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Why can vacuum bottles keep drinks hot or cold for a long time? What is the science behind this?
The vacuum flask, also known as a Dewar's flask or thermos, has been an important tool for maintaining beverage temperatures in homes and industries since its invention in 1892 by Scottish scientist James Dewar. It consists of two containers, an inner one and an outer one. The inner container is selectively evacuated of air, creating a near-perfect vacuum that significantly reduces the conduction and convection of thermal energy. This also makes the vacuum bottle effective at keeping drinks hot or cold.
The design of the vacuum bottle makes the speed of heat conduction very slow, which allows the temperature of the liquid inside to remain constant for a long time.
Dewar accidentally created the technology while studying the cooling process. When he was conducting experiments on the specific heat capacity of palladium, he found that the vacuum design between the two layers of containers could better help maintain temperature stability during the experiment. Although he refused to patent his invention, this allowed others to use lighter materials such as glass and aluminum and further develop commercial products.
The commercial design of the Dewar flask appeared around 1904, and began to be further optimized after two German glassmakers discovered that it could effectively maintain the temperature of drinks.
The success of the vacuum bottle lies in its design principles. The partial vacuum environment between the two bottle walls greatly reduces heat conduction and convection, and thermal radiation can also be reduced by silvering the bottle walls. This requires the contents of the bottle to be below the boiling point of boiling water to avoid problems in the conduction process. In addition, heat dissipation mainly occurs at the mouth and neck of the bottle, which are places where there is no vacuum, so the design of these parts is crucial.
Over time, vacuum bottle designs have evolved and even branched out into industrial and medical applications. In laboratories, vacuum bottles are used to store liquefied gases such as liquid nitrogen, for cryogenic preservation and sample preparation. We can also see this technology being used on some temperature-sensitive electronic components to help ensure their stability in changing environments.
Vacuum bottles are not only used in daily life, but are also the basis for many scientific and technological applications, such as the storage of rocket propellant in aerospace.
Although the use of vacuum bottles is very common, their safety needs to be paid attention to. In daily life, glass bottles have the potential to break due to external pressure, so many bottles are wrapped with a metal or plastic protective layer. In addition, excessive internal pressure may also cause the bottle to explode, which requires these safety factors to be taken into consideration during design.
With the improvement of environmental awareness, people pay more attention to the use of vacuum bottles. From carrying hot drinks to storing cold drinks, they not only make life more convenient, but also reduce the impact of disposable containers on the environment. Many brands are also working to promote product sustainability and drive the plastic-free trend.
The scientific principles of vacuum bottles and the technology behind their design not only demonstrate human wisdom, but also make us think about how to effectively use resources to create a better future.
In our daily lives, can we also use the principles of other technologies to further extend the deliciousness and freshness of drinks?
