Experimental study on the condensation of sonic steam in the underwater environment

Zhaoming Meng,Wei Zhang,Jiazhi Liu,Ruihao Yan,Geyu Shen 한국원자력학회 2019 Nuclear Engineering and Technology Vol.51 No.4

Steam jet condensation is of great importance to pressure suppression containment and automaticdepressurization system in nuclear power plant. In this paper, the condensation processes of sonic steamjet in a quiescent subcooled pool are recorded and analyzed, more precise understanding are got in directcontact condensation. Experiments are conducted at atmospheric pressure, and the steam is injected intothe subcooled water pool through a vertical nozzle with the inner diameter of 10 mm, water temperaturein the range of 25e60 C and mass velocity in the range of 320e1080 kg/m2s. Richardson number iscalculated based on the conservation of momentum for single water jet and its values are in the range of0.16e2.67. There is no thermal stratification observed in the water pool. Four condensation regimes areobserved, including condensation oscillation, contraction, expansion-contraction and double expansioncontractionshapes. A condensation regime map is present based on steam mass velocity and watertemperature. The dimensionless steam plume length increase with the increase of steam mass velocityand water temperature, and its values are in the range of 1.4e9.0. Condensation heat transfer coefficientdecreases with the increase of steam mass velocity and water temperature, and its values are in the rangeof 1.44e3.65 MW/m2 C. New more accurate semi-empirical correlations for prediction of the dimensionlesssteam plume length and condensation heat transfer coefficient are proposed respectively. Thediscrepancy of predicted plume length is within ± 10% for present experimental results and ± 25% forprevious researchers. The discrepancy of predicted condensation heat transfer coefficient is with ± 12%.

Heat transfer and flow characteristics of a cooling thimble in a molten salt reactor residual heat removal system

Zonghao Yang,Zhaoming Meng,Changqi Yan,Kailun Chen 한국원자력학회 2017 Nuclear Engineering and Technology Vol.49 No.8

In the passive residual heat removal system of a molten salt reactor, one of the residual heat removalmethods is to use the thimble-type heat transfer elements of the drain salt tank to remove the residualheat of fuel salts. An experimental loop is designed and built with a single heat transfer element toanalyze the heat transfer and flow characteristics. In this research, the influence of the size of a threelayerthimble-type heat transfer element on the heat transfer rate is analyzed. Two methods are usedto obtain the heat transfer rate, and a difference of results between methods is approximately 5%. The gasgap width between the thimble and the bayonet has a large effect on the heat transfer rate. As the gasgap width increases from 1.0 mm to 11.0 mm, the heat transfer rate decreases from 5.2 kW to 1.6 kW. Inaddition, a natural circulation startup process is described in this paper. Finally, flashing natural circulationinstability has been observed in this thimble-type heat transfer element.

Air horizontal jets into quiescent water

Weichao Li,Zhaoming Meng,Jianchuang Sun,Weihua Cai,Yandong Hou Korean Nuclear Society 2023 Nuclear Engineering and Technology Vol.55 No.6

Gas submerged jet is an outstanding thermohydraulic phenomenon in pool scrubbing of fission products during a severe nuclear accident. Experiments were performed on the hydraulic characteristics in the ranges of air mass flux 0.1-1400 kg/m²s and nozzle diameter 10-80 mm. The results showed that the dependence of inlet pressure on the mass flux follows a power law in subsonic jets and a linear law in sonic jets. The effect of nozzle submerged depth was negligible. The isolated bubbling regime, continuous bubbling regime, transition regime, and jetting regime were observed in turn, as the mass flux increased. In the bubbling regime and jetting regime, the air volume fraction distribution was approximately symmetric in space. Themelis model could capture the jet trajectory well. In the transition regime, the air volume fraction distribution loses symmetry due to the bifurcated secondary plume. The Li correlation and Themelis model showed sufficient accuracy for the prediction of jet penetration length.

Development of analysis program for direct containment heating

Jiang Herui,Shen Geyu,Meng Zhaoming,Li Wenzhe,Yan Ruihao 한국원자력학회 2022 Nuclear Engineering and Technology Vol.54 No.8

Direct containment heating (DCH) is one of the potential factors leading to early containment failure. DCH is closely related to safety analysis and containment performance evaluation of nuclear power plants. In this study, a DCH prediction program was developed to analyze the DCH loads of containment vessel. The phenomenological model of debris dispersal, metal oxidation reaction, debris-atmospheric heat transfer and hydrogen jet burn was established. Code assessment was performed by comparing with several separate effect tests and integral effect tests. The comparison between the predicted results and experimental data shows that the program can predict the key parameters such as peak pressure, temperature, and hydrogen production in containment well, and for most comparisons the relative errors can be maintained within 20%. Among them, the prediction uncertainty of hydrogen production is slightly larger. The analysis shows that the main sources of the error are the difference of time scale and the oxidation of cavity debris

Investigation of Characteristics of Passive Heat Removal System Based on the Assembled Heat Transfer Tube

Xiangcheng Wu,Changqi Yan,Zhaoming Meng,Kailun Chen,Shaochuang Song,Zonghao Yang,Jie Yu 한국원자력학회 2016 Nuclear Engineering and Technology Vol.48 No.6

To get an insight into the operating characteristics of the passive residual heat removalsystem of molten salt reactors, a two-phase natural circulation test facility was constructed. The system consists of a boiling loop absorbing the heat from the drain tank, acondensing loop consuming the heat, and a steam drum. A steady-state experiment wascarried out, in which the thimble temperature ranged from 450℃ to 700℃ and the systempressure was controlled at levels below 150 kPa. When reaching a steady state, the systemwas operated under saturated conditions. Some important parameters, including heatpower, system resistance, and water level in the steam drum and water tank wereinvestigated. The experimental results showed that the natural circulation system isfeasible in removing the decay heat, even though some fluctuations may occur in theoperation. The uneven temperature distribution in the water tank may be inevitablebecause convection occurs on the outside of the condensing tube besides boiling withdecreasing the decay power. The instabilities in the natural circulation loop are sensitive toheat flux and system resistance rather than the water level in the steam drum and watertank. RELAP5 code shows reasonable results compared with experimental data.

Scaling analysis of the pressure suppression containment test facility for the small pressurized water reactor

Liu, Xinxing,Qi, Xiangjie,Zhang, Nan,Meng, Zhaoming,Sun, Zhongning Korean Nuclear Society 2021 Nuclear Engineering and Technology Vol.53 No.3

The small PWR has been paid more and more attention due to its diversity of application and flexibility in the site selection. However, the large core power density, the small containment space and the rapid accident progress characteristics make it difficult to control the containment pressure like the traditional PWR during the LOCA. The pressure suppression system has been used by the BWR since the early design, which is a suitable technique that can be applied to the small PWR. Since the configuration and operating conditions are different from the BWR, the pressure suppression system should be redesigned for the small PWR. Conducting the experiments on the scale down test facility is a good choice to reproduce the prototypical phenomena in the test facility, which is both economical and reasonable. A systematic scaling method referring to the H2TS method was proposed to determine the geometrical and thermohydraulic parameters of the pressure suppression containment response test facility for the small PWR conceptual design. The containment and the pressure suppression system related thermohydraulic phenomena were analyzed with top-down and bottom-up scaling methods. A set of the scaling criteria were obtained, through which the main parameters of the test facility can be determined.

Liquid entrainment through a large-scale inclined branch pipe on a horizontal main pipe

Gu, Ningxin,Shen, Geyu,Lu, Zhiyuan,Yang, Yuenan,Meng, Zhaoming,Ding, Ming Korean Nuclear Society 2020 Nuclear Engineering and Technology Vol.52 No.6

T-junction structures play an important role in nuclear power plant systems. Research on liquid entrainment is mostly based on small-scale branch pipes (d/D ≤ 0.2) and attention paid to large-scale branch pipes (0.33 < d/D < 1) is insufficient. Accordingly, this study implements a series of experiments on the liquid entrainment of T-junction with different angles (32.2°,47.9°,62.3°,90°) through a large-scale branch (d/D = 0.675). The onset liquid entrainment is related to the gas phase Froude number Fr_g, the dimensionless gas chamber height h_b/d and the branch pipe angle 𝜃. As Fr_g increases, h_b/d also rises. With a constant h_b/d, the onset liquid entrainment changes from droplets entrainment by the gas phase to that by the rising liquid film. The steady-state liquid entrainment is related to w_3g, h/d and 𝜃. With constant w_3g and h/d, the branch quality grows as the branch angle increases. With a certain h/d, the branch quality increases, as the w_3g number increases.

Experiment investigation on flow characteristics of open natural circulation system

Xiangjie Qi,Zichen Zhao,Peng Ai,Peng Chen,Zhongning Sun,Zhaoming Meng 한국원자력학회 2022 Nuclear Engineering and Technology Vol.54 No.5

Experimental research on flow characteristics of open natural circulation system was performed, tofigure out the mechanism of the open natural circulation behaviors. The influence factors, such as theheating power, the inlet subcooled and the level of cooling tank on the flow characteristics of the systemwere examined. It was shown that within the scope of the experimental conditions, there are five flowtypes: single-phase stable flow, flash and geyser coexisting unstable flow, flash stable flow, flash unstableflow, and flash and boiling coexisting unstable flow. The geyser flow in flash and geyser coexisting unstable flow is different from classic geysers flow. The flow oscillation period and amplitude of the formerare more regular, is a newly discovered flow pattern. By drawing the flow instability boundary diagramand sorting out the flow types, it is found that the two-phase unstable flow is mainly characterized byboiling and flash, which determine the behavior of open natural circulation respectively or jointly. Moreover, compared with full liquid level system, non-full liquid level system is more prone to boilingphenomenon, and the range of heat flux density and undercooling degree corresponding to unstableflow is larger

Model of the onset of liquid entrainment in large branch T-junction with the consideration of surface tension

Liu, Ping,Shen, Geyu,Li, Xiaoyu,Gao, Jinchen,Meng, Zhaoming Korean Nuclear Society 2021 Nuclear Engineering and Technology Vol.53 No.3

The T-junction exists widely in industrial engineering, especially in nuclear power plants, which plays an important part in nuclear power reactor thermal-hydraulics. However, the existing prediction models of the liquid entrainment are mainly based on the small branches or small breaks while there are a few researches for large branches (d/D > 0.2). Referring to the classical models about the onset of liquid entrainment of the T-junction, most of previous models regard liquid as ideal working fluid and ignore surface tension. This paper aims to study the effect of surface tension on the liquid entrainment, and develops an improved model based on the reasonable assumption. The establishment of new model employs the methods of force analysis, dimensional analysis. Besides, the dimensionless Weber number is adopted innovatively into the model to show the effect of surface tension. What is more, in order to validate the new model, three kinds of working fluids with different surface tensions are creatively adopted in the experiments: water, silicone oil and ethyl alcohol. The final results show that surface tension has a nonnegligible effect on the onset of liquid entrainment in large branch T-junction. The new model is well matched with the experimental data.