Determination of flow profiles in sugar industry clarifiers using technetium-99m radiotracers

SummaryIn this work, we introduce HI-Light, a surface-engineered glass-waveguide-based “shell-and-tube” type photothermal reactor which is both scalable in diameter and length. We examine the effect of temperature, light irradiation, and residence time on its photo-thermocatalytic performance for CO2 hydrogenation to form CO, with a cubic phase defect-laden indium oxide, In2O3-x(OH)y, catalyst. We demonstrate the light enhancement effect under a variety of reaction conditions. Notably, the light-on performance for the cubic nanocrystal photocatalyst exhibits a CO evolution rate at 15.40 mmol gcat−1 hr−1 at 300°C and atmospheric pressure. This is 20 times higher conversion rate per unit catalyst mass per unit time beyond previously reported In2O3-x(OH)y catalyst in the cubic form under comparable operation conditions and more than 5 times higher than that of its rhombohedral polymorph. This result underscores that improvement in photo-thermocatalytic reactor design enables uniform light distribution and better reactant/catalyst mixing, thus significantly improving catalyst utilization.

A steady state, three‐dimensional, turbulent flow model has been developed in‐house for analysis of melt flow and residence time distribution phenomena in steelmaking tundish system. The governing equations of flow, turbulence and tracer dispersion were derived in terms of the Cartesian co‐ordinate systems and solved numerically with their associated boundary conditions adapting a control volume based finite difference procedure. In the numerical solution scheme, the pressure‐velocity coupling was treated via the popular Simple (semi implicit method for pressure linked equations) algorithm.Prior to carrying out elaborate numerical predictions for tundish geometry, the model was applied to several standard test problems and evaluated against corresponding bench mark results. Thus, several typical test problems such as, flows in a cubic cavity, flows in ducts of rectangular cross‐section, flow over flat plate and so on were simulated numerically to assess the adequacy and appropriateness of the computational procedure developed. Results thus obtained together with the bench mark solutions indicated that the mathematical model is internally consistent and sufficiently robust. Accordingly, the turbulent flow model was applied to simulate flow and Residence Time Distributions (RTD) in four different tundish designs . These included, a single strand and a two strand slab casting tundish systems, a six strand rectangular shaped tundish and a six strand delta shaped billet casting tundish. Various RTD parameters (e.g., minimum break through time, tmin, time at which peak concentration occurs, tpeak and average residence time, tav) were computed numerically in the four tundish systems and these were subsequently compared with corresponding experimental measurements derived from equivalent water model tundish systems. Except for the single strand tundish system, large differences between measurements and prediction (particularly on tmin and tpeak) were noted for the other three tundish geometries. Furthermore, the extent of such discrepancy was found to be relatively more pronounced for the multi‐strand tundish system. The possible reasons for such discrepancy is discussed in the text and it was shown computationally that relatively better agreement between theory and measurement can be achieved if, instead of the high Reynolds number k‐ε turbulence model, a low Reynolds number turbulence model is applied in the computational procedure.

Liquid flow field and residence time distribution in a baffleless oscillatory flow coil reactor

In this work it is presented a study on the residence time distribution (RTD) of particles in a co-current pilot-plant spray dryer operated with a rotary atomization system. A nuclear technique is applied to investigate the RTD responses of spray dryers. The methodology is based on the injection of a radioisotope tracer in the feed stream followed by the monitoring of its concentration at the outlet stream. The experiments were performed during the drying of aqueous suspensions of gadolinium oxide. The RTD responses obtained experimentally presented good reproducibility, indicating that the technique applied is well suited to investigating fluid-dynamics of spray dryers. In addition to the experimental investigation, a mathematical model was used to describe the RTD experimental curves.

Investigation of gas mixing and gas distributor performance in fluidized beds

Gas flow maldistribution in moving beds of monosized particles

Electrodialysis (ED) cells are based on the selective transport of ions through membranes which ideally exclude the co-ions, so that when a potential difference is applied to the cell all ions are transported in solution but only the counter ions can cross the membrane. Thus, concentration polarization occurs in solutions adjacent to membrane surfaces due to the different transport number between the membrane and the solution. The concentration profiles formed in the solution near the membrane depends on the mass transport fluxes and hydrodynamic pattern in the channel; operating conditions and geometrical configuration of the cell affect greatly the concentration polarization [1]. Therefore, the performance of ED cells depends not only on the membrane properties but also on the electrolyte hydrodynamics being important to provide an adequate flow patter avoiding channeling, stagnant zones, jet formation, among others flow deviations. Keeping a homogeneous flow patter minimizes variations of mass transfer fluxes and current density over the membrane surface preventing high polarization zones that could give rise to water dissociation, low efficiency and premature membrane failure. The examination of relevant mass transport mechanisms by modelling can help to evaluate the effect of design characteristics and operating conditions on the performance of an electrodialysis cell through the analysis of concentration, potential and current density distributions. In this task, CFD has proven to be a valuable tool for the analysis of flow and mass transfer in membrane separation systems [2]. Therefore, this work presents the modelling of a laboratory ED cell coupling hydrodynamics and mass transport, taking into consideration changes of Donnan potential. The flow pattern inside channels of ED cell were obtained by 3D CFD modeling and the results were used to calculate the residence time distribution (RTD) to compare with experimental RTD. The hydrodynamic behavior was used then to solve the mass transport model to obtain a description of the concentration distribution of each of the ionic species in the cell, as well as of the amounts derived as fluxes of each of the components, current density and Donnan potentials at every point of the membrane.[1] Gurreri L., Tamburini A., Cipollina A., Micale G., Ciofalo M., CFD prediction of concentration polarization phenomena in spacer-filled channels for reverse electrodialysis J. Membr. Sci. 468, 133–148 (2014).[2] Fimbres-Weihs G.A., Wiley D.E., Review of 3D CFD modeling of flow and mass transfer in narrow spacer-filled channels in membrane modules, Chem. Eng. Process. 49 759–781 (2010).

The behaviour of passive tracer particles in capillary Poiseuille flow is investigated with regard to the residence time in short axial sections of length z, in which z/a < Va/D, where a is the capillary radius, V is the mean velocity and D the coefficient of molecular diffusion. While methods exist for calculating moments of the cross-sectionally averaged axial concentration distribution as a function of time (e.g. Smith 1982b), much less is known about the distribution of residence time as a function of axial distance. An approximate theoretical solution for point sources in high-Péclet-number flows reveals that the mean residence time 〈t(z)〉, which is asymptotic to z/V0 near the source, will then rise faster than z/V0 before converging to z/V for large z, provided the source is not at the capillary wall. V0 is the advective velocity at the point of release. The variance 〈t2(z)〉 is found to increase initially in proportion to z3 provided the source is not at the capillary wall or on the axis. A Monte Carlo method based on the solution to the diffusion equation in the capillary-tube cross-section is developed to compute particle trajectories which are used to analyse both axial and residence-time distributions. The residence-time distribution is found to display significant changes in character as a function of axial position, for both point sources and a uniform flux of particles along the tube.

Several polymeric coatings are dried by blowing jets of hot air on them from the top and bottom sides in multizone dryers. The goal of quickly removing solvent from a coating by manipulating air flow and temperature, together called operating conditions in this work, conflicts with the goal of producing blister-free coatings. Optimum operating conditions ensure both minimum residual solvent and no defects. Determining optimum conditions for multizone dryers is a difficult task with severe convergence problems. In this work, an easy method is developed to determine near-optimum operating conditions and residence times. The results indicate that the air flow on the top side should always be lower than or equal to that on the bottom side; the minimum residence time in first zone should be such that, toward the end, the solvent concentration starts to fall at the bottom. As long as the residence times are reasonably long, several different combinations of residence times in the second and subsequent zones nea...

This book provides a comprehensive overview of the main nuclear characterization techniques used to study hydrogen absorption and desorption in materials. The various techniques (neutron scattering, nuclear magnetic resonance, ion-beams, perturbed angular correlation, muon spin rotation) are explained in detail, and a variety of examples of recent research projects are given to show the unique advantage of these techniques to study hydrogen in materials. Most of these nuclear techniques require very specialized instrumentation, and there are only a handful of these instruments available worldwide. Therefore, the aim of this book is to reach out to a readership with a very diverse background in the physical sciences and engineering and a broad range of hydrogen-related research interests. The same technique can be used by researchers interested in the improvement of the performance of hydrogen storage materials and by those focused on hydrogen ingress causing embrittlement of metals. The emphasis of this book is to provide tutorial material on how to use nuclear characterization techniques for the investigation of hydrogen in materials information that cannot readily be found in conference and regular research papers. Provides a comprehensive overview of nuclear techniques used for hydrogen-related research Explains all nuclear techniques in detail for the non-expert Covers the whole range of hydrogen-related research Features chapters& nbsp;written by world-renowned experts in nuclear technique and hydrogen-related research

With a back‐propagation neural network, the residence time distribution (RTD) characteristics in a buss kneader were modeled on a series of experimental RTD data measured by a digital image processing method. The operating conditions (screw speed and feed rate) were chosen as the inputs of the network. The four‐layered back‐propagation neural network predicted not only the RTD character indices, including the shortest delay time, mean residence time, and variance of distribution, but also the complete RTD curve. On the basis of the mean residence time, the average degree of fill in the extruder was also calculated. Furthermore, the effects of the operating conditions on the RTD and average degree of fill were analyzed. The method provided herein can also be used to predict RTDs in other kinds of extrusion equipment. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Experimental study and modelling of the residence time distribution in a scraped surface heat exchanger during sorbet freezing

Based on some experimental investigations of liquid phase residence time distribution (RTD) in an impinging stream reactor, a two-dimensional plug-flow dispersion model for predicting the liquid phase RTD in the reactor was proposed. The calculation results of the model can be in good agreement with the experimental RTD under different operating conditions. The axial liquid dispersion coefficient increases monotonously with the increasing liquid flux, but is almost independent of gas flux. As the liquid flux and the gas flux increase, the liquid dispersion coefficient of center-to-wall decreases. The axial liquid dispersion coefficient is much larger than that of center-to-wall, which indicates that the liquid RTD is dominated mainly by axial liquid dispersion in the impinging stream reactor.

This is the first report on hydrodynamic models to determine current and water residence time patterns for Matarinao and Murcielagos bays in the Philippines, which have a long history of harmful algal blooms (HABs). Field surveys were conducted in Matarinao Bay in April and August 2010 and in Murcielagos Bay in February 2011. Hydrodynamic models of the bays were developed, and spatially explicit water residence times were estimated from the models based on rates of concentration decrease of a tracer within the bay. Both bays exhibited two distinct areas – the mouth with faster current flow and low residence time, and the head area with slower current flow and higher residence time. During the southwest monsoon, the residence time at Matarinao Bay was 5 d longer than that during the northeast monsoon. Phytoplankton sampling in both bays confirmed blooms of Pyrodinium bahamense, but the spatial distribution did not consistently correlate with the simulated residence time patterns. While residence time plays a significant role in algal blooms, extraneous factors may also influence the distribution of phytoplankton within embayments.

Drying of biomass or biofuels is a major issue during pretreatment because of a high initial moisture content, which results in low energy efficiency and combustion temperature and high emission of hydrocarbons. As the motion behaviors of biomass fuels play an important role in the drying process, it is of great significance to investigate the motion of biomass. In this study, visualization experiments on the motion of flexible nonspherical biomass particles in a baffled rotating cylindrical tube were performed. The residence time of biomass particles was obtained and analyzed by taking into account gas velocity, mass flow rate of flexible biomass, initial moisture content of biomass particles, slope and rotational speed of the cylindrical tube, and other parameters under several operational conditions. The results indicated that the mean residence time of flexible biomass increased with the increase in the mass flow rate and initial moisture content and decreased with the increase of the cylindrical tube’s rotational speed and slope and the velocity of the gas phase. Despite the quite small sliding friction coefficient between the tube’s inner wall and biomass particles, a larger slope could lead to stronger sliding friction force in the axial direction when these biomass particles moved to the bottom of the tube. Mean residence time is observed to decrease significantly and gradually decrease with the increase in rotational speed from 6 to 9 rpm and from 9 to 18 rpm, respectively. In addition, the mean residence time increased from 78.5 to 99.4 s when the inlet mass flow rate increased from 60 to 240 kg/h without the gas phase, but it increased from 57.4 to 78.5 s within the same range of the inlet mass flow rate at a gas velocity of 0.3 m/s.