Numerical Modeling of Phase Change Phenomena in Particulate Flows

本研究项目的主要目的在于对重力作用下微粒流动中相变现象的行为有一个基本的了解。这种理解将有助于在冶金和应用材料工程中设计新技术，例如铸造耐高温合金，这将有助于节省能源和保护环境。众所周知，经典的多相模型（欧拉-欧拉）往往不能预测多组分材料的重力驱动凝固。考虑到这一点，另一种方法，如欧拉-拉格朗日模型，可以用来充分预测金属合金铸造过程中发生的凝固/熔化过程。在这种方法中，固体粒子的运动是用牛顿运动定律单独处理的。然而，到目前为止，基于欧拉-拉格朗日的相变相关问题模型在文献中很少受到关注，尽管它们可能为包括相变效应在内的复杂流动的可靠数值模拟提供了巨大的潜力。拟进行的研究主要有以下目的：

The main objective of this research project consists in gaining a fundamental understanding of the behaviour of phase-change phenomena in particulate flows under the influence of gravity. This understanding will help to design novel technologies in metallurgical and applied materials engineering, e.g. such as casting high-temperature resistant alloys, which go on to help save energy and protect the environment. It is well known that the classical multiphase model (Euler-Euler) often fails to predict a gravity-driven solidification of multicomponent materials. In view of this, an alternative approach such as the Euler-Lagrange model can be used to adequately forecast solidification/melting processes occurring during casting of metal alloys. In this approach the motion of the solid particles is treated individually using Newton’s law of motion. So far, however, Euler-Lagrange-based models for phase-change-related problems have met with little attention in the literature, even though they might provide great potential for reliable numerical simulations of such complex flows including phase-change effects. The proposed research focuses on the following aims: 1. Development and validation of an Euler-Lagrange model for particulate flows with phase-change effects, where the particles undergoing the phase change are modelled using the three-dimensional (3D) discrete element model (DEM) formulated in Lagrangian space, while the liquid phase is simulated using a computational fluid dynamics (CFD)-based model formulated in Eulerian space. 2. Development of subgrid models for interfacial heat and mass transfer applied to moving particles undergoing phase change. These models serve as a coupling between DEM and CFD models. 3. Validation of numerical models against experiments carried out for a defined reference system under well-defined boundary conditions: this is the melting of ‘ice’ particles settling in water. Here the Direct Numerical Simulation (DNS) of existing ‘ice’ experiments are planned to validate subgrid models for interfacial heat and mass transfer between solid and liquid phases. 4. Investigation of the phase distribution and flow anomalies in the liquid phase, such as the interplay between buoyancy and Archimedes forces in dependence on the volume fraction of solid. The vision followed by the project in the long-term consists in the development of an Euler-Lagrange model for a numerical simulation of binary alloy (AlSi) columnar-equiaxed solidification. To reach this goal it is necessary to understand the ruling principles of the melting (solidification) of solid particles moving in the liquid phase. Recent experimental studies published in the literature show that special attention should be paid to explaining anomalies relating to interaction between the gravity-induced forces. The short-term goal of this project is to develop and validate a subgrid semiempirical model for the behaviour of solidifying/melting particles depending on specific nondimensional numbers such as the Archimedes number (Ar), the Grashof number (Gr) and the Stefan number (Ste). The project's success will help advance knowledge on the fundamentals of solidification and on the accurate forecast of multicomponent material properties. The practical significance of this research consists in the development and validation of simplified models describing the interfacial heat and mass transfer between solid and liquid phases undergoing phase changes. The models developed in this project will contribute to a significant improvement in the computational software used in the industry to improve processes, reducing the production costs of advanced materials in Canada.