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Swarm effects in bubble columns result from the interaction of the bubbles at higher gas holdup. The flow around individual bubbles in a swarm influences the movement of the following bubbles and this has a feedback on the flow regime on a larger scale. That is, hydrodynamics that can no longer be described with models for single rising bubbles. The experimental investigation of the multiscale hydrodynamics in three-dimensional bubble columns was so far limited by the available measurement techniques. In this study, ultrafast X-ray tomography (UFXCT) was applied on bubbly flows in a lab scale bubble column to determine inter-bubble distances and clustering characteristics for different gas holdups and bubble diameters. Applying the pair correlation function reveals a pronounced vertical clustering for large bubbles with Eo ≥ 3.82, whereas no clustering has been observed for bubbles of lower Eo. It was found that clustering orientation mainly depends on deformability of the bubbles but not on gas holdup.

The design of bubble column reactors require a comprehensive understanding of the fluid dynamics. The type of gas distributor has a main impact on bubble size distribution and flow regime. With increasing gas flow rate, the interaction of the bubble increases and the dispersion of the bubbles changes. Although these effects play an important role also on the mass transfer in bubble columns, the distance parameters of bubbles in dense swarms has been poorly investigated so far. This contribution presents an experimental study carried out with ultrafast X-ray CT (UFXCT) on a dense bubbly flow. Experiments were conducted in a bubble column of 10 cm inner diameter and for gas superficial velocities up to 3.5 cms-1. UFXCT allows for non-invasive plane measurement of the phase distribution at different scanning heights of the column. Based on the extracted coordinates of the bubble centers the distances of nearest neighbors of all bubbles were computed. In addition, pair correlation function has been applied to reveal information on the near order of bubbles. The Sauter Mean Diameter was found to have a remarkable influence on the clustering characteristics and the near order of the bubbles.

The chemical absorption reaction of CO2 in a circular bubble column reactor was simulated with an Euler/Lagrange CFD method and results were compared with data from a laboratory scale bubble column. The experimental data comprises gas holdup and bubble size distributions obtained with ultrafast X-ray tomography and hydroxide ion conversion obtained with a wire-mesh sensor. Large Eddy Simulation (LES) is used for calculating the fluid flow and modelling the turbulence in the continuous phase, considering the effect of sub-grid-scale (SGS) turbulence on bubble motion, and also SGS turbulence modification by bubbles. Lagrangian bubble tracking is conducted considering all relevant forces, bubble oscillation via stochastic generation of eccentricity and motion angle and consequently non-steady mass transfer via a dynamic Sherwood number. The comparison of experimental and simulation results shows very good agreement for the given data.

This data set contains the processeddata from ultrafast X-ray tomography measurements in a bubble column. Measurements were performed in a bubble column with 100 mm inner diameter and with deionized water and nitrogen as liquid and gas phase, respectively. This data set contains the measurement from the measurement height located 0.7m above the gas sparger. Hydrodynamic data, such as bubble size distribution and gas holdup distribution are provided. Furthermore, inter-bubble distances of gas bubbles (distance of the nearest neighbours) are given. Further detailes on the experiments and the processed data is provided in the corresponding journal paper.

This data set contains gas phase hydrodynamic data obtained from ultrafast X-ray tomography measurements in a bubble column. Global and local gas holdups, as well as bubble size distributions are given for I) non reactive conditions with nitrogen (gas) and sodium hydroxide solution (liquid) and II) reactive conditions with carbon dioxide (gas) and sodium hydroxide solution (liquid). Additionally the data set contains the corresponding consumption rates obtained from wire-mesh sensor measurements. Furhter details on the experiments are explained in the corresponding journal paper.

In this study we present an investigation on the impact of sparger configuration and fluid properties on the local gas phase dynamics for up to 17% total gas holdup. Experiments in a bubble column with 100 mm inner diameter were conducted with deionized water and NaOH solution of up to cNaOH = 32 mmol·l−1. Ultrafast X-ray computed tomography (UFXCT) was applied to obtain local hydrodynamic parameters, such as gas holdup distribution, bubble sizes and average bubble rise velocities. Radial gas holdup profiles show wall peaking, which is attributed to the uniform bubbly flow regime generated by the needle sparger used in this study. The addition of NaOH leads to similar gas holdup values but significant changes on local bubbly dynamics, such as bubble size distribution and axial gas phase velocity. The Sauter mean diameter was found to decrease with increasing concentration of NaOH, whereby the decrease is larger at higher gas flow rate.

For the investigation of bubble column hydrodynamics an experimental study using ultrafast electron beamX-ray tomography (UFXCT) has been carried out. Local hydrodynamic parameters were measured in a DN100 bubble column usingtwo types ofcapillary gas sparger, which are named as 'Type A' and 'Type B' . Nitrogen is used as gas phase and deionized water as liquid phase. For Type B sparger additionally, experiments with sodium hydroxide of different concentrations are given. Experiments were carried out at two different measurement heights, which are located at 10 (L/D = 1) and 70 cm (L/D = 7) above the gas sparger An additional readme.txt file provides all required information and is necessary for the interpretation of the experimental data.

Physical activity (PA) patterns track from childhood through to adulthood. The study aimed to determine the levels and correlates of sedentary time (ST), total PA (TPA), and moderate-to-vigorous PA (MVPA) in preschool-aged children. We conducted cross-sectional analyses of 1052 children aged three-to-four-years-old from six studies included in the International Children’s Accelerometry Database. Multilevel linear regression models adjusting for age, gender, season, minutes of wear time, and study clustering effects were used to estimate associations between age, gender, country, season, ethnicity, parental education, day of the week, time of sunrise, time of sunset, and hours of daylight and the daily minutes spent in ST, TPA, and MVPA. Across the UK, Switzerland, Belgium, and the USA, children in our analysis sample spent 490 min in ST per day and 30.0% and 21.2% of children did not engage in recommended daily TPA (≥180 min) and MVPA (≥60 min) guidelines. There was evidence for an association between all 10 potential correlates analyzed and at least one of the outcome variables; average daily minutes spent in ST, TPA and/or MVPA. These correlates can inform the design of public health interventions internationally to decrease ST and increase PA in preschoolers.

For a stable operation of exothermic processes in bubble column reactors, an appropriate heat control is required, e.g. through dense tube bundle heat exchangers installed in the column. However, their impact on flow morphology, phase distribution, mixing and mass transfer is scarcely reported and the derivation of reliable scaling approaches for bubble columns with internals is challenging. Thus, a narrow column (DN100) and a pilot-scale column (DN400) were equipped with tubes in two common patterns with triangular and square pitches to study local fluid dynamics. The results of both reactors are discussed with regard to their hydrodynamic similarity.

Bubble column reactors are widespread in the chemical industry [1]. Hydrodynamics and mass transfer processes in bubble column reactors are difficult to predict, as they occur at different length and time scales. Thus, numerous parameters affect the performance of bubble column reactors in terms of yield and selectivity. These are the gas holdup, bubble size, bubble interfacial area, liquid-phase velocity, and mass transfer coefficients. In addition, the kinetics of the chemical reactions in a bubble column and the mixing of the reactants play a significant role and may even feedback on mass transfer and hydrodynamics. Within a German DFG Priority Programme we investigate the coupling between hydrodynamics, mass transfer and reaction in bubbly flows across the scales and with real chemical reaction systems [2]. Within this framework, our group studies the macroscale processes in laboratory bubble columns with selected experimental techniques. In our presentation, we will introduce two different ways for time-resolved local chemical species concentration measurement, i.e. the analysis of OH- consumption during chemisorption of CO2 in alkaline solution by electrochemical analysis using a wire-mesh sensor as well as chemical conversion of NO in Fe(II) (EDTA) solution with a fiber optical photospectrometry technique.

The complex flow patterns in bubble columns can be phenomenologically described by the two-bubble class approach. For the first time, this approach is applied to bubble columns with dense internals. Internals of square and triangular pitch tube patterns of two tube sizes (8×10-3 and 13×10-3 m) with flat and U-tube bottom design and cross-sectional occupation of ~25% were inserted in a bubble column of 0.1 m diameter and 2 m height. Contrary to the well-known gas disengagement technique, dual-plane ultrafast X-ray computed tomography data have been used for the bubble class allocation. Experiments were performed at superficial gas velocities ranging from 0.02 m s-1 to 0.20 m s-1 to cover homogeneous and heterogeneous flow conditions. The contributions of small and large bubble classes on total holdup, flow structure and bubble rise velocities were determined. Furthermore, the regime transition onset was determined based on the two-bubble class approach. Eventually, new correlations for regime transition, small and large bubble rise velocity, large bubble holdup as well as total holdup are proposed based on sub-channel area, sub-channel hydraulic diameter and occlusion area.

Topics of current research activities within the DFG priority program SPP 1740 “Reactive Bubbly Flows” are studies on local mass transfer and reaction processes in order to gain a deeper understanding about the coupling of hydrodynamics, mass transfer and reaction kinetics in reactive bubbly flows as well as its influence on yield and selectivity in case of complex chemical reactions. Precondition for experimental investigations is the availability of sensors for local concentration measurements of components in the liquid phase. Due to limitations of currently available non-invasive measuring techniques, local concentration measurements in dense bubbly flows at technical scale pose technological challenges. Therefore, a minimal-invasive photometer probe have been qualified to measure concentrations of intermediates and products within the liquid phase of dense bubbly flows with high temporal and spatial resolution. This work was supported by the German Research Foundation (DFG), reactive bubbly flows (SPP 1740).

Bubble columns are widely applied reactors in the chemical process industry due to their excellent heat and mass transfer properties as well as their simple design and easy manufacturing without any moving part. Fischer-Tropsch and methanol syntheses are typical processes carried out in such columns. Most of the involved reactions are highly exothermic and require an efficient heat removal, for example, via internal tube bundle heat exchangers. Heat exchangers, with up to 60 m2 m-3 surface area, can be installed as dense tube bundles covering up to 60 % of the cross-sectional area, which accordingly, alter hydrodynamics, flow patterns, mixing and mass transfer significantly. Therefore, this study aims at revealing the influence of common tube bundle layouts, i.e. triangular and square pitches, at various tube diameters at approx. 25 % cross-sectional area coverage. The studies were carried out using narrow and pilot-scale bubble columns with 100 and 400 mm diameter, respectively, operated with air and water. Ultrafast X-ray tomography as well as wire-mesh sensors were applied to study the columns’ hydrodynamics as well as the flow in individual sub-channels. In particular, holdup and bubble size distributions were measured and compared for both columns. Furthermore, it is discussed to which extend hydrodynamic parameters, such as radial holdup profiles and gas velocity profiles etc., can be utilized for scale-up purposes based on hydrodynamic similarity at both reactor scales.

In this paper we report for the first time on the utilization of the wire-mesh sensor for the measurement of chemical species conversion during the chemical absorption of carbon dioxide in sodium hydroxide solution. The wire mesh-sensor obtains cross-sectional images of the liquid phase conductivity which changes with the conversion of hydroxides during the reaction. A theoretical model has been applied to verify the use of conductivity as indicator for the reaction progress. Demonstration experiments have been carried out in a lab-scale bubble column reactor using two wire-mesh sensors in different reactor heights. Results obtained from reactor model and experimental data show a very good agreement. The results demonstrate the potential of this imaging instrument to follow the course of a chemical reaction via ionic species concentration even in a dense bubbly flow. This way, a better understanding of the coupling of hydrodynamics, mass transfer and reaction in bubble columns and other reaction devices can be gained.

Introduction: Systematic reviews have identified the lack of intervention studies with young children to prevent obesity. This feasibility study examines the feasibility and acceptability of adapting the Nutrition and Physical Activity Self-Assessment for Child Care (NAP SACC) intervention in the UK to inform a full-scale trial.\ud Methods and analysis: A feasibility cluster randomised controlled trial in 12 nurseries in England, with 6 randomly assigned to the adapted NAP SACC UK intervention: nursery staff will receive training and support from an NAP SACC UK Partner to review the nursery environment (nutrition, physical activity, sedentary behaviours and oral health) and set goals for making changes. Parents will be invited to participate in a digital media-based home component to set goals for making changes in the home. As this is a feasibility study, the sample size was not based on a power calculation but will indicate the likely response rates and intracluster correlations. Measures will be assessed at baseline and 8–10 months later. We will estimate the recruitment rate of nurseries and children and adherence to the intervention and data. Nursery measurements will include the Environmental Policy Assessment and Observation score and the nursery staff's review of the nursery environment. Child measurements will include height and weight to calculate z-score body mass index (zBMI), accelerometer-determined minutes of moderate-to-vigorous physical activity per day and sedentary time, and diet using the Child and Diet Evaluation Tool. Questionnaires with nursery staff and parents will measure mediators. A process evaluation will assess fidelity of intervention delivery and views of participants.\ud Ethics and dissemination: Ethical approval for this study was given by Wales 3 NHS Research Ethics Committee. Findings will be made available through publication in peer-reviewed journals, at conferences and to participants via the University of Bristol website. Data will be available from the University of Bristol Research Data Repository.

Introduction Systematic reviews have identified the lack of intervention studies with young children to prevent obesity. This feasibility study examines the feasibility and acceptability of adapting the Nutrition and Physical Activity Self-Assessment for Child Care (NAP SACC) intervention in the UK to inform a full-scale trial. Methods and analysis A feasibility cluster randomised controlled trial in 12 nurseries in England, with 6 randomly assigned to the adapted NAP SACC UK intervention: nursery staff will receive training and support from an NAP SACC UK Partner to review the nursery environment (nutrition, physical activity, sedentary behaviours and oral health) and set goals for making changes. Parents will be invited to participate in a digital media-based home component to set goals for making changes in the home. As this is a feasibility study, the sample size was not based on a power calculation but will indicate the likely response rates and intracluster correlations. Measures will be assessed at baseline and 8–10 months later. We will estimate the recruitment rate of nurseries and children and adherence to the intervention and data. Nursery measurements will include the Environmental Policy Assessment and Observation score and the nursery staff's review of the nursery environment. Child measurements will include height and weight to calculate z-score body mass index (zBMI), accelerometer-determined minutes of moderate-to-vigorous physical activity per day and sedentary time, and diet using the Child and Diet Evaluation Tool. Questionnaires with nursery staff and parents will measure mediators. A process evaluation will assess fidelity of intervention delivery and views of participants. Ethics and dissemination Ethical approval for this study was given by Wales 3 NHS Research Ethics Committee. Findings will be made available through publication in peer-reviewed journals, at conferences and to participants via the University of Bristol website. Data will be available from the University of Bristol Research Data Repository. Trial registration number ISRCTN16287377.

Wire-mesh sensors (WMS) are today well established measurement tools to obtain both temporally and spatially highly resolved structural information as well as averaged phase fraction and phase fraction distribution data in air-water and steam-water two-phase flow experiments. Those data, with a spatial resolution of down to 0.5 mm and frame rates up to 10,000 frames per second are suitable to validate CFD code developments. During the last decade, the technology has widely spread in research laboratories all over the world and has been more and more developed towards a turnkey machine for researchers. In this work we summarize the most recent developments in hardware for high temperature and high pressure applications, new electronics with integrated void fraction calculations and flow pattern identification for industrial applications and latest software developments for data analysis and visualization. A big issue for the application of wire-mesh sensor technology to high pressure high temperature facilities is the complicated pressure-proven and temperature-resistant insulated support and feedthrough of the measuring electrodes. Our new development facilitates a compact metallic body with flanges on both sides with a slot in sensor unit consisting of ceramic insulators and a stainless steel frame. The feedthrough of the wires is realized by commercially available multiple feedthrough fittings. The most common and proved codes for WMS data analysis have been capsulated in our wire-mesh sensor data processing FrameWork. The tool has got a new, user friendly graphical interface and allows the implementation of new algorithms by the end user. The resulting data and profiles can be visualized within the software and a batch processing tool allows automated “over the weekend” jobs. The wire-mesh sensor technology so far is a scientific tool for researchers. The huge amount of data, several gigabytes for one measurement of a couple of seconds, has to be stored and processed offline later on. For industrial applications, the users need online data on liquid/gas holdups and flow pattern in the pipelines. An industrial type of wire-mesh sensor electronics has been developed based on an FPGA (field programmable gate array) microcontroller calculating the frame averaged void fraction instantaneously and moreover identifying the flow pattern based on statistical values of the last 10 seconds from the two-phase flow using Fuzzy clustering algorithm.

Blasensäulenreaktoren bieten aufgrund ihrer einfachen Bauweise und ihres ausgezeichneten Wärme- und Stofftransportverhaltens einen häufig genutzten Reaktortyp in der chemischen Industrie. Besonders die Beschreibung der Hydrodynamik und der Geschwindigkeitsprofile der unterschiedlichen Phasen, sowie deren radiale Verteilung haben einen erheblichen Einfluss auf den Stofftransport und chemische Reaktion. In diesem Beitrag sollen die Ergebnisse der Untersuchung zur Flüssigphasengeschwindigkeit in Blasenströmungen vorgestellt werden. Die Anwendbarkeit von Heißfilmsonden ist bei Vorliegen einer Mehrphasenströmung stark begrenzt. In Blasensäulen beinhaltet das gemessene Geschwindigkeitssignal Anteile der Gas- und Flüssigphase. Zur Untersuchung der Umströmung von Blasen und zur Bestimmung von Turbulenzparametern ist es notwendig diese Anteile voneinander zu trennen. Ausschließlich bei geringen Gasgehalten bietet der charakteristische Signalverlauf bei der Interaktion von Blase und Sonde eine Möglichkeit dazu. In dieser Arbeit kann mit Hilfe der Zwei-Ebenen Tomographie, die genaue Position der Heißfilmsonde und die vorliegende Phase an dieser Stelle in der Blasensäule bestimmt werden. Weiterhin können neben der Flüssigphasengeschwindigkeit auch Parameter der Hydrodynamik der Gasphase, wie Blasenform, Blasengröße bestimmt werden und in Abhängigkeit zur Flüssigphasengeschwindigkeit gestellt werden.

Design and operation of bubble columns are of main importance, since they strongly influence yield and selectivity of chemical reactions. In order to improve the process efficiency, a fundamental understanding of flow phenomena in bubble columns is necessary. A lot of research has been carried out for the investigation of hydrodynamics of bubble columns. Nonetheless, hydrodynamics is changing in the presence of a chemical reaction (e.g. shrinkage of bubbles due to mass-transfer processes). Hence, there is a strong interaction of hydrodynamics, mass-transfer and chemical reaction within bubble columns, which has been investigated in the past, amongst others, using the reaction of sodium hydroxide and carbon dioxide. However, most works are restricted to low gas holdups or provide only single point information due to the use of local probes (e.g. pH measurement). This contribution comprises the experimental investigation of the reaction of sodium hydroxide and carbon dioxide, applying Wire-Mesh Sensors for determining the locally occurring reaction steps at different operating conditions (e.g. gas flow rate of carbon dioxide, initial concentrations of sodium hydroxide). In turn, experimental results are compared with concentration profiles derived from known reaction kinetics. The application of Wire-Mesh Sensors for this purpose allows the visualization of the concentration distribution within the cross-section of the bubble column. Additionally, ultrafast X-ray computer tomography is used simultaneously to study the change of hydrodynamics during the reaction.

Bubble columns are a favored reactor type for the operation of gas-liquid reactions (e.g. oxidation and hydrogenation processes) in chemical industries. The improved design and operation of bubble column reactors requires a detailed understanding of the flow phenomena as well as mass transfer processes within these reactors. This study presents the experimental investigation the gas liquid mass transfer in a bubble column on the basis of the chemical absorption of CO2. This contribution presents ultrafast X-ray CT measurements within a bubble column. The mass transfer has been determined by the analysis of the decrease of gas the gas phase, especially the shrinkage of the CO2 bubbles.

Wire-Mesh Sensors (WMS) are applied in many research applications to determine the distribution of the phase fraction and to visualize the flow behavior within a pipe. However their application in industries is restricted due to the procedure of data acquisition. Here a new design of Wire-Mesh Sensor for monitoring void fraction and flow pattern behavior is presented. As result of online data evaluation cross-sectional void fraction information is provided in almost real-time. Additionally, the present flow pattern is determined by statistical analysis of recorded data of a time period of 10 s. This is the first time a Wire-Mesh Sensor was used for this purpose. With the help of fuzzy methodology a distinction of the four main flow patterns of vertical upward gas-liquid flow is possible. Furthermore transition regions can be identified. The algorithm is based on the evaluation of statistical void fraction distribution as result of Wire-Mesh Sensor data. Validation experiments of the new adopted algorithms are carried out in a 50 mm-ID two-phase air-water flow-loop at Tulsa University Horizontal Well and Artificial Lift Projects (TUHWALP).