• Welcome to Overclockers Forums! Join us to reply in threads, receive reduced ads, and to customize your site experience!

Could someone measure the temps of their computer exhaust air during a game?

Overclockers is supported by our readers. When you click a link to make a purchase, we may earn a commission. Learn More.

DumpALump

Member
Joined
Jun 24, 2002
Location
California, US
I was wondering if anyone has measured the temps that exhaust out the back of their case while running a game or benchtests (furmark/prime)? Shouldn't take long to get the heat up in the case.

I am debating whether I should put my extra rs120 radiator on the back of my case. I'm thinking that if water temps are say 35C and exhaust is 35C then there really isn't a point and all it'd be doing is increasing noise.
 
Having other people's data sets is not going to be relevant to your system. Cases are different, airflow in the case is different. Some have GPU's that exhaust out the back and would be cooler than say a card that doesnt......etc.

This is overclockers.com. Put it on there. :)
 
I was wondering if anyone has measured the temps that exhaust out the back of their case while running a game or benchtests (furmark/prime)? Shouldn't take long to get the heat up in the case.

I am debating whether I should put my extra rs120 radiator on the back of my case. I'm thinking that if water temps are say 35C and exhaust is 35C then there really isn't a point and all it'd be doing is increasing noise.

If you don't already have one, and this is interesting to you, I'd suggest you go to a local hardware store (if they have none a petshop will but you will overpay) and get a small digital probe thermometer. You can place the face, which is a 1" display in the front of your case behind a little cutout. Easy mod to do. The cable can be run behind the mobo plate very easily and the temp sensor probe secured to your exhaust via zip tie. Then you always have a readout of exhaust temp. The batteries last a good while and they remain accurate for several years. I've used them for aquariums for a very long time. Great in and out of water.
 
lol I know, but if I do stick it on there and it doesn't reduce temps, then it would be worse off. Since an extra rad increases resistance, noise, reduces exhaust cfm, and extra tubing takes up space.

If I can get a general idea of ambient to exhaust I can see how much the single rs120 would help.
 
Its going to help regardless. Its going to be cooler than what you are cooling with it so it has to help. Just b/c its getting 30C air while your intake is getting 25C air doesnt mean it will make it worse.

As far as the difference from intake to exhaust with a water cooled system, the difference in my case (800D) was only 2-4C really.

Water guru's please correct that if I am wrong...
 
If you don't already have one, and this is interesting to you, I'd suggest you go to a local hardware store (if they have none a petshop will but you will overpay) and get a small digital probe thermometer. You can place the face, which is a 1" display in the front of your case behind a little cutout. Easy mod to do. The cable can be run behind the mobo plate very easily and the temp sensor probe secured to your exhaust via zip tie. Then you always have a readout of exhaust temp. The batteries last a good while and they remain accurate for several years. I've used them for aquariums for a very long time. Great in and out of water.

Oh I have a infrared, digital, and a thermistor thermometers. Just don't have an up and running system atm since I'm putting sound deadening in my case. I'll go play some l4d2 on my gf's comp and test her's. Haven't got around to installing the I5 2400 + GTX460 in hers yet. So it's still just a C2D + 8800GT.
 
Its going to help regardless. Its going to be cooler than what you are cooling with it so it has to help. Just b/c its getting 30C air while your intake is getting 25C air doesnt mean it will make it worse.

As far as the difference from intake to exhaust with a water cooled system, the difference in my case (800D) was only 2-4C really.

Water guru's please correct that if I am wrong...

The water temps only end up being 30-35C typically and I believe Martin or Skinnee found that temps throughout the loop only vary by 2C or so because of the amount of water being moved. So even if the CPU is 60C, water temps will still be around 30-35C. If I'm trying to cool a 30C water temp with 30C air, then it wouldn't do anything.
 
Its going to help regardless. Its going to be cooler than what you are cooling with it so it has to help. Just b/c its getting 30C air while your intake is getting 25C air doesnt mean it will make it worse.

As far as the difference from intake to exhaust with a water cooled system, the difference in my case (800D) was only 2-4C really.

Water guru's please correct that if I am wrong...

nope, you're right.

The water temps only end up being 30-35C typically and I believe Martin or Skinnee found that temps throughout the loop only vary by 2C or so because of the amount of water being moved. So even if the CPU is 60C, water temps will still be around 30-35C. If I'm trying to cool a 30C water temp with 30C air, then it wouldn't do anything.

that would have been vapor, he works with skinnee, but I think this was back before then. It's in the XS sticky.
 
Bah I'll just install it lol.

Thanks for the help guys. It won't be a huge increase, but maybe a 1C drop in water temps.
 
I think I understand what you are getting at. There is no way that the laws of thermodynamics will allow the water in your loop to cool below the air temp flowing over the radiator. The exchange of heat energy is based on the amount of air flowing over the radiator, the amount of water through the loop, the surface area on the radiator, and the difference in temperatures between all of those components (quick and dirty version here, but im sitting in the coffee shop and dont have access to my thermo reference materials.) Since the temperatures of the water and the temperatures of the air are very close already, your setup is more than capable of dispersing the heat load from your gear.

the rough equation that is limiting your water cooled rig is this:

q = H*A (delta T)

where:
q is the amount of energy you are transferring per unit time, measured in Watts;
H is the thermal coefficient, or the amount of energy per unit area that the radiator and water can transfer;
A is the surface area that the radiator and water share;
delta T is the difference in temperature between the two;

The equation is repeated between the radiator and air as well, and there is another equation to compute the transfer of heat from one side of the radiator to the other. All of these are resticted by the difference in temperatures. If the difference in temperatures between the water and air is small, the amount of energy that can be transferred is small as well. Since the water temp never gets very high, I would say that your system is already more than adequate and that you would see a negligable difference in temperatures with an additional radiator. Should you decide to increase the wattage of your system (higher CPU wattage, additional graphics card, anything that dumps more heat energy into your water loop), then the radiator might come in handy, until then, yes it will just be more noise.

I think I got everything right, but i may have missed something. This was only a half-assed attempt made while on my lunch break. I hope it helps nonetheless.

Ethan
 
Have you considered the flow of air? You need fluid dynamics for that on top of the thermo
 
I'm assuming that he has a fan mounted to the radiator, and that it is running at a constant speed. Not perfect, I know. If this is the case, the airflow should be a relatively consistent turbulent flow, which is what you want. Besides, the point was that the whole equation is restricted by the temperature difference, and that doesn't change no matter the type of air flow over the radiator.

Energy transfer is more efficient with a turbulent airflow, as it exposes more air molecules to the radiator surface. Same goes for the fluid. If the flow is laminar (lacking turbulence) the same air molecules, or water molecules, flow over the radiator surface the entire time, and thus the heat must be transferred through them into the neighboring molecules. The nature of the flow is dependent on the geometry of the object it is flowing through or around, and the velocity of the flow.

The equations that govern the nature of the airflow are very tricky, but one can determine whether the flow is laminar or turbulent using the Reynolds Number. Here is the equation for the Reynolds # in a pipe:

R=pVL/u

p = density
V = fluid velocity
L = length of pipe
u = dynamic viscosity

This gives you the Reynolds Number for the flow through the pipe, which you then compare to a chart to determine whether the flow is laminar or turbulent. I would be willing to bet that the flow over the radiator fins is turbulent just based on the geometry of the device and the velocity of the air moving over it. Unfortunately, there is no easy equation to determine that.

I have cut this thermo- and fluid-dynamics lesson short but please keep the discussion going.

Ethan
 
Ahh yeah, it was Vapor who found the loops to be pretty much the same throughout. Read so much information and you forget where you get it from.

I only went so far in physics then majored in econ. So I really only know the basics, but I'm loving these sweet formulas you're posting :D I'm pretty much going off the idea that a fan doesn't cool and applying basic ideas to figure things out. What you had posted Ethan E is exactly what I was thinking of (though haven't studied the actual physics of it).

I have an air in-water out delta of ~5C. Then assuming a 2C difference throughout the loop and the max delta would be ~7C. If it was 21C ambient then the water would be only 28C and I know the temperatures inside a case can get pretty warm. My video card dumps all it's heat into the case and the majority of the cpu heat is dumped back into the case.

I just checked XS stickies and had forgot about the data that HESmelaugh had found. I don't know rules on linking to other forums so I'm going to post his chart here. I don't know rules on posting his chart either. Hopefully it's ok :eh?:

hesmelaughchart.jpg


Here the temps between a stacked rad and single rad are pretty much the same. He did find that there was a pressure drop for the fan(s), which ultimately affected temps. The difference in my case is a 2xradiator on the intake and a radiator on the exhaust, which should not have that pressure drop from the increased resistance. So there will be an improvement from that, but all the computer components (especially video card) will be making heat that will then be going through the exhaust. So now I'm not so sure if I should attach the extra rad to the back.
 
Dont hotlink it, but host it here/imageshack and give credit and all is well (which you did). Thanks for that pic I have never seen that before!
 
If I were in your situation, and my case could do it, I would have all radiators on intake, and a good high CFM exhaust fan with no radiator to block its flow. This would allow the highest delta T possible, as well as good exhaust flow. But at this point its all speculation as I don't know your exact setup.

Good to hear there is another economist out there. I am a double major in Mechanical Engineering and Economics myself. I assume you realize that there will be diminishing marginal returns on your water cooling.;)

Ethan
 
If I were in your situation, and my case could do it, I would have all radiators on intake, and a good high CFM exhaust fan with no radiator to block its flow. This would allow the highest delta T possible, as well as good exhaust flow. But at this point its all speculation as I don't know your exact setup.

Good to hear there is another economist out there. I am a double major in Mechanical Engineering and Economics myself. I assume you realize that there will be diminishing marginal returns on your water cooling.;)

Ethan

Well I am trying to optimize my behavior by figuring out the marginal utility of the radiator :D

I have a MCR320 6xGT1850 + RX120 GT1450 on the intakes.
 
This is just too much (very interessting) math to make a decision. Without it you had your answer (but I like to see this kind of stuff!).
 
Back