Mass Transfer Loss Research Articles

Fabrication of novel carbon nanofiber membrane microporous layer to improve water management ability of PEMFC

The issue of water flooding in proton exchange membrane fuel cells (PEMFC) under conditions of humidity levels leads to significant mass transfer losses. To address this challenge, a fiber-structured microporous layer (MPL) with high porosity is developed, and investigates the impact of carbon nanotube (CNT) on its heat treatment process. The inclusion of CNT facilitates the cyclization of polyacrylonitrile in the pre-oxidation process. Thereby reduces the fracture of nanofibers, improved the microstructure and the porosity of the membrane during carbonization. The carbon nanofiber membranes containing CNT shows a higher oriented arrangement of carbon grains after graphitization. The high porosity of the fiber membrane MPL confers exceptional mass transfer capabilities. At 100% RH, the MPL sample CFP-2C improves the maximum power density and a maximum current density of PEMFC by 47.5% and 55.3%, respectively, compares to the conventional carbon black particles MPL.

Research on Water Flow Control Strategy for PEM Electrolyzer Considering the Anode Bubble Effect

At higher current densities, the bubble effect in the anode flow field of the PEM electrolyzer (PEM EL) worsens mass transfer losses and energy consumption. This study employs a moderate increase in the water flow rate to remove accumulated bubbles under fluctuating electrical input, thereby improving PEM EL system efficiency. An enhanced PEM EL equivalent circuit model incorporating bubble over-potential based on the oxygen volume fraction is developed. Considering the energy consumption of auxiliary equipment and the reduction in losses from mitigating the bubble effect, a numerical simulation evaluates the impact of flow rate variations on overall electrolysis energy consumption, leading to a comprehensive energy consumption model for the PEM EL system, incorporating electrical, chemical, and thermal energy conversions. The control objective is to maximize system efficiency by optimizing the water flow rate, with a performance-preset-based controller implemented in MATLAB/Simulink. The simulation results show that the controller can accurately track the target flow rate, and the dynamic regulation time improved by 1.5 s compared to the traditional performance constraint function, better matching the rate of change in electrical energy. Under the water flow control mode, hydrogen production increased by 6.6 L within 130 s of the simulation, available energy increased by 8.32 × 106 J, and the efficiency of the PEM EL system improved by 2.79%.

Effect of wide reactant relative humidity on PEMFC electrochemical and thermodynamic performance from both global and local perspectives

For realizing high-power and high-efficiency operation of proton exchange membrane fuel cell (PEMFC), influence mechanism of relative humidity (RH) on the fuel cell performance was explored in this study. Combining experimental and simulation methods, the effect of wide gas humidification on the fuel cell output power and irreversible losses were comprehensively studied. Rising RH negatively influenced PEMFC electrochemical and thermodynamic properties at I=1.6 A/cm2. Humidification of the gas can lead to a maximum increase of 36%, 43% and 14.5% in cell exergy efficiency at I=0.2-0.4 A/cm2, I=0.4-1.2 A/cm2 and I=1.2-1.4 A/cm2, respectively. The effect of RH on the pressure drop at a wide current densities was identified using a two-phase multiplier, and further can be categorized into three zones. Electrochemical impedance spectroscopy (EIS) results showed that mass transfer losses and activation losses are keys to influence the characteristics of the above regions. Cathode catalyst layer (CCL) and proton exchange membrane (PEM) contributed more than 90% to thermal irreversible loss, whose entropy generation rates change is consistent with activation loss. These study results can provide theoretical support for the development of PEMFC with high output power and high exergy efficiency at wide gas humidification conditions.

A Spectroscopic and Interferometric Study of W Serpentis Stars. I. Circumbinary Outflow in the Interacting Binary W Serpentis

W Serpentis is an eclipsing binary system and the prototype of the Serpentid class of variable stars. These are interacting binaries experiencing intense mass transfer and mass loss. However, the identities and properties of both stars in W Ser remain a mystery. Here, we present an observational analysis of high-quality, visible-band spectroscopy made with the Apache Point Observatory 3.5 m telescope and Astrophysical Research Consortium Echelle Spectrograph spectrograph plus the first near-IR, long-baseline interferometric observations obtained with the Center for High Angular Resolution Astronomy Array. We present examples of the appearance and radial velocities of the main spectral components: prominent emission lines, strong shell absorption lines, and weak absorption lines. We show that some of the weak absorption features are associated with the cool mass donor, and we present the first radial velocity curve for the donor star. The donor’s absorption lines are rotationally broadened, and we derive a ratio of donor to gainer mass of 0.36 ± 0.09 based on the assumptions that the donor fills its Roche lobe and that it rotates synchronously with the orbit. We use a fit of the All-Sky Automated Survey light curve to determine the orbital inclination and mass estimates of 2.0M ⊙ and 5.7M ⊙ for the donor and gainer, respectively. The partially resolved interferometric measurements of orbital motion are consistent with our derived orbital properties and the distance from Gaia EDR3. Spectroscopic evidence indicates that the gainer is enshrouded in an opaque disk that channels the mass transfer stream into an outflow through the L3 region and into a circumbinary disk.

Investigation of oxygen transport in porous transport layer with different porosity gradient configurations using phase field method

Minimizing oxygen accumulation in the porous transport layer (PTL) is crucial for reducing mass transfer losses in proton exchange membrane (PEM) electrolyzer. This study develops a two-dimensional transient model of gas-liquid two-phase flow at the anode of PEM electrolyzer using the phase field method. The model investigates the mechanisms of oxygen transport and the interactions among various oxygen paths in PEM electrolyzer. We explore the impact of porosity gradient configurations in the PTL and the presence of a surface microporous layer (MPL) on oxygen transport. The findings indicate that for PTL with an average porosity of 60%, forward gradient configuration—where porosity increases from the catalyst layer (CL) towards the channel (CH)—promotes the merging of bubble sites and path contraction, thereby reducing oxygen saturation. The optimal gradient configuration, with porosities of 50% at the CL and 70% at the CH, achieves a 29.5% reduction in oxygen saturation. Conversely, reverse gradient configuration, with decreasing porosity from CL to CH, results in increased oxygen saturation. The addition of surface MPL further lowers oxygen saturation and shortens oxygen breakthrough time; smaller MPL particle sizes correspond to lower oxygen saturation and shorter breakthrough times. This study provides valuable insights for the optimal design of PTL structures in PEM electrolyzers.

A Current‐Adaptive Evaporator with Optimized Energy Utilization for Self‐Cleaning High‐Salinity Desalination

AbstractSolar steam generation (SSG) shows great potential in brine desalination to address the global water crisis. However, the salt accumulation has become a severe bottleneck that destroys devices and weakens efficiencies. Traditional evaporators are difficult to simultaneously realize clean salt‐rejection and efficient operation during high‐salinity desalination. In this work, a weaved cylinder evaporator with both efficient static and dynamic energy utilization is fabricated for self‐cleaning high‐salinity desalination. The energy utilization performance is optimized through a balanced water supply, omnidirectional solar absorption, infiltration content regulation, and dynamic current adaptation. Hence, an outstanding SSG rate of 1.91 kg·m−2·h−1 is achieved under 1 sun radiation. The dynamic self‐cleaning characteristics ensure competitive and durable high‐salinity desalination (≈11 kg·m−2·day−1) during weekly practical operation without salt deposition. Overall, the design overcomes the trade‐off between desired mass transfer and undesired heat loss.

Hydrogen Limiting Current Test Diagnostic Tool for Analyzing PEMFC Durability in Accelerated Stress Tests

The durability of Polymer Electrolyte Membrane Fuel Cells (PEMFC) is a crucial factor for enhancing their competitiveness in the heavy-duty vehicle sector thus it is essential to assess the impact of the major degradation mechanisms on the performance and lifetime of the technology. To this end, accelerated stress tests have been standardized over the years with the aim of expediting the development of durable materials and being able to evaluate the durability in MEA. In this framework, it is extremely important to be able to separate different sources of voltage loss. Specifically, the degradation of mass transfer loss is extremely important because impacts the maximum power density available, efficiency and thermal management of the stack. Mass transfer loss is correlated at the material level, to the loss in electrocatalyst active surface (ECSA) being a consequence of the limitations in oxygen transport across the ionomer thin film. In this work mass transfer degradation is analyzed by ASTs that accelerate real-world ageing [1]. In this work, in addition to standard diagnostic tools, hydrogen limiting current test are investigated. Previous work reported that using hydrogen as reacting gas for limiting current test can give additional information on the sources of mass transfer loss compared to oxygen, specifically information on the ionomer thin film resistance [2]. In this work, limiting current tests were carried out as diagnostic tools during ASTs for electrocatalyst durability and novel ASTs that better mimick real-world vehicle operation within the IDFAST H2020 project and in the Italian project PERMANENT to investigate the degradation [2]. Correlation between mass transfer resistance in ionomer between oxygen and hydrogen limiting current test is found. Additional effects in the high potential region are observed and attributed to platinum oxide formation by means of a 1D MEA model that is adopted to investigate this effect.[1] Spingler F.B., Phillips A., Schuler T., Tucker M.C., Weber A.Z. (2017) International Journal of Hydrogen Energy, 13960-13969[2] Colombo E., Baricci A., Mora D., Guetaz L., Casalegno A., (2023) Journal of Power Sources, 580 , art. no. 233376

Performance evaluation and field synergy analysis of PEMFC with novel snake coil flow field

In the development process of proton exchange membrane fuel cells (PEMFC), the design of the flow field structure plays an important role in improving its mass transfer and performance. In this survey, a novel serpentine channel flow field (SCFF) construction is initially proposed, a 3D multiphase mathematical model is developed, and the accuracy of the mathematical model is confirmed by means of experimental data. Secondly, based on the fluid simulation software, the performance difference between SCFF with different numbers of turns and conventional flow fields (single serpentine and parallel flow fields) in terms of electrochemical reaction and reactant transportation is comparatively analyzed. Finally, the effect on PEMFC performance of the mass transport capability with the novel flow field is evaluated by the theory of mass-transfer loss rate and field synergy. The studies indicate that as the number of turns grows, the output performance of the proposed flow field progressively enhances. The net power density of the flow channel structure with five turns (SC-5) is increased by 35.3% compared with that of the flow channel structure with two turns (SC-2), and the SC-5 flow field also has higher output performance compared with the two conventional flow fields, with an increase of 7.2% and 27.9% in net power, respectively. Meanwhile, the synergistic efficacy between velocity vector field and concentration field is gradually enhanced with the increase in the number of turns, and the results show that SC-5 has the most optimal mass-transfer capability.

Experimental evaluation of a hydrogel composite desiccant wheel for dehumidification with high water uptake and low regeneration temperature

Rotary dehumidification, a key method for continuous solid adsorption dehumidification, is extensively utilised in various industrial and practical applications. The performance of the adsorbent within the desiccant wheel is a major determinant of its energy efficiency in practical applications. While studies on Metal Organic Frameworks (MOFs) and polymer desiccant wheels exist, the majority of rotary dehumidification systems continue to employ traditional adsorbents like silica gel and zeolite, which are plagued by low dehumidification capacity and high energy consumption issues. Super hygroscopic hydrogel, enhanced with a hygroscopic agent, has gained prominence in air treatment because of its outstanding hygroscopicity and low regeneration temperature. With the goal of integrating advanced materials into practical engineering applications and mitigating the heat and mass transfer loss and adsorption/desorption performance degradation due to volume expansion and viscous agglomeration post-water uptake in large-scale super hygroscopic hydrogel applications, this study successfully developed a hydrogel wheel, measuring 350 mm in diameter and 200 mm in thickness, using a honeycomb-shaped glass fibre paper substrate. Experimental findings demonstrate that the hydrogel desiccant wheel outperforms both the MOF and commercial low-temperature silica gel wheels under all tested environmental conditions. This advantage is particularly noticeable at 15 °C and 30 % Relative Humidity (RH), where the moisture content differential (Δd) in the hydrogel system is 2.96 g/kg, 1.89 times greater than the MOF system’s 1.56 g/kg and 5.19 times higher than the silica gel’s 0.57 g/kg. Furthermore, the controlled variable method was used to assess the impact of each operational parameter on the hydrogel wheel’s performance in both low and high moisture conditions, offering design insights for engineering applications.

Comprehensive Analysis of the Gradient Porous Transport Layer for the Proton-Exchange Membrane Electrolyzer.

A reasonable porous transport layer (PTL) is crucial to decreasing the mass-transfer loss in proton-exchange membrane water electrolyzers (PEMWEs). In this study, it was experimentally demonstrated that the gradient porosity PTL is beneficial in improving the performance of electrolyzers. The research comprehensively investigates the impact of gradient porosity PTL structures on the performance of the PEMWE, considering mass transfer and interfacial contact. It offers insights into the two-phase (oxygen-water) flow transport mechanisms within the PTLs using a 2D numerical model based on the actual PTL geometry. At the microscopic level, it analyzes how the interfacial contact impacts proton and electron transport mechanisms, affecting not only the contact resistance but also the number of effective catalytic sites for the oxygen evolution reaction. Experimental results demonstrate that the cis-gradient porosity PTL leads to a performance enhancement of 9.3% at 2.2 A/cm2. Numerical simulations reveal that the drivers of oxygen transport include the surface tension of the fibers and the pressure drop influenced by the local PTL porosity. Further analysis indicates that the lower oxygen saturation in the bottom region of the PTL with cis-gradient porosity favors a lower oxygen coverage area in the catalyst layers (CL) since the narrower pore space and higher capillary pressure increase the number of water flow paths into the CL. Overall, this study provides valuable insights for designing high-performance PTLs for use in electrolyzers.

20-Fold Increased Limiting Currents in Oxygen Reduction with Cu-tmpa by Replacing Flow-By with Flow-Through Electrodes.

Electrochemical oxygen reduction is a promising and sustainable alternative to the current industrial production method for hydrogen peroxide (H2O2), which is a green oxidant in many (emerging) applications in the chemical industry, water treatment, and fuel cells. Low solubility of O2 in water causes severe mass transfer limitations and loss of H2O2 selectivity at industrially relevant current densities, complicating the development of practical-scale electrochemical H2O2 synthesis systems. We tested a flow-by and flow-through configuration and suspension electrodes in an electrochemical flow cell to investigate the influence of electrode configuration and flow conditions on mass transfer and H2O2 production. We monitored the H2O2 production using Cu-tmpa (tmpa = tris(2-pyridylmethyl)amine) as a homogeneous copper-based catalyst in a pH-neutral phosphate buffer during 1 h of catalysis and estimated the limiting current density from CV scans. We achieve the highest H2O2 production and a 15-20 times higher geometrical limiting current density in the flow-through configuration compared to the flow-by configuration due to the increased surface area and foam structure that improved mass transfer. The activated carbon (AC) material in suspension electrodes, which have an even larger surface area, decomposes all produced H2O2 and proves unsuitable for H2O2 synthesis. Although the mass transfer limitations seem to be alleviated on the microscale in the flow-through system, the high O2 consumption and H2O2 production cause challenges in maintaining the initially reached current density and Faradaic efficiency (FE). The decreasing ratio between the concentrations of the O2 and H2O2 in the bulk electrolyte will likely pose a challenge when proceeding to larger systems with longer electrodes. Tuning the reactor design and operating conditions will be essential in maximizing the FE and current density.

Quantification of Hydrogen and Transition Metals in the Cathode Catalyst Layer of Anion Exchange Membrane Electrolyzer By Ion Beam Techniques

Anion Exchange Membrane Water Electrolyzer (AEMWE) has increased interest in H2 production at low cost and high scalability. The efficiency is strongly dependent on the membrane electrode assembly (MEA) with appropriate ionomer and catalyst layers. Herein, we report AEMWE with MoNi4-MoO2 cathode catalyst layer in ionomer-free Catalyst Coated Substrate (CCS) configuration. The optimized MEA for AEMWE demonstrated the superior performance of 225 mA/cm2 at 2V with more than 48 hours of durability. The X-ray diffraction confirmed the NiMoO4 phase transformation to MoNi4-MoO2 and SEM-EDS was used to study the morphology and elemental composition of the deposited catalyst. X-ray photoelectron Spectroscopy demonstrated the dominant metallic MoO2 formed after H2/Ar annealing. Rutherford Backscattering Spectroscopy (RBS) was also employed to measure the depth composition profile of the catalyst layer exhibiting the reduction of Ni concentration in the bulk after annealing. Further, we introduce hydrogen depth profiling by Nuclear Reaction Analysis (NRA) via the resonant 1H(15N,αγ)12C reaction as a versatile method for the highly depth-resolved visualization of hydrogen(H) in the near-surface region, including transitions of hydrogen between the surface and the bulk, and between shallow interfaces of the nanostructured cathode catalyst layer. The diffusion of the H atoms was observed with a 40% atomic percent of Hydrogen after H2/Ar annealing of the catalyst for 180 minutes (about 3 hours) and decreased to 10% atomic percent of hydrogen after 24 hours of electrolyzer operation. This technique also enabled the measurement of the zero-point vibrational energy of hydrogen atoms absorbed on the surfaces of the catalyst layer. Overall, this work better explains the cathode catalyst degradation effects and hydrogen diffusion in the cathode catalyst layer responsible for voltage and mass transfer losses in AEM electrolyzers.

Comparison of lifetime performance of PEMFC stacks with two cooling strategies under different humidity

While reducing the size and Pt loading can achieve a lower proton exchange membrane fuel cell (PEMFC) stack cost, it is also very important to focus on the performance changes of the PEMFC stack during the long-term operation. A 3D PtCo catalysts long-term performance model is established in this study, and PEMFC stacks with one cooling unit per cell (1-cell stack) and three cells (3-cell stack) are employed as the computational domains, respectively. The effective area of each cell is 50 cm2, and the changes in current density as well as effective catalytic area of PEMFC stacks with two cooling strategies before and after long-term operation under different humidity conditions are investigated at low Pt loadings. The results show that there are large differences in the output voltage and current density distributions between the three cells due to the poor membrane hydration affected by the non-uniform temperature distribution, although the 3-cell stack can significantly reduce the size. Localized catalyst degradation in both 3-cell and 1-cell stacks is closely related to the geometry of the cathodic flow field, and non-uniform catalyst degradation is found to increase the activation and mass transfer losses and change the distribution of current density within the membrane. In addition, the 3-cell stack is found to perform even better in terms of durability, especially under high humidity conditions, which provides a potential solution to improve the durability of PEMFC stacks operating in harsh conditions.

Influence and Improvement of Membrane Electrode Assembly Fabrication Methods for Proton Exchange Membrane Water Electrolysis

The performance of proton exchange membrane water electrolysis (PEMWE) is crucial for its commercialization. The membrane electrode assembly (MEA) preparation process determines the catalyst layer’s (CL) structure, thereby influencing PEMWE performance. Herein, the effects of conventional preparation methods, i.e., direct spray deposition and decal transfer, on the CL were investigated. It was found that the MEA prepared via the decal process exhibits lower activation and Ohmic overpotential. For decal transfer CL, this is due to the improved electrochemically active surface area and proton conduction, derived from the improved catalyst-ionomer agglomerates interconnection and CL-membrane interfacial contact. For direct spray deposition CL, the crack and larger pores in CL facilitate its water-gas transport. On this basis, a hierarchical CL was designed in order to combine the advantages of direct spray deposition and decal transfer. As a result, the hierarchical CL shows better performance than both direct spray deposition and decal transfer CL. The Ohmic and mass transfer losses are reduced by 13% and 15% at 4 A cm−2, respectively. This work provides valuable insights for MEA development, crucial for the large-scale application of PEMWE.

Spectroscopic and photometric investigations of the totally eclipsing contact binary V1320 Cas

We analyzed the light curve of the total eclipse contact binary V1320 Cas, obtained reliable photometric solutions, confirmed it to be a W-type contact binary with a mass ratio of 3.404 and a contact degree of 23.9%, a cool spot is discovered on the less massive component. Orbital period analysis indicates that the period of V1320 Cas is decreasing at a rate of dPdt=1.78×10−7 day yr−1, superimposed with a cyclic modulation with a period of 1.425 yr, long-term period decrease may be caused by the combination of mass transfer and angular momentum loss, and the cyclic modulation may be caused by the third companion. Using the photometric solutions and Gaia distance, we calculated the absolute physical parameters and plotted mass-luminosity and mass–radius diagrams to analyze the evolutionary status of V1320 Cas, the more massive component is a main sequence star, while the less massive component has higher luminosity and radius than those of main sequence stars with the same mass. With the decreasing orbital period, the two components of V1320 Cas will be gradually closer, while the binary may evolve toward deep contact.

Effect of manifold size on PEMFC performance with metal foam flow field

Metal foam flow fields are considered as an alternative to conventional channel/rib flow field in polymer electrolyte membrane fuel cell (PEMFC) because of the advantages of three-dimensional pore structure. In this study, the effect of metal foam flow field with different manifold size on PEMFC performance was investigated, with a 25 cm2 unit cell. Polarization curve and electrochemical impedance spectroscopy results were analyzed to investigate the effects of gas stoichiometry and relative humidity on performance. The mass transfer loss was decreased with reduced manifold size. However, mass transfer loss was increased due to difficulty of water discharge in small manifold case. The metal foam flow field offer advantages in water discharge and mass transfer loss. At 100% relative humidity, performance was improved with increased air stoichiometry for different manifold size. At 25% relative humidity, performance was a little improved with increased air stoichiometry for small manifold case. Regardless of relative humidity, fuel cell performance with metal foam flow field was most improved in case of smallest manifold size based on air stoichiometry due to the high pressure drop.

Modelling and operation characteristics of air-cooled PEMFC with metallic bipolar plate used in unmanned aerial vehicle

The air-cooled proton exchange membrane fuel cell stack composed of the metallic bipolar plate with simple system and lightweight characteristics, is regarded as an ideal power source for unmanned aerial vehicles. A zero-dimensional model is developed to analyze the operation characteristics at heights in the range of 0–3000 m. The temperature should not exceed 60 °C to ensure safe and effective operation. The peak power decreases by 20 % and the stack has good adaptability to altitudes. The performance degradation can be largely attributed to the lower oxygen pressure at high altitudes through normalization analysis. It is more significant at higher current densities owing to increased air starvation. The increase of the air stoichiometry is conducive to heat dissipation and reduces mass transfer loss. The voltage initially increases and then decreases as the air stoichiometry increases, and the optimal air stoichiometry corresponding to the maximum voltage is determined. Appropriately increasing the air stoichiometry can improve the consistency of the temperature and voltage distributions.

Localized oxygen evolution and transport analysis in PEM water electrolysis on local static pressure, temperature and current density

With the escalating severity of the global climate crisis and the strengthening global demand for carbon neutrality, hydrogen produced from renewable energy offers a pathway towards achieving carbon neutrality. To reduce the cost of eco-friendly hydrogen production, we need to increase the current density in proton exchange membrane water electrolysis for green hydrogen production, a promising technology. One problem arising from an increase in current density is that it leads to a significant generation of oxygen, resulting in mass transfer losses. However, there have been few studies on oxygen transport near the anode catalyst layer, with most studies only measuring current density. In this study, local static pressure and temperature were measured in real-time to elucidate the relationship between voltage and current. At 2.1 V (corrected voltage = 2.03 V), the static pressure amplitude is approximately −5 to 5 kPa. At 2.55 V (correction voltage = 2.41 V), it decreased by about 50 % to about −2.5 to 2.5 kPa, and the frequency became faster. With increasing voltage, the decrease in static pressure amplitude and the increase in frequency occur because oxygen rapidly increases in the catalyst layer, resulting in a reduction in residence time. At 1.65 V (corrected voltage = 1.63 V), there is little change in local static pressure, indicating the dominance of the liquid single phase. At 3.6 V (corrected voltage = 3.05 V), there is little change in local static pressure. This is due to the rapid detachment of oxygen bubbles, leading to the dominance of the gas single phase. This elucidates how oxygen bubbles are influenced by fluctuations in local static pressure, leading to the conclusion that efficient design patterns for future anode flow fields can be achieved.

The effect of pretreatments on the drying of persimmon with infrared energy

AbstractThe effects of various pretreatments, including edible coatings, on drying kinetics and some physical quality parameters of persimmon varieties (Fuyu and Rojo Brillante) and differences between varieties were investigated. The experiments were conducted at an infrared radiation intensity of 1210 W m−2 and air velocity (v) of 1.5 m s−1. Drying time differed depending on pretreatments and varieties. Pretreatments generally shortened the Fuyu variety's drying time and increased the Rojo Brillante variety's drying time. Lower specific energy consumption and higher diffusion coefficient values were recorded for the Rojo Brillante variety compared to the Fuyu. In terms of quality parameters, the Fuyu variety generally obtained lower values for shrinkage. Rehydration rate was higher for the Rojo Brillante variety. Total color change was lower in the Rojo Brillante variety. Based on the pretreatments applied, xanthan gum gave better results in terms of operational parameters. In terms of quality parameters, ascorbic acid had better results for rehydration rate and shrinkage. For total color change, better results were obtained in arabic gum pretreatment. As a result, when an evaluation is made regarding variety differences and pretreatments applied, the Rojo Brillante variety can be recommended for drying.Practical applicationsPersimmon is a popular fruit in appearance, flavor, and rich nutritional content. The high moisture and sugar content in the fruit increases spoilage in a short time, making it difficult to consume in all seasons. For this reason, different preservation methods are being investigated to extend the shelf life. Sun drying and other drying methods developed as an alternative to these methods have many disadvantages. Different pretreatments prevent the negativities that occur in other drying methods. Especially, edible coatings can increase product quality by preserving color and appearance as well as controlling mass transfer, flavor, and aroma losses. This study investigated the effects of various pretreatments, including edible coatings, on drying kinetics and some physical quality parameters of persimmon varieties, as well the differences between varieties. Based on variety differences and pretreatments applied, the Rojo Brillante variety can be recommended for drying in terms of both processing and drying characteristics.

Multiphase flow dynamics in metal foam proton exchange membrane fuel cell

Porous metal foam holds substantial promise as a material for bipolar plates in high-performance proton exchange membrane fuel cells (PEMFC) due to its exceptional properties in reactant redistribution. However, the intricate structure of metal foam flow field (MFF) presents challenges for mass transfer and water management. In this study, a three-dimensional two-phase flow model for metal foam is developed to analyze and capture flow patterns. MFFs are reconstructed based on detailed structural analysis and various pore sizes are discussed. Employing the Volume of Fluid (VOF) method, we delve into multiphase flow dynamics, specifically focusing on the removal of liquid droplets within the MFF. It reveals the MFF with moderate pore sizes exhibit a trade-off performance, striking a balance between optimal mass transfer and minimal parasitic loss. The porous structure's pivotal role is highlighted, contributing significantly to both through-plane and in-plane mass transfer and convection. Furthermore, we classify three flow patterns of liquid droplet, with the “split-up” pattern emerging as the most effective for water management and mass transfer. This study illuminates water behavior in porous metal foam bipolar plates, introduces a systematic methodology for assessing mass transfer and water management capabilities in MFFs for PEMFC.