Conduction and convection?
can anyone explain how a thick woollly jumper reduces energy transfer by conduction and convection?
Answers:
conduction and concection have nothing to do with it. its insulation that reduces energy transfer. the air between the two layers of clothing traps heat, just like in double glazing. hope this helps
wool is an insulator, or barrier. it doesnt conduct heat. it stores it, and releases the energy.. (well it stays warm after you take it off the radiator doesnt it?)
Wool makes a POOR thermal conductor because the fibers do not conduct heat well, they are curly, providing a longer path from end to end, and the air spaces between them act as an insulator as well, making convection difficult, as air cannot pass easily through the weave.
If it were wet, it would lose the ability to trap air and heat, because it becomes more conductive, and transfer convectionary heat also
Heat is transferred in 3 main ways - conduction, convection and radiation.
Convection occurs in air where hot air rises and is replaced by cooler air from below. Conduction is transfer of heat directly along a medium, e.g. metals are good conductors of heat. Insulators are materials that conduct heat very poorly, e.g. plastics and of course wool.
A woolly jumper prevents heat transfer mainly by being a poor conductor, but also by trapping air that happens to be a poor conductor of heat also. It needs to be a good fit since a baggy jumper would allow heat to escape by convection.
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Answers:
conduction and concection have nothing to do with it. its insulation that reduces energy transfer. the air between the two layers of clothing traps heat, just like in double glazing. hope this helps
wool is an insulator, or barrier. it doesnt conduct heat. it stores it, and releases the energy.. (well it stays warm after you take it off the radiator doesnt it?)
Wool makes a POOR thermal conductor because the fibers do not conduct heat well, they are curly, providing a longer path from end to end, and the air spaces between them act as an insulator as well, making convection difficult, as air cannot pass easily through the weave.
If it were wet, it would lose the ability to trap air and heat, because it becomes more conductive, and transfer convectionary heat also
Heat is transferred in 3 main ways - conduction, convection and radiation.
Convection occurs in air where hot air rises and is replaced by cooler air from below. Conduction is transfer of heat directly along a medium, e.g. metals are good conductors of heat. Insulators are materials that conduct heat very poorly, e.g. plastics and of course wool.
A woolly jumper prevents heat transfer mainly by being a poor conductor, but also by trapping air that happens to be a poor conductor of heat also. It needs to be a good fit since a baggy jumper would allow heat to escape by convection.
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