H型鳍片管传热过程的研究

采用MATLAB程序对于描述H型鳍片中传热过程的偏微分方程求解,对于影响传热过程的各个结构因素和热力参数进行了分析,得出优化鳍片管性能的途径.     

Heat Transfer and Fluid Flow Analysis for Plate-Fin and Oval Tube Heat Exchangers With Vortex Generators

This article investigates the effectiveness of embedded vortex generators in enhancing the heat transfer performance of a plate-fin heat exchanger with a four-row staggered oval tube bundle. Two different types of vortex generator are considered, namely annular and inclined block. Numerical simulations are performed to analyze the effects of the three-dimensional turbulence induced by the vortex generators on the heat transfer and fluid flow characteristics of the heat exchanger. The results indicate that compared to a plate-fin heat exchanger with circular tubes, the use of oval tube fins and vortex generators increases the heat transfer rate by 3 to 16% and reduces the pressure drop by 17 to 35% for inlet velocities in the range of 1 to 8 m/s. Furthermore, the vortex generators make possible an average area reduction ratio of 14 to 18%. Overall, the results show that the inclined block shape vortex generators yield the greatest improvement in the heat transfer performance at medium to high inlet velocities.     

H型鳍片管的传热与流动特性试验研究

H型鳍片管是一种新型高效强化传热管。对一定结构的H型鳍片管与螺旋翅片管换热器进行了比较性半工业试验研究,得到了H型鳍片管换热与阻力准则关系式,并与相同结构参数的螺旋翅片管进行比较。根据实验结果得出:H型鳍片管换热与阻力特性均优于同结构参数的螺旋翅片管。     

矩形通道内八边形翼纵向涡发生器强化传热的试验研究

在矩形翼的基础上,提出一种新型的八边形翼纵向涡发生器.在矩形通道内,通过试验比较了矩形翼和八边形翼纵向涡发生器的流动与传热特性.分别在Re相同和阻力损失相同的条件下,分析了不同纵向涡发生器的强化传热效果.结果表明:与矩形翼相比,八边形翼纵向涡发生器的强化传热效果更好,而阻力系数没有明显增加;在阻力损失相同的条件下,矩形翼和八边形翼纵向涡发生器的传热增强率小于在Re相同时的传热增强率.     

非对称翅片管换热器传热和阻力特性的数值分析

基于COMSOL软件建立了一种非对称翅片管换热器的三维模型,对空气侧的流动和传热特性进行了数值研究,与平直翅片管换热器进行对比,并进一步分析了不同雷诺数下交错角β对非对称翅片管换热器性能的影响.结果表明:在Re为3 239~9 700内,与平直翅片管换热器相比,非对称翅片管换热器的传热因子增大,平均增大量为13.95%,阻力因子减小,且随着Re增大其减小效果更加明显,平均减小量为4.80%;以MJF作为评价标准,且其他结构参数不变时,β=30°时MJF最大,换热器的综合性能最好.     

纵向翅片管传热计算研究与工业应用

主要研究了纵向翅片管的传热计算流程及工程应用.根据纵向翅片管的基本传热机理,系统深入地总结了纵向翅片管在不同传热条件下换热系数的计算方法,提出了纵向翅片管换热器的设计流程;通过具体工程实例,纵向翅片管换热器的设计理论得到验证,同时计算结果表明,与传统的光管相比,纵向翅片管传热系数高,设备传热性能好,是一种行之有效的节能...     

H形翅片管束传热和阻力特性的试验与数值模拟

根据大型电站锅炉省煤器的运行工况,对单H形和双H形翅片管束气侧的传热与阻力特性进行了模化试验研究,并利用Fluent软件对H形翅片管束的流场和温度场进行了数值模拟,得到单H形和双H形翅片管束的传热与阻力特性变化规律.结果表明:H形翅片管束的传热和阻力特性与气体的Re有关,随着气体Re的增大,气侧Nu不断增大,传热性能提高,而Eu则逐渐减小,并趋于定值;在相同Re下,单H形翅片管束气侧Nu大于双H形翅片管束气侧Nu,而气侧Eu则小于双H形翅片管束气侧Eu;数值计算结果与试验结果误差较小,采用数值计算方法能比较准确地分析H形翅片管束的流动与传热特性.     

纵向涡强化换热的优化设计及机理分析

对带纵向涡发生器的椭圆管翅片换热器空气侧表面的换热和流动特性进行了三维数值模拟.深入分析了纵向涡对流场和温度场的影响,并通过场协同原理揭示了纵向涡强化换热的根本机理,即减小了速度和温度梯度之间的夹角,改善了速度场和温度场的协同性.在此基础上,对纵向涡发生器的布置位置(上游布置和下游布置)和纵向涡发生器的攻角α(15°,30°,45°,60°)进行了优化设计.结果表明:当纵向涡发生器布置于换热管下游时,具有更好的强化换热能力;在纵向涡发生器采用下游布置的前提下,当纵向涡发生器的攻角α=30°时,具有最佳的强化换热能力.     

纵向涡发生器传热强化的研究进展

通过对纵向涡发生器研究进展的回顾,可以看出以往的研究主要集中在纵向涡发生器对气体介质的传热强化上,而对液体介质的传热强化作用的研究较少.运用场协同原理对纵向涡的产生和传热强化作用机理作出了初步解释.下一步的研究工作首先应对纵向涡发生器的几何尺寸进一步优化,其次针对矩形窄通道内液体的强化传热进行深入研究,最后以水为介质时,针对纵向涡发生器对窄间隙矩形通道内临界热流密度的影响机理进行研究.     

带纵肋环形烟管流动与传热试验研究

提出了一种新型的油田加热炉强化对流换热的烟管结构－－带纵内肋的环形烟管,并对其进行了流动及对流换热的试验研究,给出了换热的准则方程式。     

波纹内翅片管内空气强化传热特性的研究

研究了一种波纹内翅片管的换热特性，得出了所测参数范围内沿程温度及换热系数分布特点，并比较了相同管径的内翅片波纹管和光管的综合换热效果，结果表明：高Re数时管子与翅片间的接触热阻对传热性能有较大影响；波纹内翅片管的综合换热效果强于光管，而且在低流速下换热强化效果更加明显。     

Comparison of Heat Transfer and Pressure Drop for the Helically Baffled Heat Exchanger Combined with Three-Dimensional and Two-Dimensional Finned Tubes

Experiments were performed to compare the shell-side heat transfer coefficient and pressure drop of a helically baffled heat exchanger with petal-shaped finned tubes to those of low-finned tubes for oil cooling using water as a coolant. The experimental results showed that for the heat exchanger with petal-shaped finned tubes, the shell-side heat transfer coefficients were augmented by 28–48%, yet the shell-side pressure drops were reduced by 35–75% at the same volumetric flow rates of oil. The possible mechanisms responsible for this heat transfer enhancement were analyzed for helically baffled heat exchanger combined with petal-shaped finned tubes.     

Convective Heat Transfer and Pressure Drop over Elliptical and Flattened Tube

A numerical study on the effect of the effect of elliptical and flattened tube bundle geometry on the convective heat transfer and pressure drop is presented in this article. The analysis has been carried out to evaluate the performance of these bundle geometries in the design of a compact and effective single phase shell and tube heat exchanger. The temperature, velocity, and pressure drop profiles are obtained from solving the mass, momentum, and energy conservation equations. The comparison is made for inline and staggered bundle with different pitch to diameter ratio and inlet velocity for elliptical and flattened tubes. The pitch to diameter ratio is varied from 1.25 to 2.5 for Reynolds number ranging from 200 to 2000 which is in the laminar flow region. The heat transfer coefficient over the staggered and inline tube bundle decrease with an increase in pitch. The same kind of variation is also observed for the pressure drop in the case of both elliptical and flattened tube bundle. The study shows that the transverse pitch with respect to cross flow affects more than the longitudinal pitch.     

Augmentation of Heat Transfer by Creation of Streamwise Longitudinal Vortices Using Vortex Generators

This paper summarizes the current state of the art related to improvement of the heat exchanger surfaces using streamwise longitudinal vortices. Primarily, the improvements related to fin-tube cross-flow heat exchangers and the plate-fin heat exchangers have been addressed. Protrusions in certain forms, such as delta wings or winglet pairs, act as vortex generators, which can enhance the rate of heat transfer from the heat-exchanger surfaces that may be flat or louvered. The strategically placed vortex generators create longitudinal vortices, which disrupt the growth of the thermal boundary layer, promote mixing between fluid layers, and hence lead to augmentation in heat transfer. The flow fields are dominated by swirling motion associated with modest pressure penalty. Heat transfer is augmented substantially for all the proposed configurations of the longitudinal vortex generators, such as delta wings, rectangular winglet pairs, and delta winglet pairs, with varying degree of pressure penalty. Both computational and experimental investigations on flow and heat transfer in the heat exchanger passages with built-in vortex generators are revisited and summarized.     

Comparisons of Local Experimental Results with Numerical Results of Heat Transfer Enhancement of a Flat Tube Bank Fin with Vortex Generators

The common way to obtain the fin pattern of a tube bank fin heat exchanger with good heat transfer performance is through experiments. Such experiments are complex, expensive, and very difficult to carry out. Recently, numerical analysis has become a powerful method for selecting the fin pattern of tube bank fin heat exchangers. In this article, we focus on testing the reliability of the numerical method by comparing local numerical results with local experimental results obtained through naphthalene sublimation. The target of numerical analyses carried out here is a flat tube bank fin heat exchanger mounted with vortex generators. The results show that using body-fitted coordinates, with proper treatment of vortex generators penetrating the fluid flow, leads to reliable local and average results.     

H型鳍片管传热特性的数值模拟及验证

基于Fluent软件,利用Realizable κ-ε湍流模型对H型鳍片管的传热性能进行了数值模拟,分析了管排数与纵向间距对H型鳍片管传热系数的影响.在计算的基础上得出了H型鳍片管传热系数的计算公式,并对该公式进行了验证.结果表明:烟气流速越高、纵向管排数越少、纵向间距越大,传热系数越大;计算值最大误差为8.3%,最小误差为5.6%;该公式计算结果与验证算例、文献试验值及已有公式的结果较吻合.     

扭曲椭圆管换热器壳程强化传热的数值研究

基于扭曲椭圆管的换热器是一种新型的新风系统换热器,针对扭曲椭圆管及其应用特点,设计了两种不同结构参数的新风系统换热器。应用FLUENT软件,在夏季工况下对两种不同结构参数的新风系统换热器壳程进行模拟分析,并通过与实验数据的对比,验证计算模型的可靠性。结果显示在相同体积流量下,随着壳程开孔面积的增大,对流换热系数h不断减小,压降Δp不断减小,综合性能系数h/Δp1/3变化不明显;随着螺距的减小,对流换热系数h不断增大,压降Δp不断增大,综合性能系数h/Δp1/3也不断增大;流场分析显示,扭曲椭圆管换热器壳程流道内,呈现出明显沿着扭曲椭圆管壁面的螺旋流,使得空气在流道内充分扰动,增强换热效果。     

一种用于船舶烟气冷却的喷雾螺旋管冷却器的传热特性研究

船舶使用的主动降噪设备需要连接到排烟支管,但高温烟气会缩短设备的使用寿命。为了降低烟气温度,建立了冷却器喷雾冷却的数值模型对支管冷却器的运行工况进行优化,通过数值模拟分析喷射压差与喷雾半角对冷态以及热态性能的影响。结果表明：最佳喷雾半角为60°,喷射压差为1.5 MPa时,冷却器性能最佳;采用液滴蒸发效率与逃逸质量分析冷却器内液滴的流动特性,根据模拟结果进行二次回归式拟合,喷雾压差和喷射半角与蒸发效率相关系数分别为0.19和0.56,其相对于逃逸质量的相关系数为0.25和0.72,喷嘴工作参数应选取较高的喷雾半角和较低的喷射压差。     

H型鳍片管传热的分析和计算

采用有限元数值求解鳍片传热和传统相似理论计算方法相结合,得到符合经验数值的合理结果;对于工程实践具有参考价值。