共查询到19条相似文献,搜索用时 109 毫秒
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本文提供了7个内径为15.54mm的内螺纹粗糙管单相流动的传热和阻力数据,为当前商用粗糙管常用尺寸提供了一系列新的内部强化数据.螺纹管结构参数为螺纹数(18~45),螺旋角(25°~45°)、螺纹高(0.33mm至0.55 mm).测试管由于螺纹处流动分离及表面积的显著增加而得到强化.测试数据范围为5.08≤Pr≤6.29.利用两种关联式来预测不同几何变量和雷诺数下St和摩擦系数.多重回归传热关联式的平均差分别为2.9%和3.8%.传热和摩擦关联式基于粗糙表面热量-动量传输比拟,标准差为分别是1.4%和5.4%.关联式能够合理地预测商用螺纹粗糙管的传热和摩擦. 相似文献
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螺纹管内污垢热阻的对比实验研究 总被引:1,自引:0,他引:1
本文对一冷却塔中的7根螺纹管进行了长时间污垢实验研究.螺纹管几何参数范围:螺纹数18~45,螺纹角25°~45°,螺纹高0.33~0.55 mm.污垢是颗粒污垢和析晶污垢的混合物.本文基于普朗特类比,引入修正因子β(β=(A_w/A_(wp))/(A_c/A_(cp)),A_w为润湿面积,A_c为截面积,下标p表示光管),对半经验污垢预测模型进行修正,证明了螺纹管内参数对污垢热阻的形成影响很大,并建立了不同结构参数的螺纹管的统一结垢模型,对工程实际有一定指导意义. 相似文献
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采用实验的方法,研究了在较宽的不凝气体含量范围内,煤油蒸汽在不同几何结构的螺旋扁管管束外的冷凝换热现象,得出了螺旋扁管的几何结构对冷凝换热的影响规律,并与同样条件下的光管管束的冷凝换热进行了分析比较。 相似文献
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超临界锅炉内螺纹管传热特性的研究 总被引:9,自引:0,他引:9
本文在全周加热和单侧加热的条件下,对600 MW超临界变压运行直流锅炉水冷壁φ28×6 mm内螺纹管进行了传热与阻力特性的试验研究。试验参数为压力13-27 MPa,质量流速400-1800 kg/m2·s,内壁热负荷200-800kW/m2。试验得出了在不同参数条件下的壁温分布、发生传热恶化的临界条件、单相及两相对流放热系数、干涸后放热系数及内螺纹管的摩擦压降,提出了计算关联式,比较了单侧加热与全周加热的区别,为超临界锅炉设计提供了重要依据。 相似文献
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一、试验装置与方法 锅炉水冷壁管采用内螺纹管结构是锅炉中防止传热恶化的主要措施之一。目前国内外有关内螺纹管在近临界压力区汽水两相流沸腾传热特性方面的研究资料还甚少。为了加速我国300MW直流锅炉的完善化,并考虑炉膛水冷壁将在近临界压力条件下工作,因此作者在西安交通大学高压汽水两相流试验装置上对这一课题进行了试验研究工作。试验用内螺纹管为我国300MW直流锅炉实际采用的φ22×5.5mm四头碳钢内螺纹管。用充水法确定其平均内径为11.69mm,螺纹高度为0.58mm, 相似文献
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本文开展了亚临界压力下垂直上升内螺纹管中水的传热特性的实验研究,并与对应条件下光管内水的传热特性进行了对比、分析.结果发现:内螺纹管和光管中两相饱和流动沸腾换热随热流密度的增加或压力的升高而增大,基本不随质量流速的变化而变化;相同工况下内螺纹管的饱和沸腾换热系数大约为光管的1.1~1.2倍。内螺纹管和光管的过冷沸腾起始干度都随质量流速的减小或者压力的升高或者热流密度的增大而增大;在相同工况下本文实验内螺纹管中的过冷沸腾起始干度比光管中的要小至少0.2。光管中主要发生偏离核态沸腾(DNB),临界干度随热流密度的减小或质量流速的增加或压力的降低而增大;内螺纹管中主要发生烧干,运行参数对临界干度的影响不大。 相似文献
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电极圆锥内螺纹的无损检测 总被引:1,自引:0,他引:1
将CT技术和图像处理技术相结合,提出了电极圆锥内螺纹的无损检测方法。目前普通螺纹常用的测量方法大多为接触测量,有关文献介绍了非接触检测方法,但它们仅限于圆柱内螺纹,圆锥内螺纹的图像处理及非接触测量未见报道。从CT技术入手,探讨了电极圆锥内螺纹的图像检测方法,即在一个系统中实现对工件内部缺陷的检测及几何参数的测量。通过使用图像预处理、阈值选取及二值化、边缘检测及提取等方法,提取了螺纹轴截面齿形轮廓,并对不同处理方法进行了比较。使用自编程序测量计算了内螺纹的螺距、牙型角和锥角,测量精度分别达到了0 03mm,0 24°和0 02°。分析了误差产生的原因。理论分析及实验结果表明该方法正确可行。 相似文献
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三维内肋管内插入螺旋扭带的强化传热实验 总被引:4,自引:0,他引:4
本文分别以水和乙二醇为工质,在Re数范围为:600~40000,Pr数范围为:5.5~110之间,对四根分别插入三种不同扭率螺旋扭带的三维内助管内的换热和流阻特性进行了实验研究。结果表明:三维内肋管内加装扭带的强化传热技术适用于低Re数下高Pr数工质的管内对流换热强化。根据实验值得到了流阻和换热关联式。 相似文献
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Tian Ran Lin 《Journal of sound and vibration》2012,331(4):902-913
An analytical solution is presented in this paper for the vibration response of a ribbed plate clamped on all its boundary edges by employing a traveling wave solution. A clamped ribbed plate test rig is also assembled in this study for the experimental investigation of the ribbed plate response and to provide verification results to the analytical solution. The dynamic characteristics and mode shapes of the ribbed plate are measured and compared to those obtained from the analytical solution and from finite element analysis (FEA). General good agreements are found between the results. Discrepancies between the computational and experimental results at low and high frequencies are also discussed. Explanations are offered in the study to disclose the mechanism causing the discrepancies. The dependency of the dynamic response of the ribbed plate on the distance between the excitation force and the rib is also investigated experimentally. It confirms the findings disclosed in a previous analytical study [T.R. Lin, J. Pan, A closed form solution for the dynamic response of finite ribbed plates, Journal of the Acoustical Society of America 119 (2006) 917–925] that the vibration response of a clamped ribbed plate due to a point force excitation is controlled by the plate stiffness when the source is more than a quarter plate bending wavelength away from the rib and from the plate boundary. The response is largely affected by the rib stiffness when the source location is less than a quarter bending wavelength away from the rib. 相似文献
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A computational study is carried out to assess the suitability of various RANS based turbulence models for slot jet impingement on flat and ribbed surfaces with various values of Reynolds number and jet to plate spacing. The com-puted results are compared with the reported experimental data. It was observed that none of the turbulence models considered predicted the heat transfer data accurately. However, some models predicted the experimental data with good trends, e.g., secondary peak and several spikes in Nusselt number for ribbed surface, with a precise computation of the stagnation point Nusselt number. Further, the effects of slot width, rib pitch and jet to ribbed surface spacing were investigated for jet impingement on a ribbed surface. It was observed that the local Nusselt number increased with slot width and rib to plate spacing. It was also observed that increasing Reynolds number had a positive effect on the local heat transfer. With increasing rib pitch the local Nusselt number increased near the stagnation zone but de-creased downstream. The observed flow pattern was different for jet impingement on a ribbed surface than that on a flat surface. 相似文献
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Voehler MW Collier G Young JK Stone MP Germann MW 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2006,183(1):102-109
The pursuit for more sensitive NMR probes culminated with development of the cryogenic cooled NMR probe. A key factor for the sensitivity is the overall resistance of RF circuitry and sample. Lowering the coil temperature to approximately 25 K and the use of superconducting coil material has greatly reduced the resistance contribution of the hardware. However, the resistance of a salty sample remains the same and evolves as the major factor determining the signal-to-noise ratio. Several approaches have been proposed to reduce the resistance contribution of the sample. These range from encapsulating proteins in a water cavity formed by reverse micelles in low viscosity fluids to the optimal selection of low mobility, low conductivity buffer ions. Here we demonstrate that changing the sample diameter has a pronounced effect on the sample resistance and this results in dramatic improvements of the signal-to-noise ratio and shorter pi/2 pulses. We determined these parameters for common 5 mm NMR tubes under different experimental conditions and compared them to the 2, 3 and 4 mm tubes, in addition, 5mm Shigemi tubes were included since these are widely used. We demonstrate benefits and applicability of studying NMR samples with up to 4M salt concentrations in cryogenic probes. Under high salt conditions, best results in terms of short pi/2 pulses and high signal-to-noise ratios are obtained using 2 or 3mm NMR tubes, especially when limited sample is available. The 4 mm tube is preferred when sample amounts are abundant at intermediate salt conditions. 相似文献