The general concept of heat preservation is short-time heating. After the circuit is connected, if the water temperature is lower than 50℃ (the critical temperature set by most brands), the thermostat will automatically turn on and the water heater will start heating. When the water temperature reaches the preset temperature of the water heater (75℃ ~ 85℃ for most brands), the thermostat will close and the water heater will stop heating. In this way, the so-called heat preservation is realized. Even without a drop of hot water, the power consumption of the water heater is only about 2 degrees /24 hours. If you don't use hot water at all in your daily life, then cutting off the power supply is energy-saving. Someone at home often takes a bath, or keeps warm and saves electricity. If you travel far, or take a few baths every week, you can also unplug the power supply and plug in the electric heater when you use it, which is not very power-consuming.

Principle of insulated water cup:

Modern thermos was invented by British physicist Sir James Dewa in 1892. At that time, he was engaged in a research project on liquefied gas. In order to liquefy the gas at low temperature, he first needs to design a container that can isolate the gas from the outside temperature, so he asks the glass technician Berg to blow a double-layer glass container for him, coat the inner walls of the two layers with mercury, and then vacuum the air between the two layers. This kind of thermos, also called "Dupin", can keep the liquid in it unchanged for a certain period of time whether the temperature is cold or hot.

Because the thermos bottle is mainly used to keep warm hot water in the family, it is also called thermos bottle. The structure of thermos bottle is not complicated.

There is a double glass bottle liner in the middle. These two layers are evacuated and plated with silver or aluminum. The vacuum state can avoid thermal convection. Glass itself is a poor conductor of heat, and silver-plated glass can reflect the heat energy radiated from the container. On the contrary, if the cold liquid is stored in the bottle, the bottle can prevent the external heat energy from radiating into the bottle.

The cork of thermos bottle is usually cork or plastic, both of which are not easy to conduct heat. The shell of thermos bottle is made of bamboo, plastic, iron sheet, aluminum, stainless steel and other materials. There is a rubber gasket at the mouth of the thermos bottle and a bowl-shaped rubber pad at the bottom of the bottle to fix the glass liner and prevent it from colliding with the shell.

The worst heat preservation and cold preservation function of thermos bottle is around the bottleneck, where the heat is mostly circulated by conduction. So when manufacturing, always try to shorten the bottleneck. The larger the capacity, the smaller the bottle mouth, and the better the insulation effect. In general, the cold drink in the bottle can be kept at about 4℃ within 12 hours. Boiling water is about 60℃.