Flow characteristics and Shannon entropy analysis of dense-phase pneumatic conveying under high pressure

Experiments of dense-phase pneumatic conveying of pulverized coal using nitrogen are carded out in an experimental test facility with the conveying pressure up to 4. 0 MPa and the gas-solid ratio up to 450 kg/m^3. The influences of different conveying differential pressures, coal moisture contents, gas volume flow rates and superficial velocities on the solid-gas ratios are investigated. Shannon entropy analysis of pressure fluctuation time series is developed to reveal the flow characteristics. Through investigation of the distribution of the Shannon entropy under different conditions, the flow stability and the evolutional tendency of the Shannon entropy in different regimes and regime transition processes are discovered, and the relationship between the Shannon entropy and the flow regimes is also established. The results indicate that the solid-gas ratio and the Shannon entropy rise with the increase in conveying differential pressure. The solid-gas ratio and the Shannon entropy reveal preferable regularity with gas volume flow rates. The Shannon entropy is different for different flow regimes, and can be used to identify the flow regimes. Both mass flow rate and the Shannon entropy decrease with the increase in moisture contents. The Shannon entropy analysis is a feasible approach for researching the characteristics of flow regimes, flow stability and flow regime transitions in dense-phase pneumatic conveying under high pressure.

Real Gas Effects on Charging and Discharging Processes of High Pressure Pneumatics

The high pressure pneumatic system has been applied to special industries. It may cause errors when we analyze high pressure pneumatics under ideal gas assumption. However, the real gas effect on the performances of high pressure pneumatics is seldom investigated. In this paper, the real gas effects on air enthalpy and internal energy are estimated firstly to study the real gas effect on the energy conversion. Under ideal gas assumption, enthalpy and internal energy are solely related to air temperature. The estimation result indicates that the pressure enthalpy and pressure internal energy of real pneumatic air obviously decrease the values of enthalpy and internal energy for high pressure pneumatics, and the values of pressure enthalpy and pressure internal energy are close. Based on the relationship among pressure, enthalpy and internal energy, the real gas effects on charging and discharging processes of high pressure pneumatics are estimated, which indicates that the real gas effect accelerates the temperature and pressure decreasing rates during discharging process, and decelerates their increasing rates during charging process. According to the above analysis, and for the inconvenience in building the simulation model for real gas and the difficulty of measuring the detail thermal capacities of pneumatics, a method to compensate the real gas effect under ideal gas assumption is proposed by modulating the thermal capacity of the pneumatic container in simulation. The experiments of switching expansion reduction （SER） for high pressure pneumatics are used to verify this compensating method. SER includes the discharging process of supply tanks and the charging process of expansion tank. The simulated and experimental results of SER are highly consistent. The proposed compensation method provides a convenient way to obtain more realistic simulation results for high pressure pneumatics.

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.

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.

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.

Development of a Novel Parallel-spool Pilot Operated High-pressure Solenoid Valve with High Flow Rate and High Speed

High-pressure solenoid valve with high flow rate and high speed is a key component in an underwater driving system.However,traditional single spool pilot operated valve cannot meet the demands of both high flow rate and high speed simultaneously.A new structure for a high pressure solenoid valve is needed to meet the demand of the underwater driving system.A novel parallel-spool pilot operated high-pressure solenoid valve is proposed to overcome the drawback of the current single spool design.Mathematical models of the opening process and flow rate of the valve are established.Opening response time of the valve is subdivided into 4 parts to analyze the properties of the opening response.Corresponding formulas to solve 4 parts of the response time are derived.Key factors that influence the opening response time are analyzed.According to the mathematical model of the valve,a simulation of the opening process is carried out by MATLAB.Parameters are chosen based on theoretical analysis to design the test prototype of the new type of valve.Opening response time of the designed valve is tested by verifying response of the current in the coil and displacement of the main valve spool.The experimental results are in agreement with the simulated results,therefore the validity of the theoretical analysis is verified.Experimental opening response time of the valve is 48.3 ms at working pressure of 10 MPa.The flow capacity test shows that the largest effective area is 126 mm2 and the largest air flow rate is 2320 L/s.According to the result of the load driving test,the valve can meet the demands of the driving system.The proposed valve with parallel spools provides a new method for the design of a high-pressure valve with fast response and large flow rate.

Experimental study on dense-phase pneumatic conveying of coal powder at high pressures

Clean utilization and conversion of coal resources is significant to China’s energy sustainable development.Entrained-flow coal gasification technology is an important method used for clean and efficient conversion of coal.The characteristics and stability of high-pressure dense-phase pneumatic conveying of pulverized coal is crucial to the safe and stable operation of dry-feed entrained-flow coal gasifiers.Dense-phase pneumatic conveying experiments were carried out using a high-volatile bituminous coal in pipes with diameters of 25,15 and 10 mm,respectively,and at back pressures of 1.0-4.0 MPag.The conveying characteristics and effects of operating and structure parameters were studied.Pressure drop models were established for horizontal and vertical upward conveying.The prediction uncertainty was within±30%for the horizontal conveying and±20%for the vertical upward conveying.The relative standard deviation of solid flow rate was proposed to explain conveying stability.The effect of operating parameters on conveying stability was systematically analyzed.The gas velocity-related criterion was proposed for stable conveying.

高压气动压力伺服系统的鲁棒控制

高压气动压力伺服系统的参数不确定性和未建模动态制约了其控制精度的提高,针对此提出了基于RISE的自适应鲁棒控制算法用于高压气动压力伺服系统的控制。考虑到核心元件高压电气伺服阀的控制性能对高压气动压力伺服系统高精度控制的影响,设计了交叉对比实验,实验结果表明,伺服阀位置控制算法有助于避免正弦信号失真、减小稳态压力抖动,系统压力控制算法能提高系统的响应速度和动态跟踪能力。

高压气动装置弹射性能分析及优化

根据高压气动弹射装置的工作原理和特点,结合实际应用给出了无缓冲腔、采用缓冲腔、采用多组高速开关阀等3种弹射装置方案,基于气体动力学理论,采用分段建模的方式,构建了内弹道方程组,计算分析了弹射装置主要参数对弹射体出筒速度、弹射过程最大瞬时过载等的影响。仿真结果表明,采用缓冲腔、采用多组高速开关阀2种方案的弹射装置均可有效降低弹射体的最大瞬时过载、提高出筒速度,且采用多组高速开关阀的效果最好。研究结果可为高压气动弹射装置的优化设计、制造与试验,提供借签。

高压气动减压阀内部湿空气凝结特性

针对高压气动减压阀内部结露结冰的现象,建立高压湿空气凝结流动数学模型,开展高压气动减压阀内部结露机理研究。以湿空气和液滴为流动介质,采用湿蒸汽凝结理论和多组分运输模型,通过C语言和Fluent-UDF编程开发了高压超音速湿空气凝结流动数值模型,搭建实验平台进行数值模型验证。利用该数值模型对高压气动减压阀内部湿空气凝结流动特性进行仿真,并分析了高压超音速流动过程中湿空气的流动凝结行为。结果表明:高压压缩气体流经节流阀口为绝热等熵过程,产生焦耳-汤姆逊正效应,气体体积迅速膨胀,压力和温度急剧下降,流速达到超音速流动;阀口附近下游区域大量成核,液滴快速增长,形成主要凝结区。高压湿空气凝结流动模型可为高压减压阀结构优化及进一步结冰机理研究提供参考。

无杆式高压气动弹射器弹射性能参数灵敏度分析

通过对参数进行影响规律及灵敏度分析,得到某无杆式高压气动弹射器弹射性能关键参数的优化计算参考。基于真实气体的热力学参数和动力学理论,建立了精确内弹道模型;并与弹射试验数据、流体仿真曲线进行比较分析,得到相对正确的理论计算模型;利用全局灵敏度法进行分析,得到了内弹道稳定性及离轨速度的7个主要参数影响规律及参数的线性主效应、二阶效应结果。影响内弹道稳定性的最灵敏参数为高压室容积,影响离轨速度的最灵敏参数为环境温度;泄漏率倍数及开阀时间自身的二阶主效应及与其余5个影响因素的二阶交互效应敏感度比较低,可以在设计中提前决定这2项因素的取值,实现设计变量的缩减。该文的研究结果可为内弹道及弹射装置优化提供理论参考。

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).

高温复合滤筒除尘器输灰方案探讨

随着高温复合滤筒除尘器的引入,与之配套的输灰系统也面临着新的挑战。本文以乾县农林生物质焚烧发电项目为例,对仓泵式气力输灰系统和机械集中(冷却)+低正压连续气力输送系统两种不同的输灰方式从技术、经济角度进行比较,最终提出了高温复合滤筒除尘器下可行的输灰方式,供同行借鉴。

高压浓相变水分煤粉输送特性及香农信息熵分析

在输送压力可达4.0MPa,固气比高达450kg/m3的高压气力输送试验台上,用氮气进行煤粉高压浓相气力输送试验研究。分别在不同的总输送差压、煤粉含水率、压力和表观速度等条件下进行了输送试验,考察操作参数对煤粉质量流量和固气比等气力输送特征参数的影响,用信息熵分析试验过程中采集到的压力波动时间序列,探讨流动稳定性和流型变迁过程中信息化趋势,建立信息熵和流型之间的关系。结果表明,在总输送差压增大的过程中,固气比和香农(Shannon)信息熵均增大;流动相图与Shannon信息熵之间呈现较好的规律性;不同流动形态的Shannon熵差异较大,不同流型之间的Shannon熵区分度较好。随着煤粉含水率的增大,煤粉的质量流量和压损减小,Shannon信息熵值下降。Shannon信息熵分析为研究高压浓相气力输送流型、稳定性及其转变特性提供了一种行之有效的方法。

不同煤粉高压密相气力输送特性实验研究

在输送压力可达3.6MPa,输送速率通量可达4600kg·s-1·m-2的气力输送中试实验台上,进行3种煤粉(内蒙、大同和兖州煤粉)、同一煤种(内蒙煤粉)不同粒径的高压密相气力输送的系统实验研究。考察输送压力、总输送差压、流化风流量、煤粉粒径和煤粉种类等因素对输送特性的影响。研究结果表明,高压条件更有利于实现较高固相速率通量的低速密相输送;输送速率通量随着流化风流量的增大而先略增后略降;系统的输送能力随着煤粉粒径和水分的增大而降低,且水分的影响更大;不同管段的压降呈现不同的特征,说明管段的布置影响流动阻力和稳定性;煤粉颗粒大小和固气比均是影响压降特征的重要因素。

压缩空气动力应用的发展现状及展望

提出压缩空气不仅可以作为工作介质 ,而且可以储存能量作为一种动力源。阐述了常规气动伺服控制系统研究的现状 ,认为以PWM和PCM调制方式为主的开关伺服控制技术仍然是研究的热点。说明了气动系统节能必须重视压缩空气生产、处理、储存、分配与控制等各个环节 ,并需根据具体情况采取合适的节能技术和方法。综述了高压气动系统和元件的研究概况 ,指出高压化是气动系统发展的一个方向。提出绿色气动动力系统 。

煤粉高压密相气力输送特性

在输送压力可达4.0MPa,固体输送流率达840kg/h的仓式泵高压气力输送试验装置上进行粉煤高压浓相气力输送试验研究.考察了流化风量、充压风量、输送总差压对煤粉输送量、固气比的影响.研究表明:随着流化风量的增大,煤粉输送量逐渐增大,固气体积比先增大然后减小;当煤粉在发料罐内被充分流化后,再加大充压风量,固气体积比逐渐减小,而煤粉输送量略有增加;输送总压差对煤粉输送量有显著影响,随着总压差的增加,煤粉输送量呈线性增加.研究结果对高压超浓相气力输送系统的设计、运行和控制具有指导作用.

高压气动容积减压分级控制原理与特性

为了提高容积减压能量补偿效果,提出分级控制容积减压的概念。通过高压气动系统定压补偿分级减压的能量原理和减压过程中的能量特性分析,证明了分级减压是一种有效的节能减压方法。通过建立控制系统的数学模型和进行仿真分析,研究了两级控制容积减压系统控制特性;两级控制容积减压系统的试验研究结果表明:建立的理论模型是符合实际的;一级减压的设定压力只要高于二级减压设定压力的临界输入压力值,就能得到稳定的控制压力输出。

高压密相气力输送弯管压降研究

在输送压力可达4MPa的气力输送实验台上,进行不同平均粒径煤粉的密相输送实验。获得了不同操作参数下的弯管压损实验数据。在Barth附加压力损失理论基础上,考虑发送压力以及煤粉物性参数对弯管压损的影响,运用量纲分析法,得到高压密相输送时附加压损系数的关联式。用关联式预测的压损值与实验值吻合得很好。研究表明,相同质量流量下,平均粒径大的煤粉在弯管中的压损要高于平均粒径小的煤粉;在密相气力输送中,压损随表观气速的降低而增加。

超高压大流量气动开关阀的原理和动态特性研究

开关容积减压是为提高效率而提出的一种新型减压方法。对其关键元件超高压大流量气动开关阀的原理、动态特性进行详细的理论和试验研究。利用气动力平衡,解决超高压主阀心驱动力大和响应慢的难题,设计出小流量驱动大开口的超高压大流量开关阀。提出以定容积过程和变容积过程为单元,以控制腔转折点气体压力为标志,对超高压气动开关阀的开启和关闭动态过程进行细分的原则;建立了基于动态过程细分原则的非线性数学模型;分析了超高压气动开关阀动态特性的影响因素、改善措施。仿真和试验表明,所建立的数学模型和理论分析与试验结果是吻合的。