Krunoslav Žižek

Transport phenomena in environmental engineering

Abstract A term transport phenomena arises as a second paradigm at the end of 1950s with high awareness that there was a strong need to improve the scoping of chemical engineering science. At that point, engineers became highly aware that it is extremely important to take step forward from pure empirical description and the concept of unit operations only to understand the specific process using phenomenological equations that rely on three elementary physical processes: momentum, energy and mass transport. This conceptual evolution of chemical engineering was first presented with a well-known book of R. Byron Bird, Warren E. Stewart and Edwin N. Lightfoot, Transport Phenomena, published in 1960 [1]. What transport phenomena are included in environmental engineering? It is hard to divide those phenomena through different engineering disciplines. The core is the same but the focus changes. Intention of the authors here is to present the transport phenomena that are omnipresent in treatment of various process streams. The focus in this chapter is made on the transport phenomena that permanently occur in mechanical macroprocesses of sedimentation and filtration for separation in solid–liquid particulate systems and on the phenomena of the flow through a fixed and a fluidized bed of particles that are immanent in separation processes in packed columns and in environmental catalysis. The fundamental phenomena for each thermal and equilibrium separation process technology are presented as well. Understanding and mathematical description of underlying transport phenomena result in scoping the separation processes in a way that ChEs should act worldwide.

Droplet Impact Phenomena in Fluidized Bed Coating Process with a Wurster Insert

The aim of this study is to determine favorable process conditions for the coating of placebo tablets. Tablets made of microcrystalline cellulose are coated with hydroxypropyl cellulose polymer and Advantia™ Prime polymeric mixture film in lab-scale fluid-bed environment with a Wurster tube. In order to determine favorable process conditions (concentration, Wurster tube position, inlet air temperature, and atomization pressure), evaluation factors expressing process efficiency were calculated. Stereomicroscopy analysis provided good results with respect to the coating layer adherence and consistency. Results showed that the increased number of the coating cycles contributes to the desired featureless film morphology, when sufficiently high temperature and pressure are applied, thus resulting in high intra- and intertablet uniformity. Additionally, this paper analyzes the coating process from a mechanistic perspective of the underlying phenomena occurring on a tablet surface. Provided diagrams can help efficiently in detecting proper conditions that will result in coated tablets with strictly defined aimed properties. Process and formulation properties synergically result in a preferential occurrence of a deposition mechanism for all experiments conducted. Moreover, collision is found as a prevalent impact regime for the coating process studied. Finally, our intention here is to correlate hydrodynamic conditions and droplet breakup occurrence with a droplet diameter.