聚丙烯中空纤维换热器的数值模拟

由于具有抗腐蚀和结垢的优点,中空纤维换热器在低温下的应用受到关注。为了提高中空纤维换热器的换热效率,以在换热器的壳程增加弓形折流挡板的方式对中空纤维换热器的结构进行了优化研究。利用Gambit 2.4软件,建立了管壳式中空纤维换热器模型;利用Fluent 6.3软件,进行有限体积分析计算。结果表明：数值模拟得到的换热器总传热系数和壳程压降与实验值的误差分别小于8%和6%。通过对比分析发现,在模拟范围内增加弓形折流挡板以后中空纤维换热器的总换热系数提高了21%左右,换热器壳程热阻占总热阻的比例从59%~70%降低到了46%~57%,换热器的壳程压降提高了约12%,但是壳程换热系数与壳程压降的比也明显升高。加弓形折流挡板的中空纤维换热器比无折流挡板的换热器具有更好的换热效率。     

双圆缺折流挡板的气体换热器

双圆缺挡板换热器可视为两个半圆柱管壳式换热器的并联,壳程气体双进双出,折流挡板由月牙板、双圆缺板交替进行。讨论了台拉华-比尔方法在壳程传热膜系数计算中的特点,通过不满排和在折流板上开泄流孔提高壳程传热膜系数、降低壳程阻力。硫酸装置是腐蚀性、易结垢气体,污垢热阻的选取是其成败的关键,探讨了强化传热的优缺点。给出了实际换热器结构参数和换热性能的计算结果。     

螺旋折流板与弓形折流板换热器性能的数值模拟

针对弓形折流板、连续螺旋折流板换热器,采用FLUENT软件,k-ε湍流模型,通过数值模拟的方法比较了4块挡板的弓形折流板换热器和4个螺旋的螺旋折流板换热器的壳程流动与换热性能。结果表明:弓形折流板换热器流动湍动程度强,换热系数更大;螺旋折流板换热器壳程流动呈螺旋状,流动阻力更小;比较单位压降换热系数,螺旋折流板换热器综合性能优于弓形折流板换热器。     

并流多通道管壳式换热器壳程流场分布比较

优化壳程流场分布和减少压降对并流多通道进出口结构(MPC)轴流管壳式换热器具有非常重要的作用。分别采用商用CFD软件FLUENT 6.3和皮托管测速方法对MPC换热器壳程流场分布与阻力性能进行数值模拟与实验研究,分别研究了管排数N、Re、不同开孔率的挡板对壳程流场分布、阻力性能的变化规律。结果表明:(1)无挡板时,随着N的减小,壳程流场分布不均现象得到有效的遏制,压降大幅降低,最大降幅达到70%以上;(2)挡板能够有效促进流场的二次分布,但亦使得阻力增大较为显著;(3)比较不同挡板,挡板1的效果最优;(4)换热器压降主要在进出口段产生。     

帘式折流片换热器强化传热数值研究

为解决折流板换热器壳程流体阻力过大和折流杆换热器低Re下传热系数较小等管壳式换热器的不足,提出了壳程流体"斜向流"的新概念,研制了新型高效节能管壳式换热器?帘式折流片换热器,其壳程传热系数高于折流杆换热器20%～30%,而壳程压力损失大幅低于折流板换热器。以场协同原理分析了斜向流的强化传热机理,指出在帘式折流片换热器壳程中流体速度场与温度梯度场间的夹角小于折流杆换热器,是其强化传热的重要原因。对帘式折流片换热器中折流栅间距、折流片倾角、折流片宽度等重要几何参数对传热和压降的影响规律进行了数值模拟研究,并据此推导了壳程传热系数和流体阻力降准数关联式,为其工程设计和推广应用提供了参考依据。     

并流多通道管壳式换热器壳程流场分布

对一种新型并流多通道进出口结构（MPC）轴流管壳式换热器壳程流场分布与阻力性能进行全面研究,分别研究了管排数、Reynolds数、不同挡板对壳程流场分布、阻力性能的影响,并且采用实验方法对数值模型与方法的正确性进行论证。研究结果表明,在无挡板的情况下,随着管排数的减小,壳程流场分布不均现象得到有效的遏制,压降大幅降低,最大降幅达到70％以上;挡板能够有效促进流场的二次分布,但是同时亦使阻力增大较为显著。     

并流多通道进出口管壳式换热器壳程传热性能比较

对一种新型并流多通道进出口结构的壳程轴流管壳式换热器壳程局部传热性能进行实验研究,在有分布挡板与无分布挡板的情况下,分别对进口段局部努塞尔数Nu的分布、局部平均Nu的分布、以及换热器整体的传热和阻力性能进行了比较与分析。研究结果揭示了壳程进口段的局部表面Nu的分布规律,并给出了合理的机理分析。结果表明,分布挡板不但能够有效促进壳程流场和局部Nu的均匀分布,而且能够提高整体传热性能,且阻力增加较小。     

折流板换热器壳程湍流流动与换热的三维数值模拟

利用FLUENT软件对折流板换热器壳程湍流流动与换热进行了三维数值模拟。得到了折流板换热器的温度场、速度场、质点迹线图、压降分布图等。根据模拟得到的结果,从多个方面对折流板换热器壳程湍流流动与强化传热进行了有益的探讨。     

异形片式倾斜折流栅换热器壳程强化传热数值模拟

采用CFD软件FLUENT,Standard k-ε模型,借助数值模拟方法对异形片式倾斜折流栅换热器和常规帘式折流片换热器流动传热性能进行研究,并利用场协同理论分析异形片式倾斜折流栅换热器的折流栅不同倾斜角度对壳程传热性能的影响。结果表明:壳程雷诺数在6 000—10 000范围内,同常规帘式折流片换热器相比,异形片式倾斜折流栅换热器折流栅与折流片平行排布时,壳程传热系数和综合性能分别增加12.7%—13.9%和6.4%—7.6%;折流栅和折流片交错排布时,壳程压降降低18.45%—19%,壳程综合性能略高于常规帘式折流片换热器;异形片式倾斜折流栅换热器折流栅倾斜25°时,壳程传热系数和综合性能最好,且速度场和温度场协同性最优,因此25°为异形片式倾斜折流栅换热器最优倾角。     

并流多通道管壳式换热器壳程传热性能

对并流多通道进出口(MPC)轴流管壳式换热器壳程传热性能进行数值模拟,分别研究了管排数N,Re,不同开孔率的挡板对壳程进口段的局部传热系数分布、局部平均Nu的分布、换热器的平均Nu等特性的影响。结果表明:在无挡板条件下,随着N的减小,壳程传热系数分布不均现象得到有效的遏制,N=7时基本上无传热死区。挡板的存在,不但使得进口段的局部传热系数分布更加均匀,而且能够提高换热器的整体传热Nu。不同参数的挡板之间,挡板1的作用最为明显,可以使得Nu提高10%—12%。     

Nanomechanical mapping of glass fiber reinforced polymer composites using atomic force acoustic microscopy

In this work, a dual‐frequency resonance tracking (DFRT) method was applied on atomic force acoustic microscopy (AFAM) and high‐resolution, quantitative nanomechanical mapping of a glass fiber–reinforced polymer composites (GFRP) was realized. Results show that even using the single‐frequency AFAM, the fiber, and epoxy can give very good contrast in amplitude images. The modulus mapping result on GFRP by DFRT AFAM was compared with that by dynamic nanoindentation, and it is found that DFRT AFAM can map the elastic modulus with high spatial resolution and more reliable results. The interface of GFRP was especially investigated using a 2 μm × 2 μm scanning area. Finite element analysis was implemented to investigate the effect of tip radius and the applied pressing force on the interface measurement using a sharp “interface”. By setting a linear‐modulus‐varied interface with finite width in finite element analysis (FEA), similar comparison between FEA and AFAM experimental results was also implemented. The average interface width is determined to be 476 nm based on the high‐resolution modulus image, indicating that AFAM is a powerful method for nanoscale interface characterization. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39800.     

A novel Bayesian inference soft sensor for real‐time statistic learning modeling for industrial polypropylene melt index prediction

A novel real‐time soft sensor based on a sparse Bayesian probabilistic inference framework is proposed for the prediction of melt index in industrial polypropylene process. The Bayesian framework consists of a relevance vector machine for predicting melt index and a particle filtering algorithm for soft sensor optimization. An online correcting strategy is also developed for improving the performance of real‐time melt index prediction. The method takes advantages of the probabilistic inference and using prior statistical knowledge of polymerization process. Developed soft sensors are validated with ten public databases from UCI machine learning repository and real data from industrial polypropylene process. Experimental results indicate the effectiveness of proposed method and show the improvement in both prediction precision and generalization capability compared with the reported models in literatures. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45384.     

Generalizing solubility parameter theory to apply to one‐ and two‐dimensional solutes and to incorporate dipolar interactions

Hildebrand and Hansen solubility parameters are commonly used to identify suitable solvents for the dispersion or dissolution of a range of solutes, from small molecules to graphene. This practice is based on a number of equations, which predict the enthalpy of mixing to be minimized when the solubility parameters of solvent and solute match. However, such equations have only been rigorously derived for mixtures of small molecules, which interact only via dispersive forces. Herein, we derive a general expression for the enthalpy of mixing in terms of the dimensionality of the solute, where small molecules are considered zero‐dimensional, materials such as polymers or nanotubes are one‐dimensional (1D) and platelets such as graphene are two‐dimensional (2D). We explicitly include contributions due to dispersive, dipole–dipole, and dipole‐induced dipole interactions. We find equations very similar to those of Hildebrand and Hansen so long as the solubility parameters of the solute are defined in a manner which reflects their dimensionality. In addition, the equations for 1D and 2D systems are equivalent to known expressions for the enthalpy of mixing of rods and platelets, respectively, as a function of surface energy. This agreement between our expressions and those commonly used shows that the concept of solubility parameters can be rigorously applied to extended solutes such as polymers, nanotubes, and graphene. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

对机械设备设计研发过程的讨论

本文对机械设备设计研发过程的基本步骤、工作方法及需要引起注意的问题进行了较详细的论述,并对机械设备设计研发工作的开展提出了一些建议.     

涂料研究开发新进展及关键科学与技术问题

阐述了近年来国内外涂料的研究开发现状,包括:利用新的树脂合成方法获得新的成膜物;直接引入无机纳米粒子以改善涂层性能;表面微纳结构构建以获得功能涂层等;提出了未来涂料技术的发展趋势,包括:环保化和健康化;通用涂层的高性能化;多功能化和智能化等;和需要突破的关键科学与技术问题。当企业发展到一定阶段和规模后,要加强科研开发的投入,加强产学研合作,加强基础研究,要敢于开发国外没有的技术和产品,敢于领先国外技术,才能真正成为涂料强国。     

TiO2‐Oligoaldaramide nanocomposites as efficient core‐shell systems for wood preservation

Homogeneous core‐shell systems were obtained with a growth, in controlled steps, of several oligoamides on TiO₂ nanoparticles. Derivatives of natural compounds, such as l ‐tartaric acid and α,α′‐trehalose, were used as diesters in the polycondensation reactions with ethylenediamine. TiO₂ anatase was chosen because of its high photo‐activity and its antimicrobial activity. The TiO₂ nanoparticles had been previously activated then functionalized using two different coupling agents, and finally, the TiO₂‐oligoamide nanocomposites were synthesized using two synthetic pathways. The final products were characterized by ¹H NMR, ¹³C NMR, FT‐IR, and transmission electron microscope. These nanocomposites can show improved properties in comparison with the single components (TiO₂ nanoparticles or oligoamides), which are useful in many fields, such as antimicrobial coatings for surfaces in cultural heritage conservation. A nanocomposite (TiO₂‐polyethylenetartaramide) was used for applicative studies, and it has shown a good efficacy against fungal attack by Trametes versicolor on wood specimens (Fagus sylvatica). © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42047.     

Poly(butylene succinate)/layered double hydroxide bionanocomposites: Relationships between chemical structure of LDH anion,delamination strategy,and final properties

A series of poly(butylene succinate) (PBS) containing organo‐modified layered double hydroxide (LDH) are prepared by melt compounding and by in situ polymerization of succinic ester and 1,4‐butanediol. Various LDHs intercalated with renewable organic anions are used. More specifically, lauryl sulfate, stearate, succinate, adipate, sebacate, citrate, and ricinoleate ions are used as LDHs organo‐modifiers. The thermal, rheological, and dynamic mechanical properties of the samples are investigated. The results reveal a general mechanical reinforcement imparted by the clays. Significant changes are observed for the in situ polymerized nanocomposites, especially for LDH stearate which improves the properties of PBS nanostructure, whereas very few differences are observed for the other samples. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1931–1940, 2013     

Preparation and testing of Nafion/titanium dioxide nanocomposite membrane electrode assembly by ultrasonic coating technique

Membrane electrode assemblies with Nafion/nanosize titanium dioxide (TiO₂) composite membranes were manufactured with a novel ultrasonic‐spray technique (UST) and tested in proton exchange membrane fuel cell (PEMFC). The structures of the membranes were investigated by scanning electron microscopy (SEM), X‐ray diffraction (XRD), and thermogravimetric analysis. The composite membranes gained good thermal resistance with insertion of TiO₂. The SEM and XRD techniques have proved the uniform and homogeneous distribution of TiO₂ and the consequent enhancement of crystalline character of these membranes. The existence of nanometer size TiO₂ has improved the thermal resistance, water uptake, and proton conductivity of composite membranes. Gas diffusion electrodes were fabricated by UST. Catalyst loading was 0.4 (mg Pt) cm^?2 for both anode and cathode sides. The membranes were tested in a single cell with a 5 cm² active area operating at the temperature range of 70°C to 110°C and in humidified under 50% relative humidity (RH) conditions. Single PEMFC tests performed at different operating temperatures indicated that Nafion/TiO₂ composite membrane is more stable and also performed better than Nafion membranes. The results show that Nafion/TiO₂ is a promising membrane material for possible use in PEMFC at higher temperature. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40541.     

Synthesis and properties of cross‐linked polymers from epoxidized rubber seed oil and triethylenetetramine

A series of epoxidized oils were prepared from rubber seed, soybean, jatropha, palm, and coconut oils. The epoxy content varied from 0.03 to 7.4 wt %, in accordance with the degree of unsaturation of the oils (lowest for coconut, highest for rubber seed oil). Bulk polymerization/curing of the epoxidized oils with triethylenetetramine (in the absence of a catalyst) was carried out in a batch setup (1 : 1 molar ratio of epoxide to primary amine groups, 100°C, 100 rpm, 30 min) followed by casting of the mixture in a steel mold (180°C, 200 bar, 21 h) and this resulted in cross‐linked resins. The effect of relevant pressing conditions such as time, temperature, pressure, and molar ratio of the epoxide and primary amine groups was investigated and modeled using multivariable nonlinear regression. Good agreement between experimental data and model were obtained. The rubber seed oil‐derived polymer has a T_g of 11.1°C, a tensile strength of 1.72 MPa, and strain at break of 182%. These values are slightly higher than for commercial epoxidized soybean oil (T_g of 6.9°C, tensile strength of 1.11 MPa, and strain at break of 145.7%). However, the comparison highlights the potential for these novel resins to be used at industrial/commercial level. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42591.     

Lipid Composition,Natural Antioxidants and Physicochemical Characteristics in Liver Oil from Rajiforms from the Gulf of Mexico

Lipid composition by class, fatty acids, natural antioxidants (carotenes, tocopherols) and physicochemical characteristics of liver oil from three commercial rays, Rhinoptera bonasus (Chucha), Aetobatus narinari (Pinta) and Dasyatis americana (Bala) from the Gulf of Mexico were analyzed. Liver oil yield for R. bonasus, A. narinari and D. americana were of 43.04, 41.2 and 38.2% (wet weight), respectively. Triacylglycerols were the most abundant lipid by class in R. bonasus (68.9%), A. narinari (85.9%) and D. americana (81.6%), while sterols esters, sterols, di- and monoacylglycerides, polar lipids and wax esters were found in minor proportions. Species showed similar carotenes concentration, 8.7, 12.8 and 8.0 μg/g for R. bonasus, A. narinari and D. americana, respectively. α-tocopherol concentration was higher (p < 0.05) for A. narinari (46.7 mg/100 g) than for R. bonasus (21.0 mg/100 g) and D. americana (13.7 mg/100 g). Omega-3 polyunsaturated fatty acids in R. bonasus were high with docosahexaenoic acid (12.1%) in a higher proportion than eicosapentaenoic acid (7%).