Variations In Water Content Research Articles

Design and Development of Vapor Lock Detection to Prevent Brake System Failure

Traffic accidents in Indonesia often occur due to failure on the braking system. The results of the KNKT investigation show that there are three phenomena that most often cause brake system failure, namely brake fading, a decrease in the volume of compressed air and vapor lock. The aim of this research is to conduct experimental studies and develop designs for vapor lock detection devices to prevent failure in the braking system. Experimental studies on vapor lock characteristics were carried out through observations and measurements of boiling points and bubbles (the beginning of vapor lock) in the brake fluid heating process with various variations in water content. Experiments on vapor lock characteristics show that increasing the percentage of water content in the brake fluid has an effect on reducing the boiling point of the brake fluid and an empirical equation is produced to predict the boiling point of the brake fluid based on the percentage of water content in it. Apart from that, we have successfully developed a design for a vapor lock detection device to prevent failure in the braking system which is equipped with a water cooler brake system to prevent the temperature from reaching the boiling point of the brake fluid.

Water content and ground temperature variations in the active layer of a rock glacier in the Central Andes of San Juan, Argentina

Water content and ground temperature variations in the active layer of a rock glacier in the Central Andes of San Juan, Argentina

Soil methane emissions from plain poplar (Populus spp.) plantations with contrasting soil textures

The forest soil methane (CH4) flux exhibits high spatiotemporal variability. Understanding these variations and their driving factors is crucial for accurately assessing the forest CH4 budget. In this study, we monitored the diurnal and seasonal variations in soil CH4 fluxes in two poplar (Populus spp.) plantations (Sihong and Dongtai) with different soil textures using the static chamber-based method. The results showed that the annual average soil CH4 flux in the Sihong and Dongtai poplar plantations was 4.27 ± 1.37 kg CH4-C ha–1 yr–1 and 1.92 ± 1.07 kg CH4-C ha–1 yr–1, respectively. Both plantations exhibited net CH4 emissions during the growing season, with only weak CH4 absorption (–0.01 to –0.007 mg m–2 h–1) during the non-growing season. Notably, there was a significant difference in soil CH4 flux between the clay loam of the Sihong poplar plantation and the sandy loam of the Dongtai poplar plantation. From August to December 2019 and from July to August and November 2020, the soil CH4 flux in the Sihong poplar plantation was significantly higher than in the Dongtai poplar plantation. Moreover, the soil CH4 flux significantly increased with rising soil temperature and soil water content. Diurnally, the soil CH4 flux followed a unimodal variation pattern at different growing stages of poplars, with peaks occurring at noon and in the afternoon. However, the soil CH4 flux did not exhibit a consistent seasonal pattern across different years, likely due to substantial variations in precipitation and soil water content. Overall, our study emphasizes the need for a comprehensive understanding of the spatiotemporal variations in forest soil CH4 flux with different soil textures. This understanding is vital for developing reasonable forest management strategies and reducing uncertainties in the global CH4 budget.

Prędkość ultradźwiękowa analizy wpływu zawartości wody na kredę fosfatyczną

Water content may have a crucial effect on the petrophysical and mechanical properties of high porosity rocks such as chalk. Consequently, the water fluctuations may significantly influence the behaviour of engineering structures that are constructed in chalks. It is the aim of this study to illustrate how the elastic and strength properties of chalk can evolve considering water content variation using P-wave velocity and analytical analyses. To study the influence of water on the ultrasonic compressional wave velocity (VP), measurements of travel time of three samples subjected to different water content were performed. The Uniaxial Compressive Strength (UCS) in dry and saturated chalk specimens was also estimated. To clarify the possible influence of lithology on the physicomechanical properties of rocks, three samples of phosphatic chalk were studied in thin sections. Automated mineral analysis and textural imaging of the samples were performed using an FEI QEMSCAN®. The analyses of the Ultrasonic tests reveal that changes in the water content are associated with variations in the P-wave velocity. Based on P-wave velocity changes as a function of water content, analytical models have been used to predict the elastic and strength properties. The data indicate that the presence of water significantly reduced the elastic and strength parameters of the chalk, a result that is in agreement with the UCS laboratory tests. The derived equations can be used for predicting the elastic and strength properties of high-porous chalk from the P-wave velocity as a function of water content. This approach may avoid the necessity for time-consuming laboratory testing.

Investigation on piezoresistivity of self-sensing cementitious composites containing nano carbon fillers under water content variations

Self-sensing cementitious composites containing nano carbon fillers have extensive application prospects in structural health monitoring (SHM) due to their excellent intrinsic piezoresistivity, good mechanical performances, high compatibility and durability. However, the piezoresistivity is prone to be affected by environmental factors, such as water content. Therefore, it is urgent to study the influence of water content on piezoresistivity to avoid unwanted effect. In the present study, piezoresistivity of self-sensing cementitious composites containing nano carbon fillers under cyclic compression with different water contents is investigated. Moreover, mechanisms are also explored comprehensively. The results indicate that the sensitivity, repeatability and stability of the piezoresistivity deteriorate with decreasing of water content. The maximum FCR and stress/strain sensitivity are decreased from 14.3 % to 4.5 % and 0.72 %·MPa−1/124–0.23 %·MPa−1/39, respectively, when water content decreases from 3.53 % to nearly 0 %. Variation of electrical conductivity pathways and networks caused by enclosed water film on surface of electrical conductive fillers take responsible for the changeable of piezoresistivity with different water content. The outcomes offered validity of self-sensing cementitious composites implementation in SHM withstand variation of water content.

Transient analytical solution for coupled water–gas transport in unsaturated soil cover of landfill

A new analytical solution for coupled water–gas transport in unsaturated landfill cover system is proposed, which can consider transient diffusive-advective transport of gas under transient water transport condition. The proposed analytical solution is first verified against the laboratory measurements and numerical simulations. Using the proposed solution, parametric studies are conducted on the coupled transient behaviors of water–gas transport. The results show that ignoring the coupling effect can lead to significant error in gas transport results under various conditions, e.g., the surface gas emission flux is underestimated by about 28.3%∼79.8% due to ignoring the spatial and temporal variations of water content induced by transient water transport. The influencing parameters (i.e., initial saturation degree, rainfall patterns, and evaporation rate) all have significant impact on the coupled water–gas transport behaviors. The magnitude of the error induced by ignoring the coupling effect increases with increasing initial saturation degree and increasing evaporation rate (e.g., for initial saturation degree increasing from 0.35 to 0.95, the accumulated percolation at cover bottom increases by 10.9 times and the gas emission flux at cover surface decreases by 64.7%). The results highlight that it’s imperative to consider the effect of transient water transport when one needs more accurate assessment of gas transport results in the cover. This analytical solution can also be utilized to aid landfill cover design and to verify other numerical models.

Single-step extraction/pre-formulation process for B-phycoerythrin using glycerol-based eutectic solvents: A step toward more sustainable production of phycobiliproteins

B-Phycoerythrin (B-PE) is a protein pigment of significant interest to the food and cosmetic industries. B-PE is obtained from algal or microalgal biomass, such as Porphyridium cruentum, after complex pre-treatment, extraction, and pre-formulation schemes. This work investigated the use of a single step process for the extraction and pre-formulation of B-PE from P. cruentum without complex biomass pretreatment. Five hydrophilic NaDES based on glycerol with varying water contents (20–40%) were implemented by ultrasound-assisted extraction using a one-step extraction procedure. The yields obtained were satisfaying, ranging from 5 to 15 mg of B-PE per gram of dry matter. Additionally, a purity index suitable for use in cosmetics and food products was achieved, with an average of >1.5. Furthermore, the extracts obtained in a eutectic medium demonstrated enhanced stability for B-PE, with an average loss of 10% after accelerated aging, allowing storage at room temperature without loss of quality. In particular, NaDES based on glycerol and glucose and/or betaine appeared to be the most effective in preserving the integrity and antioxidant activity of B-PE, with a range of 15–30% quenched DPPH. The ComplexGAPI tool demonstrated that our single-step NaDES process is more environmentally friendly than conventional extraction processes, thanks to lower energy consumption, reduced unitary operations, and less waste production. These results provide a solid foundation for sustainable management of the valorization of P-BE for cosmetic or food industries.

Enhanced photocatalytic aerobic oxidative desulfurization of diesel over FeMo6Ox nanoclusters decorated on CuS nanosheets

Photocatalytic aerobic oxidative desulfurization (PAODS) presents a promising and carbon-neutral avenue for desulfurizing petroleum products. However, existing photocatalysts encounter limitations in activating oxygen and show sluggish kinetics in sulfide-to-sulfone conversion, hampering widespread implementation. Herein, we present a FeMo6Ox nanocluster-modified CuS photocatalyst for PAODS reaction using air as an oxygen source. Through experimental characterization and density functional theory (DFT) calculations, we elucidate that the incorporation of FeMo6Ox nanoclusters can modulate the CuS electron density, which results in the generation of electron trap states and facilitates the separation of electron-hole pairs. We show that the variation of water content in air alters the generation efficiency of different reactive oxygen species (ROS), highlighting the potential to optimize moisture levels for achieving the highest catalytic efficiency. The optimized catalytic system exhibits a record specific activity of 10.42 mmol g−1 h−1, and more importantly, achieves deep desulfurization of authentic diesel, showcasing its appealing application prospects.

On the Variability in the Temporal Stability Pattern of Soil Moisture Under Mediterranean Conditions

In recent decades, there has been increasing interest in studying the variability in soil water properties and, specifically, the spatiotemporal variability in the soil water content. This is motivated by the notable theoretical and applied research interests in soil moisture dynamics and their implications for many natural processes. This study aimed to study whether there are variations in the spatial pattern of the temporal stability of soil moisture over time and to analyze the possible influences of certain hydroclimatic (soil water content, precipitation, and evapotranspiration) and soil factors (texture, bulk density, and organic matter content) on these variations. This study was conducted within the Soil Moisture Measurement Stations Network of the University of Salamanca (REMEDHUS, Spain) under Mediterranean conditions, with daily surface moisture data (0–5 cm depth) obtained from 20 stations for the 2006-2023 period. The results showed differences between the average pattern obtained with the 18-year data series and that obtained with the data series for each year. In more than half of the years studied, the representative station differed from that derived from the average pattern. The mean annual precipitation and summer precipitation characteristics seem to be the main factors influencing the variability in the spatial pattern of the temporal stability of soil moisture.

Synthesis and Characterization of Low Molecular Weight Irradiated Chitosan in Various Water Levels and Gamma-Ray Doses

Chitosan is a biopolymer derived from marine animal shell waste that exhibits numerous pharmacological activities. However, its high molecular weight limits the application in various fields due to its low solubility. Therefore, this study aims to synthesize low molecular weight chitosan using varying water content and doses of gamma irradiation. To initiate chitosan degradation, H2O (5 and 10 mL) was added, followed by gamma ray irradiation at doses of 5 and 10 kGy. The Molecular Weight (MW) of degraded chitosan was determined using Gel Permeation Chromatography (GPC), while Fourier Transform Infrared Spectroscopy (FTIR) was used to characterize the functional groups and degree of deacetylation of chitosan. The study found that the molecular weight of irradiated chitosan decreased as the irradiation dose and H2O addition increased. The addition of 10 mL of water and gamma irradiation at a dose of 10 kGy has been found to reduce the molecular weight of chitosan to 118 kDa, with a high deacetylation degree of 86.78%. The FTIR analysis showed no significant changes in the functional groups, indicating that gamma irradiation did not affect the structure of chitosan.

Effect of air exposure time on erodibility of intertidal mud flats

This study investigates the influence of air exposure time on the erodibility of intertidal mud flats, emphasizing the role of evaporation in altering sediment strength and cohesion. Through a comprehensive approach combining laboratory experiments, fieldwork, and numerical modelling, it explores the dynamic interactions between sediment properties and environmental conditions. The research reveals that drying significantly reduces sediment erodibility, with pronounced effects observed during the initial hours of air exposure. Laboratory tests demonstrate a direct correlation between drying time and increased yield stress for both artificial and field-derived mud samples. Field observations further support these results, showing spatial and temporal variations in water content and shear strength across various locations on a tidal flat. The study emphasizes the critical impact of mud content on water retention and the subsequent effect on sediment stability. The incorporation of drying time into erosion formulations within a numerical model highlights the importance of considering evaporation processes in predicting the morphological evolution of tidal flats. This research contributes to a better understanding of sediment transport dynamics in intertidal zones, offering insights into the mechanisms driving the growth and stability of mud flats. It underscores the necessity of integrating evaporation effects into cohesive sediment transport models to enhance the accuracy of predictions concerning the erosion and accretion of intertidal environments.

Surface conductivity of clays

SUMMARY Clay minerals are extensively used in a wide range of applications. In particular, clay-bearing formations are considered as suitable radioactive waste repository. Electrical resistivity tomography is an appropriate tool to monitor the properties of clay-bearing locations. However, an inherent drawback of a conventional resistivity survey is its ambiguity in distinguishing between the effects of groundwater salinity, clay content and porosity. A discrimination can be achieved on the basis of the induced polarization method that provides a complex conductivity. The main purpose of this study is the investigation of the complex conductivity of clay samples with a special focus on the contribution of surface conductivity produced by an excess of ions in the electrical double-layer coating the solid particles. Six clay mixtures were selected that include an almost pure kaolinite sample, a sample consisting of a mixture of kaolinite, illite and smectite, a crushed saponite breccia, a Ca-bentonite sample and two illite clay samples. Besides the enriched kaolinite, the other samples are natural geomaterials that contain more than 40 weight per cent clay minerals. The mineralogical compositions of the samples were determined by quantitative X-ray diffraction analysis. The clay powder was mixed with a varying volume of sodium chloride solution to get plastic state clay samples with varying water content. The samples were investigated by the spectral induced polarization method in a frequency range between 1 mHz and 1 kHz. The resulting complex conductivity spectra indicate a decrease of the real part of the electrical conductivity with rising water content for the illite, bentonite and saponite breccia samples. The overall conductivity of these clay samples is dominated by their surface conductivity. In contrast, the electrical conductivity of kaolinite and kaolinite–illite mixture does not show any significant changes with the water content. For all samples, the imaginary part of electrical conductivity increases at low water content. The real part of the surface conductivity indicates a linear dependence on the volumetric clay content. The slope of this linear relationship can be used to distinguish the types of clay. The ratio between imaginary conductivity and surface conductivity, which decreases with increasing clay content, proves to be a suitable parameter that characterizes the connectivity of clay aggregates in the sample. The surface conductivity of the pure kaolinite sample has been determined in an additional multisalinity experiment. The resulting surface conductivity is in good agreement with the experiment of varying water content. The multisalinity experiment has shown that the resulting petrophysical parameters depend on the procedure of sample packing, which may lead to anisotropy. The effect of anisotropy is attributed to the alignment of the plate-like kaolinite particles in the course of the packing and consolidation procedure.

Analysis of Thermal Characteristics of Potato and Hop Pollen for Their Cryopreservation and Cross-Breeding.

This study investigated the thermal properties of potato and hop pollen for cryopreservation and subsequent cross-breeding. Phase transitions and frozen water content in selected pollen samples were measured using a differential scanning calorimeter (DSC). Unlike hop pollen, potato pollen showed high variability in thermal properties and water content. Three specific types of pollen samples based on their thermal characteristics and water content were distinguished by DSC in potato: (1) 'glassy', with a water content lower than 0.21 g water per g dry matter; (2) 'transient', with a water content between 0.27 and 0.34 g of water per g of dry matter; (3) 'frozen', with a water content higher than 0.34 g of water per g of dry matter. Only the 'glassy' pollen samples with a low water content showed suitable properties for its long-term storage using cryopreservation in potato and hops. Cryopreservation of pollen did not significantly reduce its viability, and cryopreserved pollen was successfully used to produce both potato and hop hybrids. The results indicate that cryopreservation is a feasible technique for the preservation and utilization of pollen of these crops in the breeding process.

Thermal behavior (in cooling) of soil mass with varying fine and water contents: Experimental and numerical investigation

This paper presents a preliminary study on the thermal behavior and response of soil samples with varying water content to assess their significance in addressing the nighttime urban heat island (UHI) effect. For this reason, the experimental program and the analysis focus on the cooling phase of the heated soil samples. To ensure a representative analysis of field conditions, the soil samples were prepared in the laboratory with varying coarse-grained (sand) and fine-grained (kaolin) soil particles. The thermal properties of the soil samples, including thermal conductivity and transmissivity, decrease with increasing fine content and particle packing. In contrast, the thermal conductivity and transmissivity values increase with water content. The thermal diffusivity followed a similar behavior but was relatively less prominent. On the other hand, the specific heat capacity is higher in samples with higher moisture and clay contents but lower with dry unit weight. However, having a higher specific heat capacity also resulted in samples retaining the heat relatively longer and releasing it slowly, which could contribute to delayed nighttime UHI. The numerical models considering natural convective conditions and their analysis further confirm that the water content of the soil samples has a relatively more prominent effect on the soil’s specific heat capacity than the increasing clay contents. To this end, it is noted that the measurement, analysis, and estimation of heat transfer and cooling mechanisms in the soil requires careful consideration of the soil type, water content, and the surrounding environmental conditions.

Satellite-Based Estimation of the Role of Cloud-Radiative Interaction in Accelerating Tropical Cyclone Development

Abstract Recent modeling studies have suggested a potentially important role of cloud-radiative interactions in accelerating tropical cyclone (TC) development, but there has been only limited investigation of this in observations. Here, we investigate this by performing radiative transfer calculations based on cloud property retrievals from the CloudSat Tropical Cyclone (CSTC) dataset. We examine the radius–height structure of radiative heating anomalies, compute the resulting radiatively driven circulations, and use the moist static energy variance budget to compute radiative feedbacks. We find that inner-core midlevel ice water content and anomalous specific humidity increase with TC intensification rate, resulting in enhanced inner-core deep-layer longwave warming anomalies and shortwave cooling anomalies in rapidly intensifying TCs. This leads to a stronger radiatively driven deep in-up-and-out overturning circulation and inner-core radiative feedback in rapidly intensifying TCs. The longwave-driven circulation provides radially inward momentum fluxes and upward moisture fluxes, which benefit TC development, while the shortwave-driven circulation suppresses TC development. The longwave anomalies, which dominate the inner-core positive radiative feedback, are mainly generated from cloud-radiative interactions, with ice particles dominating the deep-layer circulation and liquid droplets and water vapor contributing to the shallow circulation. Moreover, the variability in ice water content, as opposed to the variability in liquid water content and the effective radii of ice particles and liquid droplets, dominates the uncertainty in TC-radiative interaction. These results provide observational evidence for the importance of cloud-radiative interactions in TC development and suggest that the amount and spatial structure of ice water content are critical for determining the strength of this interaction. Significance Statement The limited investigation of tropical cyclone (TC)-radiative interaction in observations impedes our understanding of TC development. This study aims to quantitatively show the spatial variation in radiation in TCs and their effect on TC development by using a set of satellite-based observations. We relate TC-radiative interaction to TC intensification and emphasize the inner-core features. Moreover, we quantitatively demonstrate the relative contribution from clouds, liquid droplets, ice particles, and water vapor to TC-radiative interaction as well as the source of the variation in radiative properties. These results provide an additional observational foundation for the importance of cloud-radiative interactions in TC development and support a quantitative validation for numerical modeling.

Use of Biopolymers as Soil Stabilizers: A Review

Abstract: Soil enhancement methods offer engineers solutions for addressing stability issues encountered during project execution. Rather than employing traditional soil treatment techniques, soil stabilization focuses on enhancing the inherent characteristics of the soil. Currently, polysaccharide biopolymers like xanthan gum, guar gum, welan gum, beta glucan, and chitosan are utilized in soil behavior enhancement to mitigate environmental concerns. Biopolymers show promise in improving soil shear strength and reducing subsidence potential at varying water contents. The effectiveness of treatment relies on factors such as soil composition and the specific biopolymer used.

Influence of cement and water content on the multifaceted capabilities of a self-sensing cement-based geocomposite: a comprehensive analysis

This study investigates the synergistic effects of cement, water, and hybrid carbon nanotubes/graphene nanoplatelets (CNT/GNP) concentrations on the mechanical, microstructural, durability, and piezoresistive properties of self-sensing cementitious geocomposites. Varied concentrations of cement (8% to 18%), water (8% to 16%), and CNT/GNP (0.1% to 0.34%, 1:1) were incorporated into cementitious stabilized sand (CSS). Mechanical characterization involved compression and flexural tests, while microstructural analysis utilized dry density, apparent porosity, water absorption, and non-destructive ultrasonic testing, alongside TGA, SEM, EDS, and x-ray diffraction analyses. The durability of the composite was also assessed against 180 Freeze-thaw cycles. Moreover, the piezoresistive behavior of the nano-reinforced CSS was analyzed during cyclic flexural and compressive loading using the four-probe method. The optimal carbon nanomaterials (CNM) content was found to depend on the water and cement ratios. Generally, elevating the water content led to a rise in the CNM optimal concentration, primarily attributed to improved dispersion and adequate water for the cement hydration process. The maximum increments in flexural and compressive strengths, compared to plain CSS, were significant, reaching up to approximately 30% for flexural strength and 41% for compressive strength, for the specimen containing 18% cement, 12% water, and 0.17% CNM. This improvement was attributed to the nanoparticles’ pore-filling function, acceleration of hydration, regulation of free water, and facilitation of crack-bridging mechanisms in the geocomposite. Further decreases in cement and water content adversely impacted the piezoresistive performance of the composite. Notably, specimens containing 8% cement (across all water content variations) and 10% cement (with 8% and 12% water content) showed a lack of piezoresistive responses. In contrast, specimens containing 14% and 18% cement displayed substantial sensitivity, evidenced by elevated gauge factors, under loading conditions.

Temporal variability in water content, temperature, and electrical conductivity of sandy soil: Responses to soil-improving cropping systems (SICS)

There is little information on the effect of soil-improving cropping systems (SICS) on the temporal variability of soil volumetric water content (WC), temperature (T), soil temperature amplitude (A_T), and electrical conductivity (EC) in low-quality sandy soils although they are increasingly being used in agriculture. The objective of this study was to determine the effects of the following SICS: liming (L), leguminous catch crops for green manure (LU), farmyard manure (M), and liming + leguminous catch crops for green manure + farmyard manure together (LLUM), and the control (C) on temporal changes in the three properties simultaneously in a field experiment on sandy soil established in 2016 in Poland. The monitoring was performed using TEROS 12 sensors in the soil layers of 5–10, 20–25, and 30–35 cm from 25 April 2019–30 April 2020 with spring wheat as the main crop. The results showed that the average WC over the entire investigation period in the 5–10 cm layer was 0.206 m3 m–3 in the control and increased in the L, LU, M, and LLUM variants to 0.245, 0.219, 0.241, 0.262 m3 m–3, respectively. The highest WC was recorded in the LLUM system during most of the investigation period. The average T in the 5–10 cm layer increased in L, LU, and M by 0.221–0.262 °C and in LLUM by 0.052 °C. The average monthly soil temperature amplitudes in the soil layer 5–10 cm tended to be higher under all SICS vs. C except LLUM vs. C. The average EC in the 5–10 cm layer in variant C (0.066 mS cm–1) increased in the L, LU, M, and LLUM systems to 0.067, 0.090, 0.151, and 0.107 mS cm–1, respectively. The shapes of the temporal variability of WC and EC were similar in all SICSs, while the increase in the response to the combined effects of the SICSs and precipitation during the growing season was greater for the EC. The temporal variability of all soil properties in response to the SICSs and weather course and their averages declined with depth. The amplitudes of soil T in all treatments were lowest in the 30–35 cm layer. This study provides helpful information for the selection of the most suitable SICS in terms of soil properties influencing productivity and other soil functions.

Recovery characteristics of reversible degradation for proton exchange membrane fuel cell stack under accelerated stress test

The reversible degradation of proton exchange membrane fuel cells (PEMFC) restricts the high efficiency and long-term durability of fuel cells. The reversible loss, restorable only through specific procedures, significantly diminishes both the operational efficiency and the predictability of their remaining service life. Consequently, it is imperative to elucidate the recovery characteristics of reversible loss in high power PEMFC stacks for engineering applications. However, most of the studies focus on small-area single cells or short stacks, researches on the full-size stacks considering the uniformity and consistency differences are scarce. The recovery characteristics of high-power PEMFC stacks remain unclear. Therefore, in this work, an accelerated stress test with the idle and rated currents as the boundary of the cyclic condition was designed for a 100 kW PEMFC stack to investigate the recovery characteristics. The periodic voltage fluctuations along with the shutdown operations indicate that the voltage recovery may be caused by the redistribution of water content within the stack, and the reversible degradation is more pronounced and readily reversible under the high current condition. The impedance results suggest that the redistribution of water within the catalyst layer takes longer compared to that in the membrane. Furthermore, analyses of single cell voltage indicate that the consistency of voltage recovery is more closely related to variations of water content within the catalyst layer. Cells with higher water content exhibit better voltage recovery.

Research on shutdown purge characteristics of proton exchange membrane fuel cells: Purge parameters conspicuity and residual water

This paper comprehensively investigates the purge mechanism of proton exchange membrane fuel cells during the shutdown process, which qualitatively examines the effect of purge parameters (including current density, stoichiometric ratio, and relative humidity) on water content variation, and further quantitatively investigates the remaining water content post-purge. In contrast to previous studies, this paper offers a novel perspective on analyzing the purge process and conducts a thorough examination of residual water content. This study presents a transient, isothermal, two-phase flow model for proton exchange membrane fuel cells, which is subsequently validated experimentally. Results indicate that the significance of purge parameters follows the descending order: stoichiometric ratio, relative humidity, and current density. During the purge, the stoichiometric ratio should be rapidly increased to above 9. Each incremental rise in the stoichiometric ratio from 6 to 14 leads to a respective reduction in residual membrane water content after purge of 2.19 %, 1.57 %, 1.18 %, 0.93 %, 0.76 %, 0.63 %, 0.53 %, and 0.46 %. Similarly, it is recommended to swiftly decrease relative humidity to below 40 %. Elevating the purge current density from 20 to 200 mA/cm2 decreases the time required to completely remove liquid water from 20.24 s to 6.59 s. Hence, employing a higher current density at the onset of the purge facilitates quicker removal of liquid water, albeit resulting in an increase in residual membrane water content post-purge, from 3.17 to 3.70. In summary, optimizing the purge strategy requires adjusting purge current densities according to the specific purge stage.