Heat transfer

 

In the previous post about heat and temperature, we established that heat flows from a hotter body to a cooler body and not the reverse. In this lesson, we shall learn three different ways by which heat can be transferred depending on the medium. Heat transfer can occur in three ways which are: conduction, convection and

radiation

• Conduction

When you place one end of a metal rod in a burning fire and hold the other end of the rod, you will discover that after some minutes the end of the rod you are holding becomes warm. When you put a silver spoon in a hot tea cup, the handle of the spoon becomes hotter than it was before. These examples are as a result of transfer of heat by conduction.

Conduction is the transfer of heat through a solid material without the displacement of the particles of the material. In conduction, heat is transferred from the hotter region of the solid to the colder region.

Most metals e.g copper, aluminum, iron are good conductors of heat ( i.e they allow heat energy to flow through them easily) while other non metals e.g. water, air, plastic, wood are poor conductors of heat or insulators. This is why most utensils are made of metals with wooden or plastic handles in order to prevent the flow of heat to the handle.

• Convection

Though liquids and gases are poor conductors or insulators, heat energy can be made to flow through them by the process of convection. This is why water can be heated on a hot stove or cooker. Heat is transferred by the actual movement of the water molecules. In this case, the heated molecules of the liquid gains more kinetic energy and begins to move from the hotter region to the cooler  region of the liquid.

Convection is defined as the process of heat transfer in a fluid (liquid or gas) by the motion of the heated molecules from the hotter to the cooler parts of the fluid.

• Radiation

When you sit close to a fire place, you will start to feel warm even without touching the fire. Have you ever wondered how the heat from the sun reaches the earth? These are as a result of the process of heat transfer by radiation.

Radiation is the process of transferring heat from a hot body to a cooler body without a material medium and without contact between the hot body and the cold body. In conduction and convection, material medium is involved while no material medium is required for radiation to occur. The form of heat energy transferred in radiation is known as radiant energy. 

Since there is no material medium involved, the radiant heat can be said to be electromagnetic radiation like the Infra-Red which travels at the speed of light.