The determination of the heat transfer rates to or from a system and, therefore, the heating or cooling times and temperature variation is the subject of the science of heat transfer.
The term convection comes from the Latin convectare, which means to take to a place. In heat transfer, the concept of convection refers to the process of moving thermal energy from or to a solid by means of an adjacent fluid in motion, in the presence of a temperature gradient
P&ID is defined as a diagram of piping and instrumentation and it shows the process flow in pipes, as well as, the equipment installed and instrumentation.
In the analysis of heat transfer processes, some bodies can be considered to behave as a unit, with an internal temperature essentially uniform (although not constant) at all times during the heat transfer process.
When speaking about the transfer of any physical property, in general three basic concepts of transport are considered: molecular, advective and convective. The concept of convection is considered a combination of molecular transport and advective transport.