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Subject: Heatsink performance with/without fan
By: nordh (IP: 193.11.208.*)
Written on: 15-10-2005 09:42

Hello!

I'm currently thinking of building a 19" rack for home use with an irregular aproach to cooling. Normal racks are cooled just by circulating lots of air throuh them but since on of the key points of this project is to reduce noise in the computer room the current plan is to have a sealed, silenced rack cooled by peltier elements. On the inside, the cool side of the peltiers I will have some kind of heatsink and a fan to cirkulate the air. My questions are:

1) Is the same reasoning regarding thermal resistance valid "the other way around" when it's strictly speaking not a heatsink but a "heatrise"?

2) If I understand thermal resistance correctly the values supplied are for non-moving air. If I add a fan blowing in a suitable way, how much can I lower the thermal resistance?

3) Any specific kind of heatsink I should use? I've considered using CPU coolers but primarly regarded them as unsuitable since the air flow is not directed. The optimal way to cool the case seems to be to take in air in the bottom of the rack, cool it and dispense it at the top.

Kindest regards
Johannes Nordh

Replies:

By: Tillmann (IP: 146.140.7.*)
Written on: 15-10-2005 23:54

1) Yes.

2) This depends on the design of the heatsink, and how the air is applied. Generally, the performance gain will be very high, but it is hard to say how much

3) I hate to disappoint you, but it's not gonna work. As you can find out in the "Peltier cooling" section, Peltier elements consume much more power than they can transport. Now imagine you build a low-power system to fit into the rack that will get along with just 200W (a high performance PC consumes much more). To transport that, you'd need peltier elements with a total power usage of maybe 500 watts. Add the 200W transported heat to that and you need to get rid of 700 Watts of heat on the outside of your rack. How are you gonna get rid of that heat without using noisy fans on the outside? What kind of power supply are you going to use to get 500W on 16V to power the Peltiers? And besides, even if you manage to overcome the technological challenges, it's still an economic and ecological nightmare.

I have experimented myself with racks for sound insulation. Your best bet is to allow air in on one side and exhaust it on another, through air ducts with sound-insulating material. Here is a picture of the box I built (just from the outside; on the inside there's sound damping material, and ducts). It is extraordinarily quiet; I used to sleep in the same room and it was no problem.

All the best,
Tillmann