T型三通管冷热流体掺混数值模拟

针对T型三通管冷热流体掺混现象经常引发管道热疲劳甚至部件失效的问题，基于FLUENT混合雷诺平均N-S方程（Reynolds averaged N S equations，RANS）和大涡模拟（large eddy simulation, LES)方法，对其管内冷热流体掺混问题进行仿真模拟。对划分的LES和RANS计算域分别采用壁面模拟LES（wall modeled LES, WMLES)和k-ω SST模型进行计算，并将数值模拟结果与实验数据进行对比。分析功率谱密度（power spectral density, PSD），预测管内冷热流体掺混过程的热疲劳敏感位置，结果表明：数值模拟预测结果与实验数据吻合度较高，热疲劳敏感位置也与实际情况相符合。混合RANS-LES方法适用于T型三通管冷热流体掺混问题研究。     

三通管内冷热掺混流动下的温度场预测

对三通管内冷热水的掺混流动过程进行试验研究,得到在30 ℃温差、不同进口流量比条件下掺混流域的温度场数据;提出基于BP神经网络的温度场预测模型,并将预测结果与实测数据进行对比。结果表明：掺混流域温度场特性的预测结果与试验数据吻合度较高,对温度振荡功率谱密度的分析也得到同样的结果,这对进一步研究管道热波动引起的管道热应力,以及进行管道热疲劳分析与寿命评估具有指导意义。     

液液喷射混合器最佳引射角度的CFD模拟

利用CFD模拟方法,研究了液液喷射混合器中引射流体进料角度的影响行为和优化选择问题。选择7种不同引射角度为考察对象,考察了喷射器内部流体的流动特性与掺混效果。结果表明:不恰当的引射角度将导致引射流体在喷嘴外围环隙的速度和流量分配不均,进而导致流场偏移;随着引射角度的增加,压力降、喷射系数、混合段流体速度和湍流耗散率呈现出先增大后减小的变化趋势;不同引射角度下流体达到混合完全所需要的距离相同,但是质量分数存在差别。综合分析,在7种引射角中,引射流体的最佳引射角度为60°,此条件下喷射器内混合段流体速度大,喷射系数高,混合效果好,同时对管壁的冲击力小。     

具有非均匀内热源的多孔介质中自然对流传热的数值研究

采用数值方法分析了填充多孔介质的竖直同心套管内,非均匀分布的内热源和内外壁面温差对自然对流的影响。考察了高宽比A、内热源分布系数m以及内外Rayleigh数之比Rai/Ra对流场、温度场和内外壁面Nusselt数的影响。结果表明：Rai/Ra较大时流场中部形成逆向环流,并出现θ＞1的高温区；内壁面Nusselt数呈现先增大后减小的趋势,大约在Z=0．8处出现转折。外壁面Nusselt数在Z＞0．8处变化加剧,表明外壁面对流传热主要集中在管上部区域。m增大流体中心逆向环流随之减小并最终消失。     

流场中沿轴向运动圆柱的附加质量计算

分别计算理想流体和黏性流体中沿轴向运动圆柱的附加质量.基于相对运动原理得出在无限流体域中不同长细比圆柱的附加质量,验证附加质量与流体黏性无关的这一结论,并发现长细比越大,附加质量因数越小.利用动网格技术的数值模拟结果表明:圆管中沿轴向运动圆柱的附加质量随管径比减小而增大,且流体的流动形态会对物体的附加质量产生一定的影响.以长细比和管径比为参数给出无限和有限流体域中圆柱附加质量与相应参变量的拟合函数.     

基于柔性热膜传感器的流体壁面剪应力测量系统

为实现流体壁面剪应力在线测量,设计了一种基于柔性热膜传感器的流体壁面剪应力测量系统.通过分析柔性热膜传感器作用机理,研发了基于LTZ1000电压基准的高精度恒流驱动电路,开发了基于DSP2812,AD7609的18位真差分同步高速数据采集模块,并通过温度补偿方法对传感器输出信号进行了环境温漂修正.系统性能测试表明:当流场温度在10 ～30℃范围变化时,剪应力测量分辨率在0～10 Pa范围内优于0.2Pa,流体温度变化引起的系统输出信号偏差为0.6％/℃,满足实际流体壁面剪应力测量要求.     

三维矢量场的流动拓扑结构抽取

提出一种基于关键点分类的三维矢量场流动拓扑结构抽取算法,可应用于三维曲线网格、结构化网格和分块网格中.在许多计算流体力学计算中,存在非滑移边界,这种边界上流体的速度为0.通过分析流场边界的表面摩擦场的拓扑,展示绕壁面流体的流动结构;使用图标定位关键点,可交互式地标记和显示涡核区域,并通过选择暗示螺旋流动的图标,沿着该关键点的实特征值对应的特征矢量方向积分流线来完成.测试结果清晰地展示了关键特征区域的流体流动特征.     

垂直管内流体性能测试创新实验研究

通过研究不同物性的液体在不同管径的换热管中流动情况,设计一种根据物性而定的换热管布膜器。采用新型布膜器进行创新实验,以不同密度、粘度、表面张力等物性的乙醇水溶液为实验液体,进行垂直管内降膜冷模实验。观察降膜流动过程,以及综合考虑液膜厚度等因素,选取最佳液膜流动。实践应用证明:新型布膜器用于换热管管径布膜的方法是可行的。     

基于弯曲振动粘度动态测量技术分析

通过求解流体流动时载流振动管弯曲振动方程,得到流体质点所受外力的动态方程.分析振动管弯曲振动能耗与流体质点受外力做功的关系,推导出流动流体在振动管做弯曲振动时的损失能耗量、流体流速和流体动力粘度的关系,从中分析流动状态下流速对粘度测量的影响,并通过实验验证了所得结论.     

翼稍装置对翼尖涡耗散的影响研究

针对不同安装角的情况下翼梢小翼对翼尖涡耗散问题,利用thin-cut技术生成六组非结构网格,采用SST k-omega湍流模型与三维雷诺平均N-S方程对不同安装角度的翼梢小翼与未安装翼梢小翼的机翼进行模拟仿真与数值计算,得到了距离机翼不同距离区域翼尖涡的涡量分布云图.研究表明,翼梢小翼通过生成正向涡旋与翼尖涡相互作用降低翼尖涡的涡旋强度,合适的翼梢小翼安装角度能大幅度提高翼尖涡耗散效率,减小翼尖涡的危害,提升民航运行效率.     

煤矿管道瓦斯流量计量技术研究

阐述了煤矿管道瓦斯流量计量技术的发展现状,分析了孔板流量计、涡街流量计、皮托管流量计、旋进漩涡流量计、V锥流量计的优缺点;针对瓦斯流量测量准确度受气体中的杂质和瓦斯体积分数变化影响的问题,提出了解决办法;建议煤矿瓦斯抽放管网中的主管、干管、支管采用V锥流量计,汇流管以及各评价单元采用多点采样的插入式流量计;指出煤矿管道瓦斯流量计量应根据不同的现场状况、工况条件及测量需求选择相应的流量计。     

Effects of incomplete surface accommodation on non-equilibrium heat transfer in cavity flow: A parallel DSMC study

The impact of incomplete surface accommodation on non-equilibrium heat transfer in a lid-driven cavity is evaluated by a parallel direct simulation Monte Carlo method. A two-dimensional partitioning technique has been employed to parallelize the code and its parallel performance is assessed. The computed results indicate that incomplete surface accommodation significantly impacts all aspects of flow and heat transfer in the cavity like the vortex center, wall heat flux rates, and the heat transfer mechanism itself. In particular, a counter-gradient heat flux pattern exists when the flow is in a non-equilibrium state, under which thermal energy is transferred from a cold region to a hot region. However, the gaseous heat transfer process changes with any increase in incomplete surface accommodation, significantly affecting the direction of heat transfer.     

海水淡化双级真空引射器的射流和混合特性研究

引射器是实现热法海水淡化系统高效节能的重要装置,该文通过三维数值模拟方法研究了双 级引射器内部流动和传输特性,分析了引射和工作流体的混合与扩散过程,探讨了降低能耗的方法。 研究结果表明,喷射器内速度最大值均在轴线处,流体在喷嘴与混合室内流线均匀,而在吸入室内产 生一个或多个涡流。不同引射流体速度下,其混动迹线为不对称分布,随着引射流体速度的增大,引 射流体入口处负压先增加后减小,漩涡量减少且漩涡变小。因此,为改善引射器运行效率,可适当提 高引射流体速度。随着偏离喷嘴中心距离的增大,湍动耗散率明显增大,而湍动能略微增大,漩涡消 散加快。     

Numerical Analysis of a Vortex Tube: A Review

Ranque–Hilsch vortex tube is a simple devise with no moving parts which could generate cold and hot air/gas streams simultaneously with compressed air/gas as a working fluid. The energy and flow separation in a vortex tube is highly depends on factors like nozzle shape, nozzle number, diameter and length of the vortex tube, inlet pressure, control valve, diaphragm hole size and cold mass fraction. As the energy separation and flow patterns in a vortex tube are highly complex and were not explained successfully by any researcher, a computational study of vortex tube flow and energy separation will give a better understanding about the physics and mechanism involved. Many researchers conducted computational fluid dynamic analysis of the vortex to have a deep insight about the process of flow separation. In this paper computational analysis of vortex by many researchers were presented along with the results obtained and suggestions to improve the performance of the vortex tube. Researchers considered Turbulence models which predict the performance precisely were discussed in the present paper. Researchers considered turbulence models like LES, k–ε, k–ω and RMS to predict the energy separation in vortex tube. Some researchers considered artificial neural networks (ANN) and Taguchi methods for their analysis. Comparison of the predictions with simulation results were also presented to give a clear idea for the reader about the CFD models prediction capabilities.     

Identification of near-wall flow structures producing large wall transfer rates in turbulent mixed convection channel flow

In this paper, we analyze the influence of aiding and opposing buoyancy on the statistics of the wall transfer rates in a mixed convection turbulent flow at low Reynolds numbers in a vertical plane channel. The analysis is carried out using a database obtained from direct numerical simulations performed with a second-order finite volume code. The aiding/opposing buoyancy produces an overall decrease/increase of the intensities of the fluctuations of the wall shear stresses in comparison with the forced convection flow. The near wall structures responsible for the positive extreme values of the fluctuations of the wall shear stress, educed by a conditional sampling technique, consist in two quasi-parallel counterrotating streamwise vortices that convect high momentum fluid towards the wall in the region between them. Buoyancy produces an overall increase of the Reynolds stresses near the cold wall in comparison with the hot wall. This affects the streamwise length, the orientation, the velocity and the intensity of these flow structures near the two walls of the channel. It is found that the flow structures near the cold wall are shorter and produce more intense fluctuations than those near the hot wall.     

Interfacial configurations and mixing performances of fluids in staggered curved-channel micromixers

We present a parallel laminar micromixer with staggered curved channels for homogeneously mixing two fluids by Dean vortex. The secondary flows are produced in curved rectangular channels by the centrifugal forces; the diffusion distance of two fluids is reduced due to the staggered structures of the flow channels. The mixing strength is increased when one stream is injected into the other. Confocal microscopy and pH indicator have been used to study the mixing. Computational fluid dynamics simulations are utilized to examine the interfacial configurations and the mixing behaviors inside the channels. The interface of the two fluids is heavily distorted and increases the interfacial area because of the unique structures. The mixing index of the staggered curved-channel mixer with tapered channels is higher than those of the other curved-channel mixers. The effects of various Reynolds numbers and channel configurations on mixing performances are investigated in terms of the experimental mixing indices and the computational interfacial patterns. The comparison between the experimental data and numerical results shows a very similar trend.     

喷射距离对喷射冷板散热性能影响的实验研究

为了增强对喷射冷板散热性能影响因素的了解,通过实验研究了喷射距离对喷射冷板散热性能与阻力值的影响,并对喷射冷板散热性能的均匀性进行了分析。实验结果表明,在流量相同的情况下,现有结构喷射冷板的总热阻随喷射距离的增大先减小后增大,在喷射距离为1.5 mm时存在一个最小值;喷射冷板的阻力值随喷射距离的增大而降低,但喷射距离对喷射冷板的阻力影响较小;喷射冷板在水流方向的散热性能存在一定不均匀性,喷射冷板进水侧散热能力要略高于出水侧。     

基于有限元模拟的薄膜热流计结构设计及优化

精确的热流测量对航空航天领域发动机设计及使用过程至关重要.薄膜热流计以其体积小、热容量小、干扰小、不破坏部件表面气流等显著优势,成为发动机热端部件表面热流测量的新方法.针对传统工程经验设计薄膜热流计精确度不高且迭代耗时长的缺点,基于有限元仿真模拟方法,建立了一种薄膜热流计有限元分析模型,综合分析了热流密度、热阻层厚度、热电堆厚度等因素对热流计冷热结点温度梯度的影响,提出薄膜热流计优化思路.分析结果表明,优化后的薄膜热流计具有更出色的热学性能与电学性能.     

An experimental inquisition of waste heat recovery in electronic component system using concentric tube heat pipe heat exchanger with different working fluids under gravity assistance

In the utilizing of the waste heat in the electronic components meets the power demand and energy utilization for the industries and domestic applications. To meet out this by the understanding and optimization of the waste heat utilization by a compact and cost effective device using heat pipe heat exchanger. This paper states with the design, fabrication, development, and observation of an experimental investigation of the heat pipe introduce in the concentric tube heat exchanger. Working fluids like Methanol, Acetone and heat transport fluid as water. The investigation is further extended by varying the inclination angles, mass flow rates, and temperatures of hot and cold fluid at inlet conditions. The influence of gravitational effect on the heat pipe heat exchanger is conducted for inclination angle from 10° to 80° and the maximum performance is obtained at 60° inclination angle. It is observed while acetone as working fluid there is an increase in 29.75% for effectiveness, 79.81% as heat transfer coefficient, 39.53% as heat transfer rate, 6.70% for Reynold's number and 10.52% decrease in thermal resistance than with methanol. It is concluded that the acetone exhibits better performance when related with methanol as a working fluid. These observations show the suitability of the designed concentric tube heat pipe heat exchanger for the utilization of waste heat dissipation in electronic component system.     

消除涡街流量计的使用障碍

文章阐述了涡街流量计在石油化工装置工程设计和使用过程中出现的问题，并着重就进口涡街流量计与管道内径匹配问题及涡街流量计在蒸汽流量测量中的温压补偿问题提供了简单的分析方法和计算公式。