Calculation Of Mass Transfer Coefficients Research Articles

MASS TRANSFER IN THE BIOREACTOR DURING GAS DISPERSION FROM THE STIRRER VORTEX CAVITY

Gas-liquid bioreactors in which the introduction of the gas substrate in the culture liquid is carried out from the vortex cavity formed by the rotation of the stirrer.  In order to simplify the design and intensify mass transfer a new method of dispersing the gas substrate from the vortex cavity is proposed and studied.  It consists in maintaining local zones with reduced pressure in the liquid behind the rotating paddles and creating the necessary conditions for the introduction of the gas substrate. On the basis of numerical simulation the pressure is calculated and the zones of low pressure in liquid behind the stirrer paddles are determined. The value of differential pressure necessary for gas dispersion has been estimated. The angular velocity of liquid rotation depending on the number of partitions on the apparatus wall and the number of mixer revolutions is presented. The gas content in the liquid during the implementation of the investigated method has been determined. The average surface diameter of gas bubbles and interfacial surface of gas-liquid medium were calculated from experimental data. The power spent on stirring in the apparatus has been established and the power criterion with regard to gas content has been determined. Mass transfer at intensive gas dispersion from gas vortex cavity into liquid has been investigated. Criterion dependence for calculation of mass transfer coefficient is presented, taking into account energy dissipation spent on mixing and interfacial surface. The fields of application of bioreactor with new method of gas dispersion are shown.

RESEARCH AND MODELING KINETICS ION EXCHANGE INTERACTIONS

In detail, this study analysed the kinetics of ammonium ion adsorption under dynamic conditions in the "clinoptilolite -ammonium ion" system. The work includes constructing a mathematical model of this process, which allows us to estimate and predict its essential characteristics. Calculations of mass transfer coefficients revealed their dependence on the intensity of medium mixing. A significant result is that ion exchange occurs in externally diffusion and intradiffusion regions. Ion exchange rate constants were calculated for the regions of external and internal diffusion, contributing to a deeper understanding of the mechanisms of this complex process. The research results will expand our knowledge about ion exchange interactions in the " clinoptilolite -ammonium ion" system. In addition, they can be used to optimise the conditions of ammonium adsorption in similar systems, which is essential for practical applications related to water purification and other media from ammonium ions.

Mass transfer model based on the spatial superposition assumption for simulating the catalytic ozone decomposition in downer reactor

A mass transfer model based on the spatial superposition assumption is proposed in this work to better reflect the effect of heterogeneous structure on the mass transfer behavior of the downer. Attributing to the special assumption of this model, fewer concentration parameters are required compared with the classic multi-scale method, which largely saves the calculation consumption. The simulation results of this model also could be in good agreement with the experimental data. Additionally, the calculated mass transfer coefficients are in the range from 10−3 to 10−1, which are approximately three orders of magnitude lower than that of the homogeneous structure. It is proved that the existence of clusters would seriously affect the gas-solid mass transfer effectiveness, thereby deteriorating the reaction rate. By simulating the distribution of ozone concentration in the catalytic ozone decomposition, it can be found that the mass transfer near the inlet region plays the dominant role while along the flow direction, the influence of reaction process becomes stronger than that of the mass transfer process and gradually turns to control the whole decomposition process. These results indicate that the present model is useful and could be applied for the simulation of mass transfer process in other gas-solid fluidized systems with heterogeneous structures.

Opportunities and prospects for the use of solar energy for refrigeration of public buildings

This paper describes the calculation of evaporative-radiant cooling of recycled water in summer air-conditioning systems. A differential equation for the heat balance of water flowing down an inclined plane is derived. As one possible way of increasing the efficiency of air conditioning systems based on cooling water by adiabatic evaporation in the air flow the use of night-time evaporative cooling of the water, followed by daytime cooling in insulated storage tanks. The temperature of the water chilled in this way is 3-4 °C lower than the temperature of the water chilled during the day, and the final water temperature is close to the saturation temperature of the outside air. The equations for calculation of mass transfer coefficients, radiation and heat transfer coefficient of an insulated bottom of an evaporative-radiant water-cooling unit are given. Based on the Mathcad program and the result of the calculation, the dependence of the final water temperature on the initial water temperature is obtained. As a result of the calculation, the specific heat capacity of the evaporative radiant water-cooling unit for the production of free cooling is determined.

Use of evaporative cooling units in solar air conditioning installations

The paper describes the calculation of evaporative-radiant cooling of recycled water in summer air-conditioning systems. A differential equation for the heat balance of water flowing down an inclined plane is derived. As one possible way of increasing the efficiency of air conditioning systems based on cooling water by adiabatic evaporation in the air flow the use of night-time evaporative cooling of the water, followed by daytime cooling in insulated storage tanks. The temperature of the water chilled in this way is 3-4 ℃ lower than the temperature of the water chilled during the day, and the final water temperature is close to the saturation temperature of the outside air. The equations for calculation of mass transfer coefficients, radiation and heat transfer coefficient of an insulated bottom of an evaporative-radiant water-cooling unit are given. Based on the Mathcad program and the result of the calculation, the dependence of the final water temperature on the initial water temperature is obtained. As a result of the calculation, the specific heat capacity of the evaporative radiant water-cooling unit for the production of free cooling is determined.

DRYING OF CENOSPHERES RECOVERED BY THE WET-BASED METHOD FROM COAL FLY ASH FOR THEIR RATIONAL USE

Since slag and coal fly ash (CFA) are major global pollutants produced by thermal power plants (TPPs), special attention should be paid to their rational disposal. Scanning electron microscopy (SEM) was used to study the morphology of CFA and it was suggested that the use potential of CFA is high due to the presence of a large number of cenospheres (CSs), that can be recovered mostly by wet methods for the production of the wide range of products with improved properties. However, such decisions regarding the application of the cenospheres are largely related to the problem of their drying after removal. The article is devoted to the investigation of the filtration method as less energy-consuming for the drying of cenospheres. The effect of the drying agent velocity on the mass transfer intensity has been established. The values of mass transfer coefficients have been calculated based on the thin-layer experimental data and equation . Calculated mass transfer coefficients for cenospheres have been correlated by the dimensionless expression , based on which equation has been proposed to calculate the mass transfer coefficients, which is important at the filtration drying equipment design stage.

Sherwood correlation for finger-test experiments

Finger-test experiments are frequently conducted in continuous-wear investigations of ceramic materials. However, mass transfer equations accurately representing these scenarios are not yet available, which can lead to erroneous estimation of dissolution-related parameters due to poor approximations. In this study, a Sherwood correlation for finger-test experiments was developed. The equation applies to rods or nearly cylindrical specimens that are rotated in a liquid contained in a cylindrical receptacle. The equation is derived from numerical results simulating the dissolution of ceramic materials in liquid slags, where the dissolution is dominated by mass transfer in the liquid. For these simulations, surface profiles from the experimental results were employed. Based on the derived equation, a methodology for the calculation of mass transfer coefficients for dissolution processes was designed that enables diffusivity determination. This equation is also suitable for heat transfer calculations. The equation is in agreement with the results obtained by simulation and other documented heat and mass transfer equation, for the latter the fit is poorer due to differences in the experiment configuration.

Roughness mass transfer function for an electro-chemical column with inserted heptagonal plate as turbulence promoter

Experiments have been done to evaluate the effect of a coaxially arranged entry area heptagonal plate as a turbulence promoter on mass transfer rates in electrolyte induced convection flow. The goal of this research is to determine mass transfer rates at the electrochemical cell's outside wall. The measured limiting currents technique was used to calculate mass transfer coefficients. This research examines the effects of several characteristics such as plate side (SP), plate number (NP), and plate spacing (H). The mass transfer coefficient increases as the velocity, side of the plate (SP), and number of plates (NP) increase, but decreases as the spacing between plates (H) grow. The correlation achieved is.g(h+)=2227.3(Re+)-0.70264SPd1.6255L/NPd-0.12198Hd-0.17904Sc0.38927

Mass Transfer Coefficient Enhancement Using Spiral Wound Rod as Turbulence P romoter in an Electrolytic Cell

Objectives: to improve efficiency of process equipment by increasing the mass transfer coefficient with a spirally wound rod as the turbulence promoter. Methods:The function of facet promoters, whirl generators, and test sections of different congruous shapes increase the mass transfer coefficients at the reaction surface. Diffusion-controlled redox (ferricyanide - ferrocyanide) reaction has been chosen for the study. Limiting current data from the reduction of ferricyanide is used for mass transfer coefficient calculation. A set of three geometric parameters such as pitch(P), height(H), and width(W) of the promoter were investigated in the current study. Findings: An increase in the mass transfer coefficient values with the increment of flow rate of electrolyte from 0.088 m/s to 0.263 m/s was observed. A rise in the promoter height from 0.03 to 0.07m enhanced the mass transfer coefficient by 25.7 fold, while the increase in the width of the promoter from 0.01 to 0.04m resulted in a rise of the mass transfer coefficient by 26.3 fold. On the contrary, the mass transfer coefficient decreased upon increase in the pitch of the promoter from 0.01 to 0.04m, but overall enhancement is 25.7 fold. The increase in the mass transfer coefficient on an average compared to a rectangular turbulence promoter was 5.71 fold. Novelty: The spiral wound rod as a promoter increased the mass transfer coefficient several folds compared to other promoters. The spiral wound rod is quite simple to manufacture, has low cost and ease of maintenance. Therefore, the promoter used in the study could be employed for heat and/or mass transfer enhancement in Industrial applications. Keywords: Limiting current; Promoter; Mass transfer Coefficient; Swirl flow; Redox reaction

Periodic porous 3D boron-doped diamond electrode for enhanced perfluorooctanoic acid degradation

Using diamond anodes for electrochemical removal of recalcitrant perfluorooctanoic acid (PFOA) pollutants has become an important strategy in recent research. However, the electrolysis removal efficiency of PFOA is still plagued by low electrochemical active surface area (EASA) and mass transfer limitation of conventional flat-plate diamond anodes. Herein, the periodic porous boron-doped diamond (PP-BDD) anodes were successfully prepared by 3D printing combined with hot-filament chemical vapor deposition (HF-CVD) technologies. The prepared PP-BDD anode achieves a higher PFOA kinetics (kapp = 0.022 min−1, the normalized rate constant is 6.6 m s−1) compared with the conventional 2D-BDD anode (kapp = 0.006 min−1, the normalized rate constant is 1.8 m s−1) at the applied density of 20 mA cm−2. The calculated mass transfer coefficient km of PFOA towards PP-BDD (2.6 × 10−5 m s−1) is about 6.1 times higher than that of 2D-BDD (0.42 × 10−5 m s−1), and the electron paramagnetic resonance (EPR) measurement verifies that PP-BDD produces more •OH and SO4•− radicals during the electrolysis process versus 2D-BDD. The unique periodic pore structure enables PP-BDD higher EASA than 2D-BDD and increases the mass transfer efficiency. Consequently, the number of electrolyte and PFOA molecule accessible diamond anode surface is increased. This work provides valuable guidance for the deterministic design of periodic pore structure-based BDD electrodes for efficient electrochemical oxidation (EO) of refractory pollutants.

Liquid-liquid mass transfer in microfluidic reactors: Assumptions and realities of non-ideal systems

The mass transfer coefficient, kLα, is often used to benchmark the liquid–liquid mass transfer performance in a microfluidic reactors. Cobalt(II) was extracted with an undiluted, highly viscous, ionic liquid from an aqueous phase in a microfluidic reactor (1 mm ID) and kLα values were determined (0.0002–0.033 s−1). It is concluded that the high viscosity of the ionic liquid causes two-phase slip, greatly reducing the efficiency of the microfluidic reactor. Furthermore, deviations (or non-idealities) from the assumptions related to mass transfer calculations (e.g., no reaction effects) can have a drastic impact on the measured kLα values. This work reports deviations between −25 and +40%. In general, it is shown how several non-idealities (i.e., a high continuous phase viscosity, non-linear equilibrium behavior and concentration effects) can affect the calculated mass transfer coefficient.

Mixture of piperazine and potassium carbonate to absorb CO2 in the packed column: Modelling study

A rate-based non-equilibrium model is developed for CO2 absorption with the mixture of piperazine and potassium carbonate solution. The model is based on the mass and heat transfer between the liquid and the gas phases on each packed column segment. The thermodynamic equilibrium assumption (physical equilibrium) is considered only at the gas–liquid interface and chemical equilibrium is assumed in the liquid phase bulk. The calculated mass transfer coefficient from available correlations is corrected by the enhancement factor to account for the chemical reactions in the system. The Extended-UNIQUAC model is used to calculate the non-idealities related to the liquid phase, and the Soave-Redlich-Kwong (SRK) equation of state is used for the gas phase calculations. The thermodynamic analysis is also performed in this study. The enhancement factor is used to represent the effect of chemical reactions of the piperazine promoted potassium carbonate solution, which has not been considered given the rigorous electrolyte thermodynamics in the absorber. The developed model showed good agreement with the experimental data and similar studies in the literature.

Calculation of mass transfer coefficients for corrosion prediction in two-phase gas-liquid pipe flow

Internal corrosion in industrial environments involving gas-liquid flow can be a serious concern. For example, in the oil and gas industry, corrosive water phase is usually transported in pipes along with liquid and/or gas hydrocarbon phases. These gas-liquid flows develop complex flow patterns where the liquid phase can distribute in quite different ways (as stratified layers, intermittent slugs, annular film, etc.) depending on the gas and liquid flow rates and pipe inclination. In these circumstances, the water phase can flow at very high velocities leading to high turbulence and mass transfer rates that can accelerate corrosion of the metallic pipe surface. In general, proper prediction of corrosion rates via mechanistic electrochemical models requires the knowledge of the mass transfer rate of corrosive species in the aqueous phase. There are very few studies in the open literature that show specific experimental data or propose ways to compute mass transfer rates in gas-liquid flow; particularly, for large pipe diameters. The present study introduces a methodology for the estimation of mass transfer rates in gas-liquid flow via the Chilton-Colburn analogy and near-wall eddy diffusivity distribution based on the mechanistic gas-liquid flow modeling. The proposed mechanistic models cover a wide range of fluid's properties and flow rates, different flow patterns and pipe inclinations, and show good agreement with mass transfer experimental data from large-scale gas-liquid flow.

SORPTION OF MANGANESE AS A COMPLEX WITH CARMOISINE ON ANIONITE AV-17-8 IN DYNAMIC MODE

In current paper, the kinetic features of manganese adsorption from dilute aqueous solutions in a dynamic mode were studied. Using dynamic and kinetic curves that take into account the change in the rate coefficient of the sorption process versus its duration, the mechanism of the formation of adsorption layers in the sorption column during the sorption of manganese(II) products which formed after coresponding redox-reaction by surface of the organopolymer anion exchanger AV-17-8 in dynamic mode. Azo dye carmoazine, which is a selective reagent for manganese(VII), was used for its preliminary binding to a strong complex prior to sorption removal. The main process that determines the adsorption interaction in the studied system is the electrostatic attraction of the anionic complex to the positively charged surface of the anionite and the formation of a strong monolayer. The additional fixation of complex is due to the hydrophobic interactions between its molecules and the phenyl radicals of the AV-17-8 matrix. Based on the calculated mass transfer coefficients of the sorption process and the corresponding sorption isotherm, the optimal conditions for the removal of the complex are established, namely: the volumetric rate of transmission of the sorbate through the sorption column is at least - 8 cm3/min; column diameter - 10.0 mm; the minimum weight of the sorbent is 0.5 g; the diameter of the ionite grains is 0.43 ÷ 0.50 mm. Based on the complex of the experimental results obtained and their interpretation, taking into account the known provisions, a mechanism of sorption in the dynamic mode and the formation of adsorption layers in the studied system was proposed. The data obtained can then be used to develop a test system in the form of an indicator tubes and as well as for quantitative sorption-spectroscopic determination of Manganese in various categories of waters via corresponding colorimetric scales.

A novel empirical method for predicting concentration polarization in forward osmosis for single and multicomponent draw solutions

Concentration polarization is one of the inherent problems in forward osmosis membrane process. A quantitative evaluation of concentration polarization is therefore vital to understand its impact on the performance of the forward osmosis. Limited data in the literature exists for the diffusion coefficient of mixed electrolyte or multicomponent solutions, which makes the calculation of mass transfer coefficient and solute resistance to diffusion in forward osmosis complicated. Therefore, an empirical method based on a limited set of well-defined experiments for evaluating and predicting the concentration polarization, water flux, and reverse solute flux is presented for single and mixed, or multi-ions draw solutions. The proposed method does not rely on the hydrodynamic conditions and flow regime in the system and provides an approach to measure and predict concentration polarization, water flux, and reverse salt flux when the diffusion coefficient of a feed solution (FS) or draw solution (DS) is challenging to determine. The developed numerical method is two steps method to measure internal and external concentration polarization using different concentrations of the draw and feed solutions. Experimental work was carried out with a single, and highly soluble sodium chloride (NaCl) DS and a mixture of NaCl and magnesium sulphate (MgSO4) were used as a selected multicomponent DS. The results showed a 95% to 99% agreement with the experimental data.

Mechanism study on flow-boiling heat transfer of R447A/lubricating oil in a smooth horizontal tube

The mechanism explanation for refrigerant and oil mixture heat transfer has puzzled the researchers for many years. Disagreements on the mechanism of heat transfer in the presence of oil persist. Therefore, in this paper, R447A and R447A/ lubricating oil mixtures were studied in a smooth horizontal cooper tube with 10 mm inner diameter (I.D). The evaporation temperatures were set to 10 and 20°C. The mass flux ranged from 100 to 300 kg/m2•s, and the heat flux ranged from 6 to 24 kW/m2. The oil concentrations ranged from 0.95% to 4.95% by mass. The results showed that the oil could enhance the heat transfer of R447A within a certain oil concentration range. In this range, as the oil concentration was increased, the heat-transfer coefficient of the R447A/oil mixture increased. To make a comprehensive understanding of the mechanism, three auxiliary experiments (phase separation, viscosity and flow pattern transition) were made to support the mechanism explanation. The surface wettability, viscosity, surface tension and phase separation caused by the addition of lubricating oil have different effects on the flow boiling at different vapor quality, and the leading factors are also different at different vapor quality.Based on the calculated mass transfer coefficients, a dimensionless thermal resistance 1/Rt was proposed. Most of the prediction results were less than 20% by using 1/Rt. R447A/oil mixture was also predicted using the new model with modified physical parameters, the prediction result was acceptable.

МАТЕМАТИЧЕСКОЕ МОДЕЛИРОВАНИЕ МАССООТДАЧИ ОТ КОЛЕБЛЮЩЕЙСЯ ТВЕРДОЙ ПОВЕРХНОСТИ

Results of modeling of mass transfer from a vibrating cone are given in the paper. Effect of such parameters as frequency, amplitude, height of the cone and diffusion coefficient on mass transfer rate is considered. An equation for calculation of mass transfer coefficient is obtained for similar processes.

The Numerical Estimation of Mass Transfer Coefficient of Oxygen in the Large-Scale Suspension Culture of iPS Cells

In order to practically apply induced pluripotent stem (iPS) cells to regenerative medicine, a large amount of undifferentiated iPS cells should be produced by using an automated/scaled-up suspension culture system. However, in large-scale culture, oxygen supply to iPS cells away from the gas-liquid interface can be insufficient. In this numerical study, the oxygen supply performance is quantitatively evaluated by estimating the volumetric mass transfer coefficient of oxygen in the suspension culture of iPS cells. And, focusing on shaking culture, where shear stress that causes death or differentiation of iPS cells is relatively reduced, we compare two different shaking methods: one direction rotation (ODR) and periodic alternate rotation (PAR). The validity of the volumetric mass transfer coefficient calculation is confirmed by comparison with the experiment. The PAR method is superior to the ODR method in terms of oxygen supply because of higher turbulence intensities, but it is much less energy efficient than the ODR method. In the ODR method, the cell size is thought to be non-uniform since iPS cells are aggregated due to cell sedimentation. On the other hand, in the PAR method, cell sedimentation is suppressed by controlling the Froude number (Fr).

SORPTION OF MERCURY(II) AS A COMPLEX WITH KARMOAZIN ON ANIONITE AV-17-8 IN DYNAMIC MODE

In present paper, the kinetic features of mercury(II) adsorption from dilute aqueous solutions in a dynamic mode was studied. Using dynamic and kinetic curves that take into account the change in the rate coefficient of the sorption process versus its duration, the mechanism of the formation of adsorption layers in the sorption column during the sorption of mercury (II) in the form of its complex with 4-sulfo-2-(4′-sulfonaphthalene-1′ -azo)naphthol-1 (Carmoasine) which formed after coresponding redox-reaction by surface of the organopolymer anion exchanger AV-17-8 in dynamic mode. Azo dye carmoazine, which is a selective reagent for mercury(II), was used for its preliminary binding to a strong complex prior to sorption removal. The main process that determines the adsorption interaction in the studied system is the electrostatic attraction of the anionic complex to the positively charged surface of the anionite and the formation of a strong monolayer. The additional fixation of complex is due to the hydrophobic interactions between its molecules and the phenyl radicals of the AV-17-8 matrix. Based on the calculated mass transfer coefficients of the sorption process and the corresponding sorption isotherm, the optimal conditions for the extraction of the complex are established, namely: the volumetric rate of transmission of the sorbate through the sorption column is at least - 2 cm3/min; column diameter - 10.0 mm; the minimum weight of the sorbent is 0.05 g; the diameter of the ionite grains is 0.43 ÷ 0.50 mm. Based on the complex of the experimental results obtained and their interpretation, taking into account the known provisions, a mechanism of sorption in the dynamic mode and the formation of adsorption layers in the studied system was proposed. The data obtained can then be used to develop a test system in the form of an indicator tubes and as well as for quantitative sorption-spectroscopic determination of mercury(II) in various categories of waters.

High-fidelity profiling and modeling of heterogeneity in wastewater systems using milli-electrode array (MEA): Toward high-efficiency and energy-saving operation

High energy consumption is a critical problem for wastewater treatment systems currently monitored using conventional “single point” probes and operated with manual or automatic open-loop control strategies, exhibiting significant time lag. This challenge is addressed in this study by profiling the variation of three critical water quality parameters (conductivity, temperature and pH) along the depth of a reactor at high spatiotemporal resolution in a real-time mode using flat thin milli-electrode array (MEA) sensors. The profiling accurately captured the heterogeneous status of the reactor under transient shocks (conductivity and pH) and slow lingering shock (temperature), providing an effective dataset to optimize the chemical dosage and energy requirement of wastewater treatment systems. Transient shock models were developed to validate the MEA profiles and calculate mass transfer coefficients. Monte Carlo simulation revealed high-resolution MEA profiling combined with fast closed-loop control strategies can save 59.50% of energy consumption (Temperature and oxygen consumption controls) and 45.29% of chemical dosage, and reach 16.28% performance improvement over the benchmark (defined with ideal conditions), compared with traditional “single-point” sensors that could only monitor the entire system through a single process state. This study demonstrated the capability of MEA sensors to profile reactor heterogeneity, visualize the variation of water quality at high resolution, provide complete datasets for accurate control, and ultimately lead to energy-saving operation with high resilience.