We study gas-liquid flows in a channel having a large aspect ratio at small capillary number. A channel of sinusoidal cross section was micro-machined in a polymeric material and covered by a transparent Plexiglas plate. The non-wetting gas (air) is injected at a controlled flow rate while the interface motion is recorded with a CCD video camera. From the convergence of asymptotic, numerical and experimental analysis, we found simple dependences for the finger width and total curvature as a function of channel aspect ratio. These results provide simple and general expressions for the pressure drop needed to over-come capillary forces and push the air finger inside the channel.

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