Bouncing drop impingement on heated hydrophobic surfaces. (December 2021)

• Record Type: Journal Article
• Authors: Samkhaniani, N.; Stroh, A.; Holzinger, M.; Marschall, H.; Frohnapfel, B.; Wörner, M.
• Is Part Of: International journal of heat and mass transfer. Volume 180(2021)
• Publication Date: 2021-12
• Subjects: Drop impingement -- Heat transfer -- Maximum spreading ratio -- Contact time -- Thermocapillary -- Phase field method -- Openfoam; Heat -- Transmission -- Periodicals; Mass transfer -- Periodicals; Chaleur -- Transmission -- Périodiques; Transfert de masse -- Périodiques; Electronic journals; 621.4022
• DOI: 10.1016/j.ijheatmasstransfer.2021.121777
• Languages: English
• ISSNs: 0017-9310

Abstract

Highlights: Phase-field simulations of drop impingement in hydrophobic surfaces. Implement energy equation in phase-field method in OpenFOAM. The influence of hydrophobic surfaces on spreading ratio and contact time is presented with new correlations. The most influencing parameter on cooling effectiveness is Weber number. Abstract: We extend a diffuse interface phase-field method for two-phase flow simulations so as to include interfacial heat transfer and the thermal Marangoni effect. The set of governing equations hold non-standard terms, which originally stem from the underlying variational consideration of the total free energy of the two-phase system. It consists of the coupled Cahn-Hilliard Navier-Stokes equations with a temperature-dependent mixing energy term and a temperature transport equation implemented in the OpenFOAM framework. The underlying solver phaseFieldFoam is validated for the test cases of thermocapillary convection in a two-fluid-layer and thermocapillary migration of a drop. In the main part of the paper, hydrodynamics and heat transfer of a droplet impinging on a heated hydrophobic surface with subsequent bouncing are studied in detail. By comprehensive simulations, the effects of impact velocity, droplet diameter (in mm range) and substrate wettability (contact angle) are investigated. The numerical results for spreading ratio, wall contact time and cooling effectiveness are found to compare well with experiments indicating that the developed code is well suited for heat transfer simulation in two-phase flow. For the maximum spreading ratio, a new generalizing correlation is proposed which models the kinetic energy and energy losses at maximum spreading by two coefficients, which are determined from simulation results. A new correlation is also proposed for the contact time, which takes into account surface wettability. For the time evolution of drop mean temperature, a crossover is observed when comparing simulations with constant and temperature-dependent surface tension, indicating that the inclusion of Marangoni effects increases both, the heat transfer between drop and wall during spreading and the heat transfer between drop and surrounding air after rebound.