Water Mass Transfer Research Articles

Study on the Mass transfer and hygroscopic behavior of glucose / ammonium sulfate aerosol droplets

Organic aerosols can form semisolid state, glassy state and high viscous state in the atmosphere, which makes aerosols show nonequilibrium kinetic characteristics following the loss of water due to the extended timescales for diffusive mixing. In this study, aerosol optical tweezers (AOTs) and confocal Raman spectroscopy are utilized to investigate the mass transfer of water and the hygroscopicity of internally mixed glucose/ammonium sulfate aerosol droplets with different organic/inorganic molar ratios (OIRs). The characteristic time ratio between the droplet radius and the RH is calculated to describe the mass transfer of water in the droplets. The results shown that the characteristic time ratio of the mixed glucose/ammonium sulfate aerosol droplets is apparently lower than that of pure glucose droplets. And the characteristic time ratio of the mixed droplets decreases with the increase of ammonium sulfate. The hygroscopicity of mixed glucose/ammonium sulfate aerosol droplets is greatly affected by high viscosity organic matter, and the glassy state of glucose suppresses the crystallization of ammonium sulfate in the system. Compared with the pure ammonium sulfate droplets, the efflorescence relative humidity (ERH) of the mixed glucose/ammonium sulfate droplets is delayed and the deliquescence relative humidity (DRH) is advanced. The ERH of the mixed aerosol droplets with molar ratios of 1:4, 1:3 and 1:2 is 35 ± 2%, 32 ± 2.5% and 30 ± 1.5% RH, respectively. And the DRH of the mixed aerosol droplets is 78 ± 1.5%, 76 ± 2% and 74 ± 2.5% RH, respectively. These results improve the understanding of the physical and chemical properties of super viscous organic/inorganic mixed aerosols, and might have important implications for atmospheric chemistry.

Mathematical model of the evaporative condenser for on-site condition simulation

Evaporative condensers (ECs) have been widely adopted in the fields of refrigeration, petrochemicals, etc. owing to the advantages of low water and energy consumption. However, due to the lack of a reliable mathematical model, the energy-saving potential of ECs remains unexplored. To realize thermodynamic performance predictions under on-site conditions, a generic model with 4 characteristic parameters, that could be identified specifically for different ECs, is innovatively proposed in this paper. Taking the refrigeration system of a food factory as a case study, a well-organized data processing method including filtering, screening, and supplementation is established. The processed real-operating data is used for characteristic parameters identification and model validation. Simulations indicate satisfactory transferability and a good agreement between the test and simulated results, with average relative errors of 2.10 % and 2.87 % for the training and test sets, respectively. Based on the proposed model, the overall performance and the working fluids’ thermodynamic state of the EC during operation are investigated carefully. It could be concluded that the air–water mass transfer is the dominating factor in enhancing EC's thermodynamic performance, and air flow shows greater significance than water in improving heat exchange capacity. The heat exchange intensity of the superheating and two-phase zones is similar, while that of the subcooling zone is the lowest, averaging only 37.9 %.

Internal solitary waves observation and feature extraction based on wavelet transform by Sentinel-1A in Lombok Strait, Indonesia

Lombok Strait is an essential pathway in trans-oceanic water mass transport. Due to this water mass transport flowing over Indonesian waters, the current is known as Indonesian Throughflow (ITF), which plays a role in the transfer of warm water masses from the Pacific to the Indian Ocean annually. Lombok Strait has intensive characteristics of the internal waves (IWs) generation because of the strong current that passes through the complex bathymetry along the strait area. IWs with large amplitude and nonlinear properties are known as Internal Solitary Waves (ISW) that can be detected by Synthetic Aperture Radar (SAR) images. A Wavelet Transform method for ISW feature extraction was applied to SAR images by Sentinel-1A (C-band). ISW packet characteristics can be distinguished from other phenomena based on their geometrical structure and shape. ISW packet pattern consists of light and dark lines which decrease intensity from front to rear. SAR observation detected 5 parameters (phase speed, soliton numbers, wavelength, first crest length, and propagation direction). The arc-like ISW in the Lombok Strait propagated to the North of the sill with average phase speeds of about 2.13 m/s and was frequently detected during the northwest monsoon (NWM). The detected soliton number is less than 6 solitons per packet with a wavelength of about 1 – 4 km, and the first crest length varies from about 12.16 km to more than 100 km. ISW detected in Sentinel-1A images were located at the bathymetry about 800 meters around the Lombok Strait area.

Approximate Analytical Solution of the Influences of Magnetic Field and Chemical Reaction on Unsteady Convective Heat and Mass Transfer of Air, Water, and Electrolyte Fluids Subject to Newtonian Heating in a Porous Medium

This paper addresses the unsteady hydrodynamic convective heat and mass transfer of three fluids namely air, water, and electrolyte solution past an impulsively started vertical surface with Newtonian heating in a porous medium under the influences of magnetic field and chemical reaction. Suitable dimensionless parameters are used to transform the flow equations and the approximate analytic method employed to solve the flow problem. The results are illustrated graphically for the velocity, temperature, and concentration profiles. Though, low Prandtl numbers produce high-thermal boundary layer thickness, however, as a novelty, the presence of the magnetic field delayed the convection motion hence, the thermal boundary layer thickness is greater for water with high Pr = 7.0 as compared to air with low Pr = 0.71 and electrolyte solution with low Pr = 1.0. Practically, water with a high-Prandtl number can effectively absorb and release heat. This makes water useful in applications such as geothermal heat pumps and solar thermal collectors, industrial processes such as chemical reactions, distillation, and drying, and in oceanography in predicting the movement and behavior of ocean currents, which in turn can impact weather patterns and climate. Another major observation from the study is that the rate of cooling associated with air, water, or electrolyte impacts differently on the product being cooled.

Modelling in the frame of hydro-mechanical infiltration column experi-ment to study the behaviour of binary mixtures of bentonite MX80

Binary mixtures of high-density MX80 bentonite pellets (80% mass ratio at a dry density of 2.0 Mg/m3) and powder (dry density of 1.1 Mg/m3) at hygroscopic water contents are studied by the French Institute of Radiation Protection and Nuclear Safety (IRSN) as an alternative in engineered barrier systems for the long-term disposal of radioactive wastes. The MX80 bentonite was studied by many authors [1–4] with this aim. These mixtures show a dry density around 1.49 Mg/m3 on pouring into infiltration column experiment tests.
 An infiltration column cell (100 mm in diameter and 350 mm high) has been developed at a reduced scale of 1/100 of the VSS (i.e., at 1/10 of the in situ VSEAL test) to reproduce asymmetric hydration using independent top (fast injection) and radial (slow injection) water pressure systems, which will undergo fast hydration from the calcareous Oxfordian formation at the top and a slower one by water reaching radially through the Callovo-Oxfordian formation. It also allows performing gas injections at different locations of the core of the bentonite mixture (top and bottom boundaries) and under various hydraulic states. The infiltration column is composed of four transparent cylinders, made of Perspex to visualise processes occurring at the interface during the hydration and gas injection phases (Figure 1a). This cell has been assembled with three stainless-steel injection rings that ensure slow radial water injection through three independent automatic pressure/volume controllers. These stainless-steel injection rings also hold the different lateral transducers (six total stress cells and three water pressure transducers embedded in the soil and three relative humidity probes installed in small dismountable chambers) (Figure 1a). The assembled cell is inserted into a rigid frame composed of two stainless steel disks on the two sides of the cylinder connected by four metallic rods.
 A numerical model has been developed to better understand the coupled hydro-mechanical response of this multi-porosity mixture and particularly of its constitiuents upon hydration.The characterisation of pellet and powder components have been focused on their water retention properties, water permeability, compressibility on loading and on suction changes, as well as on their swelling pressure response and the progressive changes of their pore size distribution on wetting. This information at component scale has allowed the upscaling into a 2D plane-strain numerical model based on the discretisation of pellets and inter-pellet powder using Code_Bright FEM [5]. This plane-strain model captures the pellet shape effect without changing the geometry of the pellets.The geometry used in the simulations corresponds to an infiltration column at constant volume mimicking the actual asymmetric hydraulic conditions of the VSS. Figure 2b presents the geometry of the model used at constant volume based on the discretisation of pellets and powder (252 pellets of 8 mm diameter and surrounded by powder filling the entire inter-pellet volume).The generated numerical mixture has a mass-basis proportion of 77.6% pellets and 22.5% powder, which is close to the mixture proportion. Figure 1b shows the three lateral slow-rate hydration boundaries, as well as the fast-rate hydration boundary at the top. The modelling has focused on analysing the global and particularly the local responses: water mass transfer between powder and pellets, evolution of local degrees of saturation and porosities (inside pellets and powder), and mean stress evolution in the pellet and powder domains. Water retention and permeability properties of the components are dependent on porosity and the degree of saturation.
 A non-linear elastic model has been considered for the components, in which volumetric deformations are induced by net mean stress and suction changes. Therefore, the pellets and powder have different hydraulic and mechanical properties as a consequence of the different initial properties, but they share the same constitutive relationship of a single structured material. Figure 1c presents the time evolution of porosities (inside the pellets and powder), showing that the mixture tends towards a more homogeneous distribution of porosity as the pellets expand and compress the highly deformable clay powder. During the transient hydration stage, the expansion of pellets at the top of the column evolves faster due to the proximity of the hydration front. Figure 1d shows the water retention curves of the pellets and powder at the initial state and after hydration as predicted by the model, compared to experimental data [6,7]. The predicted water retention curves of the pellets and powder adequately follow the trend of the data reported by [7] and also seem to reproduce the mixture model data suggesting a homogenisation of the retention properties of the material after hydration.

Estimation of effective water vapour diffusion and mass transfer during quinoa (Chenopodium quinoa Willd.) drying

This study shows the modeling of the convective drying operation of quinoa (Chenopodium quinoa Willd. var. Hualhuas) grains implemented in the General Algebraic Modeling System (GAMS) software. The proposed model was based on Fick’s second law. The drying experiences were carried out using a pilot-scale oven. The drying air conditions were: 40, 60, and 80°C and 0.2 and 0.7 m s-1. The mathematical modeling was employed to describe the behavior of the drying operation according to variations of the average moisture over time. The effective diffusivity of moisture and mass transfer were studied for the different operating conditions. The model was validated by experimental data. It was possible to model the quinoa grains drying process, obtaining a high precision between the experimental and estimated values. Quinoa drying curves can be represented properly by the studied model. In the operating ranges tested, the effective diffusivity values of moisture were between 2.52 10-10 and 1 10-9 m2 s-1 and the mass transfer values were between 7.20 and 11.47 cm s-1. The effective diffusivity (Deff) showed significant differences (P<0.05) with the speed of the drying air, while the mass transfer coefficient (k) was significantly affected (P<0.05) by the temperature of the drying air.

Standardizing practices and flux predictions in membrane science via simplified equations and membrane characterization

The development of membranes and membrane-based separation processes should be accompanied by a standardization of the protocols applied for membrane characterization and for data analysis. Here, streamlined equations for the estimation of the water flux and of the observed salt permeability coefficient in pressure-driven processes deploying dense membranes are presented. Also, a protocol for the experimental characterization of the transport properties of dense membranes is presented and the results are validated against the proposed equations. The proposed water flux equation is algebraic, whereas the ordinary equation needs to be solved iteratively. Moreover, in contrast to the traditional expression for the solute transport coefficient, which requires estimation of the concentration polarization, the respective equation proposed in this study only requires bulk parameters. Dimensionless variables for water flux, driving pressure, and mass transfer are introduced, and a filtration efficiency is defined, a useful parameter in terms of process design.

The dynamics of biophysical characteristics of the northern Black Sea pelagic ecosystem in the first decades of the XXI century

Wind speed, sea surface temperature chlorophyll-a concentration (satellite data such MODIS-Aqua/Terra), bioluminescence intensity and zooplankton biomass (data from the research vessel), the value of fish traded, the indices of lower-than-normal atmospheric pressure and water mass transfer (model calculations) are the factors used to estimate a modern state of the pelagic ecosystem and its functional characteristics. It has been shown that, in the last two decades (2000-2020), after natural cataclysms associated with eutrophication and trophic stress of invasive plankton species in the 1990s, the ecosystem of the open areas in the northern portion of the Black sea has reached a state of relative stability in its structure and functioning. This state is characterized by the absence of changes in the interannual variability of the factors particular for it. Concepts are discussed which concern regional differences in physical factors and biological interactions over many years.

Influence mechanism of thermally enhanced phase change on heat transfer and soil vapour extraction

Thermal enhanced soil vapour extraction (T-SVE) is a remedial technique involving gas, aqueous, solid and nonaqueous phases along with mass and heat transfer. Interphase mass transfer of contaminants and water evaporation/condensation will cause the redistribution of phase saturation, eventually affecting the performance of T-SVE. In this study, a multiphase, multicompositional and nonisothermal model was developed to simulate the T-SVE treatment of contaminated soil. The model was calibrated using published data from the SVE laboratory and T-SVE field experiments. The temporal and spatial distributions of the contaminant concentrations in the four different phases, the mass transfer rates and the temperatures are presented to reveal the coupling interactions that occur between multiple fields during T-SVE. A series of parametric studies were carried out to investigate the effect of water evaporation and adsorbed/dissolved contaminants on the T-SVE performance. It was found that endothermic evaporation, exothermic condensation and the interaction between different removal paths of a contaminant played critical roles in the thermal enhancement of SVE. Ignoring them can result in significant differences in the removal efficiency values.

Rotating Packed Bed Reactor Integrated with Plasma: Mass Transfer Intensification and Wastewater Treatment

When oxygen plasma contacts with liquid, abundant reactive species are generated to degrade the contaminant. Ozone is the main reactive species in the gas phase, but only part of it is utilized during wastewater treatment owing to its low solubility. In this work, a novel rotating packed bed reactor integrated with plasma (plasma-RPB) was developed to fully utilize ozone and enhance wastewater treatment. The ozone–water mass transfer efficiency of the plasma-RPB with different liquid distributor structures was evaluated. Subsequently, a dimensionless correlation for predicting the volumetric mass transfer coefficient of the plasma-RPB with the rotating cylinder was established, and the deviation between the predicted and experimental values was within ±6%. Employing the plasma-RPB, sulfamethoxazole and TOC removal efficiency reached up to 87.6 and 82.7% within 5 min, respectively, exhibiting prominent degradation performance compared with other advanced oxidation processes. This work provides an effective route for wastewater treatment.

Modeling and Optimal Design of a Desalination System Integrated Between a Glass-Covered Solar Collection Water Chamber and a Heat Dissipating Chimney

Abstract Solar thermal energy is trapped in a glass-covered water chamber/basin to provide the heat for evaporation of brackish water in a novel desalination system. To harvest clean water, a chimney is integrated with the water basin, which draws air into the chamber to be humidified by the vapor and then being ventilated via buoyance force. Uniquely, thermal conductive metal sheet is recommended to make the chimney, which allows the vapor in the humid air condenses easily when flowing up. The condensate at the inner wall of the chimney flows down to be collected as clean water. Mathematical modeling and numerical computation have been carried out to delineate the coupling of the buoyance-force-driven flow with the heat and mass transfer of air and water in the solar collection chamber and the condensation of vapor in the heat-dissipating chimney. The objective of the simulation and optimization of the system is to find the best match of the dimensions of the water chamber with a chimney to maximize the production of clean water and energy efficiency. The model has been used to simulation several cases (of water from 40 °C to 50 °C) with available experimental data from the authors’ previous work, and the agreement was satisfactory. The optimization studies found that there is a maximum air flowrate corresponding to a critical chimney height due to the requirement that the chimney is designated to dissipate heat as much as possible to condense water vapor. With the chimney height greater than the critical height, the airflow rate will have a slight decrease. Nevertheless, higher than a critical height is still needed for a chimney to condense more moisture. Optimized chamber diameters at different chimney heights are provided for reference of optimal system designs.

Stokes flow solutions in infinite and semi‐infinite porous channels

AbstractWe derive a class of exact solutions for Stokes flow in infinite and semi‐infinite channel geometries with permeable walls. These simple, explicit, series expressions for both pressure and Stokes flow are valid for all permeability values. At the channel walls, we impose a no‐slip condition for the tangential fluid velocity and a condition based on Darcy's law for the normal fluid velocity. Fluid flow across the channel boundaries is driven by the pressure drop between the channel interior and exterior; we assume the exterior pressure to be constant. We show how the ground state is an exact solution in the infinite channel case. For the semi‐infinite channel domain, the ground‐state solutions approximate well the full exact solution in the bulk and we derive a method to improve their accuracy at the transverse wall. This study is motivated by the need to quantitatively understand the detailed fluid dynamics applicable in a variety of engineering applications including membrane‐based water purification, heat and mass transfer, and fuel cells.

RESEARCH OF THE TECHNOLOGICAL MODE OF THE PROCESS OF PORIZATION OF LIQUID GLASS COMPOSITE MATERIALS FOR THERMAL INSULATION IN THE CONDITIONS OF UHF RADIATION

The paper presents the results of research into the technological regime of the process of liquid-glass composition porization under the action of microwave radiation to achieve effective removal of all types of water and obtain heat-insulating materials with high operational properties. It was established that with a radiation power of 500 W in a vacuum environment without rotation of the sample, despite the achieved high temperature value of 110-115 oC, intense swelling was not observed. The decrease in the mass of the sample is due to the mechanism of water removal using a vacuum, which is reduced to a higher mass transfer rate without a vaporization stage. In a vacuum environment, with sample rotation, intense swelling and the formation of a large number of “craters” on the surface of the sample and large through pores in the macrostructure are observed. At atmospheric pressure, there is a sharp drop in temperature at the beginning of the process, which indicates insufficient power of microwave radiation to intensify the swelling process due to significant condensation of moisture on the surface of the sample. With a higher radiation power of 650 W in a vacuum environment, a sharp rise in temperature occurs at the beginning of the process to 90-95 oC, which is due to the beginning of intensive vaporization of free and constitutional water and the creation of a pressure gradient in the sample and its gradual decrease to 55-60 oC, which leads before drying the material. That is, it is impractical to obtain these materials in a vacuum environment, since there are competing processes of water mass transfer and its evaporation. The most optimal conditions for obtaining composite TIMs are the output power of the installation of 650 W and atmospheric pressure. At the very first minute of the process, the temperature rises sharply to 85-90 0C, which slowly increases to 115-120 0C and does not change further. This period is characterized by the most intensive swelling process. The process itself was characterized by ease of adjustment, and the obtained sample has an attractive appearance and a low average density.

Drying of peaches by a combination of convective and microwave methods

AbstractThe aim of this work is to study a method to extend the storage life of peaches reducing energy and time consumption and ensuring food quality. The conventional method of hot air dying presents many drawbacks, whereas the microwave drying usually leads to overheating and textural damage. Thus, in this work, a combination of convective and microwave methods, more specifically a two‐stage drying process with an initial convective air drying followed by a microwave drying (microwave finishing), was studied for the drying of peaches. Peaches dried at 70°C for various times, 200, 278, 355, 433, and 510 min, were then dried in a microwave oven at powers of 300, 500, and 800 W. Drying rates were examined, whereas dry peaches were characterized for their color, antioxidant capacity, shrinkage, and rehydration ability under optimized conditions for the situations with and without pretreatment with ascorbic acid. Mass transfer of water was described by nine empirical models and by the diffusional approach. The shrinkage of peach tissue during microwave finishing was evaluated and diffusion coefficients were assessed with shrinkage considered. The microwave finishing reduced the drying time by 89 ± 40%, while a smaller shrinkage was observed, with better rehydration characteristics.Practical applicationsPeaches are important commodities in terms of global agricultural production. As peach is a perishable product with a short shelf‐life, the food industry has been forced to find methods, such as drying, that extend its storage life by months. The conventional method of hot air dying presents many disadvantages. Last decades, microwave drying proposed an alternative way to improve the quality of dehydrated products. However, microwave is rarely used alone as a drying method and is usually combined with other drying techniques. The main goal of this work is to study an innovative method to extend the storage life of peaches reducing energy and time consumption and ensuring food quality.

Experimental study and modeling of water transport through short-side-chain perfluorosulfonic acid membranes

Perfluorosulfonic acid polymer membranes are state-of-the-art electrolytes in PEMFCs and PEMWEs, and their degradation represents still one of the limiting factor to increase lifetime of electrochemical devices. Due to significant role of water in stressing degradation mechanisms, this work, through an experimental and theoretical analysis, deepens comprehension of materials and constructive properties of short-side-chain (SSC) membranes on dynamic water transport. A systematic analysis is carried out by analysing samples with different membrane thickness and EW, coupled with different gas diffusion layers. A model was adopted to analyse both steady-state and transient water transport tests, evaluating individual contributions to the total water mass transfer. Particular attention was given to swelling/shrinking mechanism, highlighting its strong impact on water sorption and membrane hydration. Membrane diffusion and interfacial mass transfer were independently investigated, identifying their interconnections with material-bulk and superficial properties. Results highlight that membrane with low EW (790 g mol−1), coupled with hydrophilic gas diffusion layers that oppose negligible interfacial resistances to water transport, allows to reduce total resistance by approximately 39% compared to reference configuration (980 g mol−1, hydrophobic).

The impact of the temperature and humidity state of the road on heat and mass transfer in winter

Sharp diurnal temperature fluctuations in Astana, Kazakhstan, in winter, as well as freezing up to 2 or more meters leading to the destruction of the roadway, especially during the spring thaw, prompted a detailed study of the state of roads. In this work, the temperature and humidity of the highway structure layers were monitored in winter, and the mass transfer of water in the gaseous state due to the negative pressure of cryosuction in the frozen layers was also considered. It was determined that mass transfer of water in the form of steam 1.44 10⁻⁴ g/h per 1 dm3 of soil at temperature fluctuations of -5-8 °C. The rate of vapor passage towards the freezing front in the soil was 0.467 m/h. The freezing of the ground base continued for 132 days in the winter period of 2021-2022 in Astana with the formation of 456.72 g of ice due to the migration of water in a gaseous state in every 1 m3 of soil, which increases the humidity by 40 % or more and significantly reduces the bearing road capacity during the spring thaw. As a solution to the problem of water migration in the form of steam, it is proposed to introduce an additional layer of vapour barrier over the soil base at a depth of -60 cm.

Research on Performance Optimization of Gravity Heat Pipe for Mine Return Air

The mine return air flow has the characteristics of basically constant temperature and humidity all year round and is a high-quality waste heat resource. Its direct discharge not only wastes energy but also causes environment pollution. It has important economic value and application prospect to solve the problem of shaft antifreeze using new technology to recover the waste heat of mine return air. Gravity heat pipe is widely used in the heat recovery of mine return air. Its heat transfer process is a complex process with multiple parameters. The current research focuses on the influence of a single factor on heat transfer, which has many limitations. To analyze the effects of different parameters on the heat recovery effect of gravity heat pipe in mine return air and to optimize heat pipe heat exchanger parameters in the heat exchange system, mathematical models of gas–water countercurrent heat and mass transfer, entransy dissipation and exergy efficiency were established in this paper, based on the entransy dissipation theory. Under the condition of the given initial parameters, the effects of different parameters on the dimensionless factor, β, of heat transfer, total heat transfer, and entransy dissipation thermal resistance were analyzed. The experimental and calculation results show the entransy dissipation theory can be used to evaluate the heat transfer performance of the gravity heat pipe. When the entransy dissipation thermal resistance was minimum, the heat transfer performance was optimal. During the heat transfer process between the mine return air and the gravity heat pipe with high humidity under a given working condition, increasing the Reynolds number was beneficial to increase the heat transfer dimensionless factor, β.

“MoFe cofactor” inspired iron mesh-based MIL-88A(Fe/Mo) for bionic photocatalytic nitrogen fixation

Biomimetic photocatalytic nitrogen fixation is considered as a potential alternative to the Haber-Bosch method, which is an ideal pathway for nitrogen reduction. The development of efficient bionanocatalysts is a serious challenge in the current field of biomimetic nitrogen fixation. Here, we introduced a second metal in the MIL-88A/Fe mesh by metal doping to build a Mo-doped MIL-88A(Fe/Mo)/Fe mesh biomimetic system. The catalyst is a rod-like structure synthesized in situ by hydrothermal method using iron mesh as the substrate, and its rough surface is favorable for the adsorption of N2. The introduction of Mo provides a two-electron transfer pathway for the reaction, and the formation of the "MoFe cofactor" effectively promotes charge separation and inhibits the photoelectron-hole complexation. In addition, we kept the catalyst above the liquid surface and provided the proton source through water vapor, which solved the problem of the low solubility of N2 in water and poor mass transfer efficiency. The results show that the biomimetic photocatalyst has good photoresponsiveness in the whole visible region, and the synergistic effect between the two metals makes the MIL-88A (Fe/Mo0.017)/Fe mesh exhibit better photocatalytic performance, and its nitrogen fixation efficiency reaches about 9.6 times that of the original MIL-88A/Fe mesh. This study provides a new idea for the design of photocatalytic ammonia biomimetic photocatalysts.

The role of coupled water and solute diffusion and product shrinkage during osmotic dehydration

Osmotic dehydration (OD) is a coupled mass transfer operation where foods are partially dewatered while simultaneously impregnated with solute from the solution. Nonetheless, water loss ( W L ) and solute gain ( S G ) are treated as independent processes for modeling purposes and the effect of their coupling on the estimation of water/solute diffusivities ( D w , D s ) and equilibrium dehydration/impregnation levels ( W L e , S G e ) has not been elucidated yet. The objective of this study was to develop a new model considering the coupled mass transport of water and solute occurring during OD of foods and to evaluate the contribution of this coupling on the estimation of D w , D s , W L e , and S G e in comparison with the rigid/shrinking solid assumption. Experimental W L , S G , and volume kinetics were obtained during OD of papaya cubes in sucrose solutions (50°Bx; 45, 55 and 65 °C) and further analyzed with the proposed model solved under different assumptions: coupled and partially coupled mass transfer equations (MTEs) in a shrinking solid and uncoupled MTEs in a rigid solid (no shrinkage) with uncorrected and corrected lengths for diffusion. Properties D w , D s , W L e , and S G e with coupled MTEs and shrinkage were estimated in the ranges of (2.52–5.48) × 10 −10 m 2 /s, (3.91–5.43) × 10 −10 m 2 /s, 0.47–0.53 g/g and 0.18–0.30 g/g, respectively, with partially coupled and uncoupled MTEs leading to a significant overestimation of diffusivities under the tested experimental conditions (up to 281% for water and 75% for solute), even when shrinkage was considered in the 3D model solution. Current findings demonstrate that, like shrinkage, coupling of W L and S G is of upmost importance for a reliable estimation of mass transfer properties during OD. • A mass transfer model is proposed to analyze the OD of shrinking foods. • Mass transfer of water and solute are fully coupled by a density-related term. • OD experiments with papaya cubes were conducted to validate the model. • The effect of different modeling assumptions on mass transfer properties is analyzed. • Non-fully coupled models overestimate diffusivities even considering food shrinkage.

Aeration performances and air—Water mass transfer on steep stepped weirs with horizontal and inclined steps

Aeration performances and air—Water mass transfer on steep stepped weirs with horizontal and inclined steps