Effects of Dissolution Fingering on Mass Transfer Rate in Three‐Dimensional Porous Media

Dissolution mass transfer from the trapped phase to the flowing phase in porous media occurs in various hydrogeology processes. One of the important phenomena is dissolution fingering and its effect on dissolution mass transfer. In this work, dissolution mass transfer in porous media with various particle sizes and distribution was investigated in pore scale and meso‐scale by using X‐ray microcomputed tomography. The specific interfacial area and mass transfer coefficient were measured by following the representative elementary volume concept, and the effect of dissolution fingering was evaluated. Linear instability theory was used for the prediction of dissolution finger width (λ) at the onset of dissolution fingering. Although dissolution fingering tends to develop when the porous media container diameter (Ly) is smaller than half of λ, its effect on mass transfer coefficient starts to occur when Ly is larger than the whole λ. Starting this point, dissolution fingering decreases the mass transfer coefficient by three times. For validation, an additional experiment with a larger porous media container size was performed, and three dissolution fingers were successfully observed. Their size was found to be comparable with the theoretical prediction based on linear instability theory. Key Points We present the first three‐dimensional observation of dissolution fingering with simultaneous observations in pore‐scale and meso‐scale Dissolution fingers effect to mass transfer occurs when the dissolution finger size is larger than the container of the porous media Dissolution fingering decreases mass transfer coefficient down to one‐third