Kishan Bellur

Kishan Bellur

Assistant Professor, Mechanical Engineering

Thin Film Evaporation & Stability

Why it matters

When a liquid evaporates from a surface (a meniscus in a heat pipe wick, the microlayer under a growing boiling bubble, or a film drying on a substrate), a large share of the heat and mass transfer is concentrated in a very thin region near the contact line. Here the film is thin enough that intermolecular (disjoining) forces, capillarity, and interfacial kinetics all compete. How this region behaves controls heat transfer limits, dryout, and whether the film stays uniform or breaks up. It is also the region that continuum CFD cannot resolve without help.

Our approach

  • Multiscale meniscus models. We connect a thin-film model of the contact-line region to a continuum model of the bulk meniscus. This gives evaporation rates and interface shapes with no adjustable parameters (Bellur et al., Physical Review Fluids, 2020).
  • Microlayer evaporation in boiling. We model the liquid microlayer left under a dewetting bubble, which contributes much of the heat transfer in nucleate boiling (Lakew et al., Fluids, 2023).
  • Dynamics and stability. We are extending these models from steady to dynamic and two-dimensional, capturing multiscale oscillations, contact line motion, and the onset of instability in evaporating films.
  • Optical diagnostics. Interferometry, optical microscopy, and ellipsometry give time-resolved measurements of film thickness and interface shape that validate the models.

Selected outcomes

  • Three talks at ASME IMECE 2025: coupled multiscale phase change, dynamic measurement of evaporating films, and multiscale oscillations in thin films
  • Two talks at ASTFE 2026 on oscillations, stability, and contact line dynamics of evaporating thin films
  • Earlier foundational work on thermo-mechanical stability of an evaporating meniscus (ASME SHTC 2019, AIChE symposium honoring Prof. Peter C. Wayner, Jr.)

Broader relevance

Thin-film evaporation, contact line dynamics, and film stability determine performance in electronics cooling, heat pipes, and vapor chambers. They also govern drying, coating, and cleaning of surfaces, where film rupture and capillary forces can leave residues or damage fine features.