30. Keeping objects cool

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Energy Transfer and Keeping Objects Cool

Sometimes we need to design objects so that they are kept cool. For example, the circuit boards of a computer need to lose the heat that is generated in the components to avoid over-heating.

Animals have also evolved design features to keep cool in hot climates.

To keep cool, the rate of heat energy transfer to the surroundings via conduction, convection and radiation needs to be made as large as possible. So what design features should the object have?

Ideally, the material should be a good conductor so that the heat can reach the surface easily in order to escape. Metal is an excellent conductor, so circuit boards can move heat energy away from critical areas using metal 'heat sinks'.

The flesh of an elephant may not be a particularly good conductor, but the elephant's blood supply can bring heat from its centre to near its skin.

The shape of the object is important, as the higher the surface area, the faster heat can be lost through convection and radiation as there is more surface for the heat to escape from.

Surface area can be increased by designing 'cooling fins'. In animals, large ears offer an excellent way to lose heat to the surroundings.

Having a dark colour and a matt surface texture will increase the rate of heat transfer via infra-red radiation. This is why an elephant's skin is a dark grey matt colour. Electrical heat sinks are usually painted a matt black.

Finally, the object's surroundings is important. Creating an air flow (ideally of cool air) that makes contact with the object will help it to lose heat via convection.

GCSE Physics Keywords: Heat transfer, Surroundings, Conduction, Radiation, Convection, Colour, Surface texture, Surface area, Air flow

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