Rotating Spiral Prototype Contactor: Design and Demonstration

Continuous counter-current flow of two phases in a rotating spiral channel is reported for the first time. In the rotating spiral channel, centrifugal force is much greater than gravity and is used to overcome surface forces to produce a nearly flat uniform interface. The position of the phase interface and the flow rate ratio of the phases are under full control by changing the rotation rate and the pressure gradient.
The work in this research has been divided into two main parts. First is the design of the rotating spiral apparatus using the existing wide channel model to decide the spiral channel dimensions and to size the various other passages. Second is using the apparatus to investigate the effect of operating conditions and physical properties of the phases. Most of the experiments were performed for the air-water system, although tests using liquids representing a range of viscosity and a case of liquid-liquid contacting are also included. The tests have shown that the apparatus has the ability, as expected, to handle a wide range of phase flow rate ratio, rotation rate, range of operating pressure and liquid viscosity for gas-liquid contacting. For the liquid-liquid system (octanol-water) equal success was found, although the range of tests was limited. This shows that the same spiral channel can be used for both gas-liquid and liquid-liquid applications.
High accuracy measurements of liquid layer thickness are achieved over the full range of tests. These show that good agreement with the wide channel model is achieved for larger rotation rates and layer thicknesses where interface meniscus effects are less significant. Liquid layer as thin as 17 µm were recorded although measurements at different positions along the channel showed that layer thickness varied by around 20% and this is due to the offset of the spiral centre from the axis of rotation for this device.