Modes of heat transfer and mass transfer

Heat transfer happens due to various reasons. The modes of heat and mass transfer can be gases and liquids too. The conduction happens between different gases due to the mingling of molecules and their striking against each other. Conduction happens everywhere, but it can’t happen when the matter is bulky. Temperature gradient is the main reason why it is induced.

Conduction on the other hand depends on the density of the material. Since liquids and gases have lower density as compared to solids, they do not experience much conduction. It is because in gases, the molecules are placed distant to each other, which results in lesser interactions between them, hence low transfer of heat. However, this is not the same when the temperatures of the gases increase.  Therefore, under increased pressure, there is an improvement of gas conductivity. Even solid bodies experience conduction.  Gases, liquids and solids are Modes of heat transfer and mass transfer.

Therefore, even atmosphere experiences some kind of convection. It happens when hot air passes one from land to another. Therefore, the circulation of hot air happens because at the equator, the radiation every unit of land is quite high. It reduces as the latitudes start to increase which causes air at the equators to circulate towards both north and south poles. Even longitudes experience some kind of circulation. It happens because water retains more heat than land. Therefore, the sea breezes happen in an attempt to equalize the temperature of both land and water.

Mass transfer refers to the state in which molecules of mass transfer from one body to another due to density difference. So, molecules move between different systems. Mass transfer coefficients determine the rate at which this transfer will happen.  The higher the density, higher will be the movement as thermodynamics says. This is the law of mass transfer.

Questions

• What is atmospheric circulation?
• Describe a convection cell.