VOF-DEM study of solid distribution characteristics in slurry Taylor flow-based multiphase microreactors

Abstract

Solid particle distribution determines the reactor internal phases placement and the contact mode between catalyst particles and the liquid phase, thus plays a key role in dictating the overall performance of slurry Taylor flow-based microreactors. This study numerically investigates the distribution characteristics of particles within liquid slugs (reactors) in a vertical capillary tube, with the aim to describe the corresponding underlying mechanisms.The Volume of Fluid (VOF) method was deployed to solve the evolution of transient gas-liquid interfaces, whilst the motion of individual particles was directly tracked using the Discrete Element Method (DEM). Various fluid forces were considered based on the fully resolved Taylor flow field. Different body-fixed frames of reference were introduced to aid the analysis of the results.The particle distribution was found strongly dependent on the liquid flow field and particle physical properties, described in this study using the slurry Reynolds number (Re') and particle Stokes number (Stp), respectively. As Re' increased, the liquid flow experienced three distinctly different circulation patterns. Accordingly, three different particle distribution patterns were observed: I, particles distributed in the slug central region when Re'≤47; II, particles were trapped inside the liquid circulations for Re'∈95,190; and III, particles distributed at the edges of the liquid circulations when Re'≥379. III was the predominant particle distribution pattern in slurry Taylor flow systems. The drag force was found to be the main force governing the vertical particle motion, whilst shear lift force and horizontal drag force were the main forces driving the lateral particle motion. Generally, as Re' or Stp increased, particles tended to migrate from the core to the edge of the liquid circulations, leading to a more nonuniform particle distribution. The solid volume fraction variance (σ2) of 0.0025 could be viewed as the threshold less than which the particle distribution in the liquid slugs was considered uniform. The relatively uniform particle distribution (with σ2≤0.0025) was achievable forRe'<550 and Stp<0.1.