Numerical investigation and analysis of heat transfer enhancement in channel by longitudinal vortex based on field synergy principle

3-D numerical simulations were presented for laminar flow and heat transfer characteristics in a rectangular channel with vortex generators. The effects of Reynolds number (from 800 to 3 000), the attack angle of vortex generator (from 15° to 90°) and the shape of vortex generator were examined. The numerical results were analyzed based on the field synergy principle. It is found that the inherent mechanism of the heat transfer enhancement by longitudinal vortex can be explained by the field synergy principle, that is, the second flow generated by vortex generators results in the reduction of the intersection angle between the velocity and fluid temperature gradient. The longitudinal vortex improves the field synergy of the large downstream region of longitudinal vortex generator (LVG) and the region near (LVG); however, transverse vortex only improves the synergy of the region near vortex generator. Thus, longitudinal vortex can enhance the integral heat transfer of the flow field, while transverse vortex can only enhance the local heat transfer. The synergy angle decreases with the increase of Reynolds number for the channel with LVG to differ from the result obtained from the plain channel, and the triangle winglet performs better than the rectanglar one under the same surface area condition. __________ Translated from Journal of Xi’an Jiaotong University, 2006, 40(9): 996–1000 [译自: 西安交通大学学报]     

Numerical study of fluid flow and heat transfer in a flat-plate channel with longitudinal vortex generators by applying field synergy principle analysis

Three dimensional numerical simulations are performed on laminar heat transfer and fluid flow characteristics of a flat-plate channel with longitudinal vortex generators (LVGs). The effects of two different shaped LVGs, rectangular winglet pair (RWP) and delta winglet pair (DWP) with two different configurations, common-flow-down (CFD) and common-flow-up (CFU), are studied. The numerical results indicate that the application of LVGs effectively enhances heat transfer of the channel. According to the performance evaluation parameter, (Nu/Nu₀)/(f/f₀), the channel with DWP has better overall performance than RWP; the CFD and CFU configurations of DWP have almost the same overall performance; the CFD configuration has a better overall performance than the CFU configuration for RWP. The basic mechanism of heat transfer enhancement by LVGs can be well described by the field synergy principle.     

纵向涡强化竖直平板自然对流换热的实验研究

对纵向涡强化竖直平板自然对流换热进行了实验研究。结果表明，在一定的Rayleigh数范围内，直角三角翼纵向涡发生器的攻角、翼高、翼宽等几何参数是影响强化换热的主要因素。存在最佳攻角；宽高比一定时，翼高和翼宽的变化会影响换热的效果。发现在直角三角翼阵列中前排直角三角翼产生的纵向涡可以强化后排直角三角翼纵向涡的换热。将直角三角翼与矩形低肋换热表面的性能作了对比性实验，在其他条件相同的情况下，直角三角翼强化换热的效果优于矩形低肋。     

Experimental study on heat transfer enhancement in the vertical nature convection by using delta‐winglet longitudinal vortex generators

This paper focuses on the study of heat transfer enhancement in natural vertical convection by using delta‐winglet longitudinal vortex generators. In the experimental range of Rayleigh numbers, the effect of attack angle, height, and width of the winglet of longitudinal vortex generator (LVG) on heat transfer performance was experimentally investigated. The results showed that there was an optimal attack angle and that the height and width can affect the heat transfer. In terms of array performance, it was shown that initial arrays could enhance the performance of later arrays. Moreover, the effects of LVG and low rectangular fins were compared. The results showed that the effect of LVGs was greater than that of low rectangular fins. © 2006 Wiley Periodicals, Inc. Heat Trans Asian Res, 35(6): 402–409, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20126     

通道内设置涡发生器时的强化传热研究现状与展望

随着强化传热技术的研究发展，各种形式的涡发生器的强化传热效果日益受到国内外的重视。文章比较全面地介绍了近年来国内外关于通道内布置各类涡发生器时的强化传热研究状况，并提出了有待进一步开展的研究内容。     

多种纵向涡发生器配置方案流动换热的数值模拟

为了深入挖掘三角翼纵向涡发生器在两个相对壁面布置的强化换热潜力,采用数值模拟方法,在雷诺数3 000～18 000的范围内研究了5种纵向涡发生器配置的流动换热情况,配置方式包括单面布置的共同上、下流配置,双面布置的共同上、下流配置,以及混合配置。结果表明：纵向涡可以很好地提高场协同效果,换热强度不完全取决于通道中的二次流强度,还取决于通道中的场协同性;在所有配置中,混合配置具有最高的二次流强度、最佳的场协同效果以及换热性能,可以将光滑通道的Nu提高28.3%～35.3%;另外4种配置可分别将光滑通道的Nu提高21.4%～32.0%,20.0%～29.2%,26.3%～34.3%和23.7%～28.0%;建议选用Re<6 000范围内的混合配置,此时其具有1.03～1.10的综合换热因子以及1.32～1.35的Nu/Nu₀。     

Numerical investigation and analysis of heat transfer enhancement in channel by longitudinal vortex based on field synergy principle

3-D numerical simulations were presented for laminar flow and heat transfer characteristics in a rectangular channel with vortex generators. The effects of Reynolds number (from 800 to 3 000), the attack angle of vortex generator (from 15° to 90°) and the shape of vortex generator were examined. The numerical results were analyzed based on the field synergy principle. It is found that the inherent mechanism of the heat transfer enhancement by longitudinal vortex can be explained by the field synergy principle, that is, the second flow generated by vortex generators results in the reduction of the intersection angle between the velocity and fluid temperature gradient. The longitudinal vortex improves the field synergy of the large downstream region of longitudinal vortex generator (LVG) and the region near (LVG); however, transverse vortex only improves the synergy of the region near vortex generator. Thus, longitudinal vortex can enhance the integral heat transfer of the flow field, while transverse vortex can only enhance the local heat transfer. The synergy angle decreases with the increase of Reynolds number for the channel with LVG to differ from the result obtained from the plain channel, and the triangle winglet performs better than the rectanglar one under the same surface area condition.     

Experimental study on heat transfer enhancement on natural convection in a vertical plate by using longitudinal vortex generators arranged in rows

Longitudinal vortices are capable of producing beneficial effects in heat transfer enhancement. Experiments in natural convection heat transfer enhancement were done on a vertical flat heating plate using delta‐winglet longitudinal vortex generators (LVGs) arranged in rows. In an experimental range of Rayleigh number, the height and width of the winglet of the longitudinal vortex generator (LVG), the array form of the longitudinal vortex generators on the heat transfer performance were experimentally investigated, and the best height of the winglet of the longitudinal vortex generator was obtained. The results showed the change of the array form of the longitudinal vortex generators could affect the heat transfer effect. Finally by arranging some longitudinal vortex generator arrays with the appropriate interval, the whole heat transfer effect of the interval could reach a prime value. © 2006 Wiley Periodicals, Inc. Heat Trans Asian Res, 35(5): 351–358, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20119     

多排纵向涡发生器强化竖直平板自然对流换热的实验研究

对多排纵向涡发生器对竖直平板自然对流的强化效果进行了研究。结果表明，在一定Rayleigh数范围内，直角三角翼纵向涡发生器的翼高、翼宽以及多排布置的阵列方式是影响强化换热的主要因素。在高宽比一定的情况下，存在最佳翼高。发现多排布置时LVG阵列方式的不同会影响换热效果；且要使得整个板的强化换热效果达到最佳，应选择沿竖直发热板长度方向间隔的布置多排LVG，并适当拉大间隔距离。     

纵向涡发生器强化传热管的实验研究

介绍了一种高效强化传热管,沿传热管内壁轴向均匀排布三列成对的纵向涡发生器,在常壁温条件下进行加热空气在管内流动的冷却实验,研究强化传热管的传热和阻力特性。结果表明,在过渡流区管内置纵向涡发生器的强化传热大大增强,Nu增大为光管的2.02.3倍,阻力损失也相应有所增加,提出一种比较优化的发生器的形状设计,探讨了传热和阻力随设置间距变化的规律。     

复合翅片传热与流动特性的数值模拟

结合纵向涡发生器和开缝的优点,提出一种复合强化传热翅片,并对该种翅片的传热与流动特性进行数值计算.由于翅片结构比较复杂,在三角形小翼及X形开缝区域应用阶梯逼近进行网格划分.复合翅片的强化作用在于两方面:一是在三角形小翼和X形开缝后的流场均产生了纵向涡,对流体产生较强的扰动;二是带状开缝的间断表面抑制了边界层的增长,平均...     

热辐射能(波)选择性强化吸收的场协同机理

从场协同原理的角度出发，分析了材料对热辐射能(波)选择性吸收过程，提出了材料对入射辐射能(波)的作用实质是材料内阻尼振子组成的力场和入射辐射场之间的相互作用；调整这两个场之间的协同关系，可以改变和改善材料的选择性热辐射性能。基于此得到了强化材料对入射热辐射能(波)选择性吸收的机理。研究表明：减弱入射辐射场与材料内阻尼振子组成的力场之间的协同关系，可以提高材料的吸收率和发射率；相反，强化这两个场之间的协同关系，可使材料表现出较高的反射率。     

Experimental verification of the field synergy principle

In this paper, the basic idea of the field synergy principle (FSP) is briefly reviewed and is validated experimentally by incompressible flow through a square duct with an imposed temperature difference between vertical walls and perfectly insulated on the horizontal walls. This creates a situation where the steamwise flow velocity is normal to the cross section temperature gradient. The experimental results show the independency of crosswise heat transfer rate on the steamwise flow velocity. Detailed discussion is provided to account for some minor deviation from the expected results of FSP.     

CFD study on local fluid-to-wall heat transfer in packed beds and field synergy analysis

To reach the target of smaller pressure drop and better heat transfer performance, packed beds with small tube-to-particle diameter ratio (D/d _p<10) have now been considered in many areas. Fluid-to-wall heat transfer coefficient is an important factor determining the performance of this type of beds. In this work, local fluid- to-wall heat transfer characteristic in packed beds was studied by Computational Fluid Dynamics (CFD) at different Reynolds number for D/d _p=1.5, 3.0 and 5.6. The results show that the fluid-to-wall heat transfer coefficient is oscillating along the bed with small tube-to-particle diameter ratio. Moreover, this phenomenon was explained by field synergy principle in detail. Two arrangement structures of particles in packed beds were recommended based on the synergy characteristic between flow and temperature fields. This study provides a new local understanding of fluid-to-wall heat transfer in packed beds with small tube-to-particle diameter ratio.     

Heat transfer enhancement by using a rectangular wing vortex generator on the triangular shaped fins of a plate‐fin heat exchanger

The present numerical analysis pertains to the heat transfer enhancement in a plate‐fin heat exchanger employing triangular shaped fins with a rectangular wing vortex generator on its slant surfaces. The study has been carried out for three different angles of attack of the wing, i.e., 15°, 20° and 26°. The aspect ratio of the wing is not varied with its angle of attack. The flow considered herein is laminar, incompressible, and viscous with the Reynolds number not exceeding 200. The pressure and the velocity components are obtained by solving the continuity and the Navier– Stokes equations by the Marker and Cell method. The present analysis reveals that the use of a rectangular wing vortex generator at an attack angle of 26° results in about a 35% increase in the combined spanwise average Nusselt number as compared to the plate‐triangular fin heat exchanger without any vortex generator. © 2010 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20285     

矩形管内纵向涡强化传热研究

将纵向涡强化换热技术应用于矩形管槽,研究以水为换热介质在过渡流状态下的换热效果。实验结果表明有纵向涡发生器的换热效果明显优于无纵向涡发生器的情况。利用PHEON ICS计算软件对实验进行数值模拟,模拟值与实验值符合较好。在此基础上,改变纵向涡的翼高和形状来模拟,发现两者均为换热影响的因素,相比之下,高宽比为0.4纵向涡发生器的换热效果比高宽比为0.5和0.6的要好。而采用相同高宽的矩形翼时,N u高于三角翼,但其换热性能指标却低于直角三角翼。     

Numerical analysis on heat transfer enhancement by waves on falling liquid film

IntroductionLiquid films flowing on a vertical or inclined wall bythe gravitational force are encountered in the wideindustrial and engineering fields['1, such as condensatefilm, evaporating falling film, gas absorb by liquid film,etc. In the case of Indnar film flow with smooth surface,heat transfer through the liquid film is mainly carried outby conduction, and it is sufficiently explained by theNusselt's theory. On the other hand, the heat transfer isfairly enhanced for films generating su…     

丁胞结构强化换热机理的场协同分析

采用数值方法计算了丁胞结构流道内对流换热过程,并运用场协同理论分析了丁胞结构强化换热的机理,分析了丁胞大小、深度以及Re等对换热过程的影响。结果发现,丁胞的前侧是换热弱化区,而后侧才是强化换热区,但总体表现为强化换热效果,在低Re条件下,Nu较普通流道高1．2～1．5倍,是一种较好的强化换热方式。     

Discussion on the convective heat transfer and field synergy principle

The convective “heat” transfer is actually mainly carried out by the motion of hotter or colder particles from one system into another system. Therefore, the best convective “heat” (strictly speaking, internal energy) transfer is the case where velocity vectors are always perpendicular to the isothermal surfaces (or isotherm in 2D cases). This conclusion has been named “field synergy principle”. In this paper, some field synergy exact solutions are presented to further develop the principle. The concrete physical meanings of the derived analytical solutions are analyzed. The method of separating variables with addition and other extraordinary approaches are adopted in the derivation.     

Study on enhancement of condensation heat transfer using an electric field

Enhancement of condensation heat transfer using a nonuniform electric field was experimentally investigated for horizontal smooth and low‐finned tubes. In the experiments, a wire electrode parallel to the tube was placed beneath the tube. The experimental parameters were the distance and voltage between the wire electrode and the tube, and the condensation heat flux. Results of the present experiment for the low‐finned tube indicate that, as the applied voltage increases, the enhancement ratio increases steeply at a certain voltage and it reaches 2.4. It was observed that the condensate flow pattern falling down from the bottom of the tube changed from a flat film to circular columns at a critical voltage. © 2000 Scripta Technica, Heat Trans Asian Res, 29(4): 269–279, 2000