Controlling sliding droplets with optimal contact angle distributions and a phase field model

We consider the optimal control of a droplet on a solid by means of the static contact angle between the contact line and the solid. The droplet is described by a thermodynamically consistent phase field model from [Abels et al., Math. Mod. Meth. Appl. Sc., 22(3), 2012] together with boundary data for the moving contact line from [Qian et al., J. Fluid Mech., 564, 2006]. We state an energy stable time discrete scheme for the forward problem based on known results, and pose an optimal control problem with tracking type objective.TU Berlin, Open-Access-Mittel - 201

Decidability Results on the Existence of Lookahead Delegators for NFA

In this paper, we study lookahead delegators for nondeterministic finite automata (NFA), which are functions that deterministically choose transitions by additionally using a bounded lookahead on the input word. Of course, the delegator has to lead to an accepting state for each word that is accepted by the NFA. In the special case where no lookahead is allowed, a delegator coincides with a deterministic transition function that preserves the language. Typical decision problems are to decide whether a delegator with a given fixed lookahead exists, or whether a delegator with some bounded lookahead exists for a given NFA. In a paper of Ravikumar and Santean from 2007, the complexity and decidability of these questions have been tackled, mainly for the case of unambiguous NFA. In this paper, we revisit the subject and provide results for the case of general NFA. First, we correct a complexity result from the above paper by showing that the existence of delegators with fixed lookahead can be decided in time polynomial in the number of states. We use two player games on graphs as a tool to obtain the result. As second contribution, we show that the problem becomes PSPACE-complete if the bound on the lookahead is a part of the input. The third result provides a bound on the maximal required amount of lookahead. We use this to show that the (previously open) problem of deciding the existence of a bounded lookahead delegator is also PSPACE-complete

Uncertainty Analysis for Data-Driven Chance-Constrained Optimization

In this contribution our developed framework for data-driven chance-constrained optimization is extended with an uncertainty analysis module. The module quantifies uncertainty in output variables of rigorous simulations. It chooses the most accurate parametric continuous probability distribution model, minimizing deviation between model and data. A constraint is added to favour less complex models with a minimal required quality regarding the fit. The bases of the module are over 100 probability distribution models provided in the Scipy package in Python, a rigorous case-study is conducted selecting the four most relevant models for the application at hand. The applicability and precision of the uncertainty analyser module is investigated for an impact factor calculation in life cycle impact assessment to quantify the uncertainty in the results. Furthermore, the extended framework is verified with data from a first principle process model of a chloralkali plant, demonstrating the increased precision of the uncertainty description of the output variables, resulting in 25% increase in accuracy in the chance-constraint calculation.BMWi, 0350013A, ChemEFlex - Umsetzbarkeitsanalyse zur Lastflexibilisierung elektrochemischer Verfahren in der Industrie; Teilvorhaben: Modellierung der Chlor-Alkali-Elektrolyse sowie anderer Prozesse und deren Bewertung hinsichtlich Wirtschaftlichkeit und möglicher HemmnisseDFG, 414044773, Open Access Publizieren 2019 - 2020 / Technische Universität Berli

Investigation of the Degradation of Chelate Complexes in Liquid Redox Desulfurization Processes

Metal complexes such as Fe‐EDTA, which are used as pseudo‐catalysts or oxygen carriers in wet oxidative desulfurization processes, are subject to a degradation mechanism that significantly influences the economics of such processes. Therefore, this study presents a methodology for determining the degree of degradation during the reactive hydrogen sulfide absorption in a Fe‐EDTA solution within a continuously operating semi‐batch reactor system. For this purpose, the reactive conversion of H2S in the liquid phase was used as a reference, and a clear dependence of the degradation on the pH could be shown. In addition, indicators are introduced that evaluate the observed pH dependency of the degradation and distinguish pH‐induced effects such as the pH‐dependent absorption performance of H2S.TU Berlin, Open-Access-Mittel - 202

Direct Numerical Simulations of Liquids on Microstructured Surfaces: Analysing the Fluid Dynamics on Packing

Structured high performance packing for packing columns have macrostructures, e.g., corrugated or folded sheets, and in many cases microstructures or surface topographies with geometrical dimensions in the same order of magnitude as the film thicknesses. For an optimal design of microstructured surfaces and for the development of novel methodologies to predict the mass transfer, a reliable description of the influence of these microstructures is crucial. To research the influence of these microstructures on the liquid film in detail, and later on optimize the geometry, Direct Numerical Simulations applying the Cahn-Hilliard-Navier-Stokes (CHNS) equations were performed for this study. The model and the implementation were validated against analytical solutions for undisturbed laminar film flows. The influence of two single microstructures (triangle and rectangle) on the gas-liquid interface and the velocity in the liquid were systematically investigated. Thereby, it was observed, that small microstructures in comparison to the film thickness have no influence on the gasliquid interface. In contrast, higher structures could increase the interfacial area. The results indicate, that systematic studies on a wide range of geometries, phase properties and gas velocities can give valuable information on the path to optimal microstructures

Startup of a reactive distillation process with a decanter

The startup of a reactive distillation process for the production of propyl acetate including a decanter is studied. A simulation model is presented which describes the whole startup from a cold and empty state and takes into account the liquid phase split in the decanter. The simulation model is successfully validated with own dynamic experimental data. Different startup strategies are developed and analysed in simulation studies showing the high influence of the initial charging of decanter and reboiler on the startup time

Experimental characterization of stable liquid rivulets on inclined surfaces: Influence of surface tension, viscosity and inclination angle on the interfacial area

In this work, liquid rivulets on inclined, smooth surfaces were examined experimentally using light-induced fluorescence. The influence of viscosity, surface tension and inclination angle was studied in terms of the Reynolds and Kapitza numbers. Detailed results on the interfacial area of the rivulets were obtained. Based on the experimental results, a correlation of the interfacial area in dependence on the Reynolds and Kapitza numbers is proposed. It is found, that the correlation can reproduce the experiments very well

Dynamic Modelling and Operation of the Chlor-Alkali Process

Chlorine it is commonly produced through the Chlor-alkali process, which is an electrochemical process – the process energy consumption dominates the production cost. Therefore, optimization of the process has become a major issue to achieve energy conservation and cost effective production. This study aims at investigating the transient and steady-state behavior of the chlorine production system through process modeling and simulation. Material balance and energy balance of the Chlor-alkali membrane process (electrolysis), brine pre-treatment, and chlorine handling are modelled and investigated using rigorous models. MOSAIC and MATLAB, are used to model and to simulate the process response when receiving dynamic input. For validation, the simulation result is compared to experimental data

Optimal Control of Surfactant containing Multiphase Systems – Challenges and Solution Strategies for a stable Mini-Plant Operation

In this contribution, a model-based approach for the control and stable operation of a mini-plant for homogeneously catalysed reactions in microemulsions is presented. Within these systems, the control of the crucial reaction and phase separation steps is hindered by sensitive shifting operation windows and immeasurable concentrations. Combining the optical observation of the separation state and an underlying phase separation model, a soft-sensor is created to identify these relevant concentrations. Together with plant measurements, a moving horizon state estimation is used to calculate a consistent and validated state of the full plant model, which is then used in a dynamic optimization to calculate optimal trajectories for the mini-plant operation. Hereby, a stable separation is achieved for up to 200 h mini-plant campaigns, alongside an efficient reaction performance with up to 38 % yield and a chemoselectivity of 95 %.DFG, 56091768, TRR 63: Integrierte chemische Prozesse in flüssigen Mehrphasensysteme

Dynamic Model of Chloralkali Membrane Process

Chloralkali is one of the most important and energy intensive processes in the chemical industry. The process produces chlorine through electrochemical conversion. The process's energy consumption is a major production cost for the chloralkali industry. Since the demand for energy efficiency and environmentally friendly processes in industry increases, ion exchange membranes are used intensively in the process. One of the prospective energy sources for this process is renewable energy, which shows strong fluctuations and highly unpredictable behavior. Dynamic behavior of the process becomes important to measure and predict the feasibility of the process. Therefore, modelling of the process dynamics is required. Rigorous model of material balance and voltage balance of the process are developed and investigated in this paper. The material transport phenomena inside the electrolyser are modelled considering a number of driving forces. The developed model also predicts the voltage and current density of the cell. The process simulation result is compared to experimental data