[jaydee]

Originally Posted by ferdb

1) Given a system, if you double the radiator area, and double the number of fans you will double the airflow through the system and reduce the coolant temperature above the ambient air temperature to roughly half what it was.

Being we are dealing with a system here you must take into account the other parts of it. If you double the rads surface area, then you also double the area the coolant will have to be pumped through. The coolants flow rate needs to be in here somewhere and adjusted accordingly.

2) Since Fan CFM is directly related to RPM on a first order approximation, if you double the fan RPM you will double the airflow and half the temperature differential. This increases the fan noise greatly

Problem with this is you are assuming identical fans. I don't know of any instanced this is true. Blade number and pitch and rpm will most likely be different on any fan that doubled the other fans CFM in the same size. (80mm, 90mm, 120mm etc..). This would be a usable fact if such a thing existed in this system. I don't think you can just double the RPM of the fans in it unless they are already turned down. And the faster the fan turns the more power it will take to keep it going because of drag (wind resistance?).

3) If you reduce the fan RPM to 1/2, you'll halve the airflow and double the temperature differential. You will reduce the fan noise greatly.

Sounds good to me.

4) If you double the radiator area, double the number of fans, but reduce their RPM to half you will end up with roughly the same system temperatures but much reduce fan noise.

Providing your coolants flow rate remained the same. Not likely though doubling the rad area and not changing the coolants flow rate.

5) If your coolant temperature is only 2C above ambient air temperature, no matter how fast you run your fans or how much radiator area you add you will not be able to reduce the system temps by more than 2C.

Huh? This has to be system spacific to a certain heat load. Makes no sense to put a certain number on this for all systems.

6) if your coolant temperature is 10C above ambient, then doubling your fan speed will roughly reduce your system temps by 5C.
If you are intending to hook up an overclocked/overvolted AMD64 CPU,6800GT video card, and Northbridge chip that is dissipating 200W into BI pro radiator, a Panaflo L1A running at full rpm couldn't possibly pull better than 50 CFM through that radiator and thus your coolant will be at least 7 C above ambient air temp, if not more.

Would love to see how you came up with this.

The equations and all these examples are only to help you make prudent design decisions. If your coolant temperature is close to ambient air temperature already, adding fans and bigger radiators is not going to improve the system significantly. If your fans are too noisy, doubling the radiator size will let you halve their rpm and thus the noise. If your coolant temperature is significantly above ambient air temperature then the airflow through your system is poor because of fans, restrictions, or sucking hot exhaust air back in. Fix accordingly.
Make use of the information as you see fit.

Let's not assume bigger rads are going to be better with the same pump. If the pump can't handle the larger rad then your results are not going to be much better.