Pool boiling performance of porous surface tubes under vacuum conditions

Two types of tube bundles are designed,which are,respectively,composed of six tubes arranged in the boiling chamber.The nucleate pool boiling performance of smooth tube bundles and sintered porous surface tube bundles with deionized water as a medium are experimentally studied at atmospheric and sub-atmospheric pressures,respectively.The experimental results indicate that the boiling heat transfer coefficients of the two types of tube bundles increase with the increase in pressure under vacuum conditions as they behave under ordinary pressure.As the pressure varies from 10 to 100 kPa,it also can be seen that the heat transfer coefficient of the sintered porous surface tube is increased by 0.2 to 4 times compared with the smooth one under the same operating parameters.In addition,the experimental data show that a definite bundle effect exists in both sintered porous surface tubes and smooth tubes under vacuum conditions.

Study on Propagation Characteristics of Plasma Surface Wave in Medium Tube

Axial propagation characteristics of the axisymmetric surface wave along the plasma in the medium tube were studied. The expressions of electromagnetic field inside and outside the medium tube were deduced. Also, the impacts of several factors, such as plasma density, signal frequency, inner radius of medium tube, collision frequency, etc., on plasma surface wave propa- gation were numerically simulated. The results show that, the properties of plasma with higher density and lower gas pressure are closer to those of metal conductor. Furthermore, larger radius of medium tube and lower signal frequency are better for surface wave propagation. However, the effect of collision frequency is not obvious. The optimized experimental parameters can be chosen as the plasma density of about 10^17 m^-3 and the medium radius between 11 mm and 19 mm.

Intersecting Line of Conical Surface and Smoothly Blending of Two Tubes Whose Axes Are Non-Coplanar

We construct two conical surfaces which take non-coplanar lines as generatrix and rational Bezier curve as ridge-line, and prove that the intersecting line of conical surface has similar properties to Bezier curve. Then, the smoothly blending of two cylinders whose axes are non-coplanar is realized by taking intersecting line of conical surface as axes.

Heat Transfer of Boiling R134a and R142b on a Twisted Tube with Machine Processed Porous Surface

The objective of this work was to investigate nucleate pool boiling heat transfer performance and mechanism of R134a and R142b on a twisted tube with machine processed porous surface （T-MPPS tube） as well as to determine its potential application to flooded refrigerant evaporators. In the experimental range, the boiling heat transfer coefficients of R134a on a T-MPPS tube were 1.8-2.0 times larger than those of R134a on a plain tube. In addition, the developed experimental correlations verified that the predictions of the heat transfer coefficients of boiling R134a and R142bon a T-MPPS tube at the experimental conditions were considerably accurate.

Pool boiling heat transfer enhancement on porous surface tube

The passive residual heat removal exchanger (PRHR HX),which is a key equipment of the passive residual heat removal system,is installed in an elevated pool.Its heat transfer performance affects security and economics of the reactor,and boiling heat transfer in the liquid surrounding the exchanger occurs when the liquid saturation temperature exceeded.The smooth tubes,which are widely used as heat transfer tubes in PRHR HX,can be replaced by some enhanced tubes to improve the boiling heat transfer capability.In this paper,the pool boiling heat transfer characteristics of smooth tube and a machined porous surface tube are investigated by using high-pressure steam condensing inside tube as heating source.Compared with smooth tube,the porous surface tube considerably enhances the boiling heat transfer,and shortens the time significantly before reaching the liquid saturation temperature.Its boiling heat transfer coefficient increases from 68% to 75%,and the wall superheat decreases by 1.5oC.Combining effect of condensation inside tube with boiling outside tube,the axial wall temperatures of heat transfer tube are neither uniform nor linear distribution.Based on these investigations,enhance mechanism of the porous surface tube is analyzed.

An Experimental Study of Porous Surface Tubes for Enhancement of Binary Liquid Mixture Pool Boiling Heat Transfer

Experiments have been conducted on the pool boiling of binary mixtures in JK tubeswith porous surface and ribbed channels,attempting to enhace the boiling heat transfer coefficientsinvolved.The binary mixtures used in this study are R113 and R11.The results show that the boilingfi1m heat transfer coefficients for the R113 and R11 binary mixtures in JK2 and JK1 tubes are 2—8tirnes and 2—5 times greater than those in smooth tubes respectively.Based on this experimentaldata and simple theoretical analysis,a correlation has been proposed to predict the boiling heattransfer coefficients for R113/R11 mixtures in a horizontal JK tube with a relative error of less than16%.

Surface treatment of 3D outside serrated integral-fin tube manufactured by rolling and extrusion

The outside serrated integral-fin tubes fabricated by rolling-plowing-extrusion processing were surface-treated through different processes of annealing in hydrogen atmosphere,electrochemical corrosion or sandblasting.The purpose was to eliminate residual stress,clear secondary micro-fins and enhance heat transfer performance.By comparing the surface characteristics,it is found that the finned tubes treated by electrochemical corrosion have the most glabrous surfaces where the fins are almost perfectly reserved.Clear layer cracks can be observed on the top of the fins.These structures are effective in enhancing heat transfer performance when being applied to flow heat exchange.Therefore,the finned tubes treated by electrochemical corrosion are proper for the tubular exchanger with water coolant.The finned tubes treated by sandblasting have rougher surfaces with layer cracks and micro gaps removed.As these structures are useful to clearing adhesive feculence,the tubes are more suitable for the tubular heat exchanger with oil coolant.

Effect of microstructure on outer surface roughening of magnesium alloy tubes in die-less mandrel drawing

The crystal orientation and outer surface roughening of magnesium alloy tubes were evaluated to clarify the effect of the mandrel on the microstructure and outer surface roughness in die-less mandrel drawing. Locally heated ZM21 tubes with an outer diameter of 6.0 mm and an inner diameter of 3.8 mm were drawn with and without a mandrel. The outer surface roughness and crystal orientation were evaluated in the same measurement area. The results indicated that the outer surface becomes rougher in the die-less mandrel drawing than in die-less drawing for a given outer circumferential strain. The outer surface roughness developed when there was large difference in the pyramidal slip system Schmid factor. Therefore, the slip deformation of the pyramidal slip system seems to be mainly responsible for the outer surface roughening in the die-less mandrel drawing. Furthermore, the crystal grain with the {2110} crystal plane vertical to the normal direction of outer surface had a larger Schmid factor than the other crystal grains. The large number of crystal grains with the {2110} crystal plane in the die-less mandrel drawing is one of the reasons that the outer surface roughness develops more in the die-less mandrel drawing than in die-less drawing for a given outer circumferential strain. These results will contribute significantly to the development of fabrication process of the microtube with high surface quality, which prevents rapid corrosion of biomedical applications.

Optimization of Draft Tube Position in a Spouted Bed Reactor using Response Surface Methodology

Optimization of draft tube position in a spouted bed reactor used for treatment of wastewater containing low concentration of heavy metals is investigated in this paper. Response surface methodology is used to optimize the draft tube height, the draft tube width and the gap between the bottom of the draft tube and the inlet nozzle. It is observed that the draft tube with a height of 60 millimeter, width of 12 millimeter and the gap of 13 millimeter between its bottom and inlet nozzle, results in optimum value of minimum spouting velocity, measured 45 cubic centimeter per second (2.7 Liter per minute) .

Platelet adhesion to the surface of a sudden tubular expansion tube under swirling flow condition

The size mismatch in an end-to-end vascular anastomosis between the host vessel and the graft may cause flow disturbance and predispose to thrombosis [1].Although a number of techniques have been employed to reduce the risk of anastomotic thrombosis due to the size mismatch。

On-Line Life Monitoring Technique for Tube Bundles of Boiler High-Temperature Heating Surface

High-temperature heating surface such as superheater and reheater of large-sized utility boiler all experiences a relatively severe working conditions. The failure of boiler tubes will directly impact the safe and economic operation of boiler. An on-line life monitoring model of high-temperature heating surface was set up according to the well-known L-M formula of the creep damages. The tube wall metal temperature and working stress was measured by on-line monitoring, and with this model, the real-time calculation of the life expenditure of the heating surface tube bundles were realized. Based on the technique the on-line life monitoring and management system of high-temperature heating surface was developed for a 300 MW utility boiler. An effective device was thus suggested for the implementation of the safe operation and the condition-based maintenance of utility boilers.

Structure and surface modification of MXene for efficient Li/K-ion storage

In this paper,three-dimensional(3D)hollow Ti_(3)C_(2)T_(x)MXene tubes(HTCTs)with more–O terminal groups and fewer–F groups are successfully prepared via the template-oriented electrostatic self-assembly and the subsequent annealing treatment.The obtained 3D hollow structure with large specific surface area,unique porous structure,and enlarged interlayer spacing could prevent the re-stacking of twodimensional(2D)sheets and shorten the diffusion pathway of ions.Furthermore,density functional theory(DFT)calculations and electrochemical tests reveal that Ti_(3)C_(2)O_(2)MXene possesses higher adsorption ability and lower diffusion barrier for K^(+)and Li^(+)compared to Ti_(3)C_(2)MXene dominated by–F terminal groups.Benefiting from the synergistic effect of the structural design and surface modification,the asprepared 3D HTCTs exhibit excellent electrochemical performance as anodes for K^(+)and Li^(+)storage compared with 2D Ti_(3)C_(2)T_(x)sheets(TCSs).

Study of the Adhesion of Clinical Strains of Staphylococcus aureus on an Abiotic Surface Using the Biofilm Ring Test^(█)

Four methicillin-sensitive (MSSA) and 4 methicillin-resistant (MRSA) strains of Staphylococcus aureus were collected and isolated at the Laboratory of Bacteriology of the Provincial General Reference Hospital of Kinshasa in the Democratic Republic of Congo. The microbial adhesion to solvents (MATS) test showed that the MRSA strains had a less hydrophobic membrane than the MSSA strains. Using the Biofilm Ring Test? (BFRT?) to investigate on the adhesion of these bacterial strains to smooth surfaces, we observed that the MSSA strains adhered more rapidly than the MRSA strains. The biomass of the produced biofilm measured by the Crystal violet staining method (CVSM) was more important with MSSA than with MRSA strains. Ethylene glycol-bis(2-aminoethylether)-N,N,N',N'-tetraacetic acid (EGTA) inhibited the adhesion and the formation of a biofilm by MRSA strains;this inhibition was reversed by calcium, magnesium and manganese. The MRSA strains adhered less to silicon tubing and the adhesion was inhibited by EGTA in 2 of the 4 MRSA strains and none of the MSSA strains. In conclusion, the MSSA and MRSA strains adhered on an abiotic surface and formed a biofilm at distinct rates and with different sensitivities to ions. The results also confirm the utility as well as the limits of the BFRT? to study the adhesion of bacteria on a surface.

基于响应面法的矿用翅片管空冷器参数优化

矿用空冷器是矿井降温系统常用的末端设备,优化矿用空冷器换热性能对提升矿井降温系统能效具有重要意义。采用Fluent建立了平直翅片管矿用空冷器模型,研究了翅片间距、翅片厚度、横向管间距和纵向管间距对传热因子、阻力因子和综合性能评价指标的影响规律;采用Box-Behnken响应面法,分析了双参数协同作用下传热因子、阻力因子和综合性能评价指标变化规律。结果表明:随着翅片间距、横向管间距的减小,以及翅片厚度增加,传热因子、阻力因子和综合性能评价指标逐渐增加;综合性能评价指标则随纵向管间距的增加而先增加后降低;横向管间距、翅片厚度是影响空冷器传热及流动性能最显著的两个参数,而翅片间距、纵向管间距的影响最小;得到了平直翅片管矿用空冷器的最优参数,传热因子提升16.3%、阻力因子增加26.3%、综合性能评价指标提升8.3%。研究结果可为矿用翅片空冷器设计参数优化提供指导。

基于响应面法的钢管混凝土系杆拱桥有限元模型修正

为探讨将钢管混凝土系杆拱桥有限元模型修正方法应用于实际工程性能评估的有效性,以某80 m单拱面钢管混凝土系杆拱桥为工程背景,采用Midas Civil与ANSYS有限元软件分别建立全桥梁格模型与拱脚精细化数值模型,基于径向基函数网络的响应面法对此多尺度模型进行修正。首先根据结构特点和实桥试验选取修正参数与目标函数,以中心复合试验设计构造不同修正水平下的修正参数样本,通过桥梁有限元模型计算得到对应的目标函数样本,并利用F检验法对修正参数的显著性水平进行判断;然后,以修正参数样本与目标函数样本分别作为响应面的输入输出,对径向基函数网络进行拟合训练;最后在修正范围内随机生成修正参数样本,并利用训练好的径向基网络预测对应的目标函数,采用期望度函数D进行优化处理以完成有限元模型的修正。研究结果表明:对于单拱面钢管混凝土系杆拱桥的有限元模型,可以通过径向基函数网络的响应面法进行修正,对比实测数据,修正后的模型误差有明显下降,可作为结构再分析的基准模型;对于使用不同程序建立的多尺度桥梁有限元模型,模型修正方法依旧有效,修正后的参数具有明确的物理意义,其误差可降到工程实践接受范围之内。研究结果为建立与修正钢管混凝土系杆拱桥的有限元模型提供参考。

翅片管蒸发器传热性能的参数灵敏度分析

采用Sobol´全局灵敏度分析方法,计算出了各个影响参数对传热系数的一阶灵敏度和总灵敏度,探索和分析了单个及多个波纹翅片管参数对波纹翅片管蒸发器传热系数影响的程度和规律,并构建了传热系数与各个参数之间关系的响应面。结果:从灵敏度数值及响应面的分析皆显示:翅片间距对传热系数的影响最大,翅片厚度的影响次之,质量流量与工资热流密度对传热系数的影响相差不大,但大于管外径的影响;且翅片间距与其余各个因素之间的交互影响在一定范围内极其剧烈,其中翅片间距与翅片厚度之间的交互影响最大,又以质量流率与工质侧热流密度之间的交互影响次之;再者,垂直于风速方向的管间距与平行于风速方向的管间距的灵敏度数值皆为0,说明两者对传热系数的影响可以忽略不计。

Pipe reduction of miniature inner grooved copper tubes through rotary swaging process

A rotary swaging machine was applied to fabricating pipe reduction for miniature inner grooved copper tube （MIGCT） heat pipes. Compared with conventional swaging method, the axial feed of the designed rotary swaging machine was reached by a constant pushing force. The deformation of grooves in pipe reduced section during rotary swaging was analyzed. The shrinkage and extensibility of pipe reduction were measured and calculated. Furthermore, four aspects, including outer diameter, surface roughness, extensibility and processing time of pipe reduction, which were influenced by the pushing force, were considered. The results show that the tube wall thickness increases gradually along the z-axis at sinking section. However, the outer diameters, surface roughness and micro-cracks at reduced section tend to decrease along the z-axis. Besides, the effect of variation in the pushing force on the extensibility is limited while an increase in the pushing force results in a decrease of surface roughness. Therefore, a large pushing force within the limit is beneficial to pipe reduction manufacturing during rotary swaging process.

木质重组材单板卷曲辊压成型平台设计与试验

低品质木制单板制备重组材是其高值化利用的重要途径,研发连续式重组材成型技术有利于提高其生产效率,对促进木材可持续发展和经济社会绿色发展具有重要意义。该研究设计一种木制重组材单板卷曲辊压成型平台,并以木质管道制备为例对工艺参数进行优化试验研究以测试平台工作性能。设计单板卷曲辊压成型平台的整机机械结构并描述其工作原理,对辊压机构、卷木轴刹车防滑机构、施胶压紧装置等关键部件进行详细设计和理论计算。对物理样机进行性能试验,以芯轴转速、单板厚度、施加压力为试验因素,木质管道的环刚度和轴向压缩强度为试验指标,运用Box-Benhnken试验方法,建立因素与试验指标的回归方程,优化参数组合为芯轴转速16 r/min,单板厚度2.15 mm,施加压力293 N。此时预测木质管道的环刚度为26 016.6 N/m^(2),轴向压缩强度为23.11 MPa验证环刚度与预测值误差为1.07%,轴向压缩强度误差为4.46%。进一步使用优化参数对内径为5.08、7.62、12.70 cm的木质管道进行试验,得到环刚度分别为43 812、32 655、17 532 N/m^(2),轴向压缩强度为25.83、24.71、20.17 MPa。该研究成果可为木质重组材卷曲辊压成型技术及装备的工业化应用提供参考。

月球熔岩管探测与开发方案设计

在总结前期探测成果和前人研究的基础上,结合对地球熔岩管洞穴的实地考察,深入分析月球熔岩管洞穴的探测开发价值与挑战。结合月球遥感探测数据,针对不同洞口构造的熔岩管,以中丰富海及静海两个典型熔岩管洞穴为案例,构建了由月面平台、探测器及自主机器人等组成的联合探测方案。围绕未来建设月球熔岩管洞穴基地的目标,深入分析熔岩管洞穴开发建设需求与挑战,进一步提出了熔岩管洞穴内部场坪建设、通信能源部署以及居住设施建造方案。

TP2铜管精整工序喷墨质量不良原因分析及改进措施初探

在精密铜管精整复绕工序中,涡流探伤装置检测到伤点后会向喷墨装置发送信号,以对铜管表面缺陷进行喷墨标记,但是该过程普遍存在喷墨不良,严重影响了对缺陷的判断。本文介绍了TP2铜管生产线中涡流探伤仪器的工作原理,对原有的涡流探伤仪器、喷墨装置以及喷枪结构进行调研,分析了原有喷墨装置喷墨时存在的漏墨和拖墨问题,探讨了等离子技术与激光刻蚀技术作为喷墨技术替代方案的可能性。文献调研、现有技术分析及其他替代试验的结果表明,采用等离子体表面处理技术对已喷墨铜管进行处理后,可以一定程度地改善铜管拖墨的问题;采用功率为300 W的激光对铜管表面进行刻蚀处理,激光头速度分别为80 mm/s和200 mm/s时,对铜管表面刻蚀呈现出的不同效果,均能够进行缺陷的有效标识。因此,铜管表面激光刻蚀技术可以作为喷墨技术的替代方案。