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What are the conventions for the direction of air flow for a fan? To state the question a different way, how can I determine the direction of air flow without actually applying a voltage to the fan? For instance, here's an image of a 24V DC fan.

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From this perspective, I believe the direction of air flow is away from the table it is resting on (unfortunately this particular fan is dead so I can't test it). I've guessed this direction because the fan blades have a visible curvature to them that makes it seem like the fan blades would push air most efficiently if the fan spun clockwise (from this perspective) and air moved away from the table. The fan has a sticker on this side, but not on the other face. Is it generally true that if you're facing the side with the sticker air will flow toward you? I've also heard fans often have a small arrow on the side indicating the direction of air flow. This one doesn't, however. Are there any other conventions besides the 3 I've mentioned for determining the air flow direction without turning the fan on? Do AC fans have different conventions than DC fans?

MattHusz
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  • Often, on one of the sides is imprinted a direction arrow... at least on the 4 I have laying around, did you look? – Solar Mike Nov 16 '20 at 05:55
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    The shape if the blades is a very good indicator of which way the fan is intended to run. From the way they curve, that fan is intended to blow air towards you if you are looking at the label. – Simon B Nov 16 '20 at 08:50
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    To expand on Simon's comment : the fan's job is to accelerate air. Therefore air entering the fan is moving slowly; air leaving it is moving fast. Therefore the angle of attack on the entry side is shallow, and on the exit side is steeper. And we can see that the shallow edge of the blade is nearer the desk, confirming your conclusion. –  Nov 16 '20 at 11:49

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