Numerical investigation on cooperative evaporation from microdroplet array on heated substrate

Abstract

The evaporative heat and mass transport characteristics from an array of continuously fed microdroplet on a heated substrate are investigated numerically by a Multiphysics model, which incorporates heat conduction, buoyant flow, Marangoni flow, Stefan flow, and vapor diffusion. The effects of droplet spacing, contact angle, and droplet size on the evaporation rate, heat flux, and convection strength were analyzed in detail with a fixed thermal and vapor concentration boundary condition. The results revealed the existence of extremely strong convection current in the ambient gas domain for evaporation from droplet array. This convection effect dominates the vapor transport process, overcomes the suppression effect from neighboring droplet, and causes the total evaporation rate to exceed the prediction from traditional diffusion-based model by up to ten times. The strength of the convective vapor transport is characterized by a dimensionless parameter, which increases first from 2.3 to 7 and then decrease to 4 with increasing contact angle from 30° to 150°, but remains invariant at 6.3 for hemispherical droplet irrespective of the change in droplet dimension. Finally, the numerical results demonstrate potential for microdroplet array evaporation to resolve the thermal management challenge of ultrahigh power electronics with heat flux up to 1 kW/cm2.