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Nitrogen dynamics at ecosystem levels profoundly impact the Earth’s surface system due to their environmental and ecological significance. Exploring the sources and transformation of nitrogen in various Critical Zones is vital to understanding biogeochemical cycles and sustainable development. This study summarized nitrogen characteristics in soil profiles and nitrogen dynamics in diverse terrestrial ecosystems based on data from typical Critical Zones of China. The results indicated that nitrogen accumulates in the deep soils of cropland ecosystems due to intensive fertilizer applications, which potentially harms soil functions and water quality. Therefore, it is necessary and meaningful to take adequate measures to alleviate nitrogen accumulation in deep soils. Additionally, surplus nitrogen transported into groundwater and riverine systems from soil has emerged as an important issue for environmental management. There are serious nitrogen pollution issues in many river water and groundwater areas, which could be addressed by reducing the fast leaching and considerable nitrogen accumulation in the vadose zone. Systematic and long-term observational studies are needed to achieve the ultimate goal of ecological conservation and high-quality development. Therefore, future research should consider monitoring and evaluating ecosystems based on the long-term Critical Zone Observatories networks to advance appropriate environmental management strategies that adapt to nature’s rules and strengthen the ecosystem service function for sustainable development.

The high-frequency vibration and resonance of armature assembly in the hydraulic servo valve are the main reasons for instability and failure. Magnetic fluid (MF) operating in the squeeze mode can be taken as an effective damper for resonance suppression in the servo valve. Due to excitation difficulty and the low signal-to-noise ratio of high-frequency vibration signals, the capability of MF to modify multiple-order modal damping ratios in a multi-degree-of-freedom system is still unclear. To reveal the mechanism of magnetic fluid for improving modal damping ratios, an algorithm for modal damping ratio identification is proposed. The modal damping ratios of the armature assembly with and without magnetic fluid are identified based on the tested resonance free decay responses. Four resonance frequencies of armature assembly are observed, and the corresponding damping ratios are identified. The equivalent modal damping ratios due to squeeze flow of MF are obtained. The results show that the proposed algorithm can identify damping ratios with an accuracy of up to 98.79%. The damping ratios are improved by double or more due to the magnetic fluid, and the maximum resonance amplitudes are significantly reduced by 65.2% (from 916.5 μm to 318.6 μm).

International audience; Deep oceans receive mercury (Hg) from upper oceans, sediment diagenesis, and submarine volcanism; meanwhile, sinking particles shuttle Hg to marine sediments. Recent studies showed that Hg in the trench fauna mostly originated from monomethylmercury (MMHg) of the upper marine photosynthetic food webs. Yet, Hg sources in the deep-sea chemosynthetic food webs are still uncertain. Here, we report Hg concentrations and stable isotopic compositions of indigenous biota living at hydrothermal fields of the Indian Ocean Ridge and a cold seep of the South China Sea along with hydrothermal sulfide deposits. We find that Hg is highly enriched in hydrothermal sulfides, which correlated with varying Hg concentrations in inhabited biota. Both the hydrothermal and cold seep biota have small fractions (

Researchers borrow ideas from biological characteristics and behavior in design to make bionic robots that can meet unstructured and complex operating environments. The elephant trunk has been widely imitated by bionic robots because of its strong dexterity and stiffness adjustability. Due to the complex structure of the current elephant trunk robot, a series-parallel elephant trunk robot based on flexible rod actuation and a 6-degree-of-freedom (6-dof) parallel module is proposed in this paper. The bionic robot has a simple structure and redundant kinematics, which can realize the control of stiffness. This work focuses on the modeling of the flexible driving rod, the kinematics of a single parallel module, and the whole biomimetic robot. The kinematics are verified by simulation, which lays a foundation for future research on stiffness regulation.

In order to describe temperature-dependent cell osmotic behaviors in a more reliable method, a novel mathematical mass transfer model coupled with dynamic temperature change has been established based on the combination of a time domain to temperature domain transformation equation and a constant temperature mass transfer model. This novel model is numerically simulated under multiple temperature changing rates and extracellular osmolarities. A microfluidic system that can achieve single-cell osmotic behavior observation and provide dynamic and swift on-chip temperature control was built and tested in this paper. Utilizing the temperature control system, the on-chip heating processes are recorded and then described as polynomial time-temperature relationships. These dynamic temperature changing profiles were performed by obtaining cell membrane properties by parameter fitting only one set of testing experimental data to the mathematical model with a constant temperature changing rate. The numerical modeling results show that predicting the osmotic cell volume change using selected dynamic temperature profiles is more suitable for studies concerning cell membrane permeability determination and cryopreservation process than tests using constant temperature changing rates.

The compact, simple, and fast-reaction pneumatic microactuator is significant for the integration and high efficiency of pneumatic systems. In this work, the structure, working principle, and multiphysical model of an on-chip pneumatic microactuator are presented. The on-chip pneumatic microactuator is mainly composed of two parts: a polydimethylsiloxane (PDMS) thin membrane and an actuated chamber. The air pressure in the actuated chamber drives the thin elastic membrane to deformation. Dynamic response mathematical models of the actuated chamber for charging and exhaust with variable volume are established, and the deformation characteristics of the polydimethylsiloxane (PDMS) actuated membrane, the capacity of the actuated chamber, and the valve opening of the on-off membrane microvalve are simulated and analyzed to explore the response characteristics of the proposed pneumatic microactuator. Samples valving analysis of the on-chip membrane microvalve and mixing performance of the micromixer integrated with the pneumatic microactuator are tested to evaluate the driving capability of the pneumatic microactuator, and the results show that the response performance of the actuated time fully satisfies the needs of a pneumatic microfluidic chip for most applications.

A compact, rapid, and portable off-chip pneumatic control valve is significant for the miniaturization and integration of external pneumatic systems for microfluidic chips. In this work, an off-chip microvalve with a high-speed electromagnetic switch actuator and a polydimethylsiloxane (PDMS) material valve body has been designed to be easily encapsulated, simulated using MATLAB/Simulink software, and tested in a micromixer. Multi-physical coupling mathematical models are developed based on the elastic deformation force of the valve membrane, the driving force of the valve core, and the fluid force in the microchannel. Two single microvalves are used to form a three-way microvalve, which can control the air pressure in a pneumatic microchannel on the microfluidic chip. The relationship between the flow–duty cycle, the flow–pressure difference of the single electromagnetic microvalve, and the load pressure of the three-way microvalve is simulated and analyzed. Sample mixing performance controlled by the proposed off-chip three-way microvalve was tested to evaluate the pneumatic control capability, and the results show that the undertaking can fully satisfy the needs of a pneumatic microfluidic chip for most applications.

Indium tin oxide (ITO) is a functional material with great transparency, machinability, electrical conductivity and thermo–sensitivity. Based on its excellent thermoelectric performance, we designed and fabricated a multilayer transparent microfluidic chip with multiple sets of on–chip heating, local temperature measurement and positive on–chip cooling function units. Temperature control plays a significant role in microfluidic approaches, especially in the devices that are designed for bioengineering, chemical synthesis and disease detection. The transparency of the chip contributes to achieve the real–time observation of fluid flow and optical detection. The chip consists of a temperature control layer made with an etched ITO deposited glass, a PDMS (polydimethylsiloxane) fluid layer, a PDMS cooling and flow control layer. The performances of the ITO on–chip microheaters, ITO on–chip temperature sensors and two coolants were tested and analyzed in different working conditions. The positive on–chip heating and cooling were proved to be area-specific under a large temperature–regulating range. This PDMS–ITO–glass based chip could be applied to both temporal and spatial stable temperature–regulating principles for various purposes.

Shearing DNA to a certain size is the first step in many medical and biological applications, especially in next-generation gene sequencing technology. In this article, we introduced a highly efficient ultrasonic DNA fragmentation method enhanced by needle-induced air bubbles, which is easy to operate with high throughput. The principle of the bubble-enhanced sonication system is introduced and verified by flow field and acoustic simulations and experiments. Lambda DNA long chains and mouse genomic DNA short chains are used in the experiments for testing the performance of the bubble-enhanced ultrasonic DNA fragmentation system. Air bubbles are an effective enhancement agent for ultrasonic DNA fragmentation; they can obviously improve the sound pressure level in the whole solution, thus, achieving better absorption of ultrasound energy. Growing bubbles also have a stretched function on DNA molecule chains and form a huge pressure gradient in the solution, which is beneficial to DNA fragmentation. Purified lambda DNA is cut from 48.5 to 2 kbp in 5 min and cut to 300 bp in 30 min. Mouse genomic DNA (asymptotic to 1400 bp) decreases to 400 bp in 5 min and then reduces to 200 bp in 30 min. This bubble-enhanced ultrasonic method enables widespread access to genomic DNA fragmentation in a standard ultrasonic water bath for many virus sequencing demands even without good medical facilities. Published under an exclusive license by AIP Publishing.

The dynamic performance of a nozzle-flapper servo valve can be affected by several factors such as the disturbance of the input signal, the motion of the armature assembly and the oscillation of the jet force. As the part of vibrating at high frequency, the armature assembly plays a vital role during the operation of the servo valve. In order to accurately predict the transient response of the armature assembly during the vibration, a mathematical model of armature assembly is established based on the distributed parameters method (DPM) and Hamilton principle. The new mathematical model is composed of three main parts, the modal eigenfunction, modal mechanical response expressions of the spring tube and the motion equation of the other armature assembly. After programing, the purpose of using the DPM to predict the dynamic response of different positions located on the armature assembly is achieved. For verifying the validity of the mathematical model, the finite element method (FEM) and classic model (CM) of armature assembly are applicated by commercial software under the same condition. The comparison results prove that the DPM can effectively predict the axial and tangential deflection of the armature assembly different positions which the CM can’t duing to its over-simplification. A certain error is generated when predicting the axial deformation at different heights by DPM, which is caused by an approximate method to simulate the torsion of the spring tube. The comparison results of the spring tube deflection at different vibration frequencies shows that the adaptability of DPM is significantly higher than the classic model, which verify the model is more adaptable for predicting the dynamic response of the armature assembly.

The emphasis of this paper lies in the fabrication of a three-layer polydimethylsiloxane chip for micro liquid sample operation. In this paper, the microchannels with a rectangular control layer cross section are fabricated based on a dry-film negative photoresist mold, while the microchannels with a rounded liquid layer cross section are fabricated by a positive photoresist reflow mold. The relationships between temperature and the time of reflow and the arc level of the liquid layer mold are discussed. Different ratios, curing temperatures, and curing times are used to fabricate the two PDMS layers to improve their toughness and plasticity separately. The PDMS slabs with microstructure networks are treated with oxygen plasma to improve their surface properties. The improved surface properties serve to reduce the temperature and time, and improve the sealing strength, which is as effective as adding PDMS in varying ratios. The micro liquid sample operation experiments show that high levels of pinching off and mixing performances on pneumatic microfluidic chips are obtained more easily.

Electro-hydraulic servo-valves are widely used components in the mechanical industry, aerospace and aerodynamic devices which precisely control the airplane or missile wings. Due to the small size and complex structure in the pilot stage of deflection flapper servo-valves, accurate mathematical models for the flow and pressure characteristics have always been very difficult to be built. In this paper, mathematical models for the pilot stage of deflection flapper servo-valve are investigated to overcome some gaps between the theoretical formulation and overall performance of the valve by considering different flow states. Here, a mathematical model of the velocity distribution at the flapper groove exit is established by using Schlichting velocity equations for in-compressible laminar fluid flow. Moreover, when the flow becomes turbulent, a mathematical model of pressure characteristics in the receiving ports is built on the basis of the assumption of the collision between the liquid and the jet as the impact of the jet on a moving block of fluid particles. To verify the analytical models for both laminar and turbulent flows, the pressure characteristics of the deflection flapper pilot stage are calculated and tested by using numerical simulation and experiment. Experimental verification of the theory is also presented. The computed numerical and analytical results show a good agreement with experimental data. Keywords: Computational fluid dynamics (CFD), Deflection flapper servo-valve, Laminar flow, Pressure characteristics, Servo-valve, Turbulent submerged jet

Two-stage electrohydraulic servo-valves play an important role in the most modern hydraulic servo control systems for fight wing controls, manufacturing robots, and many engineering applications. The existence of cavitation inside the pilot stage is one of the root causes of self-excited noise, cavitation erosion, system jam, and frequent failures of electrohydraulic servo-valves. Thus, experimental and numerical investigations of the flow field and cavitation phenomena inside the pilot stage of deflector jet servo-valve under different supply pressures conditions are conducted in this paper. An assembly for experimental verification of the flow visualization process that represents the deflector jet pilot stage is produced and discussed. To test and verify the numerical simulations for cavitation phenomena, the flow field characteristics in the deflector jet pilot stage are investigated by using experimental flow visualization. The cavitation inception inside the pilot stage of the deflector jet servo-valve is experimentally confirmed through flow visualization. More importantly, the attached cloud-like cavitation or bubble shedding is observed along with the jet flow and the significant locations of cavitation inception are also identified for varying supply pressures. The profile of turbulent intensity confirms to conclude that turbulent pressure fluctuations contribute to cavitation. The result also shows that the increment of supply pressure intensifies cavitation and output pressure plays a significant role in reducing the intensity of cavitation inside the pilot stage of deflector jet servo-valve. Finally, the numerical results show good agreement with experimental results.

Correction for ‘Bubble-enhanced ultrasonic microfluidic chip for rapid DNA fragmentation’ by Lin Sun et al., Lab Chip, 2022, 22, 560–572, https://doi.org/10.1039/D1LC00933H.

This article reports mixability experiments and their RGB color model analysis for a simple structured micromixer based on the pneumatic-driven membrane in multiple microreagent mixing applications. First, a novel and simple structure consisting of a mixing chamber and a pneumatic chamber is designed and fabricated of polydimethylsiloxane (PDMS) material, which facilitates integration with microfluidic chips. Then, experiment results and their RGB color model about mixing efficiency are investigated. Compared with conventional methods, the RGB color model for mixing results is easy and intuitive. In addition, the designed micromixer operation relies on less external laboratory infrastructure because of its simple structure.

For a progressive multifocal liquid lens with an elastic membrane deformed by liquid pressure, to realize a reasonably power distribution, asymmetric deformation characteristics of the membrane surface are needed. Based on the asymmetric freeform surface structure, this paper proposed progressive multifocal liquid lenses focused by liquid with nonuniform thickness membranes. The structure and mathematical model of power distribution for the lens are introduced. The membrane deformation and the corresponding power distribution of the lenses with asymmetric freeform surface are predicted and compared under uniform pressure load and different boundary conditions using the finite element method. An optical testing system is constructed to analyze the optical characteristics of the fabricated lenses through observing the focusing performance of the F target image at different regions of the lenses. Experimental results show that the liquid lenses can realize as asymmetrical progressive multifocal liquid lenses after liquid accommodation; meanwhile, the trends of power distribution of the lenses generally agree well with simulations.

Mixing a small amount of magnetic beads and regents with large volume samples evenly in microcavities of a microfluidic chip is always the key step for the application of microfluidic technology in the field of magnetophoresis analysis. This article proposes a microfluidic chip for DNA extraction by magnetophoresis, which relies on bubble rising to generate turbulence and microvortices of various sizes to mix magnetic beads with samples uniformly. The construction and working principle of the microfluidic chip are introduced. CFD simulations are conducted when magnetic beads and samples are irritated by the generation of gas bubbles with the variation of supply pressures. The whole mixing process in the microfluidic chip is observed through a high-speed camera and a microfluidic system when the gas bubbles are generated continuously. The influence of supply pressure on the mixing characteristics of the microfluidic chip is investigated and discussed with both simulation and experiments. Compared with magnetic mixing, bubble mixing can avoid the magnetic beads gather phenomenon caused by magnetic forces and provide a rapid and high efficient solution to realize mixing small amount of regents in large volume samples in a certain order without complex moving structures and operations in a chip. Two applications of mixing with the proposed microfluidic chip are also carried out and discussed.

For a liquid progressive multifocal lens with an elastic membrane deformed by liquid pressure, to realize a reasonably power distribution, an asymmetric deformation characteristics of membrane surface is needed. Based on the asymmetric freeform surface structure, this paper proposed liquid progressive multifocal lenses focused by liquid with non-uniform thickness membranes and different boundary constraints. The structure and mathematical model of power distribution for the lens are introduced. The membrane deformation and the corresponding power distribution of the lenses with asymmetric freeform surface are predicted and compared under uniform pressure load and different boundary constraints. A membrane deformation testing system is constructed to analyze the power distribution of fabricated lenses through measuring the surface sag using laser displacement sensor and corresponding optical power distribution can be calculated. Experimental results show that the liquid lenses can realize as liquid progressive multifocal lenses after liquid accommodation, meanwhile, the trends of power distribution of the lenses generally agree well with simulations.

Unstable liquid flow in syringe pump-driven systems due to the low-speed vibration of the step motor is commonly observed as an unfavorable phenomenon, especially when the flow rate is relatively small. Upon the design of a convenient and cost-efficient microfluidic standing air bubble system, this paper studies the physical principles behind the flow stabilization phenomenon of the bubble-based hydraulic capacitors. A bubble-based hydraulic capacitor consists of three parts: tunable microfluidic standing air bubbles in specially designed crevices on the fluidic channel wall, a proximal pneumatic channel, and porous barriers between them. Micro-bubbles formed in the crevices during liquid flow and the volume of the bubble can be actively controlled by the pneumatic pressure changing in the proximal channel. When there is a flowrate fluctuation from the upstream, the flexible air-liquid interface would deform under the pressure variation, which is analogous to the capacitive charging/discharging process. The theoretical model based on Euler law and the microfluidic equivalent circuit was developed to understand the multiphysical phenomenon. Experimental data characterize the liquid flow stabilization performance of the flow stabilizer with multiple key parameters, such as the number and the size of microbubbles. The developed bubble-based hydraulic capacitor could minimize the flow pulses from syringe pumping by 75.3%. Furthermore, a portable system is demonstrated and compared with a commercial pressure-driven flow system. This study can enhance the understanding of the bubble-based hydraulic capacitors that would be beneficial in microfluidic systems where the precise and stable liquid flow is required.

To quantitatively study the pressure fluctuations induced by the process of droplet formation in a T-junction microdroplet generator, the mathematical model which can accurately predict the amplitude and the frequency of the pressure fluctuations is demonstrated. Different geometries of the T-junction microchannels are designed for the experiments of droplet formation, and the time-varying pressure difference between the upstream and downstream of each droplet is measured during the droplet production progress. From both theoretical and experimental study, it can be observed the pressure difference is a periodic function of time for the whole process of droplet generation. In particular, the frequency of the pressure fluctuations coincides with the production rate of droplets, and the amplitude of the pressure fluctuations varies with the geometrical parameters of the T-junctions. Additionally, good agreements are shown between the theoretical calculations and the experimental measurements of the magnitude of the pressure fluctuations. Therefore, our mathematical model is validated experimentally, and the magnitude of the pressure fluctuations can be drastically reduced by optimization of the geometrical parameters of the T-junction.

In this work, different microfluidic colour-changing devices are implemented by using dry film photoresist-based moulds instead of standard photolithography moulds. EtertecHT-115T negative dry film photoresist is employed to realise the rapid fabrication of the moulds for colour-changing layers. The major factors that may affect the fidelity of the dry film moulds during fabrication are summarised and analysed, including the optimum exposure times and the appropriate developing times. Especially, the impacts of different concentrations of sodium carbonate (Na2CO3) solution on developing rate are investigated for 1–5 layers (50–250 μm thick) of EtertecHT-115T dry film photoresists by experiments. The created dry film moulds show the advantages of low cost, high manufacturing efficiency and requiring no professional training. Each application of the microfluidic colour-changing devices presents high transparency and good colour-changing effect. The microfluidic colour-changing layers based on dry film moulds can be used in different wearable devices of human, and also can be applied for realising surface camouflage and display functions of soft machines/robotics.

The compact, lightweight, and energy-efficient heat exchanger is significant for the miniaturization of hydraulic power unit in quadruped robot. In this work, a rectangular staggered fins heat exchanger (RSFHE) as an ideal lightweight heat exchanger for miniaturized hydraulic power units is investigated and optimized based on the experimental correlations of heat transfer and flow resistance for the fluids with different Prandtl number. Function models including the related mass, outlet temperature and pressure drop are defined. A sensitivity analysis is presented to investigate the effect of key parameters on function models, which can evaluate the contributions of variables to the comprehensive performance of the heat exchanger. Based on these function models, the heat exchanger key parameters are optimized using genetic algorithm (GA). Moreover, numerical simulations are conducted to explore the thermal-hydraulic performance of the original and optimized heat exchangers and the simulation results are almost equal to the theoretical results calculated by experimental correlations. Compared with the original heat exchanger, the total weight of the optimized exchanger reduces by 25.49% and its heat transfer capacity increases by 24.22% taking the inlet-outlet temperature difference of the hydraulic oil as the index, which is a great improvement for the miniaturization and lightweight of the hydraulic power unit.

Most current Internet of Things systems face many problems like privacy leakage, information island and low application value, because they are designed from the perspective of Internet of Things service providers. However, the practicality and privacy security of Internet of Things services are more important from the perspective of Internet of Things system users. Considering that there aren’t too many Internet of Things devices to use and manage for ordinary people and service, a more service-oriented architecture of the lightweight private IOT remote system is proposed in this paper. To verify this system, verifications like remote sensors, remote actuators, and a micromixing application are developed and illustrated. Owing to its distributed server architecture, this system has high flexibility, practicability, parallelism, and low coupling. This novel system architecture provides a new perspective to develop practical valuable private Internet of Things services.

In this work, a microfluidic colour-changing glasses controlled by shape memory alloy (SMA) actuators is designed and presented by circulating colour liquids in the microfluidic channels on the lens. For liquids controlling, a unidirectional NiTi SMA spring is employed to design and fabricate a simple microfluidic actuator, which can provide the maximum restoring force of 5.27 N and the fastest recovering rate of 2.71 mm/s. After the responding characteristics of the SMA controller are tested and calculated under different conditions, the pressure changes at the channel inlet are investigated in liquids circulation process for different channel designs. This liquid colour-changing glasses show fast response, rapid prototyping and high controllability compared with the traditional solid colour-changing way. Meantime, the impacts of different channel designs on response performances are validated, which can provide foundations for further optimization of the channel designs. Soft lithography technology is applied for the fabrication of the colour-changing layer made of transparent silicone PDMS (polydimethylsiloxane) instead of conventional mechanical machining. Organosilicon coating based on methyltrimethoxysilane and phenyltrimethoxysilane (PTMS) is firstly fabricated for modification of PDMS surface to increase the wear resistance of the colour-changing lens.

Herein, micromixing was utilized to achieve chemical reaction, homogenization, emulsification, and in applications of microfluidics. In these applications, efficient mixing is one of the most fundamental and difficult-to-achieve characteristics. To quantitatively represent the mixing performance, nearly all the methods to characterize the micromixing processes in miniaturized devices depend on the images obtained by a microscope coupled with a CCD device or a video camera. The experimental images are generally stored in an RGB or gray-scale format. Intensity information of the micromixing images is most often used to estimate the mixing performance. Reliable quantification of the mixing effects is one of the most important and fundamental issues to study the performances of mixers and to optimize the designs. Thus, mixing indexes are of great significance to quantify the mixing effects. However, mixing indexes merely based on dispersion information cannot always produce reliable results if the variation of the mean intensity with enhanced mixing is neglected. Therefore, mixing indexes that consider the combination of mean and dispersion information from the intensity images in two specific forms were proposed. In addition, two practical criteria were used to evaluate the performances of the quantitative mixing indexes. One is the reliability and the other is repeatability precision. According to the comparisons of different mixing indexes studied herein, mixing indexes that consider the combination of mean and dispersion information can ensure the reliability of the calculated result every time and the repeatability precision was less than ±3.5%. Therefore, it can be concluded that the mixing indexes that consider the combination of mean and dispersion information can more reliably represent the mixing performance.

The numerical analysis is performed by using the commercial computational fluid dynamics software STAR CCM + to investigate the pressure gain coefficients, the flow field and cavitation distributions in the pilot stage under same supply pressure and return pressure with structural optimization of the deflector V-groove shape and the length of the inlet nozzle for the various deflector displacement are carried out. By analyzing with different structural parameters, possible influential parameters have been obtained contributing to flow cavitation phenomena in the pilot stage of the deflector jet servo valve. The aim of this analysis is to evaluate the deflector jet servo valve fluid dynamic performance, exploiting computational fluid dynamics (CFD) techniques, in order to give the reliable indications needed to define the deflector nozzle design criteria and avoid expensive experimental tests. Finally, the effectiveness of the innovative deflector shape in reducing cavitation intensity and overall better performance has been achieved.

The deflector jet servo valve, whose static and dynamic performance can be deteriorated by the generated flow cavitation phenomenon, is a vital segment in achieving precise control of electro-hydraulic servo valves. Thus, the distribution of the flow field in the pilot stage of the deflector jet servo valve has a serious impact on the performance of the valve and even the capability of the entire system. This paper is mainly presented in the three-dimensional modeling and simulation of the pilot stage flow field. For observing the characteristics of cavitation, Eulerian multiphase model, standard k-e turbulent model, and vapor fraction transport equation model are used. The result shows that the increment of inlet pressure intensifies cavitation in the area of null clearance of the deflector jet amplifier segment and at the edge of receiving ports A & B. Moreover, large eddy simulation is used to calculate turbulent characteristics and the governing equations are solved for transient state condition to capture the characteristic of generating, growing, and merging cavity shedding phenomenon. The numerical cavitation distributions are simulated inside the deflector jet pilot stage at different oil viscosities. The result concludes that cavitation phenomenon is intensified with the decreasing of fluid viscosity. It is also observed from the numerical analysis that output pressure plays a significant role in controlling cavitation intensity around the pilot stage of the deflector jet servo valve.

Hydraulic control system is one of the fundamental subsystems of the various aircraft systems, e.g., flight control system, brake system and fuel regulation system. As a pivotal actuator of the hydraulic control system, the nozzle-flapper servo valve converts the control signals to the hydraulic output. The flow cavitation in the valves could lead to some intractable problems, e.g., vibration, noise and erosion, which could produce detrimental effects on the performance and reliability of the hydraulic system, even damage the aircraft. This work provides a numerical investigation on the cavitation attenuation in the nozzle-flapper valve using triangular nozzle exit. The flow imaging and mass flow rate measurement are conducted to qualitatively and quantitatively verify the numerical model, respectively. It is observed that the presence of the vapour phase is remarkably suppressed under the effect of the triangular nozzle exit. For both circular and triangular nozzle exits, the occurrence of the vapour phase is highly affected by the nozzle-to-flapper distance, inlet pressure and chamber diameter while the flapper diameter exerts an insignificant impact on the formation of the vapour phase. Compared with the circular nozzle exit, the triangular nozzle exit could effectively reduce the flow cavitation at the same geometry and inlet pressure. The physical mechanism behind the cavitation suppression may be ascribed to the generation of the inclined impinging jet upon the chamber wall and the wall jet without impingement.

The air bubbles can be used in a controlled fashion for multiphase microfluidics but also frequently plague microfluidic devices when unrestrained. However the phenomenon of the undesired air bubble growth in microfluidic channels has not been systemically studied yet. Based on a coupled-physics model, herein we try to explain the process of unwanted air bubble growth during microfluidic negative pressure-driven flow in polydimethylsiloxane (PDMS) channel corners with both theoretical and experimental approaches. The air bubble growth is the result of multiphase interactions among solid–liquid–gas contact, and it is mainly determined by interfacial air mass transfer and pressure variation of the flowing liquid. The intangible physics during the bubble growth is revealed and calculated through theoretical analysis. To validate the developed model, the air bubble growth rate variation range of 0.44 × 10−13 m3/s to 3.4 × 10−13 m3/s is observed under different experimental conditions. Both of the simulation and experiment data indicate that the rate of air bubble growth can be quantitatively correlated with the bubble location in the channel and the negative driving pressure. The reported studies can both benefit air bubble prevention and removal strategies while providing a theoretical framework for the systematic design of multiphase microfluidics where motive mass transfer exist.

The stability and dynamic performance of a flapper–nozzle pilot valve significantly depend on the flow forces acting on the flapper. Due to the shape of the flapper and flow structure in the flapper–nozzle pilot valve there are undesired lateral forces acting on the flapper, which are very potential to interfere with the stability of the flapper. Aiming to reduce these undesired lateral forces, an innovative flapper shape is proposed and a comparative study of flow forces acting on the two different flapper shapes is conducted. A simple rectangle shape is selected as the innovative flapper shape. The flow forces acting on the traditional flapper shape and innovative flapper shape are evaluated by means of CFD (Computational Fluid Dynamics) simulations and verified with the results from the semi-experimental approach. The evaluation of the flow forces is performed for each flapper shape with two different flapper–nozzle clearances of 0.10 mm and 0.05 mm under seven different flow conditions with the variation of inlet pressures from 1 MPa to 7 MPa. A good agreement between CFD results and semi-experimental results shows that the proposed innovative flapper shape has no effect on flow control characteristics since it is giving approximately the same flow rate and main flow force as the traditional flapper shape at every flow condition. Meanwhile the innovative flapper shape effectively reduces the undesired lateral forces acting on the flapper by altering the flow structure and reducing the strength of the jet flow and cavitation occurred in the flow field of flapper–nozzle pilot valve. At the lower part of the flapper with clearance 0.05 mm, the ratio between the X-direction lateral force and main flow force of traditional flapper is around 1.24–11.14%, while it is reduced to 0.18–0.42% by the innovative flapper. Also, the ratio is reduced from 7.93–18.44% to 0.69–0.93% with clearance 0.10 mm. For the Z-direction forces at the lower part, the ratio decreases from 0.20–11.77% and 7.84–17.94% (traditional flapper) to 0.92–2.65% and 1.63–4.08% (innovative flapper) with clearances 0.05 mm and 0.10 mm respectively.

The pressure-driven device is designed to control the flow rates of the droplet microfluidic systems, which can significantly reduce the flow-rate fluctuations coming from the pump source. As monodisperse droplets are formed in the microchannel, periodic pressure fluctuations can be induced by the dynamic process of droplet formation, which can influence the stability and control precision of the pressure-driven flows. The effects of the pressure fluctuations induced by the droplet formation process on the dynamic characteristics of the open-loop and closed-loop control pressure-driven devices are comparatively studied. Particularly, a proportional–integral controller (PI controller) is integrated with the closed-loop control pressure-driven device and the effects of the PI controller parameters on the stability and control accuracy of the pressure-driven flows are tested experimentally. Particularly, by properly choosing the parameters of the PI controller, the magnitude of the periodic pressure fluctuations can be reduced drastically, which obviously increases the control precision of the pressure-driven flows.

Background In this paper, a liquid progressive multifocal lens with solid-liquid structure is demonstrated, which mainly consists of two elastic polydimethylsiloxane (PDMS) membranes, a solid substrate and liquid. Methods To realize the adjustment of the focuses progressively, the thickness of one of the membrane is designed non-uniform. By controlling the liquid pressure working on the membranes, the curvature of the membrane can be changed continuously and the power of the lens can be altered simultaneously. In this paper, the structure and a fabrication method of the lens is introduced, and a power distribution model is built for the calculation of the power distribution characteristics. Moreover, the deformation of the non-uniform elastic membrane of the lens under different pressures is analysed with finite element method (FEM). Results Finally, a prototype of the lens is developed and tested by applying a micro laser displacement sensor, and it is demonstrated that the progressive multifocal lens is feasible. Conclusion A novel liquid progressive multifocal lens with a non-uniform thickness elastic membrane is proposed. From the simulation and experimental investigation, it can be concluded that the proposed liquid lens can realize progressive multifocal through using non-uniform elastic membrane and the power can be adjusted by the pressure which is controlled by the liquid volume filled in the lens.

The occurrence of self-excited noise felt as squealing noise is a critical issue for an electrohydraulic servovalve that is an essential part of the hydraulic servocontrol system. Aiming to highlight the root causes of the self-excited noise, the effect of oil viscosity on the noise production inside a two-stage servovalve is investigated in this paper. The pressure pulsations' characteristics and noise characteristics are studied at three different oil viscosities experimentally by focusing on the flapper-nozzle pilot stage of a two-stage servovalve. The cavitation-induced and vortex-induced pressure pulsations' characteristics at upstream and downstream of the turbulent jet flow path are extracted and analyzed numerically by comparing with the experimental measured pressure pulsations and noise characteristics. The numerical simulations of transient cavitation shedding phenomenon are also validated by the experimental cavitation observations at different oil viscosities. Both numerical simulations and experimental cavitation observations explain that cavitation shedding phenomenon is intensified with the decreasing of oil viscosity. The small-scale vortex propagation with the characteristic of generating, growing, moving, and merging is numerically simulated. Thus, this study reveals that the oil viscosity affects the transient distribution of cavitation and small-scale vortex, which, in turn, enhances the pressure pulsation and noise. The noise characteristics achieve a good agreement with pressure pulsation characteristics showing that the squealing noise appears accompanied by the flow field resonance in the flapper-nozzle. The flow-acoustic resonance and resulting squealing noise possibly occurs when the amplitude of the pressure pulsations near the flapper is large enough inside a two-stage servovalve.

Squeal noise often occurs in a two-stage electrohydraulic servo-valve, which is an unfavorable issue of modern hydraulic energy systems. The root causes of such noise from the servo-valve are still unclear. The objective of this paper is to explore the noise mechanism in a servo-valve excited by the pressure pulsations from the hydraulic energy system perspective. The suppressing capability of squeal noise energy is investigated by changing the pressure pulsation frequency and natural frequency of the flapper-armature assembly. The frequencies of the pressure pulsations are adjusted by setting different speeds of the hydraulic pump varying from 10,400–14,400 rpm, and two flapper-armature assemblies with different armature lengths are used in the tested hydraulic energy system. The first eight vibration mode shapes and natural frequencies of the flapper-armature assembly are obtained by numerical modal analysis using two different armature lengths. The characteristics of pressure pulsations at the pump outlet and in the chamber of the flapper-nozzle valve, armature vibration and noise are tested and compared with the natural frequencies of the flapper-armature assembly. The results reveal that the flapper-armature assembly vibrates and makes the noise with the same frequencies as the pressure pulsations inside the hydraulic energy system. Resonance appears when the frequency of the pressure pulsations coincides with the natural frequency of the flapper-armature assembly. Therefore, it can be concluded that the pressure pulsation energy from the power supply may excite the vibration of the flapper-armature assembly, which may consequently cause the squeal noise inside the servo-valve. It is verified by the numerical simulations and experiments that setting the pressure pulsation frequencies different from the natural frequencies of the flapper-armature assembly can suppress the resonance and squeal noise.

The fluid-solid interaction phenomenon in the pilot stage of flapper-nozzle servo valve and armature assembly structural stress field is the main reason of self-excited noise and instability. The cavitation phenomenon is the main source of servo valve noise and cavitation erosion. In order to study the mechanism of transient cavitation in the pilot stage of flapper-nozzle servo valve, the three-dimensional model, ICEM CFD software was used for meshing, star-ccm+ simulation software was used to simulate the cavitation and flapper movement characteristics in the flow field under the pilot stage fluid-structure interaction dynamic characteristics of the servo valve. The results show that the fluid-solid interaction of the flow field in the flapper-nozzle pilot valve can cause the periodic change of cavitation in the flow field, and the increase of inlet pressure at the nozzle and the movement of the flapper will aggravate the cavitation phenomenon. The conclusions in this paper can provide theoretical basis for the stability of servo valve and the prevention of cavitation.

To precisely control the size of monodisperse droplets for droplet microfluidics, we here establish a closed-loop control system with real-time feedback of droplet length during droplet generation. Particularly, the microvalves are integrated into the system to control the flow rates of the two immiscible fluids. From experimental measurements, we observe that the droplet length is a linear function of the flow-rate ratio for low capillary numbers (Ca ≤ 0.1). More importantly, the coefficients of the linear relation are determined by the geometry of the microchannel, and independent of the viscosity of the fluids. Based on MATLAB Simulink, the deviation between the predicted and measured droplet length is quantitatively studied. By using a PI controller, both the response speed and control accuracy of the droplet length can be greatly improved for the closed-loop control system. As a result, high monodispersity and uniformity of droplet generation can be achieved in a T-junction microdroplet generator.

The existence of undesired flow-induced phenomenon, cavitation, in the flapper–nozzle pilot valve of two-stage servo-valves is a critical issue in practical applications. Here, taking innovation on the flapper shape is one of possible approaches to reduce cavitation in the pilot valve. By means of CFD (Computational Fluid Dynamics) simulations, it has been proved by setting a simple rectangle shape as an innovative flapper shape in our previous attempt. Therefore, in this work, the effectiveness of rectangle-shaped flapper in reducing cavitation is experimentally confirmed by comparing with traditional shape and square shape. The experimental observations of cavitation phenomena in three different flapper shapes are conducted for two different flapper–nozzle null clearances (0.2 mm and 0.1 mm) under four different flow conditions with the variation of inlet pressure in the range of 3–6 MPa. To provide verification on experimental results and a comprehensive understanding, CFD simulations of cavitation phenomenon in each flapper shape are also performed. The results are qualitatively analyzed and compared. The results explain that the cavitation intensity in the flapper–nozzle pilot valve associates with the strength of the turbulent jets and it increases with the increment of flapper–nozzle null clearance and inlet pressure. According to the experimental observations and CFD simulated results, the curved surface of traditional flapper shape is attributed to the spread of turbulent jets and consequent massive cavitation. Compared to traditional shape, the square shape relatively reduces cavitation due to lack of curved boundary on the flapper. However, on the other hand, its shorter flat land and larger annulus are not much effective to control the spread of turbulent jet which is responsible for cavitation in annulus region. Compared to two other flapper shapes, the rectangle shape significantly suppresses the cavitation by attenuating the turbulent jets on its straight and relatively longer flat lands. Therefore, the effectiveness of rectangle shape in reducing cavitation in the flapper–nozzle pilot valve is confirmed in this work.

In order to comfort and protect human eyes in an environment with strong lights by using colour-changing glasses, a microfluidic system for liquid colour-changing glasses with shutter shade effect is developed in this paper. The colour-changing layer of the lens is made of polymer (PDMS) film with high optical transparency. Microfluidic channels for liquid circulating are fabricated inside the film by soft lithography technology to get a shutter shade effect on the glasses. Microfluidic channels with three different dimensions of a simple serpentine shape are fabricated and investigated. Some other personalized designs of the channels are also proposed to meet various requirements of wearers. A manual actuating way for the microfluidic system is given as an actuating example. The colour-changing response times of the glasses at different actuating pressures are calculated theoretically and measured by experiments. This microfluidic colour-changing system shows good controllability, fast response characteristics and good reversibility.