Rotating spiral channels enable any two immiscible fluid phases to flow counter currently in parallel layers allowing independent control of phase flow rates and layer thicknesses. This opens the possibility of application over the full range of fluid contacting operations, including distillation, absorption, extraction and multiphase reaction with separation. A device has been developed that enables wide-ranging experimental studies to support model refinement and design of first generation applied devices. In this first work with the new device hydrodynamic characteristics are studied for gas liquid systems as functions of phase flow rates, rotation rate and liquid viscosity. Measurement of the heavy phase layer thickness, using image analysis based on the Young-Laplace theory for interface shape, and measurement of volume flow rate of each phase and pressure and temperature in the spiral channel allows rigorous comparisons with an existing 'wide-channel' model relating flow rates and layer thicknesses to phase properties, geometry and rotation rate. The measured thickness of the heavy phase layer is predicted well by the wide channel model at high rotation and phase flow rates, where the deviation from a uniform layer thickness due to menisci at the channel end walls and interface tilt from gravity are small. At low rotation rates, where significant meniscus height and tilt develop, the layer thickness is over-predicted by the wide channel model. The sub 20 pin heavy-phase layer thicknesses measured suggest operation at optimum thickness is possible with the rotating spiral over a wide range of phase and solute systems. (C) 2014 Elsevier Ltd. All rights reserved,