【作者】 唐新宜；

【导师】 朱冬生；

【作者基本信息】 华南理工大学 ， 化学工程， 2012， 博士

【摘要】 换热装置是工业传热过程中必不可少的设备，应用在动力、化工、冶金、食品、轻工等一切工业部门。随着技术的进步，以及节约资源和能源的紧迫性，一些新型的换热设备被开发并应用在污水处理，余热利用等领域。因此开发新型换热设备，提高换热器的热量传递性能和能源的利用率意义重大。本文基于这样的背景下，对矩形通道内的流动与强化传热进行了实验和数值研究，主要通过流场内的湍动能，速度，流线，压力等参数的变化对通道内的流动微细结构进行分析，同时分析了通道内的温度场分布和局部努塞尔数的变化。除此之外，对通道的整体传热和阻力特性进行了分析，运用场协同理论和综合性能评价标准，总结了矩形通道内强化传热的机理，对比了不同表面结构在不同结构参数下的综合性能因子变化，总结了流场中出现的各种涡流对强化传热的影响。本文对传统的强化传热表面结构进行了改良，从而达到增大综合性能因子，提高换热效率的目的。本文从以下几方面进行了实验和数值模拟。横向肋通道广泛应用于高效换热器、核反应器和传质设备。本文提出通道内加装导流片把流体引导向肋间流动，增加了壁面附近流体的扰动，从而提高通道内的换热效果。加装导流片后通道的整体努塞尔数提高了14.8%~22.7%。虽然这种强化传热的方式阻力较大，但是导流片加工安装方便，以较低的成本对原有设备进行改造。此外，研究四种形状不同的导流片对传热和阻力影响，发现斜板导流片的传热效果最好。考察了导流片在上下游位置对传热的影响，发现导流片的位置在两肋片中部的传热效果最好。提出了一种间断斜壁肋片与凹槽的交错排列方式，并与平行肋排列的矩形通道的传热与阻力特性进行实验和数值研究。研究表明，交错肋槽结构的综合性能因子比平行肋结构提高了10%~13.6%。另外研究了交错肋槽结构的倾斜角及肋间距等几何参数对传热的影响。结果表明，突肋的倾斜角α为45°时通道的综合性能因子最好。梯形静态混合器可在通道内产生纵向涡，纵向涡能以较少的压降强化通道内的换热。在此基础上，提出了下端开口的梯形扰流片，并对流动方式及开口位置进行了实验研究及数值模拟。结果表明，对于完整扰流片逆流的努塞尔数比顺流的大，综合性能因子对比结果表明，低雷诺数下逆流的比顺流的大，高雷诺数下顺流的比逆流的好。而对于不同开口位置而言，完全开口的扰流片在顺流的方式及高雷诺数下，综合性能最好；外侧开口的扰流片在逆流的方式及低雷诺数下，综合性能最好。因此，开口的扰流片能提高矩形通道内传热效率。球凸和球凹通道是一种比较新型的表面强化传热结构并引起人们的兴趣。本文提出了一种内嵌圆球或椭球球凹或者球突的结构并进行了数值模拟的研究。结果表明，与普通球突通道相比，综合性能因子提高了近10%。通道内的涡流碰撞，流动分离以及马蹄涡对强化传热有着重要的贡献。对于内嵌球突的球凹结构而言，其综合性能因子比普通球凹提高了13.8%~15.4%。从流场分析结果发现，与普通球凹通道相比，内嵌球突的球凹结构能有效地降低通道内的阻力。这是由于凹槽内的回流涡受到球突的分离和抑制作用，从而使球凹的阻力减少。可见，突肋结构与凹槽结构在本文提出的结合方式下，能够提高矩形通道的传热效率。更多还原

【Abstract】 Heat exchanger is a vital device used in the industrial heat transfer process. Itsapplication includes power engineering, chemical engineering, food engineering etc. With thetechnological development and the urgency of resource and energy saving, some novel heatexchangers were developed and used in the sewage treatment. Thus, it is greatly significantthat new heat exchangers are developed to increase the heat transfer rate and energyutilization. Under these circumstances, this paper presents some novel surface structures toenhance heat transfer in rectangular channel by experimental and numerical methods with themicroscopic analysis of turbulent kinetic energy, velocity profiles, streamlines and pressure.Meanwhile, temperature and local Nusselt number distribution are also analyzed bysimulation. Additionally, overall Nusselt number and friction factor are compared andanalyzed by field synergy principle and overall thermal enhancement factor. The mechanismof heat transfer enhancement in rectangular channel with different geometrical protrusionsand cavity surfaces and the effect of vertical flow on heat transfer enhancement weresummarized. The aim of this paper is to modify the traditional surface structures with thepurpose of overall performance maximization.Transversal ribs are widely used in heat exchanger, reactor and mass transfer equipment.This paper presents a deflector which transports the fluid in the mainstream to the near-wallregion between two ribs, inducing the flow disturbance in this region and increasing the heattransfer rate. Compared with the ribbed channel, the overall Nusselt number is enhanced by14.8%~22.7%. In spite of higher flow resistance, the old devices are modified with low costand installation convenience. Moreover, four kinds of deflector and the locations of deflectorare investigated, finding that inclined flat deflector indicates superior heat transfer rate toother cases.Discrete inclined ribs and grooves with crossed arrangement and parallel arrangementare presented to study the fluid flow and heat transfer by experiment and simulations,showing that overall performance of discrete inclined ribs and groove with crossedarrangement is about10%~13.6%higher than that of parallel arrangement. The effects of inclined angle and rib pitch on the heat transfer are also investigated, finding that the best ofinclined angle is45°.A pair of longitudinal vortices is formed by trapezoidal static mixer, enhancing the heattransfer with less pressure loss. A trapezoidal vortex generator with clearance is presented toincrease overall thermal enhancement factor. Flow mode and the location of clearance areconsidered as parameters which influence heat transfer and flow resistance. The results showthat the Nusselt number with case of full size tab and flow forward is higher than thetraditional trapezoidal vortex generator. At lower Reynolds number, the case of backwardflow is better than that of forward flow. At higher Reynolds number, the case is reverse.Therefore, the tab with clearance can increase heat transfer efficiency.Spheric protrusion or dimple is a novel surface structure of heat transfer enhancementwhich attracts much interest all over the world. This paper presents a hemispheric protrusionwith imprinted dimple or dimple with imprinted protrusion and the studies on heat transferand flow characteristics are conducted by numerical method. The results show that the overallthermal enhancement factor of novel structure can be enhanced by10%compared to generalprotrusion due to the unique flow characteristic such as flow separation, vortex impingementand horseshoe vortices. The analysis of flow pattern shows that drag reduction of dimpledchannel with imprinted protrusion is attributed to the separation and suppression ofre-circulating vortices in the cavity, leading to the reduction of pressure drop betweenupstream region and downstream region. In conclusion, the combination of protrusion andcavity in the present way can increase the heat transfer efficiency.更多还原