two options a thinner heatsink(fan is closer to cpu) or larger heatsink, physics?

[bigslammer]

well I've forgot my physics formulas but what is gonna be better. on my cel 366 I can put a smaller thin heatsink where the fan would be much closer to the cpu. my second option is this taller/larger heatsink which has more surface area to dissapate the heat but the fan seems to be 1.5 inches further from the bottom of the heatsink. the top of my heatsink is cooler in this case but the bottom part connected to the ppga cpu is hotter. thx

[scotter]

your best bet is to try them both and see which works the best for your system I've got a few diff heat sinks the one I'm using is a alpha ph6035 but I have another little dinky thing that keeps my chip almost as cool as the alpha that was $10.00 with a 5000 rpm fan http://www.sysopt.com/forum/smile.gif
with the big sinks like the alpha you really have to have a high speed fan that moves a lot of air like the Y-tech 27cfm

one thing you can do to the small one to make it work just a little bit better is lap it even my alpha was a little warped http://www.sysopt.com/forum/smile.gif

[bigslammer]

thx yeah in my experiments the bigger surface area is better but it does require a really good fan .thx

[800XL]

It depends on a lot of variables. With higher airflow speeds, you can actually decrease performance of a heatsink in some cases. The air has to slow enough to be able to pick up heat from the fins of the 'sink, yet not slow down so much that it picks up too much heat before it gets back out of the 'sink. Otherwise, it can pass the heat right back into the metal.
Generally, more surface area is better, and more airflow (volume and speed) is better. The more heatsink you have touching the air and the more air you have touching the heatsink, the better things cool.

[dexmax]

800xl is right. Remeber the thing about the bypass factor. The air nearer to the surface of radiating heat is warmer than the air in the center. So there is less heat absorbed by a certain mass of air compared to a slower. But if its too slow, the air can't catch up w/ the heat being added.

Have you noticed in older cars, the condenser(air con) fan is at the front, but in newer models the fan's at the back. This is due to the fact that, the sucked air has a lesser velocity than the blown air.

[PaulSinclair]

Don't know if this basic physics may help...but once the heat gets out of the chip into the heatsink then the main issue is down to heatsink Watts/degC and airflow. A thinner heatsink won't help to much unless you also get superior power dissipation with it, because once heat crosses the thermal barrier chip->sink the size of the heatsink per se isn't too important, its more relevant how easily heat is drawn from the chip and passed to the air.

A *well designed* larger sink can often dissipate better than a small one as it's better able to draw heat fruther from the chip and expose it to more airflow.

So if you're happy about airflow and fans (the guys above have got that bit right) consider getting watts/degC info on the sink itself and be guided by that. Pure physical size is not so relevant to performance. Maybe also consider using a thermal paste if you're *really* concerned - this is very cheap & like toothpaste, smear between the chip and sink to enhance the quality of thermal contact.