# Questions tagged [fan]

The fan is an electrical appliance using the principles of a motor.

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### Variation of fan air temperature with angle

On a very hot summer's day, I was on my porch using an electric fan and I noticed that the air it blew had different temperatures. As you move away from the center and towards the outer border, I ...
1 vote
22 views

### Output of ventilator and air friction

Imagine you have a ventilator with straight rectangular ventilator blades which are rotated at some small angle from a perpendicular line to the rotating axis. The ventilator has 100% efficiency (all ...
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### Does a second fan in the tube accelerate the flow even more?

For example, if there is a tube with a certain diameter and one fan in this tube that generates a flow of air with velocity X, will an additional fan (or several fans) accelerate the air even more? If ...
49 views

### Is stoßlüften - quick exchange of air through windows actually more efficient than slow exchange through a wall ventilation fan?

In German areas with near air-tight homes, it is recommended that full house ventilation is performed by stoßlüften - opening windows fully to exchange as much air as possible in shortest amount of ...
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1 vote
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### Airflow through tube

I have a tube with an inline fan moving 100 cfm (cubic feet per minute). If I add an additional fan in the same tube capable of moving 100 cfm, what would happen? Would I increase my cfm to 200? Would ...
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272 views

### How distance affect wind speed from a fan?

I noticed that when you feel the wind force from a fan close up, it feels like more force than from far away. Can someone give me an equation, where given a base wind speed $v$ in mph of the fan, and ...
64 views

### Why are the blades of a pedestal fan so different from the blades on an aircraft propeller?

Both fans and propellers move a quantity of air. In the former, that is the end goal. In the latter, this movement of air creates a force in the direction opposite to the airflow. So, why are the ...
182 views

### What factors determine the suction of an exhaust fan?

What factors determine the suction of an electric exhaust fan used in kitchens? I thought about fan-speed, voltage, air-pressure, difference in air pressure, circulation.
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1 vote
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### Comparison of 2 fans [closed]

I have 2 20" box fans. The first fan draws .65 Amp and claims 1780 CFM. The second fan draws .45 Amp and claims 2300 CFM. The fans are new, and the electric motors are of similar design, so I ...
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1 vote
53 views

### Equilibrium of air volume in and out of an inflated bag

I want to use a small squirrel cage fan to blow air into (and inflate) a closed bag. The bag will also have a number of small holes in it to release air at various points across the bag. But, I want ...
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35 views

### Why do we feel cool after switching fan? [duplicate]

Please see that my actual question is not similar to this: Why do we feel cool when we turn our fans on? Suppose I switched my fan on. The air particles start moving. Since, their kinetic energy ...
44 views

### The motion of a spring due to wind (Wind induced oscillations)

Consider a spring held in the direction of wind as shown in the image. the spring body is wrapped with paper so that the spring oscillates with the wind in a circular manner. Is there any mathematical ...
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### Fan in a sealed box

Let's say that there is a helium balloon attached to a large, sealed box. The box is off the ground and there is neutral buoyancy. The box + balloon are simply floating in air, not moving. Inside the ...
1 vote
178 views

### Propeller Spiral Slipstream

I know the common accepted answer is that in an airplane, the propeller pushes air back but imparts rotational flow to the air, and the rotating air around the body of the aircraft hits the back ...
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### Why don't CPU fans have the buzzsaw effect (as in planes), even when their blades spin faster than 5k RPM? [closed]

I saw my CPU fan using HWinfo spinning faster than 5k RPM, in which the buzzsaw effect starts in an A3xx plane. Why doesn't my CPU fan do the buzzsaw effect, even though it's spinning faster than 5k ...
69 views

### Why do pages of a book oscillate when kept under fan?

I have noticed that when one of my book is kept under a ceiling fan, its pages keep on moving up and down due to the wind of the fan. Why don't they just settle in equilibrium ? What causes them to ...
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4k views

### Forces acting on ceiling fan

What are the forces acting on ceiling fan vertically? I know that there is gravitational force acts on it downwards but what is the opposite force?
13k views

### Why do fans spin backwards slightly after they (should) stop?

Today, I've decided to observe my PC fan as I shut the computer down. The fan slowly lost angular momentum over time. What I've found really interesting is the fact that the momentum vector change did ...
1 vote
102 views

### Why does the car move faster?

I build this propeller-powered car (in image). The propeller pushes air backwards and the car moves forward. I observed something weird. While I place my palm behind the propeller (about 2-3 cm from ...
1 vote
51 views

### How would a small desk fan improve the air flow of a room?

Say one were sitting in a room with poor ventilation. If wind doesn't rebound off of surfaces, how would a small desk fan alter the airflow of the room?
1 vote
244 views

### Why adding fan to dry cabinet not improve dry performance? [closed]

My dry cabinet is basically rubber sealed cabinet with peltier module to condense moisture and drain it out. The drying process run quit slow from ambient humidity around 50% to 70% it take about 3 ...
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1 vote
2k views

### How does a spinning fan create low pressure for suction?

Most answers about how spinning devices create suction often mention how air moves from high pressure to low pressure. The spinning fan creates low pressure and thus we have air moves from freestream (...
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2k views

### Why a fan make us feel colder instead of warmer in a cold room? [duplicate]

Stay in a cold closed room, turn on a fan directed at you, it makes you feel colder instead of warmer. why? Here is the definition of heat: Matter exists in different physical forms – solids, liquids,...
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### What might cause water vapor to move against the flow of air in an enclosed space?

I have a rectangular tent that I'm planning to use as a mushroom fruiting chamber. It measures approximately 120 x 60 x 150 cm and has two duct fans installed--an intake fan near the top of the left ...
147 views

### Ceiling fans with just one large winglet? [closed]

I am from India and in India ceiling fans have generally three wings. Today while laying on my bed a question came in my mind. First of all, I know that if we use just a single wing at a time of same ...
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1 vote
78 views

### Why is not both sides of a fan equally effective? [duplicate]

I have a fan on my desktop. I started to wondering if it would not be just as effective if I flipped it 180 degrees. Since all the wind that comes out of the front has to be sucked in from behind, ...
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### How do handheld folding fans create airflow?

Google provides no answers to this question. Google only tells how it cools but not how it it creates airflow. Could someone explain how handheld folding fans create an airflow despite only moving ...
780 views

### Why does a running fan produces some sound?

We see that a running fan produces some "humming" sound - "The sound of air". What kind of sound it is? Why does a running fan produce some sound?
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### Why does a running fan causes some soundproofing in the room?

I notice that when I switch on my fan inside my room, the room becomes soundproof to a great extent to the outside noises. The greater is the speed of the fan, the greater is the soundproofing. When ...
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1 vote
164 views

### Why does this ducted fan have 10 blades (instead of some odd number of blades)? [closed]

I've searched online and learnt that odd number of blades reduce turbulence and noise. I counted my home's ceiling fan, it has 3 blades, then I counted my laptop's fan, 13 blades! Amazing! But later, ...
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### Could an electric centrifugal fan in space be used to propel a substance to create force?

Would an electric centrifugal-force fan (like that found in a blower motor) work in space to create force, by putting a substance (like silica sand or something slippery) through the centrifugal fan ...
9k views

### Is this cheap "air conditioner" able to cool a room?

My parents bought this "air conditioner", but I am very skeptical that this can cool a room, or even cool anything. I doubt that it even has a cooling element, I suspect that it is just a fan + ...
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1 vote
3k views

### Conversion between Power and Flow rate of Fan taking into consideration the geometry of the fan

I need to find the relation between two properties of a fan, that is between power and flow-rate. I expect such a formula to depend on the pressure and on the geometry of the fan. I have found in ...
90 views

### calculate CFM of a ceiling fan

I'm trying to calculate, or even understand what data do i need to calculate the CFM of a ceiling fan. in many countries this is a given data in the product details but not where I'm from. I have the ...
41 views

### At what wind speed will a ceiling fan 10 feet above my desk move a sheet of paper? [closed]

We sell fans. An engineer asked this question. He wants to buy a fan large enough to cool without being so large it blows paperwork off his desk. Q: At what wind speed will a ceiling fan 10 feet ...
36 views

### Aligning fans in a tube

So, I have a lot of old PC fans and got thinking, what would the airflow look like if I lined them all up in a straight tube and powered them all? Would the speed of the airflow increase a steady ...
1 vote
3k views

### Thermodynamics - best fan speed to heat a room (for the same heating power)

Let's assume we have a cold empty room (with no person in it, therefore - barely little air movement) and we want to heat it up. In the room, we have a hot-air blower that has two fan speed-settings, ...
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### Air pressure drop off rate

I’ve been thinking about this for a while, and at first, I assumed that the inverse square law applied, but seeing as how air isn’t a form of radiation, I’m not sure that it still applies. So if we ...
6k views

### How to calculate the force of a fan?

Let's say that we want to build a helicopter, if we want it to hover in the air then the pushing force of it's fan must equal the force of gravity but in the opposite direction, so how do we calculate ...
1 vote
1k views

### Will a room heat quicker with a fan blowing on a hot surface? Why?

I got into an argument with someone who thinks that blowing air across a fireplace will make the room heat more slowly, but based upon the principles computer heat sinks use to get heat away the room ...
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### Angle of attack of a propeller blade

What will be the best angle of attack for a propeller blade that is in the airfoil shape?
207 views

### Propeller blades flat vs wing shape

Does a propeller blade with the shape of a wing produce more lift than a flat blade and will a blade with a wing shape produce lift in a ducted fan situation?
245 views

### How is steam affected by a fan?

Scenario Consider a humidifier with a fan behind it. Assume same room, moderate temperature, low fan speed. ...
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1 vote
261 views

### why shadow of a glass oscillates under the rotating fan behind which there is a lightsource

So today I was sitting in mess, and light coming to me was fluctuating mainly because of rotating fan which was cutting the light source just right above it. But then i observed that the shadow of the ...
1 vote
145 views

### Cool a room with a fan, what sens orientation? [duplicate]

It is really hot these days, and at night, I try to cool my room before going to sleep but I'm wondering in which sens I should orient my Fan Answer A : Push the hotter air with my fan outside. ...
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### Room not getting cooled

I am in a room which is heated up duringg day, in night outside temp is quite low, but my room with a ceiling fan running still feels hot as it was in day if I step outside door its cold. There is ...
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1 vote
62 views

### How would the Stroboscopic Effect appear if the blades were reflective?

The Stroboscopic Effect is an optical illusion in which rotating spokes can appear to rotate differently than the true rotation. What will the observation be like if fan blades are coated ...
1 vote
946 views

### How the velocity of the air is slowing down in different distances from a fan?

Is it determined completely by the air pressure and the temperature? Do I need to take into account also the geometry of the "air cone" of the fan or is it determined by the speed of the air ...
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1 vote
4k views

### Why do we feel cold when we switch on the fan? [duplicate]

We know that on increasing the kinetic energy of a gas its temperature increases: $$\text{Kinetic Energy} = \frac32 kT$$ where $k$ is the Boltzmann constant. This equation is derived from the kinetic ...
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