Search

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. [ABSTRACT FROM AUTHOR]

Given that two-phase closed thermosiphons (TPCT) are a prevalent and efficacious means of heat transfer. However, non-condensable gas (NCG) may potentially impact the heat transfer performance of the aforementioned devices. Nevertheless, the theoretical analysis of heat transfer in TPCT containing NCG is not fully comprehensive and therefore requires further supplementation by means of relevant experiments. This paper presents the development and experimental investigation of a theoretical heat transfer model for a TPCT containing NCG. The research encompasses the optimal fluid-filling ratio of R22 and R410a working fluid and the impact of NCG on heat transfer in the condenser section of TPCT. Experimental findings indicate that TPCT with R22 and R410a working fluids at a fluid-filling ratio of 60% and 50%, respectively, demonstrate excellent isotherm and heat transfer efficiency. The presence of NCG affects the condenser section heat transfer process of the vapor, leading to a 2 °C decrease in the average temperature of the condenser section of the TPCT (Tca). In comparison with the TPCT without NCG, it was observed that an increase in the mass of NCG from 0.0097 to 0.0197 mol resulted in a reduction in the effective length of the condenser section (La) and effective heat transfer rate (κ) of R22 TPCT. The decrease in La was 75.1 mm, while the decrease in κ was 15.02%. Furthermore, at the same NCG mass, the effective heat transfer rate of R410a TPCT is evidently superior to that of R22 TPCT. The NCG in the TPCT can be removed by using a check valve. Nevertheless, this will result in a reduction in the fluid-filling ratio of the TPCT. The temperature of the R410a TPCT containing 0.0197 mol NCG with a fluid-filling ratio of 50% is comparable to that observed in fluid-filling ratio of 40% after the NCG is exhausted. [ABSTRACT FROM AUTHOR]

Condensation on surfaces in the presence of non-condensable gas (NCG) is a ubiquitous and critical phenomenon in many industrial fields. However, current empirical correlations for predicting condensation heat transfer coefficients in the presence of NCG may exhibit significant deviations from reality. Machine learning algorithms are now being dedicated to this field, but the models developed can only predict the condensation heat transfer coefficients of steam or vapor of a non-aqueous working fluid with similar physical properties to water in the presence of NCG. In the present study, a comprehensive theoretical analysis was conducted to investigate the total condensation heat transfer coefficients with NCG, and 16 dimensionless numbers were identified as input variables for machine learning models. Based on a filtered database consisting of 4377 data points extracted from 37 papers, the Spearman correlation coefficients were calculated to evaluate the relationship between the total heat transfer coefficients and the input variables, indicating the magnitude of the impact of the 16 dimensionless variables. Four machine learning models, namely Gradient Boosting Regression (GBR), Extreme Gradient Boosting (XGBoost), Random Forest Regression (RFR), and Multilayer Perceptron (MLP), were developed to predict the total heat transfer coefficients for water and non-aqueous working fluids. The mean absolute percentage errors for the four models were 1.38%, 1.63%, 3.00%, and 4.42%, respectively, with the GBR model exhibiting the highest degree of accuracy. The determination of the application scope of these models was conducted by analyzing the value ranges for each dimensionless parameter and its corresponding frequency distribution. • Four machine-learning models were developed to predict condensation heat transfer. • Sixteen dimensionless variables were determined as input parameters for these models. • These models can predict condensation heat transfer under different working conditions. • Conditions were diverse in types of wall geometry, convection, working fluid and NCG. [ABSTRACT FROM AUTHOR]

SMART100 has a containment pressure and radioactivity suppression system (CPRSS) for passive containment cooling system (PCCS). This prevents overheating and over-pressurization of a containment through direct contact condensation in an in-containment refueling water storage tank (IRWST) and wall condensation in a CPRSS heat exchanger (CHX) in an emergency cool-down tank (ECT). The Korea Atomic Energy Research Institute (KAERI) constructed scaled-down test facilities, SISTA1 and SISTA2, for the thermal-hydraulic validation of the SMART100 CPRSS. Three separate effect tests were performed using SISTA1 to confirm the heat removal characteristics of SMART100 CPRSS. When the low mass flux steam with or without non-condensable gas is released into an IRWST, the conditions for mitigation of the chugging phenomenon were identified, and the physical variables were quantified by the 3D reconstruction method. The local behavior of the non-condensable gas was measured after condensation inside heat exchanger using a traverse system. Stratification of non-condensable gas occurred in large tank of the natural circulation loop. SISTA2 was used to simulate a small break loss-of-coolant accident (SBLCOA) transient. Since the test apparatus was a metal tank, compensations of initial heat transfer to the material and effect of heat loss during long-term operation were important for simulating cooling performance of SMART100 CPRSS. The pressure of SMART100 CPRSS was maintained below the design limit for 3 days even under sufficiently conservative conditions of an SBLOCA transient.

The two-phase ejector is a simple and compact pressure boosting device and widely used in ejector steam-generator water feeding systems and core emergency cooling systems. The direct contact condensation of water and steam is the key process of a two-phase ejector. Usually, the high-temperature and high-pressure steam will inevitably induce non-condensable gases. The existence of non-condensable gases will reduce the condensation heat transfer rate between steam and water, and harm the equipment. This study carried out 3D numerical simulations of a two-phase ejector based on an inhomogeneous multiphase model. The steam inlet pressure and the non-condensable gas mass fraction rang in 0.6–2.9 MPa and 1–10%, respectively. The heat and mass transfer characteristics were analyzed under different conditions. The results show that the heat transfer coefficient and plume penetration length increased with the steam inlet pressure. Non-condensable gas prevents direct contact condensation between the steam and water. The non-condensable gas mass fraction rises from 1% to 10%, the heat transfer between steam and water deteriorates, and leads to a lower heat transfer coefficient. [ABSTRACT FROM AUTHOR]

The direct-contact condensation heat transfer of vapor in the presence of non-condensable gas (NCG) on the falling water column in a convergent tube was simulated with a two-phase boundary layer approach, and the variations of the condensation heat transfer parameters and the vapor condensation length were analyzed. Results show that the convergent angle has an important influence on the condensation heat transfer parameters. Both Nusselt and Stanton numbers rose as the convergent angle went up from 0° to 40°. The increment in the convergent angle enhanced the condensation heat transfer coefficient from 1.06 to 4.8 times at the range of the vapor pressure from 1 atm to 3.6 atm. The increase in the inlet NCG mass fraction caused a reduction in the condensation heat transfer parameters. and its accumulation in the downstream where its mass fraction was over 90 %. The nozzle diameter and the inlet velocity and temperature of falling water column affected importantly the condensation heat transfer parameters. The vapor condensation length was increased with the rising inlet velocity. of falling water column, the vapor pressure and the nozzle diameter, while decreased with the ascending of the inlet NCG mass fraction and the convergent angle. The increment in the vapor pressure enhanced effectively the condensation heat transfer parameters, and weakened the adverse effect of NCG on the direct-contact condensation heat transfer. • The direct contact condensation with NCG in a convergent tube was studied. • The condensation heat transfer parameters were enhanced as the convergent angle rose. • The mass fraction of NCG was augmented as the convergent angle went up. • The vapor condensation length was reduced with the increasing of convergent angle. • The vapor pressure weakened the adverse effect of NCG on its condensation. [ABSTRACT FROM AUTHOR]

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

Given that two-phase closed thermosiphons (TPCT) are a prevalent and efficacious means of heat transfer. However, non-condensable gas (NCG) may potentially impact the heat transfer performance of the aforementioned devices. Nevertheless, the theoretical analysis of heat transfer in TPCT containing NCG is not fully comprehensive and therefore requires further supplementation by means of relevant experiments. This paper presents the development and experimental investigation of a theoretical heat transfer model for a TPCT containing NCG. The research encompasses the optimal fluid-filling ratio of R22 and R410a working fluid and the impact of NCG on heat transfer in the condenser section of TPCT. Experimental findings indicate that TPCT with R22 and R410a working fluids at a fluid-filling ratio of 60% and 50%, respectively, demonstrate excellent isotherm and heat transfer efficiency. The presence of NCG affects the condenser section heat transfer process of the vapor, leading to a 2 °C decrease in the average temperature of the condenser section of the TPCT (Tca). In comparison with the TPCT without NCG, it was observed that an increase in the mass of NCG from 0.0097 to 0.0197 mol resulted in a reduction in the effective length of the condenser section (La) and effective heat transfer rate (κ) of R22 TPCT. The decrease in La was 75.1 mm, while the decrease in κ was 15.02%. Furthermore, at the same NCG mass, the effective heat transfer rate of R410a TPCT is evidently superior to that of R22 TPCT. The NCG in the TPCT can be removed by using a check valve. Nevertheless, this will result in a reduction in the fluid-filling ratio of the TPCT. The temperature of the R410a TPCT containing 0.0197 mol NCG with a fluid-filling ratio of 50% is comparable to that observed in fluid-filling ratio of 40% after the NCG is exhausted.

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.

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.

In this study, three condensation models of the CUPID code, i.e., the resolved boundary layer approach (RBLA), heat and mass transfer analogy (HMTA) model, and an empirical correlation, were tested and validated against the COPAIN and CAU tests. An improvement on HMTA model was also made to use well-known heat transfer correlations and to take geometrical effect into consideration. The RBLA was a best option for simulating the COPAIN test, having mean relative error (MRE) about 0.072, followed by the modified HMTA model (MRE about 0.18). On the other hand, benchmark against CAU test (under natural convection and occurred on a slender tube) indicated that the modified HMTA model had better accuracy (MRE about 0.149) than the RBLA (MRE about 0.314). The HMTA model with wall function and the empirical correlation underestimated significantly, having MRE about 0.787 and 0.55 respectively. When using the HMTA model, consideration of geometrical effect such as tube curvature was essential; ignoring such effect leads to significant underestimation. The HMTA and the empirical correlation required significantly less computational resources than the RBLA model. Considering that the HMTA model was reasonable accurate, it may be preferable for large-scale simulations of containment.

• Built an apparatus to study non-condensable gas interactions with refrigerant. • Two non-condensable gas fault intensities were imposed at various test conditions. • Ideal Gas assumption causes theory to overestimate non-condensable gas. • A new model quantifies non-condensable gas in typical residential air-conditioners. Non-condensable gas (NC) can be introduced into a vapor compression refrigeration cycle through improper installation or service, and decrease system efficiency, increase burden on the compressor, and reduce the compressor life span. Therefore, detecting this fault early can prevent energy waste and prolong the operating life of the system. However, diagnostic methods are not widely available, and neither are methods to quantify NC amounts based on easily measured variables. Therefore, an experimental test apparatus was built to provide data to improve understanding of NC-refrigerant interactions. Two NC fault intensities (50%, 100%), each at four charge levels (70%, 80%, 100%, 120%), were tested under five different ambient temperatures (0-40°C). Dry nitrogen gas was used for the NC. The results showed that the theoretical estimation method is inaccurate. The trends of the results from experimental tests are consistent with those from theoretical calculations, but the thresholds obtained from experimental tests are larger than those from theoretical calculations. This paper explains these differences, and provides a model to quantify the NC fault intensity using easily-measured variables. The specific model is applicable to typical residential air-conditioner and heat pump systems that use R410A refrigerant, but the general findings are applicable to other refrigerants. [ABSTRACT FROM AUTHOR]

As a key physical process, water vapor condensation has attracted significant attention because of its potential in engineering applications. The non-condensable gas in the surrounding vapor has a significant influence on condensation heat transfer. Considering as a crucial aspect, this work developed a transient multiphysics coupled solver to investigate droplet condensation in a moist air environment (considering dry air as the non-condensable gas). The current solver couples the time-dependent vapor-liquid phase-change heat transfer, mass transport of water vapor, and two-phase fluid flow. In contrast to the classical thermal resistance theory model, this solver can capture the dynamic and strong coupling characteristics during condensation comprehensively. The results demonstrate that for small-scale droplets, vapor condensation is driven by the coupled internal conduction-dominated heat transfer and external vapor diffusion. As the droplet grows and the contact angle increases, internal convection driven by the Marangoni effect becomes increasingly important. The enhanced fluid mixing inside the droplet can affect both the internal heat transfer and the external vapor diffusion. Because of the significant diffusion resistance, the droplet growth rates in a moist air environment are reduced up to 1-2 orders of magnitude compared with the case of pure steam. For large-scale droplets, the internal convection can increase the droplet growth rate up to 18.7%. Furthermore, the contact angle, the subcooling temperature, and the relative humidity have significant influences on droplet condensation in a moist air environment. This work not only promotes the mechanistic understanding of condensation heat transfer in a moist air ambient but also provides a flexible solver for vapor-liquid phase change problems. [ABSTRACT FROM AUTHOR]

The system-integrated modular advanced reactor 100 (SMART100), an integral-type pressurized water small modular reactor, is based on a novel design concept for containment cooling and radioactive material reduction; it is known as the containment pressure and radioactivity suppression system (CPRSS).There is a passive cooling system using a condensation with non-condensable gas in the SMART CPRSS. When a design basis accident such as a small break loss of coolant accident (SBLOCA) occurs, the pressurized low containment area (LCA) of the SMART CPRSS leads to steam condensation in an in-containment refuelling water storage tank (IRWST). Additionally, the steam and non-condensable gas mixture passes through the CPRSS heat exchanger (CHX) submerged in the emergency cooldown tank (ECT) that can partially remove the residual heat. When the steam and non-condensable gas mixture passes through the CHX, the non-condensable gas can interrupt the condensation heat transfer in the CHX and it degrades CHX performance.In this study, condensation heat transfer experiments of steam and non-condensable gas mixture in the natural circulation loop were conducted. The pressure, temperature, and effects of the non-condensable gas were investigated according to the constant inlet steam flow rate with non-condensable gas injections in the loop.

To study oscillation characteristic of steam and non-condensable gas direct contact condensation through multi-hole sparger at low mass flux, a series of experiments of pure steam and mixture gas condensation have been carried out under the conditions of steam mass flux of 20–120kg/m2s, water temperature of 20–95 °C and mass fraction of non-condensable gas of 0–5%. The regime map of pure steam condensation through multi-hole sparger is divided into steam chugging, separated bubble, aggregated bubble and escaping aggregated bubble. The bubbles behavior of synchronization in the same hole columns and desynchronized excitation between different hole columns can be found. The coalescence effect of mixture bubbles increases with water temperature and non-condensable gas content increasing. Pressure oscillation intensity of pure steam condensation first increases and then decreases with water temperature increasing, and increases with steam mass flux increasing. Pressure oscillation intensity of mixture gas condensation decreases with water temperature and non-condensable gas content increasing, which is significantly weaker than that of pure steam condensation. The oscillation dominant frequency decreases with the rise of water temperature and non-condensable gas content. The correlations for oscillation intensity and dominant frequency respectively are developed in pure steam and mixture gas condensation at low mass flux.

Exploitation of the vast reserve of geothermal energy for power generation and direct use has been elevated to the top of China's energy agenda, while the environmental impacts and human health risk have received little attention. This review systematically summarizes the environmental and human health impacts of geothermal utilization in China, and identifies the key technologies and policy measures that can be implemented to mitigate them. Geothermal fluids are typically enriched with a range of dissolved species and non-condensable gases, which originate from magma degassing and/or water-rock interaction under high temperature and pressure, and often low pH conditions in the reservoirs, and their releases could pollute local surface water, groundwater, soil, and air, and adversely affect biodiversity. The toxic elements (primarily As and F) could negatively impact the health of people living in geothermal areas through contaminated surface water, groundwater, and food crops. Among the gaseous pollutants, hydrogen sulfide often poses the most significant health concern, while radon might pose potentially significant radiological risk to the workers of geothermal spa and hot spring facilities. Improper disposal of the geothermal wastes enriched with natural radionuclides might elevate the radiation exposure of workers at geothermal facilities and people living in their vicinity. To minimize the potential environmental impacts and human health risk from large-scale expansion of geothermal exploitation, heat-extraction-only technologies should be promoted, while geothermal facilities should actively adopt pollution control and prevention measures. Government regulation and supervision can further ensure the negative environmental and human health impacts are adequately mitigated. [ABSTRACT FROM AUTHOR]

Axial temperature profiles of the vapor phase can provide valuable indication of the condensation process along the heat transfer path and highlight the impact of non‐condensable gases on a unit's performance. The local measurements at moderate vacuum conditions for condensation of a binary mixture are presented alongside the implementation and assessment of optical sensors in a heat transfer process. The results show a good depiction of the characteristic temperature behavior during the condensation process. The relation between temperature, partial pressure and mole fractions are shown. [ABSTRACT FROM AUTHOR]

The two-phase ejector is a simple and compact pressure boosting device and widely used in ejector steam-generator water feeding systems and core emergency cooling systems. The direct contact condensation of water and steam is the key process of a two-phase ejector. Usually, the high-temperature and high-pressure steam will inevitably induce non-condensable gases. The existence of non-condensable gases will reduce the condensation heat transfer rate between steam and water, and harm the equipment. This study carried out 3D numerical simulations of a two-phase ejector based on an inhomogeneous multiphase model. The steam inlet pressure and the non-condensable gas mass fraction rang in 0.6–2.9 MPa and 1–10%, respectively. The heat and mass transfer characteristics were analyzed under different conditions. The results show that the heat transfer coefficient and plume penetration length increased with the steam inlet pressure. Non-condensable gas prevents direct contact condensation between the steam and water. The non-condensable gas mass fraction rises from 1% to 10%, the heat transfer between steam and water deteriorates, and leads to a lower heat transfer coefficient.

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

This article deals with the possibility of separating water vapour from flue gases after oxyfuel combustion using condensation processes. Those processes can generally be described as condensation of water vapour in the presence of non-condensable gases. Hence, the effect of noncondensable gas (NCG) on the condensation process has been theoretically and experimentally analysed in this study. The theoretical model was developed on the basis of the heat and mass transfer analogy with respect to the effect of the NCG, the flow mode of the condensate film, the shear stress of the flowing mixture, subcooling and superheating. Subsequently, an experimental analysis was carried out on a 1.5m long vertical pipe with an inner diameter of 23.7mm. The mixture of vapour and air flowed inside the inner tube with an air mass fraction ranging from 23% to 62%. The overall heat transfer coefficients (HTC) from the theoretical model and experimental measurement are significantly lower than the HTC obtained according to the Nusselt theory for the condensation of pure water vapour. The overall HTC decreases along the tube length as the gas concentration increases, which corresponds to a decrease in the local condensation rate. The highest values of the HTC are observed in the condenser inlet, although a strong decrease in HTC is also observed here. Meanwhile, there is a possibility for an HTC enhancement through turbulence increase of the condensing mixture in the condenser outlet. Results also showed that the heat resistance of the mixture is several times higher than the heat resistance of the condensate film. The developed theoretical model based on heat and mass transfer analogy is in good agreement with experimental results with the standard deviation within +25% and −5%. The model is more accurate for lower NCG concentrations.

A condensation heat transfer model is essential to accurately predict the performance of the passive containment cooling system (PCCS) during an accident in an advanced light water reactor. However, most of existing models tend to predict condensation heat transfer very well for a specific range of thermal-hydraulic conditions. In this study, a new correlation for condensation heat transfer coefficient (HTC) is presented using machine learning technique. To secure sufficient training data, a large number of pseudo data were produced by using ten existing condensation models. Then, a neural network model was developed, consisting of a fully connected layer and a convolutional neural network (CNN) algorithm, DenseNet. Based on the hold-out cross-validation, the neural network was trained and validated against the pseudo data. Thereafter, it was evaluated using the experimental data, which were not used for training. The machine learning model predicted better results than the existing models. It was also confirmed through a parametric study that the machine learning model presents continuous and physical HTCs for various thermal-hydraulic conditions. By reflecting the effects of individual variables obtained from the parametric analysis, a new correlation was proposed. It yielded better results for almost all experimental conditions than the ten existing models.

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]

The film condensation of steam is very common in several industrial areas, such as condensers in power plants, seawater desalination, and air-conditioning systems. In some studies, the non-condensable gas and liquid film are overlooked for the sake of simplicity. To provide an integral computational scheme, in the present study, the film condensation of steam in the presence of non-condensable gas on a vertical plate has been simulated using a two-dimensional CFD model combining a wall condensation model and volume of fluid (VOF) model. After verification, the proposed computational scheme is used to simulate the steam condensation process, with the mass fractions of non-condensable gas varying from 5% to 45%. The results indicate that the concentration of non-condensable gas in the boundary layer decreases gradually with the condensation process, resulting in a decline in the synergy between temperature and velocity field. It can also be found that the fluctuation of the liquid film can influence the concentration distribution of the non-condensable gas layer. For cases with high concentrations of steam, the thermal resistance of liquid film can reach more than 20% of the total thermal resistance, which should not be ignored.

Cryogenic turbopumps are used in high-performance, lightweight liquid rocket engines for space applications. The development of bearings and shaft seals for cryogenic turbopumps requires detailed characterization of the internal flow, taking into account the effects of boiling and multi-component two-phase flow. Here, a flow network solver was developed to analyse the secondary flow circuit of a cryogenic turbopump where the propellant is mixed with high-temperature helium after bearing cooling. The network solver is based on an extension of a classic 1D homogeneous model, originally developed for a pure substance, to the case of two-phase multi-component flow. The solver is capable of predicting pressures, temperatures, flow rates, and species concentrations in a complex two-phase flow in the presence of non-condensable gases. The unsteady mass, momentum, and energy conservation equations are implemented in conjunction with the thermodynamic equations of state using a general-purpose finite volume formulation, where the pressure drop and the heat transfer are calculated using correlations. The numerical tool was validated by comparing its predictions with experimental data obtained during tests on the secondary circuit of an oxygen turbopump developed at Avio S.p.A. A number of engine operating conditions were considered (inlet helium temperature in the range of 250–280 K , helium/liquid oxygen drain in the range of 165–230 K). The predicted temperature values showed good agreement with the experimental data in most conditions. [ABSTRACT FROM AUTHOR]

The paper deals with a detailed analysis of published analytical relations for heat transfer during steam condensation in a vertical tube. The historical development of the approaches and the chronological development of the used analytical relations are presented. Attention is focused on the description of the processes at the gas phase-condensate film interface as well as on the inclusion of the influence of the presence of non-condensable gases. The analytical relations in 12 modifications are compared with each other for the same geometrical configuration of the vertical tube and identical boundary conditions. The authors performed comparative experimental measurements of the heat transfer coefficient during condensation of the vapour-gas mixture in vertical tubes of three diameters, namely 16, 20 and 26 mm. Based on a comparison of the experimental results and analytical relations, recommendations are made on the validity interval of the tested relations.

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.

The wall film-wise condensation plays an important role in the heat transfer processes of heat exchangers, refrigerators, and air conditioner. In the field of nuclear engineering, steam condensation is often utilized in safety systems to remove the core decay heat under both transient and accident conditions. In particular, passive containment cooling system (PCCS), are designed to ensure containment safety under severe accident conditions. A computational fluid dynamics (CFD) scale analysis has been conducted to calculate the heat transfer rate of the PCCS. However, despite the increase in computing power, there are challenges in the long-term transient simulation of containment using CFD scale codes. In this study, a heat structure coupling between the CFD and system analysis codes was performed to efficiently analyze PCCS. In addition, the component unstructured program for interfacial dynamics (CUPID) was improved to analyze the condensation behavior of ternary gas mixtures. Thereafter, the condensation heat transfer on the primary side was calculated using the improved CUPID and CFD code, whereas that on the secondary side was simulated using MARS. Both the coupled codes were validated against the CONAN facility database. Finally, conjugate heat transfer simulations with wall condensation in the presence of non-condensable gases were appropriately performed.

• Steam-air bubble condensation is studied by visualization experiment. • Bubble parameters are obtained by image processing and bubble reconstruction. • The effect of non-condensable gas on bubble condensation is studied. • A correlation considering the variation of diffusion resistance is proposed. Direct contact condensation of steam bubbles with non-condensable gas is common in nuclear safety equipment. It was insufficient research on the direct contact condensation heat transfer model of steam bubbles with non-condensable gas at high Reynolds numbers (Re > 22000) in previous works. To study the effect of non-condensable gas on heat transfer of steam–air bubbles at high Reynolds numbers, a high-speed camera was used to capture the behavior of bubbles and used image processing and bubble reconstruction to obtain size and dynamic parameters of bubbles. The size and upward motion behavior of bubbles were analyzed. The heat transfer coefficient during the bubbles condensation experiment were calculated and experimental results were compared with correlations proposed by previous works. In order to better explain the heat transfer characteristics and predict the heat transfer coefficient of bubbles at high Reynolds numbers, a modified heat transfer correlation based on the correlation of rigid sphere was proposed which are functions of bubble Reynolds number, liquid Prandtl number, Jacob number, and dimensionless time. This correlation considers the influence of both forced convection around bubbles and variations in steam fractions on bubble condensation. Comparison of experimental data and the corresponding predicted values shows that the deviation between the experimental data and predicted values is within ± 25 % which indicates the modified correlation accurately predicts the experimental data in this paper. [ABSTRACT FROM AUTHOR]

• Utilizing a fully three-dimensional approach based on a mixture model and multiphase flow condensation model enables the accurate acquisition of calculated parameters at various positions on the shell side of the condenser. • The heat transfer effect in this research is influenced by two main factors: the steamflow rate and the air mass fraction. • The heat transfer coefficient on the wall of the tubes reaches its maximum value in the "high-speed and low concentration" zone. • The air mass fraction exhibits significant sensitivity to variations in the steam massflow rate. The condenser plays a crucial role in nuclear power plants, impacting equipment economics and safety through shell-side two-phase flow and heat transfer. However, existing research has oversimplified the tube bundles, lacking comprehensive information for optimal performance. In this research, a three-dimensional method incorporating mixture and multiphase flow condensation models was used to investigate flow behavior and heat transfer characteristics without simplifying the internal structure. Calculation details were enhanced by omitting the porous medium approach. The numerical model achieved reasonable accuracy when compared to theoretical calculations for a range of steam mass flow rates. Analysis of numerical results, including pressure, velocity, temperature, air mass fraction, and heat transfer coefficient, revealed that steam flow rate and air mass fraction were key factors influencing heat transfer. This research demonstrates the method's capability to capture intricate calculation details, providing valuable insights for optimization design considerations in condenser performance. [ABSTRACT FROM AUTHOR]

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

• Lack of studies on thermosyphon charged with non-condensable gas. • Thermal hydraulic behavior of thermosyphon charged with non-condensable gas was investigated. • The necessity for new model is presented. • A new model along with framework of calculation is proposed. • The new model and the framework are being demonstrated to design thermosyphon, and the results are being compared with experimental data. Thermosyphon or wickless heat pipe has been applied in many fields of industry due to its high thermal conductance and passive working principle. Many studies have been done to elucidate the complex thermal hydraulic phenomena inside thermosyphon. Parameters such as geometry, type of working fluid, inclination angle of operation, confinement and entrainment have been major focal points in discussion related to thermosyphon research. However, in recent experimental studies, it has been reported that adding non-condensable gas along with working fluid during the initial charging of thermosyphon increase its entrainment limitation. This finding is important, considering some previous studies regard the presence of non-condensable gas as a hinderance on thermosyphon's condenser performance. In this study, experiments were conducted on a pressurized thermosyphon charged with water and argon gas as a non-condensable substance. Observations have been made especially on the case where cooling temperature on the outside of the condenser is far below operation temperature inside thermosyphon. It was found that low thermal conductivity of non-condensable gas causes large temperature gradient along the condenser. For this condition, currently available correlations cannot be applied. Therefore, experiments were required to prove this hypothesis, involving varying amounts of non-condensable gas. These amounts were expressed by the initial pressure values, ranging from 13 kPa to 160 kPa. The analysis of heat transfer in the evaporator and the condenser was conducted using correlations available in the literature. It was found that a new model is required to describe thermal-hydraulic phenomena in the condenser. The model is currently being validated with experimental data and good agreement has been achieved. [ABSTRACT FROM AUTHOR]

This paper is focused on the effects of different evacuation pressures on thermal performance of vertically placed flat-plate pulsating heat pipe (FP-PHP). Experimental results show that the difference in the amount of non-condensable gas (NCG) caused by evacuation pressures is an important reason for the difference in thermal performance of FP-PHP. The water FP-PHP under evacuation pressure of 200 Pa with 18.9 wt% NCG requires the least start-up power and time. NCG will increase the operation instability after ethanol FP-PHP has started up. Evacuation pressure has the least effect on HFE-347 FP-PHP, which can start up successfully without any evacuation. [ABSTRACT FROM AUTHOR]

Condensation is a phase-change heat-transfer phenomenon crucial in many industries involving latent heat release and mass transfer. Shell-and-tube condensers are essential contributors to the condensation process, and their tube bundles serve as a substrate. Here, the thermal-hydraulic characteristics of condensation in a longitudinal-flow shell-and-tube condenser were investigated numerically. The shell-side longitudinal-flow condensation on the horizontal tube bundles was studied considering inlet flow rate, overheating temperature, and non-condensable gases. Related pressure drops and heat transfer coefficients were subdivided into several components to provide further insights. Two-phase interface behavior analyses were conducted to demonstrate the outcomes with respect to the non-condensable gas layer, vapor quality, and non-condensable gas type. Based on the thorough quantitative analyses outlined above, the thermal resistance of the condensation on the horizontal tube bundle was investigated. The thermal resistance outside the tube was found to dominate the condensation process. Finally, hexagon clamping baffles (HCBs) were introduced as a novel solution to impair condensate boundary layers and provide perturbations to intensify condensation heat transfer. The results revealed that the HCBs enhanced the total heat transfer coefficients by 8.1%–40.7% while reducing the critical overheating temperature and the threshold ratio between sensible and latent heat. [ABSTRACT FROM AUTHOR]

Wall functions are generally used in a numerical simulation of turbulent flows with computational fluid dynamics (CFD) codes. The logarithmic law is widely adopted for the wall functions, but its validity has not been confirmed for dimensionless profiles of temperature and steam mass fraction in condensation fields due to lack of data. In this study, we evaluated dimensionless profiles of temperature and steam mass fraction in flows of saturated steam and air mixtures in a vertical pipe with the diameter of 49.5 mm. The local Nusselt number Nuy and Sherwood number Shy (which were proposed in our previous study) were used for defining the dimensionless temperature T+ and steam mass fraction Ys+, respectively, because physical properties in computation cells in contact with the condensation surface are generally used in a CFD analysis. The T+ and Ys+ values obtained from the measured temperature profiles were smaller than the existing logarithmic law due to condensation in the turbulent boundary layer (i.e. mist generation), and correlations for T+ and Ys+ were obtained by using the least square method. The standard deviation of the correlations were 3.8 % and 0.75 °C for the steam mass fraction of Xs = 0.05-0.63 and the mixture temperature of Tg = 63-97 °C, respectively. [ABSTRACT FROM AUTHOR]

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

Experimental studies of the steam pyrolysis of oil sludge were performed using a flow-type pilot plant with 300 kg/h capacity (raw material) to obtain energy-valuable products, such as liquid hydrocarbons (30.4 wt%), semi-coke (39.6 wt%), non-condensable gas-phase compounds (26.5 wt%), and bitumen (3.5 wt%). The pyrolysis process was conducted at a temperature of 650 ° C and with a steam flow rate of 150 kg/h. Liquid hydrocarbons were considered a target product. Comprehensive studies of their physicochemical characteristics, atomization process, droplet ignition, and combustion were carried out. The studied sample had physicochemical characteristics similar to traditional fuel oil (calorific value—42.6 MJ/kg, sulfur content—0.8 wt%). The jet spraying angle was 25° in view of the improved rheological properties of the test sample, with a homogeneous jet structure and a predominant droplet diameter of no more than 0.4 mm. The flame combustion process was accompanied by the formation of microexplosions, the frequency and intensity of which depended on the temperature of the air (Tg = 450–700 °C). This study, in view of its applied nature, is of interest in the design of new installations and technological systems for hydrocarbon pyrolysis. [ABSTRACT FROM AUTHOR]

Open natural circulation systems are widely applied in the field of energy and chemical industries. Under some special conditions, open natural circulation systems with low height difference need to be applied, but research on this type of systems is not sufficient. In this paper, the flow modes of sucha natural circulation system were experimentally studied at low power level by adopting steam heating. In addition, the flow modes and physical phenomena of the natural circulation system were analyzed in detail under different heating power conditions. It is found that there are four flow modes at different power levels in the natural circulation system due to the influence of non-condensable gas and subcooled boiling. The inlet and outlet temperatures of heating section are analyzed in different flow modes. The result shows that the outlet temperature of heating section can be used as a judgment criterion for different flow modes.

The Enhanced Geothermal System (EGS) is a recognized geothermal exploitation system for hot dry rock (HDR), which is a rich resource in China. In this study, a numerical simulation method is used to study the effects of geothermal fluid dryness and non‐condensable gas content on the specific enthalpy of geothermal fluid. Combined with the organic Rankine cycle (ORC), a numerical model is established to ascertain the difference in power generation caused by geothermal fluid dryness and non‐condensable gas content. The results show that the specific enthalpy of geothermal fluid increases with the increase of geothermal fluid temperature and geothermal fluid dryness. If the dryness of geothermal fluid is ignored, the estimation error will be large for geothermal fluid enthalpy. Ignoring non condensable gas will increase the estimation of geothermal fluid enthalpy, so the existence of the non‐condensable gas tends to reduce the installed capacity of a geothermal power plant. Additionally, both mass flow of the working medium and net power output of the ORC power generation system are increased with increasing dryness of geothermal fluid, however there is some impact of geothermal fluid dryness on thermal efficiency. [ABSTRACT FROM AUTHOR]

• A two-fluid model for water-incondensable gases and including heat and mass transfer is proposed. • Out-of-equilibrium source terms are modeled in a non-classical form considering two-fluid models. • The pressure relaxation effect is discretized using a new scheme. • Influence of the different relaxation effects is examined thanks to experimental results of a blowdown. Two phase flows including liquid water, vapor and non-condensable gases are often encountered in industrial applications. In this paper, an extension of the classical Baer-Nunziato two-fluid model is presented in order to account for the non-condensable gases. In this model, the vapor and non-condensable gases form a miscible mixture of gases at temperature equilibrium and kinematic equilibrium. The complete model then allows to account for the full kinematic and thermodynamic disequilibrium between the liquid phase and the gas phase. Moreover, a new form for the mass-transfer source-term has been retained. It leads to a more straightforward numerical integration. When focusing on the numerical scheme, a new algorithm is proposed here for the pressure relaxation effect. At last, some numerical experiments are performed in order to assess the behavior of the model with respect to the relaxation time-scales. [ABSTRACT FROM AUTHOR]

Cryogenic turbopumps are used in high-performance, lightweight liquid rocket engines for space applications. The development of bearings and shaft seals for cryogenic turbopumps requires detailed characterization of the internal flow, taking into account the effects of boiling and multi-component two-phase flow. Here, a flow network solver was developed to analyse the secondary flow circuit of a cryogenic turbopump where the propellant is mixed with high-temperature helium after bearing cooling. The network solver is based on an extension of a classic 1D homogeneous model, originally developed for a pure substance, to the case of two-phase multi-component flow. The solver is capable of predicting pressures, temperatures, flow rates, and species concentrations in a complex two-phase flow in the presence of non-condensable gases. The unsteady mass, momentum, and energy conservation equations are implemented in conjunction with the thermodynamic equations of state using a general-purpose finite volume formulation, where the pressure drop and the heat transfer are calculated using correlations. The numerical tool was validated by comparing its predictions with experimental data obtained during tests on the secondary circuit of an oxygen turbopump developed at Avio S.p.A. A number of engine operating conditions were considered (inlet helium temperature in the range of 250–280 K, helium/liquid oxygen drain in the range of 165–230 K). The predicted temperature values showed good agreement with the experimental data in most conditions.

In our previous study, we measured the radial and axial temperature distributions of steam-air mixture in a vertical circular pipe (diameter, 49.5 mm; cooling height, 610 mm). The measured temperatures were used to evaluate the condensation heat flux qc and heat transfer coefficient hc, where the bulk quantities were defined at the center of the circular pipe. It is sometimes difficult to define the bulk quantities in a three-dimensional computation for a complex geometry or complex flow field. In this study, therefore, we evaluated a prediction method for hc without the definition of the bulk quantities by using the measured temperature distributions. We applied existing hc correlations to an arbitrary radial location y from the condensation surface, and obtained the distribution of local hc. As a result, we found that hc was radially almost constant in the turbulent boundary layer (dimensionless distance of y+ > 20). This means that existing hc correlations are applicable to computational cells of y+ > 40 in a three-dimensional computation. [ABSTRACT FROM AUTHOR]

Recent core-scale visualization studies performed by us have highlighted the promising potential of utilizing hydrocarbon solvents in alternating with steam injection for optimizing post-steam-assisted gravity drainage (SAGD) processes. This technique not only improves hydrocarbon recovery but also improves economic viability and reduces greenhouse gas (GHG) emissions. However, further investigations, including tests with non-hydrocarbon solvents and SAGD sandpack experiments, are necessary to provide robust comparisons and recommendations. This study focuses on SAGD sandpack experiments using both hydrocarbon (heptane) and non-hydrocarbon (carbon dioxide gas) solvents for post-SAGD applications. The experiments—conducted under reservoir conditions—demonstrated significant improvements in heavy-oil/bitumen recovery by up to 50 %, compared to conventional methods. Moreover, the use of non-hydrocarbon and liquid hydrocarbon solvents could eliminate the need for aggressive steam utilization, thus enhancing energy efficiency. Additionally, the potential for solvent recovery was evaluated to optimize the process further. • The effectiveness of solvents in post-SAGD applications was examined. • A series of core flooding and visual experiments with solvents was performed. • Heptane injection delivered the utmost outcomes in terms of oil recovery. • Mid-stage injection cases were more favorable than late-stage injection cases. • Post-SAGD solvent recovery is possible and economically viable process. [ABSTRACT FROM AUTHOR]

Spray cooling is an efficient cooling technology with high heat dissipation, and has been extensively utilized in various industry areas. The interaction mechanism between the spray droplet and environmental space with high pressure and temperature is extremely complex, especially with non-condensable gas. In this paper, a pseudopotential multicomponent multiphase lattice Boltzmann model for droplet migration with non-condensable gas in high temperature and pressure was proposed. The mechanism of transfer characteristics for droplet in steam were studied. It is found that the mass transfer of droplet is controlled by density and condensation, droplet growth is mainly impacted by density at initial stage, and in later period, the growth is greatly weakened by the condensation suppression of non-condensable gas. The calculated results show that when Fo > 0.4, mass transfer is significantly decreased. Heat transfer is also affected by non-condensable gas, and 2% gas declines the droplet heat transfer rate by about 10%. It is also found that the mass transfer rate is approximately linearly associated with the ratio of non-condensable gas content inside and outside the droplet. The results can be used for development of spray cooling model, and have positive guiding significance for optimizing spray cooling system. • A heat and mass transfer model of droplet and steam with non-condensable is established. • The mechanism of transfer characteristics for droplet in steam were studied. • The mass transfer of droplet is controlled by density and condensation in different stage. • The mass transfer rate is approximately linearly associated with the ratio of non-condensable gas content. [ABSTRACT FROM AUTHOR]