Vacuum flasks are thermally insulated double wall vessels. The narrow space between the two walls is evacuated which dramatically reduces thermal transfer. The near absence of air molecules minimizes thermal transfer by convection. Reflective surfaces in the vacuum space minimize radiant thermal transfer and the separation between the inner and outer wall minimizes thermal transfer by conductance. In summary, a vacuum flask thermally decouples a flask's payload from the external environment. The most common application of vacuum flasks is the storage or transmission of cryogenic fluids such as liquid nitrogen or liquid natural gas which can be maintained at extremely very low temperatures for extended durations.
Vacuum flasks provide very effective thermal insulation. The insulation is passive and the largest portion of thermal transfer into the vacuum flask occurs by conductance through the neck of the inner wall and by the electrical wiring or mechanical feed through entering the vacuum flask (thermal leakage). The small amount of conductance eventually raises the inner temperature within the vacuum flask which limits the payload's duration within hostile high temperature environments to a finite duration. Vaccum Flasks are often used as cola water bottle, insulated sports bottle or insulated coffee mug.
An additional form of heat gain in the vacuum flask is the heat generated by the electronics within the vacuum flask. Since the vacuum flask thermally decouples the contents of the flask from the external environment, the heat dissipated by the electronics can not escape from the vacuum flask and consequently increases the inner temperature within the vacuum flask which also limits the payload's duration within hostile high temperature environments.
Similar with the vacuum flasks, a thermo travel coffee mug is designed for taking hot beverages, such as coffee, tea, and hot chocolate, along while traveling. These mugs are most frequently used when traveling by car. However, they can also be used for carrying beverages on board buses, trains, and even boats. Though travel mugs are frequently used in vehicles, they also make frequent appearances at parks, sporting events, meetings, malls, and similar locations.
A travel mug usually has a spill-proof lid. This lid is designed to keep liquids from spilling out when cars go over bumps or as the result of the user's bouncy stride. The spill-proof design is also helpful for keeping heat inside the cup. Many have mechanisms that allow the user to take a quick sip of his or her beverage and reclose the lid with very little effort. This type of lid is often referred to as a spill-proof, drink-through lid.
When choosing a travel mug, a insulated coffee tumbler, a gallon water jug, a outdoor water bottle, a sports water jug or a protein shaker, many individuals recommend avoiding those with snap-on lids. These lids are known to pop off at the most inopportune times, sometimes causing painful burns. Even if users manage to escape burns, they may not be as fortunate when it comes to spills and stains. Screw-on lids are considered a far safer alternative.