Pneumatic resistance network analysis and dimension optimization of high pressure electronic pneumatic pressure reducing valve

The structure and working principle of a self-deigned high pressure electronic pneumatic pressure reducing valve (EPPRV) with slide pilot are introduced.The resistance value formulas and the relationship between the resistance and pressure of three typical pneumatic resistances are obtained.Then,the method of static characteristics analysis only considering pneumatic resistances is proposed,the resistance network from gas supply to load is built up,and the mathematical model is derived from the flow rate formulas and flow conservation equations,with the compressibility of high pressure gas and temperature drop during the expansion considered in the model.Finally,the pilot spool displacement of 1.5 mm at an output pressure of 15MPa and the enlarging operating stroke of the pilot spool are taken as optimization targets,and the optimization is carried out based on genetic algorithm and the model mentioned above.The results show that the static characteristics of the EPPRV are significantly improved.The idea of static characteristics analysis and optimization based on pneumatic resistance network is valuable for the design of pneumatic components or system.

Simulation and experimental study of high pressure switching expansion reduction considering real gas effect

Switching expansion reduction(SER)uses a switch valve instead of the throttle valve to realize electronically controlled pressure reduction for high pressure pneumatics.A comprehensive and interactive pneumatic simulation model according to the experimental setup of SER has been built.The mathematical model considers heat exchanges,source air pressure and temperature,environmental temperatures and heat transfer coefficients variations.In addition,the compensation for real gas effect is used in the model building.The comparison between experiments and simulations of SER indicates that,to compensate the real gas effect in high pressure discharging process,the thermal capacity of air supply container in simulation should be less than the actual value.The higher the pressure range,the greater the deviation.Simulated and experimental results are highly consistent within pressure reduction ratios ranging from 1.4 to 20 and output air mass flow rates ranging from 3.5 to 132 g/s,which verifies the high adaptability of SER and the validity of the mathematic model and the compensation method.

Effect of Molecular Interactions between the Solid Wall and Liquid on the Flow Properties in Microtubes

The flow properties in microtubes, such as velocity profiles and pressure distributions, are different from those in macrotubes. We attribute this phenomenon to the molecular interactions between the solid wall and inner liquid. The apparent viscosity, which takes into consideration the molecular interactions, is introduced in the present study and the Navier-Stokes equations are solved. Water is adopted in the calculation. For the hydrophilic material wall, the water is more like to adhere to the wall. The velocity near the wall is smaller than that of conventional theory, while the centerline velocity and pressure gradients are much larger. Such a phenomenon becomes much more obvious with the decrease in tube diameter.

Dynamic Response Analysis of the Equivalent Water Depth Truncated Point of the Catenary Mooring Line

The real-time computer-controlled actuators are used to connect the truncated parts of moorings and risers in the active hybrid model testing system. This must be able to work in model-scale real time, based on feedback input from the floater motions. Thus, mooring line dynamics and damping effects are artificially simulated in real time, based on a computer-based model of the problem. In consideration of the nonlinear characteristics of the sea platform catenary mooring line, the equations of the mooring line motion are formulated by using the lumped-mass method and the dynamic response of several points on the mooring line is investigated by the time and frequency domain analysis method. The dynamic response of the representative point on the mooring line is analyzed under the condition of two different corresponding upper endpoint movements namely sine wave excitation and random wave excitation. The corresponding laws of the dynamic response between the equivalent water depth truncated points at different locations and the upper endpoint are obtained, which can provide technical support for further study of the active hybrid model test.

Control of stochastic resonance in bistable systems by using periodic signals

According to the characteristic structure of double wells in bistable systems, this paper analyses stochastic fluctuations in the single potential well and probability transitions between the two potential wells and proposes a method of controlling stochastic resonance by using a periodic signal. Results of theoretical analysis and numerical simulation show that the phenomenon of stochastic resonance happens when the time scales of the periodic signal and the noise-induced probability transitions between the two potential wells achieve stochastic synchronization. By adding a bistable system with a controllable periodic signal, fluctuations in the single potential well can be effectively controlled, thus affecting the probability transitions between the two potential wells. In this way, an effective control can be achieved which allows one to either enhance or realize stochastic resonance.

Concentric Annular Clearance-Controllable Pressure Characteristics Research of a High Pressure Pneumatic Pressure Assembly

High pressure is an important development orientation in pneumatic field,since it can not only improve dynamic characteristics of pneumatic system but also decrease the size of components and mounting space.Due to the advantages of high energy density and high instant expansibility,high pressure gas has been widely used in many applications.However,systematic researches are lacked especially in pressure characteristics which are very important in pneumatic system at present.In a high pressure pneumatic system,the pressure of a fixed cavity with annular clearance needs to be controlled within a wide range,so a single stage proportional slide valve is proposed to satisfy the requirements of high pressure and low flow rate.First,working principle and structure of the pressure assembly and the slide valve are introduced.Then mathematical model of the high pressure pneumatic system is built up;controllable pressure range is simulated,and influence of uncertain factors,such as fit clearance of the pressure valve and the cavity on controllable pressure,is discussed.Finally,a test bench of the pressure assembly is built up,and the controllable pressure and step response experiments are carried out.Both simulation and experimental results show that the designed slide valve can satisfy the requirements well.The proposed clearance presumption method based on simulation and experimental results is valuable for indirect measurement of processing tolerance.

Optimal bounded control for maximizing reliability of Duhem hysteretic systems

The optimal bounded control of stochastic-excited systems with Duhem hysteretic components for maximizing system reliability is investigated. The Duhem hysteretic force is transformed to energy-depending damping and stiffness by the energy dissipation balance technique. The controlled system is transformed to the equivalent non- hysteretic system. Stochastic averaging is then implemented to obtain the It5 stochastic equation associated with the total energy of the vibrating system, appropriate for eval- uating system responses. Dynamical programming equations for maximizing system re- liability are formulated by the dynamical programming principle. The optimal bounded control is derived from the maximization condition in the dynamical programming equation. Finally, the conditional reliability function and mean time of first-passage failure of the optimal Duhem systems are numerically solved from the Kolmogorov equations. The proposed procedure is illustrated with a representative example.

Fluctuations and dissipations in stochastic energetic resonance

By analyzing the fluctuations and dissipations of a Brownian particle colliding with the molecules in a fluid, the work exchanged between the Brownian particle constrained in a bistable potential well and an external periodic force is investigated. Characters of the stochastic energetic resonance are found and studied at different intensities of fluctuations and dissipations. The microscopic mechanism of energy exchange between the Brownian particle and the external force is revealed. The method used in this study provides a novel way of controlling the stochastic energetic resonance.

Effects of Particle Concentration on the Dynamics of a Single-Channel Sewage Pump under Low-Flow-Rate Conditions

Single-channel sewage pumps are generally used to transport solid-liquid two-phase media consisting of a fluid and solid particles due to the good non-clogging property of such devices.However,the non-axisymmetric structure of the impeller of this type of pumps generally induces flow asymmetry,oscillatory outflow during operations,and hydraulic imbalance.In severe cases,these effects can jeopardize the safety and stability of the overall pump.In the present study,such a problem is investigated in the framework of a Mixture multiphase flow method coupled with a RNG turbulence model used to determine the structure of the flow field and the related motion of transported particles.It is shown that under different inlet particle concentrations,the flow field in the pump exhibits periodic variations of the pressure.The volume fraction of solid particles at the trailing edge of the suction surface of the blade is the largest,and solid particles tend to be concentrated at the outer edge of the pump body.With a rise in import particle content,the pressure and volume fraction of particles in the sewage pump also increase;for a fixed inlet particle concentration,the pressure pulsation amplitude increases with an increase in the flow rate.In addition,under small flow conditions,as the inlet particle concentration increases,the flow field leaving the sewage pump diaphragm near the outlet of the volute becomes more turbulent,and even a secondary back-flow vortex appears.

Evaluation of the hemolysis and fluid dynamics of a ventricular assist device under the pulsatile flow condition

When the rotary blood pumps are used as ventricular assist devices,the pump flow rate will have a pulsatile component even at a constant impeller rotational speed due to the remaining beating of the natural heart.However,previous studies on the in vitro hemolysis evaluation of a rotary blood pump have always been conducted under steady states and this pulsation was not taken into account.In this study,the hemolysis in a centrifugal blood pump is evaluated under the pulsatile flow condition in vitro.The required time-varying flow rate is obtained by conducting a system simulation of the pump-assisted cardiovascular system,and realized by controlling a pulsation unit in the experiments.The results of our tests indicate a significant increase in hemolysis under the pulsatile flow condition compared with the non-pulsatile condition.To reveal the flow characteristics responsible for the higher hemolysis,transient computational fluid dynamic simulations are then performed.This study suggests that traditional hemolysis evaluation under the steady states may not fully represent the hemolytic performance in the clinical use.For the ventricular assist pumps at the design stage,eliminating the concern about the extra hemolysis under the pulsatile condition will be helpful for the subsequent in vivo experiments.

High-performance coherent population trapping clock based on laser-cooled atoms

We present a coherent population trapping clock system based on laser-cooled^(87)Rb atoms.The clock consists of a frequency-stabilized CPT interrogation laser and a cooling laser as well as a compact magneto-optical trap,a highperformance microwave synthesizer,and a signal detection system.The resonance signal in the continuous wave regime exhibits an absorption contrast of~50%.In the Ramsey interrogation method,the linewidth of the central fringe is31.25 Hz.The system achieves fractional frequency stability of 2.4×10^(-11)/(√τ),which goes down to 1.8×10^(-13)at 20000 s.The results validate that cold atom interrogation can improve the long-term frequency stability of coherent population trapping clocks and holds the potential for developing compact/miniature cold atoms clocks.

Thermal simulation and optimization design on a high-power LED spot lamp

In this paper, thermal characteristics of the high-power LED spot lamp are reported. The emphasis is placed upon optimizing design of the heat sink of LED spot lamp using the optimization module and the orthogonal-experiment method. Results demonstrate that the weight of the heat sink is decreased to 46.1% of that for the initial structure, and the influence of each factor on junction temperature and weight of the heat sink is acquired by range analysis. Finally, the influence of ambient temperature and natural convection coefficient on the LED maximum temperature is analyzed. The results and the optimizing methodology are of great importance to the thermal design of LED lamps.

Fluid Dynamics of Flapping Insect Wing in Ground Effect

The fluid dynamics of flapping insect wing in ground effect is investigated numerically in this study. To model the insect wing cross-section in forward-flight mode, the laminar flow over a NACA0012 airfoil animated by a combination of harmonic plunge and pitch rotation is considered. To implement the simulation, the proposed immersed boundary-lattice Boltzmann method is employed. By fixing the Reynolds number and the amplitude of motion, we systematically examine the influences of the distance between the foil and the ground and the flapping frequency on the flow behaviors. As compared to the situation out of ground effect, the forces for foil placed in close proximity to the ground show some differences. The mean drag coefficient is increased at low frequency and decreased at high frequency. Meanwhile, the mean lift coefficient is increased at both low and high frequencies and decreased at middle frequency. Moreover, an interesting phenomenon with oblate vortices due to vortex interaction with the ground is observed.

Study of Polytropic Exponent Based on High Pressure Switching Expansion Reduction

Switching expansion reduction(SER) uses a switch valve to substitute the throttle valve to reduce pressure for high pressure pneumatics.The experiments indicate that the simulation model well predicts the actual characteristics.The heat transfers and polytropic exponents of the air in expansion tank and supply tanks of SER have been studied on the basis of the experiments and the simulation model.Through the mathematical reasoning in this paper,the polytropic exponent can be calculated by the air mass,heat,and work exchanges of the pneumatic container.For the air in a constant volume tank,when the heat-absorption is large enough to raise air temperature in discharging process,the polytropic exponent is less than 1;when the air is experiencing a discharging and heat-releasing process,the polytropic exponent exceeds the specific heat ratio(the value of 1.4).

Progress in fundamental research on thermal desorption remediation of organic compound-contaminated soil

Thermal desorption(TD)is a mainstream technology for the remediation of organic compound-contaminated soil.By reviewing the domestic and foreign research on the remediation of organic compound-contaminated soil by TD,this paper systematically introduces the principle,characteristics,and classification of TD.The impact of key operating parameters(such as heating temperature and heating time),certain physical and chemical properties(such as soil texture,moisture content),and external conditions(such as additives and the carrier gas)on the TD process is summarized.Next,pollutants’migration and their transformation processes,as well as the laws governing the TD process,are briefly described.Finally,the prospects of TD,in terms of its future research and development directions,are described,with the aim of providing references for the application and promotion of TD.

Study on the relationship between waste classification,combustion condition and dioxin emission from waste incineration

Domestic waste in China is mainly collected as a combination of different types of materials.The components are variable and complex,with very different combustion characteristics making it difficult to optimize the burning to reduce pollution.There are still some controversies about the accuracy of using carbon monoxide(CO)emission to characterize waste incineration performance.Here,we investigated the relationship between waste classification,incineration conditions and dioxin emission and concluded that the concentration of CO in flue gas could not be used as the only criterion of combustion efficiency and safety.Considering the close relationship between the formation of polychlorinated dibenzo-p-dioxins and dibenzofurans(PCDD/Fs)and products of incomplete combustion,the relatively low concentrations of CO are not a reliable indicator that an incinerator equipped with an activated carbon injection system and fabric filter could achieve the national standards for PCDD/F emission.The goal,therefore,is not only to lower the emission of PCDD/Fs and other pollutants through clas-sifying the waste components at the source,but also to reduce the need for the treatment of incinerated waste to protect the environment and to increase the power generation efficiency of municipal solid waste incineration(MSWI)plants.As the demand for waste disposal continues to rapidly increase,the need for a safe waste incineration system with dioxin emission controls makes the classification of waste an indispensable part of future MSWI systems.

Compensation of Pressure Enthalpy Effects on Temperature Fields for Throttling of High-Pressure Real Gas

For the pressure enthalpy of high pressure pneumatics, the computational fluid dynamics(CFD)simulation based on ideal gas assumption fails to obtain the real temperature information. Therefore, we propose a method to compensate the pressure enthalpy of throttling for CFD simulation based on ideal gas assumption.Firstly, the pressure enthalpy is calculated for the pressure range of 0.101 to 30 MPa and the temperature range of 190 to 298 K based on Soave-Redlich-Kwong(S-R-K) equation. Then, a polynomial fitting equation is applied to practical application in the above mentioned range. The basic idea of the compensation method is to convert the pressure enthalpy difference between inlet air and nodes into the compensation temperature. In the above temperature and pressure range, the compensated temperature is close to the real one, and the relative temperature drop error is below 10%. This error is mainly caused by the velocity difference of the orifice between the real and ideal gas models. Finally, this compensation method performs an icing analysis for practical high pressure slide pilot valve.

Orientation of the fiber suspending in the flow through a tube containing a sphere

Fiber suspensions flow through a tube containing a sphere in the dilute and concentrated regimes is simulated numerically with the Lattice Boltzmann Method （LBM）. The numerical results of fiber orientation distribution based on a statistical scheme are obtained and agree qualitatively with the experimental ones for the flow through a parallel plate channel comaining a cylinder. The results show that the sphere in the tube results in a change in the fiber orientation distribution downstream of the sphere along the flow and transverse directions. The influences of the sphere on the fiber orientation distribution are more significant for the concentrated suspensions than for the dilute one. The effect of the initial fiber orientations on the fiber orientation distribution is significant upstream of the sphere but small downstream of the sphere.

Review of low-temperature plasma nitrogen fixation technology

Nitrogen fixation is essential for all forms of life,as nitrogen is required to biosynthesize fundamental building blocks of creatures,plants,and other life forms.As the main method of artificial nitrogen fixation,Haber–Bosch process(ammonia synthesis)has been supporting the agriculture and chemical industries since the 1910s.However,the disadvantages inherent to the Haber–Bosch process,such as high energy consumption and high emissions,cannot be ignored.Therefore,developing a green nitrogen fixation process has always been a research hotspot.Among the various technologies,plasma-assisted nitrogen fixation technology is very promising due to its small scale,mild reaction conditions,and flexible parameters.In the present work,the basic principles of plasma nitrogen fixation technology and its associated research progress are reviewed.The production efficiency of various plasmas is summarized and compared.Eventually,the prospect of nitrogen fixation using low-temperature plasma in the future was proposed.

The method to control the submarine horseshoe vortex by breaking the vortex core

The quality of the inflow across the propeller is closely related with the hydrodynamic performance and the noise characteristics of the propeller. For a submarine, with a horseshoe vortex generated at the junction of the main body and the appendages, the submarine wake is dominated by a kind of highly non-uniform flow field, which has an adverse effect on the performance of the submarine propeller. In order to control the horseshoe vortex and improve the quality of the submarine wake, the flow field around a submarine model is simulated by the detached eddies simulation （DES） method, and the vortex configuration is displayed using the second invariant of the velocity derivative tensor. The state and the transition process of the horseshoe vortex are analyzed, then a modified method to break the vortex core by a vortex baffle is proposed. The flow numerical simulation is carried out to study the effect of this method. Numerical simulations show that, with the breakdown of the vortex core, many unstable vortices are shed and the energy of the horseshoe vortex is dissipated quickly, and the uniformity of the submarine wake is improved. The submarine wake test in a wind tunnel has verified the effect of the method to control the horseshoe vortex. The vortex baffle can improve the wake uniformity in cases of high Reynolds numbers as well, and it does not have adverse effects on the maneuverability and the speed ability of the submarine.