Practical trainings, student assistants and theses

Competitive bubble-particle attachment from a particle mixture in a model stirred cell (Id 405)

Master theses / Diploma theses / Compulsory internship

Foto: Particles on bubble in cell ©Copyright: Dr. Milad Eftekhari Flotation is a widely used technique worldwide to extract valuable minerals from less valuable ones. To make the process more efficient, several methods have been developed to investigate how various factors affect particle floatability (recovery). Traditionally, this is done by measuring the hydrophobicity of the particles. However, floatability is a much broader concept that encompasses not only hydrophobicity but also other factors such as hydrodynamic conditions. In our research, we introduce a novel approach to quantify particle floatability from a mixture through dynamic bubble surface coverage experiments, considering hydrodynamic effects. Our focus is to understand how the different particles attach to a single bubble from a system containing two (or three) different particle types (chalcopyrite and/or pyrite + quartz). In particular, how one type of particle affects the recovery of another type.

Our objective is:

  • To study the effect of pH and collector concentration on particle floatability.
  • To establish a correlation between floatability and flotation recovery.
Experimental methods/techniques:
  • Image acquisition and analysis
  • Particle size analysis techniques such as laser diffraction and dynamic light scattering

Department: Transport processes at interfaces

Contact: Dr. Eftekhari, Milad, Öktem, Gülce

Requirements

  • duration min. 6 month, workplace: HZDR

Online application

Please apply online: english / german

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Dynamics of bubble-particle attachment in a model stirred cell (Id 404)

Master theses / Diploma theses / Compulsory internship

Foto: Dynamics of bubble-particle attachment in a model stirred cell ©Copyright: Dr. Milad EftekhariA process called flotation is widely used throughout the world to separate valuable minerals from non-valuable ones. Successful flotation relies on several sub-processes, such as promoting the attachment of certain sizes of particles to bubbles while preventing the attachment of others. Therefore, it is important to advance our knowledge about the particle attachment process, particularly, when different particle sizes are considered. Here we use our in-house setup to study:

  • The effect of ultrafine particles on the attachment rate of fine particles.
  • The effect of various parameters e.g., particles hydrophobicity on the packing density of the particles.
Experimental methods/techniques:
  • Image analysis
  • Particle size analysis techniques such as laser diffraction and dynamic light scattering

These experimental methods and the topic of particles at interfaces can prepare you for a variety of jobs after graduation, as these concepts are widely applicable in various fields such as mineral processing, recycling, pharmaceuticals, cosmetics, painting, and so on.

Department: Transport processes at interfaces

Contact: Dr. Eftekhari, Milad, Dr. Schwarzenberger, Karin

Requirements

  • Study in process engineering, chemical engineering (or comparative field of study)
  • Motivation, interest in this field of research, experimental experience
  • Optimally: basic knowledge of particle measurement techniques

Conditions

duration min. 6 month, start: from now, workplace: HZDR

Online application

Please apply online: english / german

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Experimental investigation of aerosol particle separation (Id 403)

Master theses / Diploma theses / Compulsory internship

Foto: swirl generator ©Copyright: Dr. Gregory LecrivainAs part of the CORAERO joint project (Airborne Transmission of SARS Coronavirus - From Fundamental Science to Efficient Air Cleaning Systems) funded by the Helmholtz Association, we are working on scientific issues relating to the formation of virus-laden aerosols, their thermodynamics and propagation in rooms, as well as strategies and technologies to prevent aerosol-borne infections.

The separation of aerosol particles in gas-liquid systems plays a central role in a variety of industrial and natural applications, among which stand out air purification and filtration systems as well as precipitation scavenging. The particle size significantly affects the separation rate. The diffusion of particles in the nanometer range is largely dominated by molecular diffusion. In this regime, predictive models accurately estimate the separation rates. Model inaccuracy increases, however, significantly when the particle size ranges from 0.1 μm to 2.5 μm. In this impaction-dominated regime, the complex interplay between the flow dynamics and the particle inertia makes it difficult to apply predictive tools.

A novel concept based on gas-liquid cyclone for particle separation is here to be conceived, tested and compared to a traditional wet filtering system. To this aim, we are looking for student interested in experimental multiphase flow investigations.

For more info please visit: https://www.coraero.de/

Department: Experimental Thermal Fluid Dynamics

Contact: Dr. Wiedemann, Philipp, Cavagnola, Marco Alejandro

Requirements

  • Currently study chemical/mechanical/process engineering or natural sciences
  • Good communication skills in German AND English
  • Enjoy working in the lab and be able to work independently

Conditions

The duration of the work should ideally be 6 months. Remuneration is available.

Online application

Please apply online: english / german

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Investigation of the flow following behavior of lagrangian sensor particles in aerated reactors (Id 398)

Master theses / Diploma theses / Compulsory internship

Foto: Sensor particle next to stirrer with bubbles ©Copyright: Lukas BuntkielData acquisition in large industrial vessels such as bio reactor, biogas fermenters or wastewater treatment plants is limited to local measurement points due to the limited access to the vessel and the non-transparent fluid. To optimize these kinds of plants the three-dimensional flow field and the spatial distribution of e.g. temperature and electrical conductivity inside the vessel needs to be known. This can be done by the autonomous flow following lagrangian sensor particles (LSP) developed at the HZDR. Equipped with a pressure sensor, an accelerometer, two gyroscopes and a magnetometer, the sensor particle can track the flow movement inside of the vessels. From this, the flow field can be reconstructed.

To achieve a good flow following behavior, the density of the LSP can be adjusted before they are released into the vessel. While this works well for non-aerated systems, the influence of aeration on the flow following capability is unknown. Another unknown is how the velocities of the rising bubbles and of the continuous phase relates to the velocity measured by the LSP.
Therefore, the aim of this master thesis is to investigate the influence of aeration on the LSPs theoretically and experimentally by tracking the LSP with a camera. This includes the following tasks:

  • Literature research on flow following behavior of large particles in fluids
  • Experiments in a bubble column (330 mm ID) with LSPs and camera
  • Data evaluation to retrieve the fluid velocity, bubble rising velocity and LSP velocity
  • Comparison and conclusions on the flow following capability of LSPs in aerated reactors and comparison to the non-aerated case.

Department: Efficient wastewater treatment

Contact: Buntkiel, Lukas, Marchini, Sara

Requirements

  • Studies in the area of chemical or mechanical engineering or similar
  • Basic chemical and fluid engineering knowledge
  • Data analysis in Python
  • Independent and structured way of working

Conditions

  • Immediate start possible
  • Duration according to the respective study regulations

Links:

Online application

Please apply online: english / german

Druckversion


Numerical investigation of particle mixing - internship or thesis (Id 396)

Master theses / Diploma theses / Compulsory internship / Volunteer internship

Foto: Mixing of Fine Particles ©Copyright: Dr. Stephan BodenFine-grained solid particles from various industrial sources, which would otherwise be discarded, should ideally be processed to valuable products or inert residues. Among others, a) shredder fines from electronics and end-of-life vehicles, and b) flue dusts from non-ferrous metallurgical processes are of timely interest. They contain valuable residuals, such as metals, that can be returned to the industrial cycle instead of being landfilled. This is one aim of the Helmholtz project FINEST in which this work is embedded.
The different finest powders need to be mixed and agglomerated for further processing. Our work in the project deals with the granular mixing. One aim is to describe particle flow based on the rheology of the bulk good while describing the mixing process among the particles using a transport equation.
The particle bulk flow in a mixing apparatus can be modelled by CFD, using e.g. FEM. The particle flow field is then coupled with the transport equation to describe the mixing process among the particles.
We are looking for someone with experience in CFD or other modelling to tackle the implementation of this model. Expertise in the numerical development of in-house multi phase flow solvers is available [Lecrivain, JCP, 2021].

Department: Particle dynamics

Contact: Baecke, Anna Magdalena, Dr. Lecrivain, Gregory

Requirements

  • Student of e.g. Process Engineering, Chemical Engineering, Computational Engineering, Mechanical Engineering, …
  • General interest in fluid mechanics and simulations
  • Preliminary experience in CFD, ideally OpenFOAM
  • Preliminary experience in code development (C++) optional

Conditions

  • Immediate start possible
  • Duration of internship or thesis according to study regulations
  • Remuneration available, scholarship holders (e.g. ERASMUS+) welcome

Online application

Please apply online: english / german

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Experimental investigation of Taylor bubble shape in narrow tubes with constrictions (Id 390)

Bachelor theses / Master theses / Diploma theses / Compulsory internship / Volunteer internship

The presence of geometrical singularities in pipes may significantly affect the behavior of two-phase flow and subsequently the liquid film thickness or bubble shape. Therefore, it is an important subject of investigation in particular when the application concerns industrial safety and design.
In this work, the shape of individual air Taylor bubble in vertical tubes with constrictions subjected to counter-current liquid is experimentally performed and the influence of the obstacle on the bubble shape is analyzed. The restrictions that the constrictions on narrow tubes imposes on the motion of the interface, and its effect on the bubble shape, will be addressed in terms of geometrical and flow parameters.

In this work, the student will experimentally investigate and record high quality images and gain knowledge about experimental work regarding two-phase flow, image acquisition with MATLAB and data organization. The results will lead to the development of a flow regime map in function of diameter and viscosity.

Institute: Institute of Fluid Dynamics

Contact: Maestri, Rhandrey

Requirements

General interest in fluid mechanics;
Preliminary experience in experimental work is desirable;
Good written and oral communication skills in either English or German.

Conditions

Immediate start;
Duration of the internship is anticipated to be 3 months but can be modified according to study regulations;
Remuneration according to HZDR internal regulations.

Online application

Please apply online: english / german

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Two phase flow in a mili-/micro-fluidic channel: rare-earth extraction/stripping with/ without magnetic field (student assistant 19 h/week for 3 months + extensions) (Id 386)

Student Assistant

Rare earth elements are group of 17 elements in periodic table. They have unique physicochemical properties which make them essential in many high-tech components, e.g. electric mobility, laser, catalyst etc. The separation of rare earths in industry is mainly done by liquid-liquid extraction, a technique of high environmental footprint. The separation is based on the marginal difference in their affinity against the extractant used. Hence, the separation factor, a parameter quantifying the “separability” of these elements, are small. Normally, hundreds of repeating stages has to take place in plants producing multiple single rare earth products.

We are actively researching a potentially more environmentally friendly alternative approach to improve the separation factor in solvent extraction of rare earths. One approach is to modulate their respective extraction kinetics. Rare-earth ions are affected due to their magnetic susceptibility in a stray field of a magnetic source. The Kelvin force that occurs, can selectively influence the extraction kinetics. Once the goal of establishing a functioning microfluidic flow system has been achieved, a magnetic field can be applied. Various experiments are carried out to separate rare earths in this way. This allows conclusions to be drawn about the reaction kinetics and a deeper understanding of the physical chemical processes can be obtained. For promising candidates there is subsequently the opportunity (Belegarbeit/ Diplomarbeit)) for further employment.

Department: Transport processes at interfaces

Requirements

1. Interest on applied optical experiment
2. Basic chemical and fluid engineering knowledge
3. can handle common lab chemicals
4. Work conscientiously and safely
5. Capable of communication and some basic data analysis skill

Conditions

1. Design and assembly the experimental setup of two two-phase-flow systems, one with a slug-flow and one with a parallel-flow of aqueous and organic solution (Fig 1).
2. Add and adjust pumping system and creation control program
3. UV - Vis Spectroscopy for different rare-earth concentrations
4. Experimental study with/ without applied magnetic field

Online application

Please apply online: english / german

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Internship on experimental investigation of aerosol propagation (Id 381)

Student practical training / Compulsory internship / Volunteer internship

Background:

Currently, there is a broad discussion whether ventilation by frequent window opening is sufficient for providing a sufficient amount of fresh air or if technical air purification devices based on e.g. HEPA filters are better solutions for public spaces. Furthermore, there is another discussion ongoing, whether a well-guided laminar flow or a high degree of mixing within a room is more beneficial. The latter, on the one hand distributes the potentially virus-laden aerosols in the whole room, but on the other hand reduces the peak concentrations of these aerosols clouds by magnitudes.

Objectives:

The objective is to perform aerosol propagation experiments and to estimate the potential aerosol inhalation of people in dynamic situations. To achieve this, an aerosol generator will be used in a demonstrator room under different flow conditions. The data from different scenarios will be processed in order to obtain a transference function that can relate the aerosol source with the aerosol receivers.

Tasks:

  • Literature survey
  • Aerosol experiments in different scenarios.
  • Post-processing of the results.

Department: Experimental Thermal Fluid Dynamics

Requirements

  • Student of natural sciences or engineering
  • Willingness to conduct experimental work

Conditions

Duration:

4-6 months

Remuneration:

According to HDZR guidelines

Online application

Please apply online: english / german

Druckversion


Numerical simulation of particles in rising gas bubbles (Id 356)

Student practical training / Master theses / Student Assistant / Compulsory internship / Volunteer internship

The separation of aerosol particles by a moving gas-liquid fluidic interface is central to a wide variety of industrial and natural applications, among which stand out air purification systems and precipitation scavenging. The particle size significantly affects the separation rate. The diffusion of particles in the nanometer range is largely dominated by molecular diffusion. In this regime, predictive models accurately estimate the separation rates. Model inaccuracy increases, however, significantly when the particle size ranges from 0.1 μm to 2.5 μm. In this impaction-dominated regime, the complex interplay between the flow dynamics on both sides of the fluidic interface and the particle inertia makes it difficult to develop suitable models.
In this work, the student will numerically investigate whether enforcing bubble deformation into a non-spherical shape leads to a higher deposition rate, hereby making the particle separation process more efficient. The results will lead to the development of an improved and reliable separation model accounting for the deformation of the fluidic interface and the associated flow changes.

Department: Experimental Thermal Fluid Dynamics

Contact: Maestri, Rhandrey

Requirements

  • General interest in fluid mechanics
  • Preliminary experience in code development (C++) is desirable
  • Good written and oral communication skills in either English or German

Conditions

  • Either an immediate start or a start in 2024 is possible
  • Duration of the internship is anticipated to be 6 months but can be modified according to study regulations
  • Remuneration according to HZDR internal regulations

Online application

Please apply online: english / german

Druckversion