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My question is how fan blade design relates to the focus of the air leaving the fan. I am looking to generate the most focused breeze I can with a fan blade, excluding additional ducting etc, the fan is in an open-air environment.

I see a mix of blade types available with different properties - a low number of very broad blades. A high number of narrow blades. A low number of narrow blades. Similarly I see designs where the blade flares towards the tips, and others where it tapers towards the tips, or where the blade is the same width from base to tip.

I have full control over the motor at hand so assume I can turn a fan blade at whichever RPM would be optimal for it.

Which type of blade design, if any, provides the most focused output airflow?

I'm also somewhat interested in what (if any) role the fan housing plays in this,(eg completely unhoused fan blades vs a circular enclosure around the blade tips, or a square enclosure like a box fan) however my primary interest is in the impact of blade design.

Cameron Roberts
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  • You might want to cause the motion of the air to ENTRAIN other ambient air into the flow. There are a number of "air amplifiers" that do this. Example https://www.youtube.com/watch?v=RveQZaYzhfE Bladeless fans utilize this principle. https://www.amazon.com/bladeless-fan/s?k=bladeless+fan – Jim Clark Aug 13 '21 at 14:22
  • You could power a 2000 hp fan with 12 volts if you had big enough wires. "12V" is insufficient. – Tiger Guy Aug 13 '21 at 21:34
  • @TigerGuy thanks, I've completely re-worded the question because the extra details I was including seemed to be taking away from what I'm actually trying to understand with this question. – Cameron Roberts Aug 13 '21 at 21:59

1 Answers1

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The air leaves the fan in turbulent flow.

You need an outlet pipe and flow straightener(s) to reduce the turbulence.

The choice of fan does affect the amount of air moved and that is also affected by the rpm that the fan was designed for. Is that fan on its original motor or a different one.

Solar Mike
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  • It's the full original radiator fan assembly so it's the original fan/motor combination (I actually have four different units and got the same results with all of them) but regardless of the speed I run it at the outflow of air is felt mainly at the outer edge of the fans and it dissipates basically right away. Compared to weaker household fans I have the radiator fans are loud and don't seem to generate an organized kind of airflow or breeze, just very turbulent air around the edges. My hope is to swap out the current radiator fan blades with household fan blades so I can get a breeze – Cameron Roberts Aug 13 '21 at 06:52
  • The car cooling fans I have used and fitted between vehicles make the household ones look like those little kids handheld jobs. Try a Kenlowe fan and make sure you have a good power supply. My car fans need about 30A… – Solar Mike Aug 13 '21 at 07:13
  • I'm not looking to use these in a vehicle, I'm looking for comfort cooling, like a household box fan but running off 12v. For my tests I ran the fans straight off a charged car battery so I assume they were at full speed. They were moving tons of air it just didn't carry any useful distance from the fan. Since the housing of a regular box fan is just a simple square, I zeroed in on the blade design as something that must be relevant. My thinking is the rad fan is not designed with outflow in mind. The fan assemblies I have were pulled from a couple different Hondas. – Cameron Roberts Aug 13 '21 at 13:13
  • Did I say you had to use then in a car? – Solar Mike Aug 13 '21 at 14:45
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    No, but nothing you've said here addresses my question, and you're recommending a specific brand of radiator fan, so it seemed like clarification was needed – Cameron Roberts Aug 13 '21 at 15:53
  • I made an example of a particular fan because I happen to know the current required for that fan. BTW I won’t continue this. However I am surprised that you have not done any research on turbulent flow and flow straightener given you have not asked sensible subsequent questions… – Solar Mike Aug 13 '21 at 16:56
  • what is your definition of a "fan?" Is it an axial fan connect to a motor without a housing? Think about your car's ventilation. It is a blower through ducts. It's the ducts that will focus and throw the air, not the fan. – Tiger Guy Aug 13 '21 at 22:26
  • @TigerGuy The big radiator cooling fan or fans under the bonnet used for cooling the engine. The blower motor shifts less… Edpecially as the OP stated in the question “a low number of very broad blades” or did you miss that? Which effectively excludes the blower type… – Solar Mike Aug 13 '21 at 23:49
  • @SolarMike, I take people at their words, and a fan is something that moves air. But does he include a shroud or does it have to be just blades in the air? – Tiger Guy Aug 16 '21 at 03:57