Fig. 1 illustrates a typical, vacuum-jacketed dewar. A loose-fitting dust cap over the outlet of the neck tubes prevents atmospheric moisture from plugging the neck and allows gas produced from vaporized liquid to escape.

• 图1说明了一个典型的带有真空夹层的杜瓦瓶。颈部出口上的宽松的防尘盖可以防止空气中的水蒸汽堵塞颈部，同时允许液体蒸发产生的气体逸出。