Do you ever wonder why in India ceiling fan has 3 blades, why not 4 or 5 blades whereas other foreign contries like U.S.A, U.K, Russia, Canada etc have 4 or 5 blades ? People generally assume that higher the number of blades, more air would be throw, but that is not the case. In this article I will give you a brief description about this question and tell you the reasons behind this engineering. Now let's start one of the most important topic.
Requirement of Fan
Why do we use a fan?
We use a fan for better air flow or better air delivery. This air flow or air delivery is related to speed. You see more speed of the fan can flow the more air. And the main purpose of a fan is to create air flow. A good fan can provide air flow in minimal noise also. A fan is designed according to the operating environment conditions and the required level of air delivery.
Theory and Comparison
In which countries what will be the number of blades, is depends upon some points like - i. Air Delivery or Air Flow, ii. Mechanical Balance, iii. Drag force and iv. Operating environment.
Air delivery or Air flow
Air delivery by a ceiling fan can be divided into two parts - one is throw and another one is circulation. Here throw means vertical circulation of air and the circulation means horizontal circulation of air.
Now see how these two are related to blades. When you need more air that means you need more speed that mean also you need more throw so that more air should be forced towards us. Now, circulation or horizontal circulation means just circulating the air in the space. and circulation is acting as suppliment to other things like air conditioner. So we can say circulation is related to less speed whereas throw is related to more speed.
We know Power, P = ωT where ω = Angular speed and T= Torque
Case 1 : In case of throw, we get high speed (ω↑). As Power (P) is always constant then Torque(T) should be less to maintain the constant power.
⇒P = ω↑* T↓
So if you need more air to flow that means you need more throw that also mean you need more speed of the fan that means you need less torque. And less torque means less no of blades.
Case 2 : In case of horizontal circulation, we need less speed then torque should be more to maintain the constant power.
⇒P = ω↓* T↑
As in horizontal circulation, you need more torque and more torque is related to more the number of blades.
In tropical countries like India, we need more speed. That's why we prefer less number of blades.
In case of cold countries like Russia, U.K, U.S.A they just need to circulate the air because it act as suppliment to air conditioner or as room heater in the winter. Since they need less speed that's why number of blades are more there.
Now I am doing a comparison of air delivery according to number of blades in case of India. Just mind in India we need more throw and less circulation and cold countries need more circulation and less throw.
Air Flow
|
2 Blades
|
3 Blades
|
4 or more Blades
|
Throw
|
Best
|
Good
|
Bad
|
Circulation
|
Bad
|
Bad
|
Good
|
Now in your mind one question may be arrived if 2 blades fan are best to throw the air then why not we use 2 blades fan instead of 3 blades fan? Now check the next point.
Mechanical Balance
There many kinds of fans like single blade fan, 2 blades fan, 3 blades fan, 4 or more blades fan, even no blades fan also exists.
So how mechanical balance works for a ceiling fan?
Less number of blades means weight is less distributed. So that stability is also less. So when we are considering a single blade fan, it is not at all stable, we can easily judge that. but when we are considering two blades, it is mechanically stable but weight is not uniformly distributed, means not more is uniformly distributed among the blades. In case of 3 blades weight is uniformly distributed among the blades which is manageable. And in case of 4 blades weight is more uniformly distributed.
So we again make a comparison of mechanical balance according to number of blades in case of India.
2 Blades
|
3 Blades
|
4 or more Blades
|
|
Mechanical
Balance
|
Worst
|
Good
|
Best
|
So mechanical balance means less no of blades provides less uniformly distribution of weight that denotes less stability of the fan. In case of 2 blades fan, as the weight is not uniformly distributed that's why there will be pressure and stress on the bearing during running condition that will reduce the longevity of the fan. In case of 3 blades fan, the weight is uniformly distributed among the fan and that will help to increase the life of a fan. That's why 3 blades fan is most preferable.
Drag Force
The force which acts opposite to the relative motion of any object moving with respect to the surrounding fluid is known as drag force.
So in case of fans, more number of blades try to pull the fan in backward. So once you are increasing the blades then more force is moving backward and the amount of stress you are putting on the bearing and the other parts of the fan may reduce their life. Hence more no of blades means more drag force and it may decrease the longevity of the fan.
So again we are making a comparison of drag force according to number of blades in case of India.
2 Blades
|
3 Blades
|
4 or more Blades
|
|
Drag force
|
Less
|
Manageable
|
High
|
Operating Environment
Operating Environment of a fan that depends upon the geographical conditions and height of the room.
As India is a tropical country, most of the areas having high temperature that's why they need high speed from the fan. So only throw is considered for india. If the height of a room is more, then you need more throw of air that means you need the air to reach more to the ground. So if the height of a room is more, then of course 2 blades fan is the first choise so that speed is more, 3 blades is also good to manage.
So again we are making a comparison of operating environment according to number of blades in case of India.
2 Blades
|
3 Blades
|
4 or more Blades
|
|
Geographical Condition
|
Best
|
Good
|
Bad
|
Height of a room
|
Best
|
Good
|
Bad
|
Here geographical condition is considered as tropical condition. We need more throw of the air. That's why 2 blades fan is a best choice, 3 blades fan is also good option whereas 4 blades fan is worst choice
Now we are merging the all comparison according to different condition and choosing the right option.
2 Blades
|
3 Blades
|
4 or more Blades
|
|
Throw
|
Best
|
Good
|
Bad
|
Circulation
|
Bad
|
Bad
|
Good
|
Mechanical balance
|
Worst
|
Good
|
Best
|
Drag force
|
Less
|
Manageable
|
High
|
Geographical Condition
|
Best
|
Good
|
Bad
|
Height of room
|
Best
|
Good
|
Bad
|
When we look at the table and the applied conditions then we can say the 3 blades fan is most preffered choice for India which is mechanical balanced also. and we can also conclude that 4 or 5 blades fan are the best choice for cold countries (like : USA, UK, Russia etc).
So I think you must now have a good idea about why are we using 3 blades fan in India. Now when you will be looking at the fan and thinking why it has 3 blades, you will have something on the back of your mind. If you have any question on this topic please comment below.
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