Portfolio Activity! This counts to ward your final grade!

What are my objectives while studying this topic?

You will learn how to draw Sankey Diagrams, and use the technique to construct a Sankey Diagram of a real process as a result of direct observation and measurement.

Sankey Diagram 1

Why is this important?

Sankey diagrams are extremely useful diagrammatic tools. They convey information about the type of energy transfer AND the amount of energy being transferred. They can be used as a tool to show efficiencies and processes as a whole allowing engineers to easily see the parts of a process that need to be improved.

Condensing Power Plant

Can I get an introduction to this topic?

Yes, why not have a look at the following:

(Produced by Don Evans, King Edward VI Aston School (9 May '07))

Who came up with this Sankey diagrams?

In 1898 Matthew Henry Phineas Riall Sankey, an Irish Sea Captain, invented a diagrammatic way of representing the energy flow though a ship’s steam engine. The system used a series of branching arrows to represent the energy transfers taking place in the engine and the size (width) of the arrow represented the amount of energy being transferred. Ever since then diagrams used to represent energy transfers (and other processes) have been named in his honour, hence Sankey Diagrams.

Matthew Henry Phineas Riall Sankey

Let’s get to it: what do I need to do?


This piece of work counts towards your Portfolio Grade! You need to produce an annotated Sankey Diagram from experimental data.

Part A

Measuring Energy Flow Demonstration


In this part of the activity you are asked to make measurements of the energy flowing into and out of a mains transformer. Look at the following diagram of the experiment:


A 12V mains power supply is connected to a mains electricity consumer unit, which in turn is connected to mains. A rheostat (acting as a fixed resistor) is connected in series with an ammeter and the power supply, and a voltmeter is connected across the rheostat. The power supply is turned to 12V, the reading on the consumer unit is recorded, the power supply is turned on, a stopwatch is started, and the current and potential difference are then recorded when they reach equilibrium. After 60 s the mains is turned off, and the electricity consumer unit reading is measured and recorded.


The whole procedure can then be repeated at different power supply voltages and different resistances.


You are expected to record your own unique measurements for one particular setting.


Part B – Calculating the energy flow


The electricity consumer unit records the electricity consumed by the experiment in ‘units’ or ‘kWh /kilowatt-hours’. 1 unit / kWh = 3.6 x 106 J of electrical energy. (Some digital consumer Units record directly into Joules)


Use this information to calculate the total electrical energy input to the power supply by the consumer unit in 60 s – in Joules.


To calculate the useful electrical energy output to the rheostat (and then converted to heat energy by the rheostat) use the following formula:


Useful Energy Output (J) = Current (A) x Potential Difference (V) x Time (s)


To calculate the wasted electrical energy (converted to heat by the transformer in the power supply) use the following formula:


Wasted energy = Total Energy Input – Useful Energy Output


Part C – Drawing a Sankey Diagram


Using a sheet of graph paper and a suitable scale, (or a Sankey diagram Drawing software tool), construct a Sankey Diagram of your data.


Use your Sankey Diagram to calculate the efficiency of the power supply on your setting(s). Use the formula:


%efficiency = Useful Energy Output x 100%

Total Energy Input


Part D – Annotating your Sankey Diagram


You now need to annotate (label) your diagram to show what each part is, AND HOW YOU CALCULATED IT.


You need to include the calculation of efficiency on your diagram.



Can I make these diagrams using software tools?

Yes, have a look at the following links for free software tools:



Part of your assessment requires you to use other peoples work, such as adapting standard procedures or finding out and using information on the internet. When you use information like this you need to reference it properly in your reports. The following link takes you to a suitable method for referencing:


Quick guide to referencing

Portfolio Follow-up

Portfolio work will be marked in accordance to the appropriate assessment criteria:


What are the key words to learn and use?

  • Sankey Diagram

  • Useful

  • Wasted

  • Efficiency

  • Consumer Unit

  • Rheostat

What will I be expected to be able to do after studying this topic?

Design, use and apply simple Sankey diagrams to describe energy transfers involved in the process of generation of heat and electricity by carbon-based (fossil) fuels

How long will this topic take to study?

On average you’ll be looking at about four hours. This includes taught time and independent study.

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