HEAT TRANSFER ENHANCEMENT DUE TO MARANGONI CONVECTION IN EVAPORATING DROPS IN MICROGRAVITY

Marangoni effects during droplets evaporation (or condensation) are investigated experimentally and numerically. The experiments are carried out with pendant drops of Silicone Oils (with different viscosities) and hydrocarbons. The temperature of the disk sustaining the drop is rapidly increased, or decreased, to study the transient heating (evaporation) or cooling (condensation) processes. When Marangoni flows occur in the droplet (as for the n-heptane, the n-octane and the Silicone oil droplets with low kinematic viscosity), the heat transfer from the disk to the droplet is enhanced. The temperature of the droplet rapidly changes and the vaporization (condensation) process is consequently promoted. When thermal Marangoni effects are negligible, larger surface temperature differences are measured along the drop surface and the transient processes are slower. Numerical simulations are performed to correlate the experimental results, taking into account the presence of Marangoni shear stresses and the phase change at liquid-air interface.