含湿混合气体纵掠镀(涂)层管外壁的传热特性

为考察不同镀(涂)层管在烟气余热回收过程中的强化传热性能,采用水蒸气和空气的混合气体(w(H_2O)=6%~16%),对其在竖直紫铜管、镍-磷(Ni-P)镀层管及聚四氟乙烯(PTFE)涂层管表面的对流凝结复合传热特性进行了实验研究。结果表明:传热系数随着水蒸气质量分数和气体流速的增加而增加,PTFE涂层具有最佳的传热效果;水蒸气在紫铜管表面发生膜状凝结,在PTFE涂层表面发生珠状凝结,而在Ni-P镀层表面的凝结形式则表现为珠膜共存。对实验数据进行了多元线性回归,得到了含湿混合气体纵掠3种管子的对流凝结复合传热的Nu实验关联式,其理论值与实验值的相对误差在±15%以内,具有较高的准确性。     

Ni-P/膨胀石墨复合材料的制备及电磁屏蔽性能

用化学镀方法将镍磷合金负载在膨胀石墨(EG)表面上从而制备了Ni-P/EG复合电磁屏蔽材料.扫描电镜观察表明,这种用化学镀制备的镍磷镀层紧密地附着在膨胀石墨基体上.X射线衍射分析显示,制备态镍磷镀层呈非晶态,经500℃热处理晶化后镀层呈多相结构.磁测量结果证实非晶镀层饱和磁化强度较低,热处理晶化后饱和磁化强度增大、矫顽...     

Nd-Fe-B永磁材料表面化学镀Ni-P工艺开发

介绍了Nd-Fe-B表面化学镀Ni-P合金的工业化生产技术.采用封孔化学镀对Nd-Fe-B进行封孔和中性化学镀加厚阻断,再进行酸性高磷化学镀的三维化学镀镍方法,使基体表面镀覆一层均匀致密、无孔隙的镍磷镀层,从根本上解决了化学镀镀层与钕铁硼基体的结合力问题,从而提高了Nd-Fe-B材料的耐腐蚀性能.     

Nd-Fe-B磁体表面镀Ni-P非晶态合金的研究

研究了稀土永磁材料Nd-Fe-B表面碱性化学镀Ni-P合金技术。应用电化学性能测试仪、浸渍实验、中性盐雾实验测定了镀层的耐腐蚀性。应用X射线衍射测定了镀层的结构,用扫描电镜观察了镀层的表面形貌。证实镀层表面平整,无晶态颗粒析出,为非晶态结构,且具有良好的耐腐蚀性。找到了最佳工艺条件:温度42±3℃,pH值8.3±0.1。     

高换热系数疏水性石墨烯/铜镍合金材料制备及其性能研究

在工业级铜合金材料表面实现蒸汽滴状冷凝的表面处理技术是高效冷凝换热领域的迫切需求技术.本文采用等离子体辅助化学气相沉积(PECVD)技术,以甲烷为碳源,氢气为还原气体,在工业级铜合金材料表面沉积石墨烯薄膜,沉积有石墨烯薄膜的铜合金表面表现为疏水特性,实现了蒸汽在其表面膜状冷凝向滴状冷凝的转变,测试表明沉积有石墨烯薄膜的铜合金管蒸汽冷凝换热性能有较大提升.通过调节沉积温度、等离子体功率、气体流量,本研究实现了对石墨烯薄膜层数和缺陷的可控制备.结果显示在铜合金表面得到了单层石墨烯、少层石墨烯(2～3层)和多层石墨烯,沉积的石墨烯缺陷越少则铜合金表面疏水性越强,对水的最大接触角达到128°,石墨烯对铜合金管外表面蒸汽冷凝换热系数能提升110％,总换热系数最高可提升26％,具有较好的应用前景.     

化学镀Ni-P合金镀层的耐蚀性试验

通过在不同浓度的酸、碱、盐等腐蚀介质中 ,Ni-P合金镀层的腐蚀速度 ,以及镀层与 2 0钢、1Cr18Ni9Ti钢的对比腐蚀试验 ,讨论化学镀Ni-P合金镀层的耐蚀性     

火电站直接空冷凝汽器性能考核评价方法

火电站直接空冷凝汽器性能决定了直接空冷机组能否安全高效运行。研究直接空冷凝汽器性能的影响因素，从而制定空冷凝汽器性能考核评价方法具有重要意义。通过分析直接空冷凝汽器的传热过程，建立凝汽器压力与凝结蒸汽流量、冷却空气流量、凝汽器传热系数、凝汽器总传热面积以及环境温度之间的关系，分析各因素对凝汽器性能的影响规律。对以凝结蒸汽量和以凝汽器压力作为性能考核标准进行了对比研究，指出了2种性能考核评价方法存在的缺点，即仅仅考核凝汽器传热能力会导致传热面积过大，系统投资增加。在考核空冷凝汽器传热能力的基础上，还需测定凝汽器传热系数，以传热系数保证值作为直接空冷凝汽器性能考核的补充指标。     

空冷凝汽器积灰对运行调节影响的计算分析

对直接空冷凝汽器空气侧温度实时监测能够获得各个单元进出口的温度变化情况,对直接空冷凝汽器各单元空气温升的分析可以得到凝汽器表面的积灰严重程度,了解凝汽器各区域的换热差异。凝汽器表面积灰降低了效能,同等条件下表现出空气温升减小及蒸汽侧的凝结换热量降低。研究结果表明:外部条件相同时空冷单元积灰,换热端差增大,而单元的温升减小;空冷单元的送风量需与空气的温升合理匹配,通过增加表面积灰单元凝汽器的风机转速,可以有效降低其背压以及均衡其内部凝结蒸汽量,为空冷机组运行调节提供合理有效的依据,从而达到有效节能的目的。     

空冷凝汽器波形翅片扁平管管束外空气流动传热特性

研究火电站空冷凝汽器广泛采用的波形翅片扁平管管束外空气流动传热特性,对于火电站空冷岛的设计与运行都具有重要意义。该文通过CFD模拟,得到不同空冷凝汽器迎面风速条件下冷却空气的流场和温度场,通过计算获得了空冷凝汽器冷却空气平均对流换热系数和摩擦系数随翅片间距和翅片高度的变化规律。结果表明：随空冷凝汽器迎面风速增加,空气对流换热增强,摩擦系数降低。对每个迎面风速而言,都存在一个最佳翅片间距,对流换热最强。翅片高度增加,对流换热系数和摩擦系数减小。对空冷凝汽器波形翅片管束空气流动传热性能综合评价指标的分析表明,最佳翅片间距和高度需要通过综合技术经济比较确定。     

达可罗涂层技术应用于NdFeB永磁体表面防护的研究

介绍了一种用于NdFeB永磁体表面防护的新型达可罗(Dacromet)涂层技术.该技术最突出的优点是无环境污染,涂层耐蚀和耐氢脆性能优异.通过正交试验得出了最佳工艺参数.测试了达克罗涂层的结合力和耐蚀性,并和电镀锌、化学镀Ni-P进行了比较.结果表明,达克罗用于NdFeB永磁体表面防护的效果很好,明显优于电镀锌和化学镀Ni-P.     

Heat transfer enhancement in steam-turbine condensers with the use of surface-active substances

A technology of the enhancement of the power efficiency of steam-turbine plants (STPs) is proposed by the treatment of surfaces of a piped condenser system over the steam and water sides with the use of surface-active substances (SAS). The transition of filmwise condensation into dropwise makes it possible to increase the heat-transfer coefficient by 50–70% because of hydrophobization of outside surfaces of the steam side that results in vacuum extension at minimum operating costs. The resulting data are verified by laboratory investigations and full-scale tests. The accumulation rate of thermobarrier deposits over the water side decreases by a factor of 6–8, and, correspondingly, the overhaul life connected with the refinement of condenser pipes increases. The maintenance of the hydrophobic film of SAS at the outside surface of condenser pipes can be provided by the periodic injection of SAS on the inlet of a low-pressure cylinder (CLP) of the turbine both in the period of short-time stops and during the operation of STPs. At the same time, because of the additional dispersion of the liquid phase, the rate of drop-impact erosion of the blade row decreases by 30%.     

Perovskite phase formation in sol-gel derived Pb(ZrxTi1−x)O3 thin films

Abstract

Thin films of lead zirconate titanate having the composition Pb_1.05(Zr_0.53Ti_0.47)O₃ were deposited by a solgel method on a set of crystalline and amorphous substrates. The thickness of the film was varied by controlling the sol concentration or by repeated coatings. Factors controlling phase formation in the films such as nature of the substrate material, film thickness, chemical composition of the film, heating rate and gaseous atmosphere during the heat treatment were studied. On glass substrates the pyrochlore phase was obtained in thin (0.4 um) films and the perovskite phase in thicker (>1.5 um) films. Crystalline substrates (except Si and stainless steel) yielded a perovskite phase in 0.6 um thick film. Low Zr/Ti ratio, rapid heating and introduction of nitrogen in the later stage of heat treatment also favoured the formation of the perovskite phase. It is shown that Pb deficiency in the film caused by diffusion of Pb into amorphous substrates or by other mechanisms is primarily responsible for inhibiting the pyrochlore to perovskite transformation. The initial crystallisation of the amorphous film into pyrochlore rather than a perovskite phase (as in powders) is proposed to be due to higher strain energy barrier which exists for the amorphous to perovskite transformation in the film.     

加填料饱和器传热传质模型研究

从水气之间的传热传质原理入手,引入水膜模型,建立加填料饱和器的数学模型。将模型的计算结果与实验结果进行了对比,验证了加填料饱和器数学模型的正确性。应用该数学模型分析了压力变化对加填料饱和器传热传质的影响,同时讨论了沿加填料饱和器高度方向的传热传质过程。研究发现,随着饱和器内工作压力的增大,饱和器出口空气更容易达到饱和,但空气的绝对湿度降低了;并且在整个传热传质过程中,质量一直从水膜传向空气主体,而热量的传递方向则有可能发生改变。     

铝合金化学镀镍磷合金和性能

以铝合金为基体材料,采用碱性-酸性双溶液体系化学镀镍磷合金,研究了镍磷合金镀层的耐蚀性和热处理对耐蚀性的影响,测定了镍磷合金镀层及改性铝合金的导电性能.结果显示,采用化学镀镍磷合金对铝合金改性处理,耐蚀性能优于不锈钢,导电性能优于不锈钢和石墨等,完全可以满足质子交换膜燃料电池对双极板的性能要求.     

Accounting for the Effect of Noncondensing Gases on Interphasic Heat and Mass Transfer in the Two-Fluid Model Used in the KORSAR Code

A model is presented of the interphasic heat and mass transfer in the presence of noncondensable gases for the KORSAR/GP design code. This code was developed by FGUP NITI and the special design bureau OKB Gidropress. It was certified by Rostekhnadzor in 2009 for numerical substantiation of the safety of reactor installations with VVER reactors. The model is based on the assumption that there are three types of interphasic heat and mass transfer of the vapor component: vapor condensation or evaporation on the interphase under any thermodynamic conditions of the phases, pool boiling of the liquid superheated above the saturation temperature at the total pressure, and spontaneous condensation in the volume of gas phase supercooled below the saturation temperature at the vapor partial pressure. Condensation and evaporation on the interphase continuously occur in a two-phase flow and control the time response of the interphase heat and mass transfer. Boiling and spontaneous condensation take place only at the metastable condition of the phases and run at a quite high speed. The procedure used for calculating condensation and evaporation on the interphase accounts for the combined diffusion and thermal resistance of mass transfer in all regimes of the two-phase flow. The proposed approach accounts for, in a natural manner, a decrease in the rate of steam condensation (or generation) in the presence of noncondensing components in the gas phase due to a decrease (or increase) in the interphase temperature relative to the saturation temperature at the vapor partial pressure. The model of the interphase heat transfer also accounts for the processes of dissolution or release of noncondensing components in or from the liquid. The gas concentration at the interphase and on the saturation curve is calculated by the Henry law. The mass transfer coefficient in gas dissolution is based on the heat and mass transfer analogy. Results are presented of the verification of the interphase heat and mass transfer used in the KORSAR/GP code based on the data on film condensation of steam-air flows in vertical pipes. The proposed model was also tested by solving a problem of nitrogen release from a supersaturated water solution.     

Strong thickness dependence of aurivillius phase formation in SrBi2Ta2O9 thin films

Sr_0.7Bi_2.4Ta₂O₉ (SBT) thin films were studied for the dependence of Aurivillius phase formation kinetics on their film thickness. SBT thin films were fabricated using a sol-gel process and spin coating, and their thickness was varied controlling the number of spin coating. The films were first heated at a low temperature for the complete crystallization of amorphous film to fluorite phase and then further heated at different elevated temperatures for the phase transformation to Aurivillius for 40 min. It was found that the phase transformation kinetics apparently increased with thickness up to ∼390 nm, and then it sharply decreased at higher values. The Aurivillius crystal size decreased and the density of crystals increased with the increase of film thickness up to ∼390 nm, implying increasing number of nuclei due to the reduced energy barrier for nucleation. Above the critical value both the size and density of crystals decreased. It is suggested that up to ∼390 nm the tensile strain energy in the films, which was stored by the shrinkage of thin films during the removal of remaining organic components from sol-gel chemistry, plays a major role for determining the phase transformation kinetics and above the critical value SBT films act as a free bulk material without substrate constraints.     

滴形管凝结换热性能的实验研究

采用特殊的管子形状和表面是最为常用、有效的强化换热手段。该文以滴形管凝结换热作为研究对象,阐述了烟气中水蒸气凝结换热过程的特点及强化换热的条件。对液滴在圆管和滴管不同位置处的受力进行分析,说明不同管形对液膜层厚度的影响程度。通过回收天然气锅炉排烟余热实验,研究滴形管的凝结换热性能,分析影响换热性能的因素,并与圆形管进行比较。结果表明：烟气通过滴形换热管的压损小于圆管,温差大于圆管,冷却水温升高于圆管,换热系数高于圆管。采用滴形管对于强化凝结换热是一种行之有效的方法。     

翅片管外有机工质TFE凝结换热特性研究

翅片管外有机工质换热特性（凝结换热系数及液膜热阻）影响冷凝器的换热性能。理论模型基于努谢尔修正膜理论,为提高计算精度,将翅片管沿管周向划分有限个微元角,建立各个微元角内翅片侧壁和翅片间基管处的层流膜状凝结换热模型,迭代求解各个微元角内的壁面温度,根据各微元角壁面与饱和蒸汽温差,推导翅壁面及翅间基管上的液膜热阻和换热量,最后求解管子平均换热系数。管壁温度随圆周角θ增大而减小;翅壁及基管上液膜热阻随圆周角θ增大而增大;基管上液膜热阻大于壁面上液膜热阻。与实验值比较,理论模型计算精度高于积分解法计算值。     

Ferroelectric Properties of Pb(Zr1 − x,Tix)O3 Prepared by Modified Metallo-Organic-Decomposition Process

Beneficial effect of nano-sized PZT powder incorporation on modifying the characteristics of Pb(Zr_0.52Ti_0.48)O₃, PZT films was demonstrated. The amorphous phase derived from metallo-organic-decomposition (MOD) process started to crystallize at a post-annealing temperature as low as 500°C and can withstand 650°C post-annealing temperature process without inducing the PbO-loss phenomenon. However, 500°C post-annealed PZT films still exhibit paraelectric properties, which can be ascribed to the co-existence of large proportion of amorphous phase, surrounding the crystalline phase. It needs at least 650°C post-annealing process to fully developed the pervoskite structure for PZT films. The remnant polarization (Pr) of the PZT films increases with the proportion of crystalline phase, achieving Pr = 24.9 μC/cm² for 650°C annealed films, with coercive field (Hc) around Ec = 373 kV/cm.