Hot answers tagged fan
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The blades of a ceiling fan are pitched out of plane slightly. As a result, when the fan spins, the blades push air either up towards the ceiling or down towards the floor. Which direction it pushes air is determined by the direction the fan is spinning, and the direction the blades are pitched. The usual convention is given by the right hand rule: if you ...
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There seems to be a lot of B.S. in the ads for this product, making it seem much more complicated than it really is.
It seems that the fan contains an ordinary fan in its base, and squirts out high speed jets of air from around the big ring. These jets of air push on the ambient air. This slows down the individual jets but pushes along a greater volume of ...
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Simply put, it's because a fan imparts momentum on the air (i.e. accelerates it), so in front of the fan you get a roughly conical jet of high speed air.
At the back side of the fan there is a low-pressure region which makes the surrounding air move towards the fan (following the pressure gradient) from a large solid angle, as you already stated.
This is ...
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Intuitively, it seems entirely possible.
The "shape" of the air current blown out by both fans looks like a hollow cylinder, since the air is blown at high velocity near the ends of the blades, and lower velocity towards the center.
If you put two of these fans facing each other, the two "cylinders" of air current will collide with each other and create a ...
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If the fan rotates the wrong way it will blow the air up onto the ceiling, so at best you'll get a turbulent breeze as the air flows along the ceiling then down. It's obviously better that the fan blows the air straight down as you'll feel a higher air speed.
I agree with Ron that the comment from Constellation Energy seems rather silly, but the thought of ...
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There are two types of energy source. 1. Voltage source 2. Current source
In voltage source, source voltage remains constant in spite of varying load resistance connected to it.
In current source, current remains constant through the load in spite of its resistance.
The main line is a voltage source.
so the power consumption (electric energy) used bye ...
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With no resistance, the full voltage is applied to the fan, and you get mechanical work done, at whatever efficiency the fan itself is capable of. Never minding the fan itself, so far as the electrical aspect goes, you could say it's 100% efficient.
With resistance in the system, for example about equal to the resistance of the fan, you have less current ...
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(The OP has commented that the room also contains a fridge and a bottle of olive oil, but no cockroach.)
The viscosity of olive oil changes with temperature. At higher temperatures it becomes more fluid. If you first make sure that the olive oil has the current room temperature (pour it into a pan and back), you can then measure how fluid it is by letting ...
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I think that you are overestimating the importance of the blade mass. The blades rotate due to aerodynamic forces which are determined by blade geometry and size, and the fluid properties of the air impinging on them. The mass does not impact the aerodynamic properties of the blades. For a fixed wind speed, neglecting small effects like friction in bearings ...
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No.
Presume the fan is in series with the regulator.
Presume the fan when run at a lower speed draws less current.
Presume the mains voltage stays the same.
Then the total current is lower at lower speed, and so the total power used is also lower.
Now, if you skip some of these presumptions, you could set up some screwy system, say, put a lightbulb in ...
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It depends on the fan, but I'd guess the majority of domestic fans will use less power at lower speeds.
I can state with authority that the fan in my car (a Ford Focus) uses roughly the same power regardless of speed because I've just had to replace the ballast resistor that is uses to control fan speed. When you select a lower speed the fan dissipates ...
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Just as the most efficient wings are long, narrow, and run at slow speed, propellers that waste the least energy are long, narrow, and turn at slow speed.
Given all that, the helix angle of the blade (as a function of radius) should be adjusted so that it makes a good angle of attack against the air moving past it. Not too low, and not too high. Not more ...
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My previous answer was based on physical principles. This answer is based on biological principles.
I noticed in the question @JoeBlack stated "I feel air" meaning you are using your own biology to sense the air flow. Air flow can be felt by pressure of turbulence on the skin. It can also be felt by perceived temperature. Usually a person turns on a fan ...
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For your first question, think of the air kind of like sand. If you just slide you hand across the surface, some grains beneath the surface will move due to friction between the sand grains transferring the energy of your hand to other sand grains. The same thing happens in the air inside the ring, as air shoots out of the slit surrounding the ring it ...
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The fans work by entrainment of surrounding air by the jet blowing out of a slit in the ring. Obviously it is optimized for entraining air from behind the ring, but it should also pull in air from the sides if the back is blocked. Most fluid dynamics textbooks will discuss the problem of a planar jet coming out of a wall, this is essentially the same ...
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Mostly trial and error - but in a computer.
A combination of Computational Fluid Dynamics (modelling how the air flows over the blade) and Finite Element Modelling (how the stresses in the metal behave)
Both of these are complex areas - and when they come to together you need a lot of expensive computers and some even more expensive engineers.
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I would guess the Lift/Drag ratio of the blades is important. Lift = wind thrust (and speed), and Drag = friction and power loss.
Since the part of the blade moves slower the closer to the center, the angle of attack needs to increase to provide the same wind speed. Keeping an even velocity profile is probably important in order to minimize losses due to ...
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I won't address the details of the fluid dynamics that cause the cage to produce noise because it is well out of my area of expertise. But I have performed an experiment in my office. The small desk fan I bought was too noisy. Since it lives on the top of a tall bookcase and well out of reach, I removed the cage completely. It is a lot quieter now.
My guess ...
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