螺旋隔板花瓣管换热器的传热强化研究

比较了螺旋用板花瓣管和螺旋隔板低肋管润滑油冷却器和空气冷却器的传热性能,实验结果表明,无论是作为油冷却器,还是作为空气冷却器,螺旋隔板花瓣换热器的综合传热性能明显优于螺旋隔板低肋管换热器,且螺旋隔板花瓣换热器还能节省３０％以上的铜管重量．     

Theoretical and Experimental Heat and Mass Transfer Analysis for a Falling Film Outside a Grooved Tube

The heat and mass transfer from a grooved tube is investigated experimentally for a falling-film flow. The experiments are conducted on a helical trapezoidal grooved tube at three temperatures of the feeding water: 30°C, 35°C, and 40°C. The Reynolds number (Re) of the air ranges between 1,500 and 3,500. Nusselt number (Nu) is expressed as a function of the Prandtl number (Pr), Re for air (Re_a), Re for water (Re_w); Sherwood number (Sh) is expressed as a function of the Schmidt number (Sc), Re_a, and Re_w, and the correlation coefficients are determined.     

铜铝复合管在空调蒸发器中应用的试验研究

主要针对铜铝复合管(CCA管)在空调蒸发器集气(液)管替代铜管应用进行了试验研究。从焊接工艺、弯曲性能和弯曲后抗压性能方面对9.52×0.7型号的铜铝复合管进行替代研究。结果表明:铜铝复合管焊接处的抗拉强度为114.1MP,延伸率为30%,可以满足产品要求。它具有良好的弯曲性能和弯曲抗压性能,经过不多于四次的弯曲试验,复合管集气管的极限压力为19MP,高于饱和制冷剂3倍工作压力。将铜铝复合管集气管的空调与原机在焓差实验室进行整机性能试验,结果表明:它们的制冷量相差10W,能效比基本不变,可以满足国家标准,对空调器的性能基本没有影响。同时在噪声实验室对整机进行噪声测试,测试结果显示,与原机型相比,在高中低三种风量状态下,噪声分别增加0.5/0.6/1 dB(A),满足原机型噪声标准。与铜管相比,在相同条件下,复合管集气(液)管可以降低成本29.2%。     

螺旋型爆磁压缩脉冲发生器2维磁流体力学数值模拟

 基于任意拉氏- 欧拉方法的2维磁流体力学程序APMFCG被用于简单绕制的螺旋型爆磁压缩脉冲发生器动力学过程的模拟,给出了德克萨斯技术大学简单绕制的爆磁压缩发生器数值计算结果,输出电流和线圈电感的模拟结果与实验测量基本吻合。该程序也用于研究由于种子电流的不同所导致的欧姆电阻非线性效应对爆磁压缩过程的影响,实验结果证明了该程序计算的可靠性。     

A one-dimensional continuous model for carbon nanotubes

The two-dimensional (2D) continuous elastic energy model for isotropic tubes is reduced to a one-dimensional (1D) curvature elastic energy model strictly. This 1D model is in accordance with the Kirchhoff elastic rod theory. Neglecting the in-plane strain energy in this model, it is suitable to investigate the nature features of carbon nanotubes (CNTs) with large deformations and can also reduce to the string model in [Z.C. Ou-Yang et al., Phys. Rev. Lett. 76, 4055 (1997)] when the deformation is small enough. For straight chiral shapes, this general model indicates that the difference of the chiral angle between two equilibrium states is about π/6, which is consistent with the lattice model. It also reveals that the helical shape has lower energy for per atom than the straight shape has in the same condition. By solving the corresponding equilibrium shape equations, the helical tube solution is in good agreement with the experimental result, and super helical shapes are obtained and we hope they can be found in future experiments.     

Dielectric effect on the rf characteristics of a helical groove travelling wave tube

A new type of partial-dielectric-loaded helical groove slow-wave structure (SWS) for millimetre wave travelling wave tube (TWT） is presented in this paper.The radio-frequency characteristics including the dispersion properties,the longitudinal electric field distribution and the beam-wave coupling impedance of this structure are analysed.The results show that the dispersion of the helical groove circuit is weakened,the phase velocity is reduced and the position of the maximum Ez is moved from the mouth to the inside of the groove after partially filling the dielectric materials in the helical groove SWS.Therefore,the dielectric-loaded helical groove SWS is suitable for a multi-beam TWT with broad band and high gain.     

Deflagration-to-detonation transition process for spherical aluminum dust/epoxypropane mist/air mixtures in a large-scale experimental tube

The deflagration-to-detonation transitions (DDTs) for clouds of spherical aluminum dust (SAD) mixed with air or epoxypropane mist (EPM) and air were investigated in a 29.6-m-long experimental tube of 199 mm in diameter. The clouds formed through the injection of SAD and SAD/liquid epoxypropane samples into the experimental tube. Explosions of the SAD/air mixture were initiated using a 7-m-long EPM/air cloud explosion ignited by a 40-J electric spark. Explosions in SAD/EPM/air clouds were initiated using a 1...     

R410A房间空调器启停过程动态模拟与实验研究

文中建立了R410A风冷房间空调器启动与停机过程的动态数学模型。其中压缩与节流过程采用稳态模型,而换热过程采用动态分布参数分相流模型。用自适应步长法对该过程进行了数值计算,得出了蒸发压力、冷凝压力、空气温度、制冷量及性能系数等随时间的变化规律,并在焓差法空调器性能实验台上对一台R410A风冷房间空调器的启、停过程进行实验研究。将实验结果与数值计算结果进行比较,验证了模型的可靠性。     

Stable single helical C-and I-chains inside single-walled carbon nanotubes

The helicity of stable single helical carbon chains and iodine chains inside single-walled carbon nanotubes(SWCNTs)is studied by calculating the systematic van der Waals interaction energy.The results show that the optimal helical radius increases linearly with increasing tube radius,which produces a constant separation between the chain structure and the tube wall.The helical angle exhibits a ladder-like decrease with increasing tube radius,indicating that a large tube can produce a small helicity in the helical structures.     

轴线起爆式螺线管型爆磁压缩发生器理论模型

 对轴线起爆式螺线管型爆磁压缩发生器进行了理论模型研究，建立了爆炸管的一维爆轰驱动模型、螺线管内空间磁场强度分布模型、爆炸管外表面磁压力模型和发生器系统的等效电路模型等，对此类发生器的物理过程进行系统描述。在此基础上，编制了相应的零维数值模拟程序CEMG 1.0，利用该程序分别对四种不同模型参数的发生器进行了理论计算和参数优化，并对其中一模型发生器爆炸管外表面的磁压力及其引起的剩余电感进行了计算，给出了剩余电感与初始输入条件及负载电感的关系，从而得到该模型的输出性能极限。对理论模型的正确性进行了实例验算证明。     

An investigation into the acoustic insulation of triple-layered panels containing Newtonian fluids: Theory and experiment

Sound insulation of triple-layered panels consisting of two impervious layers with the middle layer being a Newtonian fluid is studied here both theoretically and experimentally. The progressive impedance model is used to predict the transmission loss (TL) provided by the panel in a normal incidence field. Corrections are then made to obtain the TL values of such panels in random incidence field. A modified B&K impedance tube was constructed for experimental evaluation. Results are presented for a Pyrex glass cylindrical tube containing motor oil, a ferromagnetic nanoparticles fluid (in the absence of a magnetic field) and air. Good agreement is obtained between the measured and analytical results for a wide range of frequencies. Also, a significant difference in TL values, particularly at low frequencies (f ? 4 kHz), is observed once the air is replaced by the fluid layer.     

Chiral single-wall gold nanotubes

Based on first-principles calculations we show that gold atoms can form both freestanding and tip-suspended chiral single-wall nanotubes composed of helical atomic strands. The freestanding, infinite (5,5) tube is found to be energetically the most favorable. While energetically less favorable, the experimentally observed (5,3) tube stretching between two tips corresponds to a local minimum in the string tension. Similarly, the (4,3) tube is predicted as a favorable structure yet to be observed experimentally. Analysis of band structure, charge density, and quantum ballistic conductance suggests that the current on these wires is less chiral than expected, and there is no direct correlation between the numbers of conduction channels and helical strands.     

燃料射流与空气协流混合中的自点火预测研究

预混燃烧室燃料与空气混合过程中出现的自点火会引起回火与挂火,烧毁燃料喷嘴。针对这一问题,利用实验台模拟贫燃燃烧室预混过程,燃料射流与预热后的空气协流同向喷入石英管预混段中,研究自点火现象。本文结合机器学习和物理规律分析,开展湍流混合过程的自点火预测研究。基于二元逻辑回归建立了机器学习模型,模型的特征由分析影响自点火的物理规律得到,训练和校验模型所需的数据由燃料射流-空气协流的自点火实验获得。结果显示,机器学习方法能快速、准确地预测混合过程中自点火的发生和火焰类型,并揭示其关键影响因素。与传统的数值计算方法相比,机器学习方法预测自点火所需的时间仅为传统数值模拟方法的几千分之一。     

Determination of kernel emission spectrum of a mini X‐ray tube for EDXRF applications

Knowing the spectrum near the output of the relatively new mini X‐ray tube (MXRT) commercial models is fundamentally important in energy‐dispersive X‐ray fluorescence scan images, especially in the in vivo applications. This information is relevant for determining the absorbed dose during a measurement and for absolute quantification by a fundamental parameter method. However, it is not possible to measure it directly using a silicon drift detector (SDD) given the high saturation in the counts. In this work, an experimental methodology is developed for determining the kernel spectrum emitted by the MXRT, enabling the quantification of its energy flux density over short distances. Different distances were used: source–detector, solid emission angle (collimation), attenuation characteristics of the medium (air), and in a vacuum, within an energy range of 1–40 keV, to determine the X‐ray tube spectrum. The spectrum is measured by an SDD, taking its efficiency and dead time into account. In order to verify the method, a spectrum that is rebuilt starting with the kernel is compared, under the same conditions, with a reference spectrum that is directly measured in air and with a theoretical spectrum obtained by the Ebel model. The results are consistent and validate the methodology employed in this work. Additionally, low‐energy peaks were detected, corresponding to the tube material's L lines, which are not present in the original spectrum reported by the manufacturer. Copyright © 2015 John Wiley & Sons, Ltd.     

Curvature-induced quantum behaviour on a helical nanotube

We investigate the effect of curvature on the behaviour of a quantum particle bound to move on a surface shaped as a helical tube. We derive and discuss the governing Schrödinger equation and the corresponding quantum effective potential which is periodic and points to the helical configuration as more energetically favorable as compared to the straight tube. The exhibited periodicity also leads to energy band structure of pure geometrical origin.     

A three-zone simulation model for a air-cooled condensers

The present paper deals with the development of a mathematical model for the performance prediction of air-cooled condensers. The model considers the heat exchanger as formed by three distinct zones: de-superheater, condenser and subcooler. To make the model as generally applicable as possible, each piece of straight tube, between two return bends, is treated as a separate heat exchanger. The coil can thus be formed by any particular composition of straihgt tubes, enabling the overall effectiveness of each zone to be determined, with the use of correlations available in the literature. Zone-ending (starting of condensation or subcooling half-way along a tube) is also considered, with appropriate modelling. The energy balances over each zone, for both air and refrigerant streams, together with the effectiveness equations, form a set of non-linear equations, which are solved numerically. Despite its simplicity the method produces results comparable with those produced by more sophisticated local analyses. In the present paper six coil configurations are studied. Predicted results are compared with existing experimental data, with generally good agreement. A few possible applications of the method are also presented.     

Tube-side heat transfer enhancement in flat-plate liquid solar collectors with wire coil inserts

This work presents an experimental study of the thermal-hydraulic characteristics in a flat-plate solar collector with two different geometries of helical coil inserts. Isothermal pressure drop tests are conducted in a horizontal tube using water as working fluid to obtain the fully developed Fanning friction factor for a range of Reynolds number Re = 80–8,000. Heat transfer tests are performed in the solar collector loop using a mixture of propylene-glycol and water at 30 wt%, covering the ranges Pr = 16–28 and Re = 140–600. A significant decrease in the temperature of the absorber is observed when the appropriate wire coil is selected for the given flow conditions, proving the beneficial effect of this type of insert device for the augmentation of the thermal efficiency in flat-plate solar collectors.     

Pressure drop,heat transfer and performance of a helically coiled tubular exchanger

Experiments have been conducted, and correlations are developed for the pressure drop and heat transfer coefficient for the tube and shell sides of a helical coil heat exchanger. In the tube side, the laminar friction factor and Nusselt numbers are represented as functions of Re√d/D, whereas in turbulent flow the results are correlated with Re·(d/D)². The pressure drop and heat transfer values for the shell side are found to follow the classical Blasius and Dittus-Boelter type relations, while a strong dependence on the coil to tube diameter ratio is detected. The performance of the exchanger has been tested not only as simulated experimental exchanger but also as a waste heat recovery device for a 60 HP gas turbine. Excellent corroboration of the effectiveness-NTU relation has been observed between the simulation and in situ experiments.     

直膨式空调人工神经网络在线自适应控制器应用研究

直接膨胀式空调系统人工神经网络控制器已经有了一些研究成果,为了解决控制器控制范围和精度的问题,引入在线自适应控制系统。该控制器的控制能力测试采用直接膨胀式空调系统实验装置进行。试验结果表明,基于人工神经网络动态模型的在线自适应控制器进行训练的前提下,该控制器能够将室内空气的干球和湿球温度控制在一定范围内,具有较高的控制精度。     

翼片加载螺旋线慢波结构的螺旋带模型

 翼片加载螺旋线慢波结构广泛应用于大功率、宽频带行波管中。建立了翼片加载螺旋线慢波结构的螺旋带模型，得到了实用的色散方程、耦合阻抗和衰减常数的表达式。利用导出的方程对实际行波管的螺旋慢波结构进行计算，并与测量结果和导电面模型进行了比较，计算结果与测量结果具有良好的一致性。分析了不同管壳半径对色散特性的影响。