Insulation Principle Of Thermos

- Jan 11, 2019-

The modern thermos was invented in 1892 by the British physicist Sir James Dewar. At the time, he was working on a liquefaction of gas. The gas was liquefied at low temperatures. First, a container that could isolate the gas from the outside temperature was designed. So he asked the glass technician Berg to blow a pair for him. In a layered glass container, the inner walls of the two layers are coated with mercury, and then the air between the two layers is removed to form a vacuum. This type of vacuum bottle is also called "du bottle", so that the liquid contained in the liquid can be kept constant for a certain period of time regardless of the temperature of the cold or the heat.

Since the thermos in the home is mainly used for hot water insulation, it is also called a thermos. The construction of the thermos is not complicated, the middle is a double-layered glass bottle, and the two layers are vacuumed and plated with silver or aluminum. The vacuum condition avoids heat convection, the glass itself is a poor conductor of heat, and the silver-plated glass reflects the outward radiated heat energy inside the container. Conversely, if the bottle contains cold liquid, the bottle prevents external heat from radiating into the bottle.

The stopper of the thermos bottle is usually made of cork or plastic, and the two materials are not easy to conduct heat. The outer wall of the thermos bottle is made of bamboo, plastic, iron, aluminum, stainless steel, etc. The bottle of the thermos has a rubber gasket, and the bottom of the bottle has a bowl of rubber pedestal. These are used to fix the glass to prevent collision with the outer casing. .

The worst place for the insulation and cold preservation function of the thermos bottle is around the bottle neck, where the heat is mostly circulated by conduction. Therefore, the bottleneck is always shortened as much as possible, and the larger the capacity and the smaller the bottle, the better the insulation effect. Under normal circumstances, the cold drink in the bottle can be kept at about 4 °C within 12 hours, and the boiling water is around 60 °C.