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Featured Application: Thermal hydraulics related to hydrogen safety in a nuclear reactor containment can be simulated by the 3D CFD code with validated steam condensation and hydrogen recombination models. In a pressurized water reactor (PWR) during a loss of coolant accident (LOCA) or a station blackout (SBO) accident, water and steam are released into the containment building. The water vapor mixes with the atmosphere, partially condensing into droplets or condensing on the containment walls. Although a significant amount of water vapor condenses, it coexists with hydrogen generated by the reactor core oxidation. As water vapor condenses, the volume fraction of hydrogen increases, raising the risk of explosion or flame acceleration. As such, water vapor's behavior directly affects hydrogen distribution. To conservatively evaluate hydrogen safety in a PWR during a severe accident, lumped-parameter codes have been heavily used. As a best-estimate approach for hydrogen safety analysis in a PWR containment, a turbulence-resolved CFD code called contain3D has been developed. This paper presents the validation results of the code and simulation results of hydrogen behavior affected by water vapor condensation and hydrogen removal by passive autocatalytic recombiners (PARs) in the APR1400 containment. The results provide insight into the three-dimensional behaviors of the hydrogen in the containment. [ABSTRACT FROM AUTHOR]

Copyright of Experimental Technology & Management is the property of Experimental Technology & Management Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The application of a two-phase ejector allows for the mixing of liquid and gas and provides effective heat transfer between phases. The aim of the study is a numerical investigation of the performance of a water-driven, condensing two-phase ejector. The research was performed using CFD methods, which can provide an opportunity to analyze this complex phenomenon in 2D or 3D. The 2D axisymmetric model was developed using CFD software Siemens StarCCM+ 2022.1.1. The Reynolds-Averaged Navier–Stokes (RANS) approach with the Realisable k-ε turbulence model was applied. The multiphase flow was calculated using the mixture model. The boiling/condensation model, where the condensation rate is limited by thermal diffusion, was applied to take into account direct contact condensation. Based on the mass balance calculations and developed pressure and steam volume fraction distributions, the ejector performance was analyzed for various boundary conditions. The influence of the suction pressure (range between 0.812 and 0.90) and the steam mass flow rate (range between 10 g/s and 25 g/s) is presented to investigate the steam condensation phenomenon inside the ejector condenser. The provided mixture of inert gas (CO2) with steam (H2O) in the ejector condenser was investigated also. The weakening of the steam condensation process by adding CO2 gas was observed, but it is still possible to achieve effective condensation despite the presence of inert gas. [ABSTRACT FROM AUTHOR]

Advanced Pressurized Water Reactors (APWRs) and Boiling Water Reactors (BWRs) employ a suppression pool as a heat sink to prevent containment overpressure. Steam can be discharged into the pool through multi-hole spargers or blowdown pipes in both normal and accident conditions. Direct Contact Condensation (DCC) creates sources of momentum and heat. The competition between these two sources determines the development of thermal stratification or mixing of the pool. Thermal stratification is of safety concern as it reduces the cooling capability compared to a completely mixed pool condition. In this work we develop a scaling approach to prediction of the thermal stratification in a water pool induced by steam injection through spargers. Experimental data obtained from large-scale pool tests conducted in the PPOOLEX and PANDA facilities, as well as simulation results obtained using validated codes are used to develop the scaling. Two injection orientations, namely radial injection through multi-hole Sparger Head (SH) and vertical injection through Load Reduction Ring (LRR), are considered. We show that the erosion rate of the cold layer can be estimated using the Richardson number. In this work, scaling laws are proposed to estimate both the (i) transient erosion velocity and (ii) the stable position of the thermocline. These scaling laws are then implemented into a 1D model to simulate the thermal behavior of the pool during steam injection through the sparger.

In a pressurized water reactor (PWR) during a loss of coolant accident (LOCA) or a station blackout (SBO) accident, water and steam are released into the containment building. The water vapor mixes with the atmosphere, partially condensing into droplets or condensing on the containment walls. Although a significant amount of water vapor condenses, it coexists with hydrogen generated by the reactor core oxidation. As water vapor condenses, the volume fraction of hydrogen increases, raising the risk of explosion or flame acceleration. As such, water vapor’s behavior directly affects hydrogen distribution. To conservatively evaluate hydrogen safety in a PWR during a severe accident, lumped-parameter codes have been heavily used. As a best-estimate approach for hydrogen safety analysis in a PWR containment, a turbulence-resolved CFD code called contain3D has been developed. This paper presents the validation results of the code and simulation results of hydrogen behavior affected by water vapor condensation and hydrogen removal by passive autocatalytic recombiners (PARs) in the APR1400 containment. The results provide insight into the three-dimensional behaviors of the hydrogen in the containment.

The condensation heat transfer coefficient of the multi-channel dryer, one of the key component of paper-making machine, directly determines the efficiency of heat energy utilization. However, the prediction of condensation heat transfer coefficient remains a challenge because the heat transfer characteristics in multi-channel dryer is a complex fundamental issue involving the thermal behavior of two-phase fluid systems. Herein, we successfully developed the four supervised machine learning models to predict the heat transfer coefficient of a multi-channel cylinder dryer under different working conditions. The multi-channel cylinder dryer experiments under different steam mass flux and cooling water mass flow rates were performed and the measured data is used as the input data for training. Interestingly, the four trained Bayesian-optimized machine models present the excellent capability of prediction for condensation heat transfer coefficient of multi-channel cylinder dryer, where the values of R2 for tested Bayesian-optimized-based SVR, ANN, linear SVR, and RF are 0.983, 0.997, 0.996, and 0.953, respectively. In addition, the feature importance of descriptors is quantified based on a random forest algorithm. Our study suggests that machine learning models can effectively predict the condensate heat transfer coefficient of two-phase fluid systems, which not only would be beneficial to optimizing the structures and operation parameters of multi-channel cylinder dryer in the industry but to develop a reasonable correlation of heat transfer coefficient in fundamental research. [ABSTRACT FROM AUTHOR]

One of the well-known technologies that fit well into the goal of reduction of greenhouse gas emissions is nuclear energy. In particular, the change in approach to the design and construction of nuclear power plants led to the development of small modular reactors (SMRs), which are characterized by a broader range of possible applications than large nuclear reactors and the ability to flexibly operate as per load demand. This paper presents an analysis of the thermal loads of a steam turbine rotor operating in a power plant with SMR. Steam-water cycle and turbine train of a 300 MW unit are presented. High-pressure steam turbine rotor and its thermal loading due to varying steam conditions are investigated for a cold startup designed with consideration of the thermal characteristics of nuclear reactors. It was shown by numerical simulations that steam condensation on rotor surfaces plays a crucial role in determining its thermal behaviour. Comparison with conventional rotors has shown that the thermal loading of nuclear turbine rotors is lower and more stable than that of conventional turbines. [ABSTRACT FROM AUTHOR]

Artificial neural network (ANN) methods have been gradually used in the field of nuclear reactor thermal-hydraulics as new methods to improve accuracy or fast prediction. This study establishes a back propagation (BP) neural network model based on the ANN methods to predict the steam condensation heat transfer coefficient outside a heat tube in the presence of air. The main factors affecting condensing heat transfer, such as pressure, air mass fraction, subcooling, and tube diameter, are used as input quantities, and the condensation heat transfer coefficient is used as output quantity. A complete set of neural networks for predicting the heat transfer coefficient for steam condensation in the presence of air is established based on the relevant experimental data collected over the world. The results predicted by the ANN model are compared with the experimental data and those of traditional correlation methods. The data from 2276 experiments are distributed within a ±10% error band at the 95% confidence level. This means that the prediction accuracy of the ANN model is higher than that of the traditional experimental correlation. Therefore, the neural network model developed in this study can be used for the prediction of the heat transfer coefficient for steam condensation in the presence of air.

The application of a two-phase ejector allows for the mixing of liquid and gas and provides effective heat transfer between phases. The aim of the study is a numerical investigation of the performance of a water-driven, condensing two-phase ejector. The research was performed using CFD methods, which can provide an opportunity to analyze this complex phenomenon in 2D or 3D. The 2D axisymmetric model was developed using CFD software Siemens StarCCM+ 2022.1.1. The Reynolds-Averaged Navier–Stokes (RANS) approach with the Realisable k-ε turbulence model was applied. The multiphase flow was calculated using the mixture model. The boiling/condensation model, where the condensation rate is limited by thermal diffusion, was applied to take into account direct contact condensation. Based on the mass balance calculations and developed pressure and steam volume fraction distributions, the ejector performance was analyzed for various boundary conditions. The influence of the suction pressure (range between 0.812 and 0.90) and the steam mass flow rate (range between 10 g/s and 25 g/s) is presented to investigate the steam condensation phenomenon inside the ejector condenser. The provided mixture of inert gas (CO2) with steam (H2O) in the ejector condenser was investigated also. The weakening of the steam condensation process by adding CO2 gas was observed, but it is still possible to achieve effective condensation despite the presence of inert gas.

Additional thermal resistance caused by fouling gathered on the heat transfer surfaces of condensers and regenerative heat exchangers within steam power plants most often results in heat transfer process deterioration. It manifests itself, among others, in a reduction in the heat power of a given heat exchanger and in an increase in the working pressure on the steam side. Moreover, the gathered deposits sometimes create irregularities with a diverse geometric structure, hence the description of the steam condensation process is not always clear in interpretation due to the coexistence of many phenomena at the same time. The paper presents selected theoretical issues regarding the presence of sediments on heat transfer surfaces as well as it shows the results of own experimental research on heat transfer within the steam condensation on a single pipe covered with sediments derived from the heat exchange apparatus of a steam power plant.

Steam condensation plays an important role in various engineering processes due to its excellent heat transfer performance. However, condensation in the presence of noncondensable gas has attracted great attention in recent years since noncondensable gas will have a negative effect on condensation heat transfer. The present study proposes a comprehensive model coupled with convective heat transfer, liquid film heat transfer and steam condensation for the heat transfer of condensation with noncondensable gas and uses it in the Program Integrated for Severe Accident Analysis (PISAA) for a nuclear power plant. The condensation heat transfer model has good universality, the calculation process is stable with less iteration and a fast convergence and it is verified and validated by comparing the simulation results of the PISAA and those from traditional containment analysis codes, as well the experiments from the Wisconsin condensation tests; then, a sensitivity analysis for the parameters of the heat transfer coefficient is performed. The validation results show that the average error of the condensation heat transfer coefficient is approximately 10%, and the maximum error does not exceed 30%. The deviation from the experimental data is limited in the acceptable range, which could fulfill the requirement for the analysis of containment accidents in nuclear power plants. [ABSTRACT FROM AUTHOR]

At present, hydrodynamic models do not allow simulation of local effects of thermal fields with sufficient accuracy, and integral models do not take into account the steam mass fraction in the heat transfer fluid. The purpose of this work is the analysis of the influence of thermophysical parameters of the reservoir and fluid on the optimal times of stages of cyclic steam stimulation of the reservoir and of additional maximum cumulative oil recovery. For the first time, an integral mode has been developed for cyclic steam stimulation, accounting for the steam mass fraction in the heat transfer fluid and the equation of state for water. The model is based on the use of heat balance relationships for each type of cyclic steam stimulation. The steam temperature in the production interval, the initial reservoir temperature, and the heat flux are determined by the data from short-term dynamic temperature studies. The oil flow rate is determined by the Dupuis formula for a zone-heterogeneous reservoir. Optimal times for cyclic steam stimulation stages and the maximum cumulative oil recovery have been determined. It is shown that the optimal time of the heat transfer fluid injection to the reservoir and the time of steam soak for the well increase with increase in the reservoir thickness, the heat transfer fluid flow rate, and the steam mass fraction in it. Limits have been identified to the applicability of cyclic steam stimulation in terms of the heat transfer fluid flow rate. [ABSTRACT FROM AUTHOR]

Concave-convex plate heat exchanger is a new type of high efficiency heat transfer equipment, its enhanced heat transfer effect lies in its plate structure. In view of the incorporation of non-condensable gas will also affect the condensing heat transfer effect of steam in the heat exchanger, so the condensation characteristics of steam containing non-condensable gas in concave-convex plate heat exchanger are studied by numerical simulation. The control variable method is used to study the influence of non-condensable gas content, height, spacing and angle of concave-convex plate heat exchanger on condensing heat transfer through numerical simulation. The simulation results show that when the content increases from 0 to 30%, and the mass fraction of steam condensate water decreases by 41.05%. By analyzing the influence of different concave-convex plate parameters on the condensation heat transfer in heat exchanger, it is found that the mass fraction of steam condensate water increases with the distance between concave-convex platforms, and the angle of concave-convex platform decreases, and it increases first and then decreases with the height of concave-convex platforms. When the distance between concave-convex plate is 1.3 mm, the height of concave-convex plate is 4 mm, and the angle between concave-convex plate is 130°, the concave convex plate heat exchanger has the best heat transfer effect. [ABSTRACT FROM AUTHOR]

During a severe accident in nuclear power plant, if passive containment cooling system fails and other pressure relief measures are also useless, the mixed gas in containment can be injected into the spent fuel pool via a injector to reduce the risk of containment overpressure failure and the release of radioactivity to the environment. A aerosol pool scrubbing facility was built to study the factors influencing the effect of aerosol pool scrubbing under the injector. This facility can perform a great variation of experiments using various measurement tools. The aerosol concentration and particle size were monitored by using the spectrometer with a 20% measurement error. TiO2 powder was used as a stimulant for the aerosols in containment, and the mass median diameter ranged from 0.5 to 1.5 μm, the geometric standard deviation ranged from 1.63 to 2.15. According to the different characteristics of gas-liquid hydrodynamic behavior, the pool scrubbing process can be divided into two regions, including injection and rise zones. In the injection zone, with the flow flux increase, the gas regime changed from bubble (We

The purpose of this Commentary is to clarify as much as possible the whole history of reactor and containment pressure changes in the Fukushima meltdown accident. It is based on a new approach for film boiling, which is kept after the Zr-H2O reactions. Most important point of this approach is that the author applied film boiling based on boiling curve, which is basic theory in boiling phenomena, for the Fukushima accident phenomena. As the reaction rate is proportional to the reactor or containment pressure under film boiling, it increases rapidly and stops suddenly, keeping the film boiling. The containment pressure change consists of three phases, namely pressurizing, keeping the high pressure and de-pressurizing. The containment is pressurized by H2 gas and steam produced by the Zr-H2O reactions and de-pressurized by a heatsink such as the containment wall and inner shield concrete after reaction stops. The high pressure between these pressure changes is kept by balancing the H2 gas produced by reaction with the leaked gas from the gap between the top lid and the containment. Core decay heat is large, but its change is negligibly small. So, the pressurization is calculated from H2 gas and steam produced by the Zr- H2O reactions. The heatsink balances with the reaction during the high pressure condition. The de-pressurization occurs after the reaction is over, so the reaction heat rate can be calculated by the heat rate of the heatsink, which is equal to the condensation rate during de-pressurization. The leak rate of the leak gas can be calculated using the reaction rate. It is very important that the rection rate is slowed by the insufficient steam supply, as the melted reactor cores in the Fukushima accident were covered with H2 gas and steam (film boiling) at 0.8MPa or lower pressure. This is different from the rate (at approx. 7MPa) in the Three Mile Island accident, as the steam specific volume at 0.8 MPa is ten times larger than that at 7 MPa. The calculation results based on this assumption show that almost all the Zr in each core of Units 1, 2 and 3 reacted with water. [ABSTRACT FROM AUTHOR]

Copyright of Atomic Energy Science & Technology is the property of Editorial Board of Atomic Energy Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

THE PURPOSE. To evaluate the effect on the condensation process of contaminants contained in the steam and deposited on the surface of the cooled fins, for which to formulate a mathematical model of the process, to investigate its properties and to obtain quantitative estimates of the characteristics.METHODS. The equations of the mathematical model are based on the laws of conservation of energy and mass, their study and evaluation are carried out using analytical methods of the theory of differential equations, methods of similarity theory and dimensions, as well as numerical methods for solving boundary value problems.RESULTS. The formulation of the problem of condensation of vapor containing solid particles on the edge is formulated. The presence of a self-similar solution is revealed, which is represented as a dimensionless function of one variable, uniform for all sets of initial parameters. The relations describing the distributions of the thickness δ(x, τ) of the sediment and the temperature ϑ(x, τ) on a straight edge of unlimited height (l = ∞) with an initially clean surface (h0 = 0) are obtained. These relations also almost accurately describe the initial stage of such a process on a straight edge of a finite height l, until a sediment of noticeable thickness covers the entire surface of the rib, as well as the initial moments in the case of an edge on a round pipe, until the width of the sediment zone with a noticeable thickness is significantly less than the radius of the pipe.CONCLUSION. Using these distributions as the initial ones for edges of limited height instead of, for example, introducing a uniform initial layer h0, will allow achieving high accuracy of numerical calculations without excessive thickening of the grid in coordinate and time.

The thermo-hydraulic characteristics of steam condensation in the presence of air inside smooth tube and corrugated tube with different sinusoidal corrugations are numerically studied. A wall condensation model is applied to predict the steam condensation with air in the corrugated tube. The effects of structural parameters and inlet velocity on the condensation heat transfer and flow are discussed. It is found that the enhancement of condensation heat transfer is caused by the gas impingement on the downstream side of the waveform domain and the strong disturbance of air concentration boundary layer due to the detached vortex. Moreover, the average heat transfer coefficient of the corrugated tube with inward sinusoidal corrugation (ISCT) is the highest, while the pressure drop of the corrugated tube with outward sinusoidal corrugation (OSCT) is the lowest. The impact of amplitude (A) on the thermal performance factor (TPF) is much higher compared to that of the wavelength (L). When the inlet velocity (v) is lower than 2 m/s, ISCT with A = 2 mm and L = 21 mm shows the highest TPF of 1.291; when v > 2 m/s, OSCT with A = 1.5 mm and L = 21 mm at v = 5 m/s demonstrates the largest TPF of 1.15. [ABSTRACT FROM AUTHOR]

For the Korean design of the PCCS (passive containment cooling system) in an innovative PWR, the overall thermal resistance around a condenser tube is dominated by the heat transfer coefficient of steam condensation on the exterior surface. It has been reported, however, that the calculated heat transfer coefficients by thermal-hydraulic system codes were much lower than measured data in separate effect tests. In this study, a new empirical model of steam condensation in the presence of a noncondensable gas was implemented into the MARS-KS 1.4 code to replace the conventional Colburn-Hougen model. The selected correlation had been developed from condensation test data obtained at the JERICHO (JNU Experimental Rig for Investigation of Condensation Heat transfer On tube) facility, and considered the effect of the Grashof number for naturally circulating gas mixture and the curvature of the condenser tube. The modified MARS-KS code was applied to simulate the transient response of the containment equipped with the PCCS to the large-break loss-of-coolant accident. The heat removal performances of the PCCS and corresponding evolution of the containment pressure were compared to those calculated via the original model. Various thermal-hydraulic parameters associated with the natural circulation operation through the heat transport circuit were also investigated.

Steam condensation plays an important role in various engineering processes due to its excellent heat transfer performance. However, condensation in the presence of noncondensable gas has attracted great attention in recent years since noncondensable gas will have a negative effect on condensation heat transfer. The present study proposes a comprehensive model coupled with convective heat transfer, liquid film heat transfer and steam condensation for the heat transfer of condensation with noncondensable gas and uses it in the Program Integrated for Severe Accident Analysis (PISAA) for a nuclear power plant. The condensation heat transfer model has good universality, the calculation process is stable with less iteration and a fast convergence and it is verified and validated by comparing the simulation results of the PISAA and those from traditional containment analysis codes, as well the experiments from the Wisconsin condensation tests; then, a sensitivity analysis for the parameters of the heat transfer coefficient is performed. The validation results show that the average error of the condensation heat transfer coefficient is approximately 10%, and the maximum error does not exceed 30%. The deviation from the experimental data is limited in the acceptable range, which could fulfill the requirement for the analysis of containment accidents in nuclear power plants.

Copyright of China Pulp & Paper is the property of China Pulp & Paper Magazines Publisher and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

• Assessments and evaluation of numerical model of steam condensation with non-condensable gases were carried out based on OpenFOAM. • A new correction of suction effect was proposed with consideration of suction region and surface curvature. • Validation based on TOSQAN, COAST, Su and Dehbi's facility was carried out with previous and new suction corrections. • Validation results of the new correction showed good agreement with experimental results with different curvatures. Steam condensation with non-condensable gases is one of the most important phenomena in containment of nuclear power plant (NPP) after accidents. With the application of passive containment cooling system (PCCS), steam is condensed on surfaces with different curvatures of PCCS and structures. Previous investigations indicated the need for suction corrections in the diffusion boundary layer model of steam condensation in the presence of non-condensable gases. By implanting different suction effect corrections in OpenFOAM, this study found that existing suction effect corrections cannot make good predictions for steam condensation with non-condensable gases on varied curvature surfaces, which resulted from cases lack of diversity. Thus, a new correction was proposed based on Gasthof number and previously corrections. This correction was validated by data sets from TOSQAN, COAST, Dehbi and Su's facilities. The relative deviations of 90.0 % simulation results based on the new correction from the experimental results were within 20.0 %. [ABSTRACT FROM AUTHOR]

Several nuclear reactors use ice condensers to condense steam in the case of a loss of coolant accident. These ice condensers have many problems that could be alleviated by using another material. The effects of low-dose neutron and gamma radiation on the thermal properties of polyethylene wax (PEW) were investigated for this purpose. PEW was irradiated in the Missouri University of Science and Technology Research Reactor (MSTR), the University of Missouri Cyclotron (MUC) and the University of Missouri Research Reactor (MURR) up to doses equivalent to 10 months in a nuclear power reactor's containment structure. The melting temperature and latent heat of fusion were determined using differential scanning calorimetry (DSC). Changes in the molecular bonds was determined using Raman spectroscopy. It was found that there was not a significant change in the thermal properties nor bonding over the investigated doses. This suggests that organic PCMs could be reliable alternatives to ice in nuclear reactor containment applications. The measured melting peak was found to be significantly wider expected by the suppliers' description. The ramifications of wide melting peaks are discussed in the context of reactor accident analysis and further experiments are suggested. [ABSTRACT FROM AUTHOR]

Under severe accident conditions, in addition to steam and air, there are also other non-condensable gases inside the containment, such as CO 2 produced by the molten corium concrete interaction (MCCI). Due to the significantly higher molecular weight and density of CO 2 compared to steam and air, CO 2 will have a significantly different impact on the steam condensation process compared to air. However, few scholars have paid attention to the impact of CO 2 on the condensation process, and there is no empirical correlation applicable to this condition. Therefore, this article investigates the effect of different CO 2 concentrations on the steam condensation heat transfer coefficient (CHTC) in the range of system pressure from 0.2 to 1.3 MPa and subcooling from 30 to 130 °C through experimental methods. Meanwhile, based on relevant experimental data, a new correlation suitable for calculating the steam CHTC in the presence of CO 2 and air was fitted. The results indicate that under low steam concentration conditions, the addition of CO 2 will reduce CHTC, while under high steam concentration conditions, CO 2 will increase CHTC. The increase in system pressure will strengthen the condensation promotion effect of CO 2 and weaken its inhibitory effect on condensation. In addition, by comparing experimental data under different component conditions, it was found that the new empirical correlation has high computational accuracy, and the calculation results of this correlation can contain more than 90 % of the data within a 15 % error range. • The study examines the effect of denser CO 2 gas on condensation heat transfer in accident conditions. • Experiments were conducted to study how varying CO 2 concentrations impact the CHTC. • The article analyzes how CO 2 and hydrogen jointly alter steam's CHTC in non-condensable gas environments. • A precise experimental formula is derived for calculating steam's CHTC in air and CO 2 mixtures. [ABSTRACT FROM AUTHOR]

• PRS steam condensation characteristics was experimentally studied. • Test data cover full range of the prototypical pressure condition. • Effects of pressure, steam quality, and mass flow rate were studied. • Test data further expand database of steam condensation in tube. The heat exchanger is an important component of the passive residual heat removal system (PRS) in the Hualong Pressurized Reactor (HPR1000). The heat released via steam condensation inside the heat transfer pipes is delivered to water stored outside of the containment. The heat transfer along the heat transfer pipes is systematically studied experimentally. Three horizontal test sections with different dimensions are designed and employed in the experiment. The test data are obtained under different pressure, steam quality, and mass flow rate conditions and compared with existing steam condensation correlation. The test results reveal that the heat transfer coefficient decreases from 41.5 kW/(m2·K) to 24.0 kW/(m2·K) with the pressure increased from 1.0 MPa to 8.3 MPa. In the higher pressure conditions, the larger condensed flow rate provides larger thermal resistance, decreasing the condensation heat transfer coefficient. The steam condensation heat transfer coefficient is increased from 14.3 kW/(m2·K) to 41.4 kW/(m2·K) as the steam quality is increased from 0.07 to 0.70. The condensation heat transfer coefficient is increased from 28.6 kW/(m2·K) to 45.8 kW/(m2·K) as the mass flow rate is increased from 0.029 kg/s to 0.072 kg/s. The maximum prediction deviation of Shah's correlation for all test data is ±34.9 %. [ABSTRACT FROM AUTHOR]

Under severe accident conditions, in addition to steam and air, there may also be hydrogen produced by the reaction of zirconium alloys and steam, CO 2 produced by the molten corium concrete interaction (MCCI) and other gases in the containment. These gases, whose properties are quite different from air, can significantly affect the steam condensation process outside the tube bundle. This paper aims to investigate the effects of non-condensable gas mixtures with varying component concentrations on the steam condensation process outside a 3 × 5 tube bundle using computational fluid dynamics (CFD) methods. The thermal conditions studied are set to a pressure of 0.4 MPa, a subcooling of 40 K, and a molar concentration of steam of 0.66. The results show that CO 2 has an acceleration effect on the flow field outside the tube bundle, which promotes the diffusion of steam to the inside of the bundle, thus increasing the condensation heat transfer coefficient (CHTC) of the bundle and decreasing the difference in CHTC between different heat transfer tubes inside the bundle. Hydrogen, on the other hand, inhibits the downward flow of the gas mixture, causing a decrease in CHTC. However, at high hydrogen concentration (X H2 >0.1), the gas mixture will form a buoyant flow upward, and then the CHTC of the tube bundle will be significantly increased by up to 177%. When the two gases act together, they will weaken each other's influence on the flow field, thus reducing the CHTC of the tube bundle. [ABSTRACT FROM AUTHOR]

The steam condensation process has been experimentally investigated in an air-cooled condenser (ACC). The ACC has been designed and built using a flattened cross-section horizontal tube. The flattened tube has an internal dimension of 102 mm x 12 mm with 4030 mm length. A range of vacuum operating conditions are applied to operate the ACC. In the experiments, parameters such as vacuum pressure, saturated temperature, wall tube temperature, rate of heat transfer, and local average steam heat transfer coefficient have been considered along the flow direction with the variation of cooling water temperature. The experimental results revealed that the steam saturated temperature and the related pressure decrease with the reduction of the cooling water temperature, and the temperatures of the upper and lower parts of the horizontal flattened tube. The results also showed that the local steam condensation heat transfer coefficient decreases along with the direction of the flow, but it there is incrementing with the decreasing of saturated steam temperature at a certain range of cooling water temperature. [ABSTRACT FROM AUTHOR]

Two-phase flow is to be found in many situations of nuclear reactor operation and accident sequences. Examples are loss of coolant accidents and boiling in fuel assemblies. Hence, modelling of two-phase flow is a primary concern in nuclear safety research. Model development and code validation frequently require experimental data, preferably taken under plant thermal-hydraulic conditions. Tomographic imaging techniques provide a way to analyze two-phase flow with high spatial resolution. In this paper we introduce recent developments in X-ray tomography and its application to three different problems related to nuclear safety.

Aiming at studying the condensate flow phenomenon and air-steam–mixture condensation heat transfer underneath a containment vessel surface, a test bench was constructed. The plate dimension was 1.5 × 0.6 m, with Carbozinc 11 coating on the surface, suspended in a pressure vessel with 2.5-m diameter and 4.5-m height. The air-steam mixture was condensed on an inclined plate through natural convection mode and jet mode. By observing flow behavior on the plate through a viewport, four basic regimes were obtained as the inclination angle gradually increased: droplet, droplet to rivulet transition, developed rivulet, and uniform film. During the experiment, we observed a steam atomization phenomenon; therefore, the model predicted better with the atomization effect considered. A simple formula from the condensation data is proposed when the air mole fraction is small. The error between the experimental results and the predicted data is within 25%. [ABSTRACT FROM AUTHOR]

To our knowledge, the potential use of CO2 as a heat-transmitting fluid for cooling applications in power plants has not been explored very extensively. In this paper, we conduct a theoretical analysis to explore the use of CO2 as the heat transmission fluid. We evaluate and compare the thermophysical properties of both dry air and CO2 and perform a simple analysis on a steam-condensing device where steam flows through one of the flow paths and the cooling fluid (CO2 or air) is expanded from a high-pressure container and flows through the other. Sample calculations are carried out for a saturated-vapor steam at 0.008 MPa and 41.5 °C with the mass flow rate of 0.01 kg/s. The pressure of the storage container ranges from 1 to 5 MPa, and its temperature is kept at 35 °C. The pressure of the cooling fluid (CO2 or dry air) is set at 0.1 MPa. With air as the heat-removing fluid, the steam exits the condensing device as a vapor-liquid steam of 53% to 10% vapor for the container pressure of 1 to 5 MPa. With CO2 as the heat-removing fluid, the steam exits the device still containing 44% and 7% vapor for the container pressure of 1 MPa and 2 MPa, respectively. For the container pressure of 3 MPa and higher, the steam exits the device as a single-phase saturated liquid. Thus, due to its excellent Joule–Thomson cooling effect and heat capacity, CO2 is a better fluid for power plant cooling applications. The condensing surface area is also estimated, and the results show that when CO2 is used, the condensing surface is 50% to 60% less than that when dry air is used. This leads to significant reductions in the condenser size and the capital costs. A rough estimate of the amount of CO2 that can be stored and utilized is also carried out for a steam power plant which operates with steam with a temperature of 540 °C (813 K) and a pressure of 10 MPa at the turbine inlet and saturated-vapor steam at 0.008 MPa at the turbine outlet. The results indicate that if CO2 is used as a cooling fluid, CO2 emitted from a 1000 MW power plant during a period of 250 days could be stored and utilized. [ABSTRACT FROM AUTHOR]

The paper presents CFD results for the transonic flow of dry and moist air through a diffuser and a compressor rotor. In both test geometries, i.e. the Sajben transonic diffuser and the NASA Rotor 37, the air humidity impact on the structure of flows with weak shock waves was examined. The CFD simulations were performed by means of an in-house CFD code, which was the RANS-based modelling approach to compressible flow solutions. It is shown that at high values of relative humidity, above 70%, the modelling of the transonic flow field with weak shock waves by means of the dry air model may produce wrong results. [ABSTRACT FROM AUTHOR]

The influence of the character of cooling medium motion in a heat exchanging apparatus on the process of steam condensation in the latter is considered in the cases of cross flow past a tube bank in the apparatus, longitudinal flow past tubes in the bank in the regimes of forward flow and countercurrent flow, superheated steam condensation, and of nonuniform distribution of the cooling medium in different zones of the apparatus. It has been established that in the case of cross flow past the first rows of the tube bank, cooling medium zones with reduced heat transfer efficiency appear in the apparatus. The dependence of the pressure losses by the steam, which condenses in a heat exchanger in regimes of countercurrent flow, forward flow, and cross flow, is investigated. Experimental data on the superheated steam temperature have been obtained and generalized. The positive influence of the throttle on the line of removal of the steam–air mixture to a steam–jet ejector in nonuniform cooling of the parallel channels of the condenser has been established experimentally, and the presence of the optimal size of the throttle on the line of removal of noncondensing gases has been confirmed. [ABSTRACT FROM AUTHOR]

Understanding local transport behaviour of steam-air-hydrogen mixture inside the containment and associated hydrogen combustion issues are essential to ensure integrity of the nuclear reactor containment in the event of a severe accident. During a severe accident, various mechanisms occurring inside and outside of reactor pressure vessel may lead to generation of steam, and subsequently hydrogen, which eventually gets released in the containment space. Hydrogen may deflagrate in the presence of an ignition source/hot spot depending on local mixture composition of steam-air-hydrogen; this may further lead to flame acceleration, deflagration to detonation transition, and finally to detonation depending upon local conditions and geometric factors, further increasing the internal pressure and temperature of the containment. The fraction of non-condensable gases may also rise due to simultaneous on-going steam condensation, which not only elevates the possibility of hydrogen combustion, but also in turn, affects the eventual local and average steam condensation rates. In this background, this paper reviews the coupled issues between steam condensation, hydrogen transport, hydrogen combustion criteria, location of its sources, and stratification inside reactor containment under plausible severe accident scenarios. Several experiments in the context of containment thermal-hydraulics and hydrogen combustion are elaborated. Looking into the complexity of the problem, necessity to adopt simulation approach is highlighted. Two types of codes, i.e., lumped-parameter (LP) and computational fluid dynamic (CFD), are scrutinized based on their specific applications and limitations. It is inferred that the containment thermal-hydraulics and ensuing safety strategies must address the issue of steam condensation and hydrogen management simultaneously, through a comprehensive and integrated approach. • Coupled issues of steam-air-hydrogen mixtures in containment spaces are emphasized. • Factors affecting severe accident progression and hydrogen combustion are discussed. • Experimental program on containment thermal hydraulics and H 2 combustion are reviewed. • Numerical models and code capabilities in predicting severe accident scenarios are highlighted. [ABSTRACT FROM AUTHOR]

• The strongly coupling relationship between curvature and inclination is discovered. • The inflection point of inclination effect on condensation characteristics is found. • The mechanism of coupling effect between inclination and curvature is revealed. • The condensation performance of various curvature and inclination is compared. Steam-air condensation is one of the critical thermal–hydraulic phenomena in containment under accident conditions. Currently, sufficient experimental research and numerical analysis have been conducted on steam–air condensation outside the tube/plate. However, few studies have investigated the influence of curvature and inclination on condensation characteristics, and the local phenomena and mechanisms that affect the condensation process have not yet been fully revealed. In addition, it is of vital importance to evaluate the coupling effect between curvature and inclination in practical applications. To investigate the above-mentioned effects, numerical simulations were conducted over a wide parameter range (P = 0.2 ∼ 1.6 MPa, ω a = 0.1 ∼ 0.9, ΔT = 20 ∼ 100 K), and the related mechanisms were analyzed in detail. The results showed that there is a strong coupling relationship between curvature effect and inclination effect and the inflection point in the influence of inclination effect on steam condensation characteristics is discovered. Compared to the traditional conclusion that condensation capability gradually increases with the decrease of inclination angle. The effect of inclination on the condensation characteristics can reverse in different curvature regions. When the curvature is greater than 5 m−1, the inclination angle is negatively correlated with the condensation capability. When the curvature is less than 5 m−1, the inclination angle is positively correlated with the condensation capability. Furthermore, the enhancement effect originate from the curvature effect will greatly decrease as the inclination angle increases. [ABSTRACT FROM AUTHOR]

To our knowledge, the potential use of CO2 as a heat-transmitting fluid for cooling applications in power plants has not been explored very extensively. In this paper, we conduct a theoretical analysis to explore the use of CO2 as the heat transmission fluid. We evaluate and compare the thermophysical properties of both dry air and CO2 and perform a simple analysis on a steam-condensing device where steam flows through one of the flow paths and the cooling fluid (CO2 or air) is expanded from a high-pressure container and flows through the other. Sample calculations are carried out for a saturated-vapor steam at 0.008 MPa and 41.5 °C with the mass flow rate of 0.01 kg/s. The pressure of the storage container ranges from 1 to 5 MPa, and its temperature is kept at 35 °C. The pressure of the cooling fluid (CO2 or dry air) is set at 0.1 MPa. With air as the heat-removing fluid, the steam exits the condensing device as a vapor-liquid steam of 53% to 10% vapor for the container pressure of 1 to 5 MPa. With CO2 as the heat-removing fluid, the steam exits the device still containing 44% and 7% vapor for the container pressure of 1 MPa and 2 MPa, respectively. For the container pressure of 3 MPa and higher, the steam exits the device as a single-phase saturated liquid. Thus, due to its excellent Joule–Thomson cooling effect and heat capacity, CO2 is a better fluid for power plant cooling applications. The condensing surface area is also estimated, and the results show that when CO2 is used, the condensing surface is 50% to 60% less than that when dry air is used. This leads to significant reductions in the condenser size and the capital costs. A rough estimate of the amount of CO2 that can be stored and utilized is also carried out for a steam power plant which operates with steam with a temperature of 540 °C (813 K) and a pressure of 10 MPa at the turbine inlet and saturated-vapor steam at 0.008 MPa at the turbine outlet. The results indicate that if CO2 is used as a cooling fluid, CO2 emitted from a 1000 MW power plant during a period of 250 days could be stored and utilized.

• Steam condensation on a downward-facing plate with inorganic zinc coating. • The effects of key parameters on condensation heat transfer. • An empirical correlation for condensation heat transfer coefficient prediction. Steam condensation on the containment vessel is a significant cooling strategy to cope with the design basis accidents in the third-generation reactors with passive safety features. Aiming to evaluate the heat removal capacity of steam condensation, a number of condensation experiments have been conducted on a horizontal plate with the same surface condition as CAP1400 containment vessel. The effects of surface sub-cooling, air concentration, bulk pressure and different steam injecting models on condensation heat transfer have been experimentally investigated. In the experiments, the condensation heat transfer coefficients (within the range of 77–1297 W/m2 K) on the downward-facing plate are successfully obtained under the conditions of bulk pressure ranging from 0.154 to 0.607 MPa, air molar fraction ranging from 1.1% to 82.9% and surface sub-cooling ranging from 12.6 to 49.3 °C. In addition, an empirical correlation for heat transfer prediction has been developed based on the experimental data in this work. Besides, the experimental data have also been compared with four existing empirical correlations proposed by Uchida, Tagami, Dehbi and Liu, respectively. The comparing results show that most of condensation heat transfer coefficient data on the test plate could be overestimated by these four correlations. [ABSTRACT FROM AUTHOR]

Many economic and environmental restrictions have resulted in the growth of dry cooling technology. The air-cooled condenser (ACC), which can be used in power plants and other facilities, represents a way toward the minimisation of the water footprint. In the paper, a semi-empirical computational tool devised for the design and thermal assessment of the ACC is introduced. In comparison to commonly used CFD-based models, the presented tool is computationally effective and inexpensive. The model is based on a control-volume computational grid, which is coupled with three sub-models for the solution of steam-side, air-side, and fan-related phenomena. A number of empirical correlations collected in the literature review were incorporated in the model. Besides the underlying functionality, which includes the determination of the steam condensation capacity, the model allows for the consideration of advanced physical phenomena such as the condensate glut control and the influence of air in the steam to the condensation process. The comparison of the model with datasheets from manufacturers of ACCs as well as with experimentally gained data from a municipal solid waste incineration plant demonstrates that the semi-empirical model is a fast and accurate tool applicable for the design and thermal assessment of the ACC. [ABSTRACT FROM AUTHOR]

A mathematical model of the development of a tropical cyclone is considered. It consists of a family of equations obtained by transforming the equation of inviscid non-heat conductive gas (air) motion to the form of equations on wind trajectories in an axially symmetric cylindrical domain. The numerical solution of these equations shows the increase of the wind velocity in accordance with the steam condensation and air warming; later, the velocity becomes stable as the liquid or small pieces of ice accumulate in the air and the friction of water against air decelerates the air updraft. [ABSTRACT FROM AUTHOR]

• Experimental data of unstable direct contact condensation of steam is provided. • Heat transfer characteristics is presented in bubble dynamics point of view. • A bubbling frequency concept and an empirical correlation are proposed. • An empirical correlation of averaged heat transfer coefficient is suggested. • The results can be employed for condensation closure model development for CFD. The study of direct contact condensation (DCC) of steam is important owing to the diverse range of DCC applications, including uses in power plants, heat exchangers, and steam ejectors. In this study, an experimental investigation was performed to study the thermal hydraulic characteristics of the DCC of steam in an unstable condensation regime. Deionized water was used as the working fluid obtained with the use of a reverse osmosis method. The experiments were performed with pool temperatures in the range of 70 to 92 °C ± 2 °C, with different steam mixture mass fluxes in the range of 5 and 64 kg/m2 s, and with a gas injection nozzle with an inner diameter of 9.525 mm. The pool temperature was measured using thermocouples, and the surface area of the bubble and the volume flow rate were evaluated with high-speed camera image acquisitions. Subsequently, image processing was used to obtain the heat-transfer coefficient and other thermal hydraulic characteristics, such as the bubble condensing frequency and the bubble centroid velocity. The calculated condensation heat-transfer coefficients were found to be 24.57–179.78 kW/m2⋅K. According to the experimental results at various boundary conditions, a unified correlation of the heat-transfer coefficient was identified at the bubbling frequency in the unstable condensation regime, regardless of the pool subcooling temperature and steam mass flux. It was also found that the characteristic frequency of the steam bubble can be determined based on the boundary conditions to allow the determination of the heat-transfer coefficient with the given boundary conditions. [ABSTRACT FROM AUTHOR]

Abstract A condensation-induced depressurization and steam purging technology has been recently developed to drive a continuous gas flow at a sub-atmospheric pressure. The technology is based on a continuous regeneration of depressurization by a system of two or multiple alternatively-operated chambers with steam condensation and refilling. Comparing with traditional methods, this new vacuum generation technology has a great potential of high energy conversion and utilization for an open-flow system. A complete operation cycle of each chamber undergoes three stages in sequence: vacuum generation by condensing pre-refilled steam, vacuuming gas from application system, and purging gas out of chamber while refilling steam. This paper presents a mechanistic model of process characteristics and parametric analysis for the thermodynamic cyclic operations. Each process stage has been separately modelled, and the complete cycle characteristics are then integrated by connecting these stages in series. The mechanistic model provides a parametric analysis capability for the optimized operation of the developed technology to vacuum driving continuous gas flows at sub-atmospheric pressures. The model result is compared with experiment data with good match. The parametric study of the steam purging process indicates that increasing the steam flowrate and pre-heating of chamber can effectively reduce the purging time required by 20–40%. Highlights • An energy efficient condensation-induced depressurization and steam purging technology is developed. • This technology is to drive a continuous gas flow at a sub-atmospheric pressure. • The thermodynamic cycle in such a vacuum chamber consists of three sub-processes. • A mechanistic model of process characteristics and parametric analysis is presented. • The mechanistic model provides the optimized operation of the developed technology. [ABSTRACT FROM AUTHOR]

Highlights • Experimental study on the condensate dripping mechanism. • Description of condensate flow patterns on a plate with the same surface condition with CAP1400 inner containment wall. • The effects of air, surface sub-cooling and pressure on regional dripping fraction are discussed. Abstract Under accident conditions of CAP1400, recycling of condensate film from the inner containment wall is a significant aspect for the water level maintenance of the in-containment refueling water storage tank, whilst dripping from the containment dome is the dominant factor that causing the condensate loss. Therefore, experimental investigations on the dripping phenomena were carried out in this study. A pressure vessel was set to simulate the condensing atmosphere in the containment, in which a 1.5 × 0.6 m2 rotatable test section was suspended with similar surface condition as CAP1400. Experimental results show that the condensate flow patterns could be divided into four types. It was found that dripping was triggered by the condensate mass flow flux exceeding the critical value on an unobstructed condensing surface. Meanwhile, the dripping fraction increases with the difference between condensate mass flow flux and the critical value. Besides, the effects of inclination, bulk pressure, air concentration etc. on dripping were experimental analyzed. In general, this study hopes to provide data support and theoretical guidance for the further studies of the condensate loss under accident conditions. [ABSTRACT FROM AUTHOR]

Abstract Previous investigations on steam condensation in the presence of air have revealed general heat transfer characteristics in vertical plates and single tubes. However, there remains limited knowledge regarding the thermal-hydraulic phenomena and heat transfer properties of tube bundles. In order to evaluate steam condensation on the external surfaces of tube bundles, STAR-CCM + code with a diffusion boundary layer steam condensation model was employed in this work. In the assessments, 3 × 3 tube bundles with various tube pitches (from 1.5d to 5d) were investigated, and the results were compared to those of a single tube. The data analyses mainly focused on three aspects: (i) global and local condensation phenomena in tube bundles; (ii) heat transfer characteristics in tube bundles; and (iii) influences of tube pitches and global parameters (such as pressure and air mass fraction) on the condensation heat transfer. The phenomena analyses indicate that the axial field profiles are mainly determined by the development of a concentration boundary layer, while the radial field profiles are mostly affected by the tube pitches. Local heat flux analyses indicate that the condensation heat flux exhibits a significant reduction downwards along the vertical tube. In comparison, the condensation heat flux fluctuates in the tube peripheral direction. In the latter case, heat transfer enhancement and inhibition regions are identified and classified. For the tube average heat transfer, only the central tube is significantly affected by the tube pitches, and the degradation may be more than 30% at a tube pitch of 1.5d. The tube pitch effect is almost independent of the bulk air mass fraction and changes slightly with an increase in the wall sub-cooling and bulk pressure. [ABSTRACT FROM AUTHOR]

Present work analyses the condensation of superheated water vapor in supersonic Barschdorff nozzle. The influence of pneumatic mounts in 3D laval nozzle is analyzed using steady and unsteady two phase non-equilibrium condensation steam flow model in Ansys CFX16. Mesh independency studies in 2D model showed that at a lower inlet total temperature and very fine mesh (e.g. 100.2°C and 77k mesh elements) there is problem with the convergence using steady simulation. This is possibly due to the ability of very fine mesh to capture the small flow unsteadiness. The variation in location of Wilson's point, Wilson's pressure and maximum sub-cooling rate at the centerline of the nozzle is below 1.5%. The 2D CFD nucleation rate is 50% stronger and droplet diameter is 18% higher compared to the 3D CFD results. The deviation in nucleation rate and droplet diameter at nozzle outlet is the result of dissipation due to wing structure in the 3D model. Nucleation zone predicted by Ansys CFX16 is far upstream the experimental one. Different correction factors in modified nucleation model were used to fit the computed pressure distribution with the experimental one. The correction factor is dependent on boundary conditions and nozzle profile. It is thus concluded that the significance of such correction factor is not unique. [ABSTRACT FROM AUTHOR]

The focus of this work is to investigate the effect of emulsifier-free emulsion fuel via steam emulsification (SD) to the diesel engine through physical properties, combustion performance, and exhaust analysis, and compare with conventional emulsion fuel with water percentages of 5% and 10% (E5 and E10) and biodiesel blend (B5). The SD was prepared using a custom 200 mL glass mixing column. The B5 fuel quantitatively was filled in the column, and then the steam was injected from the bottom of the mixing column through the porous frit glass with the pores ranging from 40 to 100 µm. The average water droplet size of SD is 0.375 µm with the average water percentage of 6.18%. The brake specific fuel consumption (BSFC) and brake thermal efficiency (BTE) of SD improved 4.19% and 3.92%, respectively, as compared to B5. The in-cylinder pressure (ICP) was lower than B5, however, yielding close to the B5 at 4 kW engine load. As for the exhaust emission test, NOx and PM for SD were reduced significantly with a percentage reduction of 25.22% and 10.68%, respectively, as compared to neat B5. The steam emulsification method offers a huge potential to be explored further as the concept offers the alternative method of making emulsion fuel without the use of conventional mechanical mixers.

In this study, we examined the condensing behavior of single and multiple bubbles of pure steam in a subcooled liquid phase using a fully compressible two-phase homogeneous mixture method that is solved by an implicit dual-time preconditioned technique. The interface between the liquid and vapor phases was determined by the advection equations using a compressive high-resolution interfacing capturing method. The spurious current reduced near the interface, a smoothing filter is applied to the progress curvature calculation. The sensitivity study carried out to predict the empirical constant by using Lee’s mass transfer model. A comparison of the numerical and experimental results highlighted that the proposed model accurately predicted the behavior of the definite condensing bubble. Furthermore, the single and multiple bubble condensation behaviors were investigated for different initial subcooled temperatures, and bubble diameters under various gradient flow, such as velocity gradient, temperature gradient, and velocity and temperature gradients. Subsequently, the effect of multiple bubbles flows in different bubble pattern forms, and their condensation was studied. The coalescence of bubbles depends on the subcooled temperature. Furthermore, the bubble diameter, the gap between the bubbles, and the flow rate of the bubbles were also observed.