The gas dissolution process of a spherical rising gas bubble in liquid was investigated experimentally and numerically at Reynolds numbers below 100. We developed an experiment al apparatus in which a charged-coupled device (CCD) camera with a microscope follows the rising bubble and precisely measures the changes in the bubble size and the rising speed when t he spherical oxygen gas bubble dissolves in silicon oil and the spherical carbon dioxide bubble dissolves in water. We then estimated Sherwood number as a function of Schmidt number (SC = v/D, where v is the kinematic viscosity and D is the diffusivity of a gas in a liquid) and the Reynolds number (Re = 2RU/v, where R is the bubble radius and U is the rising speed) based on the changes in the bubble size and the rising speed. We al so numerically estimated Sherwood number for a dissolution of a spherical gas bubble in an infinite liquid by directly solving the Navier-Stokes and the diffusion equations. The comparison between experiment al and numerical results shows that the drag coefficients and Sherwood number of oxygen gas bubbles in silicon oil agrees well with those of fluid sphere and those of carbon dioxide bubble in water agrees well with those of solid particle. Moreover, we compared the experimental results with several proposed equations for estimating the drag coefficients and Sherwood number and clarified the applicable regions of each equation.
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