Heat Transfer
Heat transfer is the movement of heat energy from one point to another due to the difference in temperature. The heat can be transferred either by conduction, convection or radiation. In conduction, heat is transferred when there is a collision between neighbouring atoms or molecules. Convection is when there is a bulk movement of the molecules in the fluid. Radiation is heat energy transmission in the form of waves. During radiation, there will not be any interaction or movement of the particles.
Conduction
In simple terms, conduction is the process of transfer of heat from one object to another when the two objects are touching each other. When our cold hands touch a hot cup of tea, we feel the warmth in our hands due to ‘conduction’ which has caused some heat transfer from the hot cup to our hands. Conduction mainly occurs in solids and liquids where the atomic particles are closely packed. There is a collision between the particles during conduction. When heat is applied on one part of the solid, the atoms in that part start vibrating rapidly. Thus they hit their neighbouring atoms and those atoms start to vibrate too. It is in this manner that the energy is transferred in conduction.
The heat transfer increases when there is a larger difference in temperature between the substances that are in contact with each other. An example of conduction is when you accidentally touch a hot pan, the heat is transferred from the hot pan to your hand. Not surprising that most pans will have their handles covered in some insulating material. Although the handles of the pans are not directly above the flame, conduction causes the handles of the pans to get heated too.
As the particles in solids are more closely packed, they are more likely to collide with each other and thereby conduction is more common in solids. In liquids and gases, the particles can move past each other without colliding. Thus conduction is not often seen in liquids and gases.
Is Boiling Water Conduction or Convection
Let us understand the concept of heat transfer by considering the example of boiling water. Is Boiling water conduction or convection? When a pan of water is placed on the stove, the pot is heated because of conduction, this pot, in turn, heats up the water molecules. As the water molecules closer to the wall of the pot get heated up, they will rise up and get replaced by the cooler molecules of water. This continuous current will result in the heat transfer due to convection within the water.
In fact, some water boiling in a vessel over a flame of fire from a cooking stove has all three modes of heat transfer occurring at different levels. While it is ‘convection’ that is helping the heat from the fire reach the vessel, it is ‘conduction’ which transfers the heat from the bottom of the vessel to the sides of the vessel (and the handle of the vessel, if any). In the water contained in the pot, the convection currents help the water get heated uniformly as the hot water molecules keep rising up and get replaced by cooler molecules. If we bring our hands or face near the flame, we can feel the heat of the flame through ‘radiation’.
