Advanced Knowledge of Convection in Fluids




Convection is the mode of heat transfer in fluids, i.e., liquids and gases. Water gets heated in spite of being a poor conductor of heat due to convection. Water at the bottom of the pot gets heated when put on a flame. Hot water being lighter moves up and cold water moves down. The process of mixing continues until the whole mass of water has a constant temperature.

Land and sea breezes are caused due to convection currents in air. Water in a pot boils also due to convection.


Convection in liquids

Take a beaker of water. Put some crystals of potassium permanganate through a tube down at the bottom of the beaker. Now remove the tube and heat the beaker with over flame. 
The crystal colours the water so that you can see the convection current in the water. The warm (purple coloured) water rises to the surface. As it does, cooler water falls to take its place. This is because warm water has expanded, and so it is less dense than cold water. The coloured water falls down from the opposite side of the beaker as it is cool, forming a continuous flow or convection current.


Uses of convection

The following are the uses of convection:
  1. Car engines are cooled by convection currents in the water pipes. Water is a very good substance to carry the unwanted heat away from the engine to the radiator.
  2. Land and sea breezes are caused due to convection currents.
  3. Rising air over the land are convection currents and are used by glider pilots to keep their gliders in the sky.
  4. Air conditioners are installed near the ceiling of the room, to allow the setting up of convection currents. The air-conditioner releases cool dry air into the room. As cool air is denser, it sinks. The warm air, being less dense, will rise. The air circulated and the temperature of the air will eventually fall to the desired value.