多孔板压降特性实验与关联式比较

多孔板作为节流元件具有整流、低噪声、低压损及压差更稳定等优点,然而多孔板压降特性的预测方法目前仍不清晰。以常温水为实验介质,在Re数为4×10⁴~1.6×10⁵范围内,对孔数为172~744、等效直径比为0.544~0.666的多孔板进行了压降特性实验研究,并将实验结果与文献中相关的关联式预测结果进行了比较。结果表明：在相同开孔直径比和流动条件下与单孔板相比,多孔板后涡流引起的黏性耗散较小,因而其压损系数明显低于单孔板;计算多孔板压损系数时,若采用等面积折算所得等效直径比按单孔板进行计算,会使得预测结果明显偏大;Holt关联式的压损系数预测结果与实验结果最为相符,表明同时考虑开孔直径比和孔板相对厚度影响的压损系数关联式预测精度较优。建议通过进一步研究建立完善的多孔板压降预测方法。     

基于ANSYS的多孔板应力应变分析

通过利用大型非线性有限元软件ANSYS对18种不同开孔数的多孔板进行数值模拟和分析,得出：多孔板的最大等效应力主要发生在多孔板开孔区最外侧开孔的对称中心处.随开孔个数的增加,最大等效应力呈增大趋势;最大等效应力的大小主要取决于Z方向的最大应力;孔的排列情况对多孔板应力有影响.结果对多孔板的设计研究具有一定参考价值.     

释压量对发泡行为的影响

通过自行设计加工的模具研究不同释压量下微发泡试样的发泡行为.首次揭示泡孔平均直径随释压量的变化规律.结果显示:泡孔平均直径并不是随着释压量的减小而减小,而是随着释压量的减小先减小后增大.通过补充添加了蒙脱土成核剂的实验,证实泡孔平均直径在小释压量时反而增大的真正原因是高熔体能量造成临界成核半径增加.因此,只有适当的控制释压量才可以得到尺寸较好的微孔结构.     

城镇燃气管道带压封堵局部应力分析

城镇燃气管道的安全运行是城镇居民安全用气的保障,针对城镇燃气管道泄漏带压封堵产生的局部应力问题,以补板修复方法为例,利用有限元分析软件ANSYS,分析内压、补板厚度和泄漏孔孔径等因素对孔结构受力的影响规律.结果表明:随着内压的增大,管道的边缘随之发生屈服,管道整体随内压呈正线性相关变化.当补口处的补板长度一定时,该位置处的补板厚度与局部应力成负相关,而与承载极限成正相关.对于开孔边缘,孔径的大小对其应力值影响最大,随着孔径的增大,其应力不断增大,直至屈服;同时孔径的大小对于孔板的交界处以及补板的内侧相对来说影响较小.     

孔分布对多孔孔板流场和噪声的影响

目前多孔孔板普遍采用均匀布孔结构,广泛用于管路限流降压以及减振降噪,为了进一步提高流动稳定性以及降低流噪声,在保持等效开孔直径不变的前提下,设计了具有不同孔间距、孔数和孔径的非均匀孔分布多孔孔板模型。基于数值计算结果,详细比较了含不同孔板模型管路流场中的速度、压力、回流特性、射流会聚和流动发展等流动特征。采用声学模型计算了孔板的噪声,在中心线以及垂直于流动方向的截面上设置监测点,对比了其频谱特性和总声压级。结果表明,与均匀多孔分布的常规孔板相比,孔间距等差递减、孔板边缘的孔数增多、以及孔径在满足不减少孔数的条件下增大,均能在不影响降压能力的情况下提高流动稳定性和降低板后噪声,且其噪声值分别最大改善了5.62, 6.10和7.00 dB。     

水平管内多孔板后的气液两相流型可视化实验

多孔板后是否形成均匀分散的泡状流流型是影响多孔板废气吸收装置吸收效果的关键因素。以空气和水作为两相介质,对气液两相混合物在水平管内流经多孔板后形成的流型进行实验。通过孔径分别为2、3、4、5 mm的4只多孔板在内径98.5 mm水平有机玻璃管内的可视化流动及高速摄像,研究了孔径大小、气相流量变化及液相流量变化对多孔板后流型的影响规律。实验结果表明：水平管内插入多孔板后,分层/塞状流转变边界向液相流量增大方向推移,塞状/泡状流转变边界向液相流量减小方向推移;随气相流量减小或液相流量增大,多孔板后流型趋于形成泡状流;孔径大小对多孔板后流型具有重要影响,减小孔径使塞状/泡状流转变边界移向更大气相流量和更小液相流量,即形成泡状流的两相流量范围增大;随孔径减小,孔板后流型趋于由分层流直接过渡至泡状流,塞状流趋于消失。为保证多孔板吸收装置的良好流型和吸收效果,建议多孔板孔径不大于3 mm。     

水平管内多孔板后的气液两相流型可视化实验

多孔板后是否形成均匀分散的泡状流流型是影响多孔板废气吸收装置吸收效果的关键因素。以空气和水作为两相介质,对气液两相混合物在水平管内流经多孔板后形成的流型进行实验。通过孔径分别为2、3、4、5 mm的4只多孔板在内径98.5 mm水平有机玻璃管内的可视化流动及高速摄像,研究了孔径大小、气相流量变化及液相流量变化对多孔板后流型的影响规律。实验结果表明:水平管内插入多孔板后,分层/塞状流转变边界向液相流量增大方向推移,塞状/泡状流转变边界向液相流量减小方向推移;随气相流量减小或液相流量增大,多孔板后流型趋于形成泡状流;孔径大小对多孔板后流型具有重要影响,减小孔径使塞状/泡状流转变边界移向更大气相流量和更小液相流量,即形成泡状流的两相流量范围增大;随孔径减小,孔板后流型趋于由分层流直接过渡至泡状流,塞状流趋于消失。为保证多孔板吸收装置的良好流型和吸收效果,建议多孔板孔径不大于3 mm。     

弹性微球通过油层孔隙的临界粒径

根据微球在孔隙中的受力情况,建立简化的力学模型,计算出通过孔喉的微球的临界粒径。结果表明,当微球物性参数不变时,微球临界粒径随孔隙孔径线性增大;当孔隙孔径不变,只改变微球物性参数中的弹性模量时,微球临界粒径随微球弹性模量的增大而减小;当孔隙孔径不变,只改变微球物性参数中的极限应力时,微球临界粒径随极限应力的增大而增大。     

旋流雾化塔盘水力学性能

对传统的垂直筛板进行改进,自主研发了旋流雾化塔盘。以空气-水为介质,对旋流雾化塔盘的水力学性能进行研究,考察孔动能因子、清液层高度、底隙高度和旋流器叶片数目对相对液相提升量和板压降的影响,并与现有垂直筛板进行对比。结果表明:旋流雾化塔板的相对液相提升量随孔动能因子增大而减小,随底隙高度增大先增大后减小,随清液层高度增大而增大,在旋流器叶片数目为5时,相对液相提升量最大。总板压降随孔动能因子、底隙高度、清液层高度增大而增大。旋流雾化塔盘的性能优于垂直筛板,满足设计要求。     

喷射型催化精馏塔构件的流体力学性能

对垂直筛板帽罩内装催化剂构成的新型塔构件进行了实验研究。考察了板孔动能因子、催化剂藏量、床层空隙率对塔构件压降、罩体喷出量以及液泛和漏液速度的影响。结果表明:压降随板孔动能因子和催化剂藏量的增加而增大,随床层空隙率的增加而减小;罩体喷出液体量随着板孔动能因子的增加先增大后减小,随床层空隙率的增加而增大,随催化剂藏量的增加而减小;漏液速度随液体流量、藏量的增加而增大,随空隙率增大而减少;液泛速度随床层空隙率、液体流量的增大而减小,随藏量增加而增大。新型塔构件流体力学性能良好。     

气液两相并流向下通过筛板孔口单元的压降特性

针对堆叠筛板填料的基本单元,采用12种不同规格的孔板,研究了气液两相并流向下通过孔口的压降特性,阐明了气液流量、孔板结构对压降的影响规律。结果表明：压降随气液流量的增加而增大;随孔径的增大而减小;在筛板常用厚度范围内,孔口锐缘效应使得压降随板厚减小而增大。根据孔口压降行为不同,以气相雷诺数Re_G=5000分界,建立了单一气相向下通过孔口的压降预测关联式;然后利用气相折算因子对关联式进行修正,得到了Re_G>5000时气液并流向下通过孔口的压降预测关联式;当Re_G<5000时,通过直接对单一气相阻力系数进行修正,得到了相应气相雷诺数范围内的气液两相压降预测关联式。     

The weeping characteristic of submerged multi-orifice plate

Weeping is an adverse phenomenon which results in higher pressure drop and poorer aeration performance. Visual experiments have been conducted to study the mechanism by which weeping impairs the work performance of multi-orifice plate. A theoretical model is improved to analyze the weeping phenomenon of multiorifice plate based on potential flow theory. The relations of different bubbling conditions and weeping rate are analyzed. Weeping condition and average weeping rate have relation with the driven pressure differential and dynamic variation of gas chamber pressure. In addition, a set of experiments are designed to study the influence of various factors on weeping rate. The bubble coalescence during bubble formation is a fatal factor determining weeping rate, so the relation between weeping rate and gas flow rate is concerned with the pitch of orifices and orifice diameter. There is a critical plate thickness which is in favor of weeping.     

Attrition of porous glass particles in a fluidised bed

Fluidisation is frequently accompanied by unwanted attrition of the bed material. This paper focuses on the mechanical aspects of fines creation by attrition in fluidised beds supported by multi-orifice distributor plates. The attrition rates of low-density porous glass particles were measured; these particles show abrasive wear behaviour rather than breakage. Positron emission particle tracking (PEPT) was used to follow particle motion in three dimensions within the fluidised bed. For a single orifice distributor with background fluidisation, the attrition rate increased exponentially with increasing orifice gas velocity. For a multi-orifice distributor, however, attrition rates were roughly proportional to excess gas velocity, except near to a critical ratio of particle to orifice diameter; as this ratio approached 2, attrition was observed to increase by an order of magnitude. A method is proposed for estimating attrition rates from a combination of small-scale experimental results and theoretical calculations of distributor jet entrainment rates.     

Numerical modelling of the gas flow through perforated plates

Perforated plates are used in many applications such as electrostatic precipitators in environmental control systems as a method of fluid flow control. The detailed structure of perforated plates causes difficulties in the design and optimization of systems by mathematical modelling. Hence, a simplified model for the perforated plates is important. In the current work, numerical experiments based on Computational Fluid Dynamics (CFD) are carried out at a microscopic, unit cell scale. The effects of a series of parameters on the flow pattern and pressure loss are investigated, including Reynolds number, open porosity, orifice diameter, plate thickness, surface roughness and plate inclination angle. Good agreement is observed between the current predictions and empirical equations/experimental data in the literature. The pressure loss is found to be determined by the large flow structures in the expansion behind the plate. The results can be potentially used for the modelling of flow distribution in electrostatic precipitators in particular.     

Local resistance characteristics of highly concentrated coal-water slurry flow through fittings

The local resistance characteristics of high concentration coal-water slurry (CWS) flowing through three types of local fittings, namely the gradual contractions, sudden contractions and 90° horizontal elbows, were investigated at a transportation test facility. Results show that the local resistance loss of gradual contractions decreases as the contraction angle increases. When pipe diameter ratio varies little, local resistance loss of sudden contractions changes insignificantly. There is an optimal value of bend diameter ratio, at which the local resistance loss of horizontal elbows is the least. As Reynolds number increases, the resistance coefficients of all the three fittings first reduce and then stabilize, while the three pipes have different ratio of equivalent length to pipe diameter L _e /D behaviors, that is, L _e /D of the gradual contractions decreases gradually and then keeps stable; that of the sudden contractions diminishes at first and then increases, and that of the horizontal elbows increases linearly. This work was presented at the 7 ^th Korea-China Workshop on Clean Energy Technology held at Taiyuan, China, June 26–28, 2008.     

垂直锐边孔口的自由出流特性(Ⅰ)流动状态和孔结构参数对孔流系数的影响

通过实验,考察了Reynolds数、液层高等操作参数和孔径、板厚等结构参数对垂直锐边孔口自由出流特性的影响。在此基础上,根据孔流系数曲线的不同规律,将孔流机理划分为“大孔机理”和“小孔机理”,并对孔流曲线进行了分区讨论,借助边界层理论,探讨了这两类孔流过程的机械能损失差异以及孔流曲线在不同操作区的机械能损失差异。     

水平管外降膜蒸发流动和传热特性数值模拟

建立三维模型并模拟了制冷剂R410A在水平管外的降膜流动和蒸发过程,探究了喷淋密度、热通量和布液孔偏离管轴心距离对降膜流动和传热的影响。结果表明：沿管周方向,液膜厚度和传热系数逐渐减小并趋于稳定,至管底处由于局部液体堆积,液膜增厚、传热系数降低;喷淋密度较小时,总传热系数随着热通量增加而降低,随着喷淋密度增加而显著提高;液膜Reynolds数达2000后,总传热系数随喷淋密度增加而缓慢提升并趋于平稳,此时热通量的增加会提升总传热系数;随着布液偏心距的增加,总传热系数先略微上升并趋于平稳,而后由于出现局部“干涸”和液膜堆积区域,总传热系数急剧下降;随喷淋密度的增加,总传热系数急剧下降的临界点会逐渐往大偏心距偏移。     

窄通道杆状发射药内孔燃气流动数值模拟

运用合理的简化假设,建立杆状发射药内孔通道燃气流动模型,利用Fluent软件求解器对长径比为40的某一特定单孔杆状发射药燃气在内孔的流动过程进行了数值模拟,在给定初始压力和温度的条件下模拟内孔燃气的速度分布及压力分布,并进行分析。结果表明,径向由孔中心到孔壁,燃气流速逐渐减小,压力逐渐增大;轴向燃气流速先逐渐减小,压力先逐渐增大,在10mm处突然形成速度和压力的震荡波,并随时间沿轴向传递,5ms后速度趋于平稳波动,压力整体保持波动并持续上升,但各点压力最终都保持稳定。