BillA: Pressure testing the Swiftech MCW6000?
 

I thought about making this an email, but other people might be interested so I'll do it in public.

I'm building a simple phase change system, and having aquired most of my parts, I need a direct die evaporator. I'm thinking about converting an MCW6000 for the following reasons:

Very interesting design.
Brazed copper connections
Should accomidate oil return nicely/won't clog easily

However I'm uncertain about pressure. I'm thinking about buying one, brazing fittings over the barbs, and then pressure testing it at a substantially higher pressure then i will use. I'm curious if you can offer any unoffcial ballpark estimates on how much pressure the block will hold before it leaks? Or if you have any comment at all before i try this?

I realize the block may break, but thats acceptable. They're cheap, and I could most likely repair it and use it as a waterblock, or build a heavier top and braze it on.

I believe it says on the site '100% quality control at the assembly line level: each block is factory tested to 25 psi (1.7 bars) to guarantee zero defect. '

So I guess 25 psi is fine ;) but probably a bit more than that. Typical engineering is to have a safety margin significantly larger than what its tested to, but considering this is a water block, and if you see 15 psi your rad will probably die, it might not be too far off.

You would not be able to braze fittings to it because the block is soldered together so the solder would melt. You could allways de solder the whole lot and braze it together. I would not trust solder to hold alot of pressure anyway.

^what he said.

the top will bow at ~40psi
do not exceed 25psi
.

Maybe make a new top then? Im not sure how high the pressures get in a phase change system.

Bear in mind that the block will be on the LOW pressure side of the loop.

It's the condenser that needs to be able to withstand high pressure.

The evaporator needs to be able to withstand very low pressures, but the pins should stop the top from collapsing.

8-ball

Gettin scary here...when the system is off the pressures will equalize. 134a will stand at about 74 PSI @ 72F. Running pressure would be about 26 PSI @ 30F. 404a is better for lower temps but pressures will be higher about 155 PSI @ 72F and 25 PSI @ -10F. Running pressures will vary with what sort of resriction is used but all in all a specially designed block would probably be needed. You could look into a low pressure refrigerant like 123 but that is usually used with a flooded evaporator and centrifugal compressors.

Thanks bill. So much for my experiment. Silly question though: is that 25 PSI above atmopshereic pressure or is that 25 PSI absolute pressure?

That might work, but i thought the bottom was already brazed. Site says "the base and housing are brazed together", which implies that the design simply isn't made for this kind of pressure regardless of modifications. I'll probably buy a 6000 regardless for watercooling. Then i could look at it and decide if i want to attempt that or not.

Correct, however once you turn the system off the pressure will equalize as the liquid refrigerant boils. Boiling point of R290/R22 at room temp: ~170 PSI. Not that the system will reach that, final pressure depends on charge and volume, but having to carefully monitor my charge to avoid blowing the top would be annoying and error prone.

Worse, I have no idea how far below the maximum possible the final pressure would be, so its possible i'd assemble the whole thing, begin charging and have to start from scratch because the pressure would be too high.

A quick look at the properties of R290 suggests that at 2 bar, liquid would be very, very roughly twice as dense as gas. So if the high and low side had equal volumes, we might expect the off system pressure to be somewhere around 3 bars, or at least not drastically higher. I'll look up exact values, and do some calculations. Perhaps with a large enough accumulator on the low side, compressor off pressure could be kept below 25 PSI.

Just try it anyway. But make sure to video it and post that where we can see it :D

My density for gasious R290 was incorrect. At room temperature the liquid is about 275 times denser then the gas is at room temperature and atmopshereic pressure. Thus unless i can get an accumulator with a volume about 150 times greater then the entire high side of my system, I cannot use a 6000 as an evaporator without exceeding safe pressure on the evaporator when the compressor is off.

Assuming my estimates and Bill's numbers are correct, I think i will let you try it first.

I really admire the idea, and would be most interested in seeing results.

Your option at this point would be to have a custom block (base and top) made. You might consider approaching a few members here, namely JayDee116, or even Jon Fettig (from wc101.com).

The last design I saw of interest was bowman1964's spiral block, in a multi-phase cooling system.

What kind of solder technique is used to make the 6000 series? Are they not solderd together with solder in the temperature range of > 400 C? Or is it just "low temperature solder" used in common electronics ( 220 C)?
I´m on the brink to do some modification on the block, but want to now is the whole thing will fell apart upon adding a little heat.

low temp solder - generally speaking
a no lead solder so it could be cleaned up and silver soldered anew
top will still pouch out though
better to machine a thicker brass cover

I ended up settleing on a Maze2. The sheer amount of material and the thickness of the solder points ensures that it should easily handle the pressure with the right high temp braze. I picked one up for a few bucks on ebay. I still haven't gotten around to modding it yet though. I've been too preoccupied with getting my accademics together for eventual gradschool aplications this past year.

I cut away the inlet on a 6000 block to repalce them with 1/2". So i had to expand the inlet with a mill to give room for the new diameter. So now i want to know the best method to solder/attach the new barbs to the top of the block.
Sorry, but i don´t follow the soldering part...
Is it first solderd with a non lead solder an then afterwards solderd with slilver (at high temperature)?
Yes, my native laguage is not english, so i can have a hard time understand somtimes. :)

make a new top
70psi is too much for the copper cover

re-read the above posts

well i´m just increasing the inlet and outlet diameter with soldering on new barbs. I´m NOT gona use more psi than the ones created from from an Ehim 1048. :)

ok, thought it was to be an evaporator in a refridgeration system
use a low temp solder and have the bp in water so as not to reflow its solder

Ok. Then i need to find a heat source with sufficent effect.
Thank you!