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Energy Glossary

Energy Flow Diagram

Energy flow diagrams show the energy flows in a more or less complex system. E.g. a wood fire or a modern combined cycle power plant.

The concept of energy flow diagrams

Understanding the concept of energy is a heavy task because energy exists in different flavours like e.g. mechanical energy, radiation energy or chemical energy. Energy flow diagrams help to understand energy flows in natural and artificial devices which convert energy:

  • Example 1:
    The sun provides energy in the form of light, a small spectrum of the full electromagnetic radiation spectrum. Light passes through space and is partially reflected by clouds, oceans and land surfaces. The other part is absorbed mostly by darker land and the oceans surfaces. There it is converted into heat - land and water heats up. Water is evaporated, air is heated up and starts to move. Some heat is radiated back into space as infrared radiation. That situation can be visualized by an energy flow diagram showing the different flows of the different types/flavours of energy.
  • Example 2:
    A simple system is a torch with an incandescent lamp. Electrical energy provided by batteries is used to heat up a very thin filament in an incandescent lamp. At a temperature of roughly 2500 Kelvin (ca. 2200 degree centigrade) this filament emits light, infrared radiation and heat.


Example for a simple energy flow diagram
corresponding to example 2 above.

Types of energy flow diagrams

Most energy flow diagrams shows energy flows qualitatively - meaning that the arrows representing the energy flow have the same thickness or the thickness gives some expression about the importance of some energy flow.

Better energy flow diagrams represent the energy flows in scale. The line width is proportional to the energy flow they represent. These energy flow diagrams are a good base for the analysis of energy flows in systems which have to be optimized for energy demand and heat release - a good example are space satellites which have to be lightweight and therefore need a lightweight power source/a reduced energy demand to be operated.

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