Why the same vacuum flask heat preservation effect is different in different time
How to heat preservation thermos bottle Home with thermos can well keep the temperature of hot water, what is the principle? Hot water is cold because of the heat convection and heat conduction and thermal radiation. Thermos bile is made to solve the three problems above. Bottle with the cork from hot and cold air convection; Double layer inside the space between the smoke into the vacuum, solve the heat conduction; Coated with a thin layer of silver on inside, make it become a mirror reflects light and heat reflection, and using the silver layer put heat turned back. In this way, the heat is not lost, the heat preservation effect.
If a cap is put on the cup, the convection of blocking the road. But this glass of water would still be cool, just time longer. This is because glass has the nature of the heat transfer, this is called heat conduction. Hot water inside use double deck glass, two layers of glass on the silver plating, like a mirror, can reflect the heat rays back, it's cut off the access of the thermal radiation. The thermos bottle into a vacuum between the two layers of glass, and destroys the condition of convection conduction. Hot water bottle caps to choose is not easy to heat transfer of cork, partition of convection heat transfer pathway. Perfectly heat transfer of the three roads are blocked, heat can remain for a long time. But the thermos of insulation is not so ideal, there is still a part of the heat can come out, so the thermos heat preservation time have a limit. Thermos of function is to keep the temperature of the hot water bottle, cut off the bottle and bottle of heat exchange, and make the "heat" inside the bottle couldn't go out, outside the "cold" into the bottle does not come. If an ice-sucker is put in a hot water bottle, the "hot" outside is not easy to run into the same bottle, ice lolly is not easy to change. So called thermos flask vacuum flask is scientific, because it can protect "hot", can also be "cold".
There are three kinds of heat transfer way: thermal radiation, heat convection and heat conduction. People under the irradiation of the sunlight, will feel hot, this is because the heat radiation of the sun to us, this is called thermal radiation. The best way to prevent thermal radiation is put it back, reflective heat mirror is the best material. A cup of boiling water on the table, because the flow of the water in the cup and the surrounding air, make the water temperature gradually becomes and the temperature of the surrounding environment, the heat convection.
