Humans can be pretty contrary because when it is cold, we want to warm ourselves but when it is hot, we want to cool down ourselves. That is because we are warm-blooded creatures who need to keep our body temperatures more or less at 37°C.
Thermal flask is also a bit like us as they like to keep things at steady temperatures. If you put hot drinks in them, they will keep them hot. If you put cold drinks in them, they will keep them cool.
How Do They Work?
Heat is an energy that moves around our world in three different ways which is through conduction, convection, and radiation.
Conduction - Occur when you touch something hot, the heat will flow straight into your body because there is a direct connection between you and the hot object.
Convection - Happen without the need for any direct contact. For example, if you switch on a heater, it will blow hot air through a grille into your room. Hot air is less dense than cold air so it rises upwards, it will cause the cooler air near the ceiling of your room moves back toward the floor to get out of the way. When heat moves in this way, using a moving liquid or gas to travel from one place to another, we call it convection. Other example of convection will be heating up a soup in a saucepan.
Radiation - Different from those two. When objects are hot, they will emit light. This happens because the atoms in hot objects become "excited" and unstable when they gain extra heat energy from the fire. Since they are unstable, the atoms quickly return to their normal state by dispersing off the energy they had as light. If the light they produce is just a bit too red for our eyes to see, it is called infrared radiation.
A thermal flask is like a super-insulated jug. Most versions have an inner chamber and an outer plastic or metal case separated by two layers of glass/stainless steel with a vacuum and a reflecting layer in between them. There will also be a tight, screw-down stopper on the top of the flask to prevent heat loss and also water leakage.
These few yet simple features will prevent almost all the heat to transfer by either conduction, convection, or radiation. The vacuum will prevent conduction, the tight stopper prevents air from entering or leaving the flask. Therefore, convection will not be possible. Radiation also will not occur because when infrared radiation tries to leave the hot liquid, the reflective lining of the inner chamber reflects it straight back in again. So, there will be no way heat can escape from a thermal flask and a hot drink stored inside will stay steaming hot for several hours or even up to days.
Thermal flask also works for cold drinks too as heat cannot escape from a thermal flask, it follows that heat cannot penetrate into a flask from outside either. The sealed stopper stops heat from getting in by convection, the vacuum stops conduction, and the metal lining between the outer case and the inner chamber stops heat radiating in either. Therefore, whether you like your coffee piping hot or icy cold, a thermal flask is an absolutely brilliant way to keep your drinks just the way you want them to be.
If you are a coffee lover, you might want to check out these Thermal Tumblers as they are very popular among coffee lovers.
Some heat might still be able to escape or gets in and that mostly will be through the stopper, but flasks like this are still a vast improvement on virtually every other kind of insulated drinks container. If you wish to know read more about our thermal flask, you may click HERE to check it out!
