Finger properties in bounded double diffusive finger convection

TL;DR

This study investigates the properties of bounded double diffusive fingers in an electrochemical cell, revealing how boundary conditions affect finger structure, ion transport, and mixing efficiency compared to unbounded fingers.

Contribution

It provides experimental analysis of bounded double diffusive fingers, comparing their properties with unbounded fingers and linking observations to linear stability theory.

Findings

Boundary layers are thinner than finger width.

Finger thickness matches half the fastest growing mode wavelength.

Ion transport is significantly reduced in bounded fingers.

Abstract

We analyze experimental data on double diffusive convection in an electrochemical cell in the finger regime. All fingers in the experiments are bounded on at least one end by a solid wall. The properties of these fingers are compared with those of fingers in other experiments which are surrounded by fluid on all sides. The compositional boundary layers are found to be thinner than the finger width. The finger thickness agrees well with half the wavelength of the fastest growing mode obtained in linear stability analysis. The ion transport through the boundary layers is reduced by two orders of magnitude compared with unbounded fingers. The overturning layers in staircases contribute negligibly to salinity mixing because of efficient transport between finger layers and convection rolls.