Sankey diagrams remain a cornerstone for visualizing and analyzing material flows within complex systems, such as supply chains, biological cycles, or energy usage in buildings. Their unique ability to depict the magnitude of flow between processes makes them particularly useful in fields where resource flow management is critical. This in-depth guide is crafted to aid individuals in understanding, relating to, and interpreting Sankey diagrams effectively.
### The Fundamentals of Sankey Diagrams
At the heart of Sankey diagrams is the concept of flux — the amount of flow that moves from one process to another. These diagrams are often characterized by two major components:
**1. Vector (Flow Lines):** Each vector represents the amount of flow between two processes. The width of these vectors expands or contracts according to the magnitude of the flow, serving as a visual barometer of the resource intensity of a process.
**2. Nodes (Areas Where Processes Happen):** Each dot or box in the diagram represents a process. The connection between these nodes via the flow lines shows the amount or energy that moves from one process to another.
Sankey diagrams are constructed based on a specific direction of flow, which can be from the left to the right (as common in materials flow diagrams) or from bottom to top (as common in energy flow diagrams).
### Key Aspects to Understanding Sankey Diagrams
**1. Direction of Flow:** Understanding that Sankey diagrams are not directional by default, but their direction is always defined by the context of the particular process or system they represent.
**2. Conservation of Mass or Energy:** Sankey diagrams adhere to the principle of conservation of flow, meaning that all the materials or energy enter from one end (left, bottom) and exit at the other end (right, top).
**3. Scale and Proportions:** It’s important to note that Sankey diagrams are not drawn to scale. The focus is on the flow between processes rather than the absolute size or quantity represented.
**4. Zero-Length Lines:** These are flow lines that appear to have a width of zero at one end or the other, indicating that there is no flow in that direction.
### Interpreting Sankey Diagrams
The effective interpretation of Sankey diagrams relies on recognizing and analyzing the following aspects:
**1. Main Flows and Branches:** Identify the major pathways of flow through the system. These typically represent the primary material or energy streams in the system being analyzed.
**2. Energy or Material Losses:** Look for “stretches” of thick lines ending nowhere or merging back into the system before exiting. These denote inefficiencies, losses, or the conversion of the material or energy to a different form.
**3. Processing Intensity:** Nodes with a large number of incoming and outgoing flow lines imply a high processing intensity. These nodes are likely places of high value-added or conversion, and thus are worth scrutinizing further.
**4. System Bottlenecks:** Identify points where the flow lines narrow significantly. These bottlenecks represent places where the system might be most constrained and are important for process optimizations.
### Creating and Visualizing Sankey Diagrams
Although there are dedicated software tools available for creating Sankey diagrams, it is also possible to draw them manually using graphing tools or spreadsheet software. The following are steps in creating a Sankey diagram:
– **Identify the Processes:** Define the processes you wish to represent in the diagram.
– **Establish Connections:** Identify and define the flow lines between processes.
– **Quantify Flows:** Assign quantitative values to the flows. These could be weights (mass, energy, etc.), volume, or any other relevant units.
– **Calculate Vector Widths:** The lengths of the flow lines will correspond to an aggregate flow measurement. Widths are calculated in proportion to the flows.
– **Draw and Label:** Place nodes for each process and draw the flow lines accordingly. Label nodes and flows to make the diagram informative.
### Conclusion
Sankey diagrams are powerful tools for analyzing and communicating energy, material, and information flows. While their construction and interpretation might initially seem straightforward, a deep understanding of both allows professionals to make informed decisions about system efficiency and sustainability. By focusing on major flows, identifying bottlenecks, and interpreting losses effectively, one can optimize processes, reduce inefficiencies, and drive improvement in material flow management.
