Why can the thermos keep warm?2019-07-24
There are three ways of heat transfer: hot radiation, hot convection, and heat conduction. Under the illumination of the sun, people will feel the heat of the body. This is because the heat of the sun has hit us. This is called hot radiation. The best way to prevent heat radiation is to block it back. The best material for reflecting heat is the mirror. Pour a cup of boiling water on the table. Because the water in the cup is the same as the temperature in the surrounding environment, this is hot convection. If you put a cover on the cup, you will block the convective road. But this cup of water will still get cold, but it will take longer. This is because the cup has a heat transfer property, which is called heat conduction. The thermos bottle is made of double-glazed glass. Both layers of glass are coated with silver. Like a mirror, it can reflect the heat rays back, which cuts off the passage of heat radiation. The vacuum between the two layers of the thermos bottle destroys the conditions of convective conduction. The thermos cap uses a cork that is not easy to transfer heat, which blocks the convective heat transfer path, perfectly blocks the three roads of heat transfer, and the heat can be retained for a long time. However, the heat insulation of the thermos is not so ideal, and some of the heat can still run out, so the holding time of the thermos has a certain limit. The function of the thermos is to maintain the temperature of the hot water in the bottle, to cut off the heat exchange between the bottle and the outside of the bottle, so that the "heat" inside the bottle can not be discharged, and the "cold" outside the bottle cannot enter. If you put a popsicle in the thermos, the "hot" outside is not easy to run into the bottle, and the popsicle is not easy to change. Therefore, it is scientific to call a thermos a thermos because it can protect both "hot" and "cold".