3/8" is too small. Stick the pipe in, and crimp the 1/2" tightly around the 3/8" before brazing. Like this:
3/8" is too small. Stick the pipe in, and crimp the 1/2" tightly around the 3/8" before brazing. Like this:
Personally I think it would braise fine, you just need to rig up some sort of "jig" to hold the 3/8" pipe central inside the 1/2" pipe to get a nice clean finish. (I noticed on yours that the pipe is pushed over to one side)
The other advantage of having it centralised in the pipe is that the gap between the two pipes is smaller (since its shared between both sides, rather than all on one side) so it should be easier to braise.
Filling a gap takes a little finesse. You back the torch off a little and butter it in. This means the metal is hot enough to liquify the filler material at the edges, but slightly more solid in the center, spreading like soft butter on a warm surface. It takes some practice.
A good torch man can cap the end of a large pipe without pinching it shut (not that this is recommended). Although a gap can be filled, it is better not to have a gap, as the joint is stronger with a snug fit. DaBits method is standard practice, and is recommended.
Last edited by Gary Lloyd; 02-13-2004 at 08:10 AM.
Would it not be possible to use a plumbers copper cap for the end, drill a 3/8" hole through it, then brase the 3/8" to the cap and in turn, the cap to the 1/2" pipe? Would look much neater if nothing else
A 3/8 X 1/2 coupling would look even neater, and would be much stronger.
Wasn't too easy to crimp the 1/2" pipe round the 3/8" but this is the result.
Looks better I think.
Need to work on my focus
I dont have any reducers at the moment. If I want them then its an online order with £5 delivery. So pinching the tube is preferable.
Here is a little update. I decided to make the subcooler for the R23. It will take the cold gas from the heat exchanger and evaporator and cool down the liquid R23, reducing the load on the heat exchanger. Its 1 meter in length:
I going to put it in a box and expanda foam it
Just finished bending the 6m heat exchanger, phew what a task. Its 1/4" inside 1/2", see below. I had an idea for the flow arrangement and cap tube subcooling. As the cap tube is going to be shorter than the length of the heat exchanger, I though about bending it in half (not equal lengths ofcourse) and running it inside the pipe like the diagram below:
Actual Coil:
Im thinking that the captube should spray into the top of the coil so any oil runs down the coil and out with the propane vapours.
Scrap the cap tube idea. I just tried it and cant bend the tube enough without squashing it. I will just wrap it around the outside. The whole thing will be encased in plastic foam so it will be insulated well.
The propane should be in the inner tube, feeding from bottom to top.
The R23 should be in the outer tube, feeding from top to bottom.
Im going to start building this thing today, hopefully have it constructed by this evening. Just going to chop up my single stage now and turn it into autocascade
Ok, got to the stage where I cant build anymore and need to pick a length for the R23 captube in the autocascade. Im aiming for 150watts max. The captube is 0.031", anyone got a ballpark length I should use?
I'm not good in captube sizing, but I would say: start with 4 meters (~12ft), then measure subcool and superheat.
About the captube: why don't you wind it around the 1/4" tube instead of bending it into a U-turn?
another great project
Quick update and then back to work. This is as far as I got last night:
Just had to join evap and hose and R23 cap tube. Did that this morning and foamed the heat exchanger. Now im vacuuming and drying the system. This is what it looks like now.
Going to static charge it with some R23 then start adding the propane and go from there. Should be an interesting afternoon.
Good luck!
First try I got it down to -60ºC.
HP: 19barg ( SCT -8ºC R23, 58ºC R290)
LP: 0.9barg ( SST -70ºC R23, -26ºC R290)
Suction line was 4ºC
I was having trouble getting the temps lower without letting the pressure go much higher. Tried juggling the gas composition, adding more R23 and R290. Had a real problem getting the suction line temp down, 4ºC was about as low as it would go.
Im off to try and get it back to -60ºC (I discharged and tried again by adding the propane first) and take the full range of measurements.
If there is anything you want a closer look at let me know and I wil take a picture. Anything else you want to know just ask. One more thing, its a 1/4HP R404a compressor so I dont expect great results.
Last edited by Russell_hq; 02-15-2004 at 12:22 PM.
what was your suction presure?
If i was an animal Id be a freezer.
0.9-1 Bar. Thats gauge pressure incase you are wondering.
I just took some Temps:
Air In:19ºC
Air Out:21ºC
Compressor Discharge:89ºC
Condensor In:39ºC
Condensor Out:21ºC
hows it lookin' captain? I could do with all the advice I can get. Any hints or tips to look out for?
Last edited by Russell_hq; 02-15-2004 at 12:57 PM.
bar........... do you know what that is in psig
dont forget we need temperatures and pressures
If i was an animal Id be a freezer.
bar times 14.5 = psi
Since there are two evaporators, we also need to know the suction line temp at the outlet of each evaporator.
Another set of temps and pressures. This time I added alot more propane, that really helps evap temps while keeping the High Side pressure down.
High Side Pressure: 16.2 barg (235psi)
Low Side Pressure: 0.6barg (9 psi)
Saturated Temps for R290: -31ºC (evap) and 50ºC (condense)
Saturated Temps for R23: -74ºC (evap) and -13ºC (condense)
Evap Temp:-71ºC
Suction Line 6" from Compressor:-3ºC
One more thing, a nice pic of some frost and digital thermometer. I know we all love seeing these
Here is a close up of the suction line setup, dont worry its covered in 25mm armaflex now.
In the picture, you have correctly identified the outlet of the R290 evaporator, and the temp at that point would give us an indication of the R290 charge.
But you have marked the junction of the suction lines as the R23 evap outlet. That doesn't do us any good. At the other end of that line, close to the evap, is the temp that would indicate the R23 charge.
The thermocouple location is telling us the resulting combination of both charges.
Last edited by Gary Lloyd; 02-15-2004 at 02:12 PM.
I've shut down the system and allowing the frost to go away then im going to rig it up to the cpu and get a heat load on this sucker. After that I will post some more temps and pressures.
In this picture, the tube along the top left is the R23 vapor in, and the disconnected tube at the bottom left is the R23 liquid out, right?
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