Experimental analysis of mass transfer of Taylor bubble flow in small channels

Multiphase flows in chemical reactors with micro- and millimeter-size channel structures such as monolith froth reactors, compact heat exchangers and fuel cells have received great attention in the last years. They are considered as a promising alternative to conventional reactors, such as fixed bed reactors and bubble columns which are mainly used for gas absorption, catalytic hydrogenation and biochemical conversions. Slug or Taylor bubble flow is a desired operating state for this type of contactors due to the frequent change of efficient gas-liquid contacting in the film around the bubbles and the enhanced mixing in the liquid slugs behind the bubbles. Consequently, capillary Taylor flow is currently a target of intensive investigations. However, a full understanding of design parameters and optimum operating conditions are still lacking. For milli- and microreactors mass transfer between gas and liquid phases depends upon various parameters such as bubble shape, relative velocity between the two phases, degree of liquid contamination and many more. To further advance the fundamental understanding of micro- and milli-channel reactors with Taylor flow, main design parameters and operating conditions were investigated, which include (a) the effect of bubble size, channel diameter and cross sectional shape of channel on the mass transfer coefficient of dissolving bubbles, (b) the influence of the presence of surface active agents on the bubble shape, velocity and also on the mass transfer rate of bubbles and (c) the intensification effect of oscillation of channels on the mass transfer performance of Taylor bubbles. For the study of gas-liquid mass transfer high-resolution X-ray radiography and tomography were used as measurement techniques. The X-ray imaging methods were chosen as their accuracy is less affected by changes in the refractive index, as it is the case for conventional optical methods. The mass transfer was calculated by measuring the changes in the size of the bubbles at constant pressure. The utilization of X-ray visualization enabled the acquisition of a series of radiographic images of bubbles. The images gave the volume, interfacial area and length of the bubble with high accuracy as a function of time and were used to evaluate the mass transfer coefficient using the mass conservation equations. In case of circular channels, the results show that Sherwood numbers have a large dependency on the bubble length and also equivalent diameter which is in accordance with previous results for larger channel diameters. However, the values of measured Sherwood numbers could not be predicted by available correlations which are valid only for larger pipes. As a result, a new mass transfer correlation in the form of Sherwood number as a function of Peclet number as well as bubble size ratio was derived. The proposed correlation is applicable for a large range of bubble sizes with high accuracy. The comparison of the results for the square and circular channels showed that despite the fact that the rise velocity of bubbles in the square channel is about three times higher than in the circular channel, the mass transfer coefficient is about the same. Furthermore, the results show that in square channels the dissolution curves are relatively even, while the dissolution curves of circular channels exhibit some distinguishable change in the slope. In addition, the results show that the calculated mass transfer coefficient based on the measured data show good agreement with the data predicted by the penetration theory. Regarding the influence of surfactants on the mass transfer in small channels with Taylor flow, it was shown that a small amount of surfactant reduces the mass transfer and its impact is more pronounced on small bubbles. Furthermore, it was demonstrated that the presence of surfactants causes the change of the bubble shape and leads to a slight increase of the liquid film thickness around the bubble and as a result the elongation of contaminated bubbles. Intensification of mass transfer in small channels with Taylor bubbles was investigated by measuring the motion, shape and dissolution rate of individual elongated Taylor bubbles of air and CO2 in water. The comparison of the results for the stationary and oscillating channel showed that mechanical vibration of the channel is able to enhance the mass transfer coefficient from 80% to 186%. Moreover, the mass transfer rate positively correlates with frequency and amplitude of oscillation, which is more pronounced at higher amplitudes. In addition, it was shown that the intensification of mass transfer with increase of amplitude/frequency of vibration is mainly attributed to the increase of bubble surface wave oscillations that causes an enlargement of contact area between the phases and also a reduction of mass transfer resistance in the liquid-side boundary layer

Effects of Epoxy-Polyester Hybrid and Nanoclay on Morphology, Rheological and Mechanical Properties of Styrene-Butadiene Rubber

Properties of SBR compounds filled with two kinds of filler, Epoxy-Polyester Hybrid resin(EPH) (10, 20, 30, 40 phr) and Nanoclay (Closite 15 A) (1, 3, 5, 7 phr) were studied. Microcomposite samples and nanocomposite samples were prepared by Haake internal mixer. Curing agents and additives i.e. dicumylperoxide Properties of SBR compounds filled with two kinds of filler, Epoxy-Polyester Hybrid resin(EPH) (10, 20, 30, 40 phr) and Nanoclay (Closite 15 A) (1, 3, 5, 7 phr) were studied. Microcomposite samples and nanocomposite samples were prepared by Haake internal mixer. Curing agents and additives i.e. containing 30 phr resin show higher value of modulus than sample containing 7 phr nanocaly. Rheological measurement showed that both fillers lead to an increase in viscosity and dynamic modulus of samples which is as a result of good interaction established between polymer/filler. Moreover, due to nanometer scale of nanoclay particles, reinforcing effect of Nanoclay was more noticeable and in micrometer scale of Epoxy-Polyester Hybrid particles, Epoxy resin cured by Polyester is used to improved wet ability of SBR compounds. SEM photomicrographs of cryogenically fractured samples confirmed the mentioned results. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3506

State of the Art in the Optimisation of Wind Turbine Performance Using CFD

Wind energy has received increasing attention in recent years due to its sustainability and geographically wide availability. The efficiency of wind energy utilisation highly depends on the performance of wind turbines, which convert the kinetic energy in wind into electrical energy. In order to optimise wind turbine performance and reduce the cost of next-generation wind turbines, it is crucial to have a view of the state of the art in the key aspects on the performance optimisation of wind turbines using Computational Fluid Dynamics (CFD), which has attracted enormous interest in the development of next-generation wind turbines in recent years. This paper presents a comprehensive review of the state-of-the-art progress on optimisation of wind turbine performance using CFD, reviewing the objective functions to judge the performance of wind turbine, CFD approaches applied in the simulation of wind turbines and optimisation algorithms for wind turbine performance. This paper has been written for both researchers new to this research area by summarising underlying theory whilst presenting a comprehensive review on the up-to-date studies, and experts in the field of study by collecting a comprehensive list of related references where the details of computational methods that have been employed lately can be obtained

Computational Fluid-Particle Dynamics Modeling for Unconventional Inhaled Aerosols in Human Respiratory Systems

The awareness is growing of health hazards and pharmaceutical benefits of micro-/nano-aerosol particles which are mostly nonspherical and hygroscopic, and categorized as “unconventional” vs. solid spheres. Accurate and realistic numerical models will significantly contribute to answering public health questions. In this chapter, fundamentals and future trends of computational fluid-particle dynamics (CFPD) models for lung aerosol dynamics are discussed, emphasizing the underlying physics to simulate unconventional inhaled aerosols such as fibers, droplets, and vapors. Standard simulation procedures are presented, including reconstruction of the human respiratory system, CFPD model formulation, finite-volume mesh generation, etc. Case studies for fiber and droplet transport and deposition in lung are also provided. Furthermore, challenges and future directions are discussed to develop next-generation models. The ultimate goal is to establish a roadmap to link different numerical models, and to build the framework of a new multiscale numerical model, which will extend exposure and lung deposition predictions to health endpoints, e.g., tissue and delivered doses, by calculating absorption and translocation into alveolar regions and systemic regions using discrete element method (DEM), lattice Boltzmann method (LBM), and/or physiologically based pharmacokinetic (PBPK) models. It will enable simulations of extremely complex airflow-vapor-particle-structure dynamics in the entire human respiratory system at detailed levels

Solving the Optimal Trading Trajectory Problem Using a Quantum Annealer

We solve a multi-period portfolio optimization problem using D-Wave Systems' quantum annealer. We derive a formulation of the problem, discuss several possible integer encoding schemes, and present numerical examples that show high success rates. The formulation incorporates transaction costs (including permanent and temporary market impact), and, significantly, the solution does not require the inversion of a covariance matrix. The discrete multi-period portfolio optimization problem we solve is significantly harder than the continuous variable problem. We present insight into how results may be improved using suitable software enhancements, and why current quantum annealing technology limits the size of problem that can be successfully solved today. The formulation presented is specifically designed to be scalable, with the expectation that as quantum annealing technology improves, larger problems will be solvable using the same techniques.Comment: 7 pages; expanded and update

Development of a Multiscale Numerical Model with Two Human Pulmonary Health Applications

Determination of the site-specific dosimetry and clearance of deposited aerosols in the human airways is critical in health risk assessment studies such as toxicant exposure evaluation and inhaled medication delivery with pulmonary topical or systemic actions. However, comprehensive evaluation still lacks informative data, i.e., high-resolution local dosimetry of inhaled aerosols in airways and systemic regions, due to the limited imaging resolutions, restricted operational flexibilities, and invasive nature of experimental and clinical examinations. Computational simulations, on the other hand, can provide a detailed explanation for the chemical dynamics in the respiratory system, intrapulmonary and extrapulmonary tissues, and systemic regions using multiscale platforms. In this study, two experimentally validated multiscale numerical analyses were developed for the post-deposition calculation of the respirable aerosols, which expands the application of mathematical models in the respiratory system to the health endpoint. First, computational fluid-particle dynamics (CFPD) is coupled with a physiologically based toxicokinetic (PBTK) model to predict the in tissue translocation and systemic disposition of inhaled volatile organic compound and toxicant constituents in an electronic cigarette (EC). The proposed framework can be used as a benchmark to identify drug or toxicant dynamics in the human body, significantly applicable in the fields of pharmacokinetics and toxicokinetics. Second, an epidemiological computational approach was programmed and optimized by connecting CFPD and host cell dynamics (HCD) models to simulate the transport and deposition of low-strain influenza A virus (IAV)-laden droplets in subject-specific human lung airways and to predict the regional responses of targeted host cells to IAV infection. Furthermore, the hygroscopic growth and shrinkage of multicomponent droplets were considered by examining the thermodynamic equilibrium between the phases. These frameworks overcome the limitation of the experimental studies by connecting levels of biological dynamics that are not measurable using clinical studies. The influence of repetitive exposure incidents on the post-deposition dynamics was determined, which is valuable for assessing the chronic health effects of inhaled airborne particles.Chemical Engineerin

How the Prevalence of Pulp Stone in a Population Predicts the Risk for Kidney Stone

Introduction: Conflicting researches exist on relationship between pulp stones and systemic disorders. Nephrolithiasis is a common disease with severe pain and discomfort with increasing prevalence worldwide. The purpose of this study is to evaluate the correlation between pulp and kidney stones to help find a method for early detection of kidney stones. Methods and Materials: the sample of this case-control study comprised of 154 subjects (77 patients with and 77 patients without kidney stone approved by sonographic examination). Two oral and maxillofacial radiologists evaluated their panoramic images for the presence of pulpal stones. Results: A total of 42.9% of subjects showed pulp stones. Most of the teeth with pulp stone in case and control groups were molars (86.30% and 72.97%, respectively). In the group with kidney stones, pulp stones were detected in 38 patients (49.4%), while in the control group, they were detected in 28 subjects (36.4%). Although there was not a significant relationship between the presence/absence of pulp stone and kidney stone (P=0.143), there was statistically significant association between number of teeth with pulp stone in a patient and the presence of kidney stone (P<0.013). The chance of having kidney stone is 5.78 times higher in the subjects having pulp stone in three teeth or more (≥ 3 teeth). Conclusion: Although there is not a correlation between the presence of pulp and kidney stone, the chance of having kidney stone is 5.78 times higher in the subjects with ≥ 3 teeth having pulp stone. Thus, the number of teeth with pulp stone can serve as a predictor for possibility of having kidney stone.Keywords: Dental Pulp Stone; Kidney Stone; Nephrolithiasis; Pulp Calcification; Radiograph

An Improved Framework for Watershed Discretization and Model Calibration: Application to the Great Lakes Basin

Large-scale (~103–106 km2) physically-based distributed hydrological models have been used increasingly, due to advances in computational capabilities and data availability, in a variety of water and environmental resources management, such as assessing human impacts on regional water budget. These models inevitably contain a large number of parameters used in simulation of various physical processes. Many of these parameters are not measurable or nearly impossible to measure. These parameters are typically estimated using model calibration, defined as adjusting the parameters so that model simulations can reproduce the observed data as close as possible. Due to the large number of model parameters, it is essential to use a formal automated calibration approach in distributed hydrological modelling. The St. Lawrence River Basin in North America contains the largest body of surface fresh water, the Great Lakes, and is of paramount importance for United States and Canada. The Lakes’ water levels have huge impact on the society, ecosystem, and economy of North America. A proper hydrological modelling and basin-wide water budget for the Great Lakes Basin is essential for addressing some of the challenges associated with this valuable water resource, such as a persistent extreme low water levels in the lakes. Environment Canada applied its Modélisation Environnementale-Surface et Hydrologie (MESH) modelling system to the Great Lakes watershed in 2007. MESH is a coupled semi-distributed land surface-hydrological model intended for various water management purposes including improved operational streamflow forecasts. In that application, model parameters were only slightly adjusted during a brief manual calibration process. Therefore, MESH streamflow simulations were not satisfactory and there was a considerable need to improve its performance for proper evaluation of the MESH modelling system. Collaborative studies between the United States and Canada also highlighted the need for inclusion of the prediction uncertainty in modelling results, for more effective management of the Great Lakes system. One of the primary goals of this study is to build an enhanced well-calibrated MESH model over the Great Lakes Basin, particularly in the context of streamflow predictions in ungauged basins. This major contribution is achieved in two steps. First, the MESH performance in predicting streamflows is benchmarked through a rather extensive formal calibration, for the first time, in the Great Lakes Basin. It is observed that a global calibration strategy using multiple sub-basins substantially improved MESH streamflow predictions, confirming the essential role of a formal model calibration. At the next step, benchmark results are enhanced by further refining the calibration approach and adding uncertainty assessment to the MESH streamflow predictions. This enhancement was mainly achieved by modifying the calibration parameters and increasing the number of sub-basins used in calibration. A rigorous multi-criteria comparison between the two experiments confirmed that the MESH model performance is indeed improved using the revised calibration approach. The prediction uncertainty bands for the MESH streamflow predictions were also estimated in the new experiment. The most influential parameters in MESH were also identified to be soil and channel roughness parameters based on a local sensitivity test. One of the main challenges in hydrological distributed modelling is how to represent the existing spatial heterogeneity in nature. This task is normally performed via watershed discretization, defined as the process of subdividing the basin into manageable “hydrologically similar” computational units. The model performance, and how well it can be calibrated using a limited budget, largely depends on how a basin is discretized. Discretization decisions in hydrologic modelling studies are, however, often insufficiently assessed prior to model simulation and parameter. Few studies explicitly present an organized and objective methodology for assessing discretization schemes, particularly with respect to the streamflow predictions in ungauged basins. Another major goal of this research is to quantitatively assess watershed discretization schemes for distributed hydrological models, with various level of spatial data aggregation, in terms of their skill to predict flows in ungauged basins. The methodology was demonstrated using the MESH model as applied to the Nottawasaga river basin in Ontario, Canada. The schemes differed from a simple lumped scheme to more complex ones by adding spatial land cover and then spatial soil information. Results reveal that calibration budget is an important factor in model performance. In other words, when constrained by calibration budget, using a more complex scheme did not necessarily lead to improved performance in validation. The proposed methodology was also implemented using a shorter sub-period for calibration, aiming at substantial computational saving. This strategy is shown to be promising in producing consistent results and has the potential to increase computational efficiency of this comparison framework. The outcome of this very computationally intensive research, i.e., the well-calibrated MESH model for the Great Lakes and all the final parameter sets found, are now available to be used by other research groups trying to study various aspects of the Great Lakes System. In fact, the benchmark results are already used in the Great Lakes Runoff Intercomparison Project (GRIP). The proposed comparison framework can also be applied to any distributed hydrological model to evaluate alternative discretization schemes, and identify one that is preferred for a certain case