Jets, ie collimated streams of matter, occur from the microscale up to the large-scale structure of the universe Our focus will be mostly on surface tension effects, which result from the cohesive properties of liquids Paradoxically, cohesive forces promote the breakup of jets, widely encountered in nature, technology and basic science, for example in nuclear fission, DNA sampling, medical diagnostics, sprays, agricultural irrigation and jet engine technology Liquid jets thus serve as a paradigm for free-surface motion, hydrodynamic instability and singularity formation leading to drop breakup In addition to their practical usefulness, jets are an ideal probe for liquid properties, such as surface tension, viscosity or non-Newtonian rheology They also arise from the last but one topology change of liquid masses bursting into sprays Jet dynamics are sensitive to the turbulent or thermal excitation of the fluid, as well as to the surrounding gas or fluid medium The aim of this review is to provide a unified description of the fundamental and the technological aspects of these subjects

Physics of liquid jets

1. Introduction to colloid science and rheology 2. Hydrodynamic effects 3. Brownian hard spheres 4. Stable colloidal suspensions 5. Non-spherical particles 6. Weakly flocculated suspensions 7. Thixotropy 8. Shear thickening 9. Rheometry of suspensions 10. Suspensions in viscoelastic media 11. Advanced topics.

Colloidal Suspension Rheology

Magnetorheological materials are a class of smart materials whose rheological properties may be rapidly varied by application of a magnetic field These materials typically consist of micron-sized ferrous particles dispersed in a fluid or an elastomer A quasi-static, one-dimensional model is developed that examines the mechanical and magnetic properties of magnetorheological materials This model attempts to account for magnetic non-linearities and saturation by establishing a mechanism by which magnetic flux density is distributed within the composite material Experimental evidence of the viscoelastic behaviour and magnetic properties of magnetorheological fluids and elastomers suggests that the assumptions made in the model development are reasonable It is shown that the model is semi-empirical in that it must be fit to the experimental data by adjusting a parameter that accounts for unmodelled magnetic interactions

http://iopscience.iop.org/article/10.1088/0964-1726/5/5/009/pdf

A model of the behaviour of magnetorheological materials

Electrorheological (ER) suspensions, typically composed of nonconducting or weakly conducting particles dispersed in an insulating liquid, undergo dramatic, reversible changes when exposed to an external electric field. Apparent suspension viscosities can increase several orders of magnitude for electric field strengths of the order of 1 kV mm −1 , with simultaneous ordering of the microstructure into particulate columns. While this electronic control of momentum transport and structure has many applications, development is severely inhibited by a lack of suitable materials and an incomplete understanding of the underlying mechanisms. This review focuses on the current understanding of the microscopic phenomena believed to control ER and the models used to describe macroscopic behavior. Particular emphasis is placed upon comparing model predictions with experimental observations, relating macroscopic behavior to microscopic mechanisms, and demonstrating the utility of mechanistic models for furthering our understanding of electrorheology.

Electrorheology : mechanisms and models

Electrorheology (ER) denotes the control of a material's flow properties (rheology) through an electric field1,2,3,4,5,6,7,8,9,10. We have fabricated electrorheological suspensions of coated nanoparticles that show electrically controllable liquid–solid transitions. The solid state can reach a yield strength of 130 kPa, breaking the theoretical upper bound on conventional ER static yield stress that is derived on the general assumption that the dielectric and conductive responses of the component materials are linear. In this giant electrorheological (GER) effect, the static yield stress displays near-linear dependence on the electric field, in contrast to the quadratic variation usually observed11,12,13,14,15,16. Our GER suspensions show low current density over a wide temperature range of 10–120 °C, with a reversible response time of <10 ms. Finite-element simulations, based on the model of saturation surface polarization in the contact regions of neighbouring particles, yield predictions in excellent agreement with experiment.

/pdf/the-giant-electrorheological-effect-in-suspensions-of-3mvjn1r3bd.pdf

The giant electrorheological effect in suspensions of nanoparticles.

https://www3.nd.edu/~sst/teaching/AME60637/reading/2004_JE_Adamiak_Atten_point_plane_simulation.pdf

Simulation of corona discharge in point–plane configuration

Electrocoalescence of water droplets in an insulating liquid

A conduction model is proposed to explain the electrorheological effect under D.C. or low frequency A.C. fields. An approximate analysis taking into account the bulk conduction of the solid and the nonlinear conduction properties of the liquid is confirmed by experiments on large scale spheres. A good agreement between measurements and predictions is also obtained when air replaces the liquid. Finally the predictions are extended to the case of surface conduction of the solid spheres.

A conduction model of the electrorheological effect

Macroscopic model of interaction between particles in an electrorheological fluid

The paper presents an algorithm to simulate the electric corona discharge in the two-dimensional hyperbolic needle-ground plate configuration. The boundary conditions for the space charge density are derived from the direct ionisation criterion. This technique doesn't rely on the Kaptzov hypothesis and can be used for any shape of the discharge electrode. The proposed algorithm has been compared with two approximate ones. One uses the Kaptzov hypothesis that the electric field on the corona electrode surface remains constant, with the value derived from the ionisation criterion, assuming that the electric field is Laplacian. The other one mechanically applies the Peek formula for the cylindrical wire, after replacing the wire radius with the surface curvature radius at given point of the electrode. The differences between all three approaches are negligible for small corona currents; they are noticeable, but still small, for higher currents.

P. Atten

Papers

Simulation of corona discharge in point–plane configuration

Electrocoalescence of water droplets in an insulating liquid

A conduction model of the electrorheological effect

Macroscopic model of interaction between particles in an electrorheological fluid

Corona discharge in the hyperbolic point-plane configuration: direct ionization criterion versus an approximate formulations