Stirred vessels are an integral part of many industrial processes. Their design is often based on only experimental data which are limited by available experimental techniques; therefore, their optimisation is usually conducted via a trial-error approach. This study offers a validated CFD simulation methodology that could be used for optimisation and design of industrially relevant stirred vessels. The methodology is based on the RANS model employing the standard k − ϵ turbulence model and the multiple reference frame approach. The methodology is validated in a vessel that mimics the geometry of a flocculation tank, for which experimental data were also measured using particle tracking velocity and tracer tracking techniques. While the experimental and calculated flow fields show high agreement, simulations of tracer transport within the vessel indicate limitations in the standard approach to the turbulent transport modelling, specifically in the constant value of turbulent Schmidt number.

A correct soil water extraction represents an initial step in stable water isotope analysis. With this aim, we present a new soil water extraction method based on the principle of complete evaporation and condensation of the soil water in a closed circuit. The proposed device has four extraction slots and can be used up to two times a day. Owing to its simple design, there is no need for any chemicals, gases, or high-pressure or high-temperature regimes. The experimental tests proved that the extraction itself does not cause any major isotope fractionation effects leading to erroneous results. Extraction of pure-water samples shifts the isotope composition by 0.04 +/- 0.06 parts per thousand and 0.06 +/- 0.35 parts per thousand for delta O-18 and delta H-2, respectively. Soil water extraction tests were conducted for five distinct soil types (loamy sand, sandy loam, sandy clay, silt loam, and clay) using 40-150 g of pre-oven-dried soil, which was subsequently rehydrated to 10 % and 20 % water content. The shift in the isotopic composition of these tests ranged between -0.04 parts per thousand and 0.07 parts per thousand for delta O-18 and 0.4 parts per thousand and 1.3 parts per thousand for delta H-2, with the standard deviations of +/- (0.08-0.25) parts per thousand and +/- (0.34-0.58) parts per thousand for delta O-18 and delta H-2, respectively. The results exhibit high accuracy, which makes this method suitable for high-precision studies where unambiguous determination of the water origin is required.

Natural organic matter (NOM) in drinking water sources can deteriorate the organoleptic properties of water, impair the efficiency of the drinking water treatment processes, and pose a risk of harmful disinfection byproduct formation. Therefore, an efficient and economic NOM removal is crucial for the sustainable production of high-quality drinking water. The study investigates the removal of NOM from natural surface water by chemical coagulation (CC), electrocoagulation (EC), and by their combination in a single treatment step - dual coagulation (DC), using chemical Al-based or Fe-based coagulants for CC and Al and Fe electrodes for EC. It is demonstrated that the dual coagulation method with relatively low EC metal dosage surpasses the NOM removal efficiency of CC and approaches the performance of EC, which, however, may have economic or technical limitations. Furthermore, ferric coagulants in both CC and EC show superior efficacy to Al coagulants. Consequently, the combination of CC by ferric coagulant with EC using Fe electrode provides the highest NOM removal (65 %) by DC compared to 57 % removal by CC (Fe coagulant) and 69 % removal by EC (Fe electrode). The cost analysis of individual coagulation methods shows that with DC, the enhancement of NOM removal efficiency may be achieved at the lowest operating costs, compared to CC and EC.

The study introduces a novel mixing approach for industries requiring sterility, easy cleanability, and low shearing. It aims at an ultrapure mixing configuration comprising an unbaffled cylindrical vessel with an asymmetrically placed levitating impeller. However, that solution may be prone to forming a poorly mixed central vortex region worsening its overall mixing characteristics. To eliminate these adverse effects, a dynamic mixing protocol consisting of periodic changes in the impeller speed and direction is developed. Experiments conducted in a pilot-scale vessel (60L) confirm that this method eliminates the poorly mixed zone and reduces homogenization time by more than 50% compared to a fixed-speed impeller. Additionally, numerical simulations reveal no excessive shearing due to speed and direction changes. It is shown that dynamic mixing protocol allows for significant improvement in vessel mixing characteristics while maintaining gentle handling of shear-sensitive materials.

Unbaffled mixing tanks with magnetically driven impellers are increasingly used in biotechnological and pharmaceutical industries, combining the benefits of a closed, sterile environment with easy equipment cleanability. On the other hand, missing internals, such as baffles or cooling coils, have an adverse effect on the equipment mixing characteristics, namely the batch homogenization time. In our previous research, we uncovered that the eccentricity and inclination of the impeller – both employed routinely to enhance the mixing characteristics of unbaffled vessels – are not fully effective in the suppression of central vortex formation resulting in the increase in the homogenization time. In this work, we propose a simple solution to counteract the central vortex formation – a periodical variation of impeller rotational speed. This approach destabilizes the central vortex, significantly reducing homogenization time while maintaining the benefits of the original unbaffled setup. This innovation can seamlessly integrate into existing industrial setups, promising efficiency gains for biotech and pharmaceutical production.

Flocculation in water treatment facilities plays a key role in the separation of colloidal inorganic and organic substances. Its optimization leads to a significant increase in its efficiency and savings of operational costs. However, it is currently based on trial-and-error experimental approaches. In this contribution, we focus on flow modeling in stirred flocculation tanks that would, after coupling with a calibrated model of particle aggregation, enable simulationbased flocculation optimization. Despite the abundance of literature on stirred tank modeling, there is no universal agreement on the methodology used to describe turbulence nor on the approach to the computational mesh creation. Consequently, there is no unified methodology for simulations and their validation. To address this, we present a best-practice methodology for economical, yet reliable flow simulations in the said device. This methodology includes the choice of the turbulence model, the approach to the design of a high quality mesh suitable for arbitrary geometries, and results evaluation. It is developed based on an extensive literature review, a multitude of flow simulations using several meshes of progressively higher quality and resolution, and various strategies to converge to steady-state flow conditions. The simulation quality indicators used here involve comparison with the experimental data on fluid velocity, stirrer power output, and flow rate through the impeller zone. Additionally, the resulting flow simulation models are compared using tracer transport simulations, hinting at their potential for coupling with particle aggregation models.

The hydraulic performance of a modular liquid-gas ejector (LGE) unit with an air-water system is experimentally evaluated across a wide range of device scales and operating conditions. To maximize the LGE efficiency, three methods of gas entrainment rate enhancement were tested: (i) LGE flow orientation; (ii) liquid jet destabilization using a swirl in front of the nozzle; and (iii) using a high-loss nozzle producing a non-coherent liquid jet. Resulting from a broad database of experimental data, the optimal geometries for various process conditions are identified. Using the recommended geometry and liquid jet destabilization, the LGE gas entrainment rate can be multiplied compared to the performance with a coherent liquid jet. Based on the LGE hydraulic analysis, a semi-empirical model for effective LGE design is developed and experimentally validated.

The experimental distillation apparatus presented here serves to simulate the hydrodynamic and mass transfer conditions in a distillation column packed with the structured packing. It produces a film of the boiling liquid mixture flowing down the inclined plate with counter-currently flowing vapour of that mixture under total reflux with the mass transfer proceeding between the phases. The inclined plate instead of the sheet of structured packing is used for its simplicity as the first approximation in this work. The apparatus enables observation of the liquid film by means of a thermal imaging camera through a heated KBr window. Thermograms of films of IR-translucent mixtures (such as the cyclohexane/n-heptane mixture) provide information on the spatial distribution of the film thickness, while those of films of IR-opaque mixtures (such as methanol/propanol mixture) should reveal the spatial distribution of the mass transfer intensity across the interface. So far the results remain qualitative. Monitoring of the IR-opaque liquid surface is complicated by the relatively well-visible vapour phase in the IR spectrum, which unpredictably and irregularly hinders the view.

The standard and well-researched stirred vessel configuration comprises a tank equipped with one or more impellers positioned in the vessel’s axis and multiple wall-mounted baffles preventing the central vortex creation. However, particular industries, such as biotechnology, have an increased need for a sterile environment that often results in the usage of atypical stirred vessel configurations. An example of a commonly equipped atypical stirred vessel is an unbaffled stirred tank with an eccentric magnetically driven impeller. However, there is only a little knowledge about the mixing characteristics of such designs. In this work, we list experimental results for both the standard and atypical stirred vessel configurations. Furthermore, we present a CFD model of the atypical configuration. The model is used to calculate its mixing characteristics that are subsequently compared against our experimental results. It is shown that for the liquid height (H) to the vessel diameter (T) ratio H/T ≲ 1.2, the characteristics of both the standard and atypical designs coincide. For higher liquid heights (i) the characteristics of the atypical design decrease dramatically, and (ii) the characteristics estimates based on approaches developed for the standard configuration become unreliable.

In the pharmaceutical and biotechnology industries, ensuring the cleanliness and sterility of the process environment is of utmost importance. To achieve this, some commercially available bioreactors are designed as unbaffled vessels with an eccentrically mounted, magnetically driven impeller. Contrary to the well-studied nature of turbulent mixing in standard baffled reactors, the mixing performance in such atypical vessels has not been thoroughly explored in the literature. This study aims to fill the knowledge gap on this subject by focusing on the mixing time in an atypical reactor using two experimental techniques, conductometry, and decolorization. The conductometric results demonstrate that the mixing times of the atypical reactor remain similar to the baffled configurations up to a height-to-diameter ratio of 1.2. Above this ratio, mixing times rapidly increase. Based on the experimental results, correlations for the design of standard and atypical vessels with small radial impellers have been proposed, also concerning the liquid height. Furthermore, the decolorization experiments in the atypical reactor revealed the formation of the segregated vortex region, in which the homogenization process takes up to four times longer period than is required for the remainder of the reactor volume. The impact of this vortex formation on the vessel mixing characteristics is discussed.

Liquid-gas ejectors (LGEs) are fascinating devices that use the kinetic energy of the liquid jet to entrain and eventually compress the gas. LGEs find applications in both industry and everyday life, e.g., as sprayers. However, a complex and reliable method for LGE design was not available in the open literature until recently. This contribution follows up on our recent works about the hydraulic behavior of LGE with undisturbed and destabilized liquid jets. This paper aims to summarize the device’s complicated hydraulics and characterize its optimal design for three industrially relevant applications - (a) LGE as the vacuum pump, (b) LGE as the gas purification equipment, and (c) LGE as the gas distributor for bioreactors.

We suggest monitoring of the interfacial mass transfer activity over the surface of the packing under distillation conditions by a thermal camera. Such a study should reveal zones with imperfect hydrodynamics and decreased mass-transfer intensity, enabling quantification of the fraction of the packing geometrical area, which is ineffective in the interfacial mass exchange. The objective of the present study is to validate that the temperature of a liquid surface measured by the camera is truly the temperature of the interface, which can substantially differ from the liquid bulk temperature under the non-zero heat and mass-transfer conditions. Validation experiments are performed using a water-air system with zero net mass transfer across the interface and non-zero heat transfer induced by cooling of the liquid phase and heating of the gas phase. The interface temperature is indirectly determined from the partial pressure of water in the air above the liquid level. The results show that the temperature reading of the thermal camera is up to 92% determined by the temperature of the interface. Its measurement opens the possibility of determining not only effective interfacial area but also local distribution of the mass-transfer and heat-transfer resistances between the phases.

The gas suction rate of a conventional liquid-gas ejector pump was measured on a modular pilot plant unit utilizing convergent nozzles and a water-air system. Hydraulic character-istics were measured for various water flow rates, suction and discharge pressures, and ejector geometries, covering a wide range of configurations and operating conditions. The device configurations, providing the most stable and reproducible results, were identified. The air flow rates measured with these configurations were correlated by a simple, three-parameter correlation with a relative standard deviation (RSD) of 11%. The performance and behavior of the ejector in less stable configurations are discussed and the recommendations for the design of optimally operating units are provided. Finally, the correlation is tested against available literature data. The ejectors with comparable geometry agree well with the proposed correlation (within 20% RSD). The reasonable agreement with the discussed differences is found for other literature data. This comparison results in the validation of the proposed correlation to provide a safe prediction of minimal gas entrainment in units of various geometries, orientation and operating conditions. (c) 2021 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved. The gas suction rate of a conventional liquid?gas ejector pump was measured on a modular pilot plant unit utilizing convergent nozzles and a water?air system. Hydraulic characteristics were measured for various water flow rates, suction and discharge pressures, and ejector geometries, covering a wide range of configurations and operating conditions. The device configurations, providing the most stable and reproducible results, were identified. The air flow rates measured with these configurations were correlated by a simple, threeparameter correlation with a relative standard deviation (RSD) of 11%. The performance and behavior of the ejector in less stable configurations are discussed and the recommendations for the design of optimally operating units are provided. Finally, the correlation is tested against available literature data. The ejectors with comparable geometry agree well with the proposed correlation (within 20% RSD). The reasonable agreement with the discussed differences is found for other literature data. This comparison results in the validation of the proposed correlation to provide a safe prediction of minimal gas entrainment in units of various geometries, orientation and operating conditions.

An ejector is a technologically simple and yet wide-application fluid machine. While it has favorable characteristics for a significant number of technological processes, its main downside is probably its high operational energy demands. The present paper is an initial result of an ongoing research aimed at improving energy efficiency of the ejector via optimization of its geometry. In the paper, we focus mostly on presenting a general multi-objective optimization framework usable for an ejector shape optimization. The approach applicability is illustrated on a simplified problem comprising only a single phase flow in an ejector mixing tube and diffuser. Nevertheless, the achieved simulation and optimization results are validated against experimental data. The proposed optimization method itself is based on multi-objective evolutionary algorithms (MOEAs) combined with computational fluid dynamics (CFD) for evaluation of the vector-valued objective function.

Activity coefficients of water at infinite dilution in 12 common oxygenated solvents (namely methanol, ethanol, propan-l-ol, propan-2-ol, 2-methylpropan-2-ol, propan-2-one, tetrahydrofuran, 1,3-dioxolane, dimethoxymethane, 1,2-dimethoxyethane, ethyl methanoate, and methyl ethanoate) were measured at several temperatures using the technique of comparative ebulliometry. A comprehensive critical review of such literature data as well as data on relevant thermal properties (enthalpies and heat capacities of water dissolution) was further carried out disclosing however total lack of this information for the five latter solvents having two oxygen atoms in their molecule. For each solvent, all available data were correlated with a suitable model equation providing adequate simultaneous descriptions of the information. As a result, the recommended temperature dependence for the activity coefficient of water as well as the respective values of infinite dilution thermodynamic functions of water in the examined solvents at 298.15 K were established. In all solvents, the infinite dilution activity coefficient of water at 298.15 K is greater than unity, increasing consistently as the relative permittivity of the solvent decreases. The variation of infinite dilution thermodynamic functions was found to be considerably interlinked by enthalpy/entropy compensation (r(2) = 0.9383). Furthermore, the performance of the Modified UNIFAC, COSMO-SAC, and MOSCED approaches to predict the activity coefficients of water in the studied solvents was examined. The predictions are quite unsatisfactory, except for those by the Modified UNIFAC for the solvents with one oxygen atom in their molecule.

We present values of the Bodenstein number, Bo(L), characterizing liquid phase axial mixing, for the atmospheric distillation of three binary mixtures of primary alcohols and a mixture of cyclohexane/n-heptane, all of which were distilled in a column packed with Mellapak 250.Y or Mellapak 452.Y. In addition, volumetric mass transfer coefficients (k(L)a, k(G)a) were evaluated from the experimental composition profiles along the distillation column. To describe the distillation process, axial mixing in the phases was considered and modelled as axial dispersion. The results of our modelling call for a reassessment of the relative importance of the process-affecting phenomena. In particular, while vapour phase mass transfer resistance was confirmed as most important, liquid phase axial mixing is shown to have a significant impact under all conditions. For the C-6/C-7 mixture on Mellapak 452.Y, liquid phase mass transfer resistance was negligible when axial mixing was taken into account. Conversely, non-zero liquid phase mass transfer resistance was found for the alcohol mixtures in all cases. However, our investigation revealed that this is most likely a relic of the usage of the simplistic plug flow model. (C) 2019 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.

The volumetric mass transfer coefficient k(L)a becomes the crucial parameter for mechanically agitated fermenters design. Prediction of k(L)a is commonly based on literature correlations. In the case of coalescent liquids, literature-based correlations don't provide results with acceptable scatter. Our aim is to establish viable k(L)a correlations for coalescent liquids that would be based on great experimental data set obtained using Dynamic Pressure Method, the physical correctness of which was verified earlier. In our previous work, the k(L)a dependencies on process conditions in a viscous liquid were described in terms of an appropriate correlation. Now, we aim at the description of dependency between impeller diameters and transport characteristics in coalescent batch. The measurements were performed in multiple-impeller vessels of both laboratory and pilot-plant scale, and for various experimental conditions (impeller frequencies, gas flow-rates, impeller diameters). The studied impellers were Rushton turbines with diverse diameters. On the base of experimental results, the accurate correlation for k(L)a prediction in coalescent batch for industrial devices was suggested. Both the experimental technique and the correlation shape could be used for an industrial design of fermenters with coalescent batches. (C) 2018 Elsevier Ltd. All rights reserved.

This paper refers on the hydraulic and mass-transfer characteristics of several high capacity structured packings Raschig Super-Pak (RSP250Y, RSP350Y, RSP500Y) under absorption conditions. Measurements were performed in column with inner diameter 0.15 m. The comparison with data published in Rejl et al. (2015) for structured packing Raschig Super-Pak 250Y performed in column with inner diameter 0.29 m allows unique assessment of column diameter effect on hydraulic and mass-transfer characteristic of packings. Such study should provide an answer whether is it possible to acquire or under which experimental conditions obtain a reliable hydraulic and mass-transfer characteristics of packing on the columns, from industrial point of view, with small diameter. Obtained characteristics on packings with three different geometric areas enable the evaluation of geometric area effect on the hydraulic and mass-transfer characteristics.

Wall wipers are commonly used in columns filled with structured packings in order to reduce the liquid flow along the column walls. In small diameter columns wall regions are prominent and wall flow, if not well tended to, can adversely affect measured mass transfer parameters, particularly the liquid side mass transfer coefficient kLae. Wire gauze wall wipers provided by some manufacturers do not properly prevent wall liquid flow. In this work, specific wall wipers designed to re-direct liquid wall flow onto packing surfaces were tested against standard wall wipers that do not always properly reduce wall flow. Tests were run on two distinct facilities each with a column diameter of about 150 mm and with bed heights from 0.42 to 1.68 m of Mellapak™ 250.Y packing. The results demonstrate that with the more effective wall wipers it is possible to measure intrinsic height independent values of kLae that match those obtained in a 300 mm diameter column with standard wall wipers.

Wall wipers are commonly used in columns filled with structured packings in order to reduce the liquid flow along the column walls. In small diameter columns wall regions are prominent and wall flow, if not well tended to, can adversely affect measured mass transfer parameters, particularly the liquid side mass transfer coefficient kLae. Wire gauze wall wipers provided by some manufacturers do not properly prevent wall liquid flow. In this work, specific wall wipers designed to re-direct liquid wall flow onto packing surfaces were tested against standard wall wipers that do not always properly reduce wall flow. Tests were run on two distinct facilities each with a column diameter of about 150 mm and with bed heights from 0.42 to 1.68 m of Mellapak™ 250.Y packing. The results demonstrate that with the more effective wall wipers it is possible to measure intrinsic height independent values of kLae that match those obtained in a 300 mm diameter column with standard wall wipers.