A major cause of liquid phase dispersion in pulsed gas-liquid downward flow through a packed bed is the difference in velocity and rapid mixing between fast moving liquid slugs and slow moving liquid films. This chromatographic behavior may be described by a model which regards the liquid phase as consisting of two continuous phases flowing concurrently at different velocities with continuous material exchange between the two streams. The liquid dispersion in the column may be characterized by a single mixing parameter. The predictions of the model agree with impulse response experiments. Due to improved mixing liquid dispersion decreases with increasing liquid flow rate and is smaller than that in the gas-continuous (trickle) flow regime. The liquid dispersion attains a constant asymptotic value for sufficiently high gas velocity.
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