共查询到17条相似文献,搜索用时 140 毫秒
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基于存在自发凝结的湿蒸汽两相流动,开发了基于汽液两相双流体模型和k-ε-k_p湍流模型的计算方法,并对喷管和二维叶栅进行数值验证,结果表明本文所开发的方法具有较高的可靠性。对某汽轮机末级除湿静叶考虑除湿槽结构的二维流场进行了数值研究,指出在叶片表面开设除湿槽结构,能够显著影响涡轮叶栅内的非平衡凝结流动。由于除湿槽对水滴的抽吸作用使得叶栅内成核率峰值降低,且变化幅度减小,因此成核过程更为稳定。除湿槽结构使得叶栅内部大水滴数目减少,尾迹区水滴平均半径减小,叶栅出口湿度下降。 相似文献
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在湿蒸汽汽轮机设计中评估湿蒸汽偏离热力学平衡态的程度及其对透平级几何、气动参数设计的影响具有重要意义。本文发展了湿蒸汽非平衡凝结流动的流线曲率法通流设计程序,对某300 MW汽轮机低压缸六级透平内的流动进行了分析,并与平衡凝结流动流线曲率法程序的计算结果进行了对比。结果表明:与平衡凝结流动相比,非平衡凝结流动中叶栅后的压力、出口汽流角、湿度以及级的反动度和效率发生了明显变化,非平衡凝结流动的效率降低2 08%,功率降低1.05 MW。本文发展的非平衡凝结流动流线曲率法通流设计程序为我国大功率火电汽轮机低压缸和核电汽轮机的通流设计提供了工具。 相似文献
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为准确描述汽轮机级内湿蒸汽凝结流动特性,采用双流体模型结合修正的均质成核和水滴生长模型,实现汽轮机初始成核级叶栅通道内非平衡凝结数值求解。通过焓损失系数与自由能理论进一步分析了进汽参数变化对汽轮机叶栅通道内湿蒸汽自发凝结流动的影响,结果表明:随着过热度的降低,非平衡凝结起始位置提前,非平衡凝结现象更剧烈,凝结产生的液相质量分数增加,热力学损失升高;进口湿度对水滴的生长和蒸发速率非常敏感,对凝结冲击位置有很大的影响;入口湿蒸汽液滴直径越大,阻碍相变的自由能壁垒越低,二次凝结现象越易发生,热力学损失越大,当湿度为0.01的液滴直径超过0.2μm时,均质成核的二次凝结现象逐渐发生;二次成核的临界水滴直径随着湿度的增加而增大。 相似文献
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一维喷管中湿蒸汽非均质凝结流动的研究 总被引:4,自引:2,他引:2
本文研究了湿蒸汽流中的非均质凝结流动现象,建立了自发凝结流动和非均质凝结流动统一的数值模型,并对一维喷管中的非均质凝结流动进行了数值分析。结果表明,蒸汽中杂质微粒浓度是影响非均质凝结流动的主要因素,在微粒浓度达到 10~(13)~10~(14)/kg 后杂质开始对凝结流动产生明显影响;在微粒浓度约为 10~(14)~10~(16)/kg 的范围内,外来凝结核并没有抑制流动热力学不平衡的发展,反而使其程度加深;在微粒浓度大于 10~(17)~10~(18)/kg 的情况下,足够多的外来凝结核充分抑制了非平衡条件下的自发凝结,整个流动过程中蒸汽始终处于平衡态附近。此外,微粒半径等因素对非均质凝结流动也有影响。 相似文献
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建立了考虑摩擦阻力的一维水蒸气超音速流凝结数学模型,对喷管内含有不同初始浓度和半径的外界核心的水蒸气超音速流凝结过程进行了数值计算。结果发现:当外界核心浓度在不同范围内时,外界核心半径对凝结有不同的影响规律;当外界核心半径在不同范围内时,外界核心浓度对凝结也有不同的影响规律;为了促进凝结的发生,要选择匹配的外界核心平均半径和浓度。选定喷管出口的液相质量分数为标准,针对计算的几种情况得出:当外界核心半径为1.0×10~(-9)m,外界核心浓度为1.0×10~(14)kg~(-1)时,对应的喷管出口处的液相质量分数最大。 相似文献
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针对非平衡态外推边界处理方法在某些条件下发生质量泄漏的问题,结合质量守恒定律对其进行修正,建立一种新的质量守恒型的边界处理格式.其基本思想是在边界处定义一个虚拟密度来修正平衡态分布函数,使得系统质量守恒.以重力作用下的密度场及磁流体模拟问题为例,利用该格式进行分析,讨论质量泄露问题的本质及各种因素的影响.通过对三种典型的流动:二维Poiseuille流、Couette流、Womersley流的模拟,验证该边界格式的计算精度和稳定性. 相似文献
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Bin Yang Xiaojing Ma Hailun Zhang Wenxu Sun Lei Jia Haoyuan Xue 《Entropy (Basel, Switzerland)》2022,24(7)
In this study, a wet steam model was used to investigate the effect of steam superheat on ejector performance and non-equilibrium condensation phenomena. The simulation data for the ejector were validated with experimental data. The simulations show that an increase in primary flow superheat will increase the entrainment ratio, while an increase in secondary flow superheat will decrease the entrainment ratio. The output fluid superheat has little effect on the entrainment ratio. As the primary flow superheat increases from 0 to 20 K, the starting position of non-equilibrium condensation moves backward by 5 mm, and the mass fraction of condensed droplets decreases by 20%. The higher the secondary flow superheat, the lower the mass fraction of liquid in the diffusion chamber. The superheat level of the output fluid has no influence on the non-equilibrium condensation phenomenon of the ejector. 相似文献
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低压蒸汽滴状冷凝过程中液滴生长特性 总被引:1,自引:0,他引:1
研究了低压条件对滴状冷凝过程液滴生长特性的影响。首先,研究了超疏水表面上空气环境和蒸汽环境中附着液滴的接触角,发现蒸汽环境中的接触角比空气环境中的小,而蒸汽压力对接触角没有显著影响。第二,实验研究了冷凝过程中的液滴的生长周期和脱落尺寸,液滴的脱落半径随压力的降低而增大,生长周期也随之延长。第三,实验研究了液滴合并生长速率,并结合理论分析直接冷凝长大的生长速率,直接冷凝生长速率随压力的减小而减小,并随过冷度的减小而下降,而实验范围内合并生长速率不受压力影响。第四,根据滴状冷凝液滴分布的时间序列模型,分析了不同压力下液滴生长的临界尺寸,随着压力的降低,液滴生长方式的临界尺寸增大。 相似文献
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Massive droplets can be generated to form two-phase flow in steam turbines, leading to erosion issues to the blades and reduces the reliability of the components. A condensing two-phase flow model was developed to assess the flow structure and loss considering the nonequilibrium condensation phenomenon due to the high expansion behaviour in the transonic flow in linear blade cascades. A novel dehumidification strategy was proposed by introducing turbulent disturbances on the suction side. The results show that the Wilson point of the nonequilibrium condensation process was delayed by increasing the inlet superheated level at the entrance of the blade cascade. With an increase in the inlet superheated level of 25 K, the liquid fraction and condensation loss significantly reduced by 79% and 73%, respectively. The newly designed turbine blades not only remarkably kept the liquid phase region away from the blade walls but also significantly reduced 28.1% averaged liquid fraction and 47.5% condensation loss compared to the original geometry. The results provide an insight to understand the formation and evaporation of the condensed droplets inside steam turbines. 相似文献
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汽轮机湿蒸汽级中凝结流动的三维数值分析 总被引:1,自引:0,他引:1
对一台凝汽式汽轮机低压末三级中的湿蒸汽自发凝结流动进行了三维数值分析,并与忽略自发凝结影响的流动计算结果进行了比较。结果表明,自发凝结流动中,湿蒸汽级组内焓降在各级之间的分配、各级反动度、级的工作压力范围、叶栅出口气流角和出口气流速度发生明显变化。各湿蒸汽级处于“变工况”运行状态,部分湿蒸汽级内流动状况显著变差,并导致叶片强度与振动方面安全性降低。除非平衡凝结损失外,凝结导致湿蒸汽透平级“变工况”运行是湿蒸汽级效率降低的重要原因。 相似文献
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基于液滴的转移方法可实现微操作任务中微对象的拾取,锥形操作探针则常作为一种毛细力微操作执行工具。主要研究在空气冷凝模式下锥形探针端面的液滴形成。建立了微液滴形成的数学模型,主要包括初始液滴的形成、液滴的合并和液滴的移动,研究了影响操作液滴的关键参数,分析表明:过冷度决定最小液滴半径。对单液滴的生长机制进行理论分析,并通过数值求解的方法模拟了锥形操作探针端面的液滴形成。搭建实验测试平台,实验研究了微尺度下锥形微操作探针端面的液滴形成。实验结果表明:在空气冷凝模式下,操作探针端面能够形成微液滴。经过初始液滴的形成,液滴的合并和移动等过程最终可形成稳定的微液滴,且不同锥顶角下液滴的形成呈现多样化。 相似文献
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Yiqiao Li Chao Niu Shengqiang Shen Xingsen Mu Liuyang Zhang 《Entropy (Basel, Switzerland)》2022,24(9)
Scholars usually ignore the non-equilibrium condensing effects in turbulence-model comparative studies on supersonic steam ejectors. In this study, a non-equilibrium condensation model considering real physical properties was coupled respectively with seven turbulence models. They are the k-ε Standard, k-ε RNG, k-ε Realizable, k-ω Standard, k-ω SST, Transition SST, and Linear Reynolds Stress Model. Simulation results were compared with the experiment results globally and locally. The complex flow phenomena in the steam ejector captured by different models, including shock waves, choking, non-equilibrium condensation, boundary layer separation, and vortices were discussed. The reasons for the differences in simulation results were explained and compared. The relationship between ejector performance and local flow phenomena was illustrated. The novelty lies in the conclusions that consider the non-equilibrium condensing effects. Results show that the number and type of shock waves predicted by different turbulence models are different. Non-equilibrium condensation and boundary layer separation regions obtained by various turbulence models are different. Comparing the ejector performance and the complex flow phenomena with the experimental results, the k-ω SST model is proposed to simulate supersonic steam ejectors. 相似文献