Sankey diagrams put a visual emphasis on the major transfers or flows within a system.

Sankey diagram - represents material, energy or cost flows with quantity proportional arrows in a process network.

It is a flow map, overlaying a Sankey diagram onto a geographical map.

Documentation of consumption (as a basic analysis of material and energy flows, e. g. with a Sankey diagram)

Sankey diagrams are a specific type of flow diagram, in which the width of the arrows is shown proportionally to the flow quantity.

Odum started with an overall model and in his early work used a diagramming methodology very similar to the Sankey diagrams used in chemical process engineering.

One of the most famous Sankey diagrams is Charles Minard's Map of Napoleon's Russian Campaign of 1812.

Often, Sankey diagrams show conserved quantities within defined system boundaries, typically energy or mass, but they can also be used to show flows of non-conserved quantities such as exergy.

Fig 1 illustrates the energy exchanges in a CLC system graphically, and shows a Sankey diagram of the energy fluxes occurring in a reversible CLC based engine.

While the first charts in black and white were merely used to display one type of flow (e.g. steam), using colors for different types of flows has added more degrees of freedom to Sankey diagrams.

Just four years later in 1902 Robert Henry Thurston among others acknowledged, that the heat distribution of the then modern steam engine was best shown by the use of the so called "Sankey Diagram".

Sankey diagrams are named after Irish Captain Matthew Henry Phineas Riall Sankey, who used this type of diagram in 1898 in a publication on the energy efficiency of a steam engine (see reproduction in, page 8).

In an 1898 article about the energy efficiency of a steam engine in the Minutes of Proceedings of The Institution of Civil Engineers Sankey introduced the first energy flow diagram: a visualisation to be christened Sankey diagram.