A numerical study of the isothermal migration of a two-dimensional bubble i
n Poiseuille flow is reported here for vapor-liquid density and dynamic vis
cosity ratios of 1/8, Re-d=1, and Ca=2. A lattice Boltzmann model with a va
n der Waals equation of state is employed to simulate the diffuse interface
for three interface thickness to bubble diameter ratios, 1/5, 1/10, and 1/
20. Point-by-point comparisons with the sharp-interface incompressible coun
terpart (reported in the literature) reveal velocity discrepancies which ar
e more evident on the vapor side. These differences are a manifestation of
a finite mass flux through the interface, associated with driven finite-thi
ckness interfaces. An analytical study of the one-dimensional analog of the
traveling diffuse interface problem explains this phenomenon and shows tha
t this flux vanishes as a result of viscous dissipation as the interface th
ickness tends to zero. This trend is corroborated by the two-dimensional la
ttice Boltzmann results. (C) 2001 American Institute of Physics.