Theory of Drop Formation

We consider the motion of an axisymmetric column of Navier-Stokes fluid with a free surface. Due to surface tension, the thickness of the fluid neck goes to zero in finite time. After the singularity, the fluid consists of two halves, which constitute a unique continuation of the Navier-Stokes equation through the singular point. We calculate the asymptotic solutions of the Navier-Stokes equation, both before and after the singularity. The solutions have scaling form, characterized by universal exponents as well as universal scaling functions, which we compute without adjustable parameters

Model-Based Analysis of the Limiting Mechanisms in the Gas-Phase Oxidation of HCl Employing an Oxygen Depolarized Cathode

The electrochemical oxidation of HCl to Cl2 plays an important role in the production of polycarbonates and polyurethanes. Recently, the gas-phase oxidation of HCl proved to be significantly more efficient than the current state-of-the-art process based on the oxidation of hydrochloric acid. In experimental investigations of this gas-phase reactor, a limiting current can be observed that is so far not understood but impedes the overall reactor performance. In the present work, a nonisothermal multiphase agglomerate model is developed to investigate the underlying reasons for this limiting behavior in more detail. It is shown that the thermal management of the cell plays a significant role and that minor changes to its thermal resistance lead to the limiting behavior being caused by either flooding of the cathode or dehydration of the membrane and anode. An optimization of operational and structural parameters of the cell based on these insights leads to an increase in the limiting current by more than 90%. Interestingly, under these conditions a third phenomenon, the rate determining Tafel step in the microkinetic reaction mechanism of the HCl oxidation, limits the overall reactor performance. These insights harbor the potential for enormous energetic savings in this industrially highly relevant process

Contributing to WUDAPT: A Local Climate Zone Classification of Two Cities in Ukraine

Local climate zones (LCZs) divide the urban landscape into homogeneous types based on urban structure (i.e.,morphology of streets and buildings), urban cover (i.e., permeability of surfaces), construction materials, and human activities (i.e., anthropogenic heat). This classification scheme represents a standardized way of capturing the basic urban form of cities and is currently being applied globally as part of the world urban database and portal tools (WUDAPT) initiative. This paper assesses the transferability of the LCZ concept to two Ukrainian cities, i.e., Kyiv and Lviv, which differ in urban form and topography, and considers three ways to validate and verify this classification scheme. An accuracy of 64% was achieved for Kyiv using an independent validation dataset while a comparison of the LCZ maps with the GlobeLand30 land cover map resulted in a match that was greater than 75% for both cities. There was also good correspondence between the urban classes in the LCZ maps and the urban points of interest in OpenStreetMap (OSM). However, further research is still required to produce a standardized validation protocol that could be used on a regular basis by contributors to WUDAPT to help produce more accurate LCZ maps in the future