Theoretically speaking a DC fan should be operating at some point on its predetermined fan curve. I was always told that a rule of thumb is to not obstruct the fan's flow half the distance of the fan's diameter. This way, the measured fan curve may still be observed in an enclosure. However, this is not always possible. What happens to the theoretical fan curve that is determined in free air, if there are now obstructions very close to the fans outlet? Is there any way to determine what happens or any general guidelines that could be used to better define the fan perfomance characterics in such a case?
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fan curve differences? 1
- Thread starter noslo21
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noslo, you said "the theoretical fan curve that is determined in free air...". I suspect you already know this, but I just want to clarify: published fan curves are typically measured (not theoretical) and the test is done over a range of pressures (not just free air).
I agree that performance is sometimes off the curve if the obstructions are very close to the fan. I don't know a good rule of thumb for it. There are a lot of significant variables: blade shape, quantity, angle; fan speed; obstruction shape and proximity; flow paths around the obstruction, etc.
It's worth asking the same question of the fan manufacturer, they may even have test data on an arrangement similar to yours, but it's more likely you'll have to test it under your conditions if you want a good answer.
Good luck
ko (
I agree that performance is sometimes off the curve if the obstructions are very close to the fan. I don't know a good rule of thumb for it. There are a lot of significant variables: blade shape, quantity, angle; fan speed; obstruction shape and proximity; flow paths around the obstruction, etc.
It's worth asking the same question of the fan manufacturer, they may even have test data on an arrangement similar to yours, but it's more likely you'll have to test it under your conditions if you want a good answer.
Good luck
ko (
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ko99, thanks for your reply. I do realize that fan curves are published values over a range of pressures. That was just bad communication on my part. In such situations that I do have obstructions near the front of the fan, I do indeed test the fan in that situation. since the measured point is no where near the publish fan curve I have in the past scaled back the measured fan curve to meet my actual operating point so that I can now compare the revised fan curve with obstructions to other systems. I'm sure that this is not an extremely valid method of determining a "revised" fan curve. I however, was interested to see if there was a better way of doing so without some sort of complex analysis.
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