Mesoscale simulation of Marangoni convection about a vapor bubble in a liquid with temperature gradients under microgravity conditions

Marangoni convection around a 2-D vapor bubble in a liquid, subjected to an imposed negative temperature gradient in the vertical direction under microgravity conditions, is simulated with a newly developed lattice Boltzmann liquid/vapor phase-change method. It is shown that a floating bubble, initially at the center of a confined space, moves gradually toward the hot wall under zero gravity condition because of Marangoni convection. With the increase of the Marangoni number, Marangoni convection along the liquid-vapor interface appears to be more and more significant. Under microgravity conditions, a sessile bubble attached on a hot bottom wall facing upward at low superheats, the high velocity region on the liquid/vapor interface moves from the triple-contact line region upward as the wettability of the solid surface changes from hydrophobic to hydrophilic. It is shown that the average Nusselt number of such a sessile vapor bubble under microgravity conditions is larger or smaller than those under zero gravity condition, depending on whether the Marangoni convection is in a direction parallel to or opposite to the direction of the gravity.