内螺旋翅片铜管充液旋压成形加工的研究

对内螺旋翅片铜管的充液旋压成形加工进行了系统研究，着重分析了充液旋压过程中形成动压油膜的条件和特点，并建立了数学模型。实验结果表明：随着旋速和润滑油粘度的提高，流体动压润滑作用逐渐明显，被加工管的拉拔力减小，且加工后管外表面粗糙度值减小。     

带有动芯轴的管料壁厚减薄缩口成形的理论解析

薄壁管口径尺寸精度要求高,须采用带有芯轴的缩径成形制造,带有芯轴的管壁厚减薄推缩径成形的理论解析研究还极少。管件的有芯推挤缩口成形的主要缺陷是管壁失稳屈曲,管子承受轴向力的能力受到限制。准确地计算出缩径力的大小和改变成形参数以找到减小缩径力的途径是最重要的。建立有芯缩口新的动可容速度场,对固定芯和动芯的推挤缩径进行了上限解析,分析了成形参数影响,并以传动轴管为例进行了试验分析,理论与实际结果非常吻合。     

Forming characteristics analysis of the cross-section of axially inner grooved copper tube

The simulation of the cross-section forming of axially inner grooved copper tube (AIGCT) is conducted using finite element (FE) software MSC.Marc. The stress–strain distribution, metal flow rule, and contact force are analyzed based on the simulation and experimental results. The results show that gaps in the groove walls are caused not only by the diametric clearance between the inner wall of the copper tube and the mandrel but also the bending deformation of the copper tube. The cross-sectional geometry and surface characteristics of grooves are determined by the multi-tooth mandrel. Smooth transition of the mandrel teeth addendum improves the metal flow and makes contact force vary slightly, which is good for preventing mandrel from failure. Improving the mandrel surface finish can also improve the inner surface quality of AIGCT. The results help to optimize the forming process parameters and improve the forming quality.     

Thermal performance of a spirally coiled finned tube heat exchanger under wet-Surface conditions

This paper is a continuation of the authors’ previous work on spiral coil heat exchangers. In the present study, the heat transfer characteristics and the performance of a spirally coiled finned tube heat exchanger under wet-surface conditions are theoretically and experimentally investigated. The test section is a spiral-coil heat exchanger which consists of a steel shell and a spirally coiled tube unit. The spiral-coil unit consists of six layers of concentric spirally coiled finned tubes. Each tube is fabricated by bending a 9.6 mm diameter straight copper tube into a spiral-coil of four turns. The innermost and outermost diameters of each spiral-coil are 145.0 and 350.4 mm, respectively. Aluminium crimped spiral fins with thickness of 0.6 mm and outer diameter of 28.4 mm are placed around the tube. The edge of fin at the inner diameter is corrugated. Air and water are used as working fluids in shell side and tube side, respectively. The experiments are done under dehumidifying conditions. A mathematical model based on the conservation of mass and energy is developed to simulate the flow and heat transfer characteristics of working fluids flowing through the heat exchanger. The results obtained from the present model show reasonable agreement with the experimental data.     

An experimental study on accelerated fouling of aluminum oxide and ferric oxide particles in internally enhanced tubes

This paper describes the results of accelerated particulate fouling tests performed on three enhanced tubes and a plain tube. The tests were performed using ferric oxide and aluminum oxide as foulant materials. Three enhanced tubes included 25 start, 10 start helically ribbed tubes and a ripple tube. Effects of the water velocity (0.9 to 1.8 m/s) and foulant concentration (750 to 2500 ppm) were investigated. At 750 ppm, the enhanced tubes fouled almost the same as the plain tube for the entire velocity range tested (0.9 to 1.8 m/s). The enhanced tube fouled faster than the plain tube for cases of high concentration combined with low velocities. Of the three enhanced tubes, the 25 start helically ribbed tube fouled faster than the ripple and the 10 start helically ribbed tubes. One thing to be noted is that the fouling concentrations used in the tests are significantly higher than would be expected in commercial heat exchangers. Also, the velocity range investigated is lower than would be expected in heat exchanger operation.

     

内螺纹翅片铜管高速旋压拉伸成形的研究

对内螺纹理片铜管的高速旋压拉伸成形加工机理进行了系统研究，分析了加工过程及参数。试验结果表明，齿深量随坯管与内螺纹管壁厚的比值及材料塑性的增加而逐渐增大，但外表面粗糙度随之变差；拉速与旋速的比值增大会导致外表面粗糙度变差，但随着旋速提高，其影响变小。     

TiO2—蒸馏水纳米流体在内螺纹铜管内表面传热试验研究

为研究TiO2—蒸馏水纳米流体在内螺纹管内的表面传热特性,自行设计并建立一套纳米流体表面传热试验系统和数据采集系统,试验系统核心部分分别采用铜光管和内螺纹铜管,将基液和TiO2—蒸馏水纳米流体分别应用于铜光管和内螺纹铜管内Re为3 000～8 000范围内进行表面传热试验研究,结果表明,在内螺纹铜管内,TiO2—蒸馏水纳米流体表面传热系数都是随着流速的增加而不断提高,随着纳米颗粒质量分数的不断增加,TiO2—蒸馏水纳米流体表面传热效果越来越差,而且弱于基液的表面传热效果,纳米颗粒质量分数不变的情况下,纳米流体表面传热效果随着流体平均温度的提高而加强。通过对纳米流体在不同圆管内试验结果进行对比,发现TiO2—蒸馏水纳米流体在内螺纹管内表面传热效果相对于光管内表面传热效果的强化程度低于基液的强化程度,TiO2—蒸馏水纳米流体不适用于内螺纹强化换热管。     

内螺旋管两相流沸腾传热和摩擦阻力特性的试验研究

本文阐述国产300MW直流锅炉采用的ψ22×5.5mm四头碳钢内螺纹管高压汽水两相流沸腾传热特性和摩擦阻力特性的试验研究结果。沸腾传热试验参数范围为：压力P＝9.8～22.6MPa,质量流速G＝650～1750kg/m 2·s,内壁热负荷q＝200～610kW/m 2。摩擦阻力试验参数范围为：压力P＝9.8～20.6MPa,质量流速G＝1530～3560kg/m 2·s,蒸汽干度x＝0～1.0。通过试验,得出了内螺纹管的壁温变化规律、发生传热恶化的条件、抑制沸腾传热恶化的效果及两相流摩擦阻力的计算式。还提出了一个反映内螺纹管的结构参数对其传热特怀影响的无因次数,并对几种头数相同的内螺纹管的传热特性进行了比较和评价。     

核电反应堆主管道接管芯轴拔长的模拟研究

大型空心锻件的锻造过程主要分为镦拔、冲孔和芯轴拔长三个工序,其中芯轴拔长为主要的成形工序。以DEFORM-3D为分析软件建立芯轴拔长的数值模型,对空心锻件的芯轴拔长过程进行数值模拟分析,并分别从金属塑性变形的流动规律、内孔畸变率以及锻件内部的应力场、应变场等方面研究不同锻造工艺参数对内在影响规律。获得合理工艺参数组合,以指导实际的生产过程。     

A new extrusion method joining tube and sheet with holed rib

Wall thickness is constant in the axial direction when aluminum tubes are formed by conventional extrusion process. Tubes with internal ribs have high strength in comparison with those without ribs. These tubes can be used, for example, as structural parts, heat sinks, and impact absorbers. The existence of some holes at ribs enhances the function and value of the tubes. The appropriate positioning of holes at ribs reduces the weight of structural parts without strength reduction. In the case of heat sinks, holes change the fluid flow and would realize effective heat transfer. In this research, a new extrusion method is proposed by authors for manufacturing tubes with holed ribs. A new extrusion method is applied by FEM analysis. Model experiment was carried out based on the results. The method involves the use of a unique mandrel that has a slit along its axis and two guides at the slit exit. A holed sheet is fed through the slit and joined to the inner surface of the tube. In particular, the effect of the guide height is clarified in this study.     

A comparison of the effect of the electrohydrodynamic technique on the condensation heat transfer of HFC-134a inside smooth and micro-fin tubes

The results of the condensation heat transfer enhancement and pressure drop of HFC-134a by using the electrohydrodynamic (EHD) technique are presented. The test section is a horizontal tube-in-tube heat exchanger where the refrigerant flows in the inner tube and water flows in the annulus. The outer tube is a smooth copper tube havign outer diameter of 21.2 mm. Two types of inner tubes, smooth and micro-fin copper tubes, are tested. The outer diameter and length of both inner tubes is 9.52 mm and 2.5 m, respectively. A stainless steel cylindrical electrode of 1.47 mm in diameter is placed in the center of the tube. Experiments are conducted under conditions providing mass flux of 400 kg/m²s, saturated temperature of 40°C, heat flux of 20 kW/m² and applied voltage of 2.5 kV. The experimental results indicate that the EHD enhancements of the smooth tube are higher than those of the micro-fin tube over the range of average quality. The maximum heat transfer enhancements for smooth and micro-fin tubes are 1.1. times and 1.08 times, respectively. For a smooth tube, the pressure drop induced by EHD is considerably small. However, the application of EHD in a micro-fin tube can lead to 10% increase in the pressure drop.     

Q235覆管对AA5052铝合金基管颗粒介质胀形行为的影响

采用AA5052铝合金挤压管作内层基管、Q235碳素结构钢卷焊管作外层覆管的钢铝复合管对复合管颗粒介质胀形行为进行研究。通过塑性理论分析胀形过程中管间切向摩擦力及法向压力对基管应力大小的影响;利用数值模拟分析管间摩擦因数和覆管各向异性对基管的应变成形极限的综合影响,并给出单管、复合管胀形时的壁厚减薄情况和基管的应力、应变分布;通过管材颗粒介质内高压胀形试验,对比单管和复合管胀形条件下铝合金管的极限胀形比,分析复合管的变形协调性。结果表明：通过施加Q235碳素结构钢覆管,减小了AA5052基管胀形区中间截面处的双向拉应力,基管胀形区壁厚减薄变小,胀形比提高了22%,复合管下基管最大减薄率为17.5 %,成形性能显著提高。     

HDC-7000铜管高速拉拔专用外模油研究

通过对油品的润滑性、粘附性、耐高温性．清洗性等进行详细的研究,开发出一种新型的高粘度铜管高速拉拔外模专用油,不仅解决了铜管生产过程中油烟对工作环境污染和对人体的伤害,而且避免了铜管表面的擦伤,保证了铜管良好的表面质量。     

新型纵向流油冷却器传热性能及压降的试验研究

对两种不同角度的螺纹翅片管,分别在螺旋折流板及新型壳程挡板支撑下的3种结构的油冷却器进行了传热与阻力性能试验,结果表明,翅片角为5°的螺纹翅片管的传热性能比翅片角为13.5°的螺纹翅片管提高10%～30%,而流动阻力相差很小。对于同角度的螺纹翅片管油冷却器,新型阻流片壳程挡板虽然传热效果不及螺旋折流板,但是其壳程压降较螺旋折流板降低30%～40%,且单位压降下的热交换量提高10%～40%,这种结构对于大流量、长径比大且对壳程压降要求较高的油冷却器有一定的研究意义。     

内螺纹铜管拉拔工艺润滑研究

鉴于工艺润滑在拉拔内螺纹铜管中的重要作用本文研究了全润滑和浮液润滑的作用，并且进行了分析，对比。另外，对全油润滑剂的粘度与油膜强度；乳液的极压特征与使用浓度与其润滑效果之间的关系也进行了实验研究。     

矩形截面L形不锈钢弯管冷推弯成形工艺研究

U形管是聚变堆实验中比较重要的一类管件,但其整体成形难度比较大,研究了U形管的一半,即矩形截面L形管件的冷推弯成形.为了防止管坯起皱,在推弯过程中,使用了3种不同的柔性芯棒形式:低熔点合金、轴承滚珠、聚氨酯橡胶.实验结果表明,采用低熔点合金芯棒,在管坯表面润滑、尾部焊接封口的情况下,可获得截面畸变小、尺寸符合、内表面品质良好的矩形截面L形弯管.聚氨酯橡胶作为芯棒的弯管弯头部分出现了内凹现象,轴承滚珠作为芯棒的弯管虽然外表面品质良好,但内表面却出现了很多压痕.     

超高速充液旋压时全膜润滑临界条件确定

采用电阻法对超高速充液旋压内螺旋翅片铜管时全膜润滑临界条件进行了研究，利用旋压接触面之间的电阻变化，确定了形成全膜润滑的临界条件，同时对影响全膜润滑油膜形成的因素进行了分析。试验结果表明，全膜润滑油膜形成主要取决于旋压速度和润滑油特性，其中旋压速度是影响全膜润滑油膜能否形成的关键条件。全膜润滑形成对轴向拉力、扭转偏角和表面粗糙度值均有一定的影响，尤其对扭转偏角和表面粗糙度值的影响更大。     

Roughness optimization of flow-formed tubes using the Taguchi method

The present study reports the effect of various flow-forming process parameters and roller geometry on the roughness of flow-formed tubes of commercial pure copper UNS C11000. Thickness reduction ratio, feed rate, angular speed of mandrel, attack angle of roller, roller tip radius, and smooth angle of roller were considered as variable parameters. The effects of these input parameters on the roughness have been critically analyzed using the Taguchi method. Through ANOVA analysis, it has been found that the roller tip radius is the most important parameter affecting roughness followed by thickness reduction ratio. Selection of an optimum combination of variable parameters was performed based on “average of results.” The minimum roughness of 1.37 μm was achieved when the process parameters were set at their optimum values.     

Flow-forming optimization based on hardness of flow-formed AISI321 tube using response surface method

Flow forming is an advanced locally plastic deformation applied to manufacture seamless tubes with thin walls and high precision dimension. One of the important mechanical properties of flow-formed tubes is hardness. In this study, after preliminary experiments for definition of effective parameters, design of experiments (DOE) is utilized to determine the influence of the parameters such as rotational speed of mandrel, feed rate, and wall thickness reduction on the hardness of flow-formed AISI 321 steel tube. Under experimental results, a mathematical model comprising effective parameters is developed to predict the optimum hardness, using response surface methodology (RSM). RSM’s Box–Behnken design is employed to specify the optimum condition caused to a minimum hardness at high optimum confidence level. The analyzed model revealed that the hardness increases with increasing of the mandrel speed and the depth of cut, and it decreases with decreasing of the feed rate. The new point of view is related to the fact that the high level of thickness reduction covers the efficiency of mandrel speed.     

管子－管板液压胀接管内缺陷的产生机理及防止

全深度液压胀接技术是核电机组蒸汽发生器及其他换热器管子－管板接头普遍采用的制造工艺。液压胀接具有操作简单、胀后变形均匀、壁厚减薄率低、残余应力小等优点,但也会产生管内划伤、胀接长度超差等管内缺陷,薄壁管厚管板胀接时胀接过渡区的管子内部缺陷产生的几率更高。对液压胀接时管子长度缩短量、壁厚减薄率进行了理论计算和测量,对过渡区胀接芯轴和管子受力进行分析,表明过渡区管子内部缺陷是由于管子长度缩短效应及管子受力共同作用产生的,胀接区的划痕缺陷主要是由于芯轴损伤及金属颗粒残留引起的,未胀区胀接长度超差主要是由于芯轴设定失误引起的。通过改进胀接芯轴密封形式和限位止环的设计,证明采用芯轴保护套及非膨胀式的限位止环等工艺措施能够有效避免管内缺陷的发生。