磁场对熔盐射流冲击传热的影响

以永磁铁构建定磁场,进行外加磁场作用下熔盐射流冲击传热的实验研究,并得到Nusselt数Nu驻点关联式和径向分布。结果表明,在驻点区范围内,Nusselt数较无磁场作用时增大,传热得到比较明显的增强,而在壁面射流区,这种强化传热效果逐渐减弱。此外,当Reynolds数Re一定时,熔盐Nusselt数随着磁场强度的增加而增大,且驻点处强化传热效果最为显著。在Reynolds数Re=6400与磁场强度B=2800 Gs条件下,熔盐驻点Nusselt数Nu₀提高约6％,可见磁场作用对熔盐射流冲击传热具有一定的强化效果。     

Influence of magnetic field on jet impingement heat transfer with molten salt

Experimental study of jet impingement heat transfer with molten salt under the influence of external constant magnetic field was generated by permanent magnets. Both stagnation correlation and radial distribution of Nusselt number under magnetic field were obtained. The results showed that the Nusselt number with magnetic field became higher than that without magnetic field at stagnation region and jet impingement heat transfer was comparatively enhanced, while in wall jet region, the enhancement of heat transfer was gradually weakened. In addition, when the Reynolds number was constant, the Nusselt number of molten salt increased with increasing of the intensity of magnetic field, and the most enhanced heat transfer existed at the stagnation point. Under the conditions of Reynolds number Re=6400 and the intensity of magnetic field B=2800 Gs, the stagnation Nusselt number of molten salt was about 6 % higher than that without magnetic field. It can be seen that the magnetic field may promote the jet impingement heat transfer of molten salt.     

Particle‐laden liquid jet impingement on a moving substrate

The impingement of high speed jets on a moving surface was studied. The jet fluids were dilute suspensions of neutrally buoyant particles in water–glycerin solutions. At these low particle concentrations, the suspensions have Newtonian fluid viscosity. A variety of jet and surface velocities, solution properties, nozzle diameters, mean particle sizes, and volume fractions were studied. For each case the splash‐deposition threshold was quantified. It was observed that for jets with very small particles, addition of solids to the jet enhances deposition and postpones splash relative to a particle‐free water–glycerin solution with the same viscosity. In contrast, jets with larger particles in suspension were more prone to splash than single phase jets of the same viscosity. It is speculated that the change in character of the splash response for the jets with larger particles in suspension occurs when the particle diameter is comparable to the lamella thickness. © 2017 American Institute of Chemical Engineers AIChE J, 63: 4673–4684, 2017     

液体阵列射流冲击冷板工质与传热结构研究进展

液体阵列射流冲击冷却是解决高热流密度散热问题的最有效技术之一,能够有效地对目标表面进行散热,具有散热能力高、能效比高和噪声低的优点,在散热方面具有巨大优势。本文简述了国内外对阵列射流冲击的研究进展,从换热工质和射流冲击冷板的换热结构两个方面,指出了其对液体阵列射流冲击换热特性的影响,并介绍了倾斜射流和旋流射流两种新型阵列射流方式。综合分析了常用的液体换热工质和纳米流体换热工质在射流冲击过程中强化换热的原理,介绍了喷嘴孔型、喷嘴的排列方式和冲击表面结构三种阵列射流结构。分析表明,不同孔型的喷嘴会影响流体的射流速度和湍流特性,不同的喷嘴排列方式会对射流流体的相互作用和有效冲击面积产生影响,不同的冲击表面会影响射流工质的循环混合,这些都将对射流冷板的换热特性产生很大影响。指出了解影响液体阵列射流冲击效果的主要因素,是改善和提高射流换热性能的根本方法。     

多喷嘴带相差射流冲击传热的数值模拟

采用数值模拟的方法对带相差的多喷嘴射流冲击传热进行数值模拟,分别得到不同相差和不同射流频率条件下的冲击传热效果。结果显示,在不同的射流喷射模式下,按相差顺序增加方式（B型）喷出的射流传热效果最好,两喷嘴间的相差为0°～180°之间时,传热板的传热效果随着相差角度的增加,传热效果得到增强,且在相差为120°时,整个传热板传热效果最均匀;在频率为0～10Hz时,频率越大,整个传热板传热越均匀,但频率的影响小于相差及喷射模式的影响。     

Design and fabrication of non‐noble metal catalyst‐based air‐cathodes for metal‐air battery

In this paper, cost‐effective non‐noble metal catalyst‐based air‐cathodes are designed, developed, and fabricated for a metal‐air battery, particularly in a non‐toxic neutral solution environment (sodium chloride). The air‐cathode and its fabrication method comprise two gas diffusion layers (GDLs) bonded on to each side of the current collector (nickel mesh) by a rolling method, and a catalyst layer bonded on one GDL by a spraying method. The GDL paste consists of carbon powder and hydrophobic chemicals, and the catalyst layer contains non‐noble metal catalyst, carbon powder, and hydrophilic chemicals. Several characterization techniques such as DTA/TG thermal analysis, electrochemical impedance spectroscopy, linear sweep voltammetry, and their associated theories are used to understand the properties and performance of the developed air‐cathodes. The advantages of the current method of forming the air‐cathode can decrease the internal electronic resistance and gas flow restriction of the system, and therefore increase air permeability as well as water transportation to the reaction sites. By using such an integrated structure of an air diffusion cathode, the cost‐effectiveness in terms of materials and manufacturing compared to the commercial air‐cathode, and the overall fabrication procedure is achieved, and the method can be easily transferred into a continuous industrial manufacturing process.     

A particle-to-particle heat transfer model for dense gas-solid fluidized bed of binary mixture

A particle-to-particle collisional heat transfer model in the frame of Eulerian-Eulerian approach was proposed in this paper. By incorporating it into the multi-fluid model to close the enthalpy equations, the heat transfer between different particle classes in a gas bubbling fluidized bed of binary mixture was investigated, based on the CFD simulations of particle mixing in literature (Cooper and Coronella, 2005). The results showed that the particle-to-particle heat exchange coefficient between different particle classes increases with increasing the size of large particle class and the superficial gas velocity. The ratios of the particle-to-particle heat transfer to the gas-to-particle heat transfer range from 8.04% to 15.0% for various calculating conditions. In order to better understand the heat transfer behavior in a dense gas-solid fluidized of binary mixture, it is important to take the particle-to-particle heat transfer into account.     

板翅式换热器翅片通道中流体流动与传热的计算流体力学模拟

针对平直形和锯齿形两种不同翅片类型,利用计算流体动力学(CFD)软件FLUENT对板翅式换热器的微小通道进行了模拟,得出了通道中流体的流动与传热特性.计算结果表明,在相同情况下,平直形和锯齿形翅片中冷热流体的局部传热系数的最大值都出现在入口处;在锯齿形翅片的相邻2个锯齿的交错面上,流体的局部传热系数和压力存在突变,流体的边界层厚度要薄于在平直形翅片中的厚度,流体的局部换热系数要和压损大于其在平直形翅片中的值.     

微通道内非共沸混合制冷剂的流动沸腾特性

采用了3种不同组分比例的R32/R134a工质在0.86 mm的微通道中进行了传热特性和阻力特性的实验研究,考察了非共沸工质不同组分比例对微通道换热特性的影响。实验结果表明:在组分质量分数比为35%/65%时,核态沸腾在小干度下换热效果最好;干度较大时,组分比例对换热的影响效果降低。在大质量流量下传热阻力效应的影响不再明显。在压降方面,组分比为15%/85%的相对压降最大,其它两种组分的压降较小。     

Deposition of magnetite particles from flowing suspensions under flow‐boiling and single‐phase forced‐convective heat transfer

The deposition rate of colloidal magnetite particles was measured under both single‐phase forced‐convective and flow‐boiling conditions. All measurements were made at alkaline pH where both the heat transfer surface and the surface of the magnetite particles appear to be negatively charged. For single‐phase forced convection, the deposition rate constant is lower than the mass transfer coefficient for colloidal particles, and the difference is attributed to the force of repulsion between the negatively charged surfaces of the particle and substrate. The deposition rate measured under flow‐boiling conditions is lower than that reported for the deposition of colloidal particles at neutral pH. The difference is, again, attributed to the force of repulsion between the particle and substrate. Particle removal rates were significantly lower than deposition rates; analysis using the theory of turbulent bursts suggests a removal efficiency of only 10^?9% for each turbulent burst. The low removal efficiency is consistent with the particle diameter being significantly smaller than the thickness of the laminar sublayer in these tests.     

Mathematical predictions of gas permeability for automotive air‐bags

The mathematical relationship combining an applied pressure drop and the resultant gas velocity through a woven fabric is important to the air‐bag industry to predict the performance of new materials before they are woven. The main difficulty in formulating a mathematical solution is the complexity of the woven fabric structure. In available publications, fabric pores had normally been represented as a series of cylindrical pipes. This article considers the same approach and analyzes some of the equations to review their industrial applicability. Because none of the equations have been found adaptable in predicting the permeability behavior of air‐bag fabrics, experimental data have been used to generate empirical equations. The data were generated using a dynamic air permeability tester that was used to project air at high pressure through a variety of air‐bag fabrics. A static permeability tester was also used to generate results through the same fabrics at lower pressures. The final equations combine the fabric cover factor and the pressure differential to give the resultant gas velocity. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2104–2112, 2000     

进风角度对椭圆管翅式换热器传热性能影响

对两排椭圆管翅式换热器实验元件在不同进风角度下（30°、45°、60°和90°）的换热性能进行了实验研究,结果表明,在测试的迎风速度范围内随着进风角度的减小换热器换热性能减弱,并给出了测试工况范围内的换热性能经验关联式;对不同进风角度下空气侧换热性能进行了数值计算,与实验结果进行对比,符合良好;最后对不同进风角度下换热器内不同通道内空气平均速度的分布进行了研究,解释了换热性能差异的原因,为相应的工程应用提供理论参考。     

Investigation of the mechanism of low‐density particle and liquid mixing process in a stirred vessel

In order to investigate the mechanism of the low‐density solid particle and liquid mixing process, a specialised agitator structure was used. Both computational fluid dynamics simulation and experiments were carried out to study the two‐phase mixing characteristics in the stirred vessel. The mixing process was captured by snapshots. The flow field and solid phase volume fraction evolution were analysed. Experimental and numerical results agreed well with each other. Solid particles floating on the liquid surface were gradually transported to the bottom through the centre of the vessel and the mixing time was predicted and tested. Results indicate that the agitator structure used in this study is able to form an obvious axial circulation in the vessel and then achieve a good performance in low‐density solid and liquid mixing operations. The study provides a valuable reference for the design and optimisation of solid–liquid mixing equipment. © 2011 Canadian Society for Chemical Engineering     

Computational fluid dynamics simulations of heat transfer between the dense‐phase of a high‐temperature fluidized bed and an immersed surface

The transient process of heat transfer between a high‐temperature emulsion packet and the wall of an immersed surface is simulated using computational fluid dynamics (CFD). From these simulations, the total heat transfer coefficient and its radiant contribution due to the emulsion (dense) phase are evaluated. The results are compared with experimental data (Ozkaynak et al., “An experimental investigation of radiant heat transfer in high temperature fluidized beds,” in Fluidization IV, 1983:371–378) and with predicted values from the generalized heterogeneous model (GHM), (Mazza et al., “Evaluation of overall heat transfer rates between bubbling fluidized beds and immersed surfaces,” Chem Eng Commun., 1997;162:125–149). The CFD simulations are in good agreement with both, experimental data and theoretical GHM predictions and provide a reliable way to quantify the studied heat transfer process. Also, the GHM is validated as a practical tool to this end. © 2011 American Institute of Chemical Engineers AIChE J, 58: 412–426, 2012     

Numerical analysis of heat transfer mechanisms to pneumatically conveyed dense phase flow

Mass and energy balances are required in power generation, chemical, pharmaceutical, food and commodity transfer processes in order to achieve efficient utilization of energy and raw materials. There is a need for accurate, reliable, on-line, continuous and non-invasive measurement of solids' mass flow rate in many industrial processes mentioned above. Thermal flowmeters, in theory, provide a true indication of the mass flow of solids in pneumatic conveying pipelines.A complicated heat transfer between a pipe wall and a gas-solid flow in a conveying pipeline inevitably takes place in a thermal solids' mass flow measurement process. A study of heat transfer mechanisms to pneumatically conveyed gas-solid dense phase flow as a means to mass flow rate measurement has been conducted experimentally and numerically to evaluate the heat transfer coefficient between the hot wall and the gas-solid dense phase flow. The prediction of the heat transfer coefficient is compared with the experimental findings. It was found that the heat transfer coefficient between the pipe wall and the gas-solid dense flow is a function of solids loading ratio. Increasing the gas stream velocity significantly augments the heat transfer between the hot wall and the gas-solid dense phase flow.     

Generation of polymer ultrafine fibers through solution (air‐) blowing

Solution (air‐) blowing, an innovative technique for generation of ultrafine polymer fibers from solutions, was developed by feeding polymer solutions (instead of melts) to a die assembly similar to that used in the conventional melt (air‐) blowing process. Micro‐ to nano‐scaled polyvinylpyrrolidone (PVP) fibers were produced using PVP solutions with water, ethanol, and/or their mixtures as the solvents; and the morphologies of the fibers were examined by scanning electron microscopy. The processing variables, including PVP concentration, air‐blowing pressure, solution‐feeding pressure, and the volatility of the solvent system (the ratio of ethanol to water), were systematically investigated. The results indicated that solution (air‐) blowing was a viable technique to produce nonwoven fabrics consisting of ultrafine polymer fibers with diameters ranging from micrometers to nanometers. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

蜂窝夹套流动与换热的数值模拟及其结构优化

基于标准k-ε湍流模型并辅以壁面函数法,对蜂窝夹套内流体流动与传热进行了三维数值模拟。计算结果与试验结果误差在10%以内,证明了该模型的可靠性。采用正交设计及因素分析法对蜂窝锥度、蜂窝间距、蜂窝高度、蜂窝直径及蜂窝排列形式等结构参数对蜂窝夹套热力性能的影响进行研究,并依据方差分析结合响应面法对结构因素进行优化组合。     

纺粘牵伸器喷射流场的测试及验证

根据纺粘非织造扁平窄狭缝流道牵伸器的特点和喷射流场的特征,采用粒子图像测速仪对纺粘牵伸器的喷射流场进行了试验测试,同时,列出用喷射流场理论模型所获得的计算数值模拟结果,并对数值模拟结果和试验结果进行比较。