Search

Numerical simulation is performed for the evaporation of a droplet impacted on a porous surface. A level-set formulation for tracking the droplet deformation is extended to include the effects of evaporation coupled to heat and mass transfer, porosity and porous drag and capillary forces. The local volume averaged conservation equations of mass, momentum, energy and vapor fraction for the porous region are simultaneously solved with the conservation equations for the external fluid region. The computations demonstrate not only the evolution of the liquid-gas interface during the whole period of droplet penetration and evaporation in a porous medium, but also the associated flow, temperature and vapor fraction fields. The effects of impact velocity, porosity and particle size on the droplet deformation and evaporation are quantified. [ABSTRACT FROM AUTHOR]

Convective drying of a moving moist object is investigated numerically solving the conservation equations of mass, momentum, energy and air moisture concentration based on a k – ∊ turbulence model in the external region of the object as well as the conservation equations of energy and object moisture concentration in the internal region. The external and internal conservation equations are coupled to the heat and mass transfer conditions on the object surface including the effects of evaporation and water activity. The numerical results show that the analogy between heat and mass transfer for the convective drying is valid only when the object temperature is close to the equilibrium temperature. The simple analytical formulations developed for the total drying rate are found to compare well with the numerical results. The effects of object velocity and thickness and the wall heat flux on the drying rate are quantified. [ABSTRACT FROM AUTHOR]

Numerical simulation is performed for liquid film formation and evaporation on a moving vertical plate, which occurs in dip coating. The liquid–gas interface is tracked by a sharp-interface level-set (LS) method, which is modified to include the effect of phase change at the interface. Numerical techniques for the liquid–gas–solid contact line on a moving plate and the conservation of particle concentration are incorporated into the LS method. The flow and thermal characteristics associated with the dip coating are investigated by solving the conservation equations of mass, momentum, energy, vapor mass fraction, and particle concentration. The effects of plate velocity and temperature on the dip coating process are investigated. [ABSTRACT FROM AUTHOR]

A level-set method is presented for computation of microdroplet evaporation including not only the effects of heat and mass transfer, phase change and contact line dynamics but also the Marangoni effect, which is a key parameter affecting the internal flow of the droplet and the particle deposition pattern. A sharp-interface formulation of the Marangoni force is derived and tested for two-phase Marangoni convection in a cavity. The computed results show good convergence in both the liquid and gas regions and are in excellent agreement with the analytical solutions. The level-set formulation is applied to microdroplet evaporation on a solid surface to investigate the Marangoni effect. [ABSTRACT FROM AUTHOR]

Microdroplet impact and evaporation on a solid surface, which is an integral part of an inkjet printing process, is studied numerically by solving the equations governing the conservation of mass, momentum, energy, and mass fraction in the liquid and gas phases. The deformed droplet shape is tracked by a sharp-interface level-set method, which is extended to include the effects of evaporation at the liquid-gas interface and dynamic contact angle at the liquid-gas-solid interline. The numerical results show that the drop-let impact and evaporation pattern depends significantly on the advancing and receding contact angles. Also, the effect of cavity sidewall on the droplet motion is investigated. [ABSTRACT FROM AUTHOR]