Mass Transfer Coefficient Research Articles

Aroma Compound Release from Starches of Different Origins: A Physicochemical Study

Sensory properties, particularly aroma, play a crucial role in consumers’ acceptance and perceived quality of food. The release and the perception of aroma compounds is affected by their interaction with nonvolatile ingredients of foods, such as proteins, lipids, and polysaccharides. These interactions, whether reversible or irreversible, significantly influence aroma retention and release. Starch, a common food constituent, has been found to interact with aroma compounds, impacting flavor dynamics through processes like complexation and encapsulation. In this study, reversed-flow gas chromatography (RF-GC) is employed for the estimation of the release behavior of polar (diacetyl) and non-polar (dl-limonene) aroma compounds from starches of various origins (corn, wheat, rice, and potato). The results show that aroma compound release is influenced by the matrix composition, environmental conditions, and physicochemical properties of both starch and aroma compounds. The temperature-dependent mass transfer coefficients and activation energies reveal the strong influence of polar and non-polar characteristics on aroma compound behavior. Additionally, significant variations in retention and release are observed based on the starch type and the type of bonds involved in aroma compound interactions, underscoring the critical role of thermodynamic and kinetic parameters in flavor dynamics.

High performance ozone nanobubbles based advanced oxidation processes (AOPs) for degradation of organic pollutants under high pollutant loading.

Advanced Oxidation Processes (AOPs) have proven to be an effective solution for chemical wastewater treatment, particularly for degradation of organic pollutants, especially dyes. Ozonation is recognized as one of the most prevalent AOPs. Nevertheless, some cases show a lowered efficiency of O3 utilization which is attributed to its inadequate distribution in the treated water causing low residence time, low mass transfer coefficient as well as shorter half-life. This study demonstrates the application of ozone nanobubbles to enhance the degradation of organics under high pollution load conditions. We propose an integrated method that utilizes bulk nanobubbles to enhance the reactivity of ozone for the degradation of organics. We examined the degradation of organic pollutants under parameters such as varying pH levels, ozone concentrations and presence of salts and surfactants. The degradation of the organic pollutant by ozone nanobubbles (0.177 L mg-1min-1) demonstrated a threefold increase in reaction rate constants compared to microbubbles (0.025 L mg-1min-1). The plausible reason for these findings is (i) higher mass transfer coefficient (ii) higher ozone solubility (iii) NBs may act as a surface for chemical reaction (iv) NBs may increase the half-life of ozone. The presence of reactive oxygen species was verified using scavenging tests. This part of the studies revealed contribution of reactive oxygen species (ROSs) such as hydroxyl radical (•OH), superoxide radical anion (O2•-) and singlet oxygen (1O2) in the degradation process. The conditions that provide total degradation of 100% in 300s for both organic pollutants (Green rit and methylene blue dye) are: 5 LPM (Litre per minute) ozone flow rate, acidic pH, monovalent salts (NaCl, 2mM) and lower concentration of surfactants (CTAB and SDS, 0.3 CMC). A degradation mechanism has been outlined based on intermediates identified by LC-MS. This work presents a new method that combines AOPs with nanobubbles, which should lead to increased environmental sustainability and efficiency.

The effect of sub-boiling temperatures on mass transfer from former manufactured gas plant residuals.

The dissolution of polycyclic aromatic hydrocarbons (PAHs) from coal tar at former manufactured gas plant (FMGP) sites is a long-term threat to groundwater quality. The dissolution rate is often limited by an increase in the viscosity of the non-aqueous phase liquid (NAPL) as the lower molecular weight compounds are depleted over time, and this slow mass transfer prevents the effective application of remediation technologies that rely on NAPL-to-water mass transfer to remove or degrade mass. Increasing subsurface temperatures has the potential to increase mass transfer at FMGP sites by increasing PAH solubility and reducing NAPL viscosity. This study investigated the mass transfer of PAH compounds from a synthetic NAPL mixture and FMGP residual at 25, 50 and 80°C using well-mixed batch experiments. Effective solubilities increased by up to an order of magnitude and mass transfer rate coefficients increased by up to a factor of 45. Enhancements were greater for higher molecular weight compounds, and for the more complex FMGP NAPL compared to the synthetic mixture due to a more substantial decrease in NAPL viscosity. Simulations using a screening-level model demonstrated the potential for sub-boiling temperature to increase NAPL mass removal at FMGP sites, with increases in concentration up to a factor of seven, and 6 to 87% of mass remaining after heating to 80°C for 120days compared to 25°C.

Strengthening H2 gas-liquid mass transfer using superaerophobic cathodes for enhanced methane production from CO2 in H2-mediated microbial electrosynthesis system.

H2-mediated microbial electrosynthesis (MES) could run under a high current density, but the low solubility of H2 limited its performance. Reducing the H2 bubble size facilitates H2 gas-liquid mass transfer and it has been reported to be realized on superaerophobic electrodes. Therefore, we adopted a CoP nanowire-modified nickel foam (CoP-NiF) as the superaerophobic cathode in a H2-mediated MES reactor to enhance the methane production from CO2. The CoP nanowire modification reduced the average diameter of H2 bubbles from∼300 μm to∼100μm, thereby exhibiting a 129% enhancement of the H2 mass transfer coefficient (KLa=0.32min-1). The maximum CH4 production rate with CoP-NiF cathode exhibited a 27% improvement (2.31 L/L/d) at a high current density of 166.67 A/m2. More importantly, a coulombic efficiency higher than 80% was achieved in the reactor. These results demonstrated that using superaerophobic cathodes is an efficient way to enhance the performance of H2-mediated MES reactors.

Advanced methanotrophic bioreactor design for efficient bioremediation of hydrogen sulfide (H₂S) And Volatile Organic Compounds (Vocs): Integrating genetic engineering and industrial scalability

The convergence of advanced microbial biotechnology and metabolic engineering has facilitated groundbreaking advancements in bioremediation. This study presents the engineered Methylomicrobium buryatense strain 5GB1C-RO1, optimized for the simultaneous removal of hydrogen sulfide (H₂S) and volatile organic compounds (VOCs) within a two-stage methanotrophic bioreactor system. Through precise CRISPR/Cas9-mediated genome editing, critical metabolic pathways for sulfide oxidation (SQR, FCCAB, SOXABXYZ) and VOC degradation (alkB, adhP, todC1C2BA) were integrated, achieving catalytic efficiencies exceeding 3.2 × 10⁷ M⁻¹s⁻¹ and substrate conversion rates above 450 nmol min⁻¹ mg⁻¹ protein. The strain demonstrates exceptional robustness under industrial conditions, maintaining 95% pollutant removal efficiency at H₂S concentrations up to 1000 ppm and VOC concentrations exceeding 500 ppm. The innovative bioreactor system incorporates enhanced gas-liquid mass transfer mechanisms, achieving mass transfer coefficients (kLa) exceeding 300 h⁻¹ and enabling stable operation for over 1000 continuous hours. Experimental results confirm the system's capacity for pollutant mineralization, generating methane-rich biogas (>95% CH₄) and high-protein microbial biomass (>85%), which are valuable for energy and agricultural applications. This integrated bioremediation approach not only reduces reliance on chemical scrubbing and flaring but also supports circular economy principles by transforming waste gases into renewable resources. The technology provides a scalable, sustainable, and cost-effective solution to mitigate industrial emissions while addressing environmental and regulatory challenges. The findings highlight the potential of combining advanced genetic engineering with innovative bioreactor design to redefine industrial pollutant management and resource recovery.

Enhancing Mass Transfer Coefficient Prediction from Field Emission Scanning Electron Microscope Images Through Convolutional Neural Networks and Data Augmentation Techniques

With the growing demand for drug products requiring lyophilization, it is essential to either expand aseptic drying capacity or improve the efficiency of existing capacity through process intensification, ensuring that resources are utilized to their full potential. In this regard, mathematical models are highly recommended to assist professionals in process optimization. To effectively utilise these models, it is also essential to develop robust techniques for determining key parameters, including the product resistance to vapour flow. Traditional experimental methods for evaluating this coefficient are time-intensive and/or require the insertion of probes into the product, which is not feasible at a manufacturing scale. This study addresses these challenges by introducing a novel deep learning framework designed to predict the mass transfer coefficient directly from Field Emission Scanning Electron Microscope images. This approach significantly streamlines the evaluation process, leveraging the high-resolution capabilities of Field Emission Scanning Electron Microscope for detailed analysis. In this work, we focus on advanced Field Emission Scanning Electron Microscope image processing, choice of strategic convolutional neural network configuration, and thorough model performance evaluation to predict the mass transfer coefficient. Given the frequent scarcity of datasets in this field, we have employed data augmentation techniques to enhance the robustness of our model. The results demonstrate good predictive accuracy (error on the interpolation test data lower than 5%), highlighting the potential of this framework to facilitate the assessment of mass transfer coefficients in freeze-dried products.

Heat and Mass Transfer in Shrimp Hot-Air Drying: Experimental Evaluation and Numerical Simulation

Shrimp is one of the most popular and widely consumed seafood products worldwide. It is highly perishable due to its high moisture content. Thus, dehydration is commonly used to extend its shelf life, mostly via air drying, leading to a temperature increase, moisture removal, and matrix shrinkage. In this study, a mathematical model was developed to describe the changes in moisture and temperature distribution in shrimp during hot-air drying. The model considered the heat and mass transfer in an irregular-shaped computational domain and was solved using the finite element method. Convective heat and mass transfer coefficients (57.0–62.9 W/m2∙K and 0.007–0.008 m/s, respectively) and the moisture effective diffusion coefficient (6.5 × 10−10–8.5 × 10−10 m2/s) were determined experimentally and numerically. The shrimp temperature and moisture numerical solution were validated using a cabinet dryer with a forced air circulation at 60 and 70 °C. The model predictions demonstrated close agreement with the experimental data (R2≥ 0.95 for all conditions) and revealed three distinct drying stages: initial warming up, constant drying rate, and falling drying rate at the end. Initially, the shrimp temperature increased from 25 °C to around 46 °C and 53 °C for the process at 60 °C and 70 °C. Thus, it presented a constant drying rate, around 0.04 kg/kg min at 60 °C and 0.05 kg/kg min at 70 °C. During this stage, the process is controlled by the heat transferred from the surroundings. Subsequently, the internal resistance to mass transfer becomes the dominant factor, leading to a decrease in the drying rate and an increase in temperatures. A numerical analysis indicated that considering the irregular shape of the shrimp provides more realistic moisture and temperature profiles compared to the simplified finite cylinder geometry. Furthermore, a sensitivity analysis was performed using the validated model to assess the impact of the mass and heat transfer parameters and relative humidity inside the cavity on the drying process. The proposed model accurately described the drying, allowing the further evaluation of the quality and safety aspects and optimizing the process.

Updated Review on the Available Methods for Measurement and Prediction of the Mass Transfer Coefficients in Bubble Columns

This review summarizes the most important measurement techniques for determination of the volumetric liquid-phase mass transfer coefficient kLa. In addition, the main empirical correlations (with their applicability ranges) for kLa estimation are presented. It is clearly underlined that in tall bubble columns, a system of two differential equations (involving the gas and liquid axial dispersion coefficients) should be solved in order to obtain the accurate kLa value. The semi-empirical correlations for kLa prediction based on the correction of the penetration theory are also summarized. The need for a correction of the penetration theory is explained. The different definitions of the gas–liquid contact time, including the one based on the local isotropic turbulence theory, are presented. Finally, the various chemical methods for the determination of the gas–liquid interfacial area are summarized. Additionally, the main correlation for the prediction of the interfacial area is reported. The effects of pressure, temperature, and viscosity on the interfacial area and kLa are discussed.

Oscillating microbubbly flows generated by a fluidic oscillator: Flow behavior and mass transfer characteristics

AbstractIn this study, a Coanda‐swept fluidic oscillator is used to generate oscillating microbubbly flows. Flow behavior measurements show that the generated microbubbly flows have periodic sweep characteristics. Massive microbubbles are generated by shear‐off‐induced breakup, dynamic erosion breakup, and wall‐fluid‐shear‐induced breakup within the fluidic oscillator. Mass transfer measurements show that the generated microbubbly flows have a higher interfacial area (a) and volumetric liquid‐side mass transfer coefficients (kL) than the other comparison groups. Furthermore, the energy efficiency is assessed in terms of kL per energy consumption (η) and energy consumption per a (ξ). For the fluidic oscillator group, the highest kLa is 0.089 s−1, corresponding to (η = 0.63 m3/(kW·s), ξ = 2.6 J/m2, a = 785 m2/m3). Although it has been reported that higher kLa is typically associated with lower energy efficiency, the results indicate that the fluidic oscillator is a promising microbubble generator.

Liquid–Liquid Flow and Mass Transfer Enhancement in Tube-in-Tube Millireactors with Structured Inserts and Advanced Inlet Designs

Liquid–liquid mass transfer is crucial in chemical processes like extraction and desulfurization. Traditional tube-in-tube millireactors often overlook internal flow dynamics, focusing instead on entry modifications. This study explores mass transfer enhancement through structured inserts (twisted tapes, multi-blades) and inlet designs (multi-hole injectors, T-mixers). Using high-speed imaging and water–succinic acid–butanol experiments, flow patterns and mass transfer rates were analyzed. Results show annular and dispersion flows dominate under tested conditions with structured inserts lowering the threshold for dispersion flow. Multi-hole injectors improved mass transfer by over 40% compared to T-mixers in plain tubes, while C-tape inserts achieved the highest volumetric mass transfer coefficient (2.43 s−1) due to increased interfacial area and droplet breakup from energy dissipation. This approach offers scalable solutions to enhance tube-in-tube millireactor performance for industrial applications.

Industrial scale-up of flue gas bio-mitigation with chemolithotrophs in packed bed reactors: Exploring metabolite synthesis, mass transfer, and techno-economic analysis.

Elevated emissions of flue gases deteriorate the quality of air, impacting both terrestrial and aquatic ecosystems through their contribution to acid rain and eutrophication. This study examines the bio-mitigation process in a packed bed reactor and its capacity to concurrently decrease the environmental consequences of industrial flue gases (CO2, NO, and SO2) and wastewater by employing mixed bacterial consortia. The highest biomass productivity achieved during the growth phase was 0.002gL-1 h-1 in the aqueous medium and 0.006gL-1 h-1 in the PU foam. The highest level of CO2 removal efficiency was 86.60%, while for NO and SO2, it was 77.03% and 82%, respectively. The comprehensive nutrient balance analysis revealed that the flue gas was primarily utilized for biomass assimilation. The FT-IR and GC-MS analysis detected metabolites, including carboxylic acids, esters, and fatty alcohols, that were produced during the process. The NMR study examined alterations in the concentration of metabolites within the cell, indicating metabolic pathways such as the TCA cycle, alanine, pyruvate, butanoate metabolism, and glycolysis. The mass transfer coefficient estimated for the gas-liquid-solid phase was ∼2.0ms-1 for the flue gases. The scale-up of the reactor based on the mass transfer coefficient up to 20,000L gives a net present value of $2,66,116.13 with a benefit-to-cost ratio of 1.47. Therefore, this study suggests that employing bacteria is a viable and energy-efficient approach to mitigate the adverse effects of flue gas on air quality. Additionally, it aids industries in minimizing waste and repurposing it for advantageous purposes, thereby diminishing their environmental footprint.

In silico optimization of a challenging bispecific antibody chromatography step.

Mechanistic modeling of chromatographic steps is an effective tool in biopharma process development that enhances process understanding and accelerates optimization efforts and subsequent risk assessment. A relatively new model for ion exchange chromatography is the colloidal particle adsorption (CPA) formalism, which promises improved separation of material and molecule-specific parameters. This case study demonstrates a straightforward CPA modeling workflow to describe an ion exchange chromatography polishing step of a knobs-into-holes construct bispecific antibody molecule. An adapted Yamamoto method was used to calculate charge and equilibrium parameters at three pH values. The remaining model parameters, binding kinetics, and effective mass transfer coefficients were determined via inverse fitting. The model was created from six experiments in total, tested on model parameter uncertainty, and evaluated on its power to predict changes in the biomolecule's retention behavior when variations in elution salt concentration occur. Finally, a three-step-gradient experiment was optimized, separating the desired bispecific antibody from its low and high molecular weight impurities, achieving a monomer yield of 68% and purity of 96%. Testing the model against a different load composition demonstrated its ability to extrapolate. An in silico one-factor-at-time and two-parameter screening of the optimized method identified the salt concentration to elute weaker binding impurities as a critical process attribute, while deviations in the buffer pH had a minor influence.

Effects of Hypergravity on Phase Evolution, Synthesis, Structures, and Properties of Materials: A Review

In a hypergravity environment, the complex stress conditions and the change in gravity field intensity will significantly affect the interaction force inside solid- and liquid-phase materials. In particular, the driving force for the relative motion of the phase material, the interphase contact interaction, and the stress gradient are enhanced, which creates a nonlinear effect on the movement mode of the phase material, resulting in a change in the material’s behavior. These changes include increased stress and contact interactions; accelerated phase separation; changes in stress distribution; shear force and phase interface renewal; enhanced interphase mass transfer and molecular mixing; and increased volume mass transfer and heat transfer coefficients. These phenomena have significant effects on the synthesis, structural evolution, and properties of materials in different phases. In this paper, the basic concepts of hypergravity and the general rules of the effects of hypergravity on the synthesis, microstructure evolution, and properties of materials are reviewed. Based on the development of hypergravity equipment and characterization methods, this review is expected to broaden the theoretical framework of material synthesis and mechanical property control under hypergravity. It provides theoretical reference for the development of high-performance materials under extreme conditions, as well as new insights and methods for research and application in related fields.

Elucidating molecular characteristics of organic compounds during ozone micro-bubbles treatment based on GC × GC-QTOF-MS and non-targeted analysis.

The ozone micro-bubbles (OCBs) technology is increasingly gaining traction as a promising alternative method for organic compounds removal in wastewater. Nevertheless, there is a scarcity of literature addressing the molecular-level transformation of organic compounds during OCBs treatment. In this work, the secondary effluent from a wastewater treatment plant was treated with ozone milli-bubbles (OLBs) and OCBs, and the fate of organic compounds at the molecular level was investigated using comprehensive two-dimensional gas chromatography quadrupole time-of-flight mass spectrometry (GC×GC-QTOF-MS). The findings revealed that, compared to OLBs, OCBs increased the total mass transfer coefficient by 1.46 times and the half-life of ozone by 4 times. Consequently, OCBs enhanced the removal rates of CODcr, NH4+-N, UV254, and TOC at the 30-min mark by 8.91%, 8.65%, 10.11%, and 2.15%, respectively. In the raw water, 710 organic compounds were detected, decreasing to 668 and 478 after treatment with OLBs and OCBs, respectively. Furthermore, the organic compounds with higher molecular weight and unsaturation degree were more prone to mineralization in the OCBs process. It was also identified that OCBs exhibited nearly 100% removal of amines, unsaturated hydrocarbons, aldehydes, phenols, and aromatic amides. It is noteworthy that, among the 15 identified emerging contaminants (ECs), the removal efficiency of OCBs (53.3%) was higher than that of OLBs (33.3%), with fewer by-products. More deeply, based on 30 common reactions, the primary reactions occurring in OLBs treatment were dealkylations, whereas the abundant hydroxyl radicals in OCBs treatment facilitated the oxidation reaction (+O). This study contributes to the exploration of the potential of OCBs technology in treating secondary effluent, providing invaluable insights for its rational application in practical scenarios.

Numerical solution of a nonlinear model of chromatography considering different isotherms and gradient profiles

In gradient chromatography, the mobile phase composition is progressively altered to regulate the propagation rates of the injected mixture components. Resultantly, improved separation of mixture components can be attained, the recycling time that must pass between two consecutive injections can be reduced, and, hence, the column’s efficiency and selectivity can be enhanced. A coupled modeling framework, integrating a lumped kinetic model and the convection–diffusion equation for solvent volume fraction, is employed to approximate the process. The influence of different isotherm models on the process dynamics is examined through numerical simulations. A semi-discrete second-order finite volume scheme is suggested to approximate the model equations. Impacts of positive and negative gradients, gradient shapes, gradient starting and ending times, axial dispersion, Henry’s constants, nonlinearity coefficients, mass transfer coefficients, and different adsorption isotherms are investigated. The theoretical findings presented in this study may facilitate further advancements in the field of gradient elution chromatography.

CFD simulation of water diffusion in fruit drying: Case of apricot hemispheres

Food drying is a storage process during which the available water is removed. The present analysis conducted for three drying temperatures 45, 55 and 65 °C and the effective water diffusivity was estimated as 1.69×10-10, 2.91×10-10 and 6.67×10-10 m2/s. Comsol Multiphysics 4.3b was used to model the problem and simulate the process. The apricot hemispheres shrinkage was modelled as function of moisture content reduction. The results showed that water diffusivity, the mass transfer coefficient between the fruit surface and drying air and the activation energy of the process increase with drying temperature. The mass transfer coefficient, km, was estimated as 1.0×10-5, 9.98×10-5 and 0.85×10-2 m/s at 45, 55 and 65 °C. The estimated activation energy was 59.6, 59.9 and 60.8 kJ/mol at 45, 55 and 65 °C. The average relative error between experimental and computational moisture content was 0.47, 0.88 and 1.32% at 45, 55 and 65 °C. The Levenberg-Marquardt (L-M) and Sparse Non-Linear Optimizer (SNOPT) optimization algorithms were implemented.

Experimental investigation on mass transfer coefficient in airlift reactor involving Boger fluid

Experimental investigation on mass transfer coefficient in airlift reactor involving Boger fluid

STUDY MASS TRANSFER PROCESS IN CAPTURING OF HYDROGEN FLUORIDE GASES

The article investigates the mass transfer process that occurs as a result of liquid droplets moving in a gas flow. Additionally, the absorption of hydrogen fluoride from dusty gas into soda ash droplets was examined. The study experimentally analyzed the influence of gas velocity and liquid flow on the mass transfer coefficient and the purification efficiency of a rotary-filter gas cleaner, considering different types of filters and liquid injection nozzles. To ensure the process is carried out effectively, optimal values for the variable parameters, specifically liquid flow and gas velocity, were recommended.

Effect of Gas Holdup and Gas Velocity on Volumetric Mass Transfer Coefficient in Bubble Column

Bubble columns are widely used in various industrial processes such as wastewater treatment, fermentation, and gas-liquid reactions due to their simplicity and effectiveness in mass transfer operations. In this study, we investigate the influence of gas holdup and gas velocity on the volumetric mass transfer coefficient in a bubble column reactor. The volumetric mass transfer coefficient is a critical parameter that affects the efficiency of gas-liquid mass transfer processes. Through experimental analysis and computational modeling, we systematically examine the relationship between gas holdup, gas velocity, and the volumetric mass transfer coefficient. In this study, volumetric mass transfer coefficient kL.a was calculated using air in water. The data obtained are in the range of superficial gas velocity (0.03-0.2398) m/s for air water system. The experiments were carried out using 0.1 m column diameter with 2 mm hole diameter and 79 holes gas distributor. From the experimental data it was found that kL.a increased with increasing of gas holdup and increasing of superficial gas velocity.

Removal of copper (II) ions from aqueous solution using acid- and alkali-treated carbonized mangosteen peel as adsorbent

The level of toxic heavy metals from the industrial effluents, seeping into neighbouring waterbodies and agricultural land, must be reduced. Biosorption is a highly effective option. Fruit peels, a typical agricultural waste, have been widely employed as low-cost biosorbents. The purpose of this study is to investigate the removal of copper (Il) ions from aqueous solution using carbonized mangosteen peel. The aim of this research is to prepare the biosorbent, activate it with H2SO4 or KOH, carbonize the pulverized mangosteen peel and to optimize parameters such adsorbent dosage, agitation speed, initial metal-ion concentration, pH and contact time on percentage removal of Cu (II) ions. The adsorption isotherms have been studied using Langmuir and Freundlich isotherms, and the internal mass transfer coefficient has been investigated. Mangosteen peel was soaked in 5 mol% H2SO4 or 5 mol% KOH for one day, dried, and carbonized at 300°C for 30 min. Optimal conditions of 300 rpm agitation, initial metal-ion concentration 150 mg/L, 100 mg adsorbent dosage, pH 2 for H2SO4 treatment, 60 min contact time for maximum copper (II) ion uptake. The Freundlich isotherm model is found to fit the experimental data satisfactorily, with an R2 of 0.8273. The correlation coefficient of 0.9993 for pseudo-second-order model gives the best fit for kinetic data studied with an internal mass transfer coefficient of 0.9976.