Numerical analysis of meniscus dynamics in monolayer-wick dropwise condensation

Abstract

The effect of hydrophobic monolayer sintered-particle wick on the growth and departure of droplets in dropwise condensation over a vertical surface is analyzed numerically using the minimum meniscus surface energy principle and the direct simulation of the meniscus and heat transfer through the partially liquid-filled pores. The condensate fills the pores, increases the capillary pressure, and joins with the menisci from adjacent pores, leading to a droplet formation. The droplet growth is supported by liquid supply from the adjacent pores until the critical droplet departure volume is reached. The heat transfer rate is controlled by the average meniscus thickness, and the droplet surface coverage. Based on these and the plain–surface limit (for very small and very large particle diameter d_p), a threshold band of d_p is predicted below which the dropwise condensation rate is slightly enhanced compared to the plain, hydrophobic surface. The analysis explains the existing experimental results (and new augmented experimental results) and the challenges in further enhancing the dropwise condensation with surface microstructures.

Acknowledgments

The authors would like to thank Phil Martin (ACT) for his experimental testing expertise. Minki Kim (UM) assisted in starting the simulations with the Surface Evolver.

Additional information

Funding

This work was funded by the Office of Science in the U.S. Department of Energy (DOE) under a Regime II SBIR grant, Award Number DE-SC-0011317 (Program Manager: Robie Lewis).