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Why is the holding time of the thermos cup far less than that of the thermos

Sep 16, 2019

The first thing to know is the three forms of heat transfer; direct conduction, convection, and radiation.

The structure of the thermos bottle is a double-layer glass liner structure. The bottle is divided into two parts: the inner liner and the outer bladder. The inner and outer bladders are only connected to the neck, and the heat transfer cross-sectional area is small, and the interlayer is collected into a vacuum (reducing gas convection). Heat), the inner wall of the liner is coated with a reflective layer (reducing radiation heat transfer), and the heat transfer of the hot water inside the thermos bottle is directly transmitted through the neck connection structure. When the hot water is full, the water will directly transfer heat to the bottle stopper. Therefore, if the heat preservation time of the thermos bottle is long, the water should not be filled.

There are many types of vacuum flasks, and if it is a glass bladder, the effect will be better. The insulation cup of the landlord is estimated to be stainless steel. The vacuum cup can also be vacuumed, but the neck structure is a metal joint structure, and the heat transfer coefficient of the metal is much higher than that of the glass. The amount of heat transfer from the vacuum flask to the outside is much higher than that of the thermos.

Since the water content of the bottle and the cup is different, that is, the total heat of the internal water is greatly different, and the heat leakage of the cup is much larger, so there is a great difference in the holding time. There is also a point that the construction cost of the thermos cup is high, the manufacturing process is difficult, and it can be carried around, so it is expensive. Just like the price difference between desktop and notebook.