Background: Hyperammonemia is neurotoxic and as such can be a medical emergency. Preanalytical factors greatly influence the blood ammonia concentration results. Aims and methods: Ammonia ...concentrations measured in the real life setting of a large hospital after pneumatic transport of blood samples and various time periods before centrifugation were compared to those based on the indications of the reagent manufacturer. In the same routine context, the effects of waiting times of centrifuged samples or after plasma storage at −20 °C and −80 °C were determined. Results: Despite the pneumatic transport, the lead times for sample arrival to the lab were even longer than those recommended for their complete handling until ammonia assay. Ammonia concentration results were not affected by the pneumatic transport of blood samples and by waiting times up to a maximum of 1.75 h before their centrifugation and 1 h after centrifugation. Ammonia stability was superior when plasma was stored at −80 °C. Conclusion: Pneumatic transport and sample handling in the routine practice of our lab do not affect ammonia concentration results provided that waiting times are limited to 1.75 h before and 1 h after centrifugation and samples are kept cold. Otherwise, it is better to freeze plasma at −80 °C.
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•Pneumatic injection of biomass was simulated by CFD MP-PIC method.•Good agreement observed among experimental data and MP-PIC simulation results.•Gas-solid hydrodynamics in the ...injection line is visualized from the simulations.•Feeder performance is maintained for injector diameter larger than 0.02 m.•A feeder operation map is developed as a function of dimensionless parameters.
Stable feeding of biomass powders into reactors represents a technical operational challenge for renewable energy generation. The injection of sawdust powders has been recently published with a horizontal pressurized gas injector under several experimental conditions. Valid numerical models based on computational fluid dynamics (CFD) are useful for hydrodynamics characterization of different equipment scales. In this study, the applicability of the CFD multiphase particle-in-cell approach (MP-PIC) for the considered injector is investigated. The model is tested under different operating conditions, showing relative deviations lower than 14% and 2% respectively for solids flux and flow concentration experimental data. The effect of model inputs (mesh refinement, drag model, particle-to-wall interaction) on the system’s hydrodynamics is discussed. The gas–solid flow hydrodynamics is obtained from the simulations providing additional insight on pulsed biomass transport. Ultimately, the model is used to investigate different injector diameters and to propose a feeder operation map as a function of dimensionless parameters.
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•We developed a new test-rig to analyse deposit formation during pneumatic conveying.•Higher powder flow rates require a higher conveying air velocity to avoid deposits.•Large ...particles deposit in the center and small in the corners of the duct.•Ceiling deposition appears for small particles due to electrostatic charging.
Deposit formation poses severe hazards and negatively affects the functionality of pneumatic powder transport systems. A novel test-rig was developed for the measurement of the deposition of polymethylmethacrylate powder in a horizontal, turbulent flow through a duct of a square cross-section. The parameters under investigation are the particles’ size, shape, and mass flow rate, the conveying air’s Reynolds number, relative humidity, and temperature, and the duct material. A continuous weighing method is used to quantify the particle deposition and resuspension rate and a Faraday cup is positioned at the duct outlet to measure the specific powder charge. For the considered conditions, the air humidity exhibits a strong influence, especially on the smallest particles. For small particles, a high charge even leads to deposition at the ceiling of the PC duct. Larger particles tend to settle at the center of the duct and smaller ones preferably at its corner.
Circulating fluidized bed (CFB) risers using Group A particles have traditionally, mostly, been considered to operate in the fast fluidization regime, which consists of a core‐annulus flow profile ...with solids refluxing in the annulus layer. High gas and solids flow riser studies, however, suggest the existence of additional types of flow behaviours. Therefore, more studies are still needed to help clear uncertainties of local solids flow patterns in CFB risers of Group A particles, especially at gas and solids flow rates at or near those in commercial units. In this study, riser density and local solids flux profiles were measured in 0.3 m diameter risers of three CFB units at gas velocities of 9–16 m/s and solids fluxes of up to 700 kg/s · m2. A variety of radial solids flux profiles were obtained, including a parabolic profile with a peak flux at about the radial centre, a nearly flat profile across the riser cross‐section and an inverted parabola with peak upwards flux near the wall. At high gas velocity and solids flux, risers have no solids downflow at the wall. Multiple fluidization regimes were found to exist in the riser. The bottom dense part of the riser was in the dense suspension upflow regime, and the dilute upper part was in the dilute pneumatic transport regime. With commercial fluid catalytic cracking (FCC) risers operating at nearly similar conditions as tested here, it is likely that they also have one or both fluidization regimes and not the traditional fast fluidization regime. The data in this study fitted well on the Kim et al. fluidization regime map.
Solids flux profiles in high flows circulating fluidized bed (CFB) risers for fluid catalytic cracking (FCC) catalyst particles at a constant solids flux for different superficial gas velocities
High gas velocity and high solids flux CFB risers can be in a dense suspension upflow fluidization regime or a dilute pneumatic transport fluidization regime or can have both simultaneosuly.
There is no solids refluxing at the wall as observed in the fast fluidization regime.
Based on laser-diffraction technique, the maximum entropy technique is applied to measure particle number concentration and size distribution in pneumatic transport. The information of particle ...number concentration and size distribution can be obtained simultaneously without distort the fluid and the particle trajectories. Detailed information about the distribution of the particle size and concentration in gas-solid two-phase flows near sand-bed surface are obtained in a large-scale wind tunnel test system. The experimental result shows that particle number concentration increases linearly with the increase of the wind speed. The mean particle size decreases exponentially with height (H > 3 cm), but almost unchanged for H < 3 cm. The weakly relationship of fluctuating velocity and particle-size dispersion is deduced from the underlying mechanism of equilibrium transport. This illustrates that transportation close to the mobile bed has selectivity for particle size.
Experimental and theoretical investigations on hydrodynamics for gas‐solid particles flow were carried out in a vertical upward converging pneumatic conveying system. One‐dimensional mathematical ...modeling and simulation were done using the FORTRAN‐95 program. The influence of convergence geometry on the hydrodynamic parameters like particle velocity, gas‐particle slip velocity, pressure drop, and particle Reynolds number (Rep) along the riser were studied. Experiments were conducted using the dilute phase mode with three types of granular cereal seeds of different sizes. Some significant differences in all hydrodynamic parameter profiles along the riser were observed between converging and uniform risers. Enhancement of Rep in the converging riser implies a higher gas‐solid transfer coefficient.
The hydrodynamics for gas‐solids particle flow in a vertical upward converging pneumatic conveying system were experimentally and theoretically investigated. The impact of convergence geometry on the hydrodynamic parameters in terms of particle velocity, gas‐particle slip velocity, pressure drop, and particle Reynolds number along the riser height during the gas‐solids particle flow was evaluated.
An analytic prediction of the frictional temperature rise of materials in pneumatic transfer systems is developed, with the aim of anticipating from first principles the onset of problematic ...formation of melt structures such as ‘angel hair’. Specifically, particulates of size d passing at velocity V through a 90° bend of radius R experience a maximum surface temperature rise ΔT = μdV2(Vρ/kcR)0.5, where μ,ρ,k,c are the particle friction coefficient, density, thermal conductivity and heat capacity respectively. Limits of applicability of this idealized (but conservative) model are discussed, and simple corrections for the mitigating effects of pipe texture and gas cooling are discussed. The expression predicts temperature increments of many tens of Kelvin for 5 mm polyethylene granules at speeds of >40 m/s, but only a few K for 1 mm organic grains at 30 m/s in a planned pneumatic sampling system for a planetary exploration mission.
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•Simple formula predicts heating in pneumatic transport.•Allows prediction of angel hair formation.•Elaborations and limitations of the theory are discussed.•Expression is applied to industrial and exploration settings.
This paper results from ongoing research into the modelling of solids friction for fluidized dense-phase pneumatic transport of fine powders. Energy loss due to particle to particle and particle to ...wall collisions have been modelled. A new model for particle velocity has been introduced using numerical analysis and variable fluidized bulk density, which has shown that slip velocity decreases with an increase in the mass flow rate of air and dimensionless length. A new modified two-layer model for solids friction factor has been developed by introducing the collision effect and particle velocity model in the model of solids friction. The results of scale-up validation in larger and longer pipelines for four different products have shown that for the majority of the cases, the new model for solids friction factor has resulted in better predictions in dense-phase flow conditions compared to the predictions obtained by an existing two-layer model.
Nomenclature
CParticle velocity m/s
Cx, Cy, CzParticle velocity in x, y z direction m/s
DInternal diameter of pipe m
∆LChange in length in control volume m
wfoFree settling velocity of an isolated particle m/s Display omitted
•Experimental data of pneumatic transport of cement, fly ash and ESP dust was used.•A new model has been developed to account for particle-particle-wall collision.•Model to determine particle velocity has been developed using numerical analysis.•Modified two-layer solids friction model has been developed using collision effect.•Modified two-layer model has provided reliable scale-up predictions in dense-phase.
Tribocharging or frictional electrification is a physical phenomenon that deals with the exchange and accumulation of electrical charges on the surfaces of bodies that are in contact and then ...separated. Several situations due to an accumulation of charges on the surfaces of materials in contact can lead to undesirable consequences such as adhesion of particles to the walls, or inception of electrostatic discharges. These situations are common in industry, more particularly in pharmaceutical or food processes. Despite several experimental and theoretical works in this field, the electrostatic charging process is not fully understood, due to the complexity of the many chemical and physical factors that can affect the phenomenon. In recent years, several authors have developed experimental devices and theoretical models to evaluate electrostatic charging during pneumatic transport. In this paper, the objective is to assess three models developed by different researchers to describe the charge generated by particle-wall collisions during the pneumatic transport in dilute phase. The predicted charge was compared with the results of a set of experiments conducted by the authors. This study has shown a good agreement between theoretical models and experimental results. However, a theoretical mathematical relationship between the parameters that are used to adjust the correspondence.
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