开缝布置方式对开缝翅片管换热器 传热与阻力特性的影响

为了获得开缝布置方式对开缝翅片管换热器传热与阻力特性的影响规律,对5种不同翅片管换热器进行了数值模拟研究,并进行了模化试验验证。结果表明：增加开缝会提高翅片管换热器的传热性能,但阻力也随之增加;与开缝位置相比,开缝数量对开缝翅片管换热器传热与阻力特性的影响更大;在Re=4800~7500日时,开缝翅片管换热器综合流动传热性能 随着Re数的增大而增大;在5种翅片中,开缝翅片的综合流动传热性能高于普通平直翅片;数值模拟与试验结果偏差较小,采用数值模拟方法能够比较准确地分析开缝翅片管换热器的传热与阻力特性。     

单向开缝翅片管换热器传热与阻力性能的数值模拟及试验研究

对一种单向开缝翅片管换热器进行了数值模拟及试验研究,分析了不同翅片间距及管径下单向开缝翅片管换热器的传热与阻力性能的变化规律。数值模拟和试验结果的对比表明,采用数值模拟方法研究单向开缝翅片管换热器的传热与阻力性能是可行的。     

管间距对开缝翅片管换热器传热与阻力特性的影响

为了获得管间距对开缝翅片管换热器传热与阻力特性的影响规律,对5种不同翅片管换热器进行了数值模拟研究,并进行了模化试验验证。结果表明:开缝翅片管束的传热和阻力特性与翅片侧气体的Re数有关,随着Re数增大,翅片侧Nu数增大,摩擦因子f逐渐减小;纵向间距S2对开缝翅片管换热器的综合流动传热性能的影响较大。数值模拟与试验结果偏差较小,采用数值模拟方法能够比较准确地分析开缝翅片管换热器的传热与阻力特性。     

翅片参数对开缝翅片管换热器换热与阻力性能的影响

在模化试验验证的基础上,通过数值模拟,获得了翅片间距P_f及开缝数量n_s对开缝翅片管换热器性能的影响规律:n_s≤6时,翅片侧Nu和流动阻力均随着P_f增大而减小;n_s6时,翅片侧Nu随P_f增大先减小后增大,而阻力逐渐降低;P_f=3.51～3.97 mm时,随n_s增大,阻力逐渐增大,n_s=4～6时,翅片侧Nu逐渐增大,n_s=6～8时,翅片侧Nu变化较小;P_f=3.97～4.43 mm时,n_s由4片增加至8片,翅片侧Nu和阻力均逐渐增大。根据不同结构的开缝翅片管换热器的综合流动换热性能,提出了P_f与n_s的最佳组合。     

翅片结构对单向开缝翅片管换热器传热与阻力性能的影响

通过对不同开缝数量、不同相对开缝高度的单向开缝翅片管换热器进行模拟,分析开缝数量、相对开缝高度对单向开缝翅片管换热器传热与阻力性能的影响规律。结果表明:在开缝数量为3～7片时,翅片侧Nu和f因子随着开缝数量的增加而增大,但Nu增幅逐渐减小;将开缝的数量取为5片能得到最好的综合性能;在相对开缝高度为0.3～0.7时,翅片侧Nu和f因子随着相对开缝高度的增加而增大,但当相对开缝高度在0.5～0.7范围内,翅片侧Nu的增幅减小;将相对开缝高度取为0.5能得到最好的综合性能。     

直接空冷凝汽器扁平钢管蛇形翅片气侧流动及传热特性数值研究

应用FLUENT软件,对直接空冷凝汽器扁钢管钎焊蛇形翅片气侧流动与换热进行数值研究,得到翅片管表面温度、翅片间距内空气速度分布图,研究了翅片高度、入口空气流速对换热性能、流动阻力和气侧综合换热性能评价指标的影响规律。并将模拟结果拟合得到实验关联式。结合某空冷凝汽器设计参数,验证了数值模拟结果的可靠性。     

加涡产生器的管片式换热器换热与阻力特性的数值研究

通过数值模拟的方法,研究了小翼式涡产生器对错排圆管管片式换热芯子换热与阻力特性的影响,比较了光板与加涡产生器强化板芯的速度场、横向平均Nu数以及平均对流换热系数、阻力系数的变化规律,为进一步提高其换热性能、改进翅片结构、设计新型换热器提供了理论依据。     

组合式翅片管换热器传热与阻力性能影响因素研究

为解决空气源热泵冬季在制热工况下因室外机内翅片换热器换热效率低引起系统供能性能下降的问题,以组合式翅片管换热器为研究对象,在模化实验的基础上,采用数值模拟的方法分别对翅片换热器的传热及流阻性能影响因素进行分析.研究结果表明:在本文研究背景下,入口风速、翅片厚度、开缝数目对前开孔后开缝型的翅片组合形式换热器传热效率具有一定程度的影响;以上述三种因素为目标函数对换热器进行多目标优化时,入口风速取3 m/s,翅片厚度为0.16 mm,后排开缝数目为6,换热器能得到较好的综合性能;在此基础上,拟合出适合于该组合形式的传热和流阻关联式.     

管束结构对单向开缝翅片管换热器传热与阻力性能的影响

通过对不同相对横向管间距S_1/d_o、相对纵向管间距S_2/d_o的单向开缝翅片管换热器进行模拟,分析研究参数范围内S_1/d_o与S_2/d_o变化对单向开缝翅片管换热器性能的影响规律,模拟结果的准确性得到了模化试验的验证。结果表明:在S_1/d_o=2.10～2.84、S_2/d_o=1.76～2.50范围内,单向开缝翅片管换热器翅片侧的阻力受S_2/d_o的影响更大;单向开缝翅片管换热器综合性能受S_1/d_o、S_2/d_o影响的程度相当。     

径向错列翅片管内凝结对流换热数值模拟分析

采用数值模拟方法,对径向错列翅片管内含不凝结气体水蒸气的凝结对流换热及阻力特性进行了综合分析。将编写的自定义函数(UDF)导入ANSYS FLUENT软件,对新型强化管传热性能和阻力性能进行了数值模拟,并根据管长方向壁面上蒸汽质量分数的变化情况,讨论分析了凝结过程中翅片管传热性能的变化规律。分析结果表明:与光管相比,内翅片管的强化传热效果随翅数增多、翅片换热接触面积增大而更加显著;另一方面,翅片管的流动阻力相应增大,对管路换热产生不良影响。在所研究翅型范围内16翅y=2x~2型翅片管综合强化换热效果更优;此外随着换热过程的持续,蒸汽凝结逐渐放缓;入口速度增大导致水蒸气凝结不充分,对换热效果的提升有一定制约。     

The Influence of Strip Location on the Pressure Drop and Heat Transfer Performance of a Slotted Fin

In this article, a numerical study is conducted to predict the air-side heat transfer and pressure drop characteristics of slit fin-and-tube heat transfer surfaces. A three-dimensional steady laminar model is applied, and the heat conduction in the fins is also considered. Five types of slit fins, named slit 1, slit 2, slit 3, slit 4, and slit 5, are investigated, which have the same global geometry dimensions and the same numbers of strips on the fin surfaces. The only difference among the five slit fins lies in the strip arrangement. Slit 1 has all the strips located in the front part of the fin surface, then, following the order from slit 1 to slit 5, the strip number in the front part decreases and, correspondingly, the strip number in the rear part increases, so that all the strips of slit 5 are located in the rear part. Furthermore, slit 1 and slit 5, slit 2 and slit 4, have a symmetrical strip arrangement along the flow direction. The numerical results show that, following the order from slit 1 and slit 5, the heat transfer rate increases at first, reaching a maximum value at slit 3, which has the strip arrangement of “front coarse and rear dense”; after that, it begins to decrease, as does the fin efficiency. Although they have the symmetrical strip arrangement along the flow direction, slit 5 has 7% more Nusselt number than slit 1, and slit 4 also has 7% more Nusselt number than slit 2, which shows that strip arrangement in the rear part is more effective than that in the front part. Then the difference of heat transfer performance among five slit fins is analyzed from the viewpoint of thermal resistance, which shows that when the thermal resistances in the front and rear parts are nearly identical, the optimum enhanced heat transfer fin can be obtained. This quantitative rule, in conjunction with the previously published qualitative principle of “front sparse and rear dense,” can give both quantitative and qualitative guides to the design of efficient slotted fin surfaces. Finally, the influence of fin material on the performance of enhanced-heat-transfer fins is discussed.     

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...     

NUMERICAL DESIGN OF EFFICIENT SLOTTED FIN SURFACE BASED ON THE FIELD SYNERGY PRINCIPLE

In this article, a numerical investigation of the flow and heat transfer in a three-row finned-tube heat exchanger is conducted with a three-dimensional laminar conjugated model. Four types of fin surfaces are studied; one is the whole plain plate fin, and the other three are of slotted type, called slit 1, slit 2, and slit 3. All four fin surfaces have the same global geometry dimensions. The three slotted fin surfaces have the same numbers of strips, which protrude upward and downward alternatively and are positioned along the flow direction according to the rule of “front coarse and rear dense.” The difference in the three slotted fins is in the degree of “coarse” and “dense” along the flow direction. Numerical results show that, compared to the plain plate fin, the three types of slotted fin all have very good heat transfer performance in that the percentage increase in heat transfer is higher than that in the friction factor. Among the three slotted fin surfaces, slit 1 behaves the best, followed by slit 2 and slit 3 in order. Within the Reynolds number range compared ( from 2,100 to 13,500), the Nusselt number of slit 1 is about 112–48% higher than that of the plain plate fin surface under the identical pumping constraint. An analysis of the essence of heat transfer enhancement is conducted from the field synergy principle, which says that the reduction of the intersection angle between the velocity and the temperature gradient is the basic mechanism for enhancing convective heat transfer. It is found that for the three comparison constraints the domain-average synergy angle of slit 1 is always the smallest, while that of the plain plate fin is the largest, with slit 2 and slit 3 being somewhat in between. The results of the present study once again show the feasibility of the field synergy principle and are helpful to the development of new types of enhanced heat transfer surfaces.     

Fin Pattern Effects on Air-Side Heat Transfer and Friction Characteristics of Fin-and-Tube Heat Exchangers with Large Number of Large-Diameter Tube Rows

Air-side heat transfer and friction characteristics of nine kinds of fin-and-tube heat exchangers, with a large number of tube rows (6, 9, and 12, respectively) and large diameter of tubes (18 mm), are experimentally investigated. The test samples consist of three types of fin configurations: plain fin, slit fin, and fin with delta-wing longitudinal vortex generators. The working fluid in the tube is steam. Results show that when the number of tube is larger than 6, the heat transfer and friction performance for three kinds of fins is independent of the number of tube rows, and slit fin provides higher heat transfer and pressure drop than the other two fins. The heat transfer and friction factor correlations for all the heat exchangers were acquired with Reynolds numbers ranging from 4000 to 10000. The air-side performance of heat exchangers with plain fin, slit fin, and longitudinal vortex-generator fin were evaluated under three sets of criteria, and the results showed that the heat exchanger with slit fin has better performance than that with vortex-generator fin, especially at high Reynolds numbers.     

Combined Experimental and Numerical Flow Field Study of Inclined Louvered Fins

In this study the flow behavior within an interrupted fin design, the inclined louvered fin, is investigated experimentally through visualization and numerically through computational fluid dynamics (CFD) simulation. The inclined louvered fin is a hybrid of the offset strip fin and standard louvered fin, aimed at improved performance at low Reynolds numbers for compact heat exchangers. The flow behavior is studied in six geometrically different configurations over a range of Reynolds numbers and quantified using the concept of “fin angle alignment factor,” which is related to the flow efficiency in louvered fins. The experimental data resulted in a discrete data set of local fin angle alignment factor values, which were used to validate the simulations. Using these validated cases it is shown that the graphical measurement method can be distorted by recirculation zones, resulting in erroneous values. Care should thus be taken when performing graphical measurement of the mean flow angle based on dye injection images. The transition from steady laminar to unsteady flow in inclined louvered fins is geometrically triggered and occurs at lower Reynolds numbers compared to slit fins and standard louvered fins. This property can potentially be used to further improve on the performance of interrupted fin surfaces.     

电子元件散热器翅片自然对流散热性能研究

针对室外电子设备在自然对流条件下的散热问题,设计开发了一种新型散热器翅片结构——翅片开孔式涡流发生器,易于加工且直接与翅片连接,不存在焊接的问题.利用数值模拟的方法探究了涡流发生器的布置方式与攻角对散热器散热的影响.结果 表明:翅片开设三角孔,在翅片间空气流动过程中起到了明显的作用,有效降低了三角形涡流发生器造成的流动...     

Study on forced air convection cooling for electronic assemblies

The slotted fin concept was employed to improve the air cooling performance of plate-fin in heat sinks. Numerical simulations of laminar heat transfer and flow pressure drop were conducted for the integral plate fin, discrete plate fin and discrete slotted fin heat sinks. It is found that the performance of the discrete plate fin is better than that of the integral continuum plate fin and the performance of slotted fin is better than that of the discrete plate fin at the same pumping power of the fan. A new type of heat sink characterized by discrete and slotted fin surfaces with thinner fins and smaller spaces between fins is then proposed. Preliminary computation shows that this type of heat sink may be useful for the next generation of higher thermal load CPUs. The limit of cooling capacity for air-cooling techniques was also addressed.     

Measurement of performance of plate-fin heat sinks with cross flow cooling

This work assesses the performance of plate-fin heat sinks in a cross flow. The effects of the Reynolds number of the cooling air, the fin height and the fin width on the thermal resistance and the pressure drop of heat sinks are considered. Experimental results indicate that increasing the Reynolds number can reduce the thermal resistance of the heat sink. However, the reduction of the thermal resistance tends to become smaller as the Reynolds number increases. Additionally, enhancement of heat transfer by the heat sink is limited when the Reynolds number reaches a particular value. Therefore, a preferred Reynolds number can be chosen to reduce the pumping power. For a given fin width, the thermal performance of the heat sink with the highest fins exceeds that of the others, because the former has the largest heat transfer area. For a given fin height, the optimal fin width in terms of thermal performance increases with Reynolds number. As the fins become wider, the flow passages in the heat sink become constricted. As the fins become narrower, the heat transfer area of the heat sink declines. Both conditions reduce the heat transfer of the heat sink. Furthermore, different fin widths are required at different Reynolds numbers to minimize the thermal resistance.     

环保用板翅式换热器的数值模拟与试验研究

选取矩形截面平直翅片板翅式换热器的矩形单通道运用fluent软件进行数值模拟。首先对不同波高和波距的三组九种几何尺寸的翅片在同一工况下进行数值模拟,选出每组中传热和阻力综合性能最优者。然后对选出的三种翅片在不同工况下进行数值模拟,最终选出一种传热和阻力综合性能最优的。并对实物换热器进行试验研究,同时将试验结果和数值模拟结果进行对比分析,验证了数值模拟的正确性。