A novel simulation approach for concentration-driven evaporation in capillaries

TL;DR

This paper presents a fast, semi-transient simulation method for predicting concentration-driven evaporation in arbitrarily shaped capillaries, improving accuracy and efficiency over traditional approaches.

Contribution

A novel semi-transient simulation approach coupling Surface Evolver and OpenFOAM enables rapid evaporation predictions in complex geometries without considering evaporation history.

Findings

Simulation runtimes of about 10 minutes for 150 hours of physical time

Strong agreement with experimental data for water evaporation in various capillaries

Applicable to complex industrial crevice geometries

Abstract

Long liquid retention times in industrial gaps, due to capillary effects, significantly affect product lifetime by facilitating corrosion on solid surfaces. Concentration-driven evaporation plays a major role in mitigating this corrosion. Accurate evaporation rate predictions are crucial for improved product design. However, simulating capillary-driven flows with evaporation in complex geometries is challenging, requiring consideration of surface tension, wetting, and phase-change effects. Traditional approaches, such as the Volume-of-Fluid method, are prone to curvature calculation errors and have long simulation times due to strict time step limitations. This study introduces a novel semi-transient simulation approach for fast evaporation rate prediction in arbitrarily shaped cavities. The approach involves a unidirectional coupling circuit, simulating the fluid surface in Surface Evolver and combining it with a vapor-in-gas diffusion simulation in OpenFOAM. The approach assumes that the evaporation rate is calculated solely based on the conditions at a given liquid filling level, without considering the evaporation history. This allows for highly parallelized simulations, achieving simulation runtimes in the order of 10 min to cover up to 150 h of physical time. Numerical investigations are conducted for water evaporation in air at a temperature of 23{\deg}C and a relative humidity of 17%, for round and polygonal-shaped capillaries with inner diameters ranging from 1 mm to 13 mm. The results are validated using experimental data and show strong agreement. Simulations are also performed for complex industrial relevant gaps, demonstrating the applicability of the approach to a wide range of crevice geometries.