PHYS - Sankey Diagrams and Energy Efficiency

Sankey diagram is a way to depict flows of energy.

In IGCSE Physics, you will come across Sankey diagrams that look like this 👉

- On the left is the total energy input.

- Deviating from the horizontal energy flow to the top or bottom are energy losses.

- On the right is the useful energy output.

- The width of the arrow is proportional to the quantity of the flow.

• There is more energy lost to flue gas than to wall or opening.
• The amount of flue gas losses and heat storage to walls and fixtures is approximately same.
• Useful energy output is approximately half of the furnace fuel input. 

To summarize 👉

Let's try to solve one example from IGCSE Physics past paper 💪

This is a Sankey diagram for the power station.

(i) State the relationship between efficiency, useful energy output and total energy input.

efficiency = (useful energy output) / (total energy input)

(ii) The efficiency of the power station is 36%. The total energy input is 1050 kJ. Calculate the total wasted energy in kJ.

0.36 = (useful energy output) / 1050kJ

useful energy output = 0.36 x 1050kJ = 378 kJ

total wasted energy = 1050kJ - 378kJ = 672kJ

(iii) Name two forms of wasted energy in this power station.

thermal energy, noise/sound, frictional heating, etc.

(i) State the relationship between efficiency, useful energy output and total energy input.

efficiency = (useful energy output) / (total energy input)

(ii) The efficiency of the power station is 36%. The total energy input is 1050 kJ. Calculate the total wasted energy in kJ.

0.36 = (useful energy output) / 1050kJ

useful energy output = 0.36 x 1050kJ = 378 kJ

total wasted energy = 1050kJ - 378kJ = 672kJ

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