Instantaneous Mass Transfer Coefficient Research Articles

Mass transfer of chemical absorption of CO2/N2 mixed gas in a microchannel

In the chemical industry, the gas phase is not always pure gas generally. The mass transfer (MT) of mixed gas in a microchannel was investigated by using organic amine aqueous solution to absorb CO2/N2 mixed gas. MT in the bubble formation stage was calculated, and the influence of operating conditions on it was investigated. When the gas contacts the liquid, the CO2 in the bubble is continuously absorbed. Combined with the reduction of bubble volume, the instantaneous MT driving force of the bubble along the microchannel is calculated. On this basis, the MT coefficient of the mixed gas is obtained. The results show that after mixed gas in a certain concentration enters the microchannel, the instantaneous MT driving force and instantaneous MT coefficient are constantly decreased during the bubble moves along the microchannel.

A mathematical model for single CO2 bubble motion with mass transfer and surfactant adsorption/desorption in stagnant surfactant solutions

Gas absorption into a liquid is an effective means of reducing the emission of environmentally unfavorable gases. The efficiency of the gas absorption is determined by the gas–liquid mass transfer. In this study, a mathematical model coupling gas–liquid mass transfer and surfactant adsorption/desorption with CO2 bubble motion in a bubble column is proposed. The kinetics of surfactant adsorption and desorption on the bubble surface are represented by two model parameters. To obtain the model parameters, we measured the eccentricity, rising velocity and volume of bubbles in a diameter range of 1.96–0.59 mm in stagnant surfactant solutions using high-speed photography. The instantaneous mass transfer coefficient is derived from the variation of the bubble volume with time. The effect of the accumulation of surfactant on the bubble shape, rising velocity, and mass transfer coefficient is discussed. The mathematical model is able to calculate the variation trends of the CO2 bubble diameter and rising velocity with an initial bubble diameter d less than 2 mm in surfactant solutions, which are consistent with the experimental results.

Investigation of mass transfer model of CO2 absorption with Rayleigh convection using multi-relaxation time lattice Boltzmann method

• MRT-LBM is used to simulate CO 2 absorption with Rayleigh convection. • The characteristics of flow and concentration fields are presented. • The gas-liquid interface division results of Rayleigh convection are presented. • A penetration/surface divergence hybrid mass transfer model is proposed. CO 2 absorption into absorbents is a widely used method to reduce carbon emissions, in which the concentration gradient near the gas–liquid interface may induce Rayleigh convection (RC). Once RC occurs, the mass transfer rate will be significantly enhanced. Therefore, it is necessary to explore the mass transfer enhancement mechanism further and develop a penetration/surface divergence hybrid mass transfer model. In this study, we conduct research on the process of CO 2 absorption into ethanol with RC. Firstly, we use a multi-relaxation time lattice Boltzmann method to simulate the absorption process and obtain the flow and concentration fields. And we also verify the reliability of the numerical simulation results by comparing with the experimental results. Then, we analyze the characteristics of non-uniform flow and concentration fields in RC. Moreover, we divide the near-interface region into diffusion-dominated and convection-dominated mass transfer zones by checking whether the horizontal average velocity is greater than 1.0×10 –4 m∙s –1 . Furthermore, based on the differences in mass transfer mechanisms of the aforementioned two zones, we propose a penetration/surface divergence hybrid model to predict the instantaneous mass transfer coefficient. The prediction results demonstrate that the hybrid model can precisely predict the instantaneous mass transfer coefficient of the entire CO 2 absorption process. Our proposed hybrid model provides a promising way to deal with the complex mass transfer problems with non-uniform flow and concentration fields.

Theoretical and experimental investigations of time-dependent mass transfer mechanism of fine particulate matter under the sink effect

The mass transfer process of fine particulate matter (PM) under the sink effect is affected by many variables, including purification device performance, environmental conditions, and time. In this paper, the time-dependent mass transfer mechanism of PM was explored while all other variables were to remain the same. Firstly, the spatial and temporal profile characteristics of particulate matter concentrations (PMC) with different size fractions were investigated. Subsequently, the apparent mass transfer coefficient Dapp of PM was calculated based on Fick's second law, and the relevant parameters were determined by laboratory-scale experiments. According to the Dapp, the instantaneous mass transfer coefficient Dins of PM was further discussed and the prediction model of PMC was established. Finally, the stability and applicability of the prediction model were verified by experiments. The results showed that the farther the distance from the purification device, the smaller the particle size, then the smaller the decrease rate of PMC and the stronger the regeneration process. The value of Dapp could reflect the mass transfer process of PM at the macroscopic level. The value of Dins could better characterize the mass transfer process of PM at the level of detail, and it could also be used to predict and evaluate the dynamic mass transfer efficiency of PM. The established PMC prediction model had strong stability and good applicability. The research results of this paper can provide an important reference basis for practical engineering applications.

Mass transfer of chemical absorption of CO2 in a serpentine minichannel

Based on the online method, the absorption kinetics and mass transfer of CO2 in potassium carbonate solution in a serpentine minichannel are studied. Three flow patterns are observed: slug-bubbly flow, slug flow, and slug flow with precipitation of SiO2. It is observed that the length of bubble decreases linearly with the increase of the travelling distance of bubble x in slug flow, based on which the volumetric mass transfer coefficient (kLa) is calculated. The results show that the average bubble velocity vb is only a function of the gas and liquid flow rates, and it remains unchanged in the whole flow process. Based on the online method, the instantaneous mass transfer coefficient, and instantaneous pH are studied. It’s found that the instantaneous mass transfer coefficients kLa and kL increase with the mass transfer of bubbles along the flow direction in the slug flow. It is concluded that the convection in the liquid slug plays a major role in controlling the mass transfer of fast chemical absorption in a serpentine minichannel.

Entransy dissipation analysis of interfacial convection enhancing gas–liquid mass transfer process based on field synergy principle

Abstract An exploration of the gas CO2 absorbed into liquid ethanol accompanied with Rayleigh convection is performed by analyzing the mass entransy dissipation; this new statistical quantity is introduced to describe the irreversibility of mass transfer potential capacity. Based on the general advection–diffusion differential equation for an unsteady mass transfer process, the variation of the included angle between the velocity vector and concentration gradient fields is investigated to reveal the underlying mechanism of interfacial convection enhancing mass transfer. Results show some identical characteristics with the qualitative analyses of the synergy effects generated by the concentration and velocity fields after interfacial convection occurring for a boundary condition of fixed surface concentration. And the equivalent mass resistance for convective mass transfer process presents the similar variation with the reciprocal of instantaneous mass transfer coefficient. Accordingly, it is reasonable to be seen that mass transfer dissipation rate could be provided to assess the convection strength and explain fundamentally how Rayleigh convection improves mass transfer performance through establishing a close relationship between the mass transfer capacity and field synergy principle from the view of mass transfer theory.

Influences of gas–liquid interface contamination on bubble motions, bubble wakes, and instantaneous mass transfer

To improve the efficiency of industrial processes and to precisely comprehend the complex mechanism of global warming, a thorough understanding of the mass transfer mechanism from a bubble to the surrounding liquid is essential. Here we investigated a single CO2 bubble (2.9mm in equivalent dia.) that ascended in a zigzag motion in purified water and in water contaminated with a very small amount of 1-pentanol. We used a laser-induced fluorescence (LIF) technique and 8-hydroxypyrene-1,3,6-trisulfonic acid (HPTS), and we employed a pH-sensitive dye that was calibrated by means of a photoelectric optical fiber probe to visualize the bubble-to-liquid-phase mass transfer and the bubble's wake structure. Two high-speed cameras were used to capture the bubble wake (including the CO2 dissolution), the bubble motion, and the bubble wake from two orthogonal directions. Based on the visualization results, we obtained the volume, surface area, velocity, orientation angle and shape of the bubble from moment to moment. The instantaneous mass transfer coefficient of the bubble was precisely calculated from the above results. Due to reiteration of the adsorption and desorption of the surfactant on the bubble surface, the direction of the Marangoni convection was very difficult to identify. Here, based on our analysis of forces that were calculated from the bubble motion, we considered the direction of action of the Marangoni convection indirectly. On the basis of these experimental results, we discuss the influences of the bubble-surface contamination on the bubble motion and the mass transfer, as well as the bubble wake.

Nonstationary Mass Transfer Near the Surface of a Cylindrical Body

The problem of nonstationary diffusion of the target component to a phase that is external relative to the surface of a cylindrical body has been formulated and solved analytically. From the found solution the dependences have been obtained for calculating the instantaneous mass transfer coefficient and the phase-contact-time mean mass transfer coefficient, on the basis of which the process of extraction of technological pollutants from fibrous materials has been analyzed.

Effects of a bubble and the surrounding liquid motions on the instantaneous mass transfer across the gas–liquid interface

To understand the mass transfer mechanism from a bubble to the surrounding liquid, one must consider the relation between the mass transfer, gravity-center and surface motions of the bubble. Bubbles in chemical and bio-reactors usually exhibit a zigzag motion. Simultaneously, such bubbles accompany periodic surface oscillation. Knowledge about the correlation between the mass-transfer mechanism and bubble motion is as yet incomplete. In this study, we used experimental results from highly precise measurements of bubble volume to clarify the instantaneous mass-transfer coefficients of a zigzagging CO2 bubble. We visualized the zigzagging motion and surface oscillation 3-dimensionally and simultaneously, using two high-speed cameras and mirrors. We also visualized the CO2 dissolution (mass transfer) process from the bubble to the surrounding liquid using the LIF/HPTS method. To obtain the precise instantaneous mass transfer coefficient and bubble motions, single bubbles were visualized in three sections: the linear-ascent, the first-inversion, and the second-inversion of the zigzag motion. The instantaneous mass-transfer coefficients in an interval of 6ms in these sections were calculated from the bubble-volume shrinkage with ms time-resolution. The instantaneous mass-transfer coefficients increased in acceleration areas—i.e., in the linear-ascent and second-inversion sections. Interestingly, in the latter, the gravity-center velocity of the bubble reached terminal velocity and was constant, but the velocity of the bubble hemisphere was accelerated due to the zigzag motion. This partial acceleration of the bubble hemisphere led to a high renewal rate of the liquid on the bubble interface. The effect of the partial acceleration on the instantaneous mass transfer was significant for bubbles categorized into zigzag motion.

507 ジグザグ上昇する気泡周囲の液相流動構造と瞬時物質移動係数の定量的考察(GS 液体工学(2))

507 ジグザグ上昇する気泡周囲の液相流動構造と瞬時物質移動係数の定量的考察(GS 液体工学(2))

G051033 ステレオPlVによる気泡の周囲液相流動の可視化と瞬時物質移動の考察([G051-03]流体工学部門,一般セッション : 混相流一分子動力学他)

The purpose of this study is to clarify the mutual relationship among the bubble motion, the surrounding liquid motion and the instantaneous mass transfer from the bubble to the liquid phase. For this specific purpose, the zigzag motion of the bubble were captured with high spatial resolution by a pair of high speed cameras, and instantaneous changes in volume and surface area of the bubble were obtained from the captured images by our originally developed method. The instantaneous mass transfer from the bubble to the surrounding liquid was enhanced at a section around the second inversion point. The enhancement in the mass transfer on the right side surface was dominant; hence the instantaneous mass transfer coefficient increased. In addition, in order to obtain the liquid motion induced by the bubble, Stereo-PIV measurement was conducted. As a result, the vortices were shed from the bubble rear in the sections. The vortices acted like transporting the liquid rich in dissolved CO_2 away from the bubble rear. The convective transportation was promoted; consequently the mass transfer was enhanced.

Mass transfer during drop formation on the nozzle: New flow expansion model

AbstractAn attempt was made to introduce a new approach for evaluating mass transfer during drop formation via definition of a parameter related to the extent of the convective mixing within the growing drop. For this purpose it was assumed that the entrance of the dispersed flow into the growing drop from the nozzle is analogous to the entrance of the flow from a smaller channel to a larger one. This transfer mechanism has been dubbed the “flow expansion.” A global time‐dependent Reynolds number of growing drop (Regd) was defined based on the equivalent diameter of growing drop as a length scale and also on a velocity scale, which is obtained using this flow expansion assumption. The results show that (Regd) has an important role on the mass transfer coefficient. The results of the model for prediction of instantaneous mass transfer coefficients and total cumulative mass transfer demonstrated relatively good agreements with experimental data. In some cases, however, for large nozzle diameter and relatively low nozzle velocity, i.e. in cases with large nozzle time scale (TN = RN / UN), the flow expansion model showed some shortcomings. Subsequently, a modification called the transient flow expansion model was introduced which could improve the results of the previous model for large TN cases. Comparison of the results of the transient flow expansion model with experimental data reported in the literature showed relatively good agreement for a wide range of operational conditions: nozzle diameter, nozzle velocity, final formation time and various liquid‐liquid systems. The capabilities of the model were also evaluated in comparison with other well‐known analytical (surface stretch and the fresh surface elements) and semi‐empirical models, along with available experimental data. The comparison of the model with the previous incorporated convection/circulating models demonstrated a high potential for this new approach. © 2005 American Institute of Chemical Engineers AIChE J, 2006

Mass-Transfer Enhancement in Large-Diameter Pipeline under Water/Gas Stationary Slug Flow

In multiphase flow, gas bubbles are produced that collapse at the liquid/solid interface. In order to examine such effects, mass-transfer studies have been performed in an electrochemical cell and in a large-diameter flow loop under water/gas two-phase stationary slug flow. A limiting current density technique was used for oxidation of or reduction of in concentrated NaOH solutions. High-frequency and high-magnitude, instantaneous mass-transfer coefficients were found by potentiostatic measurements and may account for the corrosion rate enhancement in water/gas slug flow. A physical model of the stationary slug flow is proposed to explain the mechanism of gas bubble formation and bubble distribution. The effect of the gas bubbles on the mass-transfer enhancement is reported and a mechanism for the mass-transfer coefficient fluctuations is proposed. This study demonstrates that gas bubbles produced in stationary slug flow have a direct enhancement impact on the mass-transfer and corrosion rate of carbon steel pipeline. © 2004 The Electrochemical Society. All rights reserved.

Modeling of transient particle–liquid mass transfer in liquid and liquid–solid systems

Models based on the film, penetration and surface renewal theories were developed for predicting the local, dynamic behavior of liquid–solid mass transfer in a fixed bed. The influence of velocity pulses of frequency less than 1 Hz in the range 0.005–0.03 m/s has been studied. A model based on the surface renewal theory estimates the local instantaneous mass transfer coefficient from the instantaneous velocity. Experimental validation is provided. Potential applications are the determination of local transient velocity in fixed beds from mass or heat transfer measurements and the assessment of mass transfer enhancement in pulsating systems.

Mass-Transfer Properties of Microbubbles. 2. Analysis Using a Dynamic Model

Gas-to-liquid mass transfer is commonly the rate-limiting step in industrial fermentations. Microbubble sparging has been shown to give extremely high volumetric mass-transfer rates, even for low power-to-volume ratios. Microbubbles are surfactant-stabilized bubbles having a radius on the order of 25 μm. The extremely high surface-area-to-volume ratios of microbubbles can result in rapid changes in their size, internal pressure, and gas composition. Consequently, an unsteady-state modeling approach is needed to adequately describe microbubble mass transfer. A dynamic model of a single microbubble immersed in an infinite pool of stagnant liquid was developed and solved numerically. The model accounts for mass-transfer resistances of the surfactant shell and surrounding bulk liquid, bubble shrinkage, changes in the gas pressure and composition inside the bubble, and changes in the liquid-phase concentration profile of the transferred gas surrounding the bubble. The model was used to explore a variety of dynamic phenomena associated with microbubble mass transfer. The presence of a nontransferred gas in the microbubble was predicted to significantly reduce the mass-transfer rate, indicating that microbubble sparging is better suited to gases with a high consumable fraction. The instantaneous mass-transfer coefficient was predicted to change significantly with time, but the time-averaged coefficient was constant enough to justify the measurement of average mass-transfer coefficients for microbubbles. Average mass-transfer coefficients predicted by the model agreed well with values measured experimentally and calculated using literature correlations.

Gas‐liquid mass transfer from a single bubble in liquid‐solid fluidized beds

AbstractExperiments were conducted to study the gas‐liquid mass transfer of a single bubble containing an ozone‐oxygen gas mixture in liquids and liquid‐solid fluidized beds. A spectrophotometric technique is developed for the measurement of the instantaneous mass transfer coefficient and the local concentration distribution around the bubble wake. The method employs an ultraviolet light source and optical fibers. Axial variations of the mass transfer rate are studied. An ozone and starchiodide complex reaction is employed to visualize the mass transfer phenomena.

MASS TRANSFER INVESTIGATIONS DURING DROPLET FORMATION BY MEANS OF A MODIFIED LIQUID SCINTILLATION TECHNIQUE

Single droplets were formed at the tip of different capillaries employing high droplet formation rates and continuous phase flow rates. The mass transfer of acetic and / or propionic acid from toluene droplets and acetone from n-butyl acetate droplets into the continuous water phase was measured during droplet formation with a time resolution of 10 msec by a modified liquid scintillation technique. The solute concentration, as a function of time, passes an inflexion point during the first 0.5 sees. By employing the mass balance and the developing droplet geometry the instantaneous mass transfer coefficient was determined, which passes a maximum at the inflexion point of the concentration vs. time curve. The influence of the location of the partition coefficient, the droplet Reynolds number and the continuous phase Reynolds number on the instantaneous mass transfer coefficient was investigated. Serious deficiencies of published models are discussed.

Mass transfer at the solid‐liquid interface for climbing film flow in an annular duct

AbstractA method utilizing a diffusion controlled electrochemical reaction was used to measure average and instantaneous mass transfer coefficients at the solid‐liquid interface in upward gasliquid climbing film flow in a vertical annular duct. These measurements give some indication of the mechanics of flow of the film, the extent of turbulence at the inner wall, and the effect of film thickness and wave motion on the mass transfer process at the inner wall. Predictions of incipient downflow of the film, shear stress at the inner wall, and interfacial shear stress were obtained from these measurements. Fluctuations in the velocity gradient at the inner wall were also studied. Results of this study are in good agreement with previous work and with theoretical predictions based on simplified momentum balance concepts.

Mass transfer from single gas bubble — a comparative study on experimental methods

AbstractA comparative study on the experimental techniques which have been used for the study of mass transfer from single gas bubble was made. The instantaneous mass transfer rates from a single carbon dioxide bubble rising through quiescent liquid medium (water) were measured using two different methods. For the first method, two movie cameras were placed on a moving platform along perpendicular directions and were used to record the position and size change of the bubble. The second method measured the mass transfer rates by recording the pressure changes in the free space at top of the bubble column, which was caused by the change of bubble size. The instantaneous mass transfer coefficients determined by either method exhibited wide scattering which is typical of work of this kind. Discussions are given on the relative merits of these two methods.

Experimental study of the behavior of single bubbles

A method is described for measurements of the rates of volume change of a rising gas bubble, its surface area, velocity of rise, and the instantaneous mass transfer coefficient. The principle of this method is to follow by means of high speed photography the motion of the bubble simultaneously with the changes in volume as indicated by the capillary of a dilatometer. In this way an almost continuous record is obtained of the bubble volume, shape and oscillation, as related to the height of the bubble in the liquid and the time elapsed from the moment of the bubble release. The reproducibility of this method was investigated and the standard deviations of the results are given and discussed. Results obtained by some other authors are shown for comparison. The effect of the bubble release time on the consistency of the K L values was found to be of importance and was studied in some detail. The above discussed procedure was developed as a part of a comprehensive study of the behavior of gas bubbles in dilute aqueous solutions.