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The interfacial shear stress and liquid film thickness are very important to establish the basic model of annular flow in practical applications. In this paper, the liquid film thickness of annular flow in a narrow vertical rectangular channel with a cross-sectional area of 70 mm × 2 mm was measured based on the PCB liquid film sensor. According to the experimental results, the average liquid film thickness, base film thickness and interfacial friction factor were calculated and analyzed. The experimental results showed that the liquid film thickness was affected by the gas phase velocity and the liquid phase velocity, but the effect of the gas phase velocity on the liquid film thickness decreased gradually with increasing gas phase velocity. Moreover, the interfacial friction factor was obvious affected by the liquid phase velocity at low gas phase velocity, but this influence gradually decreased with increasing gas phase velocity. Existing correlations for above parameters were summarized and evaluated with the current data, and there was a large deviation between the predicted results and the experimental results. Therefore, a new correlation for above parameters was proposed, respectively.

Centrifugal separation is a kind of common technology, which is used in a broad range of applications. And the axial inlet separators using the swirler to generate vortex are caught great attention owing to their compact size, low pressure drop and high separation efficiency. Some axial separators with different light phase outlet designs are introduced and their macroscopic parameters such as separation efficiency and pressure drop are investigated under different flow conditions. In order to figure out the change on flow field at different conditions, a Lagrange method was used to analyze the bubble trajectory inside an axial separator with two light phase outlets. In this paper, the single bubble was injected into the swirl chamber and the motion of the bubble was tracked by a high-speed camera. Besides, separation length defined as a parameter to evaluate the swirl intensity in the pipe was processed by statistical method. The experimental results show that a higher Reynolds number and a larger split ratio lead to a smaller separation length. Additionally, improving the proportion of split ratio of light phase outlet 1 is effective to decrease the separation length.

Entrained droplets play an important role in heat and mass transfer in annular flow, but there are few studies on droplet size of annular flow in narrow rectangular channels. In this paper, we use the HELOS/KR Vario particle size analyzer to measure droplet size of vertically upward annular flow in a narrow rectangular channel. The results show that the Sauter mean diameter of droplets in narrow rectangular channel decreases with increasing gas velocity and increase with the increase of liquid velocity. Meanwhile, the distribution of droplet sizes has two types: single-peaked distribution and double-peaked distribution. Furthermore, we propose a correlation that can predict the droplets Sauter mean diameter of annular flow in a narrow rectangular channel.

The coolant may vaporize in the centrifugal pump to cause cavitation in pool-type nuclear heating reactor. Installing a jetting device at the pump suction port is an effective means of applying jetting technology to solve the problem of preventing cavitation in centrifugal pumps. In this paper, an annular multi-nozzles ejector was designed and an experimental system was constructed to test the actual supercharging performance of the device. When the high-energy fluid at the pump outlet flowed through the device, it was first mixed uniformly in the annular chamber, and then injected through the nozzles to mix with the main flow to increase the pressure of the main flow. The static pressure at the suction port of the pump increased. Accordingly, the available Net Positive Suction Head (NPSHa) of the pump increased. The test was constructed around the total flow flux through the pump invariable and the main loop flow flux invariable two schemes. The results show that when the proportion of the return flow flux was same, the greater the total flow flux through the pump, the higher the pressure increment at the pump suction port; when the proportion of the return flow flux was larger, the difference in the pressure increment corresponding to different total flow fluxes was larger. When the flow flux through the main circuit of the system was same, the pressure increment increased nonlinearly with the increase of the return flow flux. Increasing the return flow flux was beneficial to the supercharging performance of the jetting device.

Fast reactor is the main reactor type of the fourth generation reactors. It has the advantages of good fuel breeding characteristics, strong transmutation ability, high thermal efficiency and good safety. The research of fast reactor is the focus of current advanced reactor. According to the characteristics of fast reactors, the differences between fast reactors and pressurized water reactors in the fuel breeding, transmutation and safety are analyzed in this paper. On this basis, the characteristics of sodium-cooled fast reactors, lead and lead-bismuth eutectic cooled fast reactors and gas-cooled fast reactors are analyzed and their feature differences are compared. According to the basic characteristics of reactor physics, thermal-hydraulics and safety, the characteristics of these fast reactors are analyzed and compared, their respective advantages are given, the technical problems and difficulties are pointed out. The advantages and suitable application fields of these fast reactors are illustrated, the development opportunities and technical challenges are discussed. Some analysis results can provide reference for the research, design and application of advanced nuclear reactors.

Using deionized water as the working fluid, an experimental study on the resistance characteristics of single-phase and two-phase flow under natural circulation conditions is carried out in a 3 × 3 rod bundle channel. For the single-phase flow, the flow regime transition of rod bundle channel is not as obvious as that of conventional channels such as a circular tube. The flow regime transition in the channel is judged by the change trend of drag coefficient and the flow regime division is obtained. The transition Reynolds number from laminar flow to turbulent flow is approximately 800, and the correlations of the single-phase frictional resistance coefficient for different flow regimes are given. The natural circulation and forced circulation conditions have no obvious influence on the flow state transition. For the two-phase flow, under vertical conditions, a new two-phase frictional pressure drop correlation is fitted on the basis of the Chisholm correlation based on the experimental results. Moreover, the experiment for two-phase flow resistance under the inclined conditions are carried out, and the variation of the two-phase resistance with the mass quality is given, and the correlations of the two-phase friction pressure drop based on different inclination angles are proposed.

Oil-water separation plays a serious role in oil exploitation to reduce the production cost. Centrifugal separation is one of the feasible methods due to its large capacity, high separation efficiency and low maintenance cost. Besides, the centrifugal separation equipment can be divided into tangential inlet separators and axial inlet separators. The ones with tangential inlet have received a large number of investigation on structure optimization but some shortcomings limit the further improvement of separation performance. In this paper, an axial separator with multiple-stage separation was introduced and investigated experimentally with water flow rate range from 3 to 7 m3/h and inlet oil fraction below 10%. Additionally, the schedule for Light Phase Outlets (LPOs) was studied experimentally and theoretically to ensure high separation efficiency and low split ratio. The results show that the multiple stage separator can keep high separation performance that the oil concentration in HPO is below 200 ppm while the split ratio ranged from 0.2 to 0.45 within experimental conditions. Besides, the reasonable schedule can lead an obvious drop in split ratio with high separation performance. Additionally, based on the analysis of flow field characteristic, the LPOs positioned in the two sides of the oil core can ensure the discharge of oil droplets in high swirl flow field and the LPO located downstream has better potential to separate small size droplets.

In order to ease the pressure on oil price, the downhole oil–water separation system has been adopted to preseparate the output production. However, both the gravity separator and the conventional ...

Gas–liquid separation is widely used in various fields. And the centrifugal separator has been witnessed as a worldwide popularity owing to its small size and high efficiency. However, the uncertainty of the inlet flow pattern limits the wide application of centrifugal separators. In this paper, a new gas–liquid separator combining gravity separation and centrifugal separation was proposed for complex and unstable two-phase flow. In this study, the performance of the separator under different liquid flow rates with wide gas volume fraction range from 5% to 90% was investigated experimentally, and the phenomena occurred in the separator were also analyzed. The results show that the separator can keep high-efficiency separation in multiple flow patterns as long as the liquid level in the downcomer is at a reasonable position. Meanwhile, the lowest and highest allowed liquid levels were defined and measured by the pressure difference and a ruler. Furthermore, the bubble column in the downcomer was analyzed.

In order to improve the scientificity and rationality of cold chain system design, the plate heat exchanger of a branch of the nuclear power plant cold chain system of nuclear power plants is taken as the research object. Based on the basic principles of optimization design, appropriate optimization calculation algorithms are developed and plate type heat exchangers are developed. The design program of the heat exchanger forms an optimal design analysis tool. Taking a plate heat exchanger as an example, taking its mass, flow resistance on the hot side and flow resistance on the cold side as the optimization objectives, a new hybrid genetic algorithm was used to carry out a multi-objective optimization case analysis. The calculation results show that there is a competitive relationship between the mass of the plate heat exchanger of the nuclear island cold chain system of the nuclear power plant and the flow resistance on the hot and cold sides, and the optimal solution cannot be obtained at the same time. There is a correlation between the flow resistance on the cold side and the flow resistance on the hot side. If the heat exchanger mass is reduced by 6.39%, the flow resistance of the hot side and cold side will increase by 6.55% and 7.71% respectively; if the flow resistance on the hot side and cold side are reduced by 32.22% and respectively 32.01%, its mass will increase by 2.16%; on the premise of keeping the mass of the heat exchanger basically unchanged, the flow resistance on the hot side of the heat exchanger is reduced by 23.84% and at the same time the flow resistance on the cold side is reduced by 19.77%, and the flow resistance on the cold side is reduced by the largest 23.35% and at the same time reduce the flow resistance on the hot side by 12.54%. Therefore, there is a lot of room for optimization in the design of nuclear island cold chain system of nuclear power plant and there are many optimization schemes. The research results can provide reference for the subsequent optimization of nuclear power plant cold chain system design and improve the scientific and economic efficiency of system design.

As a key physical parameter in annular flow, liquid film thickness is crucial to study the behavior characteristics about gas-liquid interface under annular flow conditions. In this study, the narrow rectangular channel is taken as the research object, and air-water were used as the media to conduct annular flow experiments under atmospheric pressure. The cross-sectional area of the narrow rectangular channel is 70mm × 2mm. The PCB liquid film sensor can realize multi-point measurement of liquid film thickness. A total of 10 × 16 measuring points are arranged in rows and columns on the surface of the channel, with a spatial resolution of 4.4mm × 4.4mm and a measurement speed of 1000 frames per second. The results show the fluctuation of liquid film is dominated by the ripple wave at low superficial liquid velocity. The frequency distribution of film thickness becomes sharper because of the increase of gas flow, i.e. the interfacial surface becomes smoother. The liquid film will become thinner with the increase of gas flow, but the effect is reduced when the gas flow reaches a certain value. The liquid film will thicken and the number of disturbance waves will increase as the increase of the liquid flow.

Background In this paper, a new axial separator for liquid-liquid separation composed of two swirlers and two separation chambers was introduced. And the dispersed phase was drained through three Light Phase Outlets (LPOs) while the continuous phase was discharged from Heavy Phase Outlet (HPO). Methods The Mixture model and Reynolds stress model were used to simulate the separation process. And the numerical results including oil distribution, separation efficiency and pressure change have a good agreement with experimental results. The flow characteristic was revealed by numerical simulation. Besides, the effects of volumetric oil fraction and water flowrate were investigated numerically and experimentally. Significant findings The results illustrate that increasing inlet volumetric oil fraction leads to a slight decrease in separation efficiency and a larger pressure change. And the difference between the wall pressure and the central pressure is larger under the lower volumetric oil fraction condition. Additionally, the pressure change and tangential velocity in the separator are proportional to flowrate. Besides, the separation performance at high inlet volumetric oil fraction, various density difference and viscosity of continuous phase conditions was discussed.

Experimental research on a swirl-vane gas–liquid separator has been conducted with the aim to explore its application in downhole gas–water separation systems. With the help of a high-speed camera, the effect of gas content, Reynolds number and flow conditioning elements on the separation performance were investigated. The change of flow pattern will lead to the oscillation of air core inside the separator, which has significant influence on the separation performance. Experimental results show that both the increase of Reynolds number and the arranging of flow conditioning elements can only restrain the oscillation of air core to a certain degree. In addition, according to the evolution of air core, the flow pattern can be divided into: rod air core flow, tadpole-shaped air core flow, oscillating air core flow and swirling annular flow. Compared with the gas–liquid flow pattern map in vertical tube with the same inner diameter, it can be found that the flow pattern of gas–liquid mixture before entering the separator has significant influence on the state of the air core. In the end, the operational envelope limits of the separator were determined experimentally. Due to the effect of flow pattern, the separator is more suitable to be operated at low gas content. This research leads to a better understanding of hydraulic characteristics in this kind of separator.

The molten fuel is first discharged into a drain tank as the molten salt reactor is shut down. Some heat transfer tubes need to be placed in the drain tank accounting for the generation of decay heat by the fission products. The tube of special structure has no need to pass through the entire drain tank. It’s a two-layer assembly where a center tube is inserted in a thimble. A single prototype tube without scaling is studied in this paper. The results show that the absorption ratio by the center tube is approximately unchanged. There is a transition zone in the nucleate boiling region before the linear change of superheat and heat flux. The ONB data was used for the validation of the models and an improved correlation was developed.

Natural circulation two-phase flow characteristics are studied under stable and rolling motion conditions in a rod bundle channel. The mass quality, flow rate and frictional pressure drop variation results with increasing heat flux are given and the effects of system pressure and inlet subcooling are analyzed. The flow rate decline is observed under high mass quality conditions since the frictional pressure drop is large enough. The flow instability characteristics for different stages with increasing heat flux are given. The main reason for the flow instability characteristics variation is that the dominant factor changes from subcooled boiling to the pressure drop oscillation. The experimental results indicate that increasing the system pressure and the inlet resistance of the test section, including moving the compressible volume to a downstream position, can delay the onset of the flow instability. The time-average flow parameters under rolling motion conditions are mainly influenced by the stable mass quality and the rolling parameters. For high stable mass quality conditions, the time-average two-phase flow parameters decrease a little compared to stable results. With the stable mass quality decreasing, the time-average mass quality gradually increases with the rolling frequency. For further lower stable mass quality conditions, the time-average values are even larger than stable values. For the frictional resistance calculation, a few correlations are evaluated and recommended. Additionally, new correlations are fitted for stable and time-average two-phase frictional pressure drop prediction in high mass quality conditions.

Flow resistance characteristics in a 3 × 3 rod bundle channel are investigated under static vertical, inclined and rolling motion conditions. The circulation mode hardly influences the frictional and local resistance and the transition Reynolds number under forced and natural circulation conditions are both around 800. Correlations are proposed to predict the frictional and local resistance coefficients. Under inclined conditions, the friction factors are slightly larger than vertical values due to the radial convection and increase with the inclination angles for the same Reynolds number. Since the flow resistance increases clearly in the laminar regime, a correlation allowing for the inclination angles is proposed to predict the friction factors in the laminar regime under inclined conditions. The spacer grid local resistance is barely influenced by the inclination instead. The natural circulation flowrate and pressure drop fluctuations are quite different from the forced circulation results in previous studies. The amplitude is much larger and no obvious phase difference is observed under natural circulation conditions. The friction factor variation rules are different from the forced circulation results as well. A new correlation is proposed considering the rolling parameters through dimensionless numbers and rolling Reynolds number. It is tested with a mass of experimental data and applicable to friction factors prediction under given conditions.

Natural circulation boiling flow resistance characteristics in a 3 × 3 rod bundle channel are experimentally studied in this paper. In order to achieve a stable two-phase natural circulation flow, the boiling flow phases are identified and measures such as decreasing the inlet fluid subcooling degree and increasing the inlet local resistance are adopted. The ONB during the experiment is determined by the wall temperature drop. The variation of pressure drop components, including the gravity pressure drop, the frictional pressure drop and the acceleration pressure drop, is given. For high mass quality conditions, the mass flow rate is observed declining with the increasing heat flux when the frictional pressure drop and the acceleration pressure drop grow faster than the gravity pressure drop reduction. A few homogeneous flow models and separated flow models for the two-phase frictional pressure drop are compared against experimental results. The homogeneous flow models can well predict the frictional pressure drops for low mass quality conditions and the Duckler model predictions are the most accurate with a mean relative error of 15.7%. In terms of the separated flow models, the Mishima and Sun models predictions are in good agreement with experimental results respectively for low and high mass quality conditions. Based on the Chisholm correlation, a new correlation is fitted by experimental results. The friction factors obtained in single-phase experiments are used to calculate the liquid phase frictional pressure drops. The comparison against experimental results and data from other literatures shows the new correlation can well predict the two-phase frictional pressure drops under given flow conditions.

As two important parameters, the velocity of disturbance wave and the wall shear stress in annular flow are very important to solve the closed equations of the mechanical model for annular flow. In this study, the disturbance wave velocity and wall shear stress of annular flow in a vertical narrow rectangular channel with a cross section of 70 mm × 2 mm were studied. According to the experimental results, it is found that the wave velocity and wall shear stress of disturbance wave increase with increasing gas phase velocity and liquid phase velocity. Also, existing correlations for predicting the velocity of disturbance wave were summarized and evaluated using the current experimental data. A new correlation for wall shear stress based on the disturbance wave velocity has been proposed. Compared with the existing correlation for predicting wall shear stress, this new correlation can well predict the current experimental data and MAPE is only 7.32%.

Gas-liquid separation is widely used in many fields, such as nuclear energy and petroleum resources. And the gas-liquid mixture separated gradually shows the characteristic of wide range of gas void fraction and variable flow patterns. However, the current separators only suit for narrow range of gas void fraction or single flow patterns. In this research, two different new type separators using centrifugal technology were designed and an experimental system was constructed to test the two separators using dry air and water under different flow patterns, including bubble, slug and churn flow. One was called inline separator consisting of three swirls and another was called double-layer cylinder separator composed of a central tube, a swirl and an outer tube. The results show that the separation performance of the inline separator was sensitive to flow patterns and the two-layer cylinder separator keeps high efficiency in different flow patterns. In bubble flow and slug flow patterns, the two separators kept high efficiency, while the oscillation of the gas core in the inline separator aggravated under slug flow condition. When increasing the gas void fraction, the turbulence of the churn flow led to the diameter of the gas core change drastically and reduce separation efficiency significantly.

The steam hammer pressure is solved though the simplified calculation. PIPENET software is applied to model the nuclear island main steam system between the steam generator and the main steam header in HPR 1000. The transient module is used to simulate the occurrence and attenuation process of steam hammer. The maximum steam hammer pressure, the maximum steam hammer stress in the pipe system, when and where the load occurs are given. The influence of the straight pipe section length and valve closing time on the steam hammer effect is analyzed. With the other conditions unchanged, the steam hammer energy decreases as the straight pipe section shortens, or the valve closing time extends.

Video 1 The pitting dynamic process of copper in alkaline chloride electrolyte (Supplementary data)

The Passive Residual Heat Removal System (PRHRS) of Swimming Pool-type Low Temperature Heating Reactor (SPLTHR) runs at low temperature and pressure condition, which is completely different from the PRHRS of other reactors. According to the previous calculation results, an experimental facility with a power of 240 kW was built. Experimental data shows that after PRHRS is running, the temperature of the reactor pool water drops rapidly. The power of PRHR heat exchanger (HX) will gradually stabilize at about 1500 s, and both the pool water temperature and the air temperature have a significant effect on the power. The experimental Nusselt number (Nu) are all bigger than the calculated values of correlations, indicating that these correlations are not applicable to the natural convection outside the PRHR HX tube bundle. After analyzing the 30 groups of natural convection data outside the PRHR HX vertical tube bundle, the fitting correlation is in good agreement with the experimental data, which can provide important reference for engineering applications.