制氧机板翅式换热器设计标准(试行)

本设计标准适用于全低压空气分离装置的板翅式换热器。1．板翅式换热器的结构:板翅式换热器的板束由翅片、(导流片)、封条等部分组成。如图1所示。在相邻二隔板之间放置翅片、(导流片)、封条组成一通道,钎焊成整体,形成板束。板束上配置适当的流体出入口封头,组成一完整的板翅式换热器。     

导流及布气方式对膜生物反应器内部流场影响的数值模拟分析

运用数值模拟,研究膜生物反应器中曝气管路布气位置及导流板对反应器内流场分布的影响,并对3种气水比(10:1、15:1、20:1)进行了优化研究.将模拟结果进行比较发现:“对齐”布气优于“间隔”布气;导流板对反应器内流场特性有较明显的影响,导流作用能有效地改善反应器内气含率的分布状况,提高氧传质效率,增大膜面剪切速度.在相同条件下,其平均膜面剪切速度分别是不加导板的“对齐”和“间隔”布气方式的1.5和1.9倍.当气水比为15:1时,各种布气方式反应器内气含率分布均较大,流场内的涡流均非常明显,整个场内形成了循环流动,膜面剪切速度也达到最大.     

弧形导流板在空调通风中的应用研究

提出将弧形导流板应用于射流碰撞类通风以改善室内流场,从而达到节能舒适的目的 .利用数值模拟的方法对弧形导流板改善室内流场的效果展开研究,并分析了导流板尺寸、形状、位置以及送风参数对其产生的影响.结果 表明,在竖壁贴附送风的应用中,合理引入弧形导流板可以消除房间角落旋涡,减少超过28％的动能损失,并且延长了竖壁贴附送风的...     

SPR+UPS+UPR并联机构的逆运动学和工作空间分析

目的 获得悬浮烘箱内具有提高风场均匀性和风刀出口气流均匀性的导流板结构,完成烘箱体结构优化。方法 采用SolidWorks软件对烘箱风室的流体域进行建模,提取现场测试数据作为边界条件,利用Fluent软件完成风室稳态流场的仿真计算。根据计算结果提出结构优化方案,并将优化结果进行对比。结果 加入导流板结构后,烘箱风室风场和风刀出口处气流的均匀性均得到了提高。提出的4种结构优化方案中,加入曲线型导流板的风室风场更为均匀,各风刀出口处气流的平均速度均方差由0.25降至0.03,总体平均均匀度由80.7%提升至92.3%。结论 曲线型结构导流板的导流效果优于直角型结构的导流板,能有效提高风室风场和风刀出口气流的均匀性,保证极片烘干效果的一致性,并为烘箱体的结构优化与设计提供理论基础。     

导流板对烟气均布作用的流场分析

袋式除尘器的流场是所有除尘器中最复杂最不均匀的,如何能够组织好内部流场就显得特别重要.依靠导流装置不仅可以获得较均匀的气流分布,也会大大减小气流对滤袋的磨损程度,提高除尘效率.本文对添加导流板前后袋式除尘器单元内部流场利用CFD软件数值模拟方法进行分析.结果表明:在添加导流板之后,单元内部流场更加均匀,速度分布更加合理...     

封头结构对板翅式换热器流体分配性能的影响

研究了板翅式换热器封头高度与流体分配之间的关系,实验结果说明板翅式换热器的流体分配与封头高度有很大关系,封头高度越高流体分配就越均匀.引入不均匀参数,以便可以对流体在出口截面的分配特性进行研究,并进一步研究封头结构型式不同对于流体分配的影响,研究表明:换热器内部流体的流速的最大值与最小值的比值由3-4减少到1.1-1.2,其不均匀度也从原来的0.331减少到0.046.     

单进口中空纤维膜接触器壳程流动特性的测定与改进

采用中空纤维膜接触器考察了不同装填因子和流速对流体在壳程中停留时间分布的影响.结果表明随着装填因子的增加,停留时间分布曲线拖尾现象更为严重;增加流速虽然可以缓解滞留的影响,但当流速很大时,流体伴有沟流发生,返混程度增大.为了改善流体的流动状态,抑制返混等非理想流动,对中空纤维膜接触器进行了改进.通过停留时间分布的测定,结果表明流体在改进后的中空纤维接触器壳程中的返混现象得到了极大的抑制.     

催化裂化密闭快分系统封闭罩内流场优化

针对催化裂化密闭快分(CVQS)系统封闭罩内上方存在的非对称不稳定的旋涡流引起的压力不稳定现象,在一套大型冷模装置上,实验测定旋涡流出现的位置与操作条件间的时空特性;为消除不稳定旋涡流,在封闭罩内添加直板形式的导流板,与不添加导流板的装置进行实验对比。结果表明,装置加入合适导流板后,封闭罩内的流场得到改善,有效消除旋涡流现象,减弱了压力波动,使系统的压降明显减小。     

不锈钢外板对 2219 铝合金拼焊板胀形性能的影响

目的现有2219铝合金板材宽度不能满足大型复杂曲面件整体流体高压成形需要,仍需采用焊接方法制备成形坯料,焊缝的存在导致铝合金拼焊板整体性能不均匀,影响成形性能及壁厚分布。方法提出2219铝合金拼焊板的双层板流体高压成形方法,采用1.8 mm厚铝合金拼焊板作为内层板,1mm厚不锈钢板作为外层板,进行双层板胀形实验研究。对比分析了单层板与双层板条件下2219铝合金拼焊板的成形极限、应变及壁厚分布。结果外层板的存在能够使板材的极限成形高度和极限应变增加,同时使壁厚分布更加均匀。结论双层板之间存在界面摩擦,可以提高内层拼焊板的成形极限、改善壁厚分布。     

螺旋导流膜分离器中流体流动特性研究

为减少膜分离中的浓差极化和膜污染,提出了一种新型的膜分离组件,螺旋导流膜分离器.通过数值模拟确定了螺旋导流膜分离器的最小工作状态,并从螺旋导流膜分离器中流体流动的轴向速度、周向速度、壁面剪切应力和压力等流场特性分析,对其分离机理有了较为全面、深入的认识.     

Pressure drop in round cylindrical headers of parallel flow MCHXs: Pressure loss coefficients for single phase flow

This paper presents the investigation of the pressure drop in headers and development of correlation for pressure loss coefficient for single phase flow through round cylindrical headers of parallel MCHXs. The working fluid was compressed air flowing through header with 1–20 m s⁻¹ based on smallest cross section while the velocity through microchannels was in the range 6–30 m s⁻¹. The experimental results indicate that the pressure loss coefficient of inlet header is a linear function of the ratio of velocities through microchannel tube and header, except for the first two microchannel tubes; the pressure loss coefficient of outlet header is a quadratic function of the ratio of velocities through microchannel tube and header, and decreases as the velocities through upstream microchannel tubes increase. Correlations for predicting pressure drop of inlet header and outlet header are developed and agreement for 98% of experimental data is within a ±15 Pa.     

Study of flow distribution and its improvement on the header of plate-fin heat exchanger

In order to enhance the uniformity of flow distribution, an improved header configuration of plate-fin heat exchanger is put forward in this paper. Based on the analysis of the fluid flow maldistribution for the conventional header used in industry, a baffle with small holes of three different kinds of diameters is recommended to install in the header. The flow maldistribution parameter S is obtained under different header configuration. When the baffle is properly installed with an optimum length, with stagger arranged and suitably distributed holes from axial line to baffle boundary, the ratio of the maximum flow velocity to the minimum flow velocity drops from 3.44-3.04 to 1.57-1.68 for various Reynolds numbers. The numerical results indicate that the improved header configuration can effectively improve the performance. The conclusion of this paper is of great significance in the improvement of plate-fin heat exchanger.     

Effect of inlet configuration on the refrigerant distribution in a parallel flow minichannel heat exchanger

The refrigerant R-134a flow distribution was experimentally studied for a round header/ten flat tube test section simulating a brazed aluminum heat exchanger. Three different inlet configurations (parallel, normal, vertical) were investigated. Tests were conducted with downward flow for mass flux from 70 to 130 kg m⁻² s⁻¹ and quality from 0.2 to 0.6. Tubes were flush-mounted in the test section, with no protrusion into the header. It is shown that normal and vertical inlet yielded similar flow distribution. As mass flux or quality increased, however, better results were obtained for normal inlet configuration. The flow distribution was worst for the parallel inlet configuration. Possible explanation is provided based on flow visualization results. Correlations were developed to predict the fraction of liquid or gas taken off by downstream channel as a function of header gas Reynolds number at immediate upstream.     

倾斜状态下板翅式换热器封头物流分配特性的实验

海上平台受到海浪的作用会发生晃动和倾斜,从而影响板翅式换热器的入口物流分配特性。通过空气—水两相物流分配实验系统,分别进行封头结构水平状态和倾斜状态下的单相以及气液两相实验,获得不同实验工况下的封头物流分配特性,研究倾斜对封头物流分配的影响,从而为换热器的安装及工艺的改进提供依据。结果表明：水平状态下物流分配受惯性力的影响,不均匀度随雷诺数和气液比的增加而增大;倾斜状态下流体受到惯性力和重力的双重影响,物流分配均匀程度显著低于水平状态,倾斜角越大物流分配越不均匀,气液比越大物流分配受倾斜影响程度越大;固定封头或安装换热器时应严格保证其水平/竖直状态,或者通过液化工艺及换热器设计的改进消除倾斜的影响。     

Effect of the header pressure drop induced flow maldistribution on the microchannel evaporator performance

This paper presents an experimental and numerical investigation of the flow maldistribution caused by the pressure drop in headers and its impact on the performance of a microchannel evaporator with horizontal headers and vertically oriented tubes. Experimental results show that the flash gas bypass method almost eliminates the quality induced maldistribution. However, refrigerant flow maldistribution caused by the header pressure drop still exists. This is mainly because the pressure drop along the headers results in uneven pressure difference and therefore non-uniform liquid refrigerant mass flow rate across each microchannel tube. A microchannel evaporator model validated by experimental results is employed to quantify header pressure drop induced flow maldistribution. Parametric analysis reveals that such maldistribution impact is significantly reduced by enlarging the outlet header size, increasing heat exchanger aspect ratio, or reducing the microchannel size while other parameters are kept constant. When ratio of outlet header to the total evaporator pressure drop is less than 30%, the cooling capacity reduction is limited below 3%.     

CFD simulation on inlet configuration of plate-fin heat exchangers

A computational fluid dynamics (CFD) program FLUENT has been used to predict the fluid flow distribution in plate-fin heat exchangers. It is found that the flow maldistribution is very serious in the y direction of header for the conventional header used in industry. The results of flow maldistribution are presented for a plate-fin heat exchanger, which is simulated according to the configuration of the plate-fin heat exchanger currently used in industry. The numerical prediction shows a good agreement with experimental measurement. By the investigation, two modified headers with a two-stage-distributing structure are proposed and simulated in this paper. The numerical investigation of the effects of the inlet equivalent diameters for the two-stage structures has been conducted and also compared with experimental measurement. It is verified that the fluid flow distribution in plate-fin heat exchangers is more uniform if the ratios of outlet and inlet equivalent diameters for both headers are equal.     

联箱-小孔型气液分离器的CFD数值模拟

在冷凝过程中采用气液分离(分液冷凝)能同时实现强化传热和降低压降.高效的气液分离是提升分液冷凝器性能的关键.本文针对联箱-小孔型气液分离器,建立了三维数值模型,研究了其气液分离特性.基于实验结果对模型进行了验证,分析了分液孔径(0.5～2.0 mm)和分液孔位置(居中、不居中)对联箱内工质流动特性的影响.结果表明:在入...     

空预器风阻对锅炉的影响分析

对于华电包头锅炉的空气预热器（容克式）,在运行中由于积灰造成预热器的堵塞,对锅炉的效率、预热器的磨损及吸风机、送风机的电耗增大等问题,本文主要介绍华电包头空气预热器水冲洗后锅炉排烟温度及吸风机、送风机电耗的影响。     

开架式气化器竖直圆管内超临界氮换热实验研究

目前国内外对液化天然气(LNG)接收站的开架式气化器中超临界天然气的流动换热实验研究非常少,本文为了研究开架式气化器中竖直管内超临界流体的流动换热特性,搭建了竖直单管超临界流体换热实验平台。以液氮代替液化天然气,研究了氮入口压力、水温和水流量等不同参数对换热的影响。结果表明:在拟临界温度以下,表面传热系数随着压力的增大逐渐减小,但拟临界温度以后,这种趋势相反;当水流量足够大时,氮出口温度取决于管外水温而不是水侧流量。最后,基于实验数据拟合出了适用于竖直圆管内超临界低温流体流动换热的半经验关联式,关联式预测值和实验值的平均绝对偏差为8.42％,可以准确预测竖直加热管中超临界氮的表面传热系数。     

汽-气液滴形管与圆管外凝结换热的研究

为了研究管型对汽-气凝结换热的影响和强化汽-气凝结换热过程,建立了汽-气在液滴形管与圆管外凝结换热所形成的气液膜的厚度及换热系数沿管壁分布的综合数学模型。通过有限差分的方法,以天然气燃烧产生的烟气为例对两种管型进行了计算比较。在有效换热面积相等的情况下,与圆管相比,液滴形管上半部分管径小,压力梯度大,有利于排液,下半部分表面曲率大,亦有利于排液;液滴形管表面形成的气膜薄,液膜亦薄,珠状凝结区域大,液珠尺寸小,凝结换热系数大;液滴形管对显热传递亦有一定的强化作用。通过实验对计算结果进行了比较验证,结果表明该模型亦适用于椭圆管和其它汽-气混合流体种类。