螺旋扭扁管强化传热与阻力性能的模拟分析

运用数值模拟的方法对螺旋扭扁管的传热与阻力性能进行了分析与研究,并与普通椭圆直管相比较,研究了管内流体的Re、Pr以及管子几何尺寸对其管内传热与流动性能的影响。结果表明,螺旋扭扁管是一种较好的强化传热元件,尤其对具有高Pr数的大粘度流体在低Re数的层流或过渡流时具有较好的强化传热效果。根据数值模拟的结果,利用多元线性回归的方法给出了努塞尔数Nu和阻力系数f的准则公式。     

Numerical evaluation of laminar heat transfer enhancement in nanofluid flow in coiled square tubes

Convective heat transfer can be enhanced by changing flow geometry and/or by enhancing thermal conductivity of the fluid. This study proposes simultaneous passive heat transfer enhancement by combining the geometry effect utilizing nanofluids inflow in coils. The two nanofluid suspensions examined in this study are: water-Al2O3 and water-CuO. The flow behavior and heat transfer performance of these nanofluid suspensions in various configurations of coiled square tubes, e.g., conical spiral, in-plane spiral, and helical spiral, are investigated and compared with those for water flowing in a straight tube. Laminar flow of a Newtonian nanofluid in coils made of square cross section tubes is simulated using computational fluid dynamics (CFD)approach, where the nanofluid properties are treated as functions of particle volumetric concentration and temperature. The results indicate that addition of small amounts of nanoparticles up to 1% improves significantly the heat transfer performance; however, further addition tends to deteriorate heat transfer performance.     

高效复合强化换热器的管程性能

通过搭建内螺纹扭曲椭圆管复合强化管换热器传热与压降性能测试平台,对内螺纹扭曲椭圆管复合强化管换热器的管程传热和流阻性能进行了实验研究,以实验数据为基础拟合得到其对流传热系数和流动摩擦阻力系数与管内流体Reynolds数的计算准则关系式,将内螺纹扭曲椭圆管与光滑圆管、内螺纹圆管、光滑扭曲管的管程传热、流阻以及综合性能进行对比分析,结果显示内螺纹扭曲管流动阻力略高于其他类型的换热管,传热效果和综合性能明显优于其他类型换热管。内螺纹扭曲管作为一种内螺纹和扭曲扁管强化传热技术的叠加技术,强化传热效果明显,具有重要的工程应用价值。     

螺旋扭曲管用于燃气轮机进气温度调节换热器的可行性研究

对将螺旋扭曲管用于燃机进气温度调节换热器进行可行性分析,模拟燃机进气加热器实际运行的工况条件进行综合传热性能实验研究,得到了传热与流阻准则关系式;引入综合评价因子概念并与传统钢铝翅片管换热器进行对比发现,螺旋扭曲管换热器是钢铝翅片管换热器的1.31~1.52倍。以某建设项目采用的E级PG9171E型机组为例,对采用螺旋扭曲管和钢铝翅片管的两种进气温度调节换热器进行对比发现：当采用螺旋扭曲管换热器时,在同样换热能力下,换热器风侧阻力增大了14.7%;在同等质量下,换热器换热能力提高9.9%左右。     

扭曲管强化传热性能实验研究

在设计的蒸汽-水换热实验台上测试了5种不同导程的椭圆扭曲管和圆管的传热和流动阻力性能.分别对5种不同导程的扭曲管和圆管管内流体努赛尔数,摩擦系数和管内综合评价因子随雷诺数变化情况进行了对比.实验结果表明:扭曲管的强化传热性能明显,且导程越小,强化传热效果越好.在实验测试的雷诺数范围内,扭曲管的努塞尔数为光滑圆管的1.0...     

扭曲椭圆管强化传热研究进展及应用

扭曲椭圆管因结构简单、强化传热及阻垢性能优异,近年来成为被动强化传热领域研究热点之一。虽已有文献对扭曲椭圆管换热器技术进行了综述,但对扭曲椭圆管强化传热特性的归纳和工程应用研究脉络的梳理存在不足,本工作着眼于扭曲椭圆管内外传热及流阻性能研究、扭曲椭圆管换热器研发和工程应用两方面内容,概括了扭曲椭圆管(束)结构、工质、流动状态对传热性能及流阻特性的影响规律;回顾了扭曲椭圆管换热器工程应用案例,总结了有关扭曲椭圆管研究尚待完善之处,并对扭曲椭圆管强化传热研究的发展趋势进行展望,为深化扭曲椭圆管理论研究和工程实践提供指导和参考。     

螺旋扁管换热器传热与阻力性能

对不同结构的螺旋扁管管内传热及流体阻力性能进行实验研究,并与光管比较,选出传热与流阻综合性能较好的管型。同时对2台螺旋扁管换热器及1台外螺纹螺旋扁管换热器进行壳程传热与流阻实验研究。根据实验结果给出了管、壳程传热膜系数与阻力系数的经验关联式。     

缩放管内插双扭带复合强化传热的数值模拟(英文)

The paper presents a 3D numerical simulation of turbulent heat transfer and flow characteristics in converging-diverging tubes(CDs) and converging-diverging tubes equipped with twin counter-swirling twisted tapes(CDTs).The effects of Reynolds number(Re 10000-20000),pitch length(P 11.25,22.5 mm),rib height(e 0.5,0.8,1.1 mm),pitch ratio(δ1:8,5:4,8︰1),gap distance between twin twisted tapes(b 0.5,4.5,8.5 mm) and tape number(n 2,3,4,5,6) on Nusselt number(Nu),friction factor(f) and thermal enhancement factor(η) are investigated under uniform heat flux conditions,using water as working fluid.In order to illustrate the heat transfer and fluid flow mechanisms,flow structures in CDs and CDTs are presented.The obtained results reveal that all geometric parameters have important effects on the thermal performance of CD and CDT,and both CD and CDT show better thermal performance than plain tube at the constant pumping power.It is also found that the increases in the Nusselt number and friction factor for CDT are,respectively,up to 6.3%-35.7% and 1.75-5.3 times of the corresponding bare CD.All CDTs have good thermal performance with η greater than 1 which indicates that the compound heat transfer technique of CDT is commendable for the maximum enhanced heat transfer rate.     

装填有矩形切口螺旋带的管中的湍动传热和压降(英文)

Heat transfer, friction factor and thermal enhancement factor characteristics of a double pipe heat exchanger fitted with square-cut twisted tapes (STT) and plain twisted tapes (PTT) are investigated experimentally using the water as working fluid. The tapes (STT and PTT) have three twist ratios ( , 4.4 and 6.0) and the Reynolds number ranges from 2000 to 12000. The experimental results reveal that heat transfer rate, friction factor and thermal enhancement factor in the tube equipped with STT are significantly higher than those fitted with PTT. The additional disturbance and secondary flow in the vicinity of the tube wall generated by STT are higher compared to that induced by the PTT is referred as the reason for better performance. Over the range considered, the Nusselt number, friction factor and thermal enhancement factor in a tube with STT are respectively, 1.03 to 1.14, 1.05 to 1.25 and 1.02 to 1.06 times of those in tube with PTT. An empirical correlation is also formulated to match with experimental data of Nusselt number and friction factor for STT and PTT.     

换热管内置螺旋形扭带阻力与传热特性的实验研究

为了研究螺旋形扭带阻力与传热特性,选取了不同宽度（6、7和8 mm）的3种扭率（2.0、3.0、4.0）、3种螺距比（1.5、2.0、2.5）的参数组合下共27根螺旋形扭带插入换热管内进行实验.实验结果表明,插入螺旋形扭带后换热管内流动阻力和传热效果都有明显提高.通过对实验数据的多元线性回归分析,建立了相应的阻力系数和努赛尔数关联式.并且由强化传热综合性能评价分析,在实验雷诺数范围内得出强化传热综合性能评价因子φ=1.063～1.587,证明了实验研究的扭带具有强化传热的应用价值.     

内插不同形状涡产生器管内层流流动与传热特性的对比分析

内插扰流元件是一种可操作性强的管内强化传热方式,其强化传热机理主要是在管内诱导产生了二次流。在均匀壁温热边界条件下,对内插不同形状涡产生器管内层流流动与传热特性进行了数值分析。研究发现：在扭带基础上裁去部分面积相同的条件下,管内插等腰梯形涡产生器的换热能力最强,直角梯形涡产生器次之,矩形涡产生器的换热能力最差,管壁上的局部Nusselt数的峰值所在圆周位置及其大小与涡产生器形状有关,而不同形状的涡产生器对管内流动的阻力系数影响较小。插入涡产生器后,管内二次流强度参数Se和平均Nusselt数Nu均随Reynolds数Re的增大而增大,二者随Reynolds数Re的变化规律具有一致性。平均Nusselt数Nu与二次流强度参数Se呈幂函数相关,内插涡产生器管内的二次流强度决定了其对流换热强度。     

Thermohydraulics of Turbulent Flow Through Heat Exchanger Tubes Fitted with Circular-rings and Twisted Tapes

The influences of circular-ring turbulators (CRT) and twisted tape (TT) swirl generators on the heat transfer enhancement, pressure drop and thermal performance factor characteristics in a round tube are reported. The circular-ring turbulators were individually employed and together with the twisted tape swirl generators in the heated section of the tube. Three different pitch ratios (l/D1.0, 1.5, and 2.0) of the CRT and three different twist ratios (y/W 3, 4, and 5) of the TT were introduced. The experiments were conducted using air as the working fluid under a uniform wall heat flux condition, for the Reynolds number between 6000 and 20000. The experimental results reveal that the heat transfer rate, friction factor and thermal performance factor of the combined CRT and TT are considerably higher than those of CRT alone. For the range examined, the increases of mean Nusselt number, friction factor and thermal performance, in the tube equipped with combined devices, respectively, are 25.8%, 82.8% and 6.3% over those in the tube with the CRT alone. The highest thermal performance factor of 1.42 is found for the combined device consisting of the CRT with l/D 1.0 and TT with y/W 3. The correlations of the Nusselt number, friction factor and thermal performance factor of the tubes with combined devices are also developed in terms of Reynolds number, Prandtl number, twist ratio and pitch ratio.     

扭曲椭圆管管内传热与压降性能的研究

通过建立扭曲椭圆管单管传热与压降性能测试平台,利用光滑圆管,对测试平台测试结果的准确性进行了验证,同时对扭曲椭圆管的传热以及压降性能进行了实验测试,以测试结果为基础,验证了数值计算模型的准确性。对不同几何尺寸的扭曲椭圆管单管传热与压力性能进行了数值计算,分析了换热管几何参数对传热与压降性能的影响,结果显示:扭曲椭圆管传热性能随着扭曲椭圆管长短轴比A/B的增大而增大,随着扭曲椭圆管扭距S的减小而增大。同时以数值计算结果为基础,拟合得到了8×103相似文献   

润滑油在内插同轴交叉翼型涡产生器管内流动与传热特性分析

以润滑油为工质,采用数值方法对圆管内插同轴交叉等腰梯形涡产生器的管内流动与传热进行了数值模拟,分析了不同结构参数如扭率（T_r=3,4,5,6）、间距比（S_s/W=0.8,0.9,1.1,1.2）和基带宽度比（W_b/W=0.30,0.45,0.60,0.75）对圆管内插同轴交叉等腰梯形涡产生器的管内流动与传热特性的影响。结果表明：在相同Re下,平均Nusselt数Nu_m、二次流强度Se、强化传热因子JF均随扭率和间距比的减小而增大,而其与基带宽度比的变化没有明显规律,阻力系数f随着扭率的减小和基带宽度比的增大而增大,间距比对f的影响甚微。在相同结构参数下,JF和Se均随Re的增大而增大。在Re=50~1000范围内,相比于光滑圆管,内插不同结构参数的同轴交叉涡产生器的Nu_m增加了32.8%~208.6%,f增加了3.38~8.92倍,JF最大可达1.434。Nu_m与Se呈幂函数相关,内插同轴交叉翼型涡产生器管内的二次流强度决定了其对流换热强度。     

螺旋叶片转子强化传热机理分析

以螺旋叶片转子为研究对象,对转子的强化换热机理进行理论分析,提出螺旋叶片转子3种强化传热机理,包括截面收缩效应强化、螺旋流动效应强化以及二次流效应强化。采用理论推导的方法,建立湍流区内Nusselt数预测关联式以及压力降预测关联式,从而预测转子几何参数等对转子强化传热特性及阻力特性的影响。同时,将关联式预测结果与对应的强化传热实验结果进行对比,对比结果表明:推导得出的Nusselt数预测关联式计算值与实验得到的Nusselt数之间的最大偏差为7.4%,阻力系数的预测关联式计算值与其实验值之间的最大偏差为10.1%。     

Extension of the Rapid Design Algorithm for Twisted‐Tube Evaporative Fluid Coolers

The thermal analysis performance of evaporative fluid coolers (EFCs) is improved by replacing plain tubes by twisted oblong tubes. Results of the system are assessed by a rapid design algorithm (RDA) and compared to conventional plain‐tube EFCs and other traditional algorithms including the effectiveness number of transfer units (?‐NTU). Based on the RDA, a relationship between heat transfer coefficients, pressure drops, heat transfer area, and mass transfer coefficient is derived. Using the maximum allowable pressure drops in this algorithm, the minimum required heat transfer area can be determined. The algorithm is validated by comparing the plain‐tube EFC design with twisted‐tube design. The RDA‐designed EFCs with twisted tubes provide higher efficiency compared with the traditional designs with plain tubes in such that the new design needs a lower heat transfer area for a given heat load.     

缠绕管式换热器的CFD优化

用ANSYS CFX软件采用基于有限元的有限体积法对简化的缠绕管式换热器的壳程流动进行模拟,考察管束导程和壳程流速等参数对缠绕管式换热器壳程流体流动特性的影响。结果表明,减小缠绕管束的导程可提高壳程流体的湍流程度,增强壳程流体的均匀程度,减少温度死区并提高换热效率,减小同一截面不同区域的压力差,进而减小因流场不均匀而对管束产生的破坏性应力。提高壳程流速可增强换热,但会增加壳程压降。     

扭曲三叶管传热与流阻性能的数值研究

扭曲管换热器是一种新型高效换热器。在扭曲管强化传热机理研究的基础上,提出了一种新的扭曲管管型--三叶管。验证了标准k-ω湍流模型在圆管及扭曲椭圆管计算中的精确度,并采用该湍流模型对扭曲三叶管Re在4000～20000范围内的传热和流阻性能进行了研究。计算结果表明,扭曲三叶管的Nusselt数比扭曲椭圆管大,虽然压差增大较多但综合传热性能比扭曲椭圆管高。这是由于扭曲三叶管特殊的三叶区结构以及过渡区曲率的变化,使得三叶管内的螺旋流动比椭圆管更为复杂,速度场与温度梯度场的协同程度更好。随着Reynolds数的增大扭曲三叶管的压差及Nusselt数都逐渐增大,但综合性能逐渐降低,在低Reynolds数下扭曲三叶管的强化传热效果较为明显。内切圆直径及过渡圆弧直径越小,扭曲三叶管的综合性能越好,其中内切圆直径的影响更为显著。     

插入物强化管内单相流体传热的研究

为寻求强化低Re数下气体传热的较好插入物型式,在Re=500-10000范围内,对6种插入物用氢气泡示踪法进行流态显示,在恒壁温条件下进行竖直管内空气传热和阻力对比试验,得出各插入物的f-Re和Nu-Re关联式,并对各插入物进行传热强化性能评价.在此基础上进行参数范围为e/D=0.067—0.234、S/e=3.89—13.25的螺旋片试验,得出其阻力和传热关联式.综合研究流态显示结果和传热性能评价,认为在层流或过渡流区,利用螺旋流与利用边界层分离二者相比较,前者可以耗能较少而获得同样的传热强化效果.     

螺旋扭曲扁管换热器传热与流阻性能试验研究

对4种不同结构的螺旋扭曲扁管换热器的管程和壳程传热与流阻性能进行了试验研究,并和采用圆管作为换热管的弓形折流板换热器进行了比较,根据试验数据回归出反映螺旋扭曲扁管换热器管程和壳程传热与流阻特性的关联式。研究结果表明,螺旋扭曲扁管换热器管程与壳程都有较好的强化传热性能,螺旋扭曲扁管的几何尺寸和流体Re对其管、壳程传热与流阻性能有重要影响。