The effects of low aspect ratio and heat exchanging internals on the bubble properties and flow regime in a pilot-plant bubble/slurry bubble column for Fischer-Tropsch synthesis

Fischer-Tropsch synthesis (F-T) is a process utilized to convert the syngas mixture of CO and H2 to synthetic fuel and chemicals that executed commercially by using the bubble/slurry bubble column reactor. The experimental results reveal that the investigated parameters, in terms the presence of internals, and reducing the aspect ratio and the solids loading, increase the local gas holdup, interfacial area, bubble passage frequency, and decrease the bubble rise velocity, bubble chord length. Meanwhile, the aspect ratio H/D = 4, and 5 provide enough height to established the fully developed flow regime. As a result of the variation in the bubble properties that in turn reflected on the flow regime transition, therefore, the presence of internals and decreasing the aspect ratio delay the transition from the transition flow regime to churn turbulent flow regime. The validated CFD codes, using Eulerian-Eulerian approach incorporated with the population balance model PBM, exhibit the capability to simulate the bubble column in bubbly and turbulent flow regimes. However, results revealed that the presence of internals enhanced the gas holdup significantly in the wall region of the column. The gas holdup radial profiles in the presence of internals in different configurations provide a uniform gas holdup profile. While the results of the effect of internals diameter exhibit that the gas holdup was increased remarkably in the center and the wall regions of the bubble column equipped by internals of 1-inch diameter more than in using internals of 0.5-inch. However, the effect of internals configurations reported that the internals with hexagonal arrangement increases the gas holdup in the center region more than the circular arrangement, and less in the wall region comparing with the circular arrangement --Abstract, page iv

Radiation reaction effects in relativistic plasmas -- the electrostatic limit

We study the evolution of electrostatic plasma waves, using the relativistic Vlasov equation extended by the Landau-Lifshitz radiation reaction, accounting for the back-reaction due to the emission of single particle Larmor radiation. In particular, the Langmuir wave damping is calculated as a function of wavenumber, initial temperature, and initial electric field amplitude. Moreover, the background distribution function loses energy in the process, and we calculate the cooling rate as a function of initial temperature and initial wave amplitude. Finally, we investigate how the relative magnitude of wave damping and background cooling varies with the initial parameters. In particular, it is found that the relative contribution to the energy loss associated with background cooling decreases slowly with the initial wave amplitude

Ponderomotive force due to the intrinsic spin for electrostatic waves in a magnetized plasma

We study the contribution from the electron spin to the ponderomotive force, using a quantum kinetic model including the spin-orbit correction. Specifically, we derive an analytical expression for the ponderomotive force, applicable for electrostatic waves propagating parallel to an external magnetic field. To evaluate the expression, we focus on the case of Langmuir waves and on the case of the spin-resonance wave mode, where the classical and spin contributions to the ponderomotive force are compared. Somewhat surprisingly, dependent on the parameter regime, we find that the spin contribution to the ponderomotive force may dominate for the Langmuir wave, whereas the classical contribution can dominate for the spin resonance mode. Naturally, this does not prevent the opposite case from being the more common one

3D CFD Simulation of a Bubble Column with Internals: Validation of Interfacial Forces and Internal Effects for Local Gas Holdup Predictions

CFD Models (Turbulent Models and Interfacial Forces) Incorporated with the Population Balance Model (PBM) Have Been Validated, Azimuthally, with the Gamma-Ray-Computed Tomography (CT) Results to Address the Effect of the Presence of Internals with Different Arrangements and Diameters. the Superficial Gas Velocity Applied Was Varied from 0.05 to 0.45 M/s. the Results Exhibit the Capability to Predict the Hydrodynamics of the Bubble Column, Further Incorporating the Population Balance Model and Promoting the Prediction of Simulation in High Superficial Gas Velocity. the Effect of Internals Revealed that the Gas Holdup Was Significantly Enhanced in the Bubble Column\u27s Wall Region, While the Gas Holdup Was Increased Remarkably in the Center and the Wall Regions of the Bubble Column Equipped by Internals of 1 In. Diameter More Than in Internals of 0.5 In. However, Internals with a Hexagonal Arrangement Increase the Gas Holdup in the Central Region and Less in the Wall Than in the Circular Arrangement

Predicting NOM Removal by Fixed-Bed GAC Adsorbers

Natural Organic Matter (NOM) normally exists in raw surface water as a complex mixture of organic compounds, mainly humic acids and fulvic acids. In water treatment plants, free chlorine reacts with NOM and forms a wide range of substances known as Disinfection Byproducts (DBPs). Granular Activated Carbon (GAC) adsorption is one of the best available technologies employed for the removal of NOM. A mathematical model for the adsorption of NOM onto GAC in a fixed bed column and in a batch reactor was built. The mathematical model was solved numerically using finite element and orthogonal collocation methods. Experiments were conducted using Rapid Small Scale Column Test (RSSCT) to evaluate the performance of GAC column to remove or reduce the concentration of NOM in raw water. The predicted values from the mathematical model showed very good agreement with the experimental measurements for a range of empty bed contact time, GAC particle size and raw water pH. Most of the mathematical model parameters were determined experimentally in adsorption equilibrium isotherm and batch reactor experiments

Natural Transport of Volatile Organic Compounds Due to Annual Variation of Soil Temperature

A theoretical investigation of factors affecting gas phase transport of volatile organic compounds in unsaturated zone is presented. Studying annual soil temperature variation with time and depth declares that there is a considerable temperature variation in the upper few meters that may affect the overall natural mass transport of volatile organic compounds. A one-dimensional mathematical model is used to study the effect of soil temperature variation on diffusive mass transport. From the analytical solution, it is clear that there is a significant net mass transport upward direction and a stimulated spatial oscillation of contaminant concentration in soil. The magnitude of these two modes of mass transport is higher as the contaminant is more volatile

Short-scale quantum kinetic theory including spin-orbit interactions

We present a quantum kinetic theory for spin-$1/2$ particles, including the spin-orbit interaction, retaining particle dispersive effects to all orders in $\hbar$, based on a gauge-invariant Wigner transformation. Compared to previous works, the spin-orbit interaction leads to a new term in the kinetic equation, containing both the electric and magnetic fields. Like other models with spin-orbit interactions, our model features "hidden momentum". As an example application, we calculate the dispersion relation for linear electrostatic waves in a magnetized plasma, and electromagnetic waves in a unmagnetized plasma. In the former case, we compare the Landau damping due to spin-orbit interactions to that due to the free current. We also discuss our model in relation to previously published works.Comment: 13 pages, 1 figur