Mass Transfer Characteristics Research Articles

Characterization of liquid-liquid two-phase flow patterns and mass transfer coefficients in Human-shaped microchannels

Based on the principle of splitting and recombining, this study designed and fabricated millimeter-scale Human-shaped microchannels. The research focused on investigating the flow patterns and mass transfer characteristics of liquid-liquid two-phase flow within the Human-shaped microchannels. The experiment utilized a water and n-butanol system to investigate the flow behavior of liquid-liquid two-phase in the channel with a flow rate ratio of 1. When the total volumetric flow rate increases from 120 µl/min to 2400 µl/min, the flow pattern experiences slug flow, slug-droplet flow, parallel flow and non-steady flow patterns respectively. The study investigated the impact of factors including total flow rate, feed method, angle, curvature, channel width, phase ration extraction efficiency and mass transfer coefficients. The Human-shaped channel exhibited superior mass transfer performance compared to conventional microchannels due to its advantageous configuration. The higher the included angle is, the stabler the flow pattern within the channel, resulting in a better mass transfer performance. Furthermore, the absence of curvature is more favorable for achieving higher mass transfer efficiency. In the experiments, the overall volume mass transfer coefficient ranged from 0.007 to 0.1742 s−1. This study can provide insights for the development and structural optimization of microchannels based on the split-recombine principle.

A Novel Numerical Model Considering Unsaturated Soil Properties and Computational Study on Heat and Moisture Transfer Characteristics of Helix Ground Heat Exchanger

Abstract A novel three-dimensional numerical simulation model for the helix ground heat exchanger was proposed in this paper, which takes into account unsaturated soil properties. This model is more suitable for real working conditions. To validate its accuracy, a miniature model heat transfer experimental platform was constructed. Additionally, the study conducted simulation research using three types of soil with significantly different thermal and moisture characteristics. Moreover, the comprehensive thermal conductivity and water diffusion coefficient of these three soil types were determined by relevant literature and experimental tests. The aim was to comprehensively explore the impact of different soil types on the heat and mass transfer of the helix ground heat exchanger. The results indicate that the numerical model developed in this paper accurately captures the heat and mass transfer characteristics of the helix ground heat exchanger to a certain extent. Increasing the comprehensive thermal conductivity and water diffusion coefficient of the soil can significantly enhance the heat exchange capacity of the exchanger. For instance, under sandy loam conditions, the heat exchange capacity is approximately 20.73% higher compared to clay loam conditions. The study also identifies two distinct areas around the helix ground heat exchanger: the severe change region and the soft change region. In the severe change region, there is a notable decrease in soil water content near the exchanger, which inevitably weakens the thermal conductivity of the soil. It is advised to minimize this effect through measures like active water spraying.

Study on the impact of methanol steam reforming reactor channel structure on hydrogen production performance

The design and operation of embedded reactors involve chemical reaction efficiency issues, with the main consideration being heat and mass transfer characteristics. The contact area of the porous catalytic coating with methanol is affected by the reactor structure, to improve the hydrogen yield and reveal the mechanism of the channel structure on the hydrogen production performance, the hydrogen production performance of circle-triangle, circle-square, square-circle, square-square, and triangle-circle channels was investigated. The reasons for the differences in methanol conversion, hydrogen, and carbon monoxide selectivity were analyzed from the perspective of heat and mass transfer using a three-rate reaction mechanism. The results showed that the circle-triangle channel performed outstandingly in the hydrogen production from methanol steam reforming with 98.61 % methanol conversion, 88.74 % hydrogen selectivity, and 29.06 % CO selectivity. The shapes and sizes of the different channel structures affect the fluid flow pattern and velocity distribution, which in turn affect the mass transfer efficiency and lead to differences in hydrogen production performance. The circle-triangle channel exhibits superior heat transfer and material transport performance, which can improve the hydrogen production efficiency of methanol steam reforming and help provide an important reference for the embedded reactor design.

Hydrodynamic simulation-informed compartment modelling of an annular centrifugal contactor

Abstract The geometrical and hydraulic parameters have a great impact on the mass transfer characteristics of annular centrifugal contactors. The objective of this study is to evaluate the mass transfer performance of a single annular centrifugal contactor by applying the computational fluid dynamics informed compartment modelling approach. In the study, a steady state compartment model of an annular centrifugal contactor is developed in gProms general purpose process modeller by using the hydrodynamic parameters obtained from computational fluid dynamics simulations performed in OpenFOAM with the GEneralised Multifluid Modelling Approach (GEMMA). The mass transfer rate predicted by the developed compartment model is compared with data obtained from uranium extraction with Tributyl Phosphate experiments performed with a laboratory-scale annular centrifugal contactor. Uranium concentrations in the organic and aqueous outlets and the mass transfer rate evaluated by the developed compartmented contactor model are in good agreement with the experimental data. The results reveal that the use of a hydrodynamic-informed compartment modelling approach raises the possibility of designing full-scale annular centrifugal contactors without the need for detailed computational fluid dynamics simulations and the prediction of mass transfer performance of the whole system from laboratory scale experiments.

Two-dimensional hydrophilic imprinted resin–graphene oxide composite for selective extraction and rapid determination of gibberellin traces in licorice samples

This study presents novel methodologies and materials for selectively and sensitively determining gibberellin traces in licorice to address food safety concerns. A novel hydrophilic imprinted resin–graphene oxide composite (HMIR–GO) was developed with fast mass transfer, high adsorption capacity, and exceptional aqueous recognition performance for gibberellin. Leveraging the advantages of molecular imprinting, hydrophilic resin synthesis, and rapid mass transfer characteristics of GO, HMIR–GO was employed as an adsorbent, showing resistance to matrix interference. Coupled with HPLC, a rapid and selective method for determining gibberellin was established. Under optimal conditions, the method exhibited a wide linear range (0.02–5.00 μg g−1, r = 0.9999), low detection limits (3.3 ng g−1), and satisfactory recoveries (92.0–98.4%), enabling the accurate and rapid detection of gibberellin in licorice. This study introduces a pioneering strategy for the selective extraction and determination of trace gibberellin levels, offering insights for similar applications in functional foods.

Gas–Liquid Microchemical Oxidation for Continuous Synthesis Processes: A Short Review

AbstractGas–liquid oxidation processes, despite their wide application in the chemical industry, still pose considerable safety concerns. Microchemical technology has received high recognition for its intrinsic safety performance and process-intensification capability in hazardous reactions. This Short Review offers a comprehensive summary on how microchemical technology can be employed to achieve gas–liquid oxidation processes for continuous synthesis of chemicals in a safe, efficient, and controlled manner. Herein, we discuss the key aspects of gas–liquid dispersion and hydrodynamics, as well as mass transfer characteristics on microscale, and present representative gas–liquid oxidation cases in microflow reactors. Finally, the current challenges in industrial applications and potential academic research directions are presented.1 Introduction2 Microbubble Generation Technology for Gas–Liquid Oxidation Reactions3 Hydrodynamic and Mass-Transfer Characteristics of Gas–Liquid Oxidation Microreactors4 Gas–Liquid Oxidation Reactions in Microreactors5 Conclusion and Outlook

Investigation of conjugate heat and mass transfer in a sleeve-type hollow fiber membrane for liquid desiccant dehumidification

In adiabatic conditions, the dehumidification capacity of hollow fibre membranes decreases as solution temperature rises. To address this limitation, this study proposed a novel approach based on sleeve-type hollow fibre membranes. The study focused on three distinct fluid streams and the sleeve-type hollow fibre membrane tube. A three-dimensional model of the dehumidifier was created, and the dehumidifier's heat transfer, mass transfer, and fluid flow characteristics were thoroughly analysed and experimentally validated. The results showed that the average values of the Sherwood number and Nusselt number on the air side are significantly influenced by the Reynolds number. On the solution side of the sleeve-type hollow membrane, the average Nusselt number and Sherwood number are approximately 4.0 and 4.6, respectively. According to the research, 76% of the resistance is accounted for by the mass transfer resistance on the membrane side.The study's conclusions provide insightful information for improving the design of sleeve-type hollow fibre membrane dehumidifiers.

Cattano Christov Double Diffusion Model for Third Grade Nanofluid Flow over a Stretching Riga Plate with Entropy Generation Analysis

The current investigation delves into the convective heat and mass transfer characteristics of third-grade radiative nanofluid flow within a porous medium over a Riga plate configuration. The Riga plate structure incorporates magnets and electrodes strategically arranged on a plate surface. To enhance the accuracy of energy and concentration expressions within the third-grade fluid flow, the Cattano Christov Double Diffusion model is employed. Entropy generation analysis is conducted by applying the second law of thermodynamics, and Darcy's model is employed to characterize the behaviour of a porous medium. Appropriate similarity transformations have been used to convert the partial differential equations monitoring the fluid flow model into dimensionless ordinary differential equations. The Galerkin weighted residual method is employed to resolve these equations numerically. The findings contain detailed explanations of how relevant factors affect the temperature field, concentration field, velocity field, entropy generation, and Bejan number, in addition to graphic representations of the results. The findings indicate that the medium's porosity and Brinkman number promote entropy generation. The Bejan number and entropy production is affected by the thermal radiation parameter, which first rises and then declines after a certain distance.

Experimental study on wavy fin desiccant coated heat exchanger for hybrid air conditioning systems

The desiccant-coated heat exchanger (DCHE) is an energy-efficient alternative dehumidification equipment for humidity control in air conditioning. It exhibits a higher dehumidification performance than other solid desiccant systems and can simultaneously handle both latent and sensible loads. Taking the clue of research outcomes from the alternative heat exchangers to enhance the performance, a wavy fin DCHE is designed, fabricated and tested. Objectives of the study are to (i) analyse the dynamic performance of DCHE, (ii) compare the heat and mass transfer characteristics of plain and wavy fin-type DCHEs, and (iii) examine the influence of different operating parameters on the performance. The experimental investigation shows that the dehumidification capacity and thermal coefficient of performance of the proposed wavy fin DCHE are 0.34 g/s and 1.041, respectively, which are 75 % and 60 % higher than the conventional plain fin type. In addition, the developed DCHE has an average cooling capacity of 0.85 kW, which is 42 % higher. Besides, the total quantity of moisture adsorbed also increased by 35 %. Furthermore, the sensitivity analysis of the parametric study identified air velocity, cold water temperature, and inlet humidity ratio as the most influential operating parameters on the performance of wavy fin DCHE.

Physics-based modeling of the effective gas transport properties of single jersey knitted fabrics based on images

In many processes and applications, the performance of textiles relies heavily on fluid transport; for example, the in-plane distribution of water and the through-plane permeation of water vapor and air. Prediction of knitted fabrics’ effective transport characteristics can enhance development workflows and bring them to new applications. Effective transport parameters that are particularly important are the permeability and diffusive mass transfer. Usually, experiments are used to determine these parameters. It is desirable to conduct a thorough investigation into how yarn structure and knitting gauge influence these properties to tailor knitted fabrics for a particular application. Our contribution in this context describes a consistent workflow to forecast the effective mass transfer characteristics of single jersey fabrics. Single jersey fabrics have been chosen for they are the simplest patterning, and are widely used in body-near worn garments. The proposed approach involves visualizing fabric samples with a light microscope, and subsequently determining relevant geometric parameters through automated image processing algorithms. With these parameters in hand, a representative elementary volume of the fabric is constructed. The yarn is modeled as an effective medium to reduce calculation time. The representative elementary volume is then used for numerical predictions of air permeability and the diffusive water vapor transport. The predicted through-plane gas transport properties are compared with experimental data to validate the approach. Six different single jersey polyester fabrics were analyzed, with different yarn structures and machine gauges. The comparison shows a good agreement between simulated and measured transport properties.

Numerical Simulation of Mass Transfer Characteristics of Gas–Liquid Bubble Columns and an Improved Mass Transfer Model

Numerical Simulation of Mass Transfer Characteristics of Gas–Liquid Bubble Columns and an Improved Mass Transfer Model

Liquid – Solid mass transfer characteristics of a heterogeneous reactor made of separated horizontal woven screens impinged by a submerged jet

The mass transfer characteristics of a submerged liquid jet impinging on a stack of separated screens were investigated by the electrochemical limiting current technique. The effects of changing the jet velocity, the nozzle diameter, and the screens’ porosity were studied. The present mass transfer data were found to be much higher than the data obtained by previous studies on jet impinging on flat surfaces. The mass transfer data also revealed that using the impinging jet greatly enhanced the mass transfer at screen surfaces with respect to other conventional forced convection methods used in previous studies. The mass transfer data were correlated by the equation: ShR=0.253Sc0.33ReN0.66ε0.745 for the conditions: Sc=1898, 8071 ≤ ReN≤ 33631, 0.668≤ε≤ 0.809. The importance of the above equation in the scale up and design of electrochemical and catalytic reactors suitable for diffusion-controlled reactions was highlighted. The calculated high energy utilization efficiency (kA/e) of the reactor lends support to its use in practice in preference to reactors made of flat surfaces impinged by a submerged jet. By supporting catalyst on the screens, the reactor also can replace stirred slurry reactors usually used in conducting biochemical and photochemical reactions in order to eliminate the time consuming and the costly step of separating the final product from the catalyst particles.

Study on the heat and mass transfer characteristics of wet air and solution on the surface of corrugated packings at lower ambient pressure

Study on the heat and mass transfer characteristics of wet air and solution on the surface of corrugated packings at lower ambient pressure

Heat and mass transfer characteristics of non-equilibrium flash at start stage

Our experiments showed that a V shape pressure drop appeared at start stage of non-equilibrium flash. V shape pressure drop firstly denoted the generating of superheat degree, which should be the starting force driving the non-equilibrium flash. Then evaporated vapor made up the pressure drop. Finally, a dynamic equilibrium was reached between the flash rate and the outflow rate, and the pressure behaved decreasing gradually. However, few published references focus on this start stage of the non-equilibrium flash. In this paper, experiments of the flash were conducted to investigate the heat and mass characteristics during V shape start stage. Dimensionless flash conversion coefficient (FCC) was proposed to normalize the flash with different initial liquid mass at start stage. The effects of initial temperature and the valve opening degree on the heat and mass characteristics of flash during the V drop start stage were studied. The results showed that the pressure of the working fluid changed dramatically during the V drop start stage. The peak of instant liquid superheat was proportional to the opening degree of the valve, which controlled the outflow rate. The flash rate increased with increasing initial temperature and valve opening degree, which had an approximately linear relationship with the flash time. FCC increased with valve opening degree. It could be deduced that flash intensity or flash rate would be higher for an expander with larger outlet area or higher working temperature.

Gas-liquid flow and mass transfer characteristics in improved heart-shaped structure microreactor

The gas-liquid two-phase flow and mass transfer characteristics in heart-shaped structure microreactor were visually investigated in an Advanced Flow Reactor (AFR). Three various flow patterns were observed in the experiment: Taylor-bubble flow, Taylor-flow, and unstable broken flow. The experiment observed that the bubbles only broke steadily under the action of the first heart-shaped unit obstacle; while in the latter heart-shaped units, the larger bubbles would break resulting in the unstable broken flow. The efficiency of CO2 absorption increases as the gas-liquid two-phase flow rate ratio decreases and the solution concentration rises. The volume mass transfer coefficient increases with the increase of the gas-liquid two-phase flow rate ratio and the solution concentration. The absorption efficiency and mass transfer coefficient in channel 2 with two rows of heart-shaped units is greater than channel 1 with one row of heart-shaped units. Additionally, there exists an optimal performance ratio for reactor under the appropriate gas-liquid flow rate ratio.

FRACTAL FRACTIONAL MODEL OF RADIATIVE HEAT AND MASS TRANSFER CHARACTERISTICS OF TIME DEPENDENT FLOW WITH VARIABLE VISCOSITY, INDUCED MAGNETIC FIELD, DUFOUR AND SORET EFFECTS: AN ENTROPY GENERATION

: In this article, the Caputo Fabrizio fractal fractional order derivatives operator with an exponential kernel was employed to examine the radiative heat and mass transfer characteristics of time dependent flow with variable fluid viscosity, induced magnetic field, Soret and Dufour effects. The local mathematical model for the flow problem is formulated by take into account the impacts of thermal radiation, heat source, and viscous dissipation. The governing equations in-terms of fractal fractional model with an exponential kernel were solved numerically using finite difference method. The influence of flow variables such as induced magnetic field, concentration field, entropy rate, thermal field, and velocity field profiles against the pertinent parameters are discussed through graphs. Increase the values of magnetic Prandtl number results to rises of induced magnetic field. Higher Dufour number significantly grows the thermal field. The fractal fractional parameters enhance the velocity field, thermal field, Bejan number, entropy rate, concentration field and induced magnetic field profiles. The velocity field profiles recede with higher values of fluid variable viscosity parameter whereas the thermal field and induced magnetic field has an opposite effect. Larger Soret number amplifies the concentration field. Increase of Brinkman number, thermal radiation parameter, and magnetic Prandtl number intensifies the entropy generation rate. Increases of Brinkman number, magnetic Prandtl number, Soret number and Dufour number leads to a decrease of Bejan number whereas Bejan number rises with an increase of thermal radiation parameter and heat source

CFD simulation and experimental study of CO2 absorption in a rotating packed bed

The rotating packed bed (RPB), a process intensification equipment, has been widely studied and applied to chemical engineering processes such as gas absorption, nanomaterial preparation, and polymer devolatilization. In this study, we presented a typical RPB model to study the intensification mechanism of high gravity on gas-liquid mass transfer. Based on this, three-dimensional computational fluid dynamics (CFD) simulations and experiments of CO2 physical absorption were conducted to investigate the gas-liquid mass transfer characteristics in the RPB. The predicted and experimental values of CO2 saturation rates of the liquid phase showed good agreement, and the errors were within ± 15 % under various operating conditions. Moreover, detailed flow field and mass transfer information that are difficult to measure experimentally, such as the distribution of CO2 mass fraction in the liquid, liquid holdup, turbulent kinetic energy dissipation rate, and gas-liquid interfacial area, were analyzed by CFD simulation results. These results provide a solid foundation for the further development and application of RPB.

Optimal design and performance analysis of anode flow channels in proton exchange membrane water electrolyzers

In proton exchange membrane water electrolysis, the water/oxygen distribution characteristics in the anode channel significantly affect the electrolyzer performance. In this paper, a three-dimensional two-phase non-isothermal numerical model of the electrolyzer is established, in which the reaction kinetics equation is modified theoretically and is validated experimentally. Two novel anode channel structures (Straight-through turbulent flow channel and Mesh-like structured flow channel) are designed and their multiphysical field distribution characteristics are compared with the traditional straight-through flow channel. Results show that, for Straight-through flow channel structure, the liquid water saturation and temperature gradient between the under-channel and under-rib areas are large, resulting in bubble accumulation under the ribs, deterioration of heat and mass transfer, and harming the electrolyzer reaction rate. The two novel structures both have velocity component perpendicular to the channel flow direction, promoting the expulsion of oxygen accumulated in the anode porous electrode, contributing to more uniform distribution characteristics of gas-liquid two-phase flow and current density. At 2.5 V, the current density of Straight-through flow channel, Straight-through turbulent flow channel, and Mesh-like structured flow channel are 4.12, 4.14, and 4.53 A/cm2, respectively. The excellent heat and mass transfer characteristics enable the Mesh-like structured flow channel to have the best electrochemical performance.

Intensification of atmospheric freeze drying for thin food slices with impinging jet

Atmospheric freeze drying obviates the complexities and costs of maintaining a high vacuum for freeze drying. One of the main drawbacks of atmospheric freeze drying is the low sublimation rate, which is restricted by drying temperatures possible at ambient pressure to prevent food products from softening during dehydration. There is a strong need to intensify the process to reduce the total drying time. This study evaluated the feasibility of using impinging jets to enhance the mass transfer characteristics of the atmospheric freeze drying process. Atmospheric freeze drying experiments on thin lamb slices between −3 to −7 °C showed that the impinging jet configuration has a significant effect in improving the rate of mass transfer flux compared to the conventional cross-flow configuration. This was consistent across different thicknesses of the lamb slices, which would have presented different degrees of internal resistance to mass transfer. Given the amount of non-frozen water in the lamb slices at the drying temperature range evaluated, a scheduled switch from cold air atmospheric freeze drying to a mild hot air drying condition was explored. This strategy enhanced the removal of the remaining water content in the lamb slices, mainly the non-frozen water.

Numerical Study on Heat Transfer and Release Characteristics of Key Components in Electrically Heated Tobacco Products

Electrically heated tobacco products (EHTPs) could release effective aerosol components from tobacco materials at relatively low temperatures without a burning phenomenon. It is essential to grasp the temperature distribution and release mechanism of key components in heated tobacco materials. The existing experimental studies have provided initial insights into the thermodynamic behavior of tobacco materials under various conditions. However, current numerical models are still in their early stages of development, with the majority failing to correlate heat transfer with component release. Based on this, a coupled numerical model of gas flow, heat transfer, and the release of key components in the electrically heated tobacco product is established in this study, which exhibits improvements in revealing the internal heat and mass transfer characteristics in the porous media of tobacco and is capable of evaluating the influence of component contents and product design parameters. The release rates of water, glycerol, and nicotine components are quantitatively described by the first-order Arrhenius formula, and the transport of heat and gas flow is simulated using the Navier-Stokes equation. The accuracy of the model is validated through experiments, including temperature monitoring at multiple measurement points and determination of residual contents in the tobacco substrate after each puff. The simulation results suggest that an appropriate component ratio and tobacco filler mass can enhance both the release amount and release efficiency of key components, and reducing either the diameter or length of the tobacco section can help to improve the heat transfer performance. A slower heating rate matched with longer preheating times enables the complementary release of water and glycerol components, which helps to regulate the uniformity of component content in the aerosol to some extent. This study helps to provide suggestions for the design and optimization of electrically heated tobacco products.