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1.
新型三维内微肋管水平管内凝结分层流局部换热系数研究   总被引:1,自引:0,他引:1  
本文研制了一种新型相交换热强化管即三维内微肋管。通过实验得到了三维内微肋管水平管内凝结流型区的类别、分层流区判据以及强化凝结换热的性能.通过分析和逐步回归得到了计算分层流区三维内微肋管水平管内凝结局部换热系数的准则关系式。该式与实验数据在±30%范围内吻合。  相似文献   

2.
通过实验研究,从工程应用角度和流型转变控制机理考虑,本文将二维内微肋管水平内凝结流型分为三区即:环状流,分层流与间歇流。木文得到了以实验数据为依据的流型图和判断流型的判据.又得到了流型转变判据和流型图的解析解.该流型图与本文作者所做实验数据在±4%范围以内吻合.  相似文献   

3.
涡流管内可压缩气体的强旋转流动是涡流管能量分离的根本原因和驱动力,因而涡流管内流场研究是揭示涡流管能量分离物理机制的首要关键问题。由于涡流管内可压缩气体的三维强旋转湍流流动,实验测量中存在诸多问题,而CFD数值模拟技术对此具有很大的优势。文中以涡流管内部流场为研究对象,建立了涡流管计算域模型并进行网格划分,讨论了边界条件、湍流模型以及线性方程组求解策略等问题,对不同冷气流率下的涡流管内三维强旋流流场结构特性进行数值模拟,获得了不同冷气流率下的旋转运动、轴向运动、径向运动和循环流的分布特性。研究表明Realizableκ-ε湍流模型能够充分反映强旋流动特点,数值模拟结果与文献中实验值基本吻合。  相似文献   

4.
R134a在水平三维内微肋管内的沸腾换热   总被引:7,自引:0,他引:7  
本文以 R134a为工质,在外径为 16 mm的两种不同几何结构的水平三维微肋管内进行了沸腾换热实验,研究了质量流率、热流密度、蒸汽干度等因素对沸腾换热系数的影响。与相同工况下的水平光管比较, 1#微肋管的换热强化因子在1.5~2.1之间,2#微肋管的换热强化因子在1.9~2.8之间。两种三维微肋管的比较结果显示,单位内表面积上具有更多的微肋数目的 2#管的平均沸腾换热系数比 1#管增加了 28~43%。  相似文献   

5.
林建忠  李俊  朱力  JamesA.Olson 《中国物理》2005,14(6):1185-1192
推导了纤维悬浮流的平均运动方程和纤维平均取向角的概率密度函数方程,提出了计算纤维平均取向角分布和悬浮流平均量与脉动量关联函数的逐级迭代方法。将推导的方程和提出的方法用于纤维悬浮管流场的计算并进行了相应的实验,计算和实验结果吻合很好。研究结果表明,在相同的压力降下,与没有纤维的牛顿流相比,纤维悬浮流具有较大的流量,因而纤维在流场中起着减阻的作用,减阻的量随着纤维浓度的增加而增大。在相同情况下,纤维悬浮流的相对湍流强度和雷诺应力比牛顿流小,这说明纤维能够抑制湍流,抑制的量与纤维的质量浓度成正比。  相似文献   

6.
透平级非设计工况气动性能的数值模拟   总被引:2,自引:0,他引:2  
采用新型 LU隐式格式和改良型高阶 MUSCL TVD格式求解全三维雷诺平均的 Navier-Stokes方程和 q-w低雷诺数双方程湍流模型,对一台NASA跨音单级透平在不同工况下的内部流场进行了详细的数值模拟,并与可能得到的实验结果进行了对比。总结了小流量工况下动叶内部流动的分离模式。  相似文献   

7.
旋流两相流动的DSM—PDF两相湍流模型   总被引:1,自引:1,他引:0  
本文提出了气相雷诺应力方程模型和颗粒概率密度输运方程模型相结合而构成的DSM—PDF两相湍流模型,并用该模型和k-ε-Kp模型模拟了文献中测量的旋流数为0.47的旋流突扩气粒两相流动.和测量结果的对照表明,两模型都能较好地模拟族流数不高的两相流动平均速度场,但DSM—PDF模型可以揭示出两相湍流的各向异性,因此有预报强旋两相流动的潜力.  相似文献   

8.
一、引言 本文在文献[1]的基础上导出了非正交曲线坐标S_1流面内的可压湍流通用流函数方程组,文中连续方程和运动方程直接转化为流函数方程形式,不受势函数的无旋流动的限制,本文用焓和熵代替运动方程中的压力项,直接求解能量方程和熵方程,避免了压力修正带来的困难。导出了非正交曲线坐标系的κ-ε湍流双方程,在近壁区采用壁面函  相似文献   

9.
本文以水蒸汽为工质对水平三维微肋管内凝结换热及阻力特性进行了实验研究.与光管和二维管相比,在相同条件下,实验中效果最好的T3管全长平均凝结换热系数分别提高了113%~410%和20%~65%,同时,与二维管相比流动阻力增加较小,最大值不超过6.3%.比较另两种管型(T1,T2管)也证明三维管以较小的流阻增加为代价换取了明显的强化效果.  相似文献   

10.
DSM-LPDF两相湍流模型及旋流两相流动的模拟   总被引:2,自引:0,他引:2  
本文由流体-颗粒速度的拉氏联合概率密度函数(PDF)输运方程出发,用Simonin建议的Langevin模型封闭颗粒所遇到流体瞬时速度的条件期望项,并用Monte Carlo方法直接求解 PDF输运方程,将其和求解流体雷诺应力方程模型的有限差分方法结合,建立了雷诺应力-拉氏PDF(DSM-LPDF,简称DL)两相湍流模型.用此模型模拟了旋流数为0.47的突扩旋流气粒两相流动,并与文献中PDPA实验和用类似于单相流动湍流模型封闭方法的时平均统一二阶矩(USM)模型的预报进行了对比.  相似文献   

11.
Experiments were conducted to investigate the flow characteristics of water flowing through rectangular microchannels having hydraulic diameters of 0.133-0.367 mm and H/W ratios of 0.333-1. Experimental results indicated that the laminar flow transition occurred at Reynolds numbers of 200-700. This critical Re for the laminar transition was strongly affected by the hydraulic diameter, decreasing with corresponding decreases in the microchannel. In addition, the size of the transition range was diminished and fully developed turbulent flow also occurred at much lower Re. The friction behavior of both the laminar and turbulent flow was found to depart from the classical thermqfluid correlations. lite friction factor, f, was found to be proportional to Re?1.98 rather than Re for the laminar condition, and proportional to Re?1.72i for turbulent flow. The geometric parameters, hydraulic diameter, and H/W were found to be the most important parameters and had a critical effect on the flow. Generally, increasing the ratio H/W increases the friction factor. The reduction of the microchannel hydraulic radius decreases the friction factor significantly for a given H/W. There exists a special range of ratio H/W (approximately 0.5 mm) at which the experimental data are lower than the predictions obtained from classical correlations. Continued reduction of channel size increases the difference between fI,expf1,theo at REcri, and the quantity of fI,exp becomes smaller within the region adjacent to H/W = 0.5, and larger when H /Wis out of this region.  相似文献   

12.
泡沫铝翅片传热和流动特性的实验研究   总被引:6,自引:0,他引:6  
对泡沫铝翅片传热和流动特性进行了实验研究,泡沫铝的空隙率为0.90,孔密度(PPI)分别为10,20,40。实验结果表明,孔密度较大时,传热系数也较大,但流动阻力系数也明显升高。通过引入无因次变量Dα,得到了泡沫铝翅片的流动阻力系数和传热的初步准则关联式。  相似文献   

13.

This experimental study performs heat transfer and pressure drop measurements in three test tubes fitted with single, twin, and triple twisted-tapes with Reynolds number (Re) varying from 1,500 to 14,000. Each element of these continuous twisted-tapes that formulates the single, twin, and triple twisted-tapes has identical width, pitch, and thickness. Heat-transfer augmentations from the plain-tube conditions in three test tubes decrease with the increase of Re, while the descending rate decreases with the increase of twisted-tape in the tube. These twisted-tapes generate the more effective heat transfer enhancements in laminar flow regime than those developed in turbulent flow regime. With 3,000 ≤ Re < 14,000, the local Nusselt numbers in the tubes fitted with single, twin, and triple twisted-tapes were, respectively, 1.5–2.3, 1.98–2.8, and 2.86–3.76 times of the Dittus-Boelter levels. The Fanning friction factors in three test tubes decrease with the increase of Reynolds number. Based on the same pumping power consumption, the tube fitted with single and triple twisted-tapes possess the highest performance factors for laminar and turbulent flows, respectively. Experimental correlations of heat transfer and Fanning friction factor were derived for three tubes fitted with single, twin, and triple twisted-tapes.  相似文献   

14.
利用实验和数值模拟方法考察了含水原油在内肋套管内的流动与传热性能,指出了在 Re=200~1200 时管子结构尺寸(肋片高度、肋片宽度和肋片长度)对传热性能的影响,并进行了实验验证.  相似文献   

15.
微型管内流动特性的实验研究   总被引:5,自引:0,他引:5  
以四氯化碳作为工质,流经内径分别为0.168 mm、0.399 mm、0.799 mm不锈钢管及内径分别为0.242 mm、0.315 mm、0.520 mm石英玻璃管,测量压降与流量的关系,从而获得摩擦因子f与雷诺数Re的关系。实验结果表明, 当雷诺数Re小于1600-1800时,除内径为0.168 mm的不锈钢管外,别的内径的微管内的摩擦因子与经典层流理论值几乎一致,而内径为0.168 mm的不锈钢管由于更大的相对粗糙度(8%-10%左右),其f值比经典理论值高约5%-10% 左右。当雷诺数Re越过1800时,f的值明显偏离经典层流理论值。  相似文献   

16.
规则结构多孔填料塔两相流动特性实验研究   总被引:1,自引:0,他引:1  
本文以空气和水为工质,对规则结构多孔填料塔的气-液逆向流动特性进行了可视化实验,研究了填料塔内气一液两相流动规律.实验结果表明:当液体流量一定时,随着气体流量的增加,压力损失增大;当气体流量一定时,随着液体流量的增加,气相压力损失增加.根据实验结果提出了采用水力雷诺数、韦伯数和无量纲流动参数的填料塔内气-液两相流动阻力系数实验关联式.  相似文献   

17.
Fluid flow and heat transfer characteristics of single-phase flows in microchannels for refrigerant R-134a were experimentally investigated. Experiments were conducted using rectangular channels micromilled in aluminum with hydraulic diameters ranging from approximately 112 to 210 w m and aspect ratios that varied from 1.0 to 1.5. Using overall temperature, flow rate, and pressure drop measurements, friction factors and convective heat transfer coefficients were experimentally determined for steady flow conditions. Effects of Reynolds number, relative roughness, and channel aspect ratio are examined in predicting friction factor and Nusselt number for the experiments. Experiment results indicated that transition from laminar to turbulent flow occurred between a Reynolds number of 2,000 and 4,000. Friction factor results were consistently lower than values predicted by macroscale correlations but exhibited the same trends with Reynolds numbers of macroscale correlations. Nusselt number results also exhibited a similar pattern of lower values obtained in the experiments than those predicted by commonly used macroscale correlations. Nusselt number results also indicated that channel size may suppress turbulent convective heat transfer and surface roughness may affect heat transfer characteristics in the turbulent regime.  相似文献   

18.
细小圆管内液体流动特性实验研究   总被引:2,自引:0,他引:2  
本文实验研究了去离子水在直径为 1.0~2.0 mm 的细小圆管中的流动阻力特性.通过比较相同直径、不同管长的压差,获得了摩擦因子及局部损失系数随 Re 数变化关系.本文实验条件下,对于不同直径的细小圆管,沿程压降及局部压降随流速变化趋势一致;随着管径减小,摩擦因子也减小,且在层流区和湍流区内均要比常规尺度条件下的小;对于不同直径的细小圆管,局部损失系数随 Re 数变化趋势基本一致,当 Re 数相同时,管径越小,对应的局部损失系数越大;对于直径为 1.0~2.0 mm 的细小圆管,临界雷诺数 Rec=2050~2300.  相似文献   

19.
This work presents an experimental study of the thermal-hydraulic characteristics in a flat-plate solar collector with two different geometries of helical coil inserts. Isothermal pressure drop tests are conducted in a horizontal tube using water as working fluid to obtain the fully developed Fanning friction factor for a range of Reynolds number Re = 80–8,000. Heat transfer tests are performed in the solar collector loop using a mixture of propylene-glycol and water at 30 wt%, covering the ranges Pr = 16–28 and Re = 140–600. A significant decrease in the temperature of the absorber is observed when the appropriate wire coil is selected for the given flow conditions, proving the beneficial effect of this type of insert device for the augmentation of the thermal efficiency in flat-plate solar collectors.  相似文献   

20.
几种典型流动条件对平板转捩过程影响的数值模拟   总被引:3,自引:0,他引:3  
采用作者构造的k方程转捩湍流模型,数值模拟了较大跨度来流湍流度情况、不同来流湍流度时几种不同顺、逆压梯度存在情况、壁面存在不同热交换强度情况下平板的转捩流动过程.与实验结果对比表明,新模型具有较好地模拟转捩流动能力。  相似文献   

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