Energy
Energy and Thermal Physics

# The first fridges

Stories from Physics for 11-14 14-16

There is evidence that, in the Egyptian Old Kingdom around 2500 BC, and as early as 3000 BC in India, evaporative cooling technology was used to cool liquids. To achieve the cooling effect, a porous earthenware pot with a narrow neck was filled with water. Water seeped through the porous earthenware walls of the container and evaporated, cooling the water remaining inside. An evaporative cooler’s efficiency is dependent on the humidity of the air — the theoretical maximum change in temperature possible is equal to the difference in reading between a wet and dry bulb thermometer.

Before the development of electric refrigerators, Australians made use of ‘Coolgardie safes’. The devices, invented in the Coolgardie gold mines in Western Australia, consist of a cupboard made from metal mesh with the walls lined with hessian. A container on top of the device kept the hessian damp via a link pipe. As water evaporates from the hessian, it cools the contents of the ‘safe’ and draws water down from the tank via the pipe. An evaporative cooler can extend the shell-life of tomatoes from 2 to 20 days.

Recognised as one of Junior Chamber International’s Ten Outstanding Young Persons of the World in 2010, Emily Cummins is an inventor and entrepreneur from Leeds. Emily reports that since her grandfather first handed her a hammer at the age of four, she was inspired to create. During her degree she invented a sustainable fridge that uses dirty water to cool food by evaporation. Her cylindrical fridges are now used across southern Africa.

### References

###### Energy
appears in the relation ΔEΔt>ℏ/2 ΔQ=mcΔθ E=hf E ∝ A^2
has the special case Photon Energy
is used in analyses relating to Emission/Absorption Spectra Phase Change