微酒窝通道与圆柱面凹槽通道对流传热强化分析

结合对流传热场协同原理分析了微酒窝通道、圆柱面凹槽通道及低肋通道强化传热特点,研究发现酒窝与圆柱面凹槽强化传热主要原因为:1)增加近壁区流体扰动,促进酒窝或凹槽内部流体与主流之间的传热;2)酒窝与凹槽均可扩展传热面积,进而提高总传热量。与低肋通道相比,酒窝与圆柱面凹槽仅对其附近流体的流动产生影响,而对主流流体的流动影响较小,进而阻力增加较少。提出传热量单元性能参数PEC_A作为评价指标,酒窝通道综合性能参数略高于圆柱面凹槽通道,而远高于低肋通道。     

含相变微粒流体热对流启动的Galerkin解

采用Bubnov-Galerkin方法对有恒壁温条件下,两平板间夹有含相变颗粒流体的自然对流热启动瑞利数进行了近似解析求解,求出了临界瑞利数Racr和波频数kcr随相变物质浓度,以及在相变温度范围内随加热表面温度的解析关系表达式.从而,为实现该类功能性潜热流体的自然对流传热强化,及其优化控制蓄热过程有理论指导意义.     

ZrO2纳米流体的对流换热系数测定及机理浅析

建立了测量圆管内纳米流体流动与传热性能的实验系统,测量了不同粒子浓度的ZrO2/水纳米流体在雷诺数为3 000～18 000范围内的管内对流换热系数以及不同位置处纳米流体对流换热系数的变化情况.实验结果显示,在液体中添加纳米粒子显著增大了液体的管内对流换热系数,例如,在相同雷诺数时,与纯水相比,如果纳米粒子的质量浓度从1.6%增大到4.1%,则纳米流体的对流换热系数增加的比例从1.09增大到1.2.此外,从颗粒的浓度、粒径两方面分析纳米流体强化传热的机理.     

基于降低污垢热阻的复合强化传热研究

复合强化传热的换热系数的增加通常要比单独使用其中的任何一种技术高,但过分增长的污垢热阻会轻而易举地将对流换热系数提高的效果加以抵消。将振动看作不仅仅意味着噪声与元件损坏的能量表达方式,就有可能利用流体诱导的传热元件振动扰动水流,提高对流换热系数;同时,用振动变形清除传热表面积垢,降低污垢热阻,从而形成一种复合强化传热的新方法。     

基于场协同原理的聚合物塑化过程数值分析

本文采用数值计算方法分析了挤出机不同螺杆塑化系统的流动与传热特性,并且提出了一种新型螺杆元件——扭转元件。结果表明,相对于普通螺纹元件,配置有扭转元件的螺杆具有更好的温度均匀性和传热性能。扭转元件中非牛顿黏弹性流体的强化传热的机理可以用场协同理论进行解释,即扭转元件的温度梯度场与速度场的协同性更好,努塞尔数更高,对流换热性能更好。     

弹性管束汽－水换热器强化传热试验研究

本文设计了一种新的传热元件－弹性管束,它对管内外流体流动具有良好的振动响应特性。利用传热表面振动提高管外对流换热系数的同时,利用振动变形减少积垢,降低污垢热阻,实现了复合强化传热。在汽水换热条件下,对流作诱导振动强化传热规律进行了试验研究,得到了管外对流换热的准则方程式。     

对流换热的物理机制分析及其应用

一、前言 在众多的传热教科书和文献中,通常认为传热有三种不同的基本方式:导热、对流和热辐射。所谓对流(或对流换热)是指“运动的流体质点以内能的形式把热量带走”,或者“流体中温度不同的各部分相互混合的宏观运动引起的热量传递现象”。由于流体中温度不均匀必然存在导热过程,因此,导热总是伴随于对流换热过程之中,所以可把对     

沟槽深宽比对泰勒涡流影响的研究

本文采用数值模拟研究了同心圆柱环隙内的泰勒涡流,利用PIV实验结果验证了模拟结果的可靠性。为掌握沟槽尺寸对环隙内流场及其传热过程的影响规律,本文研究了四种不同深宽比模型内的流场及温度场分布,通过对比不同模型的计算结果,获得如下结论:环隙间存在恒定温度梯度时,随着深宽比增加,泰勒涡轴向尺寸逐渐增加;深宽比影响了环隙内流体的径向速度分布,当深宽比为0.75时流体的径向速度最大;深宽比为0.75时内圆柱壁面热流密度最大,当深宽比大于0.75并继续增加时,环隙内流体的传热性能并没有得到明显加强。综上所述,本文所研究的4种不同深宽比的模型中,深宽比为0.75的模型具有最优的传热效果,沟槽深度在一定范围内能够强化流体与壁面之间的对流换热。     

管内对流换热的场协同分析及换热强化

导出管内湍流换热Nu与局域时均参数的关系式,将对流换热的场协同理论扩展至湍流换热。分析了管内对流换热的特点,并根据场协同理论提出强化湍流换热的方法,发展了一种新型强化换热管一交叉椭圆管,既适合于层流换热强化也适合于湍流换热强化,其强化传热效果显著而流阻较小。     

管外流诱导管束振动强化传热试验研究

本文提出了利用管外流体诱导振动实现强化传热的新方法.采用了一种新的传热元件-弹性管束,它对管外流体流动具有良好的振动响应特性.提出了正置三角柱脉动流发生装置,该装置可诱导起弹性管束一定频率的周期性振动,并对强化传热具有显著的促进作用.在恒热流条件下,对管外水流诱导振动强化对流换热规律进行了试验研究,得到了管外对流换热的准则方程式.     

层流对流换热中的势容耗散极值与最小熵产

在一定的约束条件下,存在一个最优的速度场,它能够使得温度场和速度场的协同程度最好,从而使得对流换热的整体传热性能达到最优。目前对传热效果的评价存在熵产最小化和势容耗散取得极值两种不同的准测。分别根据这两种优化准则,用变分方法推导了在粘性耗散一定的条件下,稳态无内热源的层流对流换热的场协同方程,并对方腔内对流换热问题进行了优化。数值计算结果表明,势容耗散取得极值时的换热效果优于熵产最小的结果,因此势容耗散极值原理更适合做为对流换热的优化准则。     

场协同理论在脉管制冷机研究中的推广

本文采用理论分析和数值计算的方法,确认由过增元教授等提出的强化换热的场协同理论同样可以应用到能量转换过程。文中用场协同理论揭示了脉管制冷机发展过程中几次重大改进的实质,并以此理论指导改进脉管制冷机的结构参数,发现了脉管的最佳长径比。     

分析金属熔滴快速凝固过程的双倒易边界元方法

本文发展了非线性边界条件相变传热过程的轴对称双倒易边界元方法,数值模拟了金属熔滴在快速冷却条件下的快速凝固过程。分别研究了在微重力落管和落塔中及喷射成形过程中金属熔滴的快速凝固过程,得到了过冷度,再辉时间,温度变化及相变界面随时间的变化等数值结果。     

二维平板通道中流动与传热的格子-Boltzmann模拟

格子-Boltzmann数值模拟方法(LBM),在最近十几年来得到迅速发展。本文发展了LBM的流动与传热模型,并对二维平板通道中的流动与传热进行了模拟,采用密度分布函数得到速度场,用单独的内能分布函数得到温度场,并与传统FVM方法所得到的多个特征量结果进行了比较,模拟结果与FVM解均吻合很好。鉴于LBM边界条件处理简单和易于实施等特点,该方法可望成为求解流动与传热的一种有效数值模拟手段。     

Comparisons of Heat Transfer Enhancement of an Internal Blade Tip with Metal or Insulating Pins

Cooling methods are needed for turbine blade tips to ensure a long durability and safe operation. A common way to cool a tip is to use serpentine passages with 180-deg turn under the blade tip-cap taking advantage of the three-dimensional turning effect and impingement like flow. Improved internal convective cooling is therefore required to increase the blade tip lifetime. In the present study, augmented heat transfer of an internal blade tip with pin-fin arrays has been investigated numerically using a conjugate heat transfer method. The computational domain includes the fluid region and the solid pins as well as the tip regions. Turbulent convective heat transfer between the fluid and pins, and heat conduction within pins and tip are simultaneously computed. The main objective of the present study is to observe the effect of the pin material on heat transfer enhancement of the pin-finned tips. It is found that due to the combination of turning, impingement and pin-fin crossflow, the heat transfer coefficient of a pin-finned tip is a factor of 2.9 higher than that of a smooth tip at the cost of an increased pressure drop by less than 10%. The usage of metal pins can reduce the tip temperature effectively and thereby remove the heat load from the tip. Also, it is found that the tip heat transfer is enhanced even by using insulating pins having low thermal conductivity at low Reynolds numbers. The comparisons of overall performances are also included.     

基于Lattice-Boltzmann方法的纳米流体流动与传热分析

纳米流体是由流体与纳米粒子组成的悬浮体。由于悬浮的纳米粒子会受到各种内力或外力的影响,这使得其运动规律和换热规律及其复杂。本文运用Lattice-Boltzmann(LB)方法建立纳米流体的传热模型,并对纳米流体和水的流动换热参数进行比较分析。     

Thermographic investigation of some surface flow patterns

Infrared (IR) thermography, due to its two-dimensionality and non-contact character, can be usefully employed in a vast variety of heat transfer industrial applications as well as research fields. The present work deals with measurements of temperature and/or convective heat transfer coefficients in several types of fluid flow configurations studied by means of the IR scanning radiometer applied to the heated-thin-foil technique. In more details, it is analysed the capability of the infrared system to study particular phenomena such as: the heat transfer, including the spiral vortical structures developing at transition, over a disk rotating in still air; the thermal exchange enhancement induced by a jet centrally impinging on the rotating disk; the complex heat transfer pattern associated with a jet in cross-flow.     

场协同理论在交变流动缝隙式回热器中的数值验证

本文对缝隙式回热器在非稳态交交流动下的流动和换热问题做了二维的数值模拟,并重点对其在交交流动下的场协同问题做了计算与分析。数值计算表明,场协同原理作为指导强化对流换热的原则,同样可以指导交交流动下的换热强化。     

A molecular dynamics simulation on the convective heat transfer in nanochannels

The understanding of the flow and heat transfer processes for fluid through micro- and nanochannels becomes imperative due to its wide application in micro- and nano-fluidic devices. In this paper, the method to simulate the convective heat transfer process in molecular dynamics is improved based on a previous study. With this method, we simulate a warm dense fluid flowing through a cold parallel-plate nanochannel with constant wall temperature. The characteristics of the velocity and temperature fields are analysed. The temperature difference between the bulk average temperature of fluid and the wall temperature decreases in an exponential form along the flow direction. The Nusselt number for the laminar flow in parallel-plate nanochannel is smaller than its corresponding value at macroscale. It could be attributed to the temperature jump at the fluid–wall interface, which decreases the temperature gradient near the wall. The results also reveal that the heat transfer coefficient is related to the surface wettabilities, which differs from that in the macroscopic condition.