Solid Bed Research Articles

A comparative study of different techniques for quantum dot nano-particles immobilization on glass surface for fabrication of solid phase fluorescence opto-sensors

Using fluorescence quenching of quantum dot nano-particles is a promising technique for determination of chemical species. In most cases these measurements have been done in liquid phase. Immobilization of quantum dot nano-particles on a solid bed offer easier separation, preconcentation, washing the interferences and quick fluorescence measurements of different analyts so that the quantum dots are reusable again. In this study three different approaches for quantum dot immobilization on a glass surface including sol-gel process, thiol-metal affinity and amide bond formation were compared in the time, temperature, atmosphere, solvent availability, pH, efficiency and tunability of attachment yield. The amide bonding was found the best strategy with 24 h reaction time, ambient temperature, air atmosphere, pH=10, no need for anhydrous solvent, highest fluorescence intensity (more than 50% of total intensities) , tunability of attachment with reproducible data (RSD<5.0%), cheap and convenient technique for immobilization of nano-particles on the glass surface.

Threshold velocity of non-Newtonian fluids to initiate solids bed erosion in horizontal conduits

Predicting the minimum velocity of non-Newtonian fluids required to erode a solids bed is an important task for guaranteeing efficient solids transport process. This paper describes a combined theoretical and experimental investigation of the threshold condition of non-Newtonian fluids, including water, water-based mud (WBM) and oil-based mud (OBM), to initiate erosion of a solids bed. Drilling fluids with different base fluids have different threshold velocities, depending on the adhesion effect generated by the presence of stagnant fluids in a solids bed. Therefore, a new semi-mechanistic model of erosion criterion is proposed. In the model, a resistive force is introduced to handle the adhesion effect produced from different fluids, and it is quantified through an empirical correlation developed from the results of drain tests. A torque balance for driving and opposing forces is then constructed and solve numerically at the contact point of a superimposed particle for the determination of the threshold velocity. Model's predictions agree with experimental data obtained from bed erosion experiments with the use of WBM and OBM having similar rheological properties.

Development of Numerical Eulerian-Eulerian Model for Computational Analysis of Potential in Chemical Process Intensification from Trickle Bed Reactors

The computational fluid dynamics techniques keep a paramount role by evaluating a reactor performance. The transitory performance of a Trickle bed reactor is readily monitored from its three phase’s flow conditions. This research review study corresponds towards the formation of boundaries in this Trickle bed reactors system to designate its comprehensive methodology with an optimized solution. The main paramount significance of computational fluid dynamics techniques is to observe the validity and an effective significance of the experimental result. The catalyst bed is modelled with the help of dynamic and steady state models by introducing mass and energy conservation equations. The Eulerian-Eulerian multiphase modelling technique is designed for hydro-desulfurization (HDS) and hydro-dearomatization (HDA) chemical process change from interactive momentum models. The effect in bed porosity on the HDS reaction process is observed from interactive mass transfer with solid bed condition in Trickle bed reactor. The congregated results from computational fluid dynamics codes show that wetting efficiency increases with increase in both hydrogen sulphide concentration and HDS conversion. The conversion of HDS reaction decreases with increase in hydrogen disulphide (H2S) concentration at both partially wetted and wetted bed conditions. On the other hand, there is small decrease in HDS conversion from 72% to 63.75% at H2S volumetric concentration of 0 to 8%. These observations also indicate that computational fluid dynamics provides random accessibility of liquid flow in Trickle bed reactor. There results also reveal that there is periodic variation in saturated liquid phase. The regions which are close to its wall are less irrigated. These characteristics can be changed and have effect on the reactor performance. Hence, the present review study presents the unprecedented results with high accuracy.

Comparison between pseudohomogeneous and resolved-particle models for liquid hydrodynamics in packed-bed reactors

Despite the advances in the modelling of Packed-Bed Reactors (PBR) it is common to find in literature works where resolved-particle models are implemented considering small-scale domains; or works where large-scale models are implemented with a pseudohomogeneous approach. In order to quantify the differences in the prediction of the local velocity between these two approaches, a CFD study was conducted for the modelling of the single-phase flow in a PBR. Six different cases, two resolved-particle and four pseudohomogeneous, were implemented and compared. The resolved-particle cases incorporated the explicit description of the solids bed distribution, considering an ordered and a randomly distributed bed of spheres, in which the punctual momentum balance was solved in the interstitial void space left by the solids. The pseudohomogeneous cases considered Darcy’s law (DL) and the Navier-Stokes-Darcy-Forchheimer (NSDF) equation, and the bed porosity as an overall average value εB=εB and as a function of the radial position of the bed εB=εBr, in order to include the effects of the solids bed without the explicit description of the solids distribution. The results show that there are significant local differences in the textural characteristics between the random packing and ordered packing for the resolved-particle cases. It was observed that the pseudohomogeneous models allow to predict the macroscopic behaviours indicated in the resolved-particle case, but fail to capture the local behaviours inside the bed. Furthermore, the inclusion of an average porosity distribution function does not improve the prediction of the local scale phenomena.

Melting Behavior of Heterogeneous Polymer Bulk Solids Related to Flood Fed Single Screw Extruders.

Melting models for flood fed single screw extruders, like the Tadmor model, describe the melting of pure thermoplastic polymers. However, the melting behavior of heterogenous polymer systems is of great interest for recycling issues, for example. In this work, the melting of polymer mixtures and that of pure bulk polymers by the drag induced melt removal principle is examined both theoretically and experimentally. The applied model experiments represent the melting of the solid bed at the barrel in single screw extruders. As polymer pellet mixtures, polypropylene-homopolymer mixed with polypropylene-block-copolymer, high density polyethylene, polyamide 6, and polymethylmethacrylate were studied using different mixing ratios. The melting rate and the shear stress in the melt film were evaluated dependent on the mixing ratio. The results show that when processing unfavorable material combinations, both shear stress and melting rate can be far below that of pure materials, which was also confirmed by screw extrusion and screw pull-out experiments. Furthermore, approaches predicting the achievable melting rate and the achievable shear stress of polymer mixtures based on the corresponding values of the pure materials are presented.

Cross-section-phenomena in rotary drums with sectional internals

The effect of sectional internals on the solid bed cross section in rotary drums is investigated with a novel, fully optical accessible rotary drum apparatus for different internal configurations. The impact on mixing behavior is analyzed for different section numbers and filling degrees as well as material configurations. The mixing kinetics is affected positively by the sections, particularly for lower rotational speeds and filling degrees. The goodness of mixing in segregating particulate systems can be improved by sectional internals. Additionally to mixing effects, the impact of sectional internals on phase interfaces of the cross section is analyzed. A mathematical model description of the solid bed cross section is created and validated with the experimental data. The gas/solid interface is increasing logarithmically compared to the bare drum. The solid/inner wall interface is increasing linearly with the number of sections and the solid/outer wall interface is not affected significantly by sectional internals.

Aiming the magic bullet

Coadministration of antibody-drug conjugates with the parent antibody improves delivery to solid tumor beds.

Heat Transfer Model in a Rotary Drum During the Fermentation Process

A new mathematical model describing heat transfer during the fermentation process in a rotary drum is proposed. The model includes representations of the kinetic reactions, the temperature of the solid bed, and physical structures within the rotary drum. The model is developed using five ordinary differential equations and was then solved using the Runge-Kutta method embedded in MATLAB software. A reasonable behaviour for the temperature profile to the fermentation process is achieved. The results show that the mass of the solid bed, contact heat transfer coefficient, and the wall temperature has a significant effect on the fermentation process in a rotary drum.

CFD study of the hydrodynamics and biofilm growth effect of an anaerobic inverse fluidized bed reactor operating in the laminar regime

The unsteady laminar flow of an inverse fluidized bed reactor was addressed in this study using computational fluid dynamics (CFD). Three-dimensional (3D) and two-dimensional (2D) simulations were carried out using the Eulerian-Eulerian approach with the Syamlal O'Brien and Gidaspow models for modeling the drag between the solid and liquid phases. Reported data of solids expansion and bed porosity were used to validate the simulations. Results show that 2D simulations can satisfactorily reproduce experimental data of fluidized bed reactors, which are essentially equal to those obtained on 3D simulations. The model of Syamlal O'Brien was found to be in better agreement with experiments than that of Gidaspow. It is shown that commonly used correlations for predicting bed porosity fail to provide a reasonable overall description of the evaluated operating conditions. The flow patterns for both phases in the bed section exhibit chaotic recirculation zones with high values of shear stress, and after this, the flow quickly becomes fully developed. The effect of biofilm thickness increase on bed porosity, under similar apparent densities of colonized particles reported for this system, is analyzed. Biofilm growth generates a decrease in the Archimedes number (i.e., decreases the buoyancy of particles) and an increase in the particle Reynolds numbers (Rep), affecting significantly the final porosity of the bed. However, this effect vanishes for Rep < 0.25. Results from this work can be used to develop scale‐up criteria and to establish safe operating conditions (e.g., maximum liquid velocity and biofilm thickness) to avoid loss of support particles.

Pure hydrogen production by steam‐iron process: The synergic effect of MnO 2 and Fe 2 O 3

In the energy transition from fossil to clean fuels, hydrogen plays a key role. Proton-exchange membrane fuel cells (PEMFCs) represent the most promising hydrogen application, but they require a pure hydrogen stream (CO < 10 ppm). The steam iron process represents a technology for the production of pure H2, exploiting iron redox cycles. If renewable reducing agents are used, the process can be considered completely green. In this context, bio-ethanol can be an interesting solution that is still not thoroughly explored. In this work, the use of ethanol as a reducing agent in the steam iron process will be investigated. Ethanol, at high temperature, decomposes mainly in syngas but can also form coke, which can compromise the process effectiveness, reacting with water and producing CO together with H2. In this work, the deposition of coke is avoided by controlling the duration of the reduction step; in fact, the data demonstrated that coke deposition is significantly dependent on reduction time. Tests were carried out in a fixed bed reactor using hematite (Fe2O3) as raw iron oxide adopting several reduction times (7 minutes-25 minutes), which correspond to different amount of ethanol fed (5 mmolC2H5OH/gFe2O3-17,95 mmolC2H5OH/gFe2O3). The effect of the addition of MnO2 to increase the reduction degree of iron oxides was explored using different amount of MnO2 (10 wt% and 40 wt% with respect to Fe2O3). The tests were performed at fixed temperatures of 675°C and atmospheric pressure. The optimization of the reduction time, in the chosen operating condition, performed only with Fe2O3, shows that, feeding an amount of 5 mmolC2H5OH/gFe2O3, coke deposition is avoided and, therefore, a pure H2 stream in oxidation is obtained. The addition of MnO2 leads to increased H2 yield and process efficiency, confirming its positive effect on the reduction degree of the solid bed. A reaction pathway to demonstrate the synergic effect of Fe2O3 and MnO2 in the reduction step was proposed in this article.

Quantifying porosity changes in solid biomass waste using a disruptive approach of water retention curves (WRC) for dry anaerobic digestion

Knowledge of the porosity distribution of biomass is crucial to understand the liquid flow through porous solid biomass treated in dry anaerobic digestion (D-AD). In this study, a novel adaptation of Water Retention Curve (WRC) analysis was validated to characterize the pore distribution of representative lignocellulosic biomasses; Cattle Manure (CM), roadside grass and corn stover. WRC analysis is composed of a drainage analysis (DA) and thermogravimetry analysis (TGA). Macro, meso and micropores values ranged from 33 to 63%, 25 to 44% and 7 to 16% for listed raw biomasses. Additionally, changes in porosity distribution of CM treated in sacrificed Leach-Bed Reactor (LBR) were quantifying; macropore volume decreased from 30.4 to 1.7% with the fiber degradation reducing considerably the permeability and increasing the solid bed compaction. The findings of this study suggest that the daily recirculated liquid volume could be progressively adapted considering the physical evolution of the solid bed.

Numerical Simulation of the Solid Particle Sedimentation and Bed Formation Behaviors Using a Hybrid Method

In the safety analysis of sodium-cooled fast reactors, numerical simulations of various thermal-hydraulic phenomena with multicomponent and multiphase flows in core disruptive accidents (CDAs) are regarded as particularly difficult. In the material relocation phase of CDAs, core debris settle down on a core support structure and/or an in-vessel retention device and form a debris bed. The bed’s shape is crucial for the subsequent relocation of the molten core and heat removal capability as well as re-criticality. In this study, a hybrid numerical simulation method, coupling the multi-fluid model of the three-dimensional fast reactor safety analysis code SIMMER-IV with the discrete element method (DEM), was applied to analyze the sedimentation and bed formation behaviors of core debris. Three-dimensional simulations were performed and compared with results obtained in a series of particle sedimentation experiments. The present simulation predicts the sedimentation behavior of mixed particles with different properties as well as homogeneous particles. The simulation results on bed shapes and particle distribution in the bed agree well with experimental measurements. They demonstrate the practicality of the present hybrid method to solid particle sedimentation and bed formation behaviors of mixed as well as homogeneous particles.

Chemical Looping of Manganese to Synthesize Ammonia at Atmospheric Pressure: Sodium as Promoter

AbstractAffordable synthetic ammonia (NH3) enables the production of nearly half of the food we eat and is emerging as a renewable energy carrier. Sodium‐promoted chemical looping NH3 synthesis at atmospheric pressure using manganese (Mn) is here demonstrated. The looping process may be advantageous when inexpensive renewable hydrogen from electrolysis is available. Avoiding the high pressure of the Haber‐Bosch process by chemical looping using earth‐abundant materials may reduce capital cost, facilitate intermittent operation, and allow operation in geographic areas where infrastructure is less sophisticated. At this early stage, the data suggest that 0.28 m3 of a 50 % porosity solid Mn bed may suffice to produce 100 kg NH3 per day by chemical looping, with abundant opportunities for improvement.

Measuring particle dynamics in a fluidized bed using digital in-line holography

The quantification of three-dimensional (3D) particle behavior in a fluidized bed is crucial for improving the fundamental understanding and engineering design of such multiphase systems commonly used in industry. This work reports recent development and application of digital in-line holography (DIH) on the in-situ measurement of (a) solid circulation rate, (b) particle size distribution, (c) 3D location, and (d) velocity distribution in the particle field. A Hough-transform-based hologram processing algorithm was developed and tested over a range of flow conditions. Using a hopper system for precise control of particle feed rate, real-time solid flow rates and particle size distributions were measured using DIH. These measurements were then compared to high-precision mass flow measurements made using an electronic balance and size-distribution measurements using a QIPIC® particle size and shape analyzer. DIH is then employed to measure particulate flows in a small-scale circulating fluidized bed system by imaging the standpipe region with 12.7 mm ID. Solid circulation rates evolution was measured and its mean value was in good agreement with the pressure-based estimations. Moreover, DIH is demonstrated to be capable of resolving fine particles with 10 – 40 µm in size, resulting from attrition in the bed of solids. Different from large particles that is dominated by gravitational settling, the motion of small particles is mainly affected by the flow, which has great potential to be used to investigate flow conditions around the large particles.

Computational and Experimental Study on Pressure Drop in a Fluidised Bed with Different Air Distributor Designs

Fluidised bed combustion (FBC) has been recognised as a suitable technology for converting a wide variety of fuels into energy. In a fluidised bed, the air is passed through a bed of granular solids resting on a distributor plate. Distributor plate plays an essential role as it determines the gas-solid movement and mixing pattern in a fluidised bed. It is believed that the effect of distributor configurations such as variation of free area ratio and air inclination angle through the distributor will affect the operational pressure drop of the fluidised bed. This paper presents an investigation on pressure drop in fluidised bed without the presence of inert materials using different air distributor designs; conventional perforated plate, multi-nozzles, and two newly proposed slotted distributors (45° and 90° inclined slotted distributors). A 3-dimensional Computational Fluid Dynamics (CFD) model is developed and compared with the experimental results. The flow model is based on the incompressible isothermal RNG k-epsilon turbulent model. In the present study, systematic grid-refinement is conducted to make sure that the simulation results are independent of the computational grid size. The non-dimensional wall distance, is examined as a key factor to verify the grid independence by comparing results obtained at different grid resolutions. The multi-nozzles distributor yields higher distributor pressure drop with the averaged maximum value of 749 Pa followed by perforated, 45° and 90° inclined distributors where the maximum pressure drop recorded to be about one-fourth of the value of the multi-nozzles pressure drop. The maximum pressure drop was associated with the higher kinetic head of the inlet air due to the restricted and minimum number of distributor openings and low free area ratio. The results suggested that low-pressure drop operation in a fluidised bed can be achieved with the increase of open area ratio of the distributor.

Study on the dynamic behavior of solid breeder materials and neutron multipliers under the perturbation of the magnetic field

The functionality of solid blanket pebble bed in a fusion reactor is inevitably subjected to heat flux and electromagnetic forces during the operation. Since the dynamic behavior under the heat flux and forces has strong influence on the packing factor of the pebble bed, and the packing factor is essential to the higher TBR (tritium breeder rate) of the neutron multiplier pebble bed, it’s necessary to study the impact of the dynamic forces on the neutron multiplier pebble bed. Some researchers have investigated the influences of the heat flux and electromagnetic forces on pebble bed. But, till date the influences of the heat flux and electromagnetic forces on the pebble bed of solid breeder materials in presence of neutron multiplier have not been studied yet. Thus, in this paper, the dynamic behavior of the particle system under the magnetic field are investigated based on the neutron multiplier pebble bed in the solid blanket. The mathematical and physical model of the particle pebble bed under the magnetic field was constructed, and the fundamental rule of the neutron multiplier pebble bed under the disturbance of the magnetic field is established. The presented work will provide basic parameters and data for the CFETR (China fusion testing reactor) pebble bed design.

Growth and development of Kochia prostrate (L.) Schrad in the extraordinary year in the north desert of Atyrau region in Kazakhstan

A system of agriculture is being developed to accumulate and preserve moisture in soil strips (5-10 cm wide, 5 cm deep, repeated every 50-55 cm in virgin soil untouched by vegetation), treated by surface raking of the loose seedbed layer to form a solid compacted bed, where an ideal condition for seed germination is created. With a favorable combination of weather and climatic conditions, this variant provides an optimal fullness of seedlings and a fairly high fruit-bearing weight of 3.9 t/ha on average for four years, including 4,8 tons in 2019. However, in extraordinary 2019-2020 crop year with extremely low precipitation (2,7 times lower than average annual norms), with the warm winter and spring (100 more than the average annual norm), incredibly intense droughts and dust storms (average of 18-19 days a month vs 4-5 mean annual norm) wind erosion dominated and dictated terms everywhere: furrows, sown with seeds of Summer Cypress were completely covered with drifts of dust with a thickness of 2-3 cm, under which the seedlings could not break through to the surface of the soil and died. In the cultivar keeping nursery, where seeds were sown directly without tillage and 15 PCs/m2 of seedlings were obtained only in the dust-inspired areas that make up one third of the area (400 m2).

Techno-economic analysis of a low carbon back-up power system using chemical looping

This work assesses the techno-economic viability of an innovative CO2-free back-up power system. A novel chemical looping reactor is at the core of the process, where a pressurized air stream is heated up by the slow oxidation of a packed bed of reduced solids, before its expansion in a gas turbine to generate electricity. In this reactor, air flows through empty gas conducts with fully permeable non-selective perforated walls. Such gas conducts traverse the bed of solids longitudinally, so that the pressure drop is minimized. A diffusionally-controlled flow of oxygen is established through the gas permeable wall, which results in long oxidation times for the bed of reduced particles. A case example is described in this study, where a reactor that uses iron materials as oxygen carrier is designed to store renewable energy (an input of 1.4 MWth of biogas) on a weekly basis and release it to supply a maximum power peak of 57 MWth in the power discharge mode for more than 8 h. A packed bed reactor of 3.3 m I.D. and 50 m length is employed for this application, which is traversed by gas conducts of 0.04 m I.D., with 0.002 m wall thickness and a fraction of orifices in the wall of 0.12. A preliminary economic analysis of the novel system indicates that this low carbon configuration could be competitive against fossil fuel back-up alternatives in several scenarios, preferably with carbon prices exceeding 100€/t CO2.

Temperature analysis in flighted rotary drums and the influence of operating parameters

Flights in rotary drums are used to improve the mixing and the heat transfer. They lift particles out of the solid bed to shower them as curtains through the gas phase of the drum. The number of particles and their distribution are influenced by several operational parameters. An indirectly heated flighted rotary drum was designed and constructed to conduct experiments relating transverse particle motion to heat transfer. Batch experiments divided into heating and cooling periods were performed with glass beads as reference material. The axial, circumferential and radial temperature distributions were measured. It was found that increasing the rotational speed as well as the volumetric airflow rate leads to quick temperature changes, while an increase in the filling degree results in a gradual decrease of the temperature drop during cooling.

A machine learning framework for computationally expensive transient models

Transient simulations of dynamic systems, using physics-based scientific computing tools, are practically limited by availability of computational resources and power. While the promise of machine learning has been explored in a variety of scientific disciplines, its application in creation of a framework for computationally expensive transient models has not been fully explored. Here, we present an ensemble approach where one such computationally expensive tool, discrete element method, is combined with time-series forecasting via auto regressive integrated moving average and machine learning methods to simulate a complex pharmaceutical problem: development of an agitation protocol in an agitated filter dryer to ensure uniform solid bed mixing. This ensemble approach leads to a significant reduction in the computational burden, while retaining model accuracy and performance, practically rendering simulations possible. The developed machine-learning model shows good predictability and agreement with the literature, demonstrating its tremendous potential in scientific computing.