喷嘴雾化特性及脱硫废水蒸发数值模拟

利用相位多普勒粒度分析仪（PDA）实验台测量了双流体喷嘴出口速度与粒径分布,利用得到的速度与粒径数据对江苏某生物质电厂进行小水量脱硫废水蒸发的数值模拟,着重研究了液滴粒径以及烟气中水蒸气的体积分数对液滴蒸发过程的影响。PDA实验结果表明,该双流体喷嘴在特定气液比条件下出口粒径均小于100μm。应用离散相模型与随机轨道模型,利用Rosin-Rammler分布模拟喷雾液滴分布范围（0～100μm）。模拟结果表明,粒径低于100μm的液滴能够完全蒸发,液滴粒径越小,完全蒸发时间越短,液滴经历的平稳吸热时间越短。随着粒径的增加,液滴完全蒸发时间增幅变大。随着烟气中水蒸气体积分数增加,液滴蒸发速率变缓,液滴开始蒸发的时间延长,且体积分数越大,出口未蒸发完全的液滴直径越大,但出口液滴粒径增大的幅度在减小。     

双流体喷嘴雾化特性实验

双流体雾化降温冷却技术是将气体和液体在喷嘴内部直接混合,在高压射流作用下直接雾化,雾化的小液滴气化时带走热量,从而降低工作区域温度。喷雾冷却降温系统广泛应用于养殖、高精度建筑及机械切削加工中刀具的冷却等。影响喷雾降温冷却的关键因素是雾滴粒径和雾滴运动速度。雾滴粒径越小,其总表面积越大,易于蒸发、气化,从而产生良好的降温效果;而雾滴运动速度加快则可以进一步加快工作区域的换热过程。文章利用相位多普勒粒子动态分析仪(PDA)对4种不同喷孔直径的喷嘴进行了较为详细的实验研究,获得了影响雾滴粒径和雾滴运动速度的重要因素,得到了双流体雾化喷嘴工作的最佳压力与孔径组合,为喷雾冷却降温的研究奠定了基础。     

蒸发式过冷水制冰中单个水滴的蒸发过冷特性

为分析蒸发式过冷水制冰中单个水滴在此低温低湿空气环境中的蒸发特性,建立了水滴蒸发过冷过程的数理模型。通过悬挂水滴实验与模拟结果的对比,验证了模型的有效性。因此利用该数学模型预测微小直径水滴的蒸发特性是可行的。通过模拟计算获得了水滴初始直径、初始水温、空气温度、空气含湿量和空气流速对水滴蒸发过冷过程的影响。结果表明,水滴初始直径越小、温度越低或空气流速越大,水滴的冷却速率就越大,达到稳态时的过冷时间就越短。另外,通过降低空气温度或含湿量不仅提高了水滴的冷却速率,而且增加了水滴达到稳态时的过冷度。通过水滴蒸发过冷特性的分析,可为制冰系统的优化设计及提高系统制冰效率提供理论参考。     

CO2-双流体细水雾抑制管道甲烷爆炸实验

搭建了尺寸为120 mm×120 mm×840 mm透明有机玻璃瓦斯爆炸管道实验平台,采用双流体喷嘴将二氧化碳和细水雾送入实验系统,从火焰速度、瓦斯爆炸超压两个方面探讨双流体细水雾的抑爆有效性。实验结果表明CO₂双流体细水雾抑制瓦斯爆炸效果显著。随着喷雾时间的延长,火焰传播速度呈缓慢增加趋势,火焰传播速度峰值大幅降低;爆炸超压曲线呈先增大后缓慢减小的趋势,超压峰值大幅降低;当CO₂压力增至0.4 MPa喷雾时间大于3 s时,经多次点火无法引爆, 说明CO₂-双流体细水雾抑制甲烷爆炸时具有协同效应,有利于提高细水雾的抑爆效率。     

CO_2-双流体细水雾抑制管道甲烷爆炸实验

搭建了尺寸为120 mm×120 mm×840 mm透明有机玻璃瓦斯爆炸管道实验平台,采用双流体喷嘴将二氧化碳和细水雾送入实验系统,从火焰速度、瓦斯爆炸超压两个方面探讨双流体细水雾的抑爆有效性。实验结果表明CO2双流体细水雾抑制瓦斯爆炸效果显著。随着喷雾时间的延长,火焰传播速度呈缓慢增加趋势,火焰传播速度峰值大幅降低;爆炸超压曲线呈先增大后缓慢减小的趋势,超压峰值大幅降低;当CO2压力增至0.4 MPa喷雾时间大于3 s时,经多次点火无法引爆,说明CO2-双流体细水雾抑制甲烷爆炸时具有协同效应,有利于提高细水雾的抑爆效率。     

气体分流板在管道喷雾中的应用

俄罗斯某5　000t/d生产线为三级预热预分解系统，在窑尾废气管道上采用双流体管道喷雾系统，为出预热器的废气调质和降温。窑尾废气供给两台烘干破碎机烘干原料。投产后窑尾废气温度不稳定，6个月后出现废气管道内侧湿壁和保温砖塌落现象，主要塌落区域为废气管道内侧。为此，我们采取了在管道内增加气体分流板调整气流的措施，使问题得到了解决。     

单液滴撞击受热枫桦木炭化表面的实验研究

通过模拟实验研究了水滴及含4% 氟表面活性剂(AFFF)液滴分别撞击室温和加热枫桦木炭化表面的碰撞动态过程。实验中加热枫桦木表面温度为124.7℃,纯水滴初始直径为(2.4±0.1)mm,含4% AFFF液滴初始直径为(1.8±0.1)mm,液滴滴落高度为15~40 cm。采用Photron Fastcam高速摄影仪记录液滴碰撞的动态过程,拍摄帧数为2000 fps。研究结果表明:水滴撞击枫桦木炭化表面后飞溅液滴数、最大铺展因子都随着水滴撞击速度的增大而增大。纯水滴撞击加热枫桦木炭化表面4 ms后迅速飞溅形成次生液滴,小液滴滚动蒸发聚合成一个大液柱,大液柱起伏多次后形成一个小液柱停留在枫桦木表面。而含4% AFFF液滴撞击受热枫桦木炭化表面时,液滴碰撞后与木材发生良好浸润现象。     

静止悬垂水滴形成甲烷水合物的生长动力学

在273.35～277.15 K,4.86～6.65 MPa条件下开展了静止悬垂水滴形成甲烷水合物的可视化实验,提出了气-液平衡时水滴表面CH_4气体溶解度的计算方法以及描述水滴表面水合物膜生长的动力学模型,预测了悬垂水滴形成甲烷水合物的生长时间。结果表明,悬垂水滴转化为水合物颗粒的时间随着系统压力的升高而缩短,随着系统温度的降低而减小。水滴越小,反应时间越短。水滴尺寸和CH_4的扩散阻力对水合反应的影响比系统压力、温度的影响大得多。CH_4在水合物膜中的扩散阻力是影响悬垂水滴转化为水合物的主要因素,进行喷雾反应釜设计时,须尽量消除扩散阻力的影响,加快气体水合物的合成速率。     

增湿塔内雾化水滴蒸发的分析与计算

本文应用连续介质力学理论分析了增湿塔内水滴的蒸发过程。得出了考虑stefen流及水滴与高温气流之间有相对运动过程的水滴蒸发速率与时间的计算公式。并同时给出了努谢尔特数不为常数时的蒸发时间的数值解。计算结果表明,当水滴与气流之间有相对运动时,水滴的蒸发时间不象以往认识的那样与粒径的平方成正比,它们之间的关系比较复杂。     

增湿塔内雾化水滴蒸发的分析与计算

本文应用连续介质力学理论分析了增湿塔内水滴的蒸发过程。得出了考虑ｓｔｅｆｅｎ流及水滴与高温气流之间有相对运动过程的水滴蒸发速率与时间的计算公式。并同时给出了努谢尔特数不为常数时的蒸发时间的数值解。计算结果表明，当水滴与气流之间有相对运动时，水滴的蒸发时间不象以往认识的那样与粒径的平方成正比，它们之间的关系比较复杂。     

Solid-liquid separation in suspension atomization

The aim of this paper is to define the conditions controlling the fragmentation process within the atomization of a suspension. Correlations for the droplet diameter of a suspension spray generated by a twin-fluid nozzle have been derived. Two separate regimes in suspension atomization have been identified with respect to the solid particle size. The atomized droplets from suspensions containing relatively fine solid particles are suspension droplets (containing liquid and solid particles). In this case a correlation for the drop size distribution in the spray of a twin-fluid nozzle has been deduced. Droplet size measurements in the suspension spray with varying solid particle sizes showed that when the suspended solid particle size exceeds a critical value, solid particles and liquid will be more and more separated. This effect is indicated by a bimodal size distribution in the suspension spray. It is shown that complete solid-liquid separation in the suspension spray may be achieved, where the pure liquid drops are significantly smaller than the separated solid particles. The critical process conditions where the solid-liquid separation process is found will be derived. Depending on the operating conditions of the atomizer, the resulting pure liquid droplet size is equal or less than the hydraulic diameter.     

Studies on the atomization and combustion performance of a twin-fluid acoustic atomizer

A twin-fluid air-assist atomizer coupled with a Hartmann type stem and cavity air-jet acoustic generator has been used to atomize water, kerosene, diesel oil and furnace oil. The effects of atomizing air pressure, air to liquid mass ratio and liquid viscosity on the mean drop size of the spray have been investigated. From the experimental results a suitable correlation has been obtained to estimate the Sauter mean diameter (SMD) of such sprays. The influence of resonating cavity on the spray pattern and lean blow-off limits for the combustion of kerosene has also been studied. Burners incorporating this type of twin-fluid acoustic atomizer are found to be particularly suitable for highly viscous oils.     

计算喷雾干燥塔直径和高度的数值积分法

提出了计算喷雾干燥塔直径和高度的一种新方法———数值积分法。该法在0.5≤Re≤3000的跨区间(包括部分层流区、全部过渡区和部分湍流区)内,阻力系数与雷诺数之间的关系用误差极小的多项式拟合计算式,取代图解积分法中绘制列线图时使用的误差较大的A llen公式,得出计算雾滴水平飞翔距离和雾滴减速运动下降距离的积分式,用精度很高的四阶复化高斯-勒让德数值积分法直接求出它们的值,然后算出塔径和塔高。算例表明,新方法计算简便、结果精确、易于编程用计算机计算、收敛速度快。     

转炉一次除尘新OG系统高效喷淋塔喷嘴雾化特性的模拟

利用离散相模型对转炉一次除尘新OG系统高效喷淋塔内喷嘴的雾化特性进行模拟,分析了喷射角度、喷射压力、喷射流量及喷嘴水平间距等因素对雾化场索太尔平均直径(SMD)和蒸发效率的影响. 结果表明,在一定范围内随喷射角度增加,液滴在雾化场中的覆盖面增大,液滴驻留时间变长,蒸发效率增加,雾化场SMD减小,喷射角度大于60o时,SMD值减小缓慢. 随喷射压力增大,液滴蒸发效率增加,雾化场SMD减小,压力大于1.0 MPa时对SMD的影响较小. 随喷射流量增加,液滴蒸发效率减小,雾化场SMD增加,流量小于0.15 kg/s时,SMD增加幅度偏小. 两喷嘴水平间距越大,液滴分布面积越大,但对雾化场SMD影响较小. 在一定条件下,喷嘴间距约为800 mm时,截面速度分布较均匀.     

An experimental study of spray flash evaporation

An experimental study has been conducted on spray flash evaporation occurring in a superheated water jet injected through a circular tube nozzle into a low-pressure vapor zone. The effects of superheat, flow rate and nozzle diameter on spray flashing were pursued at 60°C jet inlet temperature. From the experimental results, an empirical equation suitable for predicting the variation of liquid temperature with residence time was deduced.     

智能高效脱销系统在水泥生产上的应用

介绍了HeSNCR智能高效脱硝系统,该系统在分解炉上分层布置喷枪,每层有相应的自动控制阀门,利用人工智能软件实时跟踪窑况变化,通过分析水泥窑系统的各操作参数,准确判断氨水需用量,精确控制每组喷枪,在最合适的喷入点喷进最适量的氨水,实现最高的脱硝效率。该系统还可以在达到最大NOx脱除率的同时,有效控制氨逃逸。从2019年3月至今,系统运行稳定,成功将氮氧化物排放量控制在100mg/m^3(标)和50mg/m^3(标)。     

Evaluating the Use of Humidification Systems During Heat Treatment of MPB Lumber

Lumber produced from lodgepole pine logs attacked by the mountain pine beetle (MPB) infestation in British Columbia, Canada, exhibits very low initial moisture content (MC). Depending on the time elapsed since attack, the initial MC can be significantly lower than the fiber saturation point (FSP ～30%). Lumber exhibiting 19% MC or less is considered ready for the dimension lumber market and does not necessarily need to be kiln dried. However, phytosanitary regulations require that lumber products be heat treated before delivery to customers. For lumber already quite dry, the Canadian Food Inspection Agency (CFIA) kiln drying/heat treatment schedules may be too long and can result in overdrying. For the significant volume of MPB lumber with an initial MC below 19%, the use of low-pressure steam or cold water spray could allow this lumber to be heat treated without causing further drying. This approach should result in improved lumber quality because overdrying would certainly be minimized and probably eliminated.

In this study, two sorts (dry and wet sort) of MPB lumber were dried in a pilot laboratory kiln humidified with low-pressure steam or cold water spray. Twelve drying runs were carried out. The experimental results indicated that the times to reach the temperature of 56°C in the core of the lumber were shortened and warp for the dry-sort lumber group was reduced when the low-pressure steam or cold water spray system was used. Thus, for MPB lumber with a low initial MC, the utilization of lower pressure steam or cold water spray during heat treatment represents an attractive alternative to reduce kiln residence time, minimize or eliminate overdrying, and improve lumber quality.     

SIMULATION OF SPRAY DRYING OF A SOLUTION ATOMIZED IN A PULSATING FLOW

Spray drying of NaCl solution was carried out under an intense oscillating flow field generated by a pulse combustor. A pulse combustion spray drying system was constructed. An optical analyzer was used to measure the particle diameter distribution of droplets atomized by a pulsating flow. The momentum, heat and mass transfer in both gaseous and particulate phases during spray drying inside the drying chamber were simulated using the computational fluid dynamics method. The simulated profiles of flow field, temperature and humidity of the gaseous phase, as well as the particulate phase, in the drying chamber were presented. The simulation showed changes of the flow field and particle trajectories in the drying chamber during one pulsating period. A large-scale vortex was observed in the upper part of the drying chamber because of the unstable state of flow field and particle trajectories. Short drying time and large evaporation rate are characteristics of pulsating spray drying. The influence of gas stream pulsation frequency on the drying process is also analyzed.