Membrane modeling and flow through it are important studies, and their applications are for gas and water separation. The examples of membrane modeling applications are artificial kidneys and reactors. Some studies are available on membrane modeling for different applications; however, optimization studies are rarely available. In the current study, an initial membrane model is simulated by COMSOL 6.3 and then optimized for input parameters to decide the optimal set at which the performance and flow profiles are better. For this study, the design of experiments table through Minitab software using the Taguchi method is generated. Then it tested for an optimal parametric selection. In this study, the focus is on the effect of dialysate concentration (Dc), partition coefficient (K), dialysate velocity (Dv), and permeate velocity (Pv) on concentration individually and then in combination. The individual effect of parameters with different values is first studied. Then an array of L16 (4×4) using the design of experiments method (DOE) concept is finalized for variance analysis (ANOVA) to study the combined effect. The result of this analysis concludes that the major impact on concentration and velocity profile is due to K. The combined effect results conclude that the effect of different parameters is in the order of K > Pv > Cd > Dv for concentration and velocity profiles. This means that the major effect is due to the partition coefficient, and the minor effect is due to the permeating velocity. Before testing new results, the current COMSOL model is validated against published experimental work to ensure its accuracy.

Membrane distillation (MD) is a promising thermally driven separation process for water desalination and purification. However, the performance of conventional MD membranes, typically made from polyvinylidene fluoride (PVDF), is limited by low thermal conductivity, suboptimal mass transfer efficiency, and susceptibility to fouling. This study aims to enhance MD performance through the development of hybrid membranes incorporating graphene oxide (GO), titanium dioxide (TiO 2 ), and silicon carbide (SiC) nanoparticles into PVDF matrices, combined with advanced nano-coatings such as superhydrophobic and omniphobic layers. The fabricated membranes were evaluated for thermal conductivity, mass transfer efficiency, and fouling resistance using a series of experiments and advanced characterization techniques. Results demonstrated that the hybrid membranes exhibited significantly improved thermal conductivity (up to 0.8 W/m·K) and mass transfer efficiency (up to 2.0 L/m 2 ·h), compared to conventional PVDF membranes. Additionally, the advanced coatings enhanced the fouling resistance, although further refinement is needed for sustained long-term performance. This comprehensive analysis suggests that the integration of nanoparticles and advanced coatings can substantially enhance MD membrane performance, paving the way for more efficient and durable desalination processes. Future research should focus on optimizing these enhancements and validating their performance under real-world conditions.

Membrane distillation (MD) has emerged as a promising technique for desalination and water purification, offering potential advantages in terms of energy efficiency and operational flexibility. However, challenges related to heat and mass transfer inefficiencies limit its widespread adoption. This study explores the use of innovative materials and optimized configurations to enhance heat and mass transfer in direct contact membrane distillation (DCMD) systems. By integrating advanced hybrid membranes with nano-coating techniques and evaluating their performance through simulation-based methodologies, we demonstrate significant improvements in thermal conductivity, mass transfer efficiency, and fouling resistance. The results indicate that the newly developed hybrid membranes not only enhance heat and mass transfer rates but also maintain high separation efficiency, ultimately leading to improved overall system performance. These findings provide a foundation for the further development of MD technologies and suggest pathways for overcoming existing limitations, paving the way for more sustainable and efficient water treatment solutions.

Membrane distillation (MD) is a thermally driven separation process that offers significant potential for applications such as desalination, wastewater treatment, and industrial water recovery. However, the efficiency of MD is often constrained by low thermal conductivity, temperature and concentration polarization, and membrane fouling. This study proposes a novel Nano-Engineered Membrane with Thermal Pathway Optimization (NEM-TPO) designed to address these challenges by integrating advanced nanomaterials and structural modifications. The NEM-TPO membrane features a multi-layered nanocomposite structure with thermally conductive nanoparticles, including hexagonal boron nitride (hBN) and graphene nanosheets, along with micro-patterned vapor transport channels and a hydrophobic, anti-fouling coating of functionalized silica nanoparticles. Experimental validation demonstrated a 30% increase in vapor flux and a significant reduction in temperature polarization compared to conventional MD membranes, with enhanced thermal conductivity reaching $0.85 \mathrm{~W} / \mathrm{m} \cdot \mathrm{K}$. The NEM-TPO membrane also exhibited excellent fouling resistance, with less than 5% flux decline over 100 hours of continuous operation. These findings highlight the NEM-TPO membrane’s potential to enhance MD performance through improved heat and mass transfer, making it a promising candidate for sustainable and efficient water treatment technologies. Future research should focus on scaling fabrication processes and further optimizing membrane design for industrial applications.

Abstract Currently, China’s agricultural irrigation consumes a huge amount of water, and traditional agricultural irrigation methods lead to low irrigation efficiency and serious water resource waste. Agricultural irrigation water management is also difficult to achieve refined management due to the lack of accurate monitoring of water use data and information in various irrigation areas. To find a more convenient flow measurement method, this paper proposes using data-driven monitoring of water pump characteristic parameters to predict flow rate. Three big data-based methods for predicting the flow rate of irrigation well pumps were compared, including RBF neural network, Support Vector Machine (SVM), and Extreme Learning Machine (ELM). The results indicate that the Extreme Learning Machine (ELM) model not only has short time consumption but also high prediction accuracy, laying the foundation for the application of big data technology in water management and high-quality irrigation water management that can save water.

In the present paper, the restricted cavitation bubble dynamics near an asymmetric Joukowsky hydrofoil are investigated theoretically and experimentally. This investigation employs the conformal transformation, the image method, and the Kelvin impulse model, together with high-speed photographic experiments. The characteristics of bubble collapse deformation and bubble wall movement are analyzed qualitatively and quantitatively, and the spatial distributions of the liquid velocity and Kelvin impulse are revealed by theoretical predictions. The main conclusions include (1) the bubble collapse deformations can be divided into three typical cases: penetrating deformation (mostly occurs when gamma < 2 with defined as the bubble-hydrofoil dimensionless distance), triangular depression (mostly occurs when 2 < < 4), and arc-shaped depression (mostly occurs when > 4). (2) The impulse acting on the bubble is governed by a point source and a point sink, which is dominant, and the impulse is inversely correlated with the bubble-hydrofoil distance, which corresponds to the experimental results. (3) The Kelvin impulse exhibits different distributions at the tail, head, and middle regions of the hydrofoil, and the impulse angle remains basically unchanged in the concave region of the asymmetric hydrofoils (i.e., the range of 240 degrees < z < 350 with theta z defined as the bubble position angle).

The present paper investigates the dynamic behaviors of a bubble restricted by two parallel plates near an elliptical wall. The typical experimental phenomena of the bubble are recorded employing the high-speed photography and a theoretical Kelvin impulse model is established. The impacts of the spatial position and the curvature of the wall on the bubble collapse behaviors are quantitatively investigated through the theoretical model and verified against the experimental results. The Kelvin impulse intensity and the direction during the bubble collapse process are compared and discussed for different elliptical-shaped walls. The main conclusions include: (1) During the bubble collapse process, the phenomenon of the bubble uneven splitting is discovered. (2) At different spatial positions and wall curvatures, the bubble collapse jet angle, movement distance, and velocity are in good agreement with the theoretical Kelvin impulse predictions. (3) As the short-to-long axis ratio increases, the differences in the distributions of the Kelvin impulse intensity and the direction near the elliptical wall gradually become larger, and the range of the influence of the impulse intensity expands.

Membrane distillation (MD) is an attractive separation process that can work with heat sources with low temperature differences and is less sensitive to concentration polarization and membrane fouling than other pressure-driven membrane separation processes, thus allowing it to use low-grade thermal energy, which is helpful to decrease the consumption of energy, treat concentrated solutions, and improve water recovery rate. This paper provides a review of the integration of MD with waste heat and renewable energy, such as solar radiation, salt-gradient solar ponds, and geothermal energy, for desalination. In addition, MD hybrids with pressure-retarded osmosis (PRO), multi-effect distillation (MED), reverse osmosis (RO), crystallization, forward osmosis (FO), and bioreactors to dispose of concentrated solutions are also comprehensively summarized. A critical analysis of the hybrid MD systems will be helpful for the research and development of MD technology and will promote its application. Eventually, a possible research direction for MD is suggested.

In the present paper, the restricted cavitation bubble dynamics near a symmetric Joukowsky hydrofoil are researched theoretically and experimentally. Using Kelvin impulse theory, the Joukowsky transformation, and the circle theorem, a theoretical model for restricted bubble dynamics is established to analyze the collapse jet characteristics. The validity of this model is then verified using high-speed photographic experiments. The velocity and direction of the collapse jet at specific position angles are quantitatively analyzed. Furthermore, the spatial characteristics of the Kelvin impulse direction near the symmetric Joukowsky hydrofoil are revealed by theoretical results. The main conclusions include the following: (1) the new theoretical model is proven to be effective in predicting the direction of the collapse jet for a restricted bubble near a symmetric Joukowsky hydrofoil. (2) As the distance between the bubble and hydrofoil increases, the collapse jet direction changes from pointing toward the nearest wall to pointing toward the center of the hydrofoil. (3) The variation rate of the Kelvin impulse direction for the restricted bubble is very sensitive to the bubble position near the two ends of the symmetric Joukowsky hydrofoil.

采用纳米多孔膜可以实现新型的具有极高热流密度的薄液膜沸腾相变传热.在薄液膜沸腾的基础研究中,通过在纳米多孔膜表面加工纳米级别厚度的铂镀层实现加热和测温.通过扫描电镜观察,发现实验样品残骸表面有"河流"状形貌形成,结合元素分析推断铂镀层局部发生热熔.本文对铂镀层进行简化并建立电网络模型,计算并分析了铂镀层局部厚度不均对整体发热极限及熔毁失效的影响.分析结果表明,镀层厚度的不均,将会使镀层在达到极限热流密度后,极易出现"河流"状熔毁,使镀层永久失效;而厚度更加均匀的铂镀层,有助于获得更高的极限热流密度.

With the help of the micro/nano-porous membranes, synergistic flows of supply water and departing vapor can be realized, which considerably enhances boiling heat transfer. Ultrahigh heat flux of 1230 W/cm2 was reported in the thin film boiling experiments, of which the sample was fabricated by depositing nanosized platinum (Pt) layer on the surface of a nanoporous membrane. As an indispensable component, the nanoporous membrane plays an essential role by functioning as both the distributor of liquid fluid and the substrate of heating surface. However, there is still a lack of comprehensive understanding of the impacts of the nanoporous membrane. In this work, the resistor network approach developed in our former study was extended to analyze the influence of the nanoporous membrane on the performance of the unique thin film boiling. What's more, two active regulation schemes were proposed for nanoporous membrane to achieve better manipulation and enhanced performance. It was found that for a nonuniform nanoporous membrane, the critical heat flux was lower than that of a uniform membrane, and any further increase of electric power after reaching CHF would result in river-shaped crack of melted Pt resistors. For the nonuniform AAO membrane, the both active regulation schemes would effectively cope with the voltage fluctuation that could have led to the melt of the Pt layer. Therefore, better performance could be achieved by applying the active regulation schemes. Hopefully, the explorative studies on the active regulation schemes could provide operation guidance for future application of the thin film boiling.

气泡泡壁传质效应指的是气泡在液体中通过扩散、对流等质量传输机制而生长或溶解的物理过程及相关效应,其在医学、声学、核领域均有广泛的应用.影响传质效应的参数主要包括气泡用于传质作用的界面面积、溶解气体的浓度、周围流场的作用等.本文对已有的传质效应及相关物理模型进行了一个较为系统的综述,对传质效应所涉及的传质方程求解、泡壁运动方程求解、阈值条件计算等进行了数学解析求解.此外,对非牛顿流体、液态金属等介质中的传质效应研究以及高浓度模型做了简要的描述与分析.

Utilizing nanoporous membranes can realize a new thin film boiling regime with ultrahigh heat flux of over 1 kW/cm2. In thin film boiling experiments, a nanoscaled platinum (Pt) layer coating serves as both heater and temperature sensor and therefore plays a fundamentally important role. However, river-shaped micro cracks were discovered in the Pt layer after experiments, of which the origin and the influence are still unclear. In this paper, based on the microscopic observation, the porous Pt layer was abstracted as a resistor network. A comprehensive model was set up to quantitatively analyze the Pt layer by obtaining the resistance and temperature of all the resistors in the network. With this model, the formation of the river-shaped cracks was successfully simulated and the influence of the thickness uniformity of Pt layer was analyzed in detail. It was found that the river-shaped cracks were formed by the successive melting of resistors, which started from the thinner or thicker resistor and its adjacent resistors that achieved critical heat flux (CHF) earlier than the rest resistors, and then spread to the other part of the Pt layer in a way similar to a chain reaction. For ideal Pt layer with uniform thickness, it could eliminate the river-shaped cracks, achieve higher CHF and endure a wider voltage variation. The in-depth modeling on Pt layer may not only help the fundamental study of the thin film phase change heat transfer, but also contribute to the research of other nanoscaled conductive layers.

锂电池由于具有能量密度高和使用寿命长等优点而被广泛应用于电动汽车.但由于其性能和寿命对温度非常敏感,因此,设计良好的锂电池热管理系统成为电动汽车发展过程中的关键技术.介绍了温度对电池性能的影响,阐述了当前形势下电池热管理系统的标准,回顾了空气冷却、液体冷却和相变材料冷却优缺点,重点介绍了以热管技术为基础的电池热管理研究现状,从电池与热管间的热量传递、热管的选型与结构设计和散热段冷却方式等3个方面阐述了当前对应于热管的有关研究及问题.最后,总结当前应用研究下的不足和需要突破的关键问题,以期促进电池热管理系统的开发和研究.

Ultrahigh heat flux of over 1 kW/cm2 can be achieved by a new thin film boiling regime, of which the variation of boiling curve is considerably different from that of pool boiling. However, there is a lack of quantitative analysis for the distinctive thin film boiling. In this work, comprehensive comparison was made between the well-studied pool boiling and the newly-achieved thin film boiling. The boiling curve of thin film boiling was divided into three segments and mathematical models were set up for each segment in a way that correlations for pool boiling were adopted and modified according to the similarity and difference between pool boiling and thin film boiling, respectively. It was found that the modeling results agreed very well with the experimental results, indicating that the hybrid model revealed the underlying mechanism for the unique behavior and ultrahigh heat flux of the thin film boiling. In brief, the higher heat transfer coefficient or larger slope of the boiling curve was related to the special water supply mode of thin film boiling, in which the water flowed vertically through the heat surface and consequently enhanced heat transfer by promoting the spread of superheated layer and the bubbles on the heating surface. As for the ultrahigh heat flux and the unique negative slope of the boiling curve, it was attributed to the very thin yet continuously decreased thickness of the liquid layer, which was another essential feature of the thin film boiling. The hybrid model in this work can provide both quantitative insight for fundamental understanding and future guidance for practical application of thin film boiling.

计量检测是国家质量基础的重要组成部分.计量检测服务业是保障各经济行业发展和保障民生的重要技术手段,是生产性服务业的高端环节,是科技服务业的重要组成部分.随着国际单位制的重新定义,测量体系正发生重构,量值溯源体系向多级溯源中心、扁平化溯源甚至零链条溯源发展.计量从传统的逐级行政化监管范畴,逐渐拓展到扁平化,紧密支撑科技创新活动对量值准确客观的需要,不断满足新兴高技术产业及技术升级后的传统产业的精确测量需求.计量检测的发展水平是一个城市和地区核心竞争力的标志之一,与该地区科技创新发展息息相关.

Characterization of thin liquid film is important for comprehensive understanding the phase-change heat transfer mechanisms in an oscillating slug flow. In this study, the thin film thickness of oscillating slug flow in a square tube was experimentally investigated using a nano-particle tracking velocimetry technique. Square tubes with inner dimension of 3.0 x 3.0, 1.6 x 1.6, 0.5 x 0.5, and 0.3 x 0.3 mm(2) were used for test tubes, water was used as test fluids. The results show asymmetric velocity distribution in the thin liquid film. An obvious decrease of response time was observed for the thin liquid film when the oscillation frequency increases. The measured thin film thickness fits well with Taylor's law when the capillary number is small. Deviation from Taylor's law was found for larger capillary number, due to the prominent effect of bubble deceleration on the thin film thickness when the oscillation frequency increases. The relationship between acceleration process and deceleration process in different oscillation frequency is also studied.

Solar collectors are very important to the photothermal utilization of solar energy in low-temperature conditions. In this paper, a solar collector comprising an oscillating heat pipe in a flat-plate structure is designed and studied experimentally. The thermal properties are studied in detail, and we finally obtain the startup temperature and the expression of the instantaneous efficiency with a relative error of 5%. The results show that the impact of inclination angles on the startup properties of the solar collector is significant to the thermal properties. The comparisons of the efficiency of the present design and similar products are also displayed and discussed, showing that an oscillating heat pipe collector in a flat-plate structure overcomes the low efficiency, high startup temperature and bad pressure resistance of conventional solar collectors. In addition, the thermal properties of the water heating system based on the novel collector were also tested, illustrating the differences between the solar irradiance and the water heating system. Some improvements (e.g., shell material and assembly method) were made in this system design process to increase the heat transfer efficiency and solve the corrosion and pressure resistance problems.

Vortex is one of typical structures of the unsteady flow inside the hydroturbines, leading to significant pressure fluctuation, prominent vibration of the units, and fatigue of turbine components. In order to reveal the complex vortex structures in the hydroturbines, a large amount of advanced methods for vortex identification and visualization have been developed and also are currently being intensively investigated by researchers. In this review, the vortex identification methods are reviewed in great detail with many illustrating examples and quantitative comparisons between different methods. The vortex identification methods are classified based on five different taxonomies. The identification of several typical vortices (e.g. vortex rope in draft tube, Kármán vortex, and inter-blade vortex) in hydroturbines (including reversible pump turbines, Francis turbine, Kaplan turbine etc.) have been shown and discussed. Furthermore, experimental techniques for vortex observation have been also summarized and discussed. This review provides a practical guidance to the researchers for performing vortex identification.

Reversible pump turbines are widely employed in the pumped hydro energy storage power plants. The frequent shifts among various operational modes for the reversible pump turbines pose various instability problems, e.g., the strong pressure fluctuation, the shaft swing, and the impeller damage. The instability is related to the vortices generated in the channels of the reversible pump turbines in the generating mode. In the present paper, a new omega vortex identification method is applied to the vortex analysis of the reversible pump turbines. The main advantage of the adopted algorithm is that it is physically independent of the selected values for the vortex identification in different working modes. Both weak and strong vortices can be identified by setting the same omega value in the whole passage of the reversible pump turbine. Five typical modes (turbine mode, runaway mode, turbine brake mode, zero-flow-rate mode and reverse pump mode) at several typical guide vane openings are selected for the analysis and comparisons. The differences between various modes and different guide vane openings are compared both qualitatively in terms of the vortex distributions and quantitatively in terms of the areas of the vortices in the reversible pump turbines. Our findings indicate that the new omega method could be successfully applied to the vortex identification in the reversible pump turbines.