气体在任意截面形状微尺度槽道中的滑移流动

利用正交函数法对气体在具有任意截面形状的微尺度槽道内的充分发展层流滑移流动特性进行了理论分析,获得了任意截面形状微槽道内的速度分布和流动阻力特性的分析解,并以矩形微槽为例分析了微槽截面上的速度分布和阻力特性.结果表明：随Kn数的增加,由于壁面处滑移流动的影响,气体流经微槽的流动阻力常数小于大尺度理论预测值;理论分析解的结果与实验结果吻合较好,表明在一定的Kn数范围内Navier-Stokes方程在考虑了速度滑移后可以描述微通道内的气体流动过程;正交函数法在微槽内滑移流动的分析中是可行的.     

3D打印槽道结构槽宽对池沸腾传热特性的影响

表面微结构化是强化沸腾传热的重要手段,研究微结构尺寸对沸腾传热特性的影响规律意义重大。本文采用选择性激光熔化技术(SLM)制备了不同宽度的槽道结构试样,并对其进行了常压下池沸腾传热特性实验研究。结果表明,相比于光滑铜面,槽长2.3mm,槽宽0.5～2.3mm槽道结构的传热系数(HTC)与临界热通量(CHF)均有显著提升。槽道结构的CHF随着槽道宽度的增大先增加后减小,HTC随着槽道宽度的增大而减小。槽道宽度为0.9mm时CHF达到最大值331.5W/cm²,为光滑铜面的3倍,同时HTC为光滑表面的1.7倍。较小的槽道宽度增加了试样的传热面积,限制了气泡脱离直径进而增加气泡的脱离频率,是HTC提升的关键因素;而槽道内气液流动阻力限制与水动力不稳定性,是槽道结构CHF提升的关键控制因素。     

间断环面槽肋片管束的传热和流动阻力

应用热 -质比拟技术 ,对间断环面槽肋片管束进行了传质与流动阻力实验 ,根据热 -质比拟关系得出传热结果 .分析了该种换热芯子在不同板间距时的传热与阻力特性 .与光板肋片管换热芯子比较 ,该种换热元件的传热与阻力都有很大提高 ,而阻力增加幅度更大 .实验结果为运用单位选用肋片管式换热器提供了依据 .     

结构参数对螺旋槽管传热与阻力性能影响的研究

利用计算流体动力学方法,研究了不同雷诺数下,几何尺寸对螺旋槽管传热及阻力性能的影响,结果表明,螺旋槽管在凸肋部前后产生了二次涡流,由螺旋形槽道形成的旋流都对边界层形成了扰动,传热性能得到了提高,同时也增加了阻力.在雷诺数相同时,槽越深,换热性能越好.同时流动阻力也有所增大;螺距、槽半径越大,换热效果降低,流动阻力也随之...     

螺旋槽管槽深对定子水冷器传热与阻力特性的影响

螺旋槽管与折流栅组合的高效水冷器的传热和阻力特性与其管、壳程的结构因素密切相关,本文就螺旋槽管槽深对水冷器管、壳程传热与阻力特性的影响进行了实验研究.结果表明：壳程流速变化对水冷器传热系数的影响更加明显,即壳侧热阻相对较大,强化传热应以强化壳侧换热为主要目标;螺旋槽管槽深对水冷器传热系数的影响很大,应在实际工程设计中确保实际槽深符合设计要求;槽深越深,管壳程阻力也相应增加,即传热的强化是以阻力增加为代价.根据实验结果还得到了不同结构水冷器的管、壳程换热与阻力计算关联式.     

对流传热过程强化与能耗分析

为了强化对流传热,工程上普遍采用提高流体流速和改变管路流体力学特性的方法,但在强化传热的同时,增加了能耗.通过实验分析了流体流速对光滑直管和螺旋槽管传热效果的影响,得到了滞流区和湍流区的传热关系式和阻力与流速的函数关系式.通过对比相同流速下光滑直管和螺旋槽管强化比与阻力的情况,得到了两种流型下强化比以及阻力与流速的关系式,为工程设计和生产操作提供了理论参考.     

板间距对三角槽道脉动流流动阻力的影响

以水为工质对不同板间距的三角槽道脉动流流动阻力特性进行了研究。基于受力平衡方程,建立了适用于三角槽道脉动流压降的数学模型,用于理论分析流动阻力的影响因素。通过实验测试与数值模拟,校验数学模型的合理性,并且对三角槽道脉动流流动阻力进行分析。结果表明,流动阻力主要受板间距、涡旋拟"能"两方面因素影响,且与板间距呈反比,与涡旋拟"能"呈正比;板间距的缩小,会使流动阻力增加,当缩小到板间距与槽深比值为1.0时,出现流动阻力的阶越式增长,上升1个数量级;造成流动阻力骤升的主要原因在于:随着板间距的缩小,流场结构逐渐变化,三角槽道内涡旋的影响区域由"三角槽内部"逐渐转变为"整个流道",且主流区壁面出现流动分离,出现涡旋流动与波状流共存现象,使流动阻力大幅提升。     

板间距对三角槽道脉动流流动阻力的影响

以水为工质对不同板间距的三角槽道脉动流流动阻力特性进行了研究。基于受力平衡方程,建立了适用于三角槽道脉动流压降的数学模型,用于理论分析流动阻力的影响因素。通过实验测试与数值模拟,校验数学模型的合理性,并且对三角槽道脉动流流动阻力进行分析。结果表明,流动阻力主要受板间距、涡旋拟“能”两方面因素影响,且与板间距呈反比,与涡旋拟“能”呈正比;板间距的缩小,会使流动阻力增加,当缩小到板间距与槽深比值为1.0时,出现流动阻力的阶越式增长,上升1个数量级;造成流动阻力骤升的主要原因在于：随着板间距的缩小,流场结构逐渐变化,三角槽道内涡旋的影响区域由“三角槽内部”逐渐转变为“整个流道”,且主流区壁面出现流动分离,出现涡旋流动与波状流共存现象,使流动阻力大幅提升。     

槽道表面沸腾强化传热机理研究

本文以不定常传热理论为基础,对槽道表面沸腾传热进行了理论分析研究。分析了气泡的生长规律,建立了气泡壁面微层液膜的流动和传热的物理和数学模型,并与气泡顶部液体的不定常传热联系起来,得到了气泡生长和传热关系式。并且由几个约束性条件,对槽道的几何尺寸进行了判定,提出了适用的槽深和槽宽的变化范围,可供设计时参考。利用本文的关系式,对水蒸气和氟致冷剂(CFC)进行了数值计算,并与实验结果进行比较,两者基本一致。     

纳米流体在芯片微通道中的流动与换热特性

对去离子水及体积分数分别为0.15%和0.26%的水基γ-Al₂O₃纳米流体在当量直径为194.5 μm的硅基梯形芯片微通道内的层流流动和换热特性进行了实验研究。考察了Reynolds数、Prandtl数以及体积分数对流动换热的影响。结果发现,使用纳米流体后,压降无明显增加,纳米流体的流动阻力特性与去离子水基本相同;对流换热Nusselt数较去离子水有明显提高,且随着体积分数的增加而增加;相同泵功下换热热阻显著下降。实验还发现纳米流体的强化传热效果在较高温度时更加明显。根据实验数据得到了梯形硅微通道内低浓度纳米流体的层流对流换热关联式。研究结果对于集成高效芯片散热系统设计具有重要意义。     

EXPERIMENTAL STUDIES ON HEAT TRANSFER AND FRICTION FACTOR CHARACTERISTICS OF TURBULENT FLOW THROUGH A CIRCULAR TUBE FITTED WITH RIGHT AND LEFT HELICAL SCREW-TAPE INSERTS

Experimental investigation on heat transfer and friction factor characteristics of a circular tube fitted with right-left helical screw inserts of equal and unequal length of different twist ratios is presented. The experimental data obtained were compared with those obtained from plain tube published data. The heat transfer enhancement for right-left helical screw inserts is higher than that for straight helical twist for a given twist ratio. The effect of right-left twist length on heat transfer augmentation is presented. The empirical relations for Nusselt number, friction factor relating Reynolds number, twist ratio, and right-left twist distance were formed and found to fit the experimental data within 10% and 20% for Nusselt number and friction factor respectively. Performance evaluation analysis was made, and the performance ratio of more than one was obtained, indicating that the proposed twist inserts can be used effectively for heat transfer augmentation without any loss in pumping power.     

EXPERIMENTAL STUDIES ON HEAT TRANSFER AND FRICTION FACTOR CHARACTERISTICS OF TURBULENT FLOW THROUGH A CIRCULAR TUBE FITTED WITH RIGHT AND LEFT HELICAL SCREW-TAPE INSERTS

Experimental investigation on heat transfer and friction factor characteristics of a circular tube fitted with right–left helical screw inserts of equal and unequal length of different twist ratios is presented. The experimental data obtained were compared with those obtained from plain tube published data. The heat transfer enhancement for right–left helical screw inserts is higher than that for straight helical twist for a given twist ratio. The effect of right–left twist length on heat transfer augmentation is presented. The empirical relations for Nusselt number, friction factor relating Reynolds number, twist ratio, and right–left twist distance were formed and found to fit the experimental data within 10% and 20% for Nusselt number and friction factor respectively. Performance evaluation analysis was made, and the performance ratio of more than one was obtained, indicating that the proposed twist inserts can be used effectively for heat transfer augmentation without any loss in pumping power.     

内置螺旋叶片转子换热管传热和阻力特性的实验研究

本文概述了转子组合式强化传热装置的强化传热和自清洁原理,通过实验研究了传热和阻力特性。实验结果表明,在相同的雷诺数条件下,内置螺旋叶片转子换热管的努塞尔数明显高于光管的努塞尔数,说明具有良好的强化传热效果;内置螺旋叶片转子换热管的阻力系数显著高于光管阻力系数,说明在强化传热的同时,使得管内阻力随之增加。此外,作者借助多元线性回归方法,建立了内置螺旋叶片转子换热管的努塞尔数与阻力系数的经验关联式。     

插入双面有三角形翅片的金属带对热交换管中流动和传热特性的影响

The convective heat transfer and friction behaviors of turbulent tube flow through a straight tape with double-sided delta wings(T-W)have been studied experimentally.In the current work,the T-W formed on the tape was used as vortex generators for enhancing the heat transfer coefficient by breakdown of thermal boundary layer and by mixing of fluid flow in tubes.The T-W characteristics are(1)T-W with forward/backward-wing arrangement,(2)T-W with alternate axis(T-WA),(3)three wing-width ratios and(4)wing-pitch ratios.The experimental result reveals that for using the T-W,the increases in the mean Nusselt number(Nu)and friction factor are,respectively,up to 165%and 14.8 times of the plain tube and the maximum thermal performance factor is 1.19.It is also obvious that the T-W with forward-wing gives higher heat transfer rate than one with backward-wing around 7%. The present investigation also shows that the heat transfer rate and friction factor obtained from the T-WA is higher than that from the T-W.In addition,the flow pattern and temperature fields in the T-W tube with both backward and forward wings were also examined numerically.     

微小非圆截面通道内气液两相流数值模拟研究

利用ANSYS FLUENT软件,采用混合(Mixture)多相流模型对当量直径均为0.6 mm,高宽比分别为0.67、1、1.5的三种不同微小非圆截面通道内两相流流动与传热进行数值模拟,获得了不同截面管道内两相流温度、截面含气率及摩擦系数等变化分布情况,分析得出三种管道中高宽比为1.5时的矩形截面管道内两相流动及传热特性最优。     

Heat transfer enhancement by twisted tapes with alternate-axes and triangular, rectangular and trapezoidal wings

The effects of twisted tapes with alternate-axes and wings on heat transfer, flow friction and thermal performance characteristics in a round tube are investigated. The influence of wing shape including triangle, rectangle and trapezoid is also studied. The experiments are performed using twisted tape with three different wing-chord ratios (d/W) of 0.1, 0.2 and 0.3 and constant twist ratio (y/W) of 4.0. The alternate-axis is made by arranging each plane of twisted tape to 60 degree difference relative to the adjacent plane. The results show that both heat transfer rate and friction factor associated by all twisted tape are consistently higher than those without twisted tape. Under the similar operating conditions, Nusselt number, friction factor as well as thermal performance factor given by the tape with alternate-axes and trapezoidal wings are higher than those given by the others. It is also found that that Nusselt number, friction factor and thermal performance increase with increasing wing-chord ratio. The maximum thermal performance factor of 1.42 is found with the use of twisted tape with alternate-axes and trapezoidal wings at d/W = 0.3, where the heat transfer rate and friction factor, respectively increase to 2.84 and 8.02 times of those in the plain tube.     

内置组合转子换热管的综合传热性能

  对螺旋叶片和开槽螺旋叶片两种结构组合转子的综合传热性能进行了实验研究。与光管相比,两种转子都显著提高了换热管内的传热性能,装有螺旋叶片转子和开槽螺旋叶片转子换热管的努塞尔数分别比光管提高了1.06～1.26倍和1.03～1.15倍,引起的阻力系数分别比光管增加了60%～68%和36%～51%。螺旋叶片转子对管内传热性能的提升更为显著,但其引起的管内阻力系数也较大。综合考虑传热和阻力两方面因素,对两种转子结构的综合评价指标值进行比较,开槽螺旋叶片转子具有更好的综合传热性能。     

内置转子套管式换热器强化传热实验

概述了转子组合式强化传热装置的强化传热和自清洁原理,通过实验研究了内置螺旋叶片转子及叶片间断型转子换热管的传热和阻力特性。实验结果表明,在相同的Re条件下,内置螺旋叶片转子换热管管内的Nusselt数高于内置叶片间断型转子换热管,阻力系数低于内置叶片间断型转子换热管,同时PEC值明显高于叶片间断型转子的PEC值,说明内置螺旋叶片转子换热管的综合性能优于叶片间断型转子。     

Enhancement of Turbulent Flow Heat Transfer in a Tube with Modified Twisted Tapes

Numerical simulations were performed to study the fluid flow and heat transfer in a tube with staggered twisted tapes with central holes. In the range of Reynolds numbers between 6000 and 28 000, the modified twisted tapes increased the Nusselt number by 76.2 ～ 149.7 % and the friction factor by 380.2 ～ 443.8 % compared to the smooth tube. Compared to the typical twisted tapes, the modified twisted tapes produced an acceleration flow through the triangle regions leading to the enhancement of heat transfer, and the holes in the modified tapes reduced the severe pressure loss. It was found that the modified twisted tapes decreased the friction factor by 8.0 ～ 16.1 % and enhanced the heat transfer by 34.1 ～ 46.8 % in comparison with the typical tapes. These results indicated that the performance ratio values of the tube with modified twisted tapes were higher than 1.0 in the range of Reynolds numbers studied. The computed performance ratios of the tube with modified twisted tapes were much higher than those of the tube with typical twisted tapes. This means that the integrated performance of the tube with staggered twisted tapes with central holes is superior to that of the tube with typical twisted tapes.     

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