Voidcask: Vacuum Flask Insulation
Thermodynamics & Statistical Physics arc, page 58 of 193. Back to The Pixelated Physics Universe
Who they are
Voidcask has one line, and says it often: “Insulated by nothing. literally.”
Voidcask is a character of the Thermodynamics & Statistical Physics arc: drawn in pixels, ruled by one piece of real physics, and never allowed to break it.
The physics
A vacuum flask suppresses conduction and convection with a vacuum gap; silvering reduces radiation.
$$ \begin{gathered} q = \frac{\sigma\,(T_h^{4} - T_c^{4})}{1/\varepsilon_1 + 1/\varepsilon_2 - 1} \end{gathered} $$
| Symbol | Meaning | SI unit |
|---|---|---|
| $q$ | radiative heat flux across the gap | W/m^2 |
| $\sigma$ | Stefan–Boltzmann constant | W/(m^2·K^4) |
| $T_h$ | inner-wall temperature | K |
| $T_c$ | outer-wall temperature | K |
| $\varepsilon_1, \varepsilon_2$ | emissivities of the silvered walls | — |
Sources
- J. Dewar, "The vacuum-jacketed vessel", Proc. Roy. Inst. Gt. Brit. 14, 1–14 (vol. 1893–95); flask made 1892, first shown at the Royal Institution 25 Dec 1892
- F. P. Incropera et al., Fundamentals of Heat and Mass Transfer, 7th ed. (Wiley, 2011), §13.3
Crossovers
Voidcask meets Creamward (Newton's Law of Cooling). Creamward's coffee loses heat by conduction, convection, evaporation and radiation. Voidcask removes the first two with a vacuum gap and cuts radiation with silvering, which slows Newton's cooling a great deal.
Voidcask meets Solitaren (Mean Free Path Vacuum). Voidcask's insulating gap works because Solitaren's rule holds: with the pressure low enough, gas molecules cross the gap without colliding, so conduction through the gas almost vanishes.
Wear the lore
Concept keywords: Vacuum Flask Insulation, Voidcask, Thermodynamics & Statistical Physics, physics lore, Pixelated Physics