Measurement Of Mass Transfer Coefficient Research Articles

Advances in design, scale and operability of the Rotating Liquid Sheet (RLS) contactor: Pressure drop, flood-point and mass transfer – Comparison to random packing

The Rotating Liquid Sheet (RLS) contactor is a novel packing-less gas-liquid contactor where multiple continuous liquid sheets form at the outlet of helical slots in a rotating central feed tube. Each liquid sheet is auger-shaped, and the rotation of the feed tube transfers momentum from the sheets to the gas. Multiple sheets travel in parallel to arrive unbroken at the column wall. The gas travels through the space between adjacent sheets providing close contact between the gas and liquid. Careful design ensures that liquid sheets travel in parallel arcs, enabling scale-up from 150–600 mm diameter column, a size suitable for the speciality chemical or pharmaceutical industries. Pressure drop and flooding measurements using an air/water system compared the RLS contactor with 25 mm Pall Rings. Results for the Pall Rings matched expected performance, while RLS contactor pressure drop was 10% of that measured for the Pall Rings. Mass transfer experiments using an air+CO2/NaOH solution system showed measured mass transfer coefficients using the RLS contactor were comparable to a packed bed (25 mm Pall Rings) of similar specific surface area, while foaming in the packed bed did not occur in the RLS contactor using the same liquid sample. The RLS contactor also displayed minimal entrainment.

Modelling particle dissolution in stirred vessels

Particle dissolution in stirred vessels is a unit operation commonly encountered in several production sectors, such as the mineral, pharma and chemical industries. It is commonly conducted batch-wise under time-dependent conditions, a circumstance that complicates model set-up. This paper presents a set of models for simulating batch dissolution of polydisperse particles in stirred vessels. These models cover all scenarios of particle batch dissolution, regardless of whether the initial particle quantity exceeds or falls short of achieving solution saturation. Consequently, they address cases where particles are either completely dissolved or remain partially undissolved. The models also account for both single-sized and multi-sized particles. Convenient model simplifications are also provided for the cases of final solute concentration much smaller than saturation (low final concentration models). All models are successfully experimentally validated. The single-size large final concentration model is employed to set up experimental runs that, apart from their use in predictive simulations, may be employed for simultaneously measuring mass transfer coefficient and interfacial solute concentration using suitable experimental runs. The ability to measure interfacial solute concentration is also exploited for assessing whether it coincides, or not, with the solute saturation concentration, a common assumption when dealing with solid-liquid mass transfer, which in the present case is found to hold true. The simpler single-size low-final-concentration model is very convenient for measuring the mass transfer coefficient alone. Finally, the multi-size model is utilised to evaluate the sensitivity of the estimated mass transfer coefficient in the single-size model to the particle size range employed during experimental measurements of mass transfer coefficients.

Critical assessment of gassing-in methods to determine mass transfer coefficient in miniature and microbioreactors with gas-liquid flow

Accurate measurements of mass transfer coefficients are critical for reliable characterization of bioreactors. While standardized methods to measure mass transfer coefficients have been established for simple stirred tank reactors, existing methods to characterize mass transfer coefficients have not yet been standardized for alternative reactor types such as miniaturized and biofiltration reactors, leading to inconsistencies in implementation and confusion about the validity of comparisons across different methodologies, volume scales, or reactor types. This study evaluated the accuracy of two commonly used lab-scale methods for the measurement of mass transfer coefficients in a miniature plug-flow reactor: the Dynamic Gassing-In and the Steady State Gassing-In Methods were evaluated. Results revealed that while both experimental methods can be equally accurate and applicable at small scales, there must be careful consideration of mass transfer and volumes peripheral to the reactor itself. To address these findings, a detailed mathematical model was developed and applied to each experimental method, which enabled accurate calculation of the mass transfer coefficients. This approach can be used to analyze experimental data and determine mass transfer coefficients for many reactor types and at any scale. We also propose best practices for mass transfer methods which will enable more consistency in testing and clarity in comparisons between studies.

Effect of distance between impeller blade tip and surface on mass transfer to a local electrode in a stirred vessel in a wide range of Sc number

ABSTRACT Stirred vessels are encountered in a wide scale of applications from bench to industrial processes, and the knowledge of the heat/mass transfer rates in these vessels is required for their design, operation and control. This work submits an investigation on the mass transfer to a small circular surface immersed in a stirred vessel in the parameter ranges of 267 < Re < 9437, 1473 < Sc < 61,422, and 0.022 < x/dK < 0.22 for the distance between the impeller blade tip and the transfer surface. The Reynolds number was based on the impeller diameter. The electrochemical limiting diffusion current technique having a potassium ferri-/ferrocyanide system was applied for mass transfer coefficient measurements. Aqueous glycerine solutions were prepared to attain a wide range of Sc numbers. The rate of mass transfer is enhanced with increasing rotation rate, decreasing blade tip-to-electrode surface distance, and decreasing glycerine concentration. The experimental data were well correlated by the relation .

Toward Sustained Product Formation in the Liquid-Phase Hydrogenation of Mandelonitrile over a Pd/C Catalyst.

The liquid-phase hydrogenation of the aromatic cyanohydrin mandelonitrile (MN, C6H5CH(OH)CN) over a carbon-supported Pd catalyst to produce the primary amine phenethylamine (PEA, C6H5CH2CH2NH2) is investigated with respect to the transition from operation in single-batch mode to repeat-batch mode. While a single-batch reaction returns a complete mass balance, product analysis alongside mass balance measurements for a six-addition repeat-batch procedure shows an attenuation in the rate of product formation and an incomplete mass balance from the fourth addition onward. This scenario potentially hinders possible commercial operation of the phenethylamine synthesis process, so it is investigated further. With reference to a previously reported reaction scheme, the prospects of sustained catalytic performance are examined in terms of acid concentration, stirrer agitation rate, catalyst mass, and hydrogen availability. Gas–liquid mass transfer coefficient measurements indicate efficient gas → liquid transfer kinetics within the experimental constraints of the Henry’s law limitation on hydrogen solubility in the process solvent (methanol). Deviations from the optimized product selectivity are attributed to mass transport constraints, specifically the H2(solv) → 2H(ads) transition, which is ultimately restrained by the availability of H2(solv). Finally, in an attempt to better understand the deactivation pathways, inelastic neutron scattering measurements on a comparable industrial-grade catalyst operated in an analogous reaction in fed-batch mode indicate the presence of an oligomeric overlayer postreaction. This overlayer is thought to be formed via oligomerization of hydroxyimine or imine species via specific pathways that are identified within a postulated global reaction scheme.

Measurement of Mass Transfer Coefficient of CO2–Amine System from Absorption Process

Carbon dioxide (CO2) is one of the main factors for climate change issues. Absorption is the technology to remove CO2 from various industries. The equipment used is the packed column to promote high mass transfer rate and to study the overall mass transfer coefficient (KGav). The KGav is an important parameter for designing and scaling up of packed column. Therefore, the objective of this work is to measure KGav for CO2 absorption into the aqueous solution of monoethanolamine (MEA) in a random-packed column and to investigate effect of parameters on KGav. The parameters are the solvent flow rate from 5.3-15.9 m3/m2h, CO2 initial loading from 0.0-0.2 mole/mole and CO2 content in gas phase from 5-15 %v/v. The results show that KGav increases as the solvent flow rate and solvent concentration increase. The CO2 content in gas phase provides relatively high impact on KGav with an increase in the CO2 content.

Bubble size and liquid-side mass transfer coefficient measurements in aerated stirred tank reactors with non-Newtonian liquids

Oxygen transfer is a key element in aerobic fermentations, especially if the culture broth’s rheology is non-Newtonian, as in the case of cultures of filamentous fungi. Viscosity negatively affects the volumetric mass transfer coefficient (kLa), but mechanisms involved in terms of change of interfacial area (a) and liquid-side mass transfer coefficient (kL) have still not been clearly identified. This lack of knowledge is in part due to the difficulty in measuring bubble size in viscous fluids. In this study, an innovative technique was used to measure bubble Sauter diameter (d32) in water and in xanthan gum solutions. Additional experiments were carried out to obtain the volumetric mass transfer coefficient and the global gas holdup (αG). It was then possible to obtain the liquid-side mass transfer coefficient and to compare it with existing models. Finally, empirical correlations were proposed to estimate d32,αG,kLa and kL in a mechanically stirred tank.

Absorption and desorption mass transfer rates as a function of pressure and mixing in a simple hydrocarbon system

Determining the time required for degassing within a gas–liquid separator is usually accomplished by assuming thermodynamic equilibrium between the two phases and calculating the time required for entrained gas bubbles to rise out of the liquid. However, if the gas–liquid separation is being performed at elevated pressures, the inlet multiphase fluid may not be at thermodynamic equilibrium, thus the chance for solution gas to evolve out of the liquid must also be accounted for. There is, however, a paucity of mass transfer data in hydrocarbon systems available at elevated pressures. For the current experimental study, the rates of absorption and desorption of methane in a n-dodecane solution were measured in a batch stirred tank system at pressures ranging from 3.45 to 10.34 MPa and mixing speeds ranging from 100 to 250 rpm. All absorption and desorption experiments were performed using the same physical and hydrodynamic conditions. Additionally, care was taken in ensuring that the gas–liquid interface during mass transfer remained flat, allowing for the explicit calculation of the liquid-side mass transfer coefficient. Within the experimental variability, the rates of absorption and desorption were found to be the same in most cases. The mixing speed was found to be the main variable affecting the rate of mass transfer, while the saturation pressure was found to have little effect. The process was well described by the theoretically derived solid surface eddy cell model presented by Lamont and Scott, resulting in an average absolute error of 12.3% between the predicted and measured mass transfer coefficients.

Measurement of mass transfer coefficient using electrochemical method at T-junction pipe

Measurement of mass transfer coefficient using electrochemical method at T-junction pipe

Effects of hydrodynamic conditions and temperature on polar organic chemical integrative sampling rates.

The effects of changing hydrodynamic conditions and changing temperatures on polar organic chemical integrative sampler (POCIS) sampling rates (Rs ) were investigated for 12 crop protection chemicals. Exposure concentration was held constant in each laboratory experiment, and flow velocities were calculated from measured mass transfer coefficients of the water boundary layer near the surface of POCIS devices. At a given temperature Rs generally increased by a factor of 2 to 5 between a stagnant condition and higher flow velocities (6-21 cm/s), but Rs for most compounds was essentially constant between the higher flow velocities. When temperature was varied between 8 and 39 °C for a given flow condition, Rs increased linearly. In general, Rs increased by a factor of 2 to 4 and 2 to 8 over this temperature range under flow and stagnant conditions, respectively. An Arrhenius model was used to describe the dependence of POCIS sampling rates on temperature. Adjustments of Rs for temperature did not fully explain observed differences between time-weighted average concentrations of atrazine determined from POCIS and from composite water sampling in a field setting, suggesting that the effects of other competing factors still need to be evaluated. Environ Toxicol Chem 2018;37:2331-2339. © 2018 SETAC.

Preliminary research on mass/heat transfer in mini heat exchanger

In the paper the authors present the facility for model investigations of heat/mass transfer in the exchanger characterised by small dimensions. Determination of heat transfer coefficients is an important issue in the design of mini heat exchangers. The built facility enables measurements of mass transfer coefficients with the use of limiting current technique. The coefficients received from the experiment are converted into heat transfer coefficients basing on the analogy between mass and heat transfer. The exchanger considered consists of nine parallel minichannels with a square cross-section of 2mm. In real conditions during the laminar flow through the minichannels the convective heat transfer occurs. Analogous conditions are maintained during the model mass transfer experiment. The paper presents the experimental facility and the preliminary results of measurements in the form of voltammograms. The voltammograms show the limiting currents being the base of mass transfer coefficient calculations.

Mass transfer coefficient measurement during brine flush in a CO2-filled packed bed by X-ray CT scanning

A clear understanding of mass transfer properties during fluid injection in porous media is important for safe CO2 storage. In this study, dynamic experiments were conducted to elucidate transport during brine injection into a gaseous CO2-filled packed bed using X-ray CT technology. Homogenous glass beads were packed into the bed. Brine was injected downward at 0.005 and 0.03mL/min. The CO2 distribution during brine injection was visualized along the flow direction, which reflected the mechanism transform between displacement and dissolution. The results showed that the distribution was related to the pore structure of the packed bed and flow rates. In addition, CO2 saturation and concentration profiles were obtained at various time points. CO2 concentrations predicted from saturation were orders of magnitude lower than equilibrium solubility. An image analysis technique was employed to determine the interfacial area, which was a function of saturation. Local and overall mass transfer coefficients which were correlated with local concentration and specific interfacial areas were calculated. This study provided a quantitative investigation of gas–liquid mass transfer in a packed bed, which contributed a calculated mass transfer rate during CO2 storage.

Visualization of natural convection heat transfer on a sphere

Natural convection heat transfer phenomena on spheres were investigated by adopting mass transfer experiments based on analogy concept. The diameters of spheres were varied from 0.01 m to 0.12 m, which correspond to the Rayleigh numbers of 1.69×108–2.91×1011. The measured mass transfer coefficients agreed well with the existing correlations. The copper electroplating patterns on the spheres visualized the local heat transfer depending on angular distance. The streak plating patterns were observed on the upper part of the sphere, resulting from the wavy flow patterns caused by the instability.

A simple online phase separator for the microfluidic mass transfer studies

A simple phase separator consisting of a hydrophobic T-connector and a hydrophilic needle was developed for microfluidic extraction studies. The phase separator based on the selective wettability of fluids has a very small volume and nearly zero hold-up of the continuous phase. It is easy to assemble, clean and repair in the laboratory. Four classical extraction systems with interfacial tensions ranging from 49.6 to 1.68mN/m worked well in this phase separator over operating flow rates ranging from 150 and 1500μL/min. Mass transfer experiments showed that the measured mass transfer coefficients from the new phase separator were more accurate than the data from the gravity phase separator. This phase separator has strong potential to be used in the kinetic study of mass transfer in tubular microfluidic device.

Limiting current technique in the research of mass/heat transfer in nanofluid

In the paper the authors focused on the application of the electrochemical limiting diffusion current technique to the study of mass transfer in nanofluid flow. As mass and heat transfer are analogical phenomena, analysing mass transfer helps understand heat transfer processes in nanofluids. The paper begins with a short review of the available literature on the subject followed by the authors' results of mass transfer coefficient measurements and the conclusions concerning mass/heat transfer enhancement in nanofluids.

PEMFC Reactant Mass Transfer Coefficient Measurement and Separation – Method Extension to the Mixed Kinetic and Mass Transfer Control Regime

Additional cost reductions are needed for proton exchange membrane fuel cells (PEMFC) to effectively compete with internal combustion engine powered vehicles. Recent trends have focused on the use of a high current density and a lower Pt catalyst loading to reduce the quantity of expensive materials. However, such strategies have led to higher mass transfer overpotentials (1). These performance losses are advantageously characterized by the mass transfer coefficient. Its separation into fundamental contributions will focus research efforts to improve cell performance. A separation method previously proposed (2) was extended, which provides information for a wider cell voltage range of relevance to duty cycling operation. The extended model yields a closed form and implicit current distribution expression (Eq. 1) where X represents the dimensionless Cartesian coordinate along the flow field channel, ie the inlet oxygen flow rate equivalent current density, ik the kinetic current density, iL ,0 the inlet limiting current density and i the current density. Experimental data obtained with a segmented single cell of 100 cm2 active area (Gore catalyst coated membrane, 18 μm thick membrane, 0.2 and 0.1 mg Pt cm- 2 catalyst loading, segmented and unsegmented Sigracet 25BC gas diffusion layer for the cathode and anode, respectively) validated Eq. 1 (Fig. 1a) and led to overall oxygen mass transfer coefficients k (derived from iL ,0 and operating conditions). A plot of 1/k versus M, the diluent molecular weight, yields a linear relation (Eq. 2) enabling the separation of the overall mass transfer coefficient into 2 contributions where ke +K represents the oxygen mass transfer coefficient in the electrolyte and the gas phase (Knudsen diffusion), km the oxygen mass transfer coefficient in the gas phase (molecular diffusion) for the specified diluent (subscript He for helium, N for N2, CF for C3F8) and b a parameter. The molecular diffusion mass transfer coefficient km is larger with a lighter diluent (Fig. 1b). Each mass transfer coefficient increases as the cell voltage is decreased. However, the increase in the mass transfer coefficient in the electrolyte and the gas phase (Knudsen diffusion) ke +K is more substantial than for the other contribution. As a result, the k/ke +K ratio decreases for lower cell voltages. Specifically for N2, the mass transfer rate limiting step is associated with the electrolyte and the gas phase (Knudsen diffusion), which suggests a focus on the micro-porous and catalyst layers to increase performance. Two reasons are proposed to explain the cell voltage dependency observed in Fig. 1b. First, the local change in gas phase composition promotes convection. This effect is particularly important before reaching the mass transfer control regime, in the mixed kinetic and mass transfer control region, as the interfacial oxygen concentration changes from its bulk flow field channel value to near 0 in the 0.75 to 0.6 V cell potential range creating a diluent enriched layer. Second, the local temperature in the gas diffusion electrode (through plane direction) is also higher at a lower cell voltage owing to additional heat production. The larger local temperatures in turn promote larger diffusion coefficients in the gas phase (molecular and Knudsen) and permeabilities in the ionomer phase. A comparison with other mass transfer coefficient values derived from impedance data (3) and the model limits of validity will also be discussed. Acknowledgments We gratefully acknowledge funding from the Army Research Office (W911NF-15-1-0188). The authors are grateful to the Hawaiian Electric Company for their ongoing support of the operations of the Hawaii Sustainable Energy Research Facility.

PEMFC Reactant Mass Transfer Coefficient Measurement and Separation – Method Extension to the Mixed Kinetic and Mass Transfer Control Regime

A kinetic and mass transfer model for a proton exchange membrane fuel cell (PEMFC) current distribution was derived and validated with data obtained with a dilute oxygen stream and three diluents (5 % O2 + 95 % He, N2 or C3F8). The overall mass transfer coefficient k increased by a factor of ~2 to ~4 with a decrease in cell potential from 0.75-0.8 to 0.2 V. Mass transfer coefficients pertaining to gas phase molecular diffusion km , and, gas phase Knudsen and solid phase ionomer diffusion ke +K respectively increased by 20 % and a factor of ~2. Below 0.6 V, the km and ke +K increase is relatively smaller and is ascribed to the larger heat generation, local temperature and diffusion coefficients. The increase in km and ke +K between 0.75 and 0.6 V is relatively larger and is attributed to the development of steep oxygen and diluent concentration gradients affecting oxygen movement.

Mass transfer correlations for dissolution of cylindrical additions in liquid metals with gas agitation

The results of an experimental study of the effect of gas agitation on mass transfer from cylindrical Si specimens to molten Al were used to deduce mean mass transfer coefficients in a two-phase flow. Then the three-dimensional gas-agitated liquid was simulated using the commercial software FLOW-3D, to obtain predictions of bubble distribution and estimates of the velocity field within the opaque liquid metal, to be used to predict mass transfer rates. An existing mass transfer correlation for a gas-agitated liquid without an external bulk flow was used to fit the experimental data within 5%. With a bulk velocity, a correlation for mass transfer from a vertical cylinder in cross flow was modified to incorporate the effect of gas injection, and it predicted the measured mass transfer coefficients within 11%.

90度エルボ管流れにおける物質移行係数の点電極測定および異なる伝達条件におけるスカラー輸送のLES解析

90度エルボ管流れにおける物質移行係数の点電極測定および異なる伝達条件におけるスカラー輸送のLES解析

Proton Transfer Reaction-Mass Spectrometry (PTR-MS) as a tool for the determination of mass transfer coefficients

We present an alternative technique for the measurement of mass transfer coefficients for bubble columns from the gas phase with the mass spectrometric technique of Proton Transfer Reaction-Mass Spectrometry (PTR-MS). Instead of liquid phase measurements, we apply gas phase measurements of the effluent gas phase with the PTR-mass spectrometer. The method is based on the inert gas stripping approach for the determination of Henry׳s law constant. Therein gas is bubbled through a liquid-water-compound mix, and the declining concentration of the compound in the gas phase is measured over time. For the determination of the mass transfer coefficients, the concentration over time profile is used. Experiments for determination of mass transfer coefficients were carried out in small lab scale under controlled isothermal (thermostated) conditions and with a glass frit sparger. In principle this setup could be performed offline with any detector that has a linear signal dependence over a wide concentration range. PTR-MS has the advantages of low limit of detection (ppt(v)–ppq(v)), wide linear range, and split second detection. We review the formulas for the determination of mass transfer coefficients. The relation with the equilibrium Henry׳s law constant is pointed out (extrapolation to origin considering gas holdup). We determine the overall volumetric mass transfer coefficient KLa, and moreover apply a method for the additional estimation of the liquid-side and gas-side mass transfer coefficients from KLa. Correlations of the superficial gas velocity to the gas holdup ε, the overall volumetric mass transfer coefficient KLa, the liquid side and gas phase volumetric side mass transfer coefficients kLa and kGa, as well as the ration kLa /ε are reported. The results demonstrate the suitability of PTR-MS to the determination of mass transfer coefficient for bubble columns.