Looking for opinions. Better to suck hot air or push cool air?

not to totally beat this subject down but after some reading i found this article stating it nice and simple "From a purely technical standpoint using a liquid cooling system is much akin to using a heat pipe. It’s a very efficient means of moving heat from where it’s generated to somewhere it can be more conveniently removed - but the heat still needs to be removed. That means dumping it to the ambient air, which requires a radiator and a fan. This is much like a conventional car, where the engine is liquid cooled, but the car is air cooled." the heatsink still needs to be up to par whether its on the component or away from it. inside a car, unless your crammed for space, you wont gain by using water cooling.

Agreed. Water cooling will move the heat from the DIN enclosure where space is tight, out to a space that is very likely to have cooler air. You still have to radiate the heat but the likelihood that the ambient air in the car is above 110 for extended periods while the PC is on is pretty low.

And yes, I'm aware that the temps in the car can reach 150 or more when closed up but those temps will fall very quickly with the windows open or air conditioner on.

In any case, I don't think Sonic is considering water cooling right now. It's about whether his system sucks or blows.:becky:

Back on topic!

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Originally Posted by surfntomm

not to totally beat this subject down but after some reading i found this article stating it nice and simple "From a purely technical standpoint using a liquid cooling system is much akin to using a heat pipe. It’s a very efficient means of moving heat from where it’s generated to somewhere it can be more conveniently removed - but the heat still needs to be removed. That means dumping it to the ambient air, which requires a radiator and a fan. This is much like a conventional car, where the engine is liquid cooled, but the car is air cooled." the heatsink still needs to be up to par whether its on the component or away from it. inside a car, unless your crammed for space, you wont gain by using water cooling.

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which is exactly what i said in the beginning :rolleyes:

As far as your other stuff....please fully read an article before posting it here-you seem to have missed what it was saying......

A fans power consumption is meaningless.....the values you need to look at are decimals produced at full speed and cubic feet/minute of air moved. This gives you some idea of the amount of cooling provided. You will likely find that larger fans are quieter when moving the same volume of air as smaller ones and in many cases do better on both measurements. Even when using smaller fans, like bugbyte said, the most important thing is where the air is moved. You may need to use internal ducting or baffling to achieve the best results but obviously it will vary based on your setup.

edit:
one other point.....take a look at what other manufacturers do for cooling in limited-space setups. Laptops do both with a single fan, most embedded hardware either uses a single exhaust fan or a dual intake/exhaust setup. In a car, equipment like amplifiers typically do the same thing either forced exhaust or a dual intake/exhaust setup (usually with internal baffling). Thats all based on a lot of money in R&D to ensure their setup performs in the harshest of environments.

hey if someone wants to come over, install a water cooling setup, and debate the pros and cons you're more than welcome to lol

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Originally Posted by Sonicxtacy02

hey if someone wants to come over, install a water cooling setup, and debate the pros and cons you're more than welcome to lol

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pay me by the hour and i'll have it water cool your seat too :p

justchat, just to clarify so that other readers are not confused....it seems there was some confusion regarding my statement about fans.

What you said is completely correct but what I was alluding to and which is a downside of pushing air into an enclosure is that the power consumption of the fan is transmitted to the air as heat. This heat can be quite large when considering high power industrial fans. I have worked with fans that each consume about 50 Watts that are used in Cisco routers. In the car pc world, our fans are tiny and should not really be a concern when considering the added heating of the inlet air.

hopefully that cleared it up, just trying to throw in my 2 cents since I'm a mechanical engineer. I think we are are on the same page

While I think that most concepts here are intuitive and have already been covered, I will chime in as well... The best airflow configuration will certainly depend on the particular geometry of the heat producing elements and the temperatures of inlet and exit air, but it will certainly be the configuration that gets the highest velocity of the coolest air over the hottest components.

In more precise terms, the heat dissipation rate is q=hA(Ts - Tamb) where
h is the average convection coefficient
A is the surface area
Ts is the surface temperature
Tamb is the ambient temperature

The convection coefficient will depend on a lot of things related to the flow, not the least of which is velocity. I would be willing to bet that you will get better velocity by pushing air rather than pulling it (which is why most heatsinks have dedicated fans to control the velocity with localized airflow).

If you want to prove it to yourself, wet your palm a little bit and stick it 3 inches in front of your mouth. First, blow air lightly and see how much heat is transferred from your hand. Now suck air into your mouth as hard as you can. Your palm is the equivalent of your CPU/heatsink or any other localized heat producing element.

My .02 (also a mechanical engineer by profession)

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Originally Posted by bluTDI09

My .02 (also a mechanical engineer by profession)

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agreed although the palm test might be a little primitive ;)

i see you drive a TDI. Audi or VW or something else?

Excellent Blu!
But you didn't say that if the air goes too fast, the heatsink does not have time to cool down.... LOL!

:sorry: I couldn't resist.... Many car buffs claim that is the reason cars overheat when high-revving or after removing the thermostat (removing thermostats on some engines makes them run cooler; others hotter).
IE - the water/coolant isn't in the radiator long enough to cool down, or it travels too fast to get rid of its heat! (Yet surprisingly it's in the engine long or slow enough to pick it up!)

I'd try to explain the non-time dependent relationship and the difference between heat transfer and temperature - eg, if travelling three times as fast it may only fall by half the normal temp drop, but it does that 3x faster - ie, more heat transferred per unit time.
And lots of other analogies....

For those that don't know why....
If fluid moves very fast, it can jetstream or streamline (pick a narrower path through the radiator etc).
Also if too fast, the driving blade (waterpump) can cavitate and hence reduce flow.
Removing the thermostat reduces restriction (back-pressure) and causes increased flow rate - unless cavitation occurs. (And increase flow may jetstream.)

Hence hi-revving engines may need to reduce waterpump speeds.
Removing thermostats depends on normal versus cavitation speeds etc.
Jetstreaming depends on the layout (water paths).


And on a related note - cavitation reduces input power. EG - a fan blockage causes the fan to speed up and its current drop.
That's the opposite to what many failed alarm systems seem to think!


Blu - is my novice explanation(s) ok?
And I assume this is valid for low speeds - too high and friction causes heating, but we are talking speeds way below that (ie, subsonic?)?

I thank you for your q formula which is devoid of time & speed (other than q being a "rate", but that's not "speed").
I must use it next time....

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Originally Posted by surfntomm

agreed although the palm test might be a little primitive ;)

i see you drive a TDI. Audi or VW or something else?

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Yep, it is a Jetta. You are right... the palm test is primitive, but effective at showing that it is extremely difficult to route air with a fan that sucks.... pun intended :)