共查询到18条相似文献,搜索用时 250 毫秒
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针对CO_2水平微细管内流动沸腾换热流态及流态转变特性进行实验研究。实验工况:热流密度(5~35 k W/m~2)、质量流率(50~600 kg/(m~2·s))、饱和温度(-40~0℃)、管径(0.5~1.5 mm)。实验表明:CO_2在微细管内实际流态分别是泡状流、弹状流、间歇流、层流、波状流、混状流、环状流和雾状流;干涸过程中的流态主要为环状流-雾状流、波状流-雾状流的过程及不稳定的环状流;通过理论计算获得CO_2微细管内流动沸腾换热流态图,流态图显示热流密度对高干度区域流态转变有显著影响,质量流率大小直接决定了换热过程所经历的流态;不同饱和温度工质热物性不同改变了流型;理论分析所采用的流态形式与实际CO2在微细管内所具有的流态类型基本一致。 相似文献
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由于多相流流型直接影响多相流动的传热特性及摩擦阻力,因此高凝原油低温集输多相流流型研究对原油安全集输及节能降耗有至关重要的意义。课题组在大庆油田现场,进行环状集输流程改造,以油井产出的油气水混合物为试验介质,在内径为67mm的水平管内,通过目测及摄影法等研究手段,进行了高凝原油低温集输多相流流型试验研究。试验原油凝点为38℃,试验环路掺水量1.5m3/h,含水质量分数84.6%,油相折算速度0.02m/s,水相折算速度0.13m/s,气相折算速度0.048m/s,实验温度为35.6~43.3℃。试验研究结果表明,在试验参数范围内,油气水多相流流型划分为分层流、油柱管芯流、满管油柱间断流三种。与温度高于原油凝固点时油气水多相流流型相比,输送温度在原油凝固点以下时,油气水三相流流型有较大差异。 相似文献
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首次实验研究了制冷剂R134a在三维微肋螺旋管内流动沸腾环状流区的流动与传热性能。对流型的可视化观察发现:当质量流速大于100kg/(m^2s)时。螺旋管内才开始出现环状流。环状流的起始干度为0.3、0.4。在流型图上给出了环状流区与其它主要流型的分区。回归了实验环状流区的传热实验数据,得到的传热关联武计算值与实验值的平均绝对误差为9.1%。 相似文献
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利用高速摄像仪采集了节距比分别为1.3和1.8,排序为10排×4列和10排×6列两种管束间的不同流型的流动图像,并针对泡状流、间歇流、雾状流三种典型流动图像,提取流型图像的信息熵序列,采用递归分析法研究了气液两相流不同流型以及过渡流型熵序列的动力学特性。研究结果表明:不同流型图像的熵序列的递归结构不同。泡状流图像的信息熵序列递归图为点状结构;间歇流为点和块相结合结构,而雾状流对角线结构最清晰。过渡流型图像的熵序列递归结构清晰的演化了流型转变过程。信息熵序列的递归结构图能够较好地反映流型演化机理,且递归特征量随气相折算流速变化敏感,为研究气液两相流流型机理提供了一种较有效方法。 相似文献
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为了研究常用湍流模型对轴流压气机转子叶尖泄漏流的预测能力,对某低速轴流压气机进行了实验研究及数值模拟,对比分析了不同湍流模型预测的转子叶尖泄漏流的流场分布、旋涡特性以及堵塞特性与实验结果的异同。结果表明:对于转子叶尖泄漏流的旋涡特性,在近失速点,k-ω模型预测的转子叶尖泄漏涡轨迹的斜率和位置在周向上的分布以及泄漏涡涡核的面积与实验结果最接近;对于转子叶尖泄漏流堵塞特性,在堵塞系数达到峰值之前,BSL模型的预测结果与实验结果最相近,而在堵塞系数达到峰值之后k-ε模型的预测结果与实验结果最相近,虽然k-ω模型预测的堵塞系数在整个流向位置都偏高,但堵塞系数沿流向的分布规律与实验结果吻合最好。 相似文献
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《International Journal of Hydrogen Energy》2023,48(19):7058-7071
Liquid hydrogen phase transition is a common phenomenon in space missions for space vehicles using low temperature liquid hydrogen as propellant. In this study, a numerical model with coupled RANS solver and VOF/Level-set method was used to simulate the liquid hydrogen phase transition in a non-isothermal horizontal circular tube under different gravity conditions (1g-10?4 g). The gas phase hydrogen produced by evaporation of liquid hydrogen was calculated by Lee model. The statistics of the overall volume, heat flux, mass flow rate, mean velocity of gas phase hydrogen was carried out. The data results shown that the flow fluctuations were strongest under the gravity acceleration of 10?1 g relative to other gravity conditions. The average bubble volume at 10?1 g was the smallest, which was 11.58% smaller than that at 10?3 g condition. The intermittent contact with the tube wall, which leaded to intermittent long bubble and flow resistance, was the main reason. 相似文献
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水平三维内微肋管在局部蒸干区的沸腾换热及其关联式 总被引:2,自引:1,他引:2
为了得到不同流型下的换热性能 ,以 R1 3 4a为实验工质在一种水平三维内微肋管内进行了流动沸腾换热实验研究 ,通过可视化等措施对得到的主要流型及其转换曲线表示在 G-x图上。对局部蒸干区的沸腾换热特点进行了讨论 ,并根据此区域换热的特点 ,沿周向管壁分成两个部分 ,即 :蒸干部分和非蒸干部分。对于非蒸干部分又分为淹没微肋的底部液体 ,且认为同环状流换热机理相同 ,而另一部分认为液休带领在沟槽中 ,从而得到了此区域的换热实验关联式 ,此换热关联式与实验值的最大偏差在± 1 6%以内 相似文献
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换热器各流路对壳侧气液两相流动特性的影响 总被引:2,自引:1,他引:1
针对工业中广泛应用的管壳式换热器,应用空气-水两相混合物实验研究了壳侧旁路,泄漏流对气液两相流体流动特性的影响,以Ishihara两相流动模型为基础,建立了以横掠管束的主流路为基础的错流区通用两相压降计算关联式,通过错流区,泄漏流的分相流动模型,分析计算了主流路,旁路,泄漏流中气液分布,也分析了泄漏流对壳侧单相,两相总流量在各个分流路的流量分配影响,研究表明,主流路和旁路中气液各自占相应总流量的比例在不同的流型下明显不同,且比例值的波动范围较大,气液流量的分布在壳侧是不均匀的,折流板/换热管之间的泄漏流对壳侧的两相流动特性影响较小,而折流板/壳体之间的泄漏流影响较大。 相似文献
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Wenzhi Cui Longjian Li Mingdao Xin Tien-Chien Jen Quan Liao Qinghua Chen 《International Journal of Heat and Mass Transfer》2008,51(1-2):169-175
In this paper, flow patterns and their transitions for refrigerant R134a boiling in a microfinned helically coiled tube are experimentally observed and analyzed. All the flow patterns occurred in the test can be divided into three dominant regimes, i.e., stratified-wavy flow, intermittent flow and annular flow. Experimental data are plotted in two kinds of flow maps, i.e., Taitel and Dukler flow map and mass flux versus vapor quality flow map. The transitions between various flow regimes and the differences from that in smooth straight tube have also been discussed. Martinelli parameter can be used to indicate the transition from intermittent flow to annular flow. The transition from stratified-wavy flow to annular or intermittent flow is identified in the vapor quality versus mass flux flow map. The flow regime is always in stratified-wavy flow for a mass flux less than 100 kg/m2 s.The two-phase frictional pressure drop characteristics in the test tube are also experimentally studied. The two-phase frictional multiplier data can be well correlated by Lockhart–Martinelli parameter. Considering the corresponding flow regimes, i.e., stratified and annular flow, two frictional pressure drop correlations are proposed, and show a good agreement with the respective experimental data. 相似文献
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The two-phase flow patterns of HFC-134a with lubricant oil mixtures inside a smooth horizontal tube were experimentally elucidated. Tests were performed in an inside diameter of 7.8 mm having a lubricating oil concentration of 5%. Tests were made of mass fluxes ranging between 150 and 590 kg/m 2 s. The most obvious difference from oil-free cases reported is the presence of froth flow pattern. Apparently, this flow pattern is related to the increase of surface tension and viscosity. With the presence of lubricant oil, the onset of transition from stratified flow region to annular flow regime shifted to a lower value of superficial gas velocity. In addition, the tearing phenomenon of the refrigerant-oil mixtures may be related to its relevant properties such as wettability and surface tension. 相似文献
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为了研究喷动流化床煤部分气化炉的气-固流动特性,采用三维欧拉多相流模型和颗粒动能理论相结合的数学模型,对一台直径100 mm的喷动流化床试验台进行了数值模拟研究.研究内容包括喷动流化床不同工况下内部射流的发展、气-固流动特性、典型工况下气体速度分布、颗粒速度分布以及由于颗粒碰撞引起的颗粒相压力分布.模拟结果表明:典型工况下,当喷动风与总风的比例为50%时,流场有利于煤气化;气体曳力和颗粒碰撞对环形区颗粒特别是靠墙区颗粒的运动影响很大.为了验证模型的合理性,采用文献中的试验工况进行计算,计算结果和文献中的测量值吻合较好. 相似文献
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H. Canière B. Bauwens C. T’Joen M. De Paepe 《International Journal of Heat and Mass Transfer》2010,53(23-24):5298-5307
A capacitive void fraction sensor was developed to study the objectivity in flow pattern mapping of horizontal refrigerant two-phase flow in macroscale tubes. Sensor signals were gathered with R410A and R134a in a smooth tube with an inner diameter of 8 mm at a saturation temperature of 15 °C in the mass velocity range of 200–500 kg/m2 s and vapour quality range from 0 to 1 in steps of 0.025. A visual classification based on high speed camera images is made for comparison reasons. A statistical analysis of the sensor signals shows that the average, the variance and a high frequency contribution parameter are suitable for flow regime classification into slug flow, intermittent flow and annular flow by using the fuzzy c-means clustering algorithm. This soft-clustering algorithm predicts the slug/intermittent flow transition very well compared to our visual observations. The intermittent/annular flow transition is found at slightly higher vapour qualities for R410A compared to the prediction of Barbieri et al. (2008) [20]. An excellent agreement was obtained with R134a. This intermittent/annular flow transition is very gradual. A probability approach can therefore better describe such a transition. The membership grades of the cluster algorithm can be interpreted as flow regime probabilities. Probabilistic flow pattern maps are presented for R410A and R134a in an 8 mm ID tube. 相似文献