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The object of this work was to investigate the interaction between rotary valves and pneumatic conveying pipelines and the effect which this can have on overall system performance. A review of previous work and current industrial practice revealed that very little work has been published on this subject, although it was evident that some manufacturers of pneumatic conveying systems do have preferred entrainment configurations. Consequently, a preliminary experimental investigation was undertaken with a transparent model of a rotary valve and drop-out box in order to observe the air and solid flow patterns inside the drop-out box. This provided the most important outcome of this work, that is, the discovery that two distinctly different modes of flow can exist in the chamber of a conventional drop-out box. The first of these is a turbulent swirling motion caused by the conveying airstream and is the most desirable operating condition because it results in the most effective entrainment of material into the conveying line. The second is a situation where the drop-out box is effectively 'choked' with product. Models to explain these two conditions have been developed and subsequently tested against data obtained from a full size positive pressure conveying system specifically constructed for this purpose. An extensive experimental programme has been carried out in which the performance of this system was examined with a selection of different entrainment configurations and different test materials. The principal variables investigated were the height and volume of the drop-out box, the orientation of the rotary valve with respect to the pipeline and the conveying air velocity. As a result of this work guidelines have been produced for interfacing rotary valves with pneumatic conveying pipelines. These have been presented as a simple list of eight points and it is anticipated that they will enable systems to be designed with more confidence than has been possible previously.

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This work firstly reviews the experimental data for centrifugal pumps operating in steady-state and transient two-phase flow. The pump head and torque become degraded in two-phase pumping operation. This degradation becomes increasingly severe and abrupt as pump specific speed falls, and is chiefly due to the reduced impeller performance. Degradation depends primarily on specific speed and pump geometry, void fraction and flow coefficient. Degradation also depends on flow regime, fluid viscosity, flow rate and system pressure. The evidence suggests that transient pump performance can be accurately predicted by steady-state tests.A pseudo-two-dimensional analysis is then presented of two-phase flow through a centrifugal pump to predict the head and torque performance over the full range of operating conditions. The loss of performance in the impeller in pumping operation is caused by the large slip that develops between the two phases as the gas slows dramatically compared to the liquid, particularly in stratified flow. In these conditions there is little or no pressure recovery by diffusion in the pump casing, with further energy losses at the impeller exit due to flow impact against the casing.The head and torque performance predicted by the model compared favourably with the results from the single-phase and two-phase experimental pump tests. The comparisons cover all 4 quadrants of pump operation over the whole voidage range for a comprehensive range of pump designs and fluid mixtures. A number of recommendations are made to improve two-phase pump performance for industrial applications.

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No description available.