Heat transfer in a gas or liquid by the circulation of currents from on region to anoth er?

Not sure what you mean here but here goes:-

I think you are after the explanation of conduction. This describes the fluid dynamics of materials in relation to temperature. When an object (the air around us or water in a boiling pan) is heated is becomes less dense and will move to the surface where the denser object will move to the bottom. This is not the case in a vacumn where heat can only travel by radiation.