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bobo5195 · 10-16-2005, 08:08 AM

ah more numbers to make my head hurt. My notes on grid turbulence similarly caused to much nonsense and last night i was up to another side project.

I’m talk about distance not degrees LHG. Fan radial flow causing the angle is wasted work (i think) either way its less important as the flow will hit the wall and settle. The 10 diameters encompasses just about any entrance flow.

Those results are too close to call. From my mixed up head i would say.
1) Moving the fan away from a rad reduces noise by providing cleaner air and less interaction between the radiator and the fan. Main effect.
2) Thermodynamically it doesn’t matter which way around the fan is. The fan is still creating a pressure differential. There is a caveat that the created pressure differential is not large enough to change the properties of the fluid. Highly unlikely.
3) For push the walls of the shroud recover air pressure as it converts radial flow to axial flow, although there are losses in the gap. Clearly no shroud and a gap is nonsensical. A special case that never happens in practice as a gap and no shroud is stupid.
4) For pull the gap and shroud (no shroud and gap is again nonsensical) the gap allows air to settle providing cleaner air to the fan. As comment 4.
5) For push having the fan close to the radiator increases head losses as air still has a rotational component that is lost when it enters the rad in push configuration (all velocity components not normal to the rad are doing anything; obviously depending on the radiator design. Some recovery does occur in the rad but settleing in free air is better). Important effect similar to 4 and 5 spaces above.
6) pulling through the rad the radiator itself may act as a lamina flow guide provided turbulence caused by the grid would be dissipated this will help. Stretching reasoning a little but I think still a valid point.
7) increasing the fan distance from the grid prevents variation in output from the fan effecting the rad. For example fan output is going to be higher at the outer edges (av m/s per m^2) as the fan blades are spinning relatively faster. By having a gap fan flow is more uniform giving a better flow. Comes with 5 and essentially the same thing.
8) The shroud may damp fan noise.

In short shroud good for noise and a little performance as there is less variation in the flow and less chance of interactions between the fan and the rad. Pull better as radiator creates lamina flow for the fan. I would recommend try it and see on your own comp if possible.

10-16-2005, 08:08 AM	#10
bobo5195 Cooling Savant Join Date: Aug 2005 Location: uk Posts: 400	ah more numbers to make my head hurt. My notes on grid turbulence similarly caused to much nonsense and last night i was up to another side project. I’m talk about distance not degrees LHG. Fan radial flow causing the angle is wasted work (i think) either way its less important as the flow will hit the wall and settle. The 10 diameters encompasses just about any entrance flow. Those results are too close to call. From my mixed up head i would say. 1) Moving the fan away from a rad reduces noise by providing cleaner air and less interaction between the radiator and the fan. Main effect. 2) Thermodynamically it doesn’t matter which way around the fan is. The fan is still creating a pressure differential. There is a caveat that the created pressure differential is not large enough to change the properties of the fluid. Highly unlikely. 3) For push the walls of the shroud recover air pressure as it converts radial flow to axial flow, although there are losses in the gap. Clearly no shroud and a gap is nonsensical. A special case that never happens in practice as a gap and no shroud is stupid. 4) For pull the gap and shroud (no shroud and gap is again nonsensical) the gap allows air to settle providing cleaner air to the fan. As comment 4. 5) For push having the fan close to the radiator increases head losses as air still has a rotational component that is lost when it enters the rad in push configuration (all velocity components not normal to the rad are doing anything; obviously depending on the radiator design. Some recovery does occur in the rad but settleing in free air is better). Important effect similar to 4 and 5 spaces above. 6) pulling through the rad the radiator itself may act as a lamina flow guide provided turbulence caused by the grid would be dissipated this will help. Stretching reasoning a little but I think still a valid point. 7) increasing the fan distance from the grid prevents variation in output from the fan effecting the rad. For example fan output is going to be higher at the outer edges (av m/s per m^2) as the fan blades are spinning relatively faster. By having a gap fan flow is more uniform giving a better flow. Comes with 5 and essentially the same thing. 8) The shroud may damp fan noise. In short shroud good for noise and a little performance as there is less variation in the flow and less chance of interactions between the fan and the rad. Pull better as radiator creates lamina flow for the fan. I would recommend try it and see on your own comp if possible.