Year

1995

Degree Name

Doctor of Philosophy

Department

Department of Mechanical Engineering

Abstract

Air-jet pumps are being used increasingly in industry to feed and transport a wide range of bulk solids because of their simplicity in structure, lack of moving parts, convenience of installation and operation and with little damage to the product. However, to date, the design of this type of equipment and associated conveying system still is a "black art" due to the shortage of theoretical analysis and experimental data reported in the literature regarding the design and application of these pumps. For this reason, this thesis aims at formulating a mathematical model to predict jet p u m p performance under air-solids flow conditions and developing a general design procedure by investigating into the effect of air-jet p u m p geometry and operating conditions on the performance of these pumps, so that options to improve efficiency can be determined.

To obtain detailed information on the interaction between the operating conditions and jet p u m p geometry, a systematic experimental investigation is undertaken into the characteristic performance of central air-jet pumps with five different nozzle geometry and annular air-jet pumps with multi-hole ring nozzles operating under both air-only and airsolid flow conditions. These experiments were conducted by varying motive pressure, back pressure respectively for each particular jet p u m p design to observe the effect of operating conditions and geometric parameters on p u m p performance. The factors affecting performance also are analysed.

Generally, the efficiency of annular air-jet pumps with multi-hole ring nozzles is less that of central air-jet pumps. Based on the experimental results, options to improve efficiency by modifying the geometrical design are suggested.

To assess the energy-effectiveness of an air-jet pump operating under different conditions, dimensional and non-dimensional parameters are defined and employed to represent jet p u m p characteristic performance and efficiency. A mathematical model to predict air-jet pump performance is formulated on the basis of fluid mechanics and a numerical solution is obtained. This model is used to predict the non-dimensional relationship between the motive, suction and discharge flow through an air-jet pump with a given geometry. The predicted performance agrees well with experimental results for numerous jet pump geometries, operating conditions and different materials.

Based on the performance prediction model and experimental results, optimum parameters for maximum efficiency are analysed and correlated with experimental data. design procedure for an air-jet pump conveying system is developed to maximise efficiency and reliability. This design procedure also is applied to the proper sizing air-jet pump for a given application requirement. A mathematical optimisation model for the optimal design of an air-jet pump system is formulated and the numerical solution this model is obtained. The optimisation results agree well with the optimum parameters obtained from experiments.

It is concluded on the basis of the analyses and experimental investigations that it is possible to improve the efficiency of air-solids jet pumps by modelling its performance and optimising its geometry for a given operating condition or adjusting the operating condition for a jet pump with a given configuration.

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