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Steam condensation in the presence of air is an important thermal-hydraulic phenomenon in containment under loss of coolant accidents (LOCAs) or main steam line break accidents (MSLBs). Previous studies have focused on the effects of thermal parameters such as air mass fraction, gas pressure and sub-cooling on heat transfer characteristics, but less on the influence and action principle of geometric parameters such as tube length, tube diameter and inclination angle. Fully understanding the influence of geometric parameters on condensation heat transfer of steam containing air is of great significance for efficient heat transfer, so as to improve the safety and economy of related applications. The effects of tube diameter (4-60 mm), tube length (0.1-7 m) and inclination angle (0°-90°) on condensation heat transfer characteristics of air containing steam were studied based on the diffusion boundary layer condensation mechanism model by using three-dimensional CFD numerical simulation method. The results show that the tube diameter, tube length and inclination angle have significant effects on condensation heat transfer characteristics of air containing steam. However, when tube diameter exceeds 30 mm, tube length exceeds 1 m and inclination angle exceeds 60°, the average condensation heat transfer coefficient is no longer sensitive to the change of geometric parameters. The average condensation heat transfer coefficient decreases with the increase of tube diameter, and the descent speed decreases rapidly. When the tube diameter is 4 mm, the average condensation heat transfer coefficient is twice that of 60 mm. It first decreases and then increases with the increase of tube length, and reaches the minimum value at about 3 m. And it increases with the increase of inclination angle. The high concentration air layer near the wall is the main thermal resistance in the condensation process of steam-air, and its thickness makes a good negative correlation with condensation heat transfer coefficient. The high concentration air layer will first accumulate and thicken along the tube wall, and then produce a certain negative pressure due to the high density and high flow rate of mixed gas near the wall, so as to form a transverse velocity, so that the air layer will be thinned slowly after 1 m from the top of the pipe. Thus, the local condensation heat transfer coefficient decreases rapidly at first and then increases slowly along the direction of tube length. In addition, the tube circumferential local condensation heat transfer coefficient is uneven obviously under the inclined arrangement, the heat transfer on the upper surface is significantly enhanced due to the thinning of air layer by natural convection scouring and falling off, and gradually weakened to both sides, while the lower surface forms a stagnation zone due to the obstruction of the tube wall, which causes the accumulation and thickening of the air layer, resulting in a certain heat transfer inhibition. Compared with the vertical tube, about 75% of the circumferential area has different degrees of heat transfer enhancement, and only the dorsal flow surface has a certain heat transfer inhibition.

In severe accident scenarios (e.g. LOCA), the steam condensation inside the containment area is of vital importance. This is because the containment pressure peak and long-term residual heat removal are closely related to the steam condensation efficiency. Note that the gas inside the containment area is a mixture of steam and air/hydrogen. Steam condensation consisting of non-condensable gases has its own characteristics. Compared to pure steam condensation, it has a much lower heat transfer coefficient and the local phenomena are more complex. Considering that steam condensation is closely related to other phenomena in containment thermal-hydraulic analysis, further studies should be carried out. In the present work, the STAR-CCM+ software is used with a diffusion boundary layer condensation model. Various cases from the COPAIN and Su experiments are simulated and discussed. In the simulation of the COPAIN experiment, the effect of the mesh density (main-stream mesh size and the Y+ value) on the boundary heat flux is compared with the experimental data. Additionally, the local velocity, temperature, and air mass fraction are compared and discussed. In the simulations of the Su experiment, calculated results for the main-stream temperature, near-wall region temperature, and heat transfer coefficient are compared with experimental results and discussed. The COPAIN numerical results indicate that (i) the boundary heat flux decreases linearly with any increase in the air layer thickness of up to 5 mm, and the effect of the air layer weakens with further increases in thickness; (ii) the convective heat flux is only responsible for up to 9.1% of the total boundary heat flux; and (iii) the automatic wall treatment gives a reasonable prediction of steam condensation. The simulations of the Su experiment show that (i) there is no obvious temperature stratification in the main-stream along the vertical direction and (ii) the thickness of the air layer close to the condensation tube is around 6 mm. These results provide basic guidance for the future design of condensation heat transfer enhancement structures. [ABSTRACT FROM AUTHOR]

The high efficiency heat extraction from the containment in severe accident is of utmost importance for nuclear power plants, and the Passive Containment Heat Removal System (PCS) is utilized for removing heat efficiently in third generation nuclear units. In order to enhance external steam-air condensation heat transfer, previous studies have primarily focused on specific structures, rib tubes, S-shaped tubes, or inclined tubes bundles, for instance. In the present study, a novel structure of helical coiled tube was designed and its external heat transfer characteristics were obtained through numerical simulation. The effects of coiled pitch, radial helical pitch, tube diameters and heights, two tube arrangements of vertical and horizontal on heat transfer characteristics were elucidated. It can be concluded that radial helical pitch and coiled pitch jointly impact the heat transfer, a proper large radial helical pitch and narrow coiled pitch can result in an approximate 9% enhancement in condensation heat transfer coefficient (h a), and the utilization of narrowed pipe diameters and longer tube heights facilitates the augmentation of heat transfer. Moreover, for vertical arrangement, h a can be enhanced over 15% by rising tube numbers, for horizontal arrangement, h a primarily influenced by tube pitch, the heat transfer is deteriorated by narrow tube pitch, but improved by widening them. • A novel effect that influences the external condensation heat transfer was proposed. • Derived condensation behavior during steam-air external condensation on helical coiled tube. • Effects of various parameters on heat transfer characteristics outside helical coiled tube were elucidated. • A helical tube bundle structure exhibiting exceptional heat transfer performance was obtained. [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]

Steam condensation containing non-condensable gases is the main method of heat removal under severe nuclear accidents. To investigate the condensation characteristic, several numerical simulation studies have been conducted. Previous numerical models generally assume that the condensate film is thin or even negligible owing to the existence of non-condensable gases. However, the condensation rate improved rapidly as steam concentration rises. As the condensation rate rises, the velocity and thickness of the film will also sharply increase, thereby affecting the condensation process. In this case, the film flow will transition to a turbulent regime. To consummate the condensation model, a two-phase condensation model with predictable turbulent film was proposed. The model can predict the condensation performance well in a broad range, with deviation generally within 20%. In addition, the prediction correlation and contour diagram were obtained to identify the thermal resistance ratio and the flow regime of the film according to the proposed model. • A two-phase condensation model with predictable turbulent films is proposed. • The mechanism of the film effect on the condensation process is revealed. • The distribution of fluid film thermal resistance ratio is given. • The discriminant method of fluid film flow regime is obtained. [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]

Steam condensation in the presence of air is a vital heat transfer process in postulated loss of coolant accidents. To numerically evaluate local and global thermal hydraulic properties, several single-phase models have been developed in previous studies. However, potential mutual interactions between the liquid and gas phase (e.g. evaporation, radioactive material retention, etc.) impose requirements on two-phase models. Accordingly, the present work performed CFD evaluations on a two-phase boundary layer model (TPBL) which concerned the gas phase, liquid phase and their mutual interactions. Assessments were performed by comparing calculated results with the COPAIN and TOSQAN experimental data. The COPAIN cases show that predicted local and average heat fluxes are generally within 25% and 15% deviation, respectively. Detailed properties were obtained on the formation, distribution, and thermal resistance of liquid film as well as the model computational costs. In the TOSQAN cases, two steady states, including steam-air mixtures and steam-air-helium mixtures were considered. Via these cases, the applicability of the TPBL model in predicting local field profiles like velocity, temperature and concentration distribution was discussed. Results demonstrate that the calculated results overall agree well with the experimental ones. In general, the TPBL model is feasible in postulated accident analysis. [ABSTRACT FROM AUTHOR]

Steam condensation containing air is a ubiquitous phenomenon in practical industrial applications. It has been extensively investigated through numerical analysis and experimental studies. The conclusion that the high concentration air layer is the primary thermal resistance of the condensation process is widely accepted. Therefore, thinning the high concentration air layer is the key to enhancing condensation performance. For this purpose, applying the extraction method to remove the high concentration air layer near the heat exchanger can potentially be a direct and effective way to enhance condensation performance. To evaluate the extraction effect, this work conducted numerical simulations for a single tube that added extractors at P = 0.3 MPa, △T = 15 °C, and ω a = 0.56. In the discussions, the condensation performance with various extraction structure parameters (e.g., extraction height Z , extraction distance △L , extractor diameter D , number of extractors n) were investigated. The results indicated that the extractor could greatly enhance the condensation performance. For the single extractor case, the extractor (Z = 0.75 m, D = 50 mm, △L = 5 mm) has the optimal enhancement effect, which can reach 42.4%. For the multi-extractor case, the enhancement effect is optimal (76.3%) when the number of extractors n is 11. • The extraction effect is proposed and its influence on condensation is discussed. • The relationship between the extraction parameters is illustrated. • The mechanism of the extraction effect on the process of condensation is revealed. • The suggestion of optimal extraction parameters scheme is given. [ABSTRACT FROM AUTHOR]

Under the severe accident of the nuclear reactor, the strong coupling phenomenon exists between the transport and condensation of the steam-air-hydrogen multi-component gas in the containment atmosphere. Under this coupling effect, the flow patterns of mixture gas induced by condensation are critical to hydrogen accumulation risk assessment. The general flow characteristics of typical flow patterns were qualitatively predicted and confirmed in our previous work. However, the transient mass transfer process of multicomponent gases is complex, and flow pattern transitions are difficult to be captured. To further clarify these contents, experiments and corresponding numerical simulations are combined in the present work. The formation mechanism of the typical flow patterns is further revealed. The flow pattern transition boundaries of the mixture are quantified based on more data in confirmatory experiments. Experiments are performed under wider wall sub-cooling (Δ T = 60–110 °C) and wider range of steam concentration (X steam) from 16% to 90%, the volume concentration of helium in non-condensable gases (X He / X Non) ranges from 10% to 70%. Results show that the homogeneous downward flow is generally formed when X He / X Non < 40%. Under medium helium concentration (X He / X Non : 42%–55%), when X steam > 30%, the flow pattern of the mixture gas is the separation flow. Under high helium concentration (X He / X Non > 55%), the flow pattern of the mixture gas is the homogeneous upward flow when X steam > 20%. Furthermore, the empirical component correlations to classify the three flow patterns are proposed for the first time. Correlations and numerical simulation have good consistency in the prediction of flow patterns under most component conditions. • Transient mass transfer of multicomponent gases induced by condensation is discussed. • The formation mechanism of the typical flow patterns is further revealed. • Flow pattern transition boundaries of the mixture gas are quantified based on test. • Empirical component correlations to classify the typical flow patterns are proposed. • Correlations and numerical simulation results have good consistency. [ABSTRACT FROM AUTHOR]

A set of condensation experiments in the steam–air and pure steam conditions has been conducted to evaluate the heat removal capacity of a vertically pin-fin tube under free convection. Condensation heat transfer coefficient and heat transfer rate have been obtained. The bulk temperature, wall temperature and temperature near tube surface are measured in detail. As a reference, a smooth tube is tested under the same condition. For pure steam case, the pin-fin tube generates restrictions on the condensation heat transfer process in low wall subcooling region. With a higher wall subcooling, the pin-fin tube shows a larger condensation heat transfer coefficient than smooth tube does. For steam–air mixtures case, the result of the temperature measurement demonstrates that there is an air rich region near the pin-fin tube. Compared with the smooth tube, the pin-fin tube generates reduction effect on the condensation heat transfer process under low air mass fraction situation. As air mass fraction increasing, the condensation heat transfer coefficient of the pin-fin tube becomes larger than that of the smooth tube. [ABSTRACT FROM AUTHOR]

A set of condensation experiments in the pure steam and steam–air conditions have been conducted to evaluate the heat removal capacity of a vertically longitudinal finned tube in natural convection situation. The bulk temperature, wall temperature and temperature near the tube wall were measured in detail. The result of the temperature measurement demonstrated that there was an air rich region near the longitudinal finned tube while gas stratification phenomenon was not found in the mainstream. Condensation heat transfer coefficient and heat transfer rate have been obtained for air mass fraction ranging from 0.07 to 0.95, total pressure ranging from 0.2 MPa to 0.7 MPa. A smooth tube was also tested under the same condition as a reference. At pure steam case, the longitudinal finned tube played a positive effect on the condensation heat transfer, showing a growth of the condensation heat transfer coefficient by a factor of 3.86–4.89. At the steam–air case, the longitudinal finned tube generated restrictions on the condensation heat transfer process when air mass fraction was below 75%. However, the longitudinal finned tube enhanced the heat transfer process for the air mass fraction in excess of 75%. [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]

• The pressure range for the experiment was 0.2~1.6 MPa and the subcooling was 28~114 °C. • The effect of tube diameter and inclination angle in the tube bundle was analyzed. • A segmented experimental correlation with high relevance was obtained. Steam condensation accompanying with air is an important thermal-hydraulic phenomenon in reactor containment. Condensation outside tubes is an important method to remove heat out of the containment under an accident. Most of the previous studies have been conducted on single tube and vertical plates, where the findings may not reflect the heat transfer in tube bundle well. The experimental studies were firstly carried out based on 3 × 3 tube bundle with diameters of 12–19 mm and inclination angles of 0–90° in the parameter range of pressure 0.2–1.6 MPa, air mass fraction of 12.1–75.2% and wall subcooling of 28.3–114.1℃. The results indicate that the effect of diameter and inclination angle in the tube bundle varies significantly in different pressure ranges. When the pressure is less than 0.8 MPa, the condensation heat transfer coefficient (CHTC) generally increases with decreasing tube diameter and inclination angle. The CHTC of the heat transfer tube with a tube diameter of 12 mm and an inclination angle of 0° increased by a maximum of 29% compared to that of the heat transfer tube with a tube diameter of 19 mm and an inclination angle of 90°. When the pressure is 0.8–1.6 MPa, the overall CHTC decreases as the diameter of the tube decreases, and the maximum reduction is about 20%. It decreases first and then increases with the decrease of the inclination angle, and the CHTC is the smallest when the inclination angle is about 60°. [ABSTRACT FROM AUTHOR]

The relative content and transport behavior of steam-air-hydrogen are of vital importance for nuclear power plants under severe accidents. Since there are many cold walls in the nuclear reactor containment building, the condensation of steam can directly change the mixture gas component and affect the air-hydrogen transport characteristics. The local accumulation of air-hydrogen increases the risk of hydrogen combustion, and then threatening the containment structural integrity. To reveal the coupling effect between steam condensation and multicomponent gas transportation, the present work established a mechanism CFD model which can locally evaluate multi-component gas heat and mass transfer. Numerical simulations were performed in pressures of 0.2–1.3 MPa, steam volume fractions of 10–90%, and hydrogen volume fractions of 10–70% in non-condensationable gas. In the whole parameter range, three flow patterns were found and classified: homogeneous downward flow, separation flow, and homogeneous upward flow. The reasons for the formation of the flow patterns were revealed and the margins amongst the three flow patterns were quantitatively marked on a Shapiro-Moffette ternary diagram. Moreover, a key component separation phenomenon induced by steam condensation was firstly discovered. [ABSTRACT FROM AUTHOR]

• Experiments were conducted at pressures up to 1.6 MPa and subcooling up to 128 °C. • The air deterioration effect obviously weakens with the increase of pressure. • The power exponents of pressure and subcooling were clarified in wider ranges. • A more generalized experimental correlation was proposed based on 1500 data points. In loss of coolant accidents, steam condensation containing air is one of the most important thermal–hydraulic phenomena inside nuclear reactor containment. To evaluate the relation amongst heat transfer coefficients (HTCs) and thermal parameters, e.g., gas pressure, concentration and wall subcooling etc., several experimental correlations were fitted in previous studies. However, these experiments were performed at pressures lower than 0.6 MPa, thus the proposed correlations may not be suitable for integrated nuclear reactor containments with a design pressure greater than 1.0 MPa. To further evaluate this problem, the study carried out experiments at pressures from 0.15 to 1.6 MPa and wall subcooling from 20 to 128 °C. The effects of pressure and wall subcooling on tube external condensation HTCs were discussed. The results indicate that the non-condensable gas deterioration effect obviously weakens with the increase of pressure, and the power exponents of pressure, wall subcooling and mass fraction were clarified according to the broad-range experimental data. Based on the 1500 data collected from the present experiment and the Su, Fan, Dehbi experiments, a more generalized experimental correlation was proposed with deviations generally within ± 15%, which unified the data from different experiments in various parameter ranges. [ABSTRACT FROM AUTHOR]

Under severe accident conditions of a pressurized water reactor, hydrogen will be released into the containment, forming a mixture of steam-air-hydrogen, and then transported to the surroundings. This process can be coupled with complex mass transfer behavior caused by wall condensation. Under the coupling effect of condensation and buoyancy introduced by hydrogen, the mixture gas will form different types of transport behaviors. This will be closely related to the stratification and flammability risk of high-concentration hydrogen. To quantitatively determine these phenomena and assess the potential causing reasons, experiments were performed with helium instead of hydrogen based on the COAST (condensation and species transport) facility. The tests cover a broad parameter range with steam concentrations of 8.4– 89%, helium concentrations of 10– 66% (X He / X Non), and pressures of 0.4– 1.3 MPa. The phenomena of steam condensation induced component separation were firstly confirmed in the tests, and the component concentration threshold was clarified at X He / X Non = 50%. The three flow patterns of steam-air- helium mixture gas was identified by Shapiro-Moffette ternary diagram. Moreover, the temperature inverse stratification caused by the high-concentration helium-air layer was discovered in the experiments, and its influence on heat transfer was clarified. • The phenomenon of hydrogen-air component separation was firstly confirmed. • Three mixture flow patterns were evaluated quantitatively in the experiments. • The temperature inverse stratification was discovered in the experiments. • The effect of mixture gas flow patterns on condensation heat transfer was clarified. [ABSTRACT FROM AUTHOR]

Abstract: A one-pot base-mediated synthesis of 5-oxopyrrolidine-2-carboxamides was developed. The reaction of Baylis–Hillman bromides 1, primary amines 2, isocyanides 3 and arylglyoxals 4 produced the 5-oxopyrrolidine-2-carboxamides 6 in good yields via a tandem Ugi condensation and intramolecular substitution at room temperature in the presence of Cs2CO3. [Copyright &y& Elsevier]

• The experimental pressure range (0.15 ~ 1.6 MPa) and subcooling range (28 ~ 122 °C) are relatively large. • The effect of tube diameter and inclination angle on the condensation with non-condensable gases was analyzed. • An experimental correlation containing the effect of tube diameter and inclination angle was obtained. Steam-air condensation is one of the important physical phenomena after reactor accidents, which has direct impacts on the discharge of containment residual heat after the accident. Previously, many researchers have proposed experimental correlations for condensation of non-condensable gas, which include the influence of pressure, concentration, and wall subcooling. However, there are relatively few studies on the influence of tube diameter and inclination angle. In order to investigate the heat transfer characteristics of the condenser at different tube diameters (19 mm, 15 mm, 12 mm) and inclination angles (0 ~ 90°), experiments were carried out in the pressure range of 0.15 ~ 1.6 MPa, air mass fraction of 14 ~ 87%, and wall subcooling of 28 ~ 122 °C. It shows that the condensation heat transfer coefficient (HTC) increases with the decrease of the tube diameter and inclination angle. The condensation HTC with a tube diameter of 12 mm and an inclination angle of 0°(Horizontally) is around 32 ~ 38% larger than that of the heat transfer tube with a tube diameter of 19 mm and an inclination angle of 90°(Vertically). Based on a total of 2276 data points from the present work and related experiments, an experimental correlation containing the effect of tube diameter and inclination angle is proposed, and its deviation is within ± 15% with 95% confidence. [ABSTRACT FROM AUTHOR]

Steam condensation with existence of air is an important thermal hydraulic phenomenon in reactor containment. Previous investigations mostly focused on the surfaces of plates or tube bundles which are in parallel with the gas flow direction, and discussions on heat transfer surfaces with various inclination angles were merely restricted to plates. In addition, there is limited information about the condensation promotion effect caused by enlarged gas flow velocity at different tube inclination angles. To investigate the coupling effects of tube inclination and flow velocity, numerical simulations were carried on a 3 × 3 tube bundle. The local thermohydraulic profiles and heat transfer mechanism of steam condensation were analyzed carefully. The results indicate that the increase of inclination angle and flow velocity can dramatically promote condensation heat transfer. At the velocity of 0.3 m/s, the condensation heat transfer enhanced 327.8% as the tube bundle orientation changes from vertical to horizontal. At the inclination angle of 0°, the condensation heat transfer increased 223.2% as flow velocity increased from 0.3 m/s to 3 m/s. The inhibition effect and stack effect in tube bundle varied by the tube inclination and flow velocity. [Display omitted] • The inclined 3 × 3 bundle condensation was simulated at velocities up to 3.0 m/s. • The inclination leads to areas with different air mass fraction in the bundle. • Classic inhibition and stack effect vary from inclination angles and velocities. • The inclination and acceleration can enhance condensation heat transfer. [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]

Condensation induced water hammer (CIWH) is a common phenomenon possibly appearing in industrial pipelines, which may cause pipeline oscillation and even serious damage to the components. Previous research on the CIWH mostly focuses on the steam-water counterflow under forced flow conditions. For new floating nuclear power plants proposed recently, the CIWH may occur in some passive natural circulation safety systems. Nevertheless, the CIWH in natural circulation systems (NCS) has never been reported publicly yet. In this paper, a series of experiments are performed to investigate the flow characteristics during the CIWH in a NCS. The basic flow and temperature characteristics of the CIWH caused by counterflow of saturated steam-water mixtures and subcooled water in the NCS are studied in detail. Thereinto, the steam condensation induced flashing (SCIF) along with CIWH is firstly observed and analyzed. Moreover, the influences of CIWH on the flow behavior of the system are discussed under natural circulation and forced circulation conditions. The experimental results indicate that the occurrence of CIWH can result in further reverse flow of the subcooled water, which causes a sudden decrease in the flow rate of NCS. Moreover, the flow rate is more unstable under natural circulation than under forced flow. • Condensation induced water hammer in natural circulation systems was experimentally investigated firstly. • Steam condensation induced flashing along with CIWH was firstly observed and analyzed. • The CIWHs under forced and natural circulation conditions were compared and analyzed. • The influence of CIWH on the flow rate of natural circulation system was analyzed. [ABSTRACT FROM AUTHOR]

Steam condensation in the presence of non-condensable gases is a dominating phenomenon inside a containment under LOCA scenarios. In numerical simulations, the basic diffusion boundary layer condensation model (BDBLM) has been proposed for containment thermal-hydraulics analysis. However, there are still some incompleteness such as the under prediction of heat transfer coefficient when the steam mass fraction is high. Besides, the effect of thermal diffusion (Soret effect) on condensation heat transfer has not been specified quantitatively. In order to compensate these shortcomings, a modified diffusion boundary layer model (MDBLM) was proposed and assessed in detail. In the modified condensation model, the under prediction of condensation heat transfer at high steam mass fraction conditions was modified by adding a suction effect parameter. The Soret effect was assessed by adding a new term including the temperature gradient, thermal diffusion coefficient, and steam mass fraction. The results indicate that the MDBLM could give a good prediction of heat transfer coefficient (HTC) at low air mass fraction conditions with deviations within 20%. The Soret effect takes less than 7% in the total mass transfer when the mainstream temperature is saturated and could be more than 80% when the mainstream temperature is superheated. [ABSTRACT FROM AUTHOR]