In design for capillary flow, which features create consistent capillary paths?

• A. Non-uniform bore transitions.
• B. Internal shoulders, grooves, or features that create consistent capillary paths.
• C. Rough internal texture and random features.
• D. Eliminating all internal geometry.

Answer: (B)

In capillary flow, keeping the liquid on a steady, predictable path is crucial. Internal features like shoulders, grooves, or other designed geometry define and preserve a uniform channel, so the capillary pressure remains consistent as the liquid moves. This steady path prevents sudden changes in radius that can pin the meniscus or cause irregular flow, leading to repeatable, controlled capillary action.

Non-uniform bore transitions introduce abrupt radius changes, which shift capillary pressure along the path and can disrupt flow or cause uneven advancement. A rough internal texture or random features create unpredictable interactions with the liquid, adding irregularities and potential stagnation points. Eliminating internal geometry would remove the channel the liquid relies on, stopping capillary flow altogether.