# How is heat transmitted worldwide

## Heat transfer

### Introduction and Definitions

warmth and the Transferring heat are an important part of human life. With heating, we generate heat when it is cold outside. We also need heat for cooking. Thousands of years ago, the first humans kindled fires because they wanted to warm themselves.

### Definitions and terms

Warmth is one Form of energy and can pass from one body to another. There are three types of Heat transfer: The Conduction, the Heat flow (convection) and the Thermal radiation. In everyday life we ​​use energy converters that generate thermal energy from electrical or chemical energy. The quality of such energy converters is determined by the Efficiency.

\$ \ eta = \ frac {Q} {E} \$,

the ratio between the heat generated \$ Q \$ and the energy fed in \$ E \$. Since there are always losses, \$ \ eta <1 \$. Another measure of the quality of an energy converter is that thermal performance

\$ P = \ frac {Q} {t} \$,

with the unit watt (W). It describes the heat generated per time.

### Conduction

The Conduction takes place at direct contact two bodies (pot and hob) or within of a body (spoon in tea) instead. Heat excites the smallest particles in a substance Vibrations that are passed on to the next neighboring particles. In this way, the whole body gradually warms up: a metal spoon in hot tea becomes hot even though only the tip is in the tea. It finds Heat transport without matter transport instead of. There are also good and bad Heat conductor. A wooden spoon, for example, hardly gets warm. Try some for yourself Experiments on heat conduction.

### Heat flow (convection)

In the Heat flow (convection) the heat transport works over Flows in gases or liquids. If you have ever bathed in a lake, you will have noticed that there are colder and warmer places: In the water there are currents of different temperatures. Even a heater only works through convection, as it heats the air in its vicinity and then distributes it throughout the room.

So convection is one Heat transfer with matter transport. The following applies to both liquids and gases: warm layers rise and cold layers fall down. This ensures a constant exchange of heat.