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Heat transfer and efficiency

Heat transfer by radiation


All objects give out and take in thermal radiation, which is also called infrared radiation. The hotter an object is, the more infrared radiation it emits.

Light from the sun reaching earth

Infrared radiation is a type of electromagnetic radiation that involves waves. No particles are involved, unlike in the processes of conduction and convection, so radiation can even work through the vacuum of space. This is why we can still feel the heat of the Sun, although it is 150 million km away from the Earth.

Some surfaces are better than others at reflecting and absorbing infrared radiation.

Comparison of surfaces abilities to reflect and absorb radiation

colourfinishability to emit thermal radiationability to absorb thermal radiation
darkdull or mattgoodgood

If two objects made from the same material have identical volumes, a thin, flat object will radiate heat energy faster than a fat object. This is one reason why domestic radiators are thin and flat. Radiators are often painted with white gloss paint. They would be better at radiating heat if they were painted with black matt paint, but in fact, despite their name, radiators transfer most of their heat to a room by convection.

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