Magnetic filtration with magnetized granular beds:Basic principles and filter performance

This study is devoted to the explanation of different characteristics of magnetic filtration and the way these characteristics affect the important filtration parameters. Magnetic fields in pores and the force effect of these fields on magnetic particles and the magnetization properties of packed beds composed of ferromagnetic spheres and metal chips are evaluated. The profile of accumulation and capture regions of the particles, the variation of the fluid velocity in these regions and analytic expressions of particle capture radius are presented. The effects of filtration regime parameters on magnetic filter performance were investigated. An analytical expression has been obtained for the dependence of the logarithmic efficiency coefficient on filtration velocity, the geometry of filter elements, the particle size and other parameters of filtration. The stationary and non-stationary equations of the magnetic filtration processes are given. An expression of magnetic filter performance is shown with dimensionless parameters obtained from the filtration system. These relations are useful for calculations in engineering practice, including the design of magnetic filters, provision of suggestions on construction, and optimization and control of filter operation.

Investigation on the interaction length and access resistance of a nanopore with an atomic force microscopy

Nanopore devices have attracted a lot of attention for their potential application in DNA sequencing. Here, we study how an occluding object placed near a nanopore affects its access resistance by integrating an atomic force microscopy with a nanopore sensor. It is found that there exists a critical hemisphere around the nanopore, inside which the tip of an atomic force microscopy will affect the ionic current. The radius of this hemisphere, which is a bit smaller than the theoretical capture radius of ions, increases linearly with the applied bias voltage and quadratically with the nanopore diameter, but is independent of the operation modes and scanning speeds of the atomic force microscopy. A theoretical model is also proposed to describe how the tip position and geometrical parameters affect the access resistance.

Analysis on the factors that influence bubble coalescence in an acoustic field

The coalescence time between two contacting bubbles was measured experimentally in different acoustic pressures and frequencies using an imaging system with a high-speed video camera,and taken an analysis to the influence of the secondary Bjerknes force and maximum oscillation velocity on the coalescence time of two contacting bubbles in this paper.It showed that under the action of different acoustic pressures and frequencies,the coalescence time increases with secondary force and maximum oscillation velocity.The analysis and comparison of the secondary Bjerknes force and maximum oscillation velocity for the effect of bubble coalescence time showed that the secondary Bjerknes force is the critical factor to influence the bubble coalescence.