What is energy flow diagram?

Energy flow diagram also known as Sankey diagram is a specific type of flow diagram in which the width of the arrows is proportional to the quantity of energy. Length of arrows has no bearings with the quantity of energy. These diagrams indicate the flow of energy in a process and help identifying the quality and quantity of energy. Quality of energy is indicated by the temperatures of inputs and outputs of energy. The input of energy begins from the left of the diagram. The outputs of energy are shown on the right side of the diagram as illustrated in the following figure: