Trough Physics

The Holy Grail -
The Spill-Proof Mug

One can find a plethora of spill-proof ideas out there. Most use moving parts but some do not. For example, a rigid center mounted straw reaching to the bottom of a mug can prevent spilling in any direction so long as the mug is less than 1/2 full.

Another idea is a straw that travels 360 degrees around the rim of the mug. This will also eliminate spills - so long as the liquid in the straw and mug is quiescent. This is almost never the case and spills often do occur with spill proof mugs.

The holy grail is a spill proof mug in a dynamic environment with no moving parts.

Troughs, as described here, are an important part of the solution (but likely not the entire solution).


There is really not much to the physics of troughs. We use them every day to hold liquid. They include coffee mugs, soup bowls, sinks, and bathtubs.

Troughs truly become interesting when we try to make them less susceptible to slosh or we try to make them work in multiple directions (let's face it a coffee mug is boring and does not need engineer to design it).

For example, a tortuous path entrance to a trap can prevent the trap from spilling during low fill fraction horizontal handling. This entrance must prevent spilling in multiple directions and also must do this during an energetic transportation environment.

Unlike all other PMD components, troughs do not use surface tension to control liquid - they use the hydrostatics present during an acceleration and require this acceleration to work. The figure to the left shows a "tire" shaped trough capable of retaining propellant in any lateral direction. The pick up assembly illustrated obeys the physics of galleries.


There really are no details. Trough physics are pretty straightforward.


For more information on the design, use, and physics of troughs please see

AIAA 95-2531 Propellant Management Device Conceptual Design and Analysis: Traps & Troughs