The vacuum reduces both conduction and convection.
rate of heat transfer between two bodies can be reduced by providing insulation between the two. e.g. As in thermos flask. where the insulation prevents heat flow from liquid/tea stored inside the flask to outside atmosphere
The vacuum flask otherwise known as a thermos flask
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The vacuum reduce heat loss by conduction and convection.
Conduction and convection are reduced by the vacuum between the two glass layers.Radiation is reduced by the mirror plating.
Vaccum between thermos walls does NOT prevent radiation, however the other forms of heat transfer(convection and conduction) are more or less eliminated. Radiation effect of heat transfer may be reduced by applying a layer of reflective material inside the bootles - to reflect the emmision back inwards.
The Thermos (vacuum) flask has a double skinned glass cylinder inside. Between the two walls of the glass cylinder is a vacuum. The glass cylinder is also silvered on all inner and outer surfaces. Both the vacuum and the silvering help to prevent the rapid cooling of a hot liquid, or the warming of a cold liquid. The vacuum inhibits heat transfer by conduction. The silvering reflects the heat and inhibits the heat escaping from the flask. Thermos (often used for a vacuum flask) is a trade-name.Eventually, as anyone who uses a vacuum flask, the once hot drink will have become cool by the end of the day.
Due to open space isolating the flask from external temperature
The flask has a double wall, with no air between the two walls (vacuum)- conduction. The walls are highly reflective silver- radiation. the flask has a small beck that is closed by a stopper or cap-convection.
The vacuum between the two layers cannot conduct heat.The silvering on the inside reflects heat back to the contents.The stopper prevents heat loss by convection.The stopper is made of poor thermal conductors.
There is a layer of vacuum which surrounds the flask, then the inside is covered by shiny material which will reflect the heat back into the flask, there are two lids, and there is an indirect gap of about 0.01mm.
It prevents heat transfer by convection as it prevents contact between the surrounding air and air inside the flask. It prevents heat transfer by conduction as it is a poor conductor of heat.