fridge put into the loop

[viceless]

i just recently thought about this, then looked thru the forums and found someone had the exact same idea. now everyone says that the fridge will eventually warm up instead of keeping it cool, so i am asking what if you use two radiators? shudnt the water that ends up in the fridge be cooler than if it were to just come straight from the computer?

and to the people who have added AC units into their loops, how is that done?

 

[Erasmus354]

You could probably do something like that, make sure that the first radiator is good enough to dissipate a good portion of the heat. Then the fridge is basically acting like a chiller. The reason why people say dont use a mini fridge is that they are not designed to handle the constant heat output of a computer. They will break down fairly quickly under the pressure, and well wont really cool the water down all that much.

If you want to do it I say go for it, I still dont think it will provide very cold temperatures on the water simply because the fridge cant cool the water down quick enough to get really high performance.

 

[rodsfree]

Another thing you can do is to put a big reservior in the fridge.

Everybody that deals with water cooling PC's forgets that it takes time to transfer heat. Give the fluid a chance to rest in a tank inside the fridge and you'll let the fridge pull more of the heat out.

Rod

 

[zer0signal667]

Another thing you can do is to put a big reservior in the fridge.

Everybody that deals with water cooling PC's forgets that it takes time to transfer heat. Give the fluid a chance to rest in a tank inside the fridge and you'll let the fridge pull more of the heat out.

Rod

No, it takes fluid motion to transfer heat. Do you cool off faster when air is sitting still around you, or when it is blowing past you?

 

[rodsfree]

Cooling happens via thermal transfer. You can't create or destroy energy - you can only move it or change it's form.

If you are moving a transfer medium (air or water) over a warm surface then it will pickup some heat, move it to a cool surface and it will release some of the heat. Move it past either surface too quickly and you are just whacking off.
Google for entropy - you know the "heat death of the universe" or enthalopy.
Take a course in thermodynamics.
Termal transfer in a materal is rated in Btu per volume per second.
Heat doesn't move as fast as electricty. That's why if you move your hand quickly through a flame you don't get burned. Try that using an electrical arc furnace!!!

No, it takes fluid motion to transfer heat. Do you cool off faster when air is sitting still around you, or when it is blowing past you?

If this were completely true then your beer must stay warm.

Most fridges and ice chests and even ovens and furnaces rely on conduction without fluid motion to transfer heat, very few of these things have fans as strong as your PC's PSU. In fact conduction is the ONLY way to move heat through a solid or liquid (non-radiantly of course - get a material hot enough and it will radiate heat when it starts glowing, the heat you feel before the glow is from conduction into the air, oh yeah thats convection ) - convection is a form of conduction.

Here is the math related to Thermal conductivity. http://www.bae.uky.edu/~snokes/BAE549thermo/physicalproperties/thermalprops.htm

Thermal conductivity (k) is another important thermal property. Normally expressed in the units W/(m-K) or Btu/(h-ft-F), it is a property that tells how well a material conducts heat. Heat conduction is the transfer of energy between neighboring molecules within a material. The following equation relates the thermal conductivity to the amount of heat that flows through the material per unit of time (dQ/dt), the cross sectional area of the material through which the heat flows (A), and the temperature difference per unit of length of the conducting material (dT/dx).

So, why does every one want these high volume pumps?
I can see wanting enough velocity to get turbulent flow in your water blocks - kinda. But velocity increases as area decreases for the same unit volume. That means that a smaller diameter tube will flow faster that a large one. 1/4" tube flows faster than 1/2" for the same volume of fluid. Check out Bernolli's Law. So why does every one want 1/2" tube blocks?

What we need is radiators that have a very large cross-secional area of flow - to reduce the velocity of the water and let it hang around long enough to transfer some heat to the surrounding air. Then you'd get more heat transferred.

Just my $0.02.
Rod

 

[zer0signal667]

Cooling happens via thermal transfer. You can't create or destroy energy - you can only move it or change it's form.

If you are moving a transfer medium (air or water) over a warm surface then it will pickup some heat, move it to a cool surface and it will release some of the heat. Move it past either surface too quickly and you are just whacking off.
Google for entropy - you know the "heat death of the universe" or enthalopy.
Take a course in thermodynamics.
Termal transfer in a materal is rated in Btu per volume per second.
Heat doesn't move as fast as electricty. That's why if you move your hand quickly through a flame you don't get burned. Try that using an electrical arc furnace!!!



If this were completely true then your beer must stay warm.

Most fridges and ice chests and even ovens and furnaces rely on conduction without fluid motion to transfer heat, very few of these things have fans as strong as your PC's PSU. In fact conduction is the ONLY way to move heat through a solid or liquid (non-radiantly of course - get a material hot enough and it will radiate heat when it starts glowing, the heat you feel before the glow is from conduction into the air, oh yeah thats convection ) - convection is a form of conduction.

Here is the math related to Thermal conductivity. http://www.bae.uky.edu/~snokes/BAE549thermo/physicalproperties/thermalprops.htm

So, why does every one want these high volume pumps?
I can see wanting enough velocity to get turbulent flow in your water blocks - kinda. But velocity increases as area decreases for the same unit volume. That means that a smaller diameter tube will flow faster that a large one. 1/4" tube flows faster than 1/2" for the same volume of fluid. Check out Bernolli's Law. So why does every one want 1/2" tube blocks?

What we need is radiators that have a very large cross-secional area of flow - to reduce the velocity of the water and let it hang around long enough to transfer some heat to the surrounding air. Then you'd get more heat transferred.

Just my $0.02.
Rod

This argument has been beaten into the ground, and I'm not going to get too far into it here. I suggest you do some further reading on heat transfer in fluid systems if you care to understand. I am fairly well-learned in the area, as well as in thermodynamics (which is not related as much as you think).

As for your beer comment, of course thermal conductivity matters, I was merely simplifying as you had in your post. However, I can guarantee that even in your fridge and in your beer can, natural convection is still the main mode of heat transfer, not conduction. If you want to call out some more laws of science, how about Stokes' Law - denser bodies will sink in less dense fluids. That means that cold beer will sink, creating fluid flow (natural convection). If you had a pump in your beer can (forced convection) it would probably take a fraction of the time it normally does to cool the can.

And the 1/2" vs smaller argument - you're right, a smaller diameter passage should yield higher water velocity. That is, if volumetric flowrate was constant. Most pumps that people use for watercooling are not able to maintain constant flow over a range of restriction. Increase restriction, and you decrease flowrate.

 

[zer0signal667]

i just recently thought about this, then looked thru the forums and found someone had the exact same idea. now everyone says that the fridge will eventually warm up instead of keeping it cool, so i am asking what if you use two radiators? shudnt the water that ends up in the fridge be cooler than if it were to just come straight from the computer?

and to the people who have added AC units into their loops, how is that done?

This would probably end up being slightly better than having both radiators in air, slightly worse than having both in a fridge. The water in the fridge isn't going to be noticeably cooler, it will be almost constant throughout the loop give or take a degree or two. But the fridge would help lower that equilibrium temp. If I had a spare minifridge and radiator around, I might try it... Or else I'd gut the fridge and just build a waterchiller, doing away with radiators altogether.

 

[Erasmus354]

So, why does every one want these high volume pumps?
I can see wanting enough velocity to get turbulent flow in your water blocks - kinda. But velocity increases as area decreases for the same unit volume. That means that a smaller diameter tube will flow faster that a large one. 1/4" tube flows faster than 1/2" for the same volume of fluid. Check out Bernolli's Law. So why does every one want 1/2" tube blocks?

What we need is radiators that have a very large cross-secional area of flow - to reduce the velocity of the water and let it hang around long enough to transfer some heat to the surrounding air. Then you'd get more heat transferred.

Just my $0.02.
Rod

It doesn't matter how long the water sticks around in the radiator...really doesn't matter at all. If you slowed down the flow of the water so it spends more time in the radiator then you would slow down the flow of the water in the waterblock, meaning that it picks up more heat in the loop and therefore has more heat to transfer out when it gets to the radiator.

The reason for high flow pumps is because flow is actually one of the most important factors in transferring the heat from the waterblock to the water...flow and turbulence. It is hard to quantify turbulence, however if you look at a good waterblock review at a place like www.procooling.com you can clearly see for every single waterblock that as the flow increases the C/W decreases (meaning an increased cooling capacity). Smaller diameter tubing provides theoretically "faster" flow, but not more flow. It adds too much restriction, try taking a widemouth soda can and a normal one, turn them upside down and see which one drains faster...the one with the bigger, less restrictive opening.

 

[rodsfree]

The reason for high flow pumps is because flow is actually one of the most important factors in transferring the heat from the waterblock to the water...flow and turbulence. It is hard to quantify turbulence, however if you look at a good waterblock review at a place like www.procooling.com you can clearly see for every single waterblock that as the flow increases the C/W decreases (meaning an increased cooling capacity).

Turbulence isn't hard to quantify.... It's called a Reynolds number. Every fitting, pipe, pump, & valve has a Reynolds number. And it's based on the friction of a fluid flowing through the pipe or whatever. You can calculate it if you have a calibrated pump in an open system, or a measured water column. You measure the decrease in flow velocity of the system when your test artifact is installed. In Industrial Piping systems we try to get our numbers as low as possible. Reduce the friction and increase the flow to a point which results in laminar flow, but not high enough to get turbulent flow. Lamilar flow is best for low power - high flow systems. Problem with lamilar flow is that molecules of the fluid near the wall of the pipe move slowly, they pick up some heat and then prevent the rest of the fluid from picking up heat quickly. The heat has to move through them to get to the other molecules of the fluid, instead of directly from the heat source.Turbulent flow forces the molecules to bounce around alot and presents new molecules to the walls of the vessel and allows them to pick up heat more quickly.

So I can see wanting high velocity - high turbulance flow inside of a water block. Because the volume of the block is very small. But the velocity of the fluid is going to drop when it hits a heater core style radiator, because the effective area of the pipe has gotten larger, the quantity of fluid remains the same, the velocity has to decrease. If you don't believe the effective area has gotten larger then look inside the radiator and count the number of passages that the fluid can flow through.
If you use something like a transmission cooler then this isn't true - the pipe remains the same effective area all the way through. It isn't as effective at cooling but it can survive high pressures, which a radiator with the oval thin-walled passages can't handle.

What I'm getting at is that the velocity of the fluid changes all the way through any system. All you have to do to slow down the fluid is put a section of larger diameter pipe into the system. If you want to speed it up then put a smaller diameter section into the system. Assuming that you've got a pump that will pump a constant volume of fluid and overcome the restrictions in the system. And nobody is going to build a really good vane or gear pump for water cooling PCs - too expensive. Bummer.

 

[thewhiteguy]

Bad idea. There's are two cases:
A) If your fridge is strong enough to handle the heat produced by your computer, then the water will chill below ambient, and the extra radiator will actually warm it up.
B) If your fridge is not strong enough to handle the heat, then no matter what you do it will burn out eventually and this is also a bad idea.

Overall it's a lose-lose situation.

 

[DFI Daishi]

Bad idea. There's are two cases:
A) If your fridge is strong enough to handle the heat produced by your computer, then the water will chill below ambient, and the extra radiator will actually warm it up.
B) If your fridge is not strong enough to handle the heat, then no matter what you do it will burn out eventually and this is also a bad idea.

Overall it's a lose-lose situation.

you have your flow direction confused. the rad outside the fridge comes before the rad inside of the fridge.

 

[thewhiteguy]

you have your flow direction confused. the rad outside the fridge comes before the rad inside of the fridge.

I didn't. Now that I think about it again the system might work alright in case B, but only with a pretty good radiator before the fridge.

 

[(cf)Eclipse]

it's an interesting idea that i like at first, but what happens to the fridge? even though you're dissipating the 'heat' of the water to the ambient air, know that you're also just transferring heat from outside the fridge into it. i think the best solution would be to either have two fridges in your loop, or make sure you can vary the amount of air flowing through the outside radiator to tweak for heat load.

 

[DFI Daishi]

I didn't. Now that I think about it again the system might work alright in case B, but only with a pretty good radiator before the fridge.

i think that i see what you were initially saying now...........you were thinking that the fridge would chill the coolant down enough that the return line would also be below ambient, and moving ambient air through the first rad would warm it above ambient before the coolant returned to the fridge.

in case "b" the loop would get the CPU closer to ambient than normally possible, however the ruturn line would still be above ambient.

 

[thewhiteguy]

in case "b" the loop would get the CPU closer to ambient than normally possible, however the ruturn line would still be above ambient.

Yeah and I don't even know if a small fridge could handle ambient without a very small flowrate.

 

[Erasmus354]

Turbulence isn't hard to quantify.... It's called a Reynolds number. Every fitting, pipe, pump, & valve has a Reynolds number. And it's based on the friction of a fluid flowing through the pipe or whatever. You can calculate it if you have a calibrated pump in an open system, or a measured water column. You measure the decrease in flow velocity of the system when your test artifact is installed. In Industrial Piping systems we try to get our numbers as low as possible. Reduce the friction and increase the flow to a point which results in laminar flow, but not high enough to get turbulent flow. Lamilar flow is best for low power - high flow systems. Problem with lamilar flow is that molecules of the fluid near the wall of the pipe move slowly, they pick up some heat and then prevent the rest of the fluid from picking up heat quickly. The heat has to move through them to get to the other molecules of the fluid, instead of directly from the heat source.Turbulent flow forces the molecules to bounce around alot and presents new molecules to the walls of the vessel and allows them to pick up heat more quickly.

So I can see wanting high velocity - high turbulance flow inside of a water block. Because the volume of the block is very small. But the velocity of the fluid is going to drop when it hits a heater core style radiator, because the effective area of the pipe has gotten larger, the quantity of fluid remains the same, the velocity has to decrease. If you don't believe the effective area has gotten larger then look inside the radiator and count the number of passages that the fluid can flow through.
If you use something like a transmission cooler then this isn't true - the pipe remains the same effective area all the way through. It isn't as effective at cooling but it can survive high pressures, which a radiator with the oval thin-walled passages can't handle.

What I'm getting at is that the velocity of the fluid changes all the way through any system. All you have to do to slow down the fluid is put a section of larger diameter pipe into the system. If you want to speed it up then put a smaller diameter section into the system. Assuming that you've got a pump that will pump a constant volume of fluid and overcome the restrictions in the system. And nobody is going to build a really good vane or gear pump for water cooling PCs - too expensive. Bummer.

I am not talking about the VELOCITY of the water, I am talking about the FLOW, the FLOW remains constant at all points in a closed loop. And no, you cannot quantify the turbulence inside a waterblock at the point where most of the heat transfers from the waterblock to the water very easily at all...sure you can measure the pressure drop/resistance of the block, but you cant effectively measure the turbulence of the block.

 

[rodsfree]

Erasmus354

Go here: http://www.cd-adapco.com/products/CCMdemo.htm

Download the app and play with all the 3d models you want.

It is possible to calculate turbulent flow, and to estimate when it will happen based on derived Reynolds numbers and features inside of a block. i.e. sharp edges protruding into the stream will produce turbulance, rounded edges will reduce turbulance.

Or let the CFD (Computational Fluid Dynamics) app do it for you. It'll even map the entire flow pattern and show points of greatest drag/turbulance.

 

[zer0signal667]

If there's going to be any more debate on fluid flow and heat transfer, might I suggest it be taken to a new thread? I know I played my part in it too, but we're really straying/staying off-topic here.
Thanks...

 

[SledgeMakeGood]

Having the first radiator cool the return water from above-ambient to closer-to-ambient before it goes to any kind of chilling process that might not be powerful enough to otherwise pull all the heat away is a great idea. Using a mini-fridge to cool a computer at all is a bad idea.

I don't know if you planned on doing this anyway, but put a fan on the radiator in the fridge so both the fridge and the radiator work the way they're supposed to. A fridge cools down everything inside it, if you move the air through the rad, the heat will disperse and become (sort of) uniform within the fridge. The cooling element in the fridge will come in contact with more of the heat, faster.

A spectacularly better idea would be, if your mini-fridge is built like most, the entire cooling element is just the tray near the top that acts as the freezer, so just attach a waterblock or three to it, and the heat will conduct right from the block to the cooling element, without having to travel through air first. Lot's more efficient. Then you can fill the rest of the fridge with newspaper or a similar insulator so the cooling element doesn't have to keep cooling air that slowly absorbs heat that seeps in.

Really, the best idea is to just insulate the chips that are being cooled and the lines that go to them, and make a block with two channels, one for the compressed refrigerant, and one for the water. But that's kind of hardcore. It's the best way to do a combined water/phase-change setup, which is what you're proposing. Ideally, I'd stop at something that could get the water to room temperature, anything more and you need ugly insulation.