High cfm fans on radiator compared

I recently got an Enermax A5 which has 6 fan controllers on it and 2 temp probes. I decided that I would put my two Delta #AFB1212VHE fans back on my radiator since I could now control the voltage as needed. I was rather disappointed to see there is only a 2C difference between running them at 130 rather than 80CFM. This minimal decrease in temps is hardly worth the added noise. I thought this might be interesting to a few of you.

On the other hand, my two 120mm fans that are supposed to cool my dual rad didn't start yesterday. I noticed that 30 mn later while surfing the internet, not because of a CPU temp alert, but I was just surprised how quieter it was. Actually the CPU temp stayed at 30 degC, just the same value than when the fans are running. Now I wonder if those fans are making any difference. Maybe I'll try to switch them off during a BF1942 and see what happen.

The thing with water-cooling radiators is that "it's all about air-flow"

However, net air-flow is directly linked to pressure, and quite frankly, axial fans suck for suppling good pressure unless you're prepared to accept the noise that they make.

The way to combat this is one of two approaches:

1) Given the same radiator, increase fan pressure until you increase your air-flow. Problem here is that pressure resistance is proportional to the air-flow squared. It takes a fan that's 4 times as powerful (and probably 4x as noisy) just to push double the air-flow through a fixed radiator size. This is what you've attempted here.

2) Increase the radiator size. This decreases the air-flow resistance, allowing more air to flow.

You would do far better by having two radiators, one for each of your quieter fans, and the cooling provided would exceed what is available by using both fans on a single radiator, as both fans, in push-pull series mode, will at best maybe increase the air-flow by about 40% over a single fan working on the radiator. Problem is that cooling performance is not linear with air-flow, so a 40% increase in air-flow may only correspond to a 20% increase in cooling ability.

Put in two radiators with a single quiet fan on each, and you immediately get near doubling of the cooling capacity of a single fan on a single radiator, probably halving your water temperature rise above ambient (provide the entry/exit of air from the two radiators are totally independent).

Put in four radiators, and, well you get the picture.

Of course, space constraints tends to be the main issue here, which is why I built an external radiator box.

Truth of the matter is, you really need a radiator that's 2-row, about 10"x10" in fin area, and single pass, to achieve radiator bliss of quiet but excellent cooling.

Cathar is there a make and model of the rad you discribe?

FizzledFiend said:

Cathar is there a make and model of the rad you discribe?

Click to expand...

Well, I was just putting something out there. I use two 9"x5.5" fin-area heater-cores in parallel to achieve the same effect myself.

However, yes, there is such a beast, and it is a car radiator, from a Morris Minor 1600.



The radiator on the left is the one. The one on the right is one of the two that I currently use, and itself is 11" long x 6" wide in total, just to give an idea of scale for the Morris Minor radiator on the left.

...and here's a picture of the radiator rigged up with 4 high-speed fans. The radiator shroud and fannage was done by myself for someone else. I never used it. The person wanted to stick it under their house so that's why they were happy to have the 4 fans on it.



Those are 12cm fans on it. Internal to the shroud the fans are separated from each other by baffles. Each fan acts on its own section of the radiator independently of any other fan. This actually makes the radiator perform better when one crunches through the mathematics of pressure resistance for one vs multiple fans in parallel.

Cathar, I take it the radiator's material is important too- is that Morris Minor (irony in the name there hehe) core made of copper?

If not, would the rad on the right (which is copper if I see that correctly) not be a more efficient performer... i.e. it does not compare to the Minor rad by scale only?

Both radiators are copper-based.

This rad is so tiny as for car rad... But still far bigger than heatercore.

Option 2 seems much more feasable since noise is a key factor. I've debated getting two heatercores to run in paralell using the MCP600 pump I recently purchased for some time now. Since I already have a D-Tek Procore, I'll add a second to my loop on a pull config using the aluminum Evercools.