几种常见翅片通道内流动与传热的数值模拟

发布时间：2018-05-16 09:22

本文选题：板翅式换热器 + 平直翅片　；参考：《天津大学》2015年硕士论文

【摘要】：板翅式换热器具有结构紧凑、效率高的特点,被广泛应用在汽车、航空、空分等领域。利用经实验验证的CFD模型来揭示狭小翅片通道内局部流动、传热特性,对优化翅片结构、开发新型翅片有实际应用价值。本文针对平直、锯齿、波纹翅片通道内流动的特点,选择合适的低雷诺数湍流模型并结合湍流普朗特数模型,建立了准确计算翅片性能的三维数值模型。通过以上两个改进措施,使得平直翅片的计算j因子的平均绝对误差从17.94%降到6.93%,提高了计算精度。同时通过计算发现翅片中心处与进口流体温差较上(下)盖板与进口流体的温差低5-18%,忽略翅片纵向导热或将模型简化为二维流动会带来误差。针对18种不同几何结构的平直翅片进行数值模拟,得到翅片性能关联式,该关联式较日本神钢“ALEX”性能曲线有更高的精度。在验证锯齿形翅片数值模型正确性的基础上,探究了雷诺数、翅片厚度、翅片节距、翅片高度等参数对流动、传热的影响;其中翅片厚度和翅片节距对性能影响较大。随着翅片厚度增加,在迎风面后侧会形成对称的涡流区域,使压降增大而对强化传热效果不明显;减小翅片节距,破坏锯齿形翅片通道内温度边界层和速度边界层更频繁,传热系数和压降均增大。通过与实验数据对比,验证了计算波纹翅片通道性能的数值模型的正确性,并比较了在不同雷诺数下翅片通道内的流动状态。在低雷诺数区域流体流动与平直翅片相似;随着雷诺数增大,流体在波峰、波谷处形成涡流区域,使壁面区域流体与主体流体发生混合,强化传热过程。在纵向方向上,靠近上下盖板区域存在对称的Taylor-Gortler涡;在过渡流区域涡流较大;而在湍流区域,湍流会抑制Taylor-Gortler涡的形成,涡流变小。
[Abstract]:Plate-fin heat exchanger is widely used in automobile, aviation, air separation and other fields because of its compact structure and high efficiency. The experimental CFD model is used to reveal the local flow and heat transfer characteristics in a narrow fin channel, which has practical application value in optimizing fin structure and developing new fin. In this paper, according to the characteristics of flow in straight, sawtooth and corrugated fin channels, a three dimensional numerical model for accurate calculation of fin performance is established by selecting appropriate low Reynolds number turbulence model and combining with turbulent Plantt number model. Through the above two improvement measures, the average absolute error of calculating j factor of flat fin is reduced from 17.94% to 6.933%, and the accuracy of calculation is improved. At the same time, it is found that the temperature difference between the center of the fin and the inlet fluid is 5-18% lower than that between the upper (lower) cover plate and the inlet fluid. The error will be caused by neglecting the longitudinal heat conduction of the fin or simplifying the model to two-dimensional flow. Based on the numerical simulation of 18 kinds of straight fins with different geometric structures, the performance correlation of the fins is obtained, which has a higher accuracy than the "ALEX" performance curve of Shengang Japan. On the basis of verifying the correctness of the sawtooth fin numerical model, the effects of parameters such as Reynolds number, fin thickness, fin pitch, fin height on the flow and heat transfer are investigated, among which the fin thickness and fin pitch have great influence on the performance. With the increase of fin thickness, a symmetrical eddy current region will be formed at the back of the windward, which will increase the pressure drop without obvious effect on the enhancement of heat transfer, decrease the fin pitch and destroy the temperature boundary layer and velocity boundary layer in the sawtooth fin channel more frequently. Both heat transfer coefficient and pressure drop increase. The correctness of the numerical model for calculating the channel performance of corrugated fin is verified by comparing with the experimental data and the flow state in the fin channel under different Reynolds numbers is compared. The fluid flow in the low Reynolds number region is similar to that in the flat fin, and with the increase of the Reynolds number, the eddy current region is formed at the peak and trough of the wave, which makes the fluid mixing with the main fluid in the wall area and strengthens the heat transfer process. In the longitudinal direction, there are symmetrical Taylor-Gortler vortices near the upper and lower cover plates; in the transitional flow region, the vortices are larger; in the turbulent region, the formation of Taylor-Gortler vortices is inhibited and the eddy current becomes smaller.
【学位授予单位】：天津大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TQ051.5

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