The phase-change help thread

[sandman001]

This is thread for all phase-change questions, such as how it works, theory, etc.

Just post a question and I (and I'm sure others), will try our best to answer it.

So, I'll start off explaining how it works.

There are Five main parts to a basic phase-change system. The Compressor, The condensor, a restriction (cap-tube, valve), the refridgerant and the evaporator.

As refridgerant expands, it take sin heat from it's envorment, and as it condenses it gives off heat. So, you want to cool it when it condenses, and put it on your processor when it is expanding (boiling).

COMPRESSOR

The compressor, this is basically a very high pressure pump. It takes in gas, and puts it under enough pressure for it to condense. This adds a lot of heat to the gas, and so it has to be cooled by the condensor to avoid burning up the system.

There are several different kinds of compressors, rotaries, hermetic, semi-hermetic, and then ones driven by a belt or external motor, such as one in your car. For a phase-change system such as a waterchiller or direct die system; you will want a 1/6 to 1/2 HP hermeticically sealed compressor , just for ease of use and efficiency. I wouldn't go any smaller than 1/6hp, because otherwise you won't be able to have the desired high to low side difference in pressure and the correct refridgerant flow. Anything bigger than 1/2HP, and it'll cost a ton to run, and you can get basically the same temps with a 1/4HP or 3/8HP compressor as anything larger given the heatloads we'll be working with.

This is a piston compressor:

This is a rotary compressor:

Both are hermetically sealed.

Condensor

The condensor's purpose is to cool the liquid refridgerant after it comes out of the compressor. This condensor will get refridgerant that can be up to 55-60C, and should have it down to nearly ambient temp by the time it comes out.

It is needed for a couple reasons, first, otherwise the system would burn up, as the compressor continually added heat, it would burn up. Also, because once the refridgerant expands in the evap, it will get cold from say 30C instead of 55C, so it's able to pull in more heat from it's environment (which is the evap). So, this helps get the evap colder, and so your computer stays cooler aswell.

This is a picture of a fairly large condensor:

Restriction

This is usually a capillary tube, which is just a very small tube that restricts the flow of refridgerant. This is so that you can pull a very low pressure on the opposite side with a small amount of refridgerant, and it'll expand. This is the Evaporator.

You can also use a small valve, but for computer application it's generally more complicated than it's worth, and a cap-tube system works basically just as well, while being easier to setup. For a beginner, I highly reccomend a standard capillary tube setup.

I don't have a picture of this, I cna get one if anyone needs one, but I think it should be fairly self explanatory, it's a very small copper tube.

Evaporator

The evaporator is where the refridgerant expands, or evaporates. This is when it pulls in heat energy from it's surroundings, and makes them cold. Thus, it's like putting a -40C block of copper on your CPU, it makes your cpu cold. Or, if you're doing a waterchiller, it makes the water cold, and then you pump it through a block, and your cpu gets cold.

An evaporator cna be lots of things, it cna be a coil of copper tubing, a finned evap like in an air conditioner, or it can be a block that goes on your cpu.

A finned one :

A block (or direct die), can have many designs, and features, so posting one wouldn't really make sense, but here's a gallery with a bunch of them:
http://www.teampuss.com/forums/viewforum.php?f=30

Refridgerant
Refridgerants are almost always a gas at room temp, this allows them to expands a ton more in the evaporator, and give you better temps. There's literally hundreds if not thousands of these, with boiling points ranging from 100C to -250C, I'm not sure what else to say about these, so ask questions.

Some common ones are R22, R134A, R290 (propane), R404A, R507, and a bunch more.

This about sums up the basic parts, I'll make a post about more specific parts, and thenone on setting up a phase-change system later today.

Sorry about typo's etc, I'll look over this post later.

 

[sandman001]

Filter/Drier
This is used to trap and hold any moisture in the system. Otherwise it cna reacts with the refridgerant and oil and produce acids that will eat away at the inside of the system. One of these is almost always necessary, and always reccomended for you to put in your system. They're cheap aswell, and can be had for under $10. There really is no reason to not have one. They can come in various forms and sizes, but they're usually fairly small and round.

Oil Seperator
These are mainly used in either very low temp single stage systems or in cascades. The oil will get too cold at the temps these system run (below say -60C), and will start to thicken up and not flow like you need it to.

They are put on the high side of the compressor, collect oil as it comes by, after a certain amount of time (varies by design/system), you turn a small valve that leads to the suction side of the compressor, and the compressor sucks the oil back in.

If you don't use one of these in a low temp unit, a few problems can occur. the oil will start slogging, and your temps will bounces all over as it slowly passes through the captube, and restrict flow.

These can be handmade failry easily and cheaply. Get a section of like 2" diameter copper tubing, and put some copper wool in there (looks like steel wool, but it's copper), make 3 holes in it, and braze some ends/pipes on it. It should end up looking like this::

Heat Exchanger
NOT FINISHED YET
Insulation
NOT FINISHED YET

 

[sandman001]

And this one is reserved for a small guide on setting up a system

order
Orientation
brazing
filling
tweaking

 

[JoT]

Great job, I look forward to the rest of your guide. *Smears glue on the thread*

 

[L337 M33P]

Clarification on the types of compressor:

Both those compressors in the pics are in fact hermetic compressors. Hermetic/semi-hermetic/open refers to the encapsulation of the motor and the compressor housing. Hermetic (which is found in the vast majority of systems <1kW heatload) means that the compressor and motor are sealed together in the same housing.

The sort you find in a fridge is a reciprocal or piston compressor, and rotary compressors can be centrifugal or helical

 

[sandman001]

Clarification on the types of compressor:

Both those compressors in the pics are in fact hermetic compressors. Hermetic/semi-hermetic/open refers to the encapsulation of the motor and the compressor housing. Hermetic (which is found in the vast majority of systems <1kW heatload) means that the compressor and motor are sealed together in the same housing.

The sort you find in a fridge is a reciprocal or piston compressor, and rotary compressors can be centrifugal or helical

Ahh, my mistake then. I was going by what I had always heard them referred to as. I stand corrected.

 

[felinusz]

Great thread, thanks for making it!

I have a few questions for you.


Does the evap that you use have a large impact on the temperatures that you will see? Specifically, I have a stock Mach II, that will eventually be regassed with R402, increasing its capacity signifigantly - the unit has a stock Mach II evap on it.

I am wondering whether it is worth my time to replace the stock evap, given that I will be dealing with a heatload much higher then the stock (very thinly based) Mach II evap is optimized for.

Is an aftermarket or custom evap a good idea, for "pre-made" (Vapochill LS, Mach II, etc.) system owners? Does it become more benefial after regassing, increasing the unit's capacity?


Secondly, I am wondering what is involved in tuning a unit's charge so that things are optimal for our processor cooling purposes?

 

[sandman001]

Great thread, thanks for making it!

I have a few questions for you.


Does the evap that you use have a large impact on the temperatures that you will see? Specifically, I have a stock Mach II, that will eventually be regassed with R402, increasing its capacity signifigantly - the unit has a stock Mach II evap on it.

I am wondering whether it is worth my time to replace the stock evap, given that I will be dealing with a heatload much higher then the stock (very thinly based) Mach II evap is optimized for.

Is an aftermarket or custom evap a good idea, for "pre-made" (Vapochill LS, Mach II, etc.) system owners? Does it become more benefial after regassing, increasing the unit's capacity?


Secondly, I am wondering what is involved in tuning a unit's charge so that things are optimal for our processor cooling purposes?

The evap has an impact, I know that you know watercooling, so look at it as going from say a maze4 to a Cascade. You might gain a couple degrees at idle, a coup0le at load. Not a big deal, the machII's evap is actually a pretty good design, now the old vapochill evaps were bad. the new vapochill ones are nice though.

Generally for tweaking the system, I'd prefer to have it hooked up to a similar heatload (peltier, processor, something), and then just tweak it from there till the lowest temp is acheived, and then keep charging it till that goes up a degree or two to allow for extra capacity.

 

[matttheniceguy]

As far as I know the evap design is largely related to the heat load and the temperature of the refrigerent. Evaps made for lower heat loads will have thinner bases with only a few fins above the core. This is enough surface area that all the heat from the processor is removed and there is little point in much surface area beyond that. On systems with much higher heat loads, a thicker base will transmit the heat out to a larger surface area allowing more effective cooling.

I always thought the Dryer had a different purpose (I might be wrong though, don't really know). I thought the purpose of it was to make sure that only liquid refrigerent went into the cap tube. I thought that the inside of the dryer was full of copper wool, like an oil seperator, and this acted to break up any bubbles and provide a surface for any gas to condense against. It is also always mounted so it is tilted such that the flow goes down in it, creating a bit of a resevoir in it.

Looks like a good guide you have comming, I have always thought this forum really needed some permenent info on phase change.

 

[felinusz]

sandman001

Generally for tweaking the system, I'd prefer to have it hooked up to a similar heatload (peltier, processor, something), and then just tweak it from there till the lowest temp is acheived, and then keep charging it till that goes up a degree or two to allow for extra capacity.

Specifically, how large a heatload would one need to use, to properly charge a unit roughly similar to a stock Mach II? I have a 172W peltier that I can use, but I am worried that an inadequate heatload will fubar my tuning.

I'm getting my Mach II regassed this week, and I am still a little bit sketchy about actually tuning it. If I mess up the tuning, the ~$200 regass job is pretty much wasted .

What is the best thing to use, for the most stable heatload? What are some inexpensive AC alternatives to using peltiers for your tuning heatload? I have read about 'load resistors', but am unsure what exactly these are, and cannot find any information .

 

[sandman001]

As far as I know the evap design is largely related to the heat load and the temperature of the refrigerent. Evaps made for lower heat loads will have thinner bases with only a few fins above the core. This is enough surface area that all the heat from the processor is removed and there is little point in much surface area beyond that. On systems with much higher heat loads, a thicker base will transmit the heat out to a larger surface area allowing more effective cooling.

I always thought the Dryer had a different purpose (I might be wrong though, don't really know). I thought the purpose of it was to make sure that only liquid refrigerent went into the cap tube. I thought that the inside of the dryer was full of copper wool, like an oil seperator, and this acted to break up any bubbles and provide a surface for any gas to condense against. It is also always mounted so it is tilted such that the flow goes down in it, creating a bit of a resevoir in it.

Looks like a good guide you have comming, I have always thought this forum really needed some permenent info on phase change.

You're more or less correct on the evaps, but there's just so many different variations that all work well. It'd be pointless to try to cover all of them.

I think what you're talking about is an accumulator, but I'm not sure.

 

[sandman001]

Specifically, how large a heatload would one need to use, to properly charge a unit roughly similar to a stock Mach II? I have a 172W peltier that I can use, but I am worried that an inadequate heatload will fubar my tuning.

I'm getting my Mach II regassed this week, and I am still a little bit sketchy about actually tuning it. If I mess up the tuning, the ~$200 regass job is pretty much wasted .

What is the best thing to use, for the most stable heatload? What are some inexpensive AC alternatives to using peltiers for your tuning heatload? I have read about 'load resistors', but am unsure what exactly these are, and cannot find any information .

Can you give that 172watt pelt 24V? If so, that'd be an awesome heatload. It'd give you some overhead, while keeping it right in the range you want for the max performance.

Load resistors are just bigass resistors that use a certain amount of power. I've seen some 50watters on E-bay, but they were always some crazy voltage (96V DC).

I'm not sure of any AC alternatives, if you fgind one, please tell me.

 

[felinusz]

Can you give that 172watt pelt 24V? If so, that'd be an awesome heatload. It'd give you some overhead, while keeping it right in the range you want for the max performance.

Yes, I can power it off of a full 24V .

So it would actually be perfect for my application? That is great news, makes things a whole lot easier for me anyhow, since I don't have to find an appropriate heatload anymore!

I'll keep my eyes open for an AC solution - I'll ask my HVAC guys as well.

 

[sandman001]

Sounds good, yea it'll work fine, just make sure to get some decent mounting pressure.

I didn't do that with my 80watter when I was just messing around and almost burnt up the pelt.

 

[redken]

Great this thread was just what I was looking for!

I've been watercooling for a while but will be changing to Phase as soon as I can understand it better. I just started to really read up on it a few days ago and it still feels like I have many more weeks of reading

I have a few questions; I hope you guys can help me out with.

1- Why do you "tune" the system? I thought that you just had to get it as cold as possible, slap it on top of the CPU and that was it.

2- Can I use my Radiator as a Condensor? I think the answer will be NO, but I just wanted to know, why?

3- Does a phase system benefit form having a larger condensor with fans on a push/pull config. like watercooling does? Will it cool more with it or will it be the same? Most systems I have seen have a small condensor like the Vapochill and MachI/II.

4- Can 1 phase system be used to cool CPU and GPU? Does it affect the performance much?

 

[@md0Cer]

Great this thread was just what I was looking for!

I've been watercooling for a while but will be changing to Phase as soon as I can understand it better. I just started to really read up on it a few days ago and it still feels like I have many more weeks of reading

I have a few questions; I hope you guys can help me out with.

1- Why do you "tune" the system? I thought that you just had to get it as cold as possible, slap it on top of the CPU and that was it.

2- Can I use my Radiator as a Condensor? I think the answer will be NO, but I just wanted to know, why?

3- Does a phase system benefit form having a larger condensor with fans on a push/pull config. like watercooling does? Will it cool more with it or will it be the same? Most systems I have seen have a small condensor like the Vapochill and MachI/II.

4- Can 1 phase system be used to cool CPU and GPU? Does it affect the performance much?

I am a phase change newbie, so I will try to answer with what I know, but I am not 100% on this.

2.) I would beleive that is not so. For one, a radiator isn't designed to carry a gas under such a high pressure. It may also not be densely coiled enough to cool the refridgerant enough to give you better temps at the evap.

3.) Yes. The more you cool down the condenser, the more cool the evaporator will be. Think about it as strecting a rubber band or balloon. You stretch it, it gets hot, you let it go, it goes back to room temp. Now if you stretch it, it gets hot, but then you wait until it cools down to room temp before returning it to its normal position, it gets cold. Same thing with the refridgerant.

4.) I beleive I have seen someone mod a vapo or mach II before to do this. I am not sure exactly how it would work or how it would have an effect on the cooling.

 

[L337 M33P]

I'll put 2 of my minor currency denomination units in

Great this thread was just what I was looking for!

I've been watercooling for a while but will be changing to Phase as soon as I can understand it better. I just started to really read up on it a few days ago and it still feels like I have many more weeks of reading

I have a few questions; I hope you guys can help me out with.

1- Why do you "tune" the system? I thought that you just had to get it as cold as possible, slap it on top of the CPU and that was it.

2- Can I use my Radiator as a Condensor? I think the answer will be NO, but I just wanted to know, why?

3- Does a phase system benefit form having a larger condensor with fans on a push/pull config. like watercooling does? Will it cool more with it or will it be the same? Most systems I have seen have a small condensor like the Vapochill and MachI/II.

4- Can 1 phase system be used to cool CPU and GPU? Does it affect the performance much?

1) Tuning refers to precisely adjusting the amount of refrigerant - what you want is under a certain heatload range - the equivalent heatload to your CPU at full OC - the temperature to be minimal. Typically this means the evaporator saturated with liquid refrigerant but no liquid left in the suction return line. With such small systems even a few 1/10ths of a gram of gas can drastically change temperatures.

2) NO! Watercooling/car radiators only withstand low-pressure (typically +0.5bar) gases and liquids, so sticking it in a refrigeration system with typical operating pressures of 15bar and above will leave bits of radiator embedded in the walls.

3) Bigger condensors are better, up to a point. As we are dealing with phase change, most of the heat energy is lost through the state change from gas to liquid, but subcooling the liquid below the condensing point improves efficiency a few %. Beyond getting constant liquid refrigerant out the normal size/performance increase curve applies.

4) 1-phase? be careful, you're talking to an EE - 1ph could mean single stage where only 1 refrigerant loop is used, or single phase mains supply

I assume you mean one normal compressor loop for 2 loads - this necessitates having evaporators in parallel with capillary tubes sized to each one. You need a meaty compressor typically found in full-height fridges and up to cope with both GPU and CPU loads. Tuning the system is also harder because you now have 2 independent variables and 2 methods by which both are controlled - the heat loads and capillary tube sized respectively. It can be done, but adjustment is harder

 

[redken]

Thanks for the replies,

Ok, for the original questions:

1- So, how are the pre-build systems "tuned" for different loads? For example, If I buy an XXX brand Phase change sys and put a Prescott on it. Can I then take the same system and hook it up to an A64 CPU? Since their heat load ranges are not the same.

2- Ok, I understand now.

3- So, by better cooling a bit larger (not huge) condensor I wouldn't see better performance.
Remember I'm coming for watercooling, were using the bigger single pass rad is better than a smaller rad (120mm size). And a push/pull shrouded setup for the rad is better than just hooking up a fan to the rad.
Maybe a better question would be, Will I benefit if I use a bit larger condensor, make a shroud for it and put 2 fans (or 4 if they fit) in a push/pull configuration?

4- Somehow I thought it would be "easier" . How large would the compressor have to be?

 

[sandman001]

Thanks for the replies,

Ok, for the original questions:

1- So, how are the pre-build systems "tuned" for different loads? For example, If I buy an XXX brand Phase change sys and put a Prescott on it. Can I then take the same system and hook it up to an A64 CPU? Since their heat load ranges are not the same.

2- Ok, I understand now.

3- So, by better cooling a bit larger (not huge) condensor I wouldn't see better performance.
Remember I'm coming for watercooling, were using the bigger single pass rad is better than a smaller rad (120mm size). And a push/pull shrouded setup for the rad is better than just hooking up a fan to the rad.
Maybe a better question would be, Will I benefit if I use a bit larger condensor, make a shroud for it and put 2 fans (or 4 if they fit) in a push/pull configuration?

4- Somehow I thought it would be "easier" . How large would the compressor have to be?

1)Well, the MachII is tunbed for something like 200-220watts, so you cna use it on both systems. Most other prebuilts that are fairly modern (mach II, vapo XE, vapo LS) are tuned for around 200watts.

3)It won't really hurt performance, it'll help a little bit, but the majority of the heat is transferred through evaporinting and condensing.

4)It's harder to get right, but I've seen it done with 1/3hp compressors, and they were pulling -50C on the cpu and gpu. If you already have a watercooling system, you might look into a waterchiller if you want to cool more than one part.

 

[redken]

If you already have a watercooling system, you might look into a waterchiller if you want to cool more than one part.

How effective is this? What kind of temps can be seen with a "compact" system? -50c?
I have seen waterchillers before but have not really looked into them because all the setups I have seen are HUGE and I have read that they take a long time to cool the water. I guess it’s because all the water they have to cool down, but I don't know why the setups I have seen use so much water instead of just cooling a normal reservoir size enclosure.