evaporator question

[JohnFish]

will start building my chiller later this week so I am planning to start with the evaporator.I am thinking for a simple tube in a res approach but i want it to be as small as possible. So i have a couple of questions.

1) thinking of using a large tube, something like 80-90mm diameter that will contain the refrigerant tubing inside (coiled). Will this work?
2) How long does the evaporator need to be approximately (was thinking of 10-12')?
3) should I go with 1/4 or 1/2 tubing for the evaporator?

Thanks in advance.

Edit: Another question, does the res need to be large enough to be able to hold some fair amount of water because I dont think that using the above evaporator it would be able to hold more than 0.5-1 gallon of water.

[JohnFish]

bump because i really need to know

[Unknown_road]

I would go for 3/8" tubing, 10-12' sounds oke. As long as the coolant flow's passed the coil and not trough the middle of the coil it will work. If the coolant isn't forced to flow passed the evap coil you'll get the same problem as overklokk (see his topic).

[afireinside]

I read use 20' of 1/4" OD copper for the evap at the guide at watercooling101. So I have 20' of 20" OD copper sitting in a 1 gallon plastic water jug insulated container thing perfectly. I'm thinking about cutting a hole and epoxying a barb on or something so I can hook the pump up easily. I'll have the return come in the top and spray right onto the evap. Should work pretty good

[chilly1]

Short of a tube in tube or brazed plate this will work fluid flow through the coling tubes must be maximized for any chiller to work well. And A .25 gal cooler would work the larger teh rez the longer to get it to cool. Although a larger chiller once cold will give you more stability under benching..

[JohnFish]

Unknown_road

If the coolant isn't forced to flow passed the evap coil you'll get the same problem as overklokk (see his topic).

Fill me in please

chilly
I am aiming for fast pulldown (if this is the word I am looking for) so i believe a small res would be more appropriate. I was thinking of something similar to this (hoping you can understand my paint skills)

[kayl]

i used 1/4 OD copper because its cheaper (20 foot), but 3/8 meant to be better, and requires shorter length

i made this evap, i have done it up side down though, gonna have to make a better one and have it evaporating from the bottom up, i am interested what the difference will be
is was very cheap and easy to make and is quiet small in size

[chilly1]

The differance of top to bottom or bottom to top one gravity works for you the other it works against you.
Like this?

[kayl]

this is insulated, pipe going to cpu will be at bottom of res, and return pipe to res will be near the top, im still testing so i dont know how it will cope under load, but it has a quick pull down of 15mins to -35deg,i need a new pump

[JohnFish]

wow. After 4-5 hours sleep I find all the answers I need. Thanks for all the input people. I think that I ll go with the simple vertical approach. thanks

[Unknown_road]

I'm working on an evap simmilar to chilly1, the big advantage of that is that the coolant flows entirely passed the evap. If you put a coil in a big shell it's much harder to accomplisch that.

[JohnFish]

chilly,
I was kinda looking at your evap design and i have some questions. I suppose this is a tube within a tube, where the inner tube carries the refrigerant and the outer tube the coolant. please correct me if i am wrong. I cant understand how you get such a performance (i have read that this design is better than a tube in a res) from a compact system (i mean the evap not the whole chiller...not that its not compact as a whole of course )?
What kind of tubing did you use for the evap and does the flow of cooland - refrigerant is in the same direction? Thanks

EDIT: Also, since you said that we have to find a way not to fight gravity, then in your case it would be that the refrigerant would get in the evap from the top and exit from the bottom. I noticed, again if i am correct, that you have it the other way around. Why?

[chilly1]

Actually the refrigerant is around the outside and the water is inside. This gives me better water flow. I will need to insulate it very good but this is easy, A tube in tube will give you lower temperatures provided you keep the fluid circulating. It works like this; the liquid in the rez is cooled to -40 degrees that liquid is pmped first through the HX where it is cooled to -45 and then goes to the cpu so the exiting temperature is colder than the liquid in the rez so if you are at or under load the temp in the rez won't rise. Also the liquid exit is at teh bottom where the refrigerant in is. Normally you would evaporate the refrigerant on the inside (the coldest layer is inside) but for the sake of flow I did this ond inside out. A larger HX would have been nessassary for flow rates that I wanted circuiting it normally. This does work well. I will have the methnol nessassary tomorrow and will post temperatures and pulldown times... BTY th egreen blue and white thing in the background is the rez/pump assy. Notice the pump motor is outside the Rez and aircooled.