Phase-Locked Capillary Oscillation for Enhanced Solar Desalination

A constructive interfacial physics experiment for increasing solar evaporation without new materials

One-Sentence Discovery

Solar thermal desalination systems systematically underperform because sub-millimeter capillary waves at the water–air interface are treated as passive surface roughness, when in fact they can be externally phase-locked to incoming solar flux to amplify evaporation.

The Physical Mechanism

Thin water films naturally support capillary wave modes determined by surface tension, density, and wavelength. When solar or thermal input is applied steadily, these modes remain weak and incoherent, limiting vapor flux to static thermal gradients.

If incident energy is modulated at or near the natural resonance frequency of these capillary modes, interfacial oscillations can phase-lock to the forcing. This produces constructive amplification of surface motion, increasing local curvature, pressure gradients, and effective vapor-pressure differentials at the interface.

The result is an evaporation rate that exceeds predictions from steady-state solar thermal models at equal mean energy input.

New Scientific Object

Capillary Resonance Coupling Coefficient (CRCC)

The CRCC is defined as the measured increase in capillary wave amplitude (nanometers) induced when modulated optical or thermal input matches the natural resonance frequency of the water surface. It is observable via laser Doppler vibrometry or high-speed surface imaging and correlates directly with evaporation flux enhancement.

Edge of Practice Experiment

Assumption under test: External modulation of solar illumination at the capillary wave resonance frequency produces significantly greater surface oscillation and evaporation than steady illumination of equal mean intensity.

Materials

  • Shallow water tray (3–5 mm depth)
  • Modulated light or thermal source (e.g., LED array or shuttered lamp)
  • Controller for periodic modulation
  • Precision scale for mass loss
  • Thermometer
  • Laser Doppler vibrometer or high-speed camera (optional but preferred)

Procedure

  1. Fill tray with a fixed depth of water.
  2. Apply steady illumination and record baseline evaporation rate.
  3. Measure surface oscillation amplitude under steady conditions.
  4. Apply modulated illumination at the calculated capillary resonance frequency while maintaining equal mean intensity.
  5. Record evaporation rate and oscillation amplitude.
  6. Alternate between steady and modulated regimes to confirm repeatability.

Binary outcome: If modulated illumination increases both CRCC and evaporation rate relative to the steady control, the effect exists. If not, it does not.

Why This Matters

This experiment opens a new axis for improving solar desalination and atmospheric water harvesting by exploiting interfacial physics rather than new materials or higher temperatures. It enables efficiency gains using passive modulation techniques compatible with low-cost, distributed water systems.

Even modest gains compound meaningfully at scale, especially in water-stressed regions where simplicity and durability dominate design constraints.

This experiment is published as part of Edge of Practice. It proposes no product, policy, or deployment claim and exists solely to test a hidden physical assumption governing real-world systems.