Hans-Joachim Warnecke

Chemo-enzymatic epoxidation of unsaturated plant oils

Abstract The kinetics of the chemo-enzymatic epoxidation of linseed oil is investigated. The multiphase process consists basically of a consecutive reaction — a lipase catalyzed peracid formation followed by a Prilezhaev epoxidation. Kinetic measurements were carried out in an enzyme-recycle reactor. The kinetics of the process are incorporated in a semi-batch model and the rate constants of the involved reactions are determined by means of non-linear regression. Simulations with this mathematical model agree with the experimental data found for the reaction system.

Heat transfer and pressure drop characteristics in rectangular channels with elliptic pin fins

Abstract Experiments have been carried out to investigate the heat transfer and flow resistance characteristics in rectangular ducts with staggered arrays of short elliptic pin fins in a crossflow of air. By employing the heat/mass transfer analogy and the naphthalene sublimation technique, the mean heat transfer coefficients on pin fins and on the endwall (base plate) of the channel have been presented, respectively. The total mean heat transfer coefficients of pin fin channels are calculated and the resistance coefficients are also investigated. The experimental results show that the heat transfer of a channel with elliptic pin fins is somewhat higher than that with circular pin fins while the resistance of the former is much lower than that of the latter in the Reynolds number range from 1000 to 10 000.

A population balance model for disperse systems: Drop size distribution in emulsion

Abstract A mechanistic model for the description and prediction of the drop size distribution in a turbulently agitated emulsion dispersion is developed. Based on this model, breakage rate and relative distribution functions are determined and used to solve the general population balance equation for a continuous flow vessel. Parameters of the models are evaluated from experimental data by means of Marquardt’s method. The model is found to be capable of predicting bimodal drop size distributions of emulsions.

Computation of Scales and Quality of mixing in a T-shaped microreactor

By definition, mixing in chemical reactors is a multi-scale process since it aims at reducing the length scale on which the chemical components are segregated. Only this way, micro-mixing can be accelerated in order to increase the intensity of mixing. Numerical simulations prove helpful to gain a better understanding of the interplay of transport mechanisms on different length scales, but require means to efficiently extract information about the scales and the quality of mixing. For this purpose, a formula from geometric measure theory is employed to compute both the finest and an integral length scale. Application to a T-shaped microreactor yields interesting information about how the scales depend on the Schmidt number.

On a mathematical model for loop reactors—I. Residence time distribution, moments and eigenvalues

Abstract A general mathematical model for the description of the mixing behaviour of loop reactors is presented. It distinguishes the different mixing sections and considers the concentration profile caused by the recycle. The residence time distribution, the moments and the eigenvalues are evaluated and a method for the determination of the model parameters is sketched.

Multifunctional system for treatment of wastewaters from adhesive-producing industries: separation of solids and oxidation of dissolved pollutants using doted microfiltration membranes

To eliminate non-biodegradable organic compounds from wastewater application of semiconductor photocatalysis has been done. Experiments have been performed on immobilizing the photocatalyst titanium dioxide in an organic PAN microfiltration membrane and illuminated by UV-A light in order to improve oxidation performance and avoid particle separation. The organic pollutants are oxidized by in situ-produced hydroxyl radicals or directly by the catalyst. The membrane causes a convective flow of the pollutant towards the catalyst. The separation properties of the membrane can be used in a multifunctional way to extract remaining solid particles. A module containing membranes and a UV light source was developed. 4-Chlorophenol was completely mineralized at a high reaction rate. A two-step process has been developed for the clarification of highly polluted waste waters from adhesive-producing plants. First, the suspended solids which reach up to 10% of the mass stream are precipitated, flocculated and separated by means of a decanting centrifuge and flotation. Then the photocatalytic process was applied on the dissolved organic contents.

VOF-Simulations of Mass Transfer From Single Bubbles and Bubble Chains Rising in Aqueous Solutions

This paper presents numerical simulations of two-phase flow with high-density ratio, taking into account mass transport of a soluble component and its interfacial mass transfer. The mathematical model and the numerical method allow for different solubility of the species in the respective fluid phases, while volume changes due to mass transfer are neglected. The discontinuous changes in species concentrations at the interface are modeled by means of Henry’s law. Simulations are carried out with an extended version of the highly parallelized code FS3D, which employs an advanced Volume-Of-Fluid (VOF) method. Transfer and transport of oxygen is examined in case of single bubbles as well as bubble chains rising in aqueous solutions. Numerical simulations show good qualitative agreement with experimental data and render the observed mass transfer phenomena correctly.Copyright

Direct numerical simulation of mass transfer between rising gas bubbles and water

This paper presents numerical simulations of two-phase flow with high-density ratio, taking into account mass transport of a soluble component and its interfacial mass transfer. The mathematical model and the numerical method allow for different solubility of the species in the respective fluid phases, while volume changes due to mass transfer a reneglected. The discontinuous changes in species concentration sat the interface are modeled by means of Henry’s law. Simulations are carried out with a next ended version of the highly parallelized code FS3D, which employs an advanced Volume-Of-Fluid(VOF) method. For the examination of mass transfer, single bubbles are held in counter-flow to investigate the transient dissolution of a dilute species. In case of small bubbles with laminar wake a rotational symmetric concentration profile occurs, in agreement with theoretical considerations, while the local mass concentrations in the wake of larger bubbles show complex patterns of varying concentration as it also has been recently observed experimentally.

Scale-up of airlift-loop bioreactors based on modelling the oxygen mass transfer

Abstract Experimental data for oxygen mass transfer have been estimated in airlift-reactors with outer loop and a volume of 2 1, 80 1 and 800 1 respectively and a 70 1 inner loop reactor. The utilized multiphase system contained air, water and, in some cases, polymer granulate as solid phase. Five oxygen-transfer models are taken into consideration, and scaling up of airlift-bioreactors with regard to oxygen transfer is discussed.

Modeling of the Suspension Polymerization Process Using a Particle Population Balance

On the basis of a population balance and the kinetic mechanism of free-radical suspension polymerization, a mathematical model of the suspension polymerization process is proposed. The population balance model which describes a mechanism involving the particle size distribution (PSD) in disperse systems leads to an integrodifferential equation. The basic numerical approach of this work is to use the finite-difference-differential technique with the logarithmic scale for particle size. The problem then was reduced to obtaining the numerical solution of a set of nonlinear ordinary differential equations. The numerical solutions were compared to experimental data, such as the reaction conversion which includes the gel effect and the particle size distributions, to yield the model parameters by Marquardts method. The regression demonstrates reasonably good accuracy.