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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]

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]

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]

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]

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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]

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 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]

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]

Abstract Steam condensation in the presence of air is a relevant phenomenon in various industrial applications. Its heat transfer property has been broadly revealed by experimental and numerical investigations on vertical plates or single tubes. However, these results may not be directly applied to tube bundle cases, since there may exist mutual interactions among adjacent tubes. To have an insight on this problem, the present work conducted numerical simulations on various tube bundles with a tube pitch 1.5 times of the tube diameter. The cases evaluated were classified into three categories including the single row, double row, and triple row. In each category, structures with various tube columns were assessed. The results indicate that tube bundles will thicken the near-wall high concentration air layer, resulting in inhibited condensation heat transfer. This phenomenon is defined as the inhibition effect. On the other hand, a heat transfer enhancement effect caused by a strengthened natural circulation driven by the density difference between the mainstream and the high concentration air region is found and defined as the stack effect. The average condensation heat transfer for tube bundles is determined by the relative magnitude between the inhibition effect and the stack effect. The stack effect becomes much intensive with the increase of tube rows and columns, which can enhance condensation heat transfer. Typically, the results in the triple row categories show that the maximum average heat transfer coefficient can be 14% greater than that of the single tube. [ABSTRACT FROM AUTHOR]

Abstract The natural convection condensation heat transfer outside the vertical smooth tube and corrugated tube was experimentally investigated in pure steam and steam–air conditions, respectively. The aim of the research was to evaluate the heat removal capacity of the corrugated tube through comparing with the test results of the smooth tube. In the experiment, a corrugated tube was tested, the bulk temperature and the wall temperature of crest and trough were measured in detail. The result of the temperature measurement demonstrated that the difference of heat transfer characteristics at the crest and trough is not significant. In the pure steam condition, the influence of subcooling on condensation heat transfer coefficient of the corrugated tube is reduced. Comparing with the smooth tube, the condensation heat transfer coefficient of the corrugated tube has been increased for more than 10%. In the steam–air test condition, the condensation heat transfer coefficients have been obtained for the air mass fraction from 0.1 to 0.95 and the total pressure from 0.2 MPa to 0.5 MPa. The corrugated tube shows a slight enhancement with an average increase of condensing heat transfer coefficient about 10%. Highlights • Steam–air mixtures condensation outside a corrugated tube is conducted. • The difference of heat transfer characteristics at the crest and trough is compared. • The corrugated tube weakens the impact of subcooling on the coefficient of condensing heat transfer. • Compared with smooth tube, the corrugated tube enhances the steam-air condensation heat transfer process slightly. [ABSTRACT FROM AUTHOR]

Hydrogen fires may pose serious safety issues in vented compartments of nuclear reactor containment and fuel cell systems under hypothetical accidents. Experimental studies on vented hydrogen fires have been performed with the HYKA test facility at Karlsruhe Institute of Technology (KIT) within Work Package 4 (WP4) - hydrogen jet fire in a confined space of the European HyIndoor project. It has been observed that heat losses of the combustion products can significantly affect the combustion regimes of hydrogen fire as well as the pressure and thermal loads on the confinement structures. Dynamics of turbulent hydrogen jet fire in a vented enclosure was investigated using the CFD code GASFLOW-MPI. Effects of heat losses, including convective heat transfer, steam condensation and thermal radiation, have been studied. The unsteady characteristics of hydrogen jet fires can be successfully captured when the heat transfer mechanisms are considered. Both initial pressure peak and pressure decay were very well predicted compared to the experimental data. A pulsating process of flame extinction due to the consumption of oxygen and then self-ignition due to the inflow of fresh air was captured as well. However, in the adiabatic case without considering the heat loss effects, the pressure and temperature were considerably over-predicted and the major physical phenomena occurring in the combustion enclosure were not able to be reproduced while showing large discrepancies from the experimental observations. The effect of sustained hydrogen release on the jet fire dynamics was also investigated. It indicates that heat losses can have important implications and should be considered in hydrogen combustion simulations. [ABSTRACT FROM AUTHOR]

In the past several decades, experimentalists have proposed a large number of correlations to estimate steam condensation rates in the presence of noncondensable gases within free convection regime. However, these correlations are in different forms, and even express conflicting dependencies of the condensation coefficient on some parameters. This study is to aim at developing a new correlation which can faithfully reflect the complex dependencies of condensation coefficient on pressure, air mass fraction and wall subcooling. Considering that more measured data can certainly help to analyze the relationship between condensation coefficient and these parameters, total 374 sets of experimental data have been obtained. It is found that there is a negative power function relation between condensation coefficient and wall subcooling, and the exponent varies with wall subcooling and total pressure. The new correlation, covering two orders of magnitude in the condensation heat transfer coefficient, is valid for pressure ranging from 0.2 to 0.5 MPa, air mass fraction ranging from 0.1 to 0.8 and wall subcooling ranging from 10 to 70 °C. Finally, we have made comparison with experimental data obtained by other investigators which shows that the new correlation is applicative for not only steam-air condensation but also steam-nitrogen and steam-argon condensation, and it can be extended to larger scope of engineering applications. [ABSTRACT FROM AUTHOR]

Large number of solar thermal power plants operating or being designed use steam as a working fluid or heat transfer fluid. Therefore, a thermal energy storage (TES) system which can directly store the energy from steam can improve the demand-supply mismatch of thermal or electrical energy. Packed bed TES systems with solid rocks as packing material are one of the most economical and robust energy storage solutions available. This study investigates thermal energy storage process in packed bed systems with steam as heat transfer fluid (HTF). Experiments were conducted to understand thermal response of cylindrical packed bed filled with uniform and chemically inert alumina particles upon saturated steam injection along the axial direction. Axial thermal gradients determine the efficiency of the storage process. Saturated steam is introduced at different flow rates leading to different thermal gradients in the axial direction during different stages of thermal storage process. Rate of steam injection significantly impacts the modes of heat transfer– advection and diffusion. These experimental studies were extended with air as a HTF to compare thermal gradients in the bed under extremely different heat injection rates. In case of steam injection, wall heat loss rate is significantly lower than heat injection rate whereas, wall heat loss rate is comparable to heat injection rate in case of hot air injection. [ABSTRACT FROM AUTHOR]

For stable sonic steam jet, conical and ellipsoidal steam plumes were observed by many researchers. Restricted by experimental method, the difference in flow and heat transfer characteristic between conical and ellipsoidal steam plumes was still unclear. To reveal the difference between the two kinds of steam plumes, three-dimensional steady numerical simulations were carried out with Eulerian multiphase model, and a thermal equilibrium phase change model was inserted into Fluent as a user defined function (UDF) to investigate the condensation phenomenon. The CFD results were compared with experimental results to testify the correctness of simulation, and good agreement was observed. Then steam pressure was varied to study its effect on the process of condensation jet. Conical and ellipsoidal steam plumes were obtained under different operating conditions. For conical steam plume, it is compressed near nozzle exit along radial direction, and the pressure in steam plume is larger than ambient pressure. However, when it comes to ellipsoidal steam plume, it expands near the nozzle exit along radial direction, when steam plume expands to the maximum extend, the pressure in steam plume is reaching the bottom, almost the same as ambient pressure. Besides, the influence of flow characteristic of steam in plume on axial temperature and steam plume shape was analyzed. When steam in plume reaches supersonic, the shape of steam plume shows ellipsoidal shape, and there is a peak along axial temperature distribution. Otherwise, it presents conical shape and axial temperature decays to ambient water temperature monotonously. [ABSTRACT FROM AUTHOR]

Hydrogen release in confined spaces is an important safety issue, which is even more important in the context of severe accident in nuclear reactors. In severe accidents, hydrogen release is associated with release of steam and the condensation of steam on walls leads to increase in concentration of hydrogen in residual gas as well as condensation induced mixing. In the present paper, a model for falling film steam condensation in the presence of noncondensable gases is presented. The steam condensation model is incorporated into an in-house developed CFD code called hydrogen distribution simulator (HDS) and is used for hydrogen distribution studies. The validation of the CFD model with steam condensation against the experimental results from the CON AN facility is discussed. Subsequently, the model is applied to a typical release situation involving release of hydrogen and steam for some time and its distribution for a long time beyond it. The heat and mass transfer aspects of the problem are highlighted. It is seen that steam condensation has an important bearing on the distribution of hydrogen and the mixing behavior of gases in the enclosure. [ABSTRACT FROM AUTHOR]

The passive containment cooling system (PCCS) is widely used in the advanced Generation III and III+ nuclear reactor systems to maintain the integrity of the containment under long term post utmost accidents like the loss of coolant accident (LOCA) and the main steam line break accident (MSLB). In the steam condensation process, the presence of large amounts of noncondensable gases (mainly air) will lead to the serious deterioration of heat transfer. Further research on steam condensation in the presence of air must be conducted. Condensation process of steam in the presence of air has been successfully modeled by applying a user defined function (UDF) added to the commercial computational fluid dynamics (CFD) package. Calculated profiles of temperature, air concentration, velocity components and condensation heat transfer coefficient (HTC) are compared to experimental results. The simulation results indicate that there is a good agreement between the experimental results and the model predictions. It also shows that both the latent and the sensible HTCs decreased with the increase of the air mass fraction, and the latent heat transfer is the dominant factor of the total condensation heat transfer when the air mass fraction less than 50%. Local latent HTC shows an upward tendency along the height direction of the heat transfer tube from bottom to top, with sensible HTC taking on an opposite trend. [ABSTRACT FROM AUTHOR]

• The effect of CO 2 on the steam condensation outside a vertical tube is numerically analyzed. • A CFD model to simulate the steam condensation in presence of CO 2 /air is validated by the experiments carried out on the COAST facility. • The steam concentration will influence of the effect of CO 2 on steam condensation heat transfer coefficient. Under severe accident conditions of a pressurized water reactor nuclear power plant, the reactor core may melt, and the molten corium even reacts with concrete in the containment, producing a large amount of CO 2 into the entire containment gas space. This may have an obvious impact on the heat transfer characteristics of steam condensation in the containment. However, there are few studies focused on this phenomenon. In this paper, a commercial CFD software, STAR-CCM+, is used to study the effect of CO 2 on steam condensation heat transfer. The calculations are based on 0.4 MPa gas pressure, 40 K wall sub-cooling, 0.66 or 0.2 steam mole fraction, and the CO 2 mole fraction varies from 0 to 0.34 or 0.8. The results show that the CO 2 demonstrates different influence laws at high and low steam concentrations, respectively. When the steam mole fraction is 0.66, as the proportion of CO 2 in the non-condensable gas increases, the condensation heat transfer coefficient (HTC) will increase, and the enhancement can reach 30%. When the steam mole fraction is 0.2, the condensation HTC will first decrease and then increase, as the proportion of CO 2 in the non-condensable gas increases. The effects of gas pressure and wall sub-cooling on the condensation HTC are also analyzed. The results show that the condensation HTC increases with the increase of the gas pressure and decreases with the increase of wall sub-cooling. [ABSTRACT FROM AUTHOR]

Abstract: A physical and revised mathematical droplet model with respect to molecular clustering is proposed to describe the state of steam molecules before condensing on the cooled solid surface in steam condensation in the presence of noncondensable gas (NCG). Based on the Dillmann and Meier''s homogeneous nucleation model, introducing the wall conditions and making some correlations, the mathematical model was used to calculate the size distribution of clusters and describe the effect of the presence of NCG on the distribution of clusters. The heat transfer model considering the effect of interfacial effects was used to calculate the shape and temperature of clusters. The predicted results of Gibbs free energy at different subcooling degrees and different saturated temperatures were given. The model well explains the effect of NCG on condensation heat transfer performance and the predicted results are in agreement with the experimental results reported in the literature. That confirms the validity of the model. [Copyright &y& Elsevier]

Abstract: An experimental research was conducted to investigate the heat transfer characteristics of steam condensation on horizontal twisted elliptical tubes (TETs) with different structural parameters. Experiments were carried out at the steam saturation temperature of around 100.5°C with the wall subcooling from around 2°C to 14°C. Experimental results indicate that the condensation heat transfer coefficients for all the tubes reduce with the increase of wall subcooling, while the enhancement factor of each TET is almost constant. Not all the tested TETs have better condensation heat transfer performance than the smooth circular tube, the average enhancement factors provided by the five TETs range from 0.87 to 1.34. Condensation heat transfer coefficients increase with the rise of the tube ellipticities. The TET No. 3 with the largest ellipticity of 0.86 has the highest condensation heat transfer coefficient augmentation of around 34%. The TET with a twist pitch of 192mm has a better condensation performance than the smooth circular tube when its ellipticity exceeds 0.77. A smaller twist pitch leads to a lower condensation heat transfer coefficient. The condensation heat transfer enhancement mechanism of the TETs has also been analysed. [Copyright &y& Elsevier]

Thin-walled storage tanks are prone to vacuum collapse due to the development of a net external pressure. Condensation of steam inside the vessel can cause a rapid development of this mode of failure. External atmospheric conditions also affect the process; specifically, the enhanced heat transfer associated with rainfall on the vessel external surface accelerates the collapse process. Short but intense rain storms are becoming more common. An expression to predict the time taken for a storage vessel to collapse while subject to external rainfall is developed. Good agreement was found between the predictions of the modelling techniques and the experimentally obtained results. It is shown that the thermal energy stored in the vessel wall is very significant in determining the collapse time especially for outdoor vessels exposed to rain. [ABSTRACT FROM AUTHOR]

Abstract: A steady-state mathematical model was developed for vapor condensation heat transfer process with high fractional noncondensable gas by taking into account the heat and mass balances on both sides of the condensing column. Meanwhile, the condensation mass transfer coefficient at the condensing side was correlated along the height of the condensing column based on the large amount of experimental data. The correlations represented the experimental data very well, which showed that the model is reasonable. Mathematical simulation results present various column height profiles including temperature of mixed gas and condensing heat transfer coefficient, noncondensable mass fraction and condensate mass flow rate [Copyright &y& Elsevier]

• A high-order implicit scheme for multi-phase flows with heat and mass transfer is proposed. • The scheme is developed for a generalized non-orthogonal grid and it is relatively simple to implement. • Accuracy of the proposed scheme is demonstrated for a series of direct contact condensation of steam bubbles in upward liquid subcooled flows. • The effects of subcooling degree and steam mass flow rate on heat and mass transfer characteristics are investigated. Reliable prediction of unsteady multiphase flows with mass changes, large density ratios, and complex flow features is very challenging due to the need to accurately resolve both complex interface deformations and steep gradients associated with material interfaces. This paper describes an application of our recently developed high-order monotonicity preserving (MP) scheme – a reliable and robust scheme for long-term computations of flows contain complex smooth structures interspersed with discontinuities (Ha and Lee, 2020) − to the solution of unsteady incompressible two-phase flows in the presence of heat and mass changes. The flow is governed by the multiphase Navier–Stokes equations, which comprises of the mixture continuity equation, the mixture momentum equations, the mixture energy equation, and the continuity equation for the individual phase. The numerical discretization is implemented on generalized curvilinear grids for facilitating flow simulations of the complex geometries. Our high-order MP scheme is applied to the calculations of the convective and surface tension terms. To obtain an effectively simultaneous solution of all equations, a novel dual-time stepping approach in conjunction with an implicit Runge–Kutta three-stage scheme is proposed. The reliability of the proposed numerical algorithm is then examined for a 1D Stefan condensation problem and two condensing flows including single bubble and steam-jet condensation problems. Particularly, for the single bubble condensation test, the bubble characteristics at different time instants are evaluated both qualitatively and quantitatively. For the steam-jet condensation test, the capability for capturing the evolution of interface deformations under different thermal and hydrodynamic flow conditions is highlighted. Finally, the effects of subcooling degree and steam mass flow rate on heat and mass transfer characteristics are investigated and discussed. [ABSTRACT FROM AUTHOR]

In this study, the experimental investigation result of steam condensation on a vertical tube in the presence of air and a light noncondensable gas is presented. This study aims at elucidating the effect of hydrogen that may be generated during the progression of a severe accident on the condensation heat transfer. Using helium as a simulant of hydrogen, a series of condensation tests were performed. A novel helium measurement system was introduced to analyze the composition of mixture gas. The condensation heat transfer coefficient was obtained under natural convection conditions on a 1 m long condenser tube having an outer diameter of 21.5 mm. A comprehensive experimental database was obtained to understand the parametric effect of the total mass fraction of noncondensable gases, molar concentration of helium in noncondensable gases, and wall subcooling degree. An empirical correlation for the degradation factor to account for the effect of a light noncondensable gas was proposed for application to the condensation model for the steam–air mixture based on the experimental data. The strategy to adopt the degradation factor was assessed against three steam–air–helium condensation tests. • A degradation of condensation heat transfer coefficient because of additional helium is identified. • The degradation factor to represent a deterioration of heat transfer coefficient is derived. • The derived degradation factor has a good agreement with previous experimental studies. [ABSTRACT FROM AUTHOR]

The all-inclusive use of the resources of geothermal heat-carriers needs the devices with active hydrodynamic regimes and optimal design parameters. The complex investigations into the heat exchange under steam condensation are conducted on models with different structures of flows in working volumes. The heat exchange coefficients depending on the regime parameters are obtained, and the basic procedures to calculate processing equipment are developed. [ABSTRACT FROM AUTHOR]

• A wall condensation model was implemented and validated in ANSYS FLUENT. • CFD calculations show good agreement with the experimental data. • The typical parameter distribution in the tubes bundle channel is quite different from that in the single tube. • The effect of tubes bundle on the condensation heat transfer is very obvious. The condensation heat transfer characteristics of steam with the non-condensable gases (NCGs) in the tubes bundle channel are quite different from those in the simple geometry structure, such as the single tube and flat plate. In the present work, to evaluate the thermal characteristics of steam condensation with NCGs in the vertical tubes bundle channel, the numerical model of steam condensation was established based on the CFD code ANSYS FLUENT, which combined the gas component transport equations and the diffusion balance model. And several conditions with different thermal parameters were simulated, the simulation results are in good agreement with the experimental data. The condensation heat transfer in a hexagonal 7-tubes bundle channel with various tube pitches (from 1.5d to 5d) is investigated. The results indicate that the distribution of typical thermal parameters, such as velocity, air mass fraction, temperature and density, is quite different from that in the single tube due to the cross and mixture in each condensation tube boundary layer. As the condensation length increases, the air mass fraction rises, the gas flow rate decreases and the sub-cooling decreases, resulting in a lower natural convection intensity. When the tube pitch is less than 4d, the condensation heat transfer capacity in the tubes bundle channel is weakened obviously, and the heat transfer coefficient with the tube pitch 1.5d is only about 32% of that in a single tube. The air mass fraction and pressure have a significant positive effect on the heat transfer coefficient, and the wall sub-cooling has a significant negative effect on that. [ABSTRACT FROM AUTHOR]

• Steam condensation on tube-bundle in presence of non-condensable gas was experimentally investigated. • The condensation heat transfer coefficient was analyzed for the present data. • The heat transfer for tube-bundle was significantly influenced by shadow and suction effects. • A bundle factor correlation was proposed to predict the heat transfer coefficient for tube-bundle. In the presence of non-condensable gases, the effects of thermal-hydraulic parameters on steam condensation on a tube-bundle heat exchanger differ from those for a single-tube because the geometry of the tube-bundle enhances shadow and suction effects. In this study, experiments were performed to investigate these effects on three types of tube-bundle heat exchangers with pitch-to-diameter ratios of 2.0, 2.5, and 3.0, and pressures, air mass fractions, and wall subcooling of 200–500 kPa, 0.2–0.7, and 20–55 K, respectively. The local bundle factor was defined as the difference in condensation heat transfer coefficients between a single-tube and tubes in a tube-bundle. Therefore, a local bundle factor correlation, which accounts for the shadow and suction effects, was developed. The applicable ranges of the local bundle factor correlation for local pressure loss, Bird's suction factor, and blockage fraction were 0.267–0.734, 1.12–1.98, and 0.044–0.304, respectively. An average bundle factor was derived from the local bundle factor. The developed correlation applying the average bundle factor predicted the heat transfer coefficients for the obtained experimental data within an error of 8.50 %. [ABSTRACT FROM AUTHOR]

• An experimental study on steam condensation heat transfer in presence of non-condensable gas under high pressure up to 4.12 MPa were conducted. • The increase in pressure or decrease in the mass fraction of non-condensable gas would enhance the steam condensation heat transfer. • A significant increase of 98.2% in condensation heat transfer coefficient of steam with 10% Ar was obtained as the system pressure increased from 1.76 MPa to 3.12 MPa. With a great level of safety and reliability, an integrated steam-gas pressurizer is applied in the NHR-200 reactor. This work provided a solid experimental database regarding the pure steam, steam-Nitrogen and steam-Argon condensation under high pressure, which could be used to support the thermohydraulic analysis in steam-gas pressurizers of small modular reactor. The pressure ranged from 0.21 to 4.12 MPa. Benchmark experiments with pure steam found that the condensation heat transfer coefficient increased with pressure, but the response characteristics to specific pressure ranges were inconsistent. As is the case at low pressures, the introduction of non-condensable gas would weaken the steam condensation heat transfer. In particular, under high pressure, the effects of pressure on steam condensation depends highly on the species of non-condensable gas. A significant increase of 92.1% in condensation heat transfer coefficient of steam with 10% Ar was obtained as the pressure increased from 1.76 to 3.12 MPa. [ABSTRACT FROM AUTHOR]

Steam condensation consisting of noncondensable gas has been broadly investigated on external surfaces of various single tube and plates. Previous numerical analyses revealed that the high concentration air layer (HCAL) is the main thermal resistance for condensation. Comparing with the single tube/plate, condensation for bundle can be more complex. The HCAL near the adjacent tube surfaces may interfere and then influencing flow and heat transfer characteristics in the bundle. To evaluate the bundle effect, this study conducted experiments based on a 3 × 3 tube bundle at a wider pressure range (0.15–1.6 MPa). The results indicate that the bundle effect can be divided into two sub-effects: the enhancement effect and the inhibition effect, and the enhancement effect can make the average heat transfer performance of the bundle better than that of the single tube. The parameter thresholds for the two sub-effects were determined according to the broaden parameter scope. Generally, at small subcooling and low pressures, the inhibition effect dominants, and the bundle condensation heat transfer coefficient (CHTC) can be 22% less than that of the single tube; at large subcooling and high pressures, the enhancement effect dominants, and the bundle CHTC can be 71% greater. • The 3 × 3 bundle condensation experiment was conducted at pressures up to 1.6 MPa. • The tube bundle both has enhancement and inhibition effects on condensation. • The enhancement effect will exceed the inhibition effect with pressure increases. • The bundle average condensation performance can be greater than that of single tube. [ABSTRACT FROM AUTHOR]