碳氢燃料在旋转通道中传热的数值模拟

本文利用数值模拟方法,对不同转速下正癸烷在U型管路的传热特性进行了研究。得到以下结论:对于U型管路来说,旋转速度越大,出口温度越高,整体管路换热能力越强;碳氢燃料在准临界温度附近的变物性对换热有比较显著的影响,会使换热恶化;浮升力也会影响旋转管路的换热,相比静止管路影响更为复杂。     

超临界压力下碳氢燃料在竖直圆管内对流换热实验研究

采用超临界压力碳氢燃料作为冷却剂的再生冷却技术是超声速燃烧冲压发动机的一种重要热防护技术。本文以工程碳氢燃料为工质,在内径2 mm的竖直圆管内进行了不同流向、流量、压力、热流密度条件下的对流换热实验研究。结果表明,在较高进口Re数条件下,相同热流密度时,向上流动和向下流动工况的壁温分布没有明显差别;在较低进口Re条件下,向上流动工况的局部壁温远高于对应向下流动工况,发生传热恶化。研究表明该碳氢燃料的临界Bo*数判据为3×10~(-7)。拟合得到适用于该碳氢燃料的对流换热关联式。     

裂解吸热反应对乙烷超临界传热的影响

本文对圆管内超临界状态下乙烷的湍流传热过程进行了数值模拟,分析了乙烷高温裂解对壁面热流密度、平均温度以及对流换热Nusselt数的影响。计算结果表明:考虑乙烷高温裂解吸热反应,管内平均温度会降低,出口处温度降低可达135 K;壁面热流密度则会显著增加,热出口处可增加近2倍;热裂解反应改善了超临界对流换热效果,Nusselt数可提高约20%。在本文计算条件下,经典的对流换热关系式可准确适用于不考虑热裂解反应的情况,而对于考虑裂解吸热反应的超临界乙烷传热情况则误差较大。     

基于ReaxFF反应分子动力学模拟的正十二烷醇的热裂解特性研究

醇类添加剂是提高碳氢燃料再生冷却效率的有效途径之一。特别是多碳醇由于自身高热值成为了潜在的主动冷却介质，而其裂解机理尚未完善。本研究基于反应分子动力学模拟的方法，分别探究了正十二烷、正十二烷醇的热解过程，从分子尺度揭示其反应动力学微观机理，并分析温度等敏感因素对反应速率、产物分布的影响。结果表明，温度的提高会极大地提升热解的反应速率，并且反应物倾向于分解成分子量更小的气体产物。相比于正十二烷，正十二烷醇的起始裂解温度以及活化能更低，其展现了作为主动冷却介质的潜力。     

板状燃料组件流道部分堵塞的安全边界研究

为掌握板状燃料组件内多个流道堵塞下的流动换热特性,获得流动堵塞致传热恶化的触发边界,以提高板状燃料反应堆的运行安全性,以典型板状燃料堆JRR-3M的标准燃料组件为对象,基于定性分析将流道堵塞事故分为非相邻流道堵塞与相邻流道堵塞两类,采用计算流体动力学软件ANSYS Fluent对两类流道堵塞事故下的流动换热特性进行模拟。模拟结果表明:非相邻流道完全堵塞或相邻流道最大堵塞率低于35%,流道内不会发生局部沸腾且燃料最高温度低于许用温度。基于上述结果,可确定JRR-3M反应堆在堵流事故下的安全运行边界。     

煤油热沉与热裂解反应特性的试验研究

本文设计了一种煤油热裂解反应特性与热沉测量试验系统,利用该试验系统和原始标定法的热损测量方法,测量出了在亚临界和超临界压力下煤油热裂解反应的热沉大小,并进行了热裂解反应主要分解产物成分含量的测定与分析。结果表明：壁温随热流密度增加而增加;在相同燃油温度条件下,压力增大,热沉降低;裂解反应气体的浓度变化主要受到燃油温度和...     

氢、碳氢燃料对向扩散火焰

对氢、正烷烃碳氢燃料与氧的对向扩散火焰,其中正烷烃包含了在工业用燃料中广泛应用的C_nH_2n+2正烷烃CH₄～C1₆H₃₄,对这些燃料的火焰结构进行了分析和比较,系统地分析了压力和拉伸率对火焰行为和热释放率等的影响,其中包含了2115个组分8157个可逆反应．研究结果表明,所有燃料的火焰厚度和热释放率与压力和拉伸率的乘积的平方根成线性关系．在相同工况下,氢的火焰厚度总是大于所有的碳氢燃料,而CH₄～C1₆H₃₄所有的碳氢燃料在相同工况下总是具有几乎相同的燃烧温度分布、燃烧产物分布、火焰厚度和热释放率,该结果表明由这些碳氢燃料组成的混合燃料具有同样的火焰特性.     

构形树状小通道内的流动沸腾换热特性

本文建立了构形树状小通道内流动沸腾换热模型,数值研究了树状通道网络内的流动沸腾换热特性,并与具有相同换热面积、入口直径的蛇形通道就泵功消耗、流动沸腾压降、通道温度变化和热有效性等指标进行了性能对比分析。研究表明,与蛇形通道相比,构形通道具有流动沸腾压降、泵功消耗小的优势,且其温度均匀性、热有效性也均优于蛇形通道。当热流密度为20 W/cm~2时,构形树状通道内流体的泵功消耗约为蛇形通道的一半,其热有效性为蛇形通道的1.9倍。     

热储周围岩石热补偿对增强型地热系统采热过程的影响

采用自行开发的增强型地热系统(EGS)地下热流动过程三维动态模拟软件,模拟不同地质条件下EGS的长期运行过程,分析热储周围岩体的热补偿对产热温度以及热储内岩石、流体温度演化的影响.该数值模型视热储为等效多孔介质,采用两个能量方程分别描述流体和岩石的温度场,深入探究岩石与循环流体之间的换热过程.研究发现,热储周围岩体的热补偿作用与热储内流场形态强烈相关,且并不总是提高EGS的生产温度.在深度方向上有较大的优势流动的热储中,热补偿作用在EGS运行早期甚至会降低采出流体的温度.随着EGS的运行,热储温度持续降低,热补偿将对热能开采的影响将逐渐转向正面,对生产流体温度的提高效果增强.     

车用潜热贮热器的流动与换热实验研究

本文通过对车用潜热贮热器流动与换热实验研究，获得了该相变过程的流动、传热特性，为修正该装置的设计提供了可靠的数据．     

Convective Heat and Mass Transfer in Magneto Jeffrey Fluid Flow on a Rotating Cone with Heat Source and Chemical Reaction

The present paper addresses the megnetohydrodynamic Jeffrey fluid flow with heat and mass transfer on an infinitely rotating upright cone. Inquiry is carried out with heat source/sink and chemical reaction effects. Further, constant thermal and concentration flux situations are imposed. Optimal homotopy analysis method (OHAM) is employed to achieve series solutions of the concerned differential equations. Important results of the flow phenomena are explored and deliberated by means of graphs and numerical tables. It is perceived that thermal boundary layer thickness possess contrast variations for the heat source and heat sink, respectively. The chemical reaction enhances the heat transfer rate but decline the mass transfer rate. Moreover, the precision of the existing findings is verified by associating them with the previously available work.     

Hydrodynamics and heat and mass transfer at chemical conversions in slot reactors

In this paper, experimental and numerical investigations of the hydrodynamics and heat transfer in a disk slot heat exchanger-reactor for a radial flow of a gas mixture reacting on the channel walls are described. Data for the coefficients of heat transfer from the wall being heated to the gas flowing inside the reactor are presented. The temperature field of a catalytically active reactor plate at heat release on it has been investigated experimentally. Calculations of the flow and heat transfer in a slot reactor element for a catalytic reaction with heat release have been performed. Partial oxidation of methane in an oxygen medium with the formation of a hydrogen-containing synthesis gas in a two-dimensional microchannel has been investigated numerically. Data for the extent of the chemical conversion of methane versus the initial mixture consumption and reaction temperature are presented.     

A novel simulation theory and model system for multi-field coupling pipe-flow system

Due to the lack of a theoretical basis for multi-field coupling in many system-level models, a novel set of system-level basic equations for flow/heat transfer/combustion coupling is put forward. Then a finite volume model of quasi-1D transient flow field for multi-species compressible variable-cross-section pipe flow is established by discretising the basic equations on spatially staggered grids. Combining with the 2D axisymmetric model for pipe-wall temperature field and specific chemical reaction mechanisms, a finite volume model system is established; a set of specific calculation methods suitable for multi-field coupling system-level research is structured for various parameters in this model; specific modularisation simulation models can be further derived in accordance with specific structures of various typical components in a liquid propulsion system. This novel system can also be used to derive two sub-systems: a flow/heat transfer two-field coupling pipe-flow model system without chemical reaction and species diffusion; and a chemical equilibrium thermodynamic calculation-based multi-field coupling system. The applicability and accuracy of two sub-systems have been verified through a series of dynamic modelling and simulations in earlier studies. The validity of this system is verified in an air–hydrogen combustion sample system. The basic equations and the model system provide a unified universal theory and numerical system for modelling and simulation and even virtual testing of various pipeline systems.     

Hybrid Isothermal Model for the Ferrohydrodynamic Chemically Reactive Species

A hybrid isothermal model for the homogeneous-heterogeneous reactions in ferrohydrodynamic boundary layer flow is established. The characteristics of Newtonian heating and magnetic dipole in a ferrofluid due to a stretchable surface is analyzed for three chemical species. It is presumed that the isothermal cubic autocatalator kinetic gives the homogeneous reaction and the first order kinetics gives the heterogeneous (surface) reaction. The analysis is carried out for equal diffusion coefficients of all autocatalyst and reactions. Heat flux is examined by incorporating Fourier's law of heat conduction. Characteristics of materialized parameters on the magneto-thermomechanical coupling in the flow of a chemically reactive species are investigated. Further, the heat transfer rate and friction drag are depicted for the ferrohydrodynamic chemically reactive species. It is evident that the Schmidt number has increasing behavior on the rate of heat transfer in the boundary layer. Comparison with available results for specific cases is found an excellent agreement.     

Upshot of Chemical Species and Nonlinear Thermal Radiation on Oldroyd-B Nanofluid Flow Past a Bi-directional Stretched Surface with Heat Generation/Absorption ina Porous Media

A three-dimensional mathematical model is developed to examine the flow of nonlinear thermal radiation Oldroyd-B nanofluid past a bidirectional linearly stretched surface in a porous medium. The flow is induced by temperature dependent thermal conductivity, chemical reaction and convective heat and mass conditions. Novel characteristics of Brownian motion and thermophoresis are accompanied by magnetohydrodynamic and heat generation/absorption. Self-similar transformations are employed to convert the system of nonlinear partial differential equations to a system of ordinary differential equations with high nonlinearity and are solved by strong analytic technique named as Homotopy Analysis method (HAM). Effects of varied arising parameters on involved distributions are reflected through graphical illustrations. From this study, it is perceived that strong magnetic field hinders the fluid's motion and leads to rise in temperature that eventually lowers heat transfer rate from the surface. Further, decrease in heat transfer rate is also observed for enhanced values of thermal radiation parameter. To validate our results, a comparison with already published paper in limiting case is also given and results are found in excellent oncurrence; hence reliable results are being presented.     

基于康托尔分形微通道流动与传热的模拟

高密度、 小体积和高集成的电子元器件散热困难, 易造成过早失效, 采用微通道换热器可以实现小体积内高热流的散热, 但流动阻力很大. 为了保证传热效果, 降低流动阻力, 本文提出了一种新型的微通道结构并对其流动与传热特性进行了数值模拟. 首先研究了微通道形状和结构, 模拟结果表明: 进出口截面宽高比为0.8 的矩形微通道的换热效果最好; 并在此基础上提出一种康托尔分型凹槽结构, 研究了有无康托尔分形以及不同分形级数对流动与传热性能的影响, 综合对比发现: 第二级康托尔分形模型 N2 既能保证热阻显著降低, 又能相比阵列结构降低压降, 具有明显的换热优势; 最后对这种康托尔分形结构的凹槽形状, 尺寸及不同方向上的分形进行研究, 结果表明梯形凹槽的下上表面长度比b/a 为0.6 、 流动方向分形比fx 为1 .25 和通道高度方向分形比fy 为1 .5 时换热流动性能最佳.     

微尺度水平管内沸腾换热特性研究

对不同质量分数下非共沸混合工质(R134a/R32)在微尺度管道内的流动沸腾换热特性进行了比较和分析,阐述了热流密度、质量流量和质量干度对换热的影响。结果表明:热流密度对换热的影响随着质量流量的增加而愈加明显;在质量分数为75%/25%和65%/35%时,换热系数随着质量流量的增大而增大;而质量分数为85%/15%时,换热系数随质量流量的变化先增加后减小;随着质量干度的增加,换热系数在各质量分数下基本上都呈上升趋势。     

近共振传能放热对氧碘化学激光器性能的影响

在氧碘化学激光器(COIL)中,O2(1Δ)与I的近共振传能反应是一个放热反应;它与水汽等的猝灭放热反应一样会对激射过程产生不利影响,而且是不可避免的。计算了猝灭放热效应对光腔气动特性输出功率的影响。得到了近共振传能放热的大小与粒子数反转和激射的光子数相关,即与光腔内的增益、光场强度分布成正比,故主要发生在激光器的上游区前半部分。模型计算表明,其影响程度大致相当于7%水汽所致的对氧碘化学激光器的影响。完善了氧碘化学激光器理论计算模型。     

温室及其蓄热层中传热与流动的研究

针对被动式太阳能温室系统,分析了玻璃顶部覆盖面倾角不同,对温室中温度及气流分布的影响。温室玻璃顶部覆盖面倾角,可以改变温室中的气流、温度分布。研究了温室蓄热层传热与流动。温室中土壤或岩床具有吸收并贮存太阳能的作用。