We have learnt that hot air is less dense therefore it rises up.
But we also learnt woolen clothes trap air that get warm by body heat, and act as a insulation layer dont allow heat to escape from body.
Why does not that hot air in sweater (woolen clothes) rise away and cool air from outside take its place (like in land breeze sea breeze) so that no insulating layer form, ?
Same why does not hot air above tea rises and make way for cool air from surrounding to come help tea to cool so that no need to blow over tea?
Best Answer
It does, but it does so more slowly than if there were no sweater because the sweater fibers block the air flow. The sweater basically lowers the convective heat transfer coefficient between the skin and the ambient air outside the sweater.
It does, but it does so more slowly because it is natural (unforced) convection, as opposed to the forced convection when blowing over the tea.
Hope this helps.