天然气降压?损失分析及余压膨胀关键技术

随着天然气产业的高速发展,采用高压力输送天然气是未来天然气输送的趋势。针对天然气调压站存在的降压余能,本文以热力学中稳定流动过程的?损失理论,分析了天然气调压站中两种降压模式的?损失。结果表明,绝热节流过程存在较大的?损失,可回收功为零,而可逆绝热膨胀过程?损失为零,可回收功为焓差。本文在分析天然气余压膨胀利用关键技术的基础上,计算了天然气膨胀复热量和发电量随进出口压力、温度和露点温度的变化规律,为天然气膨胀工艺的设计提供了一些优化思路。     

测量线性压缩机活塞位移和PV功的新方法

提出利用激光三角法测量压缩机的活塞位移,结合压力传感器测得的气体压力,计算得到压缩机的活塞PV功;忽略活塞间隙的漏气损失,可计算得压缩机的输送PV功。设计了适用于激光测量活塞位移的带可视化窗口的压缩机外壳。针对一台特定压缩机,理论计算活塞与气缸之间的漏气量并通过实验验证了漏气量为小量。不同工况下对压缩机活塞位移进行测量,计算得到相应的活塞PV功和输送PV功,并与热线测量的输送PV功进行相互验证。利用激光测活塞位移的方法,观察脉冲管制冷机降温过程中压缩机活塞位移、压力、PV功及相位角的变化,给出相关分析。     

垃圾水分的燃烧影响分析及闭环调节式干燥工艺研究

通过对垃圾水分的燃烧影响分析，表明了高水分垃圾对其能量回收、焚烧效果、锅炉设计及运行均会带来一系列不利影响；通过对垃圾闭环调式干燥工艺研究，证明了垃圾闭环调节式干燥工艺具有简单、实用、经济、安全环保等优点，是一种适合我国国情的垃圾焚烧处理新技术。     

低温液体送入热管道后的升压过程

分析了低温液体输入热管道后升压过程，并对输送过程中的临界质量流进行了计算，结合有关文献的实验数据，给出输送过程中的压力计算公式。并提出了减少压力最大值的方法，对于低温液体输送参数的确定，管道的设计提供参考。     

粮食颗粒群密相变径气力输送的流动特性

针对稀相气力输送能耗和粉料破碎率高以及稳定性差等缺陷,在计算流体力学软件FLUENT上,选择Euler双流体模型与k-ε湍流模型对粮食颗粒在水平变径管内的密相流体输送进行数值模拟,并将仿真数据与实验结果相论证。发现湍流对两相流动过程中的稳定性有较大影响;分析管道内颗粒浓度、输送气体速度和压力损失随管道长度的变化规律,探讨密相气力输送主要参数间的影响关系,得出气流速度、压力损失会随着变径长度的增大分别下降15%、20%。     

降低氧气管网压力的实践

鞍钢股份有限公司现有氧气输送方式能量损失较大,提出了降低氧气管网压力,达到节能降耗目的的改进方案。简介鞍钢股份有限公司氧气分厂现有空分设备配置情况和氧气输送方式,结合空分设备及氧气管网实际,分析降低氧气管网压力的可行性、实践和效果,最后阐述节能效益。     

七氟丙烷气体灭火系统沿程压力损失计算方法

七氟丙烷气体灭火系统管网的设计中,不可避免遇到压力损失的问题。本文根据经验提出了一种基于修正系数的七氟丙烷气体管网压力损失的计算方法。这种方法根据伯努利方程与热量损失定律对灭火系统的压力损失方程进行了推导,根据管网参数与设计流量调整了雷诺数,确定了压力损失的系数计算值,对压力损失计算的结果进行了调整,最后通过实验验证了管网的压力损失值,证明该计算方法有效可行。     

矿用汽车抗性消声器性能及参数分析

针对不同类型的矿用汽车为消声器的预留空间不同，分别讨论长径比、扩张比、穿孔率、内插管长等参数对抗性消声器的选型影响。利用SIDLAB软件对各参数组合下的抗性消声器的传递损失和压力损失分别进行计算。研究表明：上述参数的变化对最大消声量、去除通过频率都有较大影响，穿孔管消声器能够达到理想的消声效果，当一端内插扩张腔长度的1/2，另一端内插1/4时，效果最佳。针对某290 t矿用汽车为消声器的预留空间的特点，通过压力损失和传递损失比较，为该矿用汽车设计了适宜的消声器。     

压力管道检验技术研究

压力管道是输送油气重要的承压设备，经过长期使用由于受到振动、腐蚀、压力等因素的影响会出现很多潜在问题，为了避免这些问题造成不必要的损失，应定期对压力管道进行检验。因此，有必要加强压力管道检验技术研究。文章对压力管道检测技术进行探讨，以期为压力管道的检测提供参考。     

液氧输送系统压力异常下降成因分析与数值研究

针对某运载火箭液氧输送系统分支管路压力异常的问题,采用CFD软件对液氧输送系统管路进行了数值模拟,并对压力异常的维持、不同过载条件与不同管路开闭条件下压力响应进行了计算分析。结果表明:随着边界条件与时间不同,液氧输送管路在运行中会形成3种型态各异的流场,造成压力异常的流场是一种稳定平衡的流场;在不同管路开闭条件下,流场会发生旋转等物理形状上的变化,从而对各并联管路的压力造成影响。计算结果阐明了压力异常状况产生的原因,对于维护运载火箭的稳定运行及后期的输送系统改进提供了指导。     

Flow characteristics and flow rate prediction of pulverized coal through a regulation valve

In this paper, experiments of dense-phase pneumatic conveying of pulverized coal were carried out in an industrial-scale system to study the control characteristics of the regulation valve and to predict the solid mass flow rate. Firstly, effects of valve sweeping gas on conveying stability and solid mass flow rate were investigated and the optimum valve sweeping gas was determined. Second, effects of valve opening on pressure distribution and solid mass flow rate were investigated by conducting experiments at different conveying pressure drops and different valve openings. A good linear relationship between the valve pressure drop ratio and the valve opening was found, and as the valve opening increased from 13 % to 70 % the solid mass flow rate increased gradually. Limit operating conditions of the regulation valve including flow blockage and control failure were consequently determined and analyzed. Finally, a robust model was established to predict the solid mass flow rate by introducing the valve sensitivity coefficient into the traditional pressure drop ratio model. The model can predict the solid mass flow rate well by providing errors mostly within ± 10 %. This study will provide certain reference for solid mass flow rate regulation in the dry coal gasification process.     

Analytical prediction of pressure loss through a sudden-expansion in two-phase pneumatic conveying lines

Estimation of separation or minor pressure losses for pipe fittings of a pneumatic conveying system at design stage is critical as much as determination of frictional pressure losses through it. The flow in many pneumatic conveying systems is a two-phase flow; it is so complex and difficult to be investigated by experimental techniques. The static pressure recovery and the minor loss coefficient through an axis-symmetric, circular cross-section, sudden-expansion fitting of a horizontal pneumatic conveying line with air–solid particle flow are analytically studied. The theoretical models proposed in the literature are scarce, and do not confirm the experimental studies. The well-known homogeneous and separated flow models proposed in the literature are initially applied to the case by means of mass and momentum conservation laws. The predictions of both the models on the pressure recovery were compared with the experimental and the numerical data in the literature and a bad agreement was observed between them; therefore, a new original analytical model is proposed by the present study. The new model is called as the slip flow model, which takes into account the slip velocity between gas and solid phases evaluated by coupling the well-known separated flow model with the empirical slip ratio predictions in the literature. The predictions of the proposed slip flow model on both the pressure recovery and minor loss coefficient are found in good agreement with the corresponding data in the literature.     

Detonation gas model for combined finite‐discrete element simulation of fracture and fragmentation

The equation of state for expansion of detonation gas together with a model for gas flow through fracturing solid is proposed and implemented into the combined finite‐discrete element code. The equation of state proposed enables gas pressure to be obtained in a closed form for both reversible and irreversible adiabatic expansion, while the gas flow model proposed considers only 1D compressible flow through cracks, hence avoiding full 2D or 3D gas flow through the fracturing solid. When coupled with finite‐discrete element algorithms for solid fracture and fragmentation, the model proposed enables gas pressure to be predicted and energy balance to be preserved. Copyright © 2000 John Wiley & Sons, Ltd.     

Discharge of a gas with solid particles from nozzles at critical velocities

Problems of the gas dynamics of two-phase flow with critical discharge conditions are considered. The flow parameters (pressure, density, and velocity of the gas) are calculated in one-dimensional approximation in convergent and cylindrical nozzles. The calculated data are compared with the experimental results obtained by investigating the discharge of a mixture of air and solid particles.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 18, No. 4, pp. 648–652, April, 1970.     

Simulation of Gas-Solid Flow in Vertical Pipe by Hard-Sphere Model

This article presents a two-dimensional study of the gas-solid flow in a vertical pneumatic conveying pipe by means of a hard-sphere model where the motion of individual particles can be traced. Simulations were performed for a pipe of height 0.9 m and width 0.06 m, with air as gas phase and particles of density 900 kg/m³ and diameter 0.003 m as solid phase. Periodic boundary conditions were applied to the solid phase in the axial direction. Different cases were simulated to examine the effects of the number of particles used, superficial gas velocity, and restitution coefficient. The results show that the main features of plug flow can be reasonably captured by the proposed simulation technique. That is, increasing the number of particles in a simulation will increase the length of plugs but does not change the velocity of plugs; the solid fraction of a plug is relatively low if the number of particles is small. In particular, it is shown that increasing superficial gas velocity will increase the velocity of plugs and the frequency of plugs, and the pressure drop through a rising plug increases linearly with the plug length, suggesting that the total pressure of a conveying system with a given length can be quantified from the information of plug length and plug frequency. Increasing the restitution coefficient can promote the momentum transfer between particles and hence the raining down of particles from the back of a plug in vertical pneumatic conveying. The simulation offers a useful technique to understand the fundamentals governing the gas-solid flow under pneumatic conveying conditions.     

Simulation of Gas-Solid Flow in Vertical Pipe by Hard-Sphere Model

ABSTRACT

This article presents a two-dimensional study of the gas-solid flow in a vertical pneumatic conveying pipe by means of a hard-sphere model where the motion of individual particles can be traced. Simulations were performed for a pipe of height 0.9 m and width 0.06 m, with air as gas phase and particles of density 900 kg/m³ and diameter 0.003 m as solid phase. Periodic boundary conditions were applied to the solid phase in the axial direction. Different cases were simulated to examine the effects of the number of particles used, superficial gas velocity, and restitution coefficient. The results show that the main features of plug flow can be reasonably captured by the proposed simulation technique. That is, increasing the number of particles in a simulation will increase the length of plugs but does not change the velocity of plugs; the solid fraction of a plug is relatively low if the number of particles is small. In particular, it is shown that increasing superficial gas velocity will increase the velocity of plugs and the frequency of plugs, and the pressure drop through a rising plug increases linearly with the plug length, suggesting that the total pressure of a conveying system with a given length can be quantified from the information of plug length and plug frequency. Increasing the restitution coefficient can promote the momentum transfer between particles and hence the raining down of particles from the back of a plug in vertical pneumatic conveying. The simulation offers a useful technique to understand the fundamentals governing the gas-solid flow under pneumatic conveying conditions.     

音速喷嘴气体流量标准装置应用的试验研究

依据音速喷嘴独特的临界流状态测量原理,通过试验数据分析,阐述温度、压力的波动对流量测量的影响趋势和影响程度;同时,空气湿度的存在造成通过音速喷嘴的实际流量较相同条件下干空气的流量小,且其影响随着湿度的增加而增加,用作传递标准时必须进行湿度修正才能保证测量准确度;通过气体状态方程的理论推导,表明通过音速喷嘴的体积流量与被检流量计的体积流量状态一致。最后,对音速喷嘴流量标准装置的设计和使用提出了相关的技术建议。     

音速喷嘴一元流动模型详解及其激波计算

针对文丘里音速喷嘴,阐述了如临界背压比等概念,指出了ISO 9300中背压比定义存在容易造成歧义的缺陷。然后基于一元等熵流动理论,从数学上证明了：当文丘里喷嘴喉部压力与上游滞止压力之比达到临界压比时,喉部产生音速,通过喷嘴的质量流量达到最大值;推导了实际条件下喷嘴的流量公式,导出的流量公式相较于ISO 9300给出的相应公式,增加了喉部状态参数下的压缩性系数修正项■。最后从气体动力学基本方程出发,讨论了在较大背压比范围内,喷嘴扩散段中产生激波的机理,给出了激波产生的位置、激波前、后的压力和马赫数的一元流动计算模型,并运用数值模拟方法对计算结果进行了验证,同时还与Craig A的实验数据作了对比。对最小出口压比对比的结果显示,一元流动模型与实验数据的最大误差≤17%。     

多因素耦合影响亚音速喷口强化气体流场分布研究

为了研究多因素耦合条件下亚音速喷口内气体流场分布演变的作用机制与影响规律,基于标准k-ε湍流模型,对压力-流速-收缩比耦合条件下的亚音速喷口构造均匀气体流场进行了数值模拟,通过定义top-hat流场分布关键参数的方式,定量评估压力-流速-收缩比对强化后流场分布的耦合影响。结果表明:多因素耦合条件下,亚音速喷口通过影响压力梯度平衡点与临界位置点在内的强化过程关键点改变强化流场分布的品质;提高气体压力可以有效减小构造流场中的边界层厚度,降低强化过程中关键点对流速的依赖,提升不同流速下边界层厚度的稳定性,收缩比的增加则会使得强化流场进一步偏离理想分布。     

基于Fluent的气液两相流喷嘴内部流动特性仿真

目的探究气液两相流喷嘴内部流动特性及工作参数对流动特性的影响。方法测量得到气液两相流喷嘴的结构图,利用Fluent软件建立喷嘴模型,并选择流体体积(VOF)两相流模型和RNG(重整化群)k-?湍流模型,以常温状态下液态水和空气为研究介质,并以气压和液压为变量,进行多参数的流动特性分析,并引入气液比的概念。结果得到了不同时刻喷嘴内部的压力、速度及液相分布云图。其中最大压力为827 kPa,出现在出口段和进气段交叉的壁面上,由于喷嘴内部出现缩口,故出口段存在负压(?1.53 MPa);喷嘴内部最高速度出现在气液两相交汇处,为134 m/s;液相在最初迅速充满喷嘴后,逐渐与气相混合,最终出口段中心液相体积占比为0.543,混合情况良好。还得到了多参数对喷嘴内部压力、速度及液相分布的影响。结论使用软件仿真的方法得到了喷嘴内部的流动特性和多参数对流动特性的影响规律,并为进一步研究优化喷嘴结构及喷雾提供了建议和参考。