Yes.johnthekid said:A standing fan is blowing air when we are right in front of it but we noticed there are dirts on the back of the fan. So, at the front, a standing fan pushes air and from the back the fan is sucking. Is this correct?
I'm not sure what sort of answer you're looking for with that question. The blades are curved to force air to move in a preferred direction.johnthekid said:If it does, why?
Ibix said:Yes. Where else would it get the air to push at you except from behind it?
russ_watters said:Yes.
I'm not sure what sort of answer you're looking for with that question. The blades are curved to force air to move in a preferred direction.
Yes, though for your typical desk or central air conditioning fan the air can be considered incompressible for calculation purposes. The key similarity then is that they both move air by creating a pressure difference from one side to the other (yes, it's a contradiction to say you can create a pressure difference without compression, but it is ignored because it doesn't affect the calculations).johnthekid said:Fans also compress air but not at the same level as specialized air compressors, is that so?
Cheaper fans use flat blades at an angle. Better fans use airfoils at an angle (like a propeller). Here is a good PF Insights article that may give you more of a feeling for how air moves around a fan/propeller and why the airflow over the back surface is slower/lower pressure (and may lead to more dust accumulation): https://www.physicsforums.com/insights/airplane-wing-work-primer-lift/johnthekid said:I don't really get the mechanism of fans so I was curious at first.
johnthekid said:A standing fan is blowing air when we are right in front of it but we noticed there are dirts on the back of the fan.
The OP seems to describe the opposite observation: More dust on the side with faster flow / lower pressure. This is also consistent with my observations on PC case fans.berkeman said:the airflow over the back surface is slower/lower pressure (and may lead to more dust accumulation)
A.T. said:The OP seems to describe the opposite observation: More dust on the side with faster flow / lower pressure. This is also consistent with my observations on PC case fans.
My intuitive idea was always that there is more turbulence / acceleration of air on the faster flow side, so the dust falls out in certain flow pockets. The dust distribution is not uniform, bus has very specific patterns.
The internet also mentions different amounts of static electricity due to the different flow dynamics. But I'm not sure about that.
The blades of any type of fan transfer kinetic energy into the mass of gas that is surrounding them.johnthekid said:A standing fan is blowing air when we are right in front of it but we noticed there are dirts on the back of the fan. So, at the front, a standing fan pushes air and from the back the fan is sucking. Is this correct? If it does, why?
A.T. said:The OP seems to describe the opposite observation: More dust on the side with faster flow / lower pressure. This is also consistent with my observations on PC case fans.
johnthekid said:Right. I was slightly confused.
I opened my PC case and checked it again: Contrary to what I wrote above there is more dust on the side with slower flow / higher pressure, but the dust is more uniformly distributed here, so it doesn't stand out visually.A.T. said:More dust on the side with faster flow / lower pressure. This is also consistent with my observations on PC case fans.
My intuitive idea was always that there is more turbulence / acceleration of air on the faster flow side, so the dust falls out in certain flow pockets. The dust distribution is not uniform, but has very specific patterns.
Just checked my fan, there are dust on the blades back and front and also on the air outlet (front) and inlet (back). Basically almost every parts of the fan. Its just for some reasons there are slightly a bit more dust on my fan's air inlet, including the motor area, than on the air outlet. So, dust are both sucked and blown away when the fan is operating. My initial thought is that dust are only sucked from behind when the fan is working.Baluncore said:Referring to the front and back can be confusing because it depends on how you look at it. Maybe refer to the air inlet and outlet, the inlet side of the blade and the outlet side of the blade.
Dust accumulates faster on the outlet side of the blade, because, as it pushes the air through the outlet, that side of the blade is hitting particles suspended in the air.