Steam Condensation Heat Transfer Research Articles

Experimental Investigation of Large-Scale Vertically Coated Tubes for Enhanced Air–Steam Condensation Heat Transfer

Non-condensable gas plays a significant role in steam condensation, primarily by reducing heat transfer efficiency. Enhanced condensation heat transfer in the presence of non-condensable gas is crucial for improving thermal efficiency, reducing energy consumption, and lowering costs. However, experimental studies on applying coatings to enhance condensation heat transfer in large-scale vertical outer tubes with non-condensable gas are scarce. This study investigates the condensation heat transfer performance of vertical stainless steel- and brass-coated tubes compared to their bare counterparts at different air concentrations (0.4, 0.3, 0.15, and 0.08). All tubes have an outer diameter of 19 mm and an effective length of 1080 mm. Visualizations reveal that condensate flow rates as high as 0.5 m/s on bare tubes cause significant disturbances to the diffusion layer. At various air concentrations, the maximum condensation heat transfer coefficient of the coated stainless steel tube exhibited increases of 22.2%, 11.9%, 4.2%, and 19.6% compared with the uncoated stainless steel tube. Similarly, the maximum condensation heat transfer coefficient for the coated brass tube showed significant increases of 58.9%, 53.5%, 68.0%, and 70.7% compared with the uncoated brass tube. Notably, the enhancement effect on heat transfer performance is more pronounced when the same type of modified surface is applied to the brass tube compared with the stainless steel tube.

Experimental study on heat transfer characteristics of steam condensation in the presence of air and CO2 outside a vertical tube

Under severe accident conditions, in addition to steam and air, there are also other non-condensable gases inside the containment, such as CO2 produced by the molten corium concrete interaction (MCCI). Due to the significantly higher molecular weight and density of CO2 compared to steam and air, CO2 will have a significantly different impact on the steam condensation process compared to air. However, few scholars have paid attention to the impact of CO2 on the condensation process, and there is no empirical correlation applicable to this condition. Therefore, this article investigates the effect of different CO2 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 CO2 and air was fitted. The results indicate that under low steam concentration conditions, the addition of CO2 will reduce CHTC, while under high steam concentration conditions, CO2 will increase CHTC. The increase in system pressure will strengthen the condensation promotion effect of CO2 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.

Effect of twisted tapes and surface extensions in enhancing the condensation heat transfer of high-temperature saturated steam in a circumferential rectangular channel

This article numerically investigates the impact of twisted tapes and extended surfaces (fins) on enhancing high-temperature steam flow in a circumferential rectangular channel, akin to the external jacket cavity of a tyre cure press. The passive enhancement techniques for improving the mold warm-up time of the tyre curing process have received limited attention in previous studies, which have primarily focused on enhancing heat transfer in configurations and working conditions typical of heat exchanger applications. The objective of this article is to enhance the condensation heat and mass transfer rate by geometrically modifying the internal flow path of the circumferential rectangular channel, resembling an external jacket cavity of a tyre cure press, using twisted tapes and extended surfaces. Four configurations are simulated: i) conventional circumferential rectangular channel, ii) channel with twisted tapes, iii) channel with surface extension, and iv) channel with both twisted tapes and surface extension. The heat transfer performance of all the modified channel configurations derived from the simulation results is assessed in comparison to the conventional channel. The channel, featuring a design that includes five twisted tapes with a twist ratio of 8 and 54 extended surfaces, records a substantial 36.85% rise in heat flux along with a notable 24% increment in the condensation mass flux. The simulation results are validated using an in-house experimental study. The tyre cure press in the experimental setup is modified to align with the design proposed by the simulation results, and a warm-up study is conducted. The warm-up time for the modified mold to attain the desired temperature is reduced by 33%, with no accompanying increase in steam consumption, compared to the warm-up time for the conventional mold. This significant reduction in mold warm-up time holds immense potential in enhancing the productivity rate, an ongoing requirement of the automobile industry.

A Predictive Machine Learning-Based Analysis for In-Tube Co-current Steam Condensation Heat Transfer in the Presence of Non-condensable Gases

AbstractThe primary objective of this study is to develop a predictive model that accurately estimates the condensation heat transfer coefficient (HTC) in the context of in-tube co-current flow condensation, with specific consideration given to the influence of non-condensable gases (NCGs). The need to find useful models and/or correlations that can accurately predict how well a passive condenser in the Economic Simplified Boiling Water Reactor will transfer heat during condensation is greatly warranted. This innovative cooling system utilizes gravity to condense water vapor, effectively dissipating heat from the containment vessel in the event of an accident and transferring the heat into the secondary cooling system. For the development of the forecasting model, we employed Multi-Gens Genetic Programming implemented in MATLAB. This approach possesses the capability of enabling visualization and articulating a transparent mathematical expression that directly establishes the connection between inputs and outputs. This model was specifically developed for forecasting the HTC during the condensation process, considering two distinct types of NCG: air, helium, and a mixture of air and helium, in addition to data for pure steam. The model was trained using a dataset comprising 2913 data points gathered from five experimental references. The model's input comprises a varied range of parameters, including local location ($$z$$ z ), temperature of the steam/NCG mixture ($${T}_{mix}$$ T mix ), condenser wall temperature ($${T}_{wall}$$ T wall ), coolant flow rate ($$\beta_{c}$$ β c ), total pressure ($${P}_{tot}$$ P tot ), condenser inner diameter ($${D}_{1}$$ D 1 ), condenser outer diameter ($${D}_{2}$$ D 2 ), molecular weight (MM), NCG mass fraction ($${w}_{NCG}$$ w NCG ), and mixture Reynolds number ($${Re}_{mix}$$ Re mix ). The output of our model corresponds to the condensation HTC ($$h$$ h ). Four specific correlations were examined with the third correlation attaining the highest anticipated values within a deviation range of ± 30, reaching 90.9%, exhibiting good performance in terms of both performance index and coefficient of determination. This correlation was validated, and its accuracy assessed by employing an unused training dataset that included nitrogen as a NCG. The outcomes showed that 92.94% of the predicted data fell within a deviation range of ± 30%. The findings of this study signify a notable advancement in the analysis of datasets obtained from experiments. Particularly, it delves into the impact of NCGs by considering their molecular weight and mass fraction.

Steam Condensation Heat Transfer in the Presence of Noncondensable Gases (NCGs) in Nuclear Power Plants (NPPs): A Comprehensive Review of Fundamentals, Current Status, and Prospects for Future Research

Efficient steam condensation is crucial for safe nuclear power plant (NPP) operations, preventing pressure buildup, overheating, and the release of radioactive materials. However, the presence of noncondensable gases (NCGs), such as air, nitrogen, hydrogen, or helium, can hinder the condensation process by creating a thermal resistance layer that impedes steam diffusion and condensation on the system’s surface. Maximizing the efficiency of steam condensation requires a thorough grasp of the fundamental processes, theories, advancements, and technical hurdles. Therefore, this work thoroughly addresses these needs, with a particular emphasis on addressing the challenges posed by NCGs by dividing the work into four thematic areas. The first theme relates to a comprehensive examination of pure steam condensation phenomena, which includes an exploration of familiar condensation scenarios and various film condensation types. The second theme examines condensation in the presence of NCGs, their mixture properties, and related theories and modelling of heat and mass transfer. The third theme investigates condensation in NPP by exploring passive cooling systems and condensation phenomena under both natural and forced convection conditions during nuclear accidents, the origin of NCGs in NPP and their transportation aspects. This is followed by experimental work related to condensation scenarios and scale. Finally, the last theme looks upon the recent advancements in computational fluid dynamics (CFD) modelling of wall condensation, system analysis codes coupling with CFD, and the implementation of machine learning (ML) for predicting the condensation HTC. By bridging the gap between fundamental knowledge and practical applications, the four thematic areas presented in this work are aimed at providing a comprehensive foundation for researchers and experts in the field of steam condensation when NCGs are involved. The ultimate objective is to bolster the safety and efficacy of NPP operations by understanding the heat and mass transfer mechanisms while mitigating the risk of catastrophic events.

Experimental investigation on steam condensation characteristics in horizontal heat transfer pipe of PRS for HPR1000

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 %.

Heat transfer characteristics in vertical tube condensers: Experimental investigation and numerical validation

The paper establishes a vertical steam condensation heat transfer experimental device to investigate the process of liquid film condensation heat transfer under the countercurrent heat transfer of a secondary coolant. An improved experimental method, integrating measurements and simulations, accurately calculates local heat transfer coefficients and heat flux. The validity of the data is confirmed through comparison with established condensation correlations, affirming the method's effectiveness. The correlations of previous research (i.e., Numrich, Carey, Oh, Lee, and Shah) demonstrate greater consistency with the experimental results, with mean relative deviations (MRD) of −4.90%, 7.18%, 11.42%, −8.63% −4.45%, and mean absolute relative deviations (MARD) of 11.61%, 21.57%, 23.60%, 18.97%, and 12.53%, respectively. Numrich's correlation demonstrated the closest congruence. Based on these results, the research proposes a new coupled heat transfer model, effectively simulating the interaction between external cooling water and steam condensation. This model simplifies the process by pre-defining coolant temperature changes per unit length, thereby reducing the need for extensive iterative calculations and eliminating assumptions about wall temperature. It accurately predicts the wall temperature, local condensing temperature, and coolant temperature in a vertical condenser. These experimental methods and models offer valuable insights for optimizing vertical condenser design and analysis. The study underscores the significance of combining simulation models with experimental measurements to enhance the understanding of heat transfer in complex systems. The findings promise to advance research in film condensation heat transfer and assist in condenser design and optimization.

Experimental investigation and visualization of steam condensation heat transfer on horizontal conical surfaces with microgrooves

ABSTRACT This paper presents a novel conical copper plate with microgrooves structure to enhance heat transfer by removing accumulated condensate in horizontal surface condensation. The experimental investigation focuses on the condensation occurring on horizontal conical plates under atmospheric pressure. Results show that the heat transfer performance of all conical grooved plates surpasses that of smooth plates. Increasing groove number enhances heat transfer coefficient while having negligible influence on pressure drop. In contrast, increasing top diameter leads to higher pressure drop values. The optimal surface heat transfer coefficient strengthening ratio reaches 1.58, providing valuable insights for future studies and practical engineering applications.

Condensation enhancement experiment investigation of pure steam and steam-air mixture over the chrome-plated tube with different plating thickness

The condensation enhancement research of pure steam and steam with non-condensable gas is of great significance for reactor safety. In this study, to evaluate the influence of chrome-plated tubes on condensation enhancement, pure steam and steam with air condensation heat transfer experiments are conducted, and the plating thicknesses of 1 μm (tube #1) and 10 μm (tube #2) are considered. The results show that dropwise condensation (DWC) occurred in the part of tube #1 surface, while tube #2 surface is filmwise condensation (FWC). For the pure steam condition, the steam condensation heat transfer coefficient (HTC) of tube #2 is higher than that of tube #1, and both are greater than the theoretical analysis of Nusselt. Thus, the condensation enhancement effect of the chrome-plated tubes is remarkable. For the steam with air condition, a new condensation HTC expression is proposed, which is related to gas pressure, wall subcooling, and air mass fraction. Compared with the widely used experimental correlations and the experimental data of polishing tubes, it is found that the condensation enhancement performance is not significant. This is because the dominant thermal resistance affecting heat transfer is the air layer at the gas-liquid interface. Thus, enhancing the disturbance of the gas layer is the key to the condensation enhancement of steam with non-condensable gas.

Research and Application of Steam Condensation Heat Transfer Model Containing Noncondensable Gas on a Wall Surface

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.

Reducing CO2 emissions and improving oil recovery through silica aerogel for heavy oil thermal production

Heavy oil reserves comprise more than 60% of global crude oil resources, and thermal oil recovery techniques, especially steam injection, are widely utilized for extracting heavy oil. However, these thermal production processes are characterized by high energy consumption and carbon emissions, which pose significant challenges in reducing CO2 emissions. In response to these challenges, this study presents a novel approach that combines silica aerogel with CO2-assisted thermal recovery technology. Our findings demonstrate that the incorporation of aerogel nanoparticles enhances the adsorption capacity of CO2 in the aqueous phase. The adsorption behavior of CO2 in silica aerogel aligns with the Langmuir model. When silica aerogel nanoparticles are employed in steam flooding, a notable improvement is observed in both oil recovery and CO2 sequestration rate. Molecular dynamics simulations reveal that the porous structure of aerogel enables the adsorption of light saturates molecules from crude oil, promoting their diffusion into the aqueous phase and ultimately enhancing oil recovery. The steam condensation experiments clearly demonstrate that the presence of aerogel and CO2 exerts a substantial influence on the condensation heat transfer of steam, resulting in a reduction in the condensation heat transfer rate between the steam and the cooling wall. Additionally, molecular dynamics simulations reveal that silica aerogel nanoparticles exhibit an affinity for adsorbing onto hydrophobic quartz surfaces, forming an insulating layer between steam and quartz, thereby facilitating CO2 sequestration. The introduction of silica aerogel nanoparticles expands the swept volume of steam heat. This study provides valuable insights into the underlying mechanisms responsible for improved CO2 sequestration and increased oil recovery through the implementation of silica aerogel nanoparticles, offering fresh perspectives on heavy oil recovery.

A Multiscale Strategy for Constructing Finned Microporous Superhydrophobic Surface for Highly‐Efficient Condensation Heat Transfer Enhancement Enabled by Lifespan Regulation of Droplets

AbstractSpontaneous droplet jumping on micro‐/nano‐structured superhydrophobic surfaces has been exploited as an efficient means for enhancing steam condensation heat transfer. However, the good performance of such surfaces quickly decays with raising the degree of subcooling, due to the mismatch between the characteristic length scales and droplet sizes when they grow up. Herein, a novel strategy for multiscale droplet regulation is proposed by combining sub‐millimeter fin structure with a hierarchical microporous superhydrophobic surface. A superior condensation heat transfer performance is attained on such hierarchical superhydrophobic finned tube (F‐SHB), in comparison to the baseline case of superhydrophobic non‐finned (SHB) tube under well‐controlled test conditions. Although the droplet jumping is not as vigorous as that on the SHB tube, the finned geometry of the F‐SHB tube leads to a condensation heat transfer enhancement even under high degrees of subcooling up to 36 K, because of the accelerated departure of large droplets by imposing Laplace force gradient in the presence of V‐shaped sub‐millimeter fins. This multiscale enhancement strategy is shown to enable a cascading regulation over the entire lifespan of condensate droplets. The fabrication of F‐SHB tubes is facile and easy to be scaled up, showing great potential in practical steam condensation applications.

Experimental study of steam condensation heat transfer characteristics in a horizontal tube under rolling motion

As an efficient heat transfer method, in-tube condensation heat transfer is widely used in various fields, including passive residual heat removal systems (PRHRS) of floating power plants under ocean conditions. The experimental investigation aimed to study the condensation heat transfer characteristics of steam in a 25 mm inner diameter horizontal tube with a heat transfer length of 1050 mm under rolling motion. The study used a mass flux of 30 kg/(m2·s) and investigated average vapor qualities, rolling amplitude, and rolling period ranging from 0.32 to 0.79, 0 °–20°, and 10 s–20 s, respectively. The experimental results show that the condensation flow patterns under rolling conditions are more complex than those under non-rolling motion due to the influence of the rolling period and rolling amplitude. The instantaneous heat transfer coefficient (IHTC) changes periodically due to the rolling motion and has the same change period. The pulsation amplitude of the IHTC increases with increasing rolling amplitude but weakens as the vapor quality increases. The effect of the rolling period on the IHTC is much less than that of the rolling amplitude. At low vapor quality, the time-averaged heat transfer coefficient (THTC) under the rolling motion condition increases with the rolling amplitude and period, and the maximum enhancement of THTC is 44%. As the vapor quality increases, the THTC under rolling conditions is the same as that under non-rolling conditions. These findings provide important insights into the condensation heat transfer characteristics of vapor in a horizontal tube under rolling motion, which can help improve the design and operation of in-tube condensation heat transfer systems in various fields.

Prediction of heat transfer coefficients for steam condensation in the presence of air based on ANN method

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.

GAS-LIQUID FILM DISTRIBUTION AND SEPARATION OF CONDENSATION FROM A DOWNWARD-FLOWING STEAM-NONCONDENSABLE GAS MIXTURE ONTO A HORIZONTAL TUBE AT SUBATMOSPHERIC PRESSURE

Based on the boundary layer, a mathematical model was established to investigate the thicknesses of liquid and gas films and the steam condensate distribution in the presence of noncondensable gas outside a horizontal tube at pressures lower than atmospheric pressure. The model accurately predicts the steam condensation heat transfer with noncondensable gas. The influences of the noncondensable gas mass fraction, pressure, velocity, and surface subcooling upon the condensation heat transfer, the thicknesses of liquid and gas films, and condensate distribution around the horizontal tube have been studied. The liquid film thickness rises as the surface subcooling raises but reduces with raising pressure and mass fraction of noncondensable gas. The gas film thickness rises with rising surface subcooling and noncondensable gas mass fraction, reducing as the pressure rises. The thicknesses of gas and liquid films and condensate distribution significantly affect the local heat transfer. The liquid film separation velocity reduces with raising pressure, surface subcooling, and mass fraction of noncondensable gas, which is most influenced by pressure.

Development of correlations for steam condensation over a vertical tube in the presence of noncondensable gas using machine learning approach

Steam condensation is an important phenomenon encountered in nuclear reactor under severe accidents. Even though many correlations for predicting steam condensation heat transfer coefficient (HTC) in the presence of noncondensable gas (NCG) have been proposed over the past decade, a more reliable and accurate model is still required. Thus, in this study, multigene genetic programming (MGGP), a biologically inspired machine learning method, is applied to develop new correlations for condensation HTC of steam-NCG mixture over a vertical tube in turbulent free convection regime. To this end, a consolidated database with 1440 data points from 18 sources is compiled. Then, using the database, both a new empirical correlation and a MGGP model are developed for better comparison. The performance of the MGGP-based correlation selected using Pareto tournaments strategy is compared with the new developed empirical correlation and another 20 relevant correlations. The results reveal the superiority of the MGGP-based correlation. In addition, it is found that the tube length is excluded in the best-trained correlation, even though it is used as the input of MGGP, which agrees well with the results of previous theoretical and experimental studies. The present study demonstrates that MGGP is promising in developing explicit, accurate, and compact models for the complex heat transfer and multiphase flow phenomena such as steam condensation in the presence of NCG.

Experimental Investigation of Coolant Side Characteristic on the Performance of Air-Cooled Condenser Structured by Horizontal Flattened Tube

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.

Experimental investigation on the heat transfer enhancement of steam condensation on tube with hydrophilic-hydrophobic hybrid surface

The heat transfer enhancement of steam condensation on tube with hydrophilic-hydrophobic hybrid surface have been investigated comprehensively through experiment. It has been found that the steam condensation heat transfer performance on the tube with hydrophilic-hydrophobic hybrid surface has been enhanced significantly compared to that with hydrophilic surface. The results show that the steam pressure, cooling water velocity (flow rate) and non-condensable gas have influences on the steam condensation heat transfer performance on both tubes. The steam condensation heat transfer enhancement on the tube with hydrophilic-hydrophobic surfaces is due to the droplet drainage from hydrophobic stripes to hydrophilic stripes accelerating the discharge and formation of condensate from the tube. This work can be a guide for the design of enhanced condensing heat exchanger.

Experimental Analysis of Steam Condensation Heat Transfer Coefficient in Water Pool at Sub-Atmospheric Pressure

The experimental analysis of steam direct contact condensation in a water pool at sub-atmospheric condition was carried out in relevant configurations for the International Thermonuclear Experimental Reactor (ITER) Vacuum Vessel Pressure Suppression System, during a postulated Ingress of Coolant Event category IV accidental scenario. This transient accident was experimentally simulated in a reduced scale (1:22) facility at University of Pisa, adopting a defined scaling law. The steam jet plumes were video recorded and image analysis was performed at stable and interfacial oscillation condensation regimes, providing steam plume average length and interfacial area. The average heat transfer coefficient was therefore computed and correlated to the condensation driving potential. Also, the steam jet length divided by orifice diameter (L/D) was characterised as function of driving potential. Empirical correlations available in literature at atmospheric conditions were modified for evaluating vacuum conditions peculiarities. The remarkable higher dependence of heat transfer coefficient (HTC) to driving potential parameter, at vacuum conditions, was highlighted by the driving potential exponent equal to 1.2 instead of 0.04 at ambient pressure. The obtained L/D and HTCcorrelations are able to predict with ± 15% and ± 30% of error the corresponding experimental data, respectively.

Numerical study on the effect of CO2 on the heat transfer characteristics of steam condensation outside a vertical tube

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 CO2 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 CO2 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 CO2 mole fraction varies from 0 to 0.34 or 0.8. The results show that the CO2 demonstrates different influence laws at high and low steam concentrations, respectively. When the steam mole fraction is 0.66, as the proportion of CO2 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 CO2 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.