1.1.2 Transport and storage
The internal functions of a system can often be modelled using only a transport and storage function. The transport functions represents the movement or displacement of physical matter such as solids, liquids or gasses, or of energy in the form of thermal, radiation, potential or kinetic energy.
If water is transported through a pipe, a transport function is used to represent this. Similarly, a transport function can be used to represent the thermal energy contained in the water, which is being transported through the pipe. A transport function is often used to model pumps or valves, as there is a direct correlation between how the pump or valve is operated, and how much water is being transported.