Lagrangian Simulation of Steady and Unsteady Laminar Mixing by Plate Impeller in a Cylindrical Vessel

Refined energy-conserving dissipative particle dynamics model with temperature-dependent properties and its application in solidification problem

It has been observed previously that the physical behaviors of Schmidt number (Sc) and Prandtl number (Pr) of an energy-conserving dissipative particle dynamics (eDPD) fluid can be reproduced by the temperature-dependent weight function appearing in the dissipative force term. In this paper, we proposed a simple and systematic method to develop the temperature-dependent weight function in order to better reproduce the physical fluid properties. The method was then used to study a variety of phase-change problems involving solidification. The concept of the "mushy" eDPD particle was introduced in order to better capture the temperature profile in the vicinity of the solid-liquid interface, particularly for the case involving high thermal conductivity ratio. Meanwhile, a way to implement the constant temperature boundary condition at the wall was presented. The numerical solutions of one- and two-dimensional solidification problems were then compared with the analytical solutions and/or experimental results and the agreements were promising.

Enhancement of Laminar Flow and Mixing Performance in a Lightnin Static Mixer

The laminar chaotic flow and mixing performance of a high-viscosity fluid in Lightnin static mixers (LSM) was numerically investigated via a Lagrangian particle method based on the Particle tracking technique in the range of Re=0.1−100. The numerical results of Z factor have a good agreement with the reported data from the literature. With the increase of Re in LSM, the Darcy friction coefficient values decrease and the product of fD · Re linearly increases. With the same aspect ratio (Ar), the product of fD · Re in LSM is higher by 36−57 % than that of KSM. The distribution evolution of circular group of massless particles is successfully investigated by particle distribution uniformity (PDU) in the first few mixing elements. A new ideal distribution model is proposed for structure radius (SR) which is successfully used to investigate uniform distribution of mixing process in the last few elements. The effects of Re and Ar of mixing elements on dispersive mixing performance are characterized by extensional efficiency and stretching rate. The logarithms of geometrical average stretching rate of massless particles increase linearly with the number of mixing elements. The stretching rate in LSM with Ar=1, 1.5, 2 is average higher by 45.91 %, 36.05 % and 24.32 % than that of KSM with Ar=1.5. As far as the creeping flow in LSM is concerned, the logarithm values of stretching rate are independent of Re and Ar. The mixing performance factor η is proposed to evaluate the enhancement mechanism of mixing performance based on the energy consumption. The η increases with the increasing Re and decreasing Ar. The profiles of η indicate that the mixing enhancement ability of LSM is better than that of KSM.