Steady Working Conditions Research Articles

Dynamic analysis for ultra-supercritical boiler water wall considering uneven heat flux distribution and combustion instability

The dynamic characteristics of water-cooled wall are of great significance to the evaluation of the safety and flexibility for the boiler during peak shaving process. However, few dynamic studies considered the uneven heat flux distribution on the water-cooled wall, let alone the variable heat load caused by the combustion instability. In this paper, a segmented dynamic model is developed for the water-cooled wall of a 660 MW ultra supercritical boiler. The model is validated under steady and dynamic working conditions, respectively. Then, the step responses of the steam temperature in different flow loops under different load conditions are comparatively studied under the disturbances of single-parameter changes. In the cases of 10 % step decrease of either the feedwater temperature, the heat load or the feedwater mass flowrate, the outlet steam temperature is influenced greatly by the step decreased feedwater temperature under 100 % BMCR condition, while it is impacted most by the step decreased feedwater mass flow under 50 % THA condition. Under these disturbances, the outlet steam temperature of the tube with higher heat loads has larger variation and longer response time. In addition, the simulated combustion instability by the sinusoidal fluctuating heat load on the water wall is employed to explore the influences of the flame fluctuation amplitude and frequency to the water wall. The maximum steam temperature rises with the increase in amplitude but drops with the frequency of flame fluctuation. The thresholds for the flame fluctuation amplitude and frequency are obtained under different load conditions.

Digital twin for zinc roaster furnace based on knowledge-guided variable-mass thermodynamics: Modeling and application

Roaster furnace is a large-scale equipment in zinc smelting process, which plays an significant role in safety production and enviromental protection. An accurate digital twin of roaster furnace can help to explore the influence of control parameters and serve as a test platform to verify the effectiveness of control strategies. However, the traditional thermodynamics cannot be used for dynamic modeling, and inability to measure key data greatly affects the accuracy of kinetic modeling. Therefore, this paper establishes a novel digital twin of zinc roaster furnace based on knowledge-guided variable-mass thermodynamics. First, based on the integration of mechanism analysis for mass balance and energy balance, a dynamic modeling method is proposed. Then, particle swarm optimization (PSO) algorithm is introduced to optimize the parameters of conversion rates guided by knowledge. Finally, by connecting the dynamic model with distributed control system (DCS) through OPC communication protocol, a digital twin of roaster furnace is constructed. Extensive experiments show that the simulation results of the digital twin roughly agree with the actual industrial data under steady and dynamic working conditions, and the application of the digital twin on the performance analysis of control parameters and testing of control strategies can provide guidance for the optimal control of roaster furnace.

Intelligent Dynamic Test System for Vehicle Engine Based on 5G Internet of Things

With the development of the automobile industry, the improvement of the reliability test level and the intelligent fault diagnosis level of the engine, as the heart component of the automobile and the assembly with the highest failure rate, becomes more and more important. In a context where technology is being upgraded, the development of intelligent automotive engine inspection system based on IoT thinking is set to become the major trend in the future. The objective of this article would be to have better knowledge about smart car engine system in the 5G IoT era. It is also through the study, a dynamic testing and characterization of the engine. The performance of the automobile engine, especially the dynamic performance, is further optimized. In this article, we focus on the PUMAOPEN test system of AVL and the system under test, the state management of the test process, and the intelligent transformation of key components. The results show that: studies and analyses the dynamic working conditions of intelligent vehicles on the Internet of Things, and compares the dynamic working conditions with the steady working conditions from qualitative to quantitative. By analyzing the influence of throttle opening change rate and speed change rate on dynamic performance and engine dynamic torque estimation, the fast sensing and response-ability in the engine testing process is improved. When the engine is accelerated by the experimental method presented in this article, and when the throttle opening is more than 30% and the engine speed varies at 100 and 200 rpm/s, the output value of the torque is higher than the output value of the steady-state torque or has little difference with the output value of the steady-state torque, and tends to be stable. In deceleration performance, the dynamic output torque of the engine is asymmetric. And it will deviate from the steady-state output torque, showing different dynamic response characteristics in different working sections. Throttle delay, overshoot characteristics, mechanical inertia, inflation coefficient, air–fuel ratio, and ignition advance angle when engine speed changes sharply will make engine dynamic characteristics deviate from steady-state characteristics.

Comparison of Different Topologies of Thermal Management Subsystems in Multi-Stack Fuel Cell Systems

The performance of a fuel cell stack is affected by the operating temperature of the stack. The thermal management subsystem of a multi-stack fuel cell system (MFCS) is particularly significant for the operating temperature control of each stack in the MFCS. To study the influence of different topologies of a MFCS thermal management subsystem, this paper proposes and establishes two different topologies. Firstly, the integrated topology is proposed. Secondly, seven component models, namely the mixer, thermostat, radiator, tank, pump, bypass value, and proton exchange membrane fuel cell stack temperature models, are described in detail. Finally, the performance of the two topologies of the MFCS thermal management subsystem under two working conditions, steady (200 A) and variable (China heavy-duty commercial test cycle, C-WTVC), is compared. Furthermore, there are two evaluating indicators, including the stability duration and deviation of the operating temperatures of the single stack in the MFCS. Results show that when the MFCS operates under steady working conditions, the integrated topology is superior in operating temperature control accuracy (ΔT<0.5 K), while the distributed topology is superior in the adjustment process (t ≤ 100 s). Moreover, when the MFCS operates under variable working conditions, the distributed topology is superior in operating temperature control accuracy.

Research on a China 6b heavy-duty diesel vehicle real-world engine out NOx emission deterioration and ambient correction using big data approach.

China VI standard proposed higher requirements for durability of heavy-duty diesel vehicles emissions. Previous research which took advantages of both on-board sensors and big data approach to get the NOx deterioration factor was rather scarce. This paper used big data approach to study the deterioration of engine out NOx emission based on 254,622 km operation data getting from the on-board sensors or ECUs (Electronic Control Unit). Meanwhile, a formula for on-board NOx correction for ambient humidity and temperature had been fitted. The analyses revealed that the engine out NOx deterioration factor (DF) of the maximum weight steady-state condition was about 1.005 after 254,622 km durability test; as for transient conditions, the DF was not more than 1.092 during 254,622 km durability test. For a same steady working condition, the engine out NOx mass flow (g/h) was negatively linearly correlated with absolute humidity (Ha) (R2 = 0.997). If Ha was lower than 12 g/kg, Ha almost had no effect on engine out NOx concentration (ppm). Otherwise, there was also a negatively linear relationship between them (R2 = 0.978). It is hoped that the methods and conclusions of this paper could provide some enlightenment for future NOx emission deterioration research.

Study on the Thermal-Electrical Balance of the kW-zclass SOFC Stack

Heat and electricity are deeply coupled in solid oxide fuel cell (SOFC) stacks, and the balance and control between them are vital to the steady working condition and outputs. Therefore, studying the balance mechanism of heat and electricity is important to achieve the safe and stable operation of the SOFC stacks. In this paper, a semi-empirical simulation model of a kilowatt-level SOFC stack was established. Based on this model, the effects of different operating temperatures, flow rates, air to H2 ratios (AHR), and steam to carbon (S/C) ratios on the thermoelectric balance state of the SOFC stack were analyzed. Results show that the I-V curve can be separated into three parts: unbalance zone, unsustainable zone, and the self-heat balance zone by the self-heat balance voltage (SHBV) and the critical voltage (CV). The approximate voltage scope of the balance zone under different conditions is 0.6~0.9 V.

Fatigue Life Prediction of a Pump Turbine Runner

The working environment of the runner of a hydro-turbine unit is complex, and it is subjected to relatively large and variable water pressure. Fatigue cracks may occur after a long period of work, and even cause the runner to lose its working ability. The fatigue crack problem of hydraulic turbines should be paid attention to. This paper introduces the nominal stress method which is often used to analyse the fatigue life of a hydraulic turbine unit. Modelling and numerical calculation are carried out for a pump turbine unit. Stress concentration points and load spectra are calculated for different working conditions of the turbine. The load spectra are processed by rain flow counting method. The fatigue life of the runner under different working conditions is carried out by Miner criterion. The results show that the fatigue life of the unit tends to be infinite under steady working conditions, and the fatigue life under variable working conditions is far less than that under steady working conditions. Therefore, from the point of view of fatigue life, the working process under variable working conditions should be minimized to improve the service life of the unit.

Effect of the MoSi2 coating on operational reliability of bipropellant rocket engine

This present study investigated the MoSi2 coating and its effect on reliability of bipropellant rocket engine. This coating is developed to protect the chamber substrate material form oxidization under hightemperature oxidative circumstance as bipropellant engine works. The multilayer structure of the MoSi2 coating shows excellent high-temperature and thermal-cycle resistance. Its characteristic of self-healing leads to the good performance under the long-time steady working condition for rocket engines. A 25000-seconds firing test was conducted to testify the performance of MoSi2 coating under high temperature above 1400℃. In addition, the influence of coating surface morphology on liquid film cooling was fully discussed in experiment and simulation. High-speed microscopy camera was used to study the effects of Weber number on the spreading and lasting of cooling liquid-film. the simulative comparison was conducted by OpenFOAM to present different transfer-heat modes, when a droplet impinges on the high-temperature surface of MoSi2 coating. All results show that higher smoothness of the coating is suitable for liquid-film cooling, strengthening liquid film spread and heat transfer. Moreover, scanning electron microscope (SEM) was used to study the effect of Mo layer residue on the coating thermal-cycle profermance. The test results indicates that Mo layer residue significantly cause penetrating cracks of the coating and then weaken the self-healing of the coating at downstream of throat. Therefore, it is important to strictly control the thickness of Mo layer by means of matching Mo target in ion plating. Thus after properly prolonging the infiltration time, Mo layer can be silicified completely without residue.

Identification of the Wear Margin of a Pipeline–Machine Subsystem

The quality of company asset management is significantly dependent on the quality of a system for asset wear margin identification. A pipeline–machine subsystem may be an essential part of assets in many production companies. It is necessary to build models of pipeline–machine subsystems and models of a system for the identification of subsystem wear margin. The method used consists of a decomposition of desired characteristics of an enterprise into desired characteristics of a pipeline–machine subsystem. Methods for the identification of real characteristics of a subsystem depend on the character of subsystem operation. In this study, hydrodynamic and thermodynamic models of the subsystem are built. Tests are conducted on industrial and laboratory objects. The boundaries of the subsystem are defined and changes in pressure, temperature and mass flow rate in the pipeline are presented. Causes of changes in the mentioned quantities are described. Desired characteristics of the subsystem resulting from decomposition are described. The presented methods of determining efficiency for steady working conditions and open flow use hydrodynamic and thermodynamic models. Energy efficiency of the subsystem is decomposed into efficiencies of main elements of the subsystem. A method is proposed for determining the subsystem’s energy efficiency in the case of the flow into a closed vessel. It is possible to determine the hydraulic efficiency of the subsystem components: the suction pipe, the discharge pipe and the machine. The efficiency of the machine determined by the hydrodynamic method is complementary to the efficiency obtained by the thermodynamic method. The machine set efficiency is composed of hydraulic efficiency of the machine; mechanical efficiency of the machine, the gearbox and motor; and electric efficiency of the motor. Hydraulic efficiency of the pipeline is related to substitute measure of wear margin—the coefficient of resistance. Pressure drop is a diagnostic symptom. Thermal efficiency of the heat exchanger is related to a substitute measure of wear margin—the coefficient of heat penetration. Temperatures and mass flow rate in the heat exchanger are diagnostic symptoms. It is possible to determine the capacity and efficiency of subsystems with one side closed—such as those filling hydrophore and gas vessels.

Viscoelasticity of Rubber Springs Affects Vibration Characteristics of a Flip-Flow Screen With the High G Value

With the high G value of vibration, outstanding sieving behaviors of a flip-flow screen are more likely to appear, but structural damages are aggravated under the high amplitude vibration. Considering rubber springs role on the vibration energy dissipation, viscoelasticity of rubber springs (i.e., shear springs and vibration isolation springs), is noticed to deal with the above contradiction. However, when rubber springs experience large amplitude vibration, viscoelastic responses influence more on the amount of damping than in the linear (i.e., small amplitude) vibration regime, as the frequency dependence of rubber springs is noteworthy. For this purpose, the Generalized Maxwell model is used to depict the frequency dependence of rubber springs and the practical damping is converted to a series damping parameters of the system, numerical models of the flip-flow screen under startup and shutdown modes and steady working conditions are proposed and verified firstly. Secondly, in order to explore kinetics responses of the elastic screen panel under different rubber springs damping coefficients, nonlinear finite element model of which is established. Finally, effects of rubber springs nonlinear damping on screen frames vibrations and screen panels nonlinear responses are studied. Results indicate that hysteretic damping of rubber springs can effectively solve the conflict between vibration strength and structural reliability of the flip-flow screen, since the low sensitivities of maximum stresses and the high sensitivities of accelerations to rubber springs damping are found.

On the steady posture of conical spindle distribution used in ball piston pump

Conical spindle distribution is a new type of hydraulic pump distribution, its steady working conditions refer to a stable position of the shaft and lubrication state under constant operating condition, which directly influences the hydraulic pump efficient and reliable work. In this paper, the Reynolds equation of the tapered flow field is used to establish the lubrication model. The static pressure boundary condition of the distribution pair is obtained by the hydraulic resistance network method. The finite difference method is employed to solve the model. The static and dynamic lubricating performances including the shaft eccentricity and the distribution gap height are obtained by solving the model with a numerical method. Accordingly, the influences of structural parameters and operating parameters on the steady state are investigated, and an experimental test rig is built to validate the model. The experimental results show that the model can predict the higher working pressure which leads to higher distribution gap and eccentricity; the higher the rotational speed is, the smaller the distribution gap and the eccentricity will become, which provides theoretical support for further guidance of the distribution design.

Research on FSI Analyses of Blade Cascade Structural Strength of Hydraulic Retarder

To solve the strength problems of blade cascade of high-power hydraulic retarder used on special vehicles, a numerical simulation is calculated to get the pressure distribution under steady working condition based on 3-D flow field theory. And the finite element model of hydraulic retarder cascade is established. Based on the one-way fluid solid interaction theory and globally conservative interpolation algorithm, the fluid pressure load from flow field mesh nodes is successfully convert to structure mesh nodes. The centrifugal force is applied on the rotating rotor. Then the equivalent stress and the total deformation distribution are obtained. The results shows that the strength analysis model is accurately and reliable, and it is an effective method for the finite element analysis of blade wheels of hydraulic component.

Sawdust-Derived Biochar Much Mitigates VFAs Accumulation and Improves Microbial Activities To Enhance Methane Production in Thermophilic Anaerobic Digestion

Sawdust-derived biochar (SDBC) was added to an anaerobic digester at 15g/L for thermophilic codigestion under semicontinuous operation for more than 130 days. With a stepwise increase of organic loading rate (OLR) from 1.6 to 5.4 gVS/L·d–1, steady CH4 yields achieved between 462.3 and 500.1 mL/gVS. In contrast, for the control digester (without biochar addition) and another digester added with sewage sludge-derived biochar (SSBC), a steady working condition could only be maintained for about 80 days with OLR and CH4 yields up to 2.7 gVS/L·d–1 and 322.3–337.9 mL/gVS, respectively. The total volatile fatty acids (VFAs) accumulation up to about 30gCOD/L tended to be the threshold to restrain steady CH4 production, but this occurred much earlier for the control and SSBC digesters at much lower OLR. By batch experiments of digestion in a methanogenesis inhibition condition and with propionate or butyrate as the sole substrate, it was found that with SDBC addition, the substrate was oxidized steadily in the 40-...

Working Mechanism of Nonresonance Friction in Driving Linear Piezoelectric Motors with Rigid Shaking Beam

A kind of nonresonance shaking beam motors is proposed with the advantages of simple structure, easy processing, and low cost due to its wide application prospects in precision positioning technology and precision instruments. The normal vibration model between the stator and slider is divided into contact and noncontact types to investigate the nonresonance friction drive principle for this motor. The microscopic kinematics model for stator protruding section and the interface friction model for motor systems during both operating stages are established. Accordingly, the trajectory of the stator protruding section consists of two different elliptical motions, which differ from those of resonance-type motors. The output characteristic of the nonresonance shaking beam motor is proposed under steady working conditions with reference to the research method of standing-wave-type ultrasonic motors. Numerical analysis is used to simulate the normal vibration and mechanical output characteristics of the motor. Experimental and theoretical data fitting validates the numerical analysis results and allows the future optimization of nonresonance-type motors.

Transient vibration analysis of unit-plant structure for hydropower station in sudden load increasing process

Abstract The vibration problem of hydraulic generating unit and plant structures in hydropower station influenced mainly by pressure fluctuation of draft tube and other factors during the transient process is dramatic, whereas the relevant theoretical research is seriously lagged behind the actual engineering practice. Aiming at this present condition, firstly, a mathematical expression of hydraulic excitation induced by draft tube vortex under different load conditions is proposed from the perspective of theoretical analysis. Then, based on the hydraulic-mechanical-electrical-structural model of hydroelectric generation system established previously, the sudden load increasing transition process is incorporated into the investigation system of unit-plant structure vibration, and the corresponding dynamic characteristics under this non-stable operation condition are studied. The calculation results show that, compared with steady working condition, the operation stability of unit shaft system is decreased and the matching vibration amplitude is obviously increased during the transient process. Meanwhile, in contract to the unit shaft system, the oscillation phenomenon of generator floor in hydropower plant is more significant. In particular, the vertical direction vibration is extremely prominent that the displacement amplification can even reach several times of that when the system is operated stably. The research in this paper can not only reflect the vibration behavior of unit-plant structure in sudden load-up process to some extent, but also provide reasonable and reliable analysis model and method for dynamic response exploration, stability investigation, as well as fault diagnosis for the hydraulic generating unit and hydropower plant structures.

Parameter optimization of PEMFC stack under steady working condition using orthogonal experimental design

Operating parameters have a huge impact on the output characteristics of a proton exchange membrane fuel cell stack. In this study, to optimize the performance of proton exchange membrane fuel cell stack, 4 sets of operating parameters, which include working temperature, cathode stoichiometric, relative humidity, and backpressure, were optimized by means of the orthogonal experimental design. The experiment was developed with the help of 4-factor and 3-level orthogonal table. Nine orthogonal experiments were performed, and the polarization curve, local current density distribution, and electrochemical impedance spectroscopy of each experiment were obtained. It is observed that cathode stoichiometric and working temperature have much stronger effects on the output voltage and output consistency of stack than that of relative humidity and backpressure. Using comprehensive equilibrium method, the optimized combination of each parameter was achieved as follows: the working temperature was 75°C, cathode stoichiometric was 2.5, relative humidity was 50%, and backpressure was 1 bar. The on-site test result showed that when the cathode stoichiometric was low, and some part of the stack would be in a starvation condition and when the temperature was low, it might cause mass transfer problems.

Cooling-capacity characteristics of Helium-4 JT cryocoolers

Cooling capacity of a Helium-4 JT cryocooler may be achieved at a temperature higher than liquid helium temperature. The latent cooling capacity, which should be obtained at liquid helium temperature, is defined as a special part of cooling capacity. With the thermodynamic analysis on steady working conditions of a Helium-4 JT cryocooler, its cooling capacity and temperature characteristics are presented systematically. The effects of precooling temperature and high pressure on the cooling capacity and latent cooling capacity are illustrated. Furthermore, the JT cryocoolers using hydrogen and neon as the working fluids are also discussed. It is shown that helium JT cryocooler has a special cooling capacity characteristic which does not exist in JT cryocoolers using other pure working fluids.

Performances of an ORC power unit for Waste Heat Recovery on Heavy Duty Engine

Reciprocating internal combustion engines (ICE) are still the most used in the sector of the on-the-road transportation, both for passengers and freight. CO2 reduction is the actual technological driver, considering the worldwide greenhouse reduction targets committed by most governments. In ICE more than one third of the fuel energy used is rejected to the environment as thermal waste through the exhaust gases. Therefore, a greater fuel economy could be achieved, if this energy was recovered and converted into useful mechanical or electrical power. This recovery appears very interesting, in particular for those engines that run at almost steady working conditions, like marine, agricultural, industrial or long-hauling vehicle applications.In this paper, an ORC-based power unit was tested on a heavy duty diesel engine. Energetic and exergetic analyses have been carried out in order to assess the real performances of the ORC unit and to individuate differences with the theoretical ones. A single stage impulse axial turbine has been tested in this work, complete with an electric variable speed generator and an AC/DC converter. The tests demonstrated that the energy conversion chain is not negligible at all and an overall net efficiency of the power unit was around 2-3 % with respect to a 10% of thermodynamic efficiency.

Modeling and simulation of a counter-rotating turbine system for underwater vehicles

The structure of a counter-rotating turbine of an underwater vehicle is designed by adding the counter-rotating second-stage turbine disk after the conventional single-stage turbine. The available kinetic energy and the absorption power of the auxiliary system are calculated at different working conditions, and the results show that the power of the main engine and auxiliary system at the counter-rotating turbine system matches well with each other. The experimental simulation of the lubricating oil loop, fuel loop, and seawater loop are completed right before the technology scheme of the counter-rotating turbine system is proposed. The simulation results indicate that the hydraulic transmission system can satisfy the requirements for an underwater vehicle running at a steady sailing or variable working conditions.

Formaldehyde gas sensor based on TiO2 thin membrane integrated with nano silicon structure

An innovative formaldehyde gas sensor based on thin membrane type metal oxide of TiO2 layer was designed and fabricated. This sensor under ultraviolet (UV) light emitting diode (LED) illumination exhibits a higher response to formaldehyde than that without UV illumination at low temperature. The sensitivities of the sensor under steady working condition were calculated for different gas concentrations. The sensitivity to formaldehyde of 7.14 mg/m3 is about 15.91 under UV illumination with response time of 580 s and recovery time of 500 s. The device was fabricated through micro-electro-mechanical system (MEMS) processing technology. First, plasma immersion ion implantation (PIII) was adopted to form black polysilicon, then a nanoscale TiO2 membrane with thickness of 53 nm was deposited by DC reactive magnetron sputtering to obtain the sensing layer. By such fabrication approaches, the nanoscale polysilicon presents continuous rough surface with thickness of 50 nm, which could improve the porosity of the sensing membrane. The fabrication process can be mass-produced for the MEMS process compatibility.