Vossimo — Vacuum Flask Heat Retention | vossimo.shop
4187 J per kg per °C at 15 °C, liquid nitrogen at -196 °C, the 1892 Dewar design, eight 1-litre ice blocks under 10 °C, and a 1.018 V standard cell held to a few parts per million.
Energy: liquid water holds 4187 J of heat for every kilogram and every 1 °C at 15 °C, so the drink carries its heat only as long as the flask slows the loss. This is the baseline against which every heat-loss path is measured: a kilogram of water cooling by 50 °C gives up roughly 209 000 J.
Temperature limits: vacuum flasks usually hold contents below 100 °C, the boiling point of water, because radiation across the gap grows with temperature. At the cold end, liquid nitrogen in laboratory flasks boils at -196 °C, and larger vessels need a pressure relief valve so the boiling gas cannot shatter the glass.
Medical cold chain: the Arktek medical dewar keeps vaccines under 10 °C using eight 1-litre ice blocks. The figure is a ceiling, not a target temperature, and the eight blocks are the specified charge for that dewar.
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History: James Dewar designed the first vacuum flask in 1892 while working in cryogenics and never patented it. The design's precision is visible in a later application: a silvered flask held a 1.018 V standard cell to a few parts per million.
Insulation mechanics: the gap between the two walls is partially evacuated of air, which reduces heat conduction and convection, and silvering the facing surfaces reduces thermal radiation. Spacers between the shells act as thermal bridges and reduce insulation where they touch.
Use these values as a reference set: energy stored, upper and lower temperature limits, a medical ceiling, a dated design and a measured electrical standard.
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