Hypergravity experiments on multiphase media evolution

The gravitational field affects the evolution of multiphase media, such as rocks, soil, and alloy melts. Hypergravity increases the body force of matter, enhancing the driving force of the relative motion between substances with different densities and accelerating the evolution of multiphase media. Hypergravity experiments provide a new approach to exploring the motion of multiphase media and solving engineering problems. Hypergravity experiments have been conducted in different disciplines,such as materials science, geological science, and geotechnical engineering. However, the knowledge barriers between various research fields have caused the development of centrifuges/inflight devices and theoretical research on the mechanisms of matter in motion in hypergravity to lag behind the application of hypergravity experiments, limiting the progress in these experiments.This article systematically summarizes and proposes the fundamentals of hypergravity experiments, while the scientific challenge of the nonlinear hypergravity effect induced by high hypergravity on multiphase media evolution is clarified. Evaluation criteria are proposed for the noninertial frame effects of the centrifugal hypergravity field. The development of the high-centrifugal acceleration, large-capacity, and long-beam centrifuges are determined as the future research direction. Representative cases are used to demonstrate the effectiveness and great potential of the hypergravity experiments for the solidification of alloy melts and physical modeling. Challenges in the experimental methodology are also clarified. This paper reviews the fundamentals and applications of hypergravity experiments in various disciplines, pointing out the research direction of hypergravity experiments on multiphase media evolution.

Work conjugate principle-constrained volume averaging technique for multiphase porous media

Volume averaging is a standard method for the development of macroscopic balance equations for modelling the thermodynamic behaviors of multiphase porous media. However, work conjugate principle which is a common practice in continuum mechanics is not emphasized by the volume averaging technique resulting in the macroscopic balance equations are not capable of comprehensively describing the kinematic behaviors of multiphase porous media due to the loss of essential macroscopic variables. This study derives the macroscopic mass and momentum balance equations for the pore fluid of a fluid-solid porous medium by use of the volume averaging technique. We show(1) if the procedure of the volume averaging is implemented in its traditional manner, only the average flux of the pore fluid described by its mass average velocity is captured;(2) if the work conjugate principle is employed to define a work-conjugate velocity for the pore fluid at the macroscale, both the average flux(described by the mass average velocity) and the dispersive flux(described by the deviation of the mass average velocity from the work-conjugate one) are reproduced. This theoretical analysis demonstrates that the work conjugate principle is an essential thermodynamic constraint to improve the volume averaging technique, in the sense that the macroscopic balance equations are required to be capable of comprehensively describing the macroscopic kinematic behaviors of multiphase porous media.