Numerical Analysis of Effects of Specularity Coefficient and Restitution Coefficient on the Hydrodynamics of Particles in a Rotating Drum

Various simulations have been conducted to understand the macroscopic behavior of particles in the solid-gas flow in rotating drums in the past. In these studies, the no-slip wall boundary condition and fixed restitution coefficient between particles were usually adopted. The paper presents a numerical study of the gas-solid flow in a rotating drum to understand the effect of the specularity coefficient and restitution coefficient on the hydrodynamic behavior of particles in the segregation process. The volume fraction, granular pressure, granular temperature and their relationships are examined in detail. The boundary conditions of the no-slip and specularity coefficient of 1 are compared. In the simulations, two different sizes of particles with the same density are considered and the Eulerian–Eulerian multiphase model and the kinetic theory of granular flow (KTGF) are used. The results reveal that the hydrodynamical behavior of the particles in the rotating drum is affected by the boundary condition and restitution coefficient. In particular, the increase of specularity coefficient can increase the active region depth, angle repose, granular pressure for both small and large particles and granular temperature for large particles. With increasing restitution coefficient, the angle of repose decreases and granular pressure and temperature increase at the same volume fraction for both small and large particles.

Zn22Al4Ag ALLOY MICROWIRES CASTING TO RAPID SOLIDIFICATION PROCESS BY ROTATING DRUM

In this work, the Zn22Al4Ag alloy was synthesized by melting in a muffle furnace.The alloy obtained was characterized by Scanning Electron Microscopy Energy Dispersive Spectroscopy and was analyzed by the X-Ray Diffraction technique, where the crystallinity of the material was verified before and after being processed. Likewise, the Differential Scanning Calorimetry technique was used to obtain the temperatures where phase transformations occurin the alloy. These results were fed to the Termocalc®, software to numerically obtain the phase diagram of the alloy. Subsequently, a section of the ingot was taken to the rapid solidification process by rotating drum. The process variables were manipulated: jet stability, nozzle diameter, distance from the nozzle surface to the cooling medium, the delay time of the molten material in the crucible, speed of the rotating drum and jet angle, until obtaining a microwire with a diameter of ~ 160µm. Finally, it was determined that inadequate control of these parameters can result in powders, flakes or blockage of the crucible outlet. Potentially uses within the micro and nanoworld as an analogy to structural elements and electrical conductors, in addition to its current use as a coating anti-corrosive. Key Words: ZnAlAg alloy, Melt spinning process, Microwire, DSC analysis, Thermodynamic simulation

Load-Balancing Strategies in Discrete Element Method Simulations

In this research, we investigate the influence of a load-balancing strategy and parametrization on the speed-up of discrete element method simulations using Lethe-DEM. Lethe-DEM is an open-source DEM code which uses a cell-based load-balancing strategy. We compare the computational performance of different cell-weighing strategies based on the number of particles per cell (linear and quadratic). We observe two minimums for particle to cell weights (at 3, 40 for quadratic, and 15, 50 for linear) in both linear and quadratic strategies. The first and second minimums are attributed to the suitable distribution of cell-based and particle-based functions, respectively. We use four benchmark simulations (packing, rotating drum, silo, and V blender) to investigate the computational performances of different load-balancing schemes (namely, single-step, frequent and dynamic). These benchmarks are chosen to demonstrate different scenarios that may occur in a DEM simulation. In a large-scale rotating drum simulation, which shows the systems in which particles occupy a constant region after reaching steady-state, single-step load-balancing shows the best performance. In a silo and V blender, where particles move in one direction or have a reciprocating motion, frequent and dynamic schemes are preferred. We propose an automatic load-balancing scheme (dynamic) that finds the best load-balancing steps according to the imbalance of computational load between the processes. Furthermore, we show the high computational performance of Lethe-DEM in the simulation of the packing of 108 particles on 4800 processes. We show that simulations with optimum load-balancing need ≈40% less time compared to the simulations with no load-balancing.

Justification of the movement and displacement of the product inside the drum dryer with a paddle agitator

The technique and technology of movement and displacement of the powder product inside the drum dryer with a paddle agitator have been developed. Theoretical studies were carried out to assess the effect of the system of forces on the product inside the rotating drum when the agitator rotating in the opposite direction is exposed to it, which allowed estimating the throughput capability of the drying unit. It is established that, with an increase in the speed of movement and mixing of the product, the drying speed increases. The results of these studies can be used in the future when designing drying units and improving the drying technology.

The additional heat flux due to adhesion at a partially immersed rotating drum heat exchanger for latent heat storage

Latent heat storages can be used to store thermal energy at a constant temperature. By actively removing the solidified phase change material from the heat exchanger surface during the discharge process, the heat flux can be kept constant and a separation of power and capacity is possible. In the presented rotating drum concept, a cooled drum is partially immersed in a tub of liquid phase change material and rotates in it. Phase change material solidifies at the submerged part of the drum. In addition, adhering liquid phase change material solidifies after the surface has left the tub. In this paper, the additional heat transfer due to adhesion is examined by determining the solidified layer thickness as well as the heat transfer by comparing measurements with adhesion and while eliminating the adhesion with a rubber lip. The measured adhering layer thickness differs by 33% from a presented analytical approach. The transferred heat is increased up to 26 % due to the adhesion.