Investigation of electrohydrodynamic effects on sessile droplet evaporation using the lattice Boltzmann method

Abstract

Droplet evaporation on hot substrates within an electric field plays an essential role during the electrospray cooling process. However, there is only a vague understanding of electrohydrodynamic (EHD) effects on droplet evaporation. In this paper, the coupled set of governing equations, including the Poisson equations, the energy equations, and the Navier-Stokes equations, is implemented within the lattice Boltzmann (LB) framework to examine the evaporation of leaky dielectric droplets. The contact angle hysteresis (CAH) as well as the influences of fluid-solid conjugate heat transfer are taken into consideration in this model. The method’s accuracy is validated quantitatively by using three basic cases. The results suggest that the sessile droplet could be elongated or flattened under EHD effects. When the droplet is elongated, the acceleration of the rate of evaporation is controlled by the interrelationship between thermal conduction and electric-induced convection in the droplet, i.e., the average Peclet number (Pe) value. As Pe is less than 1.0, the interior of the droplets is controlled by thermal conduction, and the applied electric field would prolong the droplet evaporation time. As Pe is greater than 2.0, the electric convection promotes evaporation compared to neutral droplets. In the case that the droplets are compressed inside the electric field, the evaporation time progressively decreases as the intensity of the electric field increases. These insights help us understand how EHD affects sessile droplet evaporation and illustrate the huge potential of electric fields for thermo-fluid manipulation.