Beer fridge...Air line cooler/Plasma.

[TimGa]

Does/will a plasma work more effective on cooler compressed air?

If so, here's my idea.

I have a small beer fridge for my garage. I want to coil some copper tubing, place inside the fridge with lines coming in and going out. I imagine I could get about 20 ft of line in the top part of the fridge...leaving room for some beer. Why do this? I want to cool off the air heading to my plasma...will this benefit me?
Here's a simple breakdown of my layout:

Compressor/40ft copper tubing/Triple air filter/Fridge idea/20ft copper tubing/Couplers(end). Somewhere in there I will also have a ball valve to release collected water. I would have another filter on the back of the plasma.

Somewhere back I seen a picture of a coiled tubing in a tub of water...that's where I got this idea.


Thanx

[Pumpkinhead]

Nope, waste of time for two reasons.
a) All that excessive Cu tube is gonna cut into your air flow, plaz's love lots of air.
2) The only cool air the plaz will see is that first blast of air between pilot arc and plasma, after that the temperature will be the same going in the fridge as out, due to the high volume being used.

[Roger]

Good idea cooling compressed air condenses water that can be filtered out. Your little bear frig doesn't have enough cooling capacity to make it work.

[jimcolt]

Actually this has been done, and it works quite well. Put your coil of 3/8" ID copper in the largest plastic tank of water...inside the fridge. The water kind of stores energy....and helps transfer the cold to the air. Cold air will condense water quite easily. Where the hose runs out of the fridge affix a verticle drop pipe that goes straight down to the floor, and attach a float operated water drain. Tap your air off the highest (near the ceiling) part of that vertical pipe. Most Plasma systems use les than 6 scfm of air......smaller the nozzle, less flow. Leave plenty of room for beer. Maybe you should get a bigger fridge?

Jim Colt

[Pumpkinhead]

And you claim to work for Hypertherm, Eh?

20 feet of 3/8" Cu tube has a volume of 0.015277 ft³ at 6CFM, that's ~400 volume changes per minute, I don't think your gonna get much cooling at that rate.

[Hotfoot]

Tim, I just noticed you were in Saskatchewan...how about a single 1/2" iron water pipe around the outside of your shop (up at gutter level)...wouldn't that be "free cooling" most months of the year? My iron pipe runs 25' up/down a wall and along the ceiling inside my South Texas shop, and I get zero water. I do have two water traps, but they are always dry. I do burp the water out of my tank periodically

[jimcolt]

I have been with Hypertherm for over 31 years......why do you ask?

Jim

[enlpck]

Lets do some math:

Specific heat of moist air (uncompressed, but it is close enough at 100PSI) in terms of FREE VOLUME: 0.019BTU/(ft^3*degF), which translates to about 7BTU/(hr degF) at 6CFM. This means, you need 7BTU/hr of cooling to drop 6CFM by one degree.

A small (6Cu ft is the one I am looking at) 'fridge might be capable of 150BTU/hr, s t would be able to drop the air temp by about 21 degF if there is good thermal transfer. A larger fridge (like the one in my kitchen) has in the ballpark of 500BTU/hr capacity, and could drop the same flow rate by about 70 degF.

This is pretty reasonable. Dropping 20deg is enough to condense a lot of water if the starting temp is about 80F. In practice, you might be able to get a 40deg drop if a water bath is used as a reservoir, due to the intermittent airflow of a plasma cutter (even a CNC unit might burn at 50 to 60% duty cycle), and a 40deg drop from 80F is about as far as you would want to go, since you need some temperature differential to get the heat out of the air, and the cooler would not want to be below freezing (32F) to avoid icing in the air line.

Sounds like a small to midsize fridge would be fine for a homebrew cooler.

I might go with several parallel lengths of smaller tubing to increase the heat transfer surface, or a longer length of the 3/8, or even 1/2"

[TimGa]

Good points.

Hotfoot, can't use iron outside here...wouldn't last, it would rust within 6 seasons...but you gave me another idea.
How about if I ran the copper tubing inside the walls of my garage? My garage, 24x24, is not finished. So I could run 3-4 straight runs of 22ft each, 1/2" pipe, back and forth. Add my filters and dump outs, insulate and sheet the inside. Doing this would allow the air in the lines to cool but not freeze. By having roughly 100ft of cool air.................wait a minute, that won't work either...what do I do in the summer? Sometime it get's up to 40 Degrees Celius...that means the walls would be hotter.

I think I'm thinking about this too much...going for a beer.

Thanx for your ideas.

[Roger]

When I lived in NW Washington State city or well water was always cold. Run one copper tube inside another tube or pipe like a beer wort cooler. Make outer tube water inner tube air with counter flow. Discharge water then goes to hose bib watering garden or lawn. This should work year round and be almost free. Dad cooled a house in summer with city water flowing through water/air heat exchanger in furnace air ducting.

[Pumpkinhead]

A small (6Cu ft is the one I am looking at) 'fridge might be capable of 150BTU/hr, s t would be able to drop the air temp by about 21 degF if there is good thermal transfer. A larger fridge (like the one in my kitchen) has in the ballpark of 500BTU/hr capacity, and could drop the same flow rate by about 70 degF.

Lemme get this straight, this 'fridge in your kitchen has the wondrous ability to lower the temperature of 6 cu. ft. of air by 70°F in one minute?

So, you're saying if this magical appliance had an internal volume of 6 ft³ and you sealed it, drew a vacuum in it, on a hot summer day (ambient 100°F), then allowed it to fill with air (again, ambient 100°F), waited a minute, the internal air temperature will be 30°F?

BILGEWATER!!!

And I am being quite generous when I say that, 'cause I could ask if you are purporting that this wondrous appliance could do that every 60 seconds. Because it sure sounds that way.

[enlpck]

You are aware that the abbreviation 'hr' stands for hour, arn't you? As in 500BTU/hr? You understand that the heat for a 1deg change for one cubic foot of air is 0.019BTU? Do the arithmetic. This is the rate of cooling required. 6cubic feet of air isn't much air. Change of state is where the large energy change comes in, but the percentage vapor at the operating pressure (about 100PSI) will be low enough to affect the temp change by only a few degrees (not all of it will condense, and it is a low portion to begin with) as long as the air has already been cooled to ambient.

You might want to adjust the medication, as your attitude seems to be acting up again.

Lemme get this straight, this 'fridge in your kitchen has the wondrous ability to lower the temperature of 6 cu. ft. of air by 70°F in one minute?

So, you're saying if this magical appliance had an internal volume of 6 ft³ and you sealed it, drew a vacuum in it, on a hot summer day (ambient 100°F), then allowed it to fill with air (again, ambient 100°F), waited a minute, the internal air temperature will be 30°F?

BILGEWATER!!!

And I am being quite generous when I say that, 'cause I could ask if you are purporting that this wondrous appliance could do that every 60 seconds. Because it sure sounds that way.

[enlpck]

By the way, pumpkin, allow me to quote you: "BILGEWATER"

This is in response to: "6CFM, that's ~400 volume changes per minute"

You do understand that the 6CFM is 6 STANDARD cubic feet per minute? Uncompressed volume at standard conditions? Compressed to 100PSIG, the volume will be about 0.9CuFt, for about 60 exchanges per minute in the volume given. Still a high rate, but not real bad. A one second timeframe is less than desirable for a large delta-T, but not horrid. I would shoot for about 5 seconds.

[BillyP]

Actually this has been done, and it works quite well. Put your coil of 3/8" ID copper in the largest plastic tank of water...inside the fridge. The water kind of stores energy....and helps transfer the cold to the air. Cold air will condense water quite easily. Where the hose runs out of the fridge affix a verticle drop pipe that goes straight down to the floor, and attach a float operated water drain. Tap your air off the highest (near the ceiling) part of that vertical pipe. Most Plasma systems use les than 6 scfm of air......smaller the nozzle, less flow. Leave plenty of room for beer. Maybe you should get a bigger fridge?

Jim Colt

...would sure make a nice air dryer if nothing else.

[jimcolt]

Contrary to the the disagreement from one poster on this subject....this works very well as an air dryer....for a plasma system that is operating at less than 100% duty cycle.

Jim Colt