Why do fans have three blades?

Now, just try to figure this out.. Why do most fans have only three blades? why could it be so?? Hmm...Any idea??

Is there any aerodynamic law that supports the efficiency of using only three blades in electric fans? Think.....! Are you thinking of any kinda complicated theorems in fluid mechanics? Are you trying to solve this query using Bernoulli's principle?

All I can say is that it's a vain attempt!

Actually an electric fan can have any number of blades depending upon certain factors. But, why is it so that most fans have only three blades? Let's see here.

Firstly, the main purpose of an electric fan is to create air-flow. So, a good fan must create a good air-flow with minimal noise. Usually an electric fan has a shaft which is rotated at a moderate speed by an electric motor. The speed of electric fans is chosen in a moderate level for safety purpose and to reduce the noise produced when a fan is operated. There are blades attached to this shaft which rotate along with the shaft.

The number of blades and their shape may vary depending upon the model and aesthetic sense. Even there are certain fans with only one blade. These are usually meant for aeroplane propellers. (see bottom)

Fans may have any number of blades placed at any position. But the weight of the blades must be balanced so that there is maximum efficiency. For that reason, fans with only one blade is not often preferred, as the weight of the blade tend to bend the blade down.

Coming to the arrangement of fans with two blades, it is obvious that these two blades must be oppositely arranged to each other. Similarly in the case of having three blades, each of them must make an angle of 120 degrees with the next blade. 

Now coming to the structure of the blades, each blade is moderately long, thin and bent a little up. Usually metal/alloy blades are preferred for their rigidity and ability to withstand mechanical stress. But, nowadays, there are plastic(polymeric) blades having a comparable strength to metal blades, are used.

Each blade is inclined a bit so that it forces air ahead of it forward. When an electric fan is switched on, the rotation of the blades increases the velocity of the air along the blades (in circular direction) Generally hot air rises upwards. This hot (less dense) air comes to contact with the whirl(rotation) of the blades and are forced back with a little higher pressure. Thus air-flow is created.

An interesting point to note is that an electric fan never creates a cooling effect, by itself. Try switching on a fan in an insulated room. After some time, the temperature will rise a bit. This is because, the electricity used by fan is not completely converted into mechanical energy, as per the second law of thermodynamics. Some amount of the electric energy is converted into heat energy due to the resistance of coil and several other effects and thus the temperature rises. But every-time when we are laid down under an fan, we feel cool breeze, isn't that true? How it happens?

The cooling effect produced by a fan is due to the fact that the air it pushes down makes our sweat evaporate at a faster rate thereby decreasing our temperature. Thus, we feel chill! So, forgot your tension, sit back and relax!

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Images in the article are taken from the web.

Why can't we push a bus from inside?

Now that we are all outing for a picnic. The bus driver shouts as there's a failure in the engine's start-up. We will do what all we can do! Some will panic while some will make others panic and some will shout at the driver and the rest will look cool undisturbed. The most optimistic approach to this situation is pushing the bus till it starts up. We all know that. While everyone is trying to push the bus, what if one pushes the bus from inside??

It's absurd idiot-ism. But "Why actually we  can't move a bus from inside?" Hmm?? Let us give it a try.

According to Newton's first law of motion, "Every body continues to be in the state of rest or in uniform motion, until an external force acts upon it".

Newton has well described the law by including the term "external" which says that there is no change of position of the object( or its centre of mass) without the application of an external force. But what exactly is this "external force"? Well, any "unbalanced" force acting on the system is said to be an external force. 

In order to get a clear picture, we shall compare the properties of internal and external forces. Generally speaking, any internal force is "balanced", i.e, there are forces whose resultant is zero, whereas there is a finite resultant in case of an external force.

When we are pushing the bus from inside, our hands are providing a finite force on the walls of the bus, while our legs are pushing the floor of the bus with more/less the same force. These forces are normal(perpendicular) to each other.

These forces cancel and the resultant comes out to be zero. Hence we cannot move the bus. 

However if there is no friction and if we run from one end of the bus to the other end, the bus moves in the opposite direction so as the keep the centre of mass in the same place. In the absence of any other force, a system tries to keep the centre of mass in the same place despite the action of a small force.

Try running from the back of the bus and jumping into the front side such that your legs hit the front surface in karate style. As no part of your body is in contact with the bus at the instant when you hit the bus, your force is purely external and moves the bus. 

And that's the same reason "why we can't lift the chair in which we are sitting". 

Can you lift yourself?? Just give it a try.

An Indian boy proves Hawking's theory wrong!

It's been a good weather for India, especially in the field of fundamental sciences and technology, I suppose. One after the other, India has been unveiling its milestone on the hall of flame. Soon after our Venki Ramakrishnan gained the world's attention for his discovery of ribosomal structure, an Indian boy Midhun Namboothiri proved that India has got the world's best brains for that he disputed Stephen Hawking's Black Hole Theory.

The world is stunned at the extravaganza of this young genius who is just a second semester B.Sc. Physics student, who hails from the Majilis Arts and Science College at Puramannur in Valanchery. Midhun has formulated his own theory gaining world attention and leaving his parents Vallaban Namboothiri, a temple priest and Sreedevi, a school teacher to wonder about his immense knowledge in fundamental science.

The high energy particle beam collision experiments which are being performed at CERN are intended to create "miniature black-holes" and to roll back to the conditions of Big Bang. Large Hadron Collider(LHC) which is the world's biggest particle accelerator performs several experiments on high energy particle beam collision especially the collision of high energy proton beam(7 TeV) to reveal the most fundamental laws of nature, based on Stephen Hawking's Black Hole Theory. After having made several analyses upon the Gamma ray emissions, Hawking suggested that after Big Bang, primordial "mini-black holes" were formed. According to his repeated observations and calculations, Stephen Hawking stated that Black holes should thermally create and radiate  sub-atomic particles which is known as "Bekenstein-Hawking Radiation". They radiate until they exhaust their energy and evaporate.

Midhun, through his substantial hope and good scientific skill, however proved that high energy particle beam collision could never produce mini-black holes, giving a good shake to the present scientific belief. He made his point by comparing the energy of the cosmic-rays from particle collisions(artificial) with that of the natural cosmic ray that emanated from the sun. He found that the energy of the cosmic ray that arose from the sun is several times greater than than of cosmic rays produced from particle beam collision.Further he justifies that there is no black hole in the sun and so it is unlikely that there will be a black hole when high energy sub-atomic particle beams collide inside the circular accelerator at CERN.

Initially he presented his theory to the Indian Institute of Science, IISc at Bengaluru. The officials redirected his theories to CERN. Having got inspired by his new idea, the CERN authorities inducted him into the LHC experiment and made him a part of ATLAS collaboration which is one of the six particle detector experiments of the LHC. 

As a crowning appreciation, he has been given online access to the experiments performed by the European Organisation for Nuclear Research (CERN) by the world's biggest brains who considered the "relativity theories" put forth by him. Midhun, now performs experiments through Internet from his home in Naduvattam.

(Thanks to "The Hindu" for the picture)

Why does paper curl when burnt?

Have you ever seen paper curling when it's burnt?
No? It isn't too late. Just try burning a sheet of paper. It curls like this.

But why? 

See, the basic constituents of paper are cellulose fibres and additives like china clay and chalk. Common paper which we use for daily chores, contains around 5% water when dry(believe it or not!) While burning, it loses water and eventually it becomes ash.

Since paper is not a good conductor of heat, heat is not transferred to the entire lamina. When we burn one of the corners, only the region in the vicinity gets heated up and loses water due to dehydration.

The cellulose fibre, being an organic polymer, tends to stretch when it gets heated up while clay and chalk tend to take up(absorb) heat without undergoing any change(state).

As the sheet of paper is being burnt, the heated side loses water faster than the other side. Hot air always rise upwards as it is less denser. Analogous to this, the heated side being less denser tends to rise upwards. But the trace amounts of clay and chalk play a significant role in absorbing the heat supplied. So, the other side tends to remain as it is. Hence it curls upwards.

Now, our part is in analysing the curl of different sheet of paper differing in thickness. It is obvious that thicker paper curls more. This is because, in thick sheets, the two sides are farther apart than in thin sheets.

Also, paper made of different materials will curl to different extent. This can be explained by the percentage composition of water in different types of papers. Percentage of water in dry sheets of paper varies from 2 % - 10%. Newspapers have the maximum percentage of water(around 10%). Even-though we have really "hot-news" on newsprint, it is the coolest paper of all!

Try these for better understanding:

#1. Take a plain sheet of paper and hold it such that the plane is horizontal. Now, burn one of the corners. You will see it curls upwards. Now just turn the sheet upside down(180 degree, it's still horizontal). Even now, it curls upwards. 

#2. Take a thick sheet of paper(post card-thick preferred) and gently wet one of the sides with water. Now, burn it. You can see only the dry part curls.

#3. Roll a sheet of paper and burn it. Curling is seen in that direction which is concave up. 

The Magic "Bloom-box"

Several thousand years ago, the city of Syracuse rejoiced the discovery of Archimedes. No sooner he stepped into the bath tub, than he shouted "Eureka!!!(I have found it)." But this Indian born American scientist makes a difference, as he never comes out to reveal the secrets of his Invention, so called "Bloom-box"- an alternate power source that will lower your electricity bills~!

Dr. K.R. Sridhar, the founder and CEO of Bloom Energy Server technologies in Silicon Valley is the talk of town, today in every nook and corner of the world. He unveils a new fuel cell system that can run on a variety of fuels. The new invention can cut off carbon-dioxide emissions in half compared to the emissions produced by the conventional power sources.


He developed this idea while working in NASA to find a way of producing oxygen for the astronauts who were making their voyage to Mars. This innovation took 8 years to complete perfectly(2002-2010).Cheers!


So, How exactly it works?? Let's see.
Bloom box is just a "planar Solid Oxide Fuel Cell (SOFC)" which uses a common "sand" like powder to produce clean electricity with neither dirty combustion nor corrosive acids. It is made up of a large number of ceramic plates stacked atop each other that can be assembled into a unit of any size.
Each cell is an alloy plate between two ceramic layers and has the dimension 100 mm x 100 mm. Each side is coated with special "inks" that can act as anode and cathode respectively. The green side represents the anode and is coated with Nickel-oxide based ink, whereas the black side (cathode?...yes it is.) is coated with Lanthanum Stronium manganite(probably). 
They use Samarium doped Ceria/Yttria stabilized Zirconia(Zirconium dioxide) electrolyte, catalysed by nickel or Ruthenium-Platinum-Tungsten alloy(PtRuW). 
Each cell produces a power of 25 watt
The scientist has given us the liberty of choosing our own fuel. But gasoline(petrol), bio-fuel and  natural gas are most preferable.(What? Ah!Strictly No Pizzas, No French fries!)
The input bulk can be stored in a talk adjacent to the unit, where the hydrocarbon fuel is to be stored. Oxide ion transfer takes place between air and fuel which pushes electrons into the external circuit, like every electrochemical cell.
The 100 kilowatt module with multiple stacks and components for converting DC power produced in the stacks into AC power to be used domestically, is alone about the size of a parking lot. This module can power a mini-supermarket, says the sources. But this is sufficient to power 1000 homes for a day.


Soft-corners of this "Bloom-box" :
1) It is "green".(Here, I didn't mean the color, ok?) The best feature is that it can hold carbon-dioxide emissions within the limit. Hydrogen is the by-product which is eco-friendly.
2) It eliminates the necessity of grids to distribute electricity. This is one of the significant features of "Bloom-box". Each industry can hire their own unit and reduce the cost of construction and maintenance of electricity grids. 
3) Durability matters! Sridhar tells the media that each unit can live up to a maximum of 10 years.
4) The unit produces no nuisance. It is clean, dry and devoid of corrosive acids. They say it produces no noise, no smell and even doesn't vibrate! Claps!! (Terribly tired of the noise here)
5) I eliminates various energy losses that reduce the efficiency of rotating turbines.
So, this seems to be a good machine, yeah? Err...Let's consider some of the drawbacks to be improvised to have a perfect finish up.


Points to be considered: 
1) High cost of installation. Each 100 kW unit costs $700,000. The fuel cost adds fuel to the fire! Roughly each kWh costs 16 cents. $700,000 is not an easy joke!
2) The efficiency is roughly 52% => 48% of input energy takes the other forms of energy(mainly heat). 
3) High temperature of around 700 degree centigrade is produced. High temperature is required to initiate the electrochemical reaction, which is then sustained by the components.
Using Platinum catalyst lowers the working temperature-range than using nickel, but the cost of platinum must also be considered. 
Such an high temperature may not be amicable. But, an arrangement for fast pyrolysis can be installed adjacent to the unit which converts bio-mass into electric power, as the operating range is close to 700 degree centigrade.


Trivia about this magical "Bloom-box": 
The name "Bloom" was credited to Sridhar's 9 years old son who believed that jobs, lives and environment would bloom. So, this creates a good opinion on the emotional qualities of the Indian-clan scientist.
As Wilson said, "As soon as you find a product that you really like, they will stop making it", Sridhar stands a good solicitor with a good kind of "cost-account" play.
Companies like Google, Walmart and ebay have bought this plan and in few months, these cells will be set into their operation. Other companies include Bank of America, Coca-cola, FedEx, Cox Enterprises and Staples. 
400 kW system powers a building at Google that contains a experimental data center. Walmart has installed Bloom modules at two locations where they generate between 60 to 80 percent of the electricity for the stores.

Watch the CEO's views on Bloom energy server.

http://www.youtube.com/watch?v=uVZAT3U_Jls

I hope, the technology shall cross the ocean soon and reach our holy land!