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heat transfer fluid dynamics guys - Page 2

post #11 of 14
Quote:
Originally Posted by jdobbs86 View Post
Let's say I have a vertically mounted rad with two fans.
Potentially sequentially operated...
so they will be divided...
The top fan is moving air hotter than the bottom would I want less area or more area for the top fan to pull from?

Ill give a little more information and maybe images later on

Thanks
Your overcomplicating it.
    
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post #12 of 14
Thread Starter 
Quote:
Originally Posted by Caleal View Post
One of the key factors in heat transfer is temperature difference.
Faster moving air through the radiator will pick up more heat per unit of time than slower moving air because there will be a greater average temperature difference between the water and air as it passes through the radiator.

Slower moving air will pick up more heat per unit of volume that passes through the radiator, but will pick up less total heat from the water per unit of time due to the lower average temperature difference between the water and air as it passes through the radiator.
Got schooled on this subject matter last night.

...and it has to be over complicated because I have to submit a design report/presentation and prove im right to steve and pat (evil super engineers)
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post #13 of 14
Quote:
Originally Posted by jdobbs86 View Post
Due to the two fans being sequential the radiator needs to be split into two shrouds.
The fans are identical, but the conditions they run at are not. The
fan on the top side of the radiator is going to be dealing with a
hotter water, so my question is should you increase the velocity of the air by
decreasing the area of the top shroud? Or should you slow the air
(larger area) to ensure maximum heat transfer?

Im with you on the second option. Just need some kind of proof to make an arguement

Dimensions and other information:

Core dimensions 145x240x35
13 fluid channels roughly 1.5mm X 32mm
Fan curve: http://www.spalusa.com/pdf/30103011_SPEC.PDF
Inlet temp can be 95c
Radiator should expel 35kW? in 35c air

i attached a file...the soda can shaped entity...is a soda can...for reference
So the point of this is to have fans blow air through a radiator with cooling fluid so it cools down my beer really fast and thanks for showing where to put my beer can.

The fluid dynamics of this is that body of liquid will flow down the digestion path of the humnoid/dog named rat to be enjoyed by a few remaining brain cells.

Another way to look at it they put radiators on the FRONT of cars to get the most cool air flow as possible in order to move the largest amount of heat prior or thermal saturation. Slow air decreases in capacity as the thermal load approaches that of the rad fins. You would only want to slow the air down if you were trying to cool with the least amount of air and therefore maximizing the thermal units vs. volume of air. But for maximum cooling you want to speed up the air.
post #14 of 14
FWIW, I couldn't quite make sense of the questions in here, but you can pretty much disregard temperature drop across the radiator. At least in water cooling, the flow rate is high enough that the drop across most radiators is only fractions of a degree.

Really doesn't matter which fan is more powerful on top or bottom, but there is a difference in distance from the radiator.

Besides air flow and volume, there is also an air turbulence effect that makes extreme shroud depth worse than placing the fan closer to the fins. About 30mm is about ideal, more depth than that and you'll loose efficiency.

I don't think there has been much testing of this sort of parallel fan setup, but it would be a similar pressure drop vs PQ of the fans. If the radiator is restrictive, you would likely net more flow from push pull which is essentially series vs shrouded parallel system.

That parallel system and overly deep shroud would also loose that proximity turbulence gain.

    
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