Alexander Penn

Technische Universität Hamburg | TUHH · Instiute of Process Imaging

Understanding and predicting the hydrodynamics of gas bubbles and particle-laden phase in fluidized beds is essential for the successful design and efficient operation of this type of reactor. In this work, we used real-time magnetic resonance imaging (MRI) to investigate the effect of baffles on gas bubble behavior and particle motion in a fluidiz...

Controlling the temperature distribution inside catalytic fixed bed reactors is crucial for yield optimization and process stability. Yet, in situ temperature measurements with spatial and temporal resolution are still challenging. In this work, we perform temperature measurements in a cylindrical fixed bed reactor by combining the capabilities of...

With the ongoing digitalization of industry, imaging sensors are becoming increasingly important for industrial process control. In addition to direct imaging techniques such as those provided by video or infrared cameras, tomographic sensors are of interest in the process industry where harsh process conditions and opaque fluids require non-intrus...

Objects released into a granular packing close to incipient fluidization may float or sink depending on their density. Contrary to intuition, Oshitani et al. [Phys. Rev. Lett. 116, 068001 (2016)] reported that under certain conditions, a lighter sphere can sink further and slower than a heavier one. While this phenomenon has been attributed to a lo...

Numerical simulations of a freely bubbling cylindrical fluidized bed are carried out using a coupled computational fluid dynamics and discrete element method (CFD-DEM) model and compared to recent experimental data. The experiments were conducted using high-resolution and high-frequency magnetic resonance imaging providing high-fidelity data of the...

An external load on a particle packing is distributed internally through a heterogeneous network of particle contacts. This contact force distribution determines the stability of the particle packing and the resulting structure. Here, we investigate the homogeneity of the contact force distribution in packings of highly nonconvex particles both in...

Rapid magnetic resonance imaging is used to study the interaction between two gas jets injected into a 3D incipiently fluidized bed. At large separation distances and in cases with larger particles, bubbles pinch off from the two jets simultaneously with one another. At small separation distances with smaller particles, a jet grows at one orifice w...

An external load on a particle packing is distributed internally through a heterogeneous network of particle contacts. This contact force distribution determines the stability of the particle packing and the resulting structure. Here, we investigate the homogeneity of the contact force distribution in packings of highly non-convex particles both in...

Real-time magnetic resonance imaging was used to study the different flow regimes which occur in a fluidized bed containing a gas injection system. The gas flow rates through the main distributor and a central orifice were varied independently. We identified six different regimes of bubbling and jetting behavior: (1) freely bubbling, (2) permanent...

Rapid magnetic resonance imaging (MRI) was used to characterize properties of a single central gas jet injected into a 3D gas fluidized bed under incipient fluidization conditions. Snapshots of both particle concentration and particle velocity are provided. The average jet height, oscillations in jet height and the size of bubbles breaking off from...

Rapid magnetic resonance imaging (MRI) was used to visualize and quantify the interaction of two bubbles injected into an incipiently fluidized bed. The particle size, bubble sizes and the vertical and horizontal separations between bubbles were varied to understand their effects on bubble behavior. Image analysis quantified the size, shape and pos...

Significance Flow of granular materials, such as sand and catalytic particles, is critical to a wide range of natural phenomena and industrial processes. However, the physics underlying granular flows is poorly understood. We report the discovery of gravitational instabilities in binary granular materials driven by a gas channeling mechanism unseen...

The effect of internals on the fluidization dynamics in three-dimensional (3D) cylindrical fluidized beds was studied using real-time magnetic resonance imaging. Instantaneous snapshots of particle velocity and particle position were acquired for gas velocities U below and above the minimum fluidization velocity Umf. Below Umf, we found local fluid...

The collapse, or reduction in size to zero volume, of bubbles injected into incipiently fluidized beds was studied using rapid magnetic resonance imaging. The collapse of a smaller lower bubble trailing a larger upper bubble and the collapse of one bubble when two bubbles rose side by side were found to occur. Under the same conditions with the use...

Rapid magnetic resonance imaging (MRI) was used to determine the volume of wakes of bubbles injected into incipiently fluidized beds. MRI was used to generate 2D maps of particle velocity surrounding bubbles with a temporal resolution of 18 ms. The bubble rise velocity, u b , was determined from the change in bubble position in successive maps, and...

Rapid magnetic resonance imaging is used to investigate the volume, shape and rise velocity of single isolated bubbles injected into incipiently fluidized beds as well as the particle velocity field surrounding these bubbles. The volume of gas injected and particle size are varied to investigate their effects on bubble behavior. Image processing is...

Rapid magnetic resonance imaging was used to take snapshots of solids volume fraction and particle velocity fields in an incipiently fluidized bed with single bubbles injected under both dry and wet conditions. Under wet conditions, cohesive liquid bridges formed between particles, altering the flow such that bubbles became flatter as compared to d...

Snapshots of particle concentration and velocity fields in bubbling gas-solid fluidized beds were acquired using magnetic resonance imaging. Using a recently developed multichannel radiofrequency receiver coil in combination with fast readout techniques, adapted from medical MRI protocols, the temporal resolution was 7 ms and 18 ms for 2D images of...

Magnetic resonance imaging is used to generate snapshots of particle concentration and velocity fields in gas-solid fluidized beds into which small amounts of liquid are injected. Three regimes of bed behavior (stationary, channeling and bubbling) are mapped based on superficial velocity and liquid loading. Images are analyzed to determine quantita...

Purpose: The goal of this study was to devise a gradient system for MRI in humans that reconciles cutting-edge gradient strength with rapid switching and brings up the duty cycle to 100% at full continuous amplitude. Aiming to advance neuroimaging and short-T2 techniques, the hardware design focused on the head and the extremities as target anatom...

Granular dynamics govern earthquakes, avalanches, and landslides and are of fundamental importance in a variety of industries ranging from energy to pharmaceuticals to agriculture. Nonetheless, our understanding of the underlying physics is poor because we lack spatially and temporally resolved experimental measurements of internal grain motion. We...

La0.6Sr0.4CoO3−δ thin films of varying thicknesses (20–170 nm) were prepared by pulsed laser deposition on yttria-stabilized zirconia (100) substrates, and their electrochemical electrode performance was correlated with the chemical surface composition and microstructure (e.g. porosity, surface area). The surface cation composition was analyzed by...

The oxygen exchange and diffusion properties of La0.6Sr0.4CoO3 − δ thin films on yttria stabilized zirconia were analyzed by impedance spectroscopy and 18O tracer experiments. The investigations were performed on the same thin film samples and at the same temperature (400 °C) in order to get complementary information by the two methods. Electrochem...

Cation diffusion was investigated in La0.6Sr0.4CoO3-δ (LSC) thin films on (100) yttria stabilized zirconia in the temperature range 625-800 °C. Isotopic ((86)Sr) and elemental tracers (Fe, Sm) were used to establish diffusion profiles of the cations in bi- and multi-layered thin films. The profiles were analyzed by time of flight-secondary ion mass...