烟气量、喷射水量和喉口开度对转炉烟气除尘文氏管内部流动与传热性能影响

文氏管是转炉湿法除尘工艺中烟气净化和回收过程的关键设备之一，根据不同吹炼时期烟气量的变化，通过调节文氏管喉口处的喷嘴水量和挡板开度，来获得较好的除尘效果和压力损失。由于文氏管内部的流动与传热较为复杂，基于离散相和连续相流动与传热模型，在FLUENT平台上，对文氏管内部的流动与传热过程进行了三维数值模拟；分析了不同烟气量、不同喷射水量和不同挡板开度对文氏管流动与传热性能的影响。     

大型脱硫塔喷淋段气液两相流动与传热的数值仿真及验证

对大型湿法脱硫塔喷淋段内部的气液两相流动和传热过程进行模拟,并将模拟结果同现场运行数据进行对比.结果表明:良好的喷淋层和喷嘴布置可对塔内烟气流动起到很好的整流作用;在烟气入口对面的浆液池上方存在一气相的最高压区;原烟气的高速冲入对浆液滴的运动轨迹产生明显的影响,使得烟气入口处形成了一个斜向下呈带状的液滴浓度高值区;喷淋塔内温度梯度变化较大的区域在靠近吸收塔入口的位置,且此区域随烟气量的增大而扩大——简单忽略塔内气相温度场的不均匀性势必将给计算带来误差;喷淋塔内的气相温度场和水蒸气浓度场分布有明显的一致性规律,证明了塔内的降温过程主要为蒸发冷却.     

双P型辐射管数值模拟及参数优化

以功率为100 k W的双P型辐射管为研究对象,利用Fluent软件对其内部的流动、燃烧及传热过程进行模拟,并对比了在有回流和无回流状况下辐射管的气相温度场及壁面温度变化情况,证明在有回流状况下,辐射管内部燃烧状态处于"无焰燃烧"状态。对六种不同空气、烟气喷口排布方式的方案进行了模拟,对比了其燃烧最高温度、烟气温度、管壁温度以及烟气中三原子分子浓度的差异。并以管壁温度和辐射管传热效率为判别依据,得到了较优的布置方案。     

烟气除湿喷淋塔出口液滴逃逸率研究

为了降低火电厂烟气含湿量,以新型的上喷淋上进气喷淋塔为研究对象,采用FLUENT模型模拟喷淋塔内部两相流体的运动,并与实验验证,采用单变量分析方法研究烟气流速、喷淋液滴直径、喷淋速度、喷淋流量四种因素对出口液滴逃逸量的影响。研究结果表明：各操作条件对出口液滴逃逸量的影响程度：液滴直径>喷淋流量>进气速度>喷淋速度;出口液滴逃逸量随着喷淋流量和进气速度的增长而线性增长;在进气速度3.5 m/s下,当液滴直径小于1 mm时,逃逸量随液滴直径减小而迅速上升;当直径大于1 mm时,液滴逃逸量几乎为0,不受喷淋流量影响。     

一种用于船舶烟气冷却的喷雾螺旋管冷却器的传热特性研究

船舶使用的主动降噪设备需要连接到排烟支管,但高温烟气会缩短设备的使用寿命。为了降低烟气温度,建立了冷却器喷雾冷却的数值模型对支管冷却器的运行工况进行优化,通过数值模拟分析喷射压差与喷雾半角对冷态以及热态性能的影响。结果表明：最佳喷雾半角为60°,喷射压差为1.5 MPa时,冷却器性能最佳;采用液滴蒸发效率与逃逸质量分析冷却器内液滴的流动特性,根据模拟结果进行二次回归式拟合,喷雾压差和喷射半角与蒸发效率相关系数分别为0.19和0.56,其相对于逃逸质量的相关系数为0.25和0.72,喷嘴工作参数应选取较高的喷雾半角和较低的喷射压差。     

湿法烟气脱硫喷淋塔的实验与反应模型研究

建立了石灰石/石膏湿法烟气脱硫喷淋塔实验台,实验研究了重要的操作参数对喷淋塔脱硫效率的影响规律。实验结果表明,提高液气比和浆液pH值、降低烟气温度和烟气速度、降低入口烟气的SO2浓度以及强制氧化均可以提高脱硫效率。将喷淋浆液分成喷淋液滴和塔壁液膜两种存在形式,并分别建模,喷淋液滴的脱硫过程采用Gerbec液滴脱硫模型计算,将塔壁液膜的流动分为层流和波动层流两种状态,发展出了新的喷淋塔脱硫反应模型。模型计算结果表明,相对于Gerbec液滴模型,本文的模型计算结果与实验数据吻合得更好。     

废水液滴蒸发的关键影响因素分析

为研究电厂脱硫废水蒸发的规律,对喷入锅炉尾部烟道内的雾化液滴进行数值模拟,分析了运行参数对雾化液滴蒸发时间的影响,并通过拟合得到了烟气温度与喷嘴最佳喷射质量流量的关系式。结果表明:当尾部烟气速度为10 m/s、雾化液滴初始速度为5 m/s时蒸发时间最短;确定了喷嘴最佳喷射质量流量,使得雾化液滴在进入电除尘器前完全蒸发,且烟气温度高于酸露点;喷嘴喷射质量流量与蒸发时间呈线性正相关,与进入电除尘器前的烟气温度呈线性负相关。     

蒸发液滴内部非稳态流动的数值计算

在气液两相流VOF(volume of fluid,VOF)模型的基础上耦合CSF(continuum surface force,CSF)表面张力模型,建立了高温平板上的铺展液滴与高温空气中悬浮液滴蒸发过程中内部非稳态流动模型,对液滴蒸发过程中内部非稳态流动进行了研究。基于相变理论,采用用户自定义函数将流体相变模型加入非稳态流动模型中进行耦合计算,获得了高温平板上的铺展液滴与高温空气中悬浮液滴蒸发过程中的内部流动及变化过程。液滴蒸发过程中非稳态内部流动由液滴表面的温度梯度引发,Marangoni流动在液滴内部形成的时间非常短,流体从液滴表面高温区域流向低温区域。计算结果表明:高温平板上随着液滴蒸发的进行,液滴内部一直保持两个对称的涡流,Marangoni流动比较稳定;高温空气环境中随着液滴蒸发的进行,液滴内部四个涡流逐渐转变成两个对称的涡流;液滴内部温度分布因Marangoni流动加强传热而变得均匀,同时由于温度分布变得均匀,Marangoni流动被削弱。     

数值研究生物质焦油在旋风分离器中分离特性

借助CFD软件FLUENT对该工况下旋风分离器内部的气液两相流进行了数值模拟,其中连续相采用雷诺应力湍流模型(RSM),离散焦油液滴采用DPM模型,通过数值模拟得出了旋风分离器内部的静压场、轴向速度场与径向速度场的分布云图、液滴相的轨迹图和焦油液滴的分离与分级效率。数值计算结果表明,对于此结构的旋风分离器,分离器内部整体形成双层流动结构,近壁处径向速度与轴向速度相比较小,同时壁面对焦油液滴具有良好的捕集效果,适合用于生物质燃气焦油液滴的脱除。     

伞型结构气化器两相流动和传热数值模拟

采用通用有限比率模型对一种新型烟气冲击浸于水的伞型结构气化器燃烧室的流场与温度场进行了数值模拟,分析了循环烟气量对燃烧室喷嘴出口烟气速度和温度的影响;采用VOF两相流模型对烟气与水滴气液两相流动的传热进行了数值模拟,分析了喷嘴高度和液面高度对烟气冲击浸于水的伞型结构的两相流动传热的影响.结果表明:当循环烟气量为燃烧产生烟气量的50%、液面高度为75mm时,冲击效果最佳,水滴被烟气充分卷起并充满气化器,气化传热得到强化.     

CFD analysis of high frequency miniature pulse tube refrigerators for space applications with thermal non-equilibrium model

High frequency, miniature, pulse tube cryocoolers are extensively used in space applications because of their simplicity. Parametric studies of inertance type pulse tube cooler are performed with different length-to-diameter ratios of the pulse tube with the help of the FLUENT^® package. The local thermal non-equilibrium of the gas and the matrix is taken into account for the modeling of porous zones, in addition to the wall thickness of the components. Dynamic characteristics and the actual mechanism of energy transfer in pulse are examined with the help of the pulse tube wall time constant. The heat interaction between pulse tube wall and the oscillating gas, leading to surface heat pumping, is quantified. The axial heat conduction is found to reduce the performance of the pulse tube refrigerator. The thermal non-equilibrium predicts a higher cold heat exchanger temperature compared to thermal equilibrium. The pressure drop through the porous medium has a strong non-linear effect due to the dominating influence of Forchheimer term over that of the linear Darcy term at high operating frequencies. The phase angle relationships among the pressure, temperature and the mass flow rate in the porous zones are also important in determining the performance of pulse tube refrigerator.     

固着液滴蒸发研究进展及展望

固着液滴是指附着于壁面上的液滴,其蒸发行为及传热传质特性是喷雾冷却、喷墨打印等相变传热传质领域的基础问题之一。文中重点针对固着液滴蒸发过程所涉及的自身形态演变规律、气液固三相耦合传热/传质/流动特性进行了综述。结合毫微尺度固着液滴基本蒸发模式、热质传递形式、气液两相流动特征和界面输运行为,分析了液滴性质、壁面条件、气相环境条件等关键因素对固着液滴蒸发过程的内在作用机制和影响规律,提出了微纳尺度固着液滴（群）热质传递过程与机理的相关研究展望。     

引射式EGR系统文丘里管内流动数值模拟分析

研究了采用文丘里管引射方式的增压柴油机EGR系统及结构,按照增压柴油机EGR系统工作原理,运用CFD-Fluent对文丘里管在不同EGR率引射情况下的内部流动进行了三维数值模拟,对文丘里管内空气与EGR废气形成的混合气的流场状态、速度场、压力场参数进行了分析.计算结果表明:EGR率对文丘里管压缩段前的初始压力恢复效果有较大影响,EGR率引射量越大,压力恢复效果越差,为了满足大EGR率的要求,应减小文丘里管扩压角,混合段喉口直径和EGR引射口直径可以适当增大,引射口的数量也可适当增加.     

Measuring the Overall Volumetric Heat Transfer Coefficient in a Vapor-Liquid–Liquid Three-Phase Direct Contact Heat Exchanger

An experimental investigation of the volumetric heat transfer coefficient in a three-phase direct contact condenser was carried out. A 75-cm-long cylindrical Perspex column with a 4 cm diameter was used. Only 48 cm of the column was utilised as the active direct contact condensation height. Pentane vapor at three different initial temperatures (40°C, 43.5°C, and 47.5°C), with differing mass flow rates, and tap water at a constant initial temperature (19°C) with five different mass flow rates were employed as the dispersed phase and the continuous phases, respectively. The results showed that the volumetric heat transfer coefficient increased with increasing mass flow rate ratio (variable dispersed phase mass flow rate per constant continuous phase mass flow rate), the continuous phase mass flow rate and holdup ratio. An optimal value of the continuous phase mass flow rate is shown for an individual dispersed phase mass flow rates. This value increases with increasing vapor (dispersed) phase mass flow rate. Furthermore, it was observed that the initial driving temperature difference had no effect on the volumetric heat transfer coefficient. While, the temperature gained by the continuous phase has a considerable effect.     

A droplet size dependent multiphase mixture model for two phase flow in PEMFCs

A droplet size dependent multiphase mixture model is developed in this paper, and the droplet size in the gas channel can be considered as a parameter in this multiphase mixture model, which includes the effect of gas diffusion layer (GDL) properties and the gas drag function and cannot be considered in the commonly used multiphase mixture model in the references. The three-dimensional two phase and non-isothermal simulation of the PEMFCs with a straight flow field is performed. The effect of droplet size on the liquid remove, the effect of liquid water on the heat transfer and the effect of gas flow pattern on the heat and mass transfer are mainly investigated. The simulation results show that the large droplet is hard to be dragged by the gas, so it produces large water saturation. The results of the heat transfer show that the liquid water hinders the heat transfer in the GDL and catalyst layer, so it produces the large relative high temperature area, and there are large temperature difference and water saturation in the PEMFCs operated with coflow pattern compared with counter flow pattern.     

Investigation of a novel bayonet tube high temperature heat exchanger with inner and outer fins

In this paper, a novel bayonet tube high temperature heat exchanger (HTHE) with inner and outer fins is presented. It can be used in the ultra high temperature environment, such as hydrogen production, very high temperature reactor and externally fired combined cycle. Numerical investigation of heat transfer performance on the inside of bayonet element has been conducted for structure design. The numerical results suggest that the inner fin and inner tube should not be welded together. It is recommended that the air enters from the inner tube and exits from the annular space in the high temperature zone. A high temperature experimental system has been established to test the heat transfer and pressure drop characteristics of the HTHE. The surface area density of the tested HTHE is 6 times higher than that of the bare bayonet tube heat exchanger. The experimental results indicate that the mass flow rate on both sides and inlet temperature on the fuel gas side have a significant effect on the heat transfer rate and effectiveness, while the pressure drop ratios are mainly affected by the mass flow rate rather than the inlet temperature. Comparison between the tested HTHE and the similar HTHE without fins indicates that the proposed HTHE has a significant potential to improve the comprehensive heat transfer performance.     

微细圆管内CO2两相沸腾换热实验研究

本文对CO_2在水平微细管内流动沸腾特性进行实验研究。实验结果表明:热流密度增加对强化核态沸腾换热和高干度区域流型转变具有显著影响,随着热流密度的增加换热系数增加,对摩擦压降影响很小;质量流率对于换热系数的影响较小,但随着质量流率的增加摩擦压降大幅增加,质量流率的大小直接决定了换热过程所经历流态;饱和温度升高换热系数相应升高,摩擦压降减小,且对流态转变特性有重要影响。在同样工况下摩擦压降最大值先于换热系数最大值出现,理论分析采用的流态形式与实际CO_2管内流动流动沸腾换热流态基本一致。     

Prediction of dryout and post-dryout heat transfer at high pressures using a one-dimensional three-fluid model

A set of closure relations, in the context of a one-dimensional three-fluid model, is presented for the prediction of dryout and post-dryout heat transfer at high pressure (P/P_cr>0.3) conditions. It is shown that the traditional models based on low pressure data for interfacial friction, droplet size and the transition criteria for onset of annular flow cannot be readily extended to high pressure situations. The proposed new relations are validated by comparing with literature data in the pressure range of 30-200 bar, mass flux range of 500-3000 kg m⁻² s⁻¹ and tube inner diameters in the range of 10-25 mm. Good agreement is obtained for the dry out quality and the tube wall temperature in the post-dry out region except for cases of low mass flux at high pressures. The predictions show that at high pressure, high mass flux conditions, annular flow may prevail for low gas phase volume fraction, the droplet and the liquid film volume fractions being an order of magnitude higher than those encountered in typical air-water experiments.     

Optimization of Venturi tube design for pipeline pulverized coal flow measurements

A Venturi flow meter was designed to accurately measure the mass flow rate of pulverized coal in power plant pipelines. Numerical simulations of the dilute turbulent gas-solid two-phase flow in a horizontal Venturi tube were used to study the effects of Venturi tube geometry on the pressure distribution in the mixture. The results show that Venturi tube geometry strongly influences the metering of the dilute gas-particle two-phase flow. The geometry can be optimized to improve the precision of the measurement and ensure stable measurements. Furthermore, the geometries of three types of Venturi tubes were optimized for an experimental study of pulverized coal mass flow rate measurements.