Materi Lesson Plan KD 4.2

Heat Transfer

Heat transfer from an objeck with higher temperature to another with lower temperature. There are three ways of heat transfer conduction, convection and radiation.

1.      Conduction

Conduction is heat transfer without any transfer of atoms within the conductor. For example, if an iron rod is heated at one end, then the heat will flow to the other end.

If L is the conductor length, A is the area, and temperature difference of both ends is it ∆T, then the amount of heat (H) flowing through the conductor is formulated as:

With H = Q/t is the amount of heat flowing per unit of time and k is the  thermal conduction coefficient.

Conduction can be regarded as the effect of kinetic energy transfer from one particle to another via collision. A heated particle will vibrate with great energy, then it will transfer some of these energy to the particle next to it. And so that particle, and so on and so fort until a conduction takes place.

2.      Convection

Heat transfer by convection only take place in liquids and gases(fluids) because their particle s can move freely. Convections is heat transfer that is accompanied by particle transfer.

Notice when water is heated. As the water boils, we can clearly see the flow of heat represented by bubbles coming up from the bottom to the surface.

The water in the lower place receives heat from flame earlier than their upper counterpart. This heated water expands, its specific mass is decreasing, therefore they move upward. Its palce is than occupied by the upper water which is cooler and has greater specific mass. And in turn, this water will undergo the same process and caries heat as it moves upward.

3.      Radiation

Heat transfer via radiation does not require any medium. For example, sun rays reaches the earth via an empty space, nonetheless we can still feel ist heat.

Heat radiation is one form of energy emission. Josep Stefan (1835-1893) investigated heat radiation on object and found the formula: