Filtration efficiency and the percolation phenomenon in a grooved-plate Separator

We present here the results of a study of the separation process in the extraction matrix of a novel high-intensity magnetic separator (HIMS). The matrix uses an ordered array of grooved plates (replacing conventional collectors, which are generally made of wires). Only experimental results are available for grooved plates in the literature, but here we propose a new theoretical approach. We report on the particles' behavior, the existence of a percolation phenomenon, and the filtration efficiency, in order to analyze and compare the performance of matrix structures (Lenoir's and Jones'). We discuss the causes of the percolation phenomenon and its effect on filtration efficiency. Correspondence between the theory and the experiments is good. We suggest appropriate uses of each matrix structure according to the property of the processed particles.     

Using Superconducting Magnet to Reproduce Quick Variations of Gravity in Liquid Oxygen

A ground based facility (OLGA), providing magnetic compensation of gravity in oxygen, has been developed. A 2-T superconducting magnetic solenoid is used to create the required magnetic field. A novel electrical supply permits to quickly vary the magnetic field, leading to rapid variation of the acceleration forces applied to oxygen. These variations can be made from overcompensation of gravity (−0.5g) to zero gravity or from zero gravity to reduced gravity (0.4g) with a time constant of 340 ms. This time is typical of the cutoff or reignition of spacecraft engines. Preliminary results on the transient flows induced by these acceleration variations in a reservoir filled with liquid and gaseous oxygen are presented.     

Magnetic percolation phenomenon in high-field high-gradientseparators

This paper deals with the modeling of paramagnetic particle capture in high-gradient magnetic separators. The model allows the simulation of the progressive saturation of the collectors of the extraction matrix. The results show that magnetic separation is a complex process to model. Yet several elementary phenomena such as magnetic percolation and effects of slight changes of geometrical conditions are pointed out. The evolution of a matrix efficiency as a function of its saturation degree is also given     

Design of a Large Oxygen Magnetic Levitation Facility

The present magnetic levitation facility offers an alternative to space means for studying fluids and especially liquid oxygen that exhibits important safety requirements. The station has great use flexibility. Thus it enables us to study hydrodynamic instabilities (acceleration and deceleration phase) and also to focus on thermal exchanges (nuclear and film boiling) and transition phase of fluids under reduced gravity such as Lunar, Martian or micro-gravity. The volume of liquid oxygen levitated is about two litres with a resulting acceleration less than 0.1 m/s². Besides the aspect ratio of the working cell can be changed.     

Ferromagnetic inserts for magnetic force field generation

We present a new way of creating a magnetic force field by using ferromagnetic inserts inside a superconducting solenoidal coil. By means of a purely analytical calculation, we describe the configuration of the ferromagnetic inserts and the force field they create. We demonstrate the relevance of the structure both by numerical computation and by experimentation with a prototype.     

Prototype "Supersat 001"--Probative results

A new type of large torque air-cored cryogenic ac machine has been presented earlier. The experimental results obtained with the first prototype Supersat 001 are discussed. The experimental results are compared with the theorical ones deduced from a three-dimensional analytical model. The main results concern the static and dynamic behavior and the analysis of the losses which have led to the consideration of a new design of the first prototype.     

Dielectric behaviour of a ferrofluid subjected to a uniform magnetic field

The electric susceptibility of samples of ferrofluids subjected to a uniform magnetic fieldHwas measured. The electric susceptibilitychiis dependent on the magnitude of the magnetic field and on the relative direction between the electric fieldEand the magnetic fieldH. 1) WhenEis perpendicular toH, frac{partialchi_{perp}}{partialH} < 02) WhenEis parallel toH, frac{partialchi_{parellel}}{partialH} > 0These results have been interpreted as a magneto-electric directive effect. A model is proposed, based on the assumption that the magnetic particles are roughly ellipsoidal and conducting grains.     

Study of fluid behaviour under gravity compensated by a magnetic field

Fluids, and especially cryogenic fluids like hydrogen and oxygen, are widely used in space technology for propulsion and cooling. The knowledge of fluid behaviour during the acceleration variation and under reduced gravity is necessary for an efficient management of fluids in space. Such a management also rises fundamental questions about thermo-hydrodynamics and phase change once buoyancy forces are cancelled. For security reasons, it is nearly impossible to use the classical microgravity means to experiment with such cryofluids. However, it is possible to counterbalance gravity by using the paramagnetic (O₂) or diamagnetic (H₂) properties of fluids. By applying a magnetic field gradient on these materials, a volume force is created that is able to impose to the fluid a varying effective gravity, including microgravity. We have set up a magnetic levitation facility for H₂ in which numerous experiments have been performed. A new facility for O₂ is under construction. It will enable fast change in the effective gravity by quenching down the magnetic field. The facilities and some particularly representative experimental results are presented.     

Magnetic-Field Modulation of Gravity: Martian,Lunar, and Time-Varying Gravity

Magnetic micro-gravity is used to simulate on Earth gravity conditions that occur on the moon, Mars or in interstellar space. The possibilities offered by this magnetic method are theoretically studied so as to develop ground-based devices enabling one to simulate various gravity conditions. The results of this theoretical study focus on perfect gravity compensation (micro-gravity), partial gravity compensation (lunar or Martian gravity) and also transient gravity compensation (acceleration or deceleration phases of spaceships).     

Magnetic Compensation of Gravity and Centrifugal Forces

This paper deals with the theoretical combination of magnetic forces, centrifugal forces, and gravity acting on low-χ magnetic fluids contained within a cylindrical shaped zone with a horizontal axis. The magnetic field is created by a combination of both quadrupolar winding and dipolar fields, as exists in superconducting coils developed for particle accelerators. Such a ground based device, if static, simulates a rotation – in space conditions – of a paramagnetic substance such as liquid oxygen. When the cylinder rotates, it creates exact gravity compensation – on Earth – for diamagnetic fluids such as hydrogen. These results go beyond a previous result that found it impossible to reach perfect magnetic compensation of gravity in a 3D domain.