Direct Contact Condensation Of Steam Research Articles

Numerical Simulation of a Steam Injector for Passive Residual Heat Removal

Abstract In the case of depressurization of a supercritical water-cooled reactor (SCWR), the steam pressure can be used to pump coolant back into the reactor, either by using a turbine driven pump or a steam injector. The latter option is cheaper, more robust, and requires less periodic inspections. The numerical simulation of a steam injector, however, has still been a challenge. In principle, a steam injector consists of a steam nozzle, a mixing chamber, and a diffuser. This paper describes a one-dimensional two-phase flow model simulating the flow and condensation phenomena occurring in the steam nozzle, the structure of shock fronts at the nozzle outlet, the direct contact condensation of steam with cold water in the mixing chamber, and the sudden pressure increase in the final condensation shock front. The model is based only on first principles and on the existing correlations. Correction factors adapting the model to experimental results have not been used yet. For validation, the model has been applied both to separate effect tests and to steam injector tests.

Experimental investigation on the interface shape of bubble condensation for vertical upward steam jet at low mass flux

Steam direct contact condensation in subcooled water is widely used in various industries. The steam-water interface shape is an essential parameter for direct contact condensation. An experimental study was carried out to investigate the flow patterns and interface shape of bubbling regime with a vertical upward steam jet. Steam mass flux and water temperature were 8.34–50.13 kg/(m2∙s) and 40–85°C, respectively. Three flow patterns such as chugging, smooth grown bubble, and rough grown bubble were found based on the dynamic behavior of steam-water interface. The bubble collapse frequency and the maximum bubble radius at the bubble growth stage were calculated. The bubble collapse frequency increased rapidly when the smooth grown bubble regime was transformed into the rough grown regime. When the water temperature was between 40-80°C, the maximum bubble radius initially increased, and then decreased with the increase of steam mass flux. A transition criterion from the smooth grown bubble regime to the rough grown bubble regime was given based on the theoretical analysis and experimental data.

Investigation on steam direct contact condensation injected vertically at low mass flux, part II: Steam–air mixture experiment

An experimental study is conducted on the condensation behavior, onset of chugging, fluid oscillation, and pressure oscillation when a steam–air mixture is injected vertically into subcooled water at a low mass flux. Air is present in the form of dispersive small bubbles after condensation at a low water temperature and in the shape of a toroid at a high water temperature. Bubble resonance is first observed experimentally; a large bubble is almost stationary below the pipe outlet and air is sustainably released by small bubbles from the upper surface. The upper air mass fraction of chugging is obtained and compared with a transient conduction–diffusion model and momentum balance model. The dependence of different parameters on the amplitude, frequency, and probability of fluid oscillation is analyzed. A new frequency correlation modified with probability is developed and shows good agreement with the experimental data. During bubble resonance, the wave shape of pressure oscillation is harmonic with the frequency at about 35 Hz, and the intensity is larger than that under pure steam conditions. When bubble resonance does not occur, the presence of air can reduce the pressure oscillation intensity.

Numerical Investigation on Unstable Direct Contact Condensation of Steam in Subcooled Water

Stable direct contact condensation of choked steam jets in subcooled water has been the focus of researchers during the last three decades. Comparatively fewer works were reported on unstable direct contact condensation of steam jets which typically occurs at low steam mass flux and low pool subcooling. The focus of this paper is on the study of unstable direct contact condensation of steam jets in subcooled water occurring at low steam mass flux using numerical techniques. A two-fluid modeling approach has been adopted with a thermal phase change model for capturing the condensation phenomena. The numerical results are compared with the available experimental data, and a reasonable agreement (average discrepancy was around 15% for overall heat transfer coefficients and 11% for average time periods) was observed. Attempts were made to understand the unstable nature of the steam jets under the simulated conditions. The effect of pool subcooling on plume shapes, heat transfer coefficients and pressure amplitudes were examined. Finally, semi-empirical models available in the literature were compared with the simulation data, and the results were analyzed. The outcome of the article will be useful in understanding the flow physics, and characterization and design recommendations for direct contact condensers operating in the unstable oscillatory regime.

Numerical investigation of heat transfer in direct contact condensation of steam to subcooled water spray

The direct contact condensation heat transfer (DCCHT) of saturated steam to subcooled water spray produced by a pressure-swirl nozzle was examined by computational fluid dynamics (CFD) in which a two-dimensional (2-D) axisymmetric swirl calculation was performed to simulate the hydraulic characteristics and the temperature profile of the water spray in the sheet region. The CFD simulations were validated by the experimental results obtained in the studies under the same operational conditions. In the simulation, the kinetic theory-based Schrage model was used for condensation flux calculation, and the interfacial area density of liquid sheet was introduced to evaluate the area of the vapor-liquid interface. The numerical simulations indicated that condensation did not significantly affect the spray cone angle, the sheet thickness and the interfacial area density although it significantly affected the sheet breakup length. Additionally, when compared with traditional film-wise condensation on solid walls, heat transfer coefficient in the DCCHT was significantly higher than that in general film-wise condensation.

Thermal hydraulic characteristics of unstable bubbling of direct contact condensation of steam in subcooled water

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

Experimental investigation on thermal stratification induced by steam direct contact condensation with non-condensable gas

Thermal stratification induced by steam direct contact condensation is a significant technical concern to consider in the energy industry. Thirty experiments have been performed to investigate the effect of steam mass flux, bulk water temperature and air mass fraction on temperature distribution in the water pool. The condensation behavior and time evolution of temperature distribution are recorded and analyzed. Two condensation regimes of chugging and bubbling are observed. Three flow patterns, namely chugging-induced synthetic jets, steam-driven negative buoyancy jets and plume, are discussed. Three thermal patterns of mixing, stratification and re-mixing are identified. A small amount of air (1–2%) could make stratification pattern occur earlier and severer. The maximum vertical temperature difference is about 30 °C in pure steam experiments and 60 °C in mixture gas experiments. Re-mixing pattern occurs when the bulk water temperature is close to 80 °C. In addition, thermal penetration depth, the velocity of thermocline moving down and the thickness of thermocline are estimated through temperature data.

Investigation on steam contact condensation injected vertically at low mass flux: Part I pure steam experiment

Steam direct contact condensation in subcooled water is an inevitable process in pressure suppression system of advanced light water reactor. Ten pure steam experiments have been performed in the range of steam mass flux 5–80 kg/m2 s and water temperature 19–96 °C. The steam condensation behave, fluid oscillation and pressure oscillation are recorded and analyzed. Prominent small bubbles are observed on the bubble surface due to the Rayleigh-Taylor instability. Vortex ring appears after aspherical bubble collapses. The upper threshold of chugging is identified by temperature data acquired continuously. The amplitude and frequency of fluid oscillation are obtained and compared with previous correlations. Two typical pressure wave shapes of continuous oscillation and pulse oscillation are identified. The pulse oscillation is induced by steam bubble collapse and observed at low water temperature. The maximum pressure pulse peak is about 1 MPa measured in the nozzle and 0.1 MPa in the pool. The pressure oscillation intensity in the water pool increases first, then decreases rapidly, and then increases slowly. It has a maximum at water temperature about 55–75 °C and the related temperature increases with the increment of the steam mass flux. The pressure oscillation dominant frequency is analyzed and compared with available correlations.

Steam condensation simulation in a scaled IRWST-ADS simulator with GOTHIC 8.1

The AP1000® advanced reactor passive safety systems are based on natural phenomena to ensure the containment integrity during an accident. One of the most important passive systems is the Passive Core Cooling System (PXS) which includes the In-containment Refueling Water Storage Tank (IRWST), a pool that serves as a heat sink for the Passive Residual Heat Removal Heat Exchanger (PRHR) and the Automatic Depressurization System (ADS).The thermal-hydraulic behavior of the pool is quite complex under accidental conditions: the pool receives steam at high velocity and temperature from the Reactor Cooling System (RCS), the pool is the heat sink of the PRHR, and eventually, it is the source for the low pressure safety injection. In order to study the behavior of the AP1000 IRWST during a steam discharge from the ADS at different stages of a SBLOCA, an experimental test rig was constructed in cooperation with the Technical University of Munich (TUM). The results obtained in the IRWST-ADS experiment were used to test the capability of GOTHIC 8.1 to simulate the phenomena observed experiments such as thermal stratification, direct contact condensation, and flashing. The GOTHIC model is based on two control volumes, one represents the channel test and the other the laboratory room. These control volumes are connected with a 3D-Connector between each other and with flow-paths to the boundary conditions. Pressure boundary conditions has been applied to the laboratory room control volume to maintain a constant pressure and temperature. Simulations were able to reproduce major occurring phenomena. Thermal stratification and flashing were predicted plausibly, however the direct contact condensation of steam and void fraction distribution are not perfectly simulated probably because of the selected mesh size. A sensitivity analysis has been conducted to the discretization scheme, the turbulence model, and the heat transfer correlation in order to test their effect upon GOTHIC model simulation.

Effect of non-condensable gas on pressure oscillation of submerged steam jet condensation in condensation oscillation regime

The pressure oscillation is an important characteristic of direct contact condensation of steam in subcooled water. Many experimental works have been performed on pure steam submerged jet condensation. However, the effect of non-condensable gas content on the characteristics of the pressure oscillation is not yet fully understood. So, present paper aims to investigate the effect of air mass fraction on the characteristics of the pressure oscillation. Experimental results show that: for pure steam jets, the pressure oscillation dominant frequency decreases with the rise of water temperature and nozzle diameter. While it increases with the rise of steam mass velocity, which is consistent with the most of previous research results. The pressure oscillation intensity increases with the rise of water temperature, steam mass velocity and nozzle diameter. For air-steam mixture gas jets, the effect of water temperature and steam mass velocity on pressure oscillation characteristics is the same as pure steam jets. The pressure oscillation dominant frequency rapidly decreases with the rise of air mass fraction. However, air mass fraction has a complex effect on pressure oscillation intensity. As the air mass fraction increases, the pressure oscillation intensity rapidly increases at first, then slowly decreases and then slowly increases. In addition, new correlations for pressure oscillation dominant frequency and intensity are developed. The predicted results agree well with the experimental results.

Transient Heat Transfer Study of Direct Contact Condensation of Steam in Spray Cooling Water

We conducted a transient experimental investigation of steam–water direct contact condensation in the absence of non-condensible gas in a laboratory-scale column with the inner diameter of 325 mm and the height of 1045 mm. We applied a new analysis method for the steam state equation to analyze the molar quantity change in steam over the course of the experiment and determined the transient steam variation. We also investigated the influence of flow rates and temperatures of cooling water on the efficiency of steam condensation. Our experimental results show that appropriate increasing of the cooling water flow rate can significantly accelerate the steam condensation. We achieved a rapid increase in the total volumetric heat transfer coefficient by increasing the flow rate of cooling water, which indicated a higher thermal convection between the steam and the cooling water with higher flow rates. We found that the temperature of cooling water did not play an important role on steam condensation. This method was confirmed to be effective for rapid recovering of steam.

Experimental studies on high-pressure high-temperature contact-condensation at falling jets in the TOPFLOW pressure-tank

Abstract We report on generic experimental studies dealing with the direct contact condensation of steam at a falling sub-cooled water jet at high pressure and temperature. This generic problem concerns some safety-relevant thermal hydraulic scenarios in light water reactors. One of such is the question for heat transfer and mixing when a sub-cooled jet of water in an emergency core-cooling scenario enters a hot pressurized component of the primary reactor circuit. The involved phenomena of heat transfer are complex in this case, reaching from direct condensation of steam via steam bubble entrainment to single phase mixing of hot and cold water. Experiments were performed in the TOPFLOW pressure tank, which is an experimental facility for high-pressure thermal hydraulics experiments in pressure equilibrium. The facility has been designed for studying steam-water two-phase flows at pressures of up to 50 bar. It enables to run experiments in flow domains of complex shape without high difference pressures across the wall. The concept therefore allows us to use thin metal walls and even glass windows to observe flows in complex geometry domains with the help of video camera and to considerably reduce cost and complexity of experimental installations. The experimental results show, that high ambient pressure promotes the direct contact condensation heat transfer of subcooled jet flow heavily.

Transient analysis of the steam‐water direct contact condensation in the packed column

AbstractThe transient heat transfer behaviour of direct contact condensation of steam in spray cooling water in a packed column was investigated experimentally and theoretically in this work for the first time. A new analysis method of the state equation was applied to analyze the molar quantity variation of steam in the course of the experiment. The results showed that increasing the cooling water flow rate properly could significantly accelerate the steam condensation rate and this was more obvious at the beginning of the operation. The higher the flow rate of the cooling water was, the shorter a time it took for the steam to be completely condensed. When the cooling water flow rate was 840 L/h, the steam was mainly condensed within 13 s, which indicated that it would rapidly handle steam by regulating cooling water flow rate. However, the effect of changing cooling water temperature on steam condensation rate is slight with the cooling water temperature inceasing from 23 °C to 42 °C. The volumetric heat transfer coefficient in this experiment is in the range of 1.47 kW · m−3 · K−1 to 10.93 kW · m−3 · K−1 with the cooling water flow rate inceasing from 120 L/h to 840 L/h, and the maximum uncertainty in the results is 2.2 %.

Heat transfer coefficient for condensation of steam on freely formed falling liquid jets

This article presents the research results of direct contact condensation of steam on freely formed falling liquid jets. After the comparison of experimental data and open literature correlations it was concluded that published correlations does not provide accurate coverage of experimental data. A new correlation was established in the following form urn:x-wiley:00011541:media:aic15233:aic15233-math-0001 © 2016 American Institute of Chemical Engineers AIChE J, 62: 2579–2584, 2016

CFD based approach for modeling steam–water direct contact condensation in subcooled water flow in a tee junction

The phenomenon of direct contact condensation (DCC) is encountered in several components of a nuclear power plant in case of some transient and accident conditions. Studies on steam jet discharged directly into a stagnant water pool have been studied extensively; however, it is sparse for direct contact condensation of steam in subcooled water in pipes. The present paper aims to investigate the low mass flux saturated steam discharged directly into subcooled water flow in a tee junction. The Volume of Fluid (VOF) two-phase flow model and Large Eddy Simulation (LES) turbulent flow model of FLUENT have been used. Also, a thermal equilibrium model considering heat and mass transfer was introduced to model steam condensation using user-defined function (UDF). The simulation results show that, for steam mass flux of 10 kg/m2 s, large chugging, small chugging and bubbling are obtained at water temperature of 303.15 K, 343.15 K and 363.16 K, respectively. In addition, it was found that, in chugging, there exist temperature and pressure oscillations at the location where the vertical branch pipe and the horizontal main pipe intersect. The phenomena of temperature and pressure oscillations at this location are called thermal cycling and water hammer, respectively. Moreover, the pressure oscillation frequency increases and the spike pressure decreases with increasing of subcooled water temperature in chugging. The Computational Fluid Dynamics (CFD) simulation results were qualitatively validated against the test results. It would be possible to improve the accuracy of the test results by employing multiple cameras.

A Physically Based, One-Dimensional Two-Fluid Model for Direct Contact Condensation of Steam Jets Submerged in Subcooled Water

A simulation model for the direct contact condensation of steam in subcooled water is presented that allows determination of major parameters of the process, such as the jet penetration length. Entrainment of water by the steam jet is modeled based on the Kelvin–Helmholtz and Rayleigh–Taylor instability theories. Primary atomization due to acceleration of interfacial waves and secondary atomization due to aerodynamic forces account for the initial size of entrained droplets. The resulting steam-water two-phase flow is simulated based on a one-dimensional two-fluid model. An interfacial area transport equation is used to track changes of the interfacial area density due to droplet entrainment and steam condensation. Interfacial heat and mass transfer rates during condensation are calculated using the two-resistance model. The resulting two-phase flow equations constitute a system of ordinary differential equations, which is solved by means of the explicit Runge–Kutta–Fehlberg algorithm. The simulation results are in good qualitative agreement with published experimental data over a wide range of pool temperatures and mass flow rates.

Aspects of the Two-Layer Model for Direct Contact Condensation of Steam on Wavy Falling Films

Detailed physical modeling of the direct contact heat transfer process of steam condensing on a falling liquid film is a very difficult task due to the complex hydrodynamics of the film. The present state of the art is restricted to film Reynolds number of the order of 100. On the other hand, empirical relations cannot offer any insight into the mechanism and features of heat transfer in liquid film. Phenomenological models are needed to bridge the gap between empirical relations and direct physical simulations. One of these models is the so-called two-layer model, which divides the falling film into a laminar conduction-dominated (substrate) layer flowing over the solid wall and a completely mixed layer representing the waves. This model is further developed here by focusing specifically on two aspects. First, the influence of temperature-dependent physical properties of the liquid on the structure and heat transfer characteristics of the substrate layer is studied, and typical results are presented in the absence of waves. Second, the relation of the main parameter of the model (i.e., thickness of the substrate layer) to local film state is discussed in detail. Generalized constitutive laws and an approach based on utilization of the experimental film thickness time series are proposed and discussed. The proposed procedures can be integrated to a generalized two-layer model for direct contact condensation.

Experimental study of direct contact steam condensation in structured packing

ABSTRACTAn experimental study of direct contact steam condensation has been conducted at both atmospheric and vacuum pressure, in a pilot scale column filled with Tupac 125Y structured packing. The local volumetric heat transfer coefficient of condensation determined by thermal balance has been given. The influences of the vapor and liquid flow rate, liquid temperature and operation pressure have been investigated. An empirical correlation based on dimensionless numbers has been put forward and verified by various experimental measurements, and the dimensionless numbers were calculated from the Delft hydrodynamic model of structured packing. The results will give some helpful guidance in the design and operation of direct contact condensers with structured packings. © 2013 Curtin University of Technology and John Wiley & Sons, Ltd.

Temperature fields induced by direct contact condensation of steam in a cross-flow in a channel

The temperature fields in the center plane of a channel with a square cross-section have been measured. Steam injected at relatively low mass fluxes through a small hole in one of the walls of the channel condensed intermittently in a small area close to the inlet. The upstream temperature of the liquid cross-flow, TL, the momentum ratio, J, and the Prandtl number proved to be important for the single-phase temperature field induced in the jet further away from the steam inlet. Jet centerlines of velocity and temperature are measured and positions are compared. Different locations for J\100 and low TL are explained from dependencies on Reynolds and Prandtl numbers. Next to the jet centerline a second high-temperature zone was found to occur, close to the wall and downstream of the steam inlet. The importance of capillary forces is investigated with the aid of 3D CFD computations.

Numerical Simulation of Direct-contact Condensation from a Supersonic Steam Jet in Subcooled Water

The phenomenon of direct-contact condensation, used in steam driven jet injectors, nuclear reactor emergency core cooling systems and direct-contact heat exchangers, was investigated computationally by introducing a thermal equilibrium model for direct-contact condensation of steam in subcooled water. The condensation model presented was a two resistance model which takes care of the heat transfer process on both sides of the interface and uses a variable steam bubble diameter. The injection of supersonic steam jet in subcooled water tank was simulated using the Euler-Euler multiphase flow model of Fluent 6.3 code with the condensation model incorporated. The findings of the computational fluid dynamics (CFD) simulations were compared with the published experimental data and fairly good agreement was observed between the two, thus validating the condensation model. The results of CFD simulations for dimensionless penetration length of steam plume varies from 2.73-7.33, while the condensation heat transfer coefficient varies from 0.75-0.917 MW·(m 2·K) −1 for water temperature in the range of 293-343 K.