Dear Bhumit,

Methods of Heat Transfer

• There are three primary methods in which heat can transfer: radiation, conduction and convection. Before understanding those, it''s best to understand a bit about heat itself. Heat is the excited motion of the atoms of a substance. Heat behaves similar to most other things in that it flows from areas of high concentration--in this case, high heat--to areas of low concentration, or low heat. This diffusion of heat energy from high heat to low heat is all done in order to reach equilibrium. Equilibrium is defined as having equal quantities across a measured area; in this case, that means having the same temperature all over what you are measuring. This diffusion of heat is called entropy, discovered by Rudolf Clausius in the 1850s.

Radiation

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  Radiation is the transfer of heat from one object to another through empty space, be it a vacuum or any other medium. Radiation can be observed in instances such as campfires. You can be standing 5 feet away from the fire and still feel its warmth, meaning that the heat from the fire radiated over empty space to reach you. In essence, thermal radiation, in the form of waves, which carry energy, travels through space from anything emitting heat and gets absorbed by anything near that emitter that can absorb the heat. A very common term heard when discussing heat transfer, also known as thermodynamics, is a black body. A black body is any object--not necessarily a black one--that absorbs 100 percent of the radiation hitting it and also emits 100 percent of its energy, theoretically. Currently no black bodies are known to exist. But many things, such as stars, come very close. With regard to radiation, a black body would absorb all of the radiated energy given off by an object.

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Conduction

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  Conduction is the transfer of heat from two objects that contact each other. This means that the two objects between which heat is transferring must be in relatively close proximity. An example of conduction is when your hand touches a very hot cooking pan. The heat from the pan is transferred directly to your hand. However, this system of transfer between your hand and the pan is also demonstrating radiation because the pot is radiating heat that is being absorbed by your hand. Conduction is a very efficient means of transferring heat due to the fact that less heat dissipates when two objects touch than when heat is being transferred through radiation.

Convection

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  Convection is the transfer of heat throughout a single substance due to a temperature difference between one part of the object and another. This temperature difference is called a temperature gradient. This is best shown in the example of boiling water. When you apply heat to the bottom of a pot of water, the water near the heat gets hot fast but the water near the top gets hot slower, making it cooler than water closer to the heat. Because heat rises, water from the bottom of the pot will rise and replace water near the top of the pot, which is cooler. The cool water sinks until it''s near the heat and becomes hotter than the water above it, causing the process to repeat. This process demonstrates a convection current. Convection currents can be seen everywhere in nature. They cause the currents in the ocean, the thermals that cause parachutists to rise upward, and the transfers of continental mass that drive plate tectonics, among other things.