A vacuum bottle is a vessel that is designed to maintain a consistent internal atmosphere by obstructing external temperatures and preventing the intrusion of outside bacteria.
Sir James Dewar, a British physicist, is credited with the invention of the modern vacuum flask in 1892. During his research on gas liquefaction, he needed a container that could insulate gas from external temperatures. He approached a glass technician named Berg, who created a double bottle for him. The inner walls of the two layers were coated with mercury, and the air between them was removed to create a vacuum. The resulting vacuum bottle, also called a "Du bottle," can maintain the temperature of its contents for an extended period of time, regardless of whether it is hot or cold. Because it is primarily used for heat preservation of hot water in households, it is commonly referred to as a thermos. The bottle's structure is simple, consisting of a double-layer glass liner vacuum-sealed to prevent heat convection. The glass itself is a poor conductor of heat, and the silver or aluminum plating reflects heat energy within the container. Similarly, if the container holds cold liquids, it prevents heat radiation from outside to inside.
A vacuum bottle is designed to upgrade the product grade using high-tech concepts and complete isolation of the contents from the air. This helps prevent oxidative deterioration and bacteria breeding due to contact with the air. The prevailing vacuum bottle on the market is an ellipsoidal container with a piston at the bottom placed inside a cylinder. The principle behind its design involves the use of spring contraction force to create a vacuum state that prevents air from entering the bottle. Additionally, atmospheric pressure is used to push the piston forward. Despite these efforts, both spring force and atmospheric pressure have limitations in providing enough force, making it difficult to attach the piston too tightly to the bottle wall. Excessive resistance prevents the piston from rising and moving forward, which requires high levels of professionalism from manufacturers in designing these bottles.