosseses togeather seamlesly.

Air duster
25-04-2007, 06:29 AM
I said that I was going to post a version of it that is designed to only operat attached to a system, so here it is! Here is two version of a cryo dryer attached to an operating plant.
(See attachments below.)

The liquid intake is pulled off the plant high pressure liquid line.

The compressor output is pumped into the plant low pressure vapor suction line.

The primary difference is inside the cryo tank You have suction line extended down into the tank with the end at the level you want to maintain the liquid in the tank.

When the liquid level gets to the desired level, then it starts sucking liquid out the suction line, returning the dried liquid to the system.

The siphon tube forces the liquid going into the suction line to come from the bottom.(The liquid that has been in the tank the longest.) And it will stop the suction line from icing up from the ice coating that will most likely form in the spray pattern from the liquid inlet capillary tube.

The cycle evaporator serves the same job. It makes sure all the liquid is vaporized before it gets to the compressor.

First pic is a system using the modified expansion valve.

Second pic is a system using a longer cap tube to provide the pressure drop, and it for pressure regulation it uses a hot gas bypass regulator set to 0PSIG. That is to match the compressor capacity to the cap tube throughput.

Hmmmm....... A 10 pound propane tank could also act as a cryotank but you would have to wrap it in a lot of insulation, and it would take a lot bigger compressor to keep the temp where it should be.........


My system was aiming for the same design goals. but differant design from what you seem to be gunning for.

It had a single shell tube type cell that passed the refrigerant through and it would freze water to the bundle, and after the cycle compleats it by passes the shell tube and purges the water out. it could be put right after the oil seporater and use the gases being distilled out of the oil to combine 2 prosseses togeather seamlesly.

Yes..... that is much simpler than my idea.............

Drats........ why didnít I think of that first........:D

The only problem with that idea (that I can see) is that that system wouldnít really maintain a standing pool of liquid refrigerant. The refrigerant in the shell would be a liquid vapor mix (if i understand it right). The 3PPM figure is for liquid refrigerant. Vapor refrigerant of the same temp will hold a lot more moisture. If ice forms in the shell from a drop of cold refrigerant, and it sticks to the bundle. But when some vapor passes by it, after the liquid drop has left, then the ice would be absorbed by the passing vapor..... (that again, is if I am envisioning your idea correctly.) (Which I am probably not...:) ...)

The only way I can see to fully trap the moisture is to turn it to ice and keep it submerged in a pool of liquid, so it can't contact vapor and be sublimate back into the refrigerant stream.

The MG Pony
25-04-2007, 06:53 AM
Due to the extream cold it would be all liquid within the tube shell, I'm still working on the whole cycle, I want to refine it till it is next to nothing as far as poarts count.


The perfect design has not been met when there is nothing left to add, but when there is nothing left to take away < I can't recall whome said that.

Air duster
25-04-2007, 08:06 AM
Due to the extream cold it would be all liquid within the tube shell, I'm still working on the whole cycle, I want to refine it till it is next to nothing as far as poarts count.

Ow......... (........bangs head.......)
I get it now!!!!!!!!!!!!!!

You will use a second refrigeration system to cool the tube shell.

It will basically be a liquid refrigerant to liquid refrigerant heat exchanger!!!

The outer shell is the second refrigeration system. The inside is the system being dried.

The only contact the refrigerant in the system being dried will have with the drying system is the tube shell.......

Cool idea............:cool: :cool: :cool:

The MG Pony
25-04-2007, 09:47 AM
exactly. Outer shell will be the refrigerant being dried as more internal volume for the ice to build up on. When it gets iced to an X degree it will shut off the intake valve and pump it out any remaining refrigerant then a second valve compleatly isolate it from the system, and allow the built up to mealt and then purge it out, for the next cycle.