Ezzat D. Doss

Analysis and application of solid-gas flow inside a venturi with particle interaction

Abstract A two-phase one-dimensional solid—gas flow model which describes the flow inside a variable area duct has been developed. The model includes multiparticle equations and considers particle—particle interaction. Predictions have been compared with experimental data for the pressure drop and pressure recovery through two venturis at different solid to gas loading ratios. Accurate knowledge of the particle-size distribution is extremely important for good comparison. No meaningful single particle-size diameter is found that yields predictions to agree with the measurements. The venturi may be used as a measuring device for solid—gas flow rates for systems if the particle-size distribution is accurately known. However, the venturi-diffuser section loses its effectiveness in recovering the pressure as the solid loading increases.

The Need For Superconducting Magnets For MHD Seawater Propulsion

An MHD model that couples a one-dimensional flow model to a two-dimensional electrical model has been developed to demonstrate the need of high strength magnetic flelds and to investigate the influence of friction and end losses on the performance of MHD thrusters. Parametric studies have been performed using the model that includes the variation of the applied magnetic fieId (5-20 1), thruster diameter (0.5-2.0 m), wall roughness (0-3 mm), flow velocity (5-20 m/s), and the load factor (1-10). The results indicate that friction and end losses can have a deleterious effect on the thruster efficiency close to a load factor equal to unity. Furthermore, the parameter studies show that the thruster efficiency increases with the strength of the magnetic field and thruster diameter and decreases with the wall roughness and the flow velocity. Careful considerations should be given to the analysis and the design of MHD thrusters for load factors close to one.

Experimental Determination of Magnetohydrodynamic Seawater Thruster Performance in a Two Tesla Test Facility

A two Tesla test facility was designed, built, and operated to investigate the performance of magnetohydrodynamic (MHD) seawater thrusters. The results of this investigation are used to validate MHD thruster performance computer models. The facility test loop, its components, and their design are presented in detail. Additionally, the test matrix and its rational are discussed. finally, representative experimental results of the test program are presented, and are compared to pretest computer model predictions. Good agreement between predicted and measured data has served to validate the thruster performance computer models.

An overview of MHD seawater thruster performance and loss mechanisms

Loss mechanisms affecting the performance of an MHD seawater thruster system have ben identified and discussed. Among those losses are the jet and nozzle losses, joule heating losses, surface potential and electro-chemical losses, frictional losses, and electrical end losses. Simple, but accurate, models have seen used to assess the relative and absolute magnitude of these losses and to investigate their influence on the overall thruster efficiency. A parametric study has been performed for a generic full size seawater vehicle propelled by an MHD thruster at different operating conditions. The results of this study confirm that higher efficiencies can be achieved at high magnetic field strengths (> 10 Tesla). Furthermore, the results indicate that higher efficiencies can be maintained over a wide range of cruising speeds (2--20 m/s or 4--40 knots) at higher magnetic fields (20 Tesla).

Three-dimensional Parametric Study For MHD Marine Propulsion

The Performance Of Mhd Seawater Thrusters Have been investigated using a dime-dimensional MHD flow model. The model incorporates the interaction between the flow fields and the electrical fields inside the thruster. A parametric study has been performed using the three-dimensional MHD flow model to analyze the performance of continuous electrode seawater thrusters under different operating parameters. The effects of these parameters on the fluid flow characteristics, and on the thruster efficiency have been investigated. Those parameters include the magnetic field (10-20 T), thruster diameter (1-2 m), surface roughness (0-2 mm), velocity (5-30 m/s), and the electric load factor (1-10). The results of the three-dimensional computations indicate that the velocity profiles are flatter over the sidewalls in comparison to the velocity profiles over the electrode walls. However such differences are not significant. The results of the parametric study show that the thruster electrical efficiency increases with the strength of the magnetic field and thruster diameter, and decreases with the flow velocity and surface roughness

Interelectrode resistance and performance of small- and large-scale MHD generators

The effect of reduced interelectrode resistance in MHD generators on the generator power output is investigated. The analytical model used in the investigation allows for the solution for the electric field and current density distributions in the cross plane of the generator. The power output, expressed as a fraction of the power output of a perfectly insulated generator, is found to be a function of the wall temperature, the ratio of boundary layer thickness to channel transverse dimension, and the product of interelectrode resistance and channel cross-sectional area. The interelectrode resistance is assumed to be inversely proportional to the channel transverse dimension and the variation of power output ratio with channel size is calculated. It is found that deterioration of performance of NHD generators, resulting from reduced interelectrode resistance, diminishes with generator size and is negligible for large-scale generators, provided that the interelectrode resistance remains larger than an order of one-tenth ohm.