Mass transfer characteristics of rotating spiral gas-liquid contacting

Abstract

The first substantial experimental measurements of mass transfer in a rotating spiral channel are reported for counter-current physical desorption of a range of organic solutes from water into air. General relations in terms of bulk properties are developed that allow analysis and comparison across different solute properties, operating conditions and contacting equipment. The phase flow rate ratio and cleaned-phase throughput per passage volume emerge as parameters of principal importance, the former measuring sufficiency of solvent phase flow and the later mass transfer effectiveness and, consequently, required device size. The analytical solution for an infinitely wide channel is used to probe the finite-width experimental results and an apparently universal pattern of differences involving a peak in mass transfer coefficient emerges. As liquid flow rate decreases, the thickness of the liquid layer decreases and the mass transfer coefficient rises. But with further decrease in liquid flow rate and liquid layer thickness, an increasing fraction of the liquid flows in the corner regions under the end-wall menisci and the poor contact in these regions leads to a falling mass transfer coefficient. The peak is found to occur at a similar liquid layer thickness regardless of gas flow rate or solute equilibrium characteristics. Comparison is made with packed columns and rotating packed beds using available data in the literature. The rotating spiral performance suggests device sizes will be many times smaller than those for the two packed devices considered. Dependence of rotating spiral device volume on the square of channel size is demonstrated, showing that further reduction in device volume is possible.