Specific Mass Transfer Research Articles

Hydrodynamic effect of dispersed phase fraction on the mass transfer and uptake rate of hexadecane by an oil-degrading microbial consortium in an airlift bioreactor

An investigation was made into the hydrodynamics related to mass transfer of the oil and gaseous phase in an airlift reactor (ALR), using a high dispersed phase fraction (φ=0.1) for biodegradation purposes, in a simulated biotic medium. The highest Reynolds differences (3400<Re<5400) and low liquid velocity differences between the aqueous and oil phase (0.02–0.05ms−1) were obtained in the riser at assayed superficial gas velocity (Ug). The hexadecane (HXD) specific mass transfer area was increased due to the presence of a greater HXD volume, which enhanced the volumetric hexadecane gas-liquid mass transfer coefficient (kLaHXD) compared to other works at φ<0.1. Thus, high HXD transfer rates were obtained through a 14-day batch culture. Conversely, the high φ value promoted a volumetric oxygen gas-liquid mass transfer coefficient (kLaO2) enhancement. The oxygen transfer rates were improved because of an increase in the oxygen saturation concentration. The maximum uptake rates obtained were 3.44–7.74g HXD L−1h−1. The increase in Ug with a high φ value, led to a positive effect that improved the mass transfer of HXD and oxygen, allowing high HXD uptake rates.

Adsorption modeling of CO2 in fluidized bed reactor

A model was proposed for studying the adsorption of CO2 in fluidized bed reactor based on combination of two-phase fluidization with tanks-in-series model. Logical combinations of ideal reactors can be of critical importance in gaining insights into the nature of FBRs and might better be further utilized in process simulation software. Implementation of the tanks-in-series model, in addition, is more consistent with hydrodynamics of the bed compared to one-phase and two-phase models. Considering this model, the fluidized bed was divided into 4 equal-volume stages, in which gas flows as completely mixed flow in emulsion phase and in bubble phase as plug flow. Using experimental data, the number of sections was found as a function of Hata number, superficial gas velocity and minimum fluidization velocity. The experimental results in a laboratory scale fluidized bed reactor with two particle sizes (335 and 605μm) at different superficial gas velocities (0.47, 0.62, 0.79, 0.94 and 1.25m/s) and aspect ratios were used for model validation. Obtained breakthrough curves from modeling were compared against experimental data to verify the validity of the model and acceptable agreement was observed. By fitting the results of the proposed model with experimental data, the reaction constant and Langmuir equilibrium constant were determined to be 0.041/s and 0.019m3/mol, respectively. Increasing the superficial gas velocity and better mixing of adsorbent result in greater adsorption capacity. Moreover, it was observed that smaller particles have higher adsorption capacity due to higher specific surface area and mass transfer coefficient than larger particles. It has also been found that the optimum superficial gas velocity was in the range of 0.62 and 0.79m/s for both particles sizes.

Design Rules for the Taylor‐Couette Disc Contactor

AbstractThe Taylor‐Couette disc contactor (TCDC) is a stirred liquid‐liquid phase contactor which is suitable for applications in bioseparations. For liquid‐liquid reactor design, information about the specific mass transfer area is inevitable. Therefore, the drop size distribution and holdup in the TCDC were investigated under various operating conditions and appropriate correlations for the prediction of these parameters have been determined. Experimental data of drop size distributions were correlated with lognormal, Gaussian, and Weibull drop size distribution functions.

Heat and Mass Transfer Aspects in Nuclear Power Generation

This paper addresses specific heat and mass transfer aspects linked to nuclear power generation safety analysis. Nuclear power plants design and licensing depends on safety analysis performed using dedicated computer codes for heat and mass transfer, thermal-hydraulics, neutron calculations in order to anticipate and address transient and any unwanted operating regimes. Fission produced or residual heat present at all times in the core of a nuclear power plant demands special systems for heat removal and the heat and mass transfer aspects are the most important nuclear systems design criteria.

Gas Hydrate Growth Kinetics: A Parametric Study

Gas hydrate growth kinetics was studied at a pressure of 90 bars to investigate the effect of temperature, initial water content, stirring rate, and reactor size in stirred semi-batch autoclave reactors. The mixing energy during hydrate growth was estimated by logging the power consumed. The theoretical model by Garcia-Ochoa and Gomez for estimation of the mass transfer parameters in stirred tanks has been used to evaluate the dispersion parameters of the system. The mean bubble size, impeller power input per unit volume, and impeller Reynold’s number/tip velocity were used for analyzing observed trends from the gas hydrate growth data. The growth behavior was analyzed based on the gas consumption and the growth rate per unit initial water content. The results showed that the growth rate strongly depended on the flow pattern in the cell, the gas-liquid mass transfer characteristics, and the mixing efficiency from stirring. Scale-up effects indicate that maintaining the growth rate per unit volume of reactants upon scale-up with geometric similarity does not depend only on gas dispersion in the liquid phase but may rather be a function of the specific thermal conductance, and heat and mass transfer limitations created by the limit to the degree of the liquid phase dispersion is batched and semi-batched stirred tank reactors.

Model based analysis of the growth kinetics of microalgal species residing in a waste stabilization pond

AbstractBACKGROUNDIn this study the growth kinetics of Chlorella and Scenedesmus, isolated from a Waste Stabilization Pond were investigated under different conditions of light intensity and temperature. Experimental data were collected by means of a combined respirometric and titrimetric set‐up and used to extend a mathematical model.RESULTSThe experimental results illustrated the interdependent relationship of light intensity and temperature, which had a significant influence on the microalgal growth. Consequently, a previously developed model was extended with a mathematical function that describes this relationship. The maximum specific growth rate and oxygen mass transfer coefficient were considered for model calibration. The optimized parameter values for Chlorella were μmax = 0.56 ± 0.0008 d−1 and KLa = 10.02 ± 0.02 d−1. For Scenedesmus, the optimized parameter values were μmax = 0.19 ± 0.0004 and KL a = 7.71 ± 0.004 d−1. The model with optimized parameter settings described the dissolved oxygen production (derived from the respirometric data) and the related proton consumption (derived from the titrimetric data) reasonably well for both microalgal species. The threshold value for Theil's Inequality Coefficient of 0.3 was never exceeded. In addition, model validation for both species was performed indicating good correspondence between model prediction and experimental values.CONCLUSIONSBased on the experimental observations, a previously developed mathematical model was extended with a function that describes the interaction between light intensity and temperature. After model calibration a difference in maximum specific growth rate between the two microalgal species was observed. This might be explained by differences in cell metabolism. © 2016 Society of Chemical Industry

Reaction Engineering Approach (REA) to Modeling Drying Problems: Recent Development and Implementations

Among the drying models available in the literature, the REA model (which was first proposed in 1996) is semi-empirical. It was described based upon a basic physical chemistry principle. The “extraction of water from moist material” is signified by applying the activation energy concept. The single expression of the extraction rate represents the competition between evaporation and condensation. It also encompasses the internal specific surface area and mass transfer coefficient, and thus is linked to material characteristics. The REA can be classified into two categories—Lumped (L) REA and Spatial (S) REA—which can be used to deal with drying a material as a whole or considering the local phenomena within the material, respectively. Both models have been proven to be very effective. The REA is effective for generating parameters since only one accurate drying run is required to establish the relative activation energy function. Both internal and external resistances are modeled by the REA. In its lumped format, the REA is employed to describe the global drying rate, while in the S-REA, the REA is used to model the local evaporation rate. This article covers fundamentals of the REA which have not been fully explained, as well as the most recent development and applications. The application of the S-REA as a non-equilibrium multiphase model is highlighted.

OpenFOAM Computational Fluid Dynamic Simulations of Two-Phase Flow and Mass Transfer in an Advanced-Flow Reactor

Advanced-flow reactor (AFR) technology is an alternative to scale-up continuous flow chemistries from micro to milli scales, while retaining mass and heat transfer performance. Here we conduct two-phase computational fluid dynamic (CFD) simulations using the open source software OpenFOAM in order to predict hydrodynamic parameters in the AFR for different operating conditions. After modification and validation of the interFoam solver based on the volume-of-fluid method to account for mass transfer across immiscible interfaces, it is applied to the AFR to predict specific interfacial areas (a) and individual mass transfer coefficients (kL) to yield overall mass transfer coefficients (kLa). The results are in good agreement with semiempirical values and the surface renewal theory of Danckwerts, except at the largest flow rates for which numerical coalescence is observed. A study of the influence of fluid properties yields the following conclusions. The contact angle is the variable that affects the flow pat...

1310 超解像度法を用いた血管内皮細胞近傍の物質濃度分布計測

Glycocalyx layer on endothelial cells (ECs) has filtering function related with the specific mass transfer. To evaluate the mass transfer, time-course measurement of concentration distribution in the glycocalyx layer is one of the effective approaches. However, spatial resolution of conventional methods was not enough to observe the layer. In the present study, in order to clarify the detail mechanism of the mass transfer, we developed a novel investigation method of mass transfer in a glycocalyx layer of an EC using a super resolution LIF. As the result of a demonstration of the method, we discovered that the effective filtering area was about 28 times wider than the glycocalyx layer of 0.43 μm thickness.

Variant and invariant states for chemical reaction systems

Models of chemical reaction systems can be quite complex as they typically include information regarding the reactions, the inlet and outlet flows, the transfer of species between phases and the transfer of heat. This paper builds on the concept of reaction variants/invariants and proposes a linear transformation that allows viewing a complex nonlinear chemical reaction system via decoupled dynamic variables, each one associated with a particular phenomenon such as a single chemical reaction, a specific mass transfer or heat transfer. Three aspects are discussed, namely, (i) the decoupling of reactions and transport phenomena in open non-isothermal both homogeneous and heterogeneous reactors, (ii) the decoupling of spatially distributed reaction systems such as tubular reactors, and (iii) the potential use of the decoupling transformation for the analysis of complex reaction systems, in particular in the absence of a kinetic model.

Interphase mass transfer of the high velocity bubbling fluidization regime

Gas–solid fluidization experiments were performed in two separate experimental setups with similar dimensions. Fast X-ray tomography (XRT) was used in setup 1, while ozone decomposition experiments were performed in setup 2. Packing and operation characteristics for the two setups were close to identical. The hydrodynamic measurements from the XRT acquisitions were used to evaluate the interphase mass transfer characteristics obtained from the ozone decomposition results. Superficial velocities (U0) spanning the bubbling up to the onset of the turbulent regime (Uc) were employed. Traditional specific interphase mass transfer (kbe) correlations are based on incipiently fluidized beds; however, results suggested that a distinction should be made between the low-interaction bubbling regime and the high-interaction bubbling regime. A change in mass transfer behaviour occurred around a U0/Uc value of 0.25. An empirical correlation for kbe of the high-interaction bubbling regime is proposed. The correlation gave the best fit for the entire velocity range with an average error of 8%, although it is not recommended for U0/Uc<0.17. It was observed that the classical approach of penetration theory for interphase mass transfer, performed exceptionally well at low velocities (U0/Uc<0.34).

Gas–Liquid Flow and Mass Transfer in an Advanced-Flow Reactor

Hydrodynamics and mass transfer of gas–liquid flow are explored under ambient conditions in an Advanced-Flow Reactor (AFR), an emerging commercial system designed for continuous manufacture. Carbon dioxide/water is the model system used in this study for a range of flow rates for gas and liquid of 5.6–103 mL/min and 10–80 mL/min, respectively. Bubble size distribution, gas holdup, specific interfacial area, pressure drop, and mass transfer coefficients are determined from flow visualization experiments and compared with conventional gas–liquid contactors. These variables are mainly influenced by the inlet flow rates and inlet composition. Average bubble sizes (dB) of 0.9–3.8 mm, gas holdup (eG) of 0.04–0.68, specific interfacial areas (a) of 160–1300 m2/m3, and overall mass transfer coefficients (kLa) of 0.2–3 s–1 were obtained for the vertical orientation of the AFR. Although effect of gravity is present for this system, no significant effect on the hydrodynamic properties was observed. The measured pre...

Non-isothermal separation of ferrofluid particles through grids: Abnormal magnetic Soret effect

Nanoparticle transport through thin non-isothermal ferrofluid layer between permeable walls is investigated. The transient mass flux is determined from measurements of particle concentration changes in two fluid chambers of different temperatures which are attached on both sides of the layer. Experiments are performed employing fluid samples of small ordinary magnetic Soret effect, which is detected by thermal grating technique. The separation measurements say that a magnetic field, aligned along a temperature gradient, causes a remarkable increase in the mass diffusion coefficient and a simultaneous decrease in particle thermodiffusion mobility. It is proposed that the observed effects may be evoked by specific microconvective mass transfer induced by nonmagnetic grid elements of the permeable walls.

The specific diffusion behaviour in paper and migration modelling from recycled board into dry foodstuffs

Recycled board plays an important role in food packaging, but the great variety of organic impurities must be considered as potential food contaminants. The diffusion behaviour of the impurities is significantly different from that in plastic materials. The two-layer concept for paper and board introduced recently is now treated in more detail. In the rate-determining surface region the diffusion coefficients of the n-alkanes in the homologous series with 15–35 carbon atoms decrease proportionally as their vapour pressures. This leads to a different equation of the diffusion coefficients in comparison with that for the core layer. Different polarities of the migrants have additional influences on the diffusion due to their interactions with the fibre matrix. A new analytical method for the quantification of aromatic impurities has previously been developed. Based on this method and on the described diffusion behaviour, a migration model for specific and global mass transfer of impurities from recycled board into dry food and food simulants is given.

Air–water mass transfer of sparingly soluble odorous compounds in granular biofilter media

Mass transfer from air to the liquid phase is a key parameter controlling the efficiency of air cleaning biofilters. Especially the removal of sparingly soluble organic compounds such as volatile odorous sulfur compounds is mass transfer limited. When determining mass transfer rates of sparingly soluble organic compounds the approach have been to either conduct measurements using highly soluble compounds or sparingly soluble compounds with chemical removal of the compounds in the water phase to maintain maximum mass transfer. These data may, therefore, not represent the correct mass transfer rates for sparingly soluble compounds. As a consequence existing mass transfer models may not be accurate for these compounds. In addition most studies of mass transfer in granular media are based on materials consisting of uniform particles. This study investigates the impact of particle size (considering materials with multiple particle sizes), gas velocity and contaminant chemical properties on the overall volumetric mass transfer coefficient based on direct measurements (without the use of chemical reactions) of volatile, sparingly soluble, odorous organic compounds in granular media. Mass transfer was found closely related to particle size, compound solubility, particle size range, specific surface area and gas velocity. Predictive models linking mass transfer, gas velocity, contaminant solubility, media specific surface area, particle size and medium CO2 mass transfer were developed.

Variant and Invariant States for Reaction Systems

Models of chemical reactors can be quite complex as they include information regarding the reactions, the transfer of species between phases, the transfer of energy, and the inlet and outlet flows. Furthermore, the effects of the various phenomena are quite intertwined and thus difficult to quantify from measured data. This paper proposes a mathematical transformation of the balance equations that allows viewing a complex reaction system via decoupled dynamic variables, each one associated with a particular phenomenon such as a single chemical reaction, a specific mass transfer or heat transfer between the reactor and the jacket. Three aspects are investigated, namely, (i) the decoupling of mole balance equations, (ii) the decoupling of mole and heat balance equations, and (iii) the applicability of the decoupling transformation for model reduction, static state reconstruction and kinetic identification.

Application of molecularly imprinted polymer particles in capillary electrochromatography

Molecularly imprinted polymer (MIP) particles prepared by molecular imprinting technique (MIT) possess the ability of specific identification and selective affinity towards template molecules and their structural analogues. They also have a large specific surface area and rapid mass transfer kinetics, thus they have been widely used as stationary phases in liquid chromatography and matrixes in solid phase extraction. Using MIP particles as capillary electrochromatography (CEC) stationary phase, which combines the high speed and efficiency of CEC with the high affinity and selectivity of MIP, has become one of the most promising separation technique in analytical science. There are several different strategies of MIP particles applied in CEC: as packing materials packed into a capillary column; as entrapping materials entrapped into different matrix frameworks inside a capillary column; as pseudostationary phases (PSPs) added into the running buffer of CEC. This review focuses on the recent developments of MIP particles in CEC and prospects the future developments in this field.

Liquid–Liquid Test Reactions to Characterize Two-Phase Mixing in Microchannels

Multiphase flow is often found in chemical engineering, food processing, or analytical devices. First contacting and droplet generation as well as coalescence and redispersion are important for the flow characteristics. In all processes, the channel geometry, fluid properties, and flow velocity determine the flow regime, droplet size, and interfacial area. The hydrolysis of alkyl acetates in organic phase with sodium hydroxide NaOH in the aqueous phase is investigated as flexible test reaction for mass transfer and interfacial area determination. The alkyl group is chosen from ethyl, isopropyl, or n-butyl, which differ in water solubility, diffusivity, and rate constant, for adequate design of the characteristic time for mass transfer. The consumption of NaOH is used for calculation of specific area and related mass transfer coefficient. Different channel geometries are characterized and design considerations are derived.

Hydrodynamics of Liquid–Liquid Dispersion in an Advanced-Flow Reactor

Hydrodynamics and mass transfer of immiscible liquid–liquid flows are explored in an Advanced-Flow Reactor (AFR). These systems are emerging as one of the major commercial systems for small scale continuous flow chemistry, and characterization of the transport phenomena is critical for reaction implementation. With hexane/water as a model system, we use flow visualization techniques to determine drop size distribution, hexane holdup, and specific interfacial areas for a phase flow rate range of 10–80 mL/min. The complex geometry of the AFR with its continuously changing cross section along the flow path and strategically placed obstacles creates pressure changes that cause drop breakup and enhance mass transfer. Observations show that a wide range of average drop size (0.33–1.3 mm) can be achieved in the AFR depending upon the inlet flow rates and inlet composition. Pressure drop measurements are performed to estimate the power consumption and are used to compare the efficiency of AFR with conventional liquid–liquid contactors. The analysis shows that, similar to microreactors, the AFR can provide specific interfacial areas (1000–10 000 m–1) and overall mass transfer coefficients (1.9–41 s–1) a few orders of magnitude larger than conventional stirred tank reactors and also the static mixers.

Gas side controlled mass transfer in a new packing with stamped horizontal lamellae operating at extremely low liquid loads

The gas side controlled mass transfer coefficient of an easy to make packing, with stamped horizontal lamellae, designed for operating at extremely low liquid superficial velocity, between 0.04 and 1m3/m2h is investigated. The absorption of SO2 in sodium hydroxide water solution is used as a model process. Based on the obtained experimental data, an equation for calculating the gas side controlled mass transfer coefficient, with deviation of ±8% is presented.The comparison between the new packing and different highly effective packings shows that the new one has lower pressure drop at the same specific area and mass transfer coefficient, respectively higher mass transfer coefficient at the same pressure drop and specific surface.Of all compared highly effective packings, only the crossed strips packing, quite difficult to produce, has close, yet higher, pressure drop at similar specific surface area and volumetric mass transfer coefficient.