Direct Contact Condensation Of Steam Research Articles

Numerical heat transfer analysis of steam injection into subcooled water

Steam direct contact condensation (DCC) into subcooled water may be encountered in different important industrial process applications, such as steam jet pumps, steam ejectors, pressurizers, and emergency cooling systems of nuclear reactor core. In this work, a numerical simulation study has been done for injection of steam into a tank full of subcooled water. In the simulations, the Eulerian multiphase flow in addition to a realizable k-epsilon turbulence model has been utilized. Moreover, a DCC model has been used for condensation capturing. Fluent software with a user-defined function (UDF) for the DCC model was employed for simulations. The results obtained from simulations were validated with experimental results, and a fair agreement was observed. This study considered the local Nusselt number (LNN) the most suitable parameter for investigating the heat transfer rate (HTR) at the computational cell level. Therefore, the contours of the LNN, its axial distribution, and radial distribution were studied with respect to the inlet pressure of injected steam, temperature of tank water, and location along the axis of the nozzle. The results reveal the fact that the value of the LNN reaches a maximum at the nozzle exit along the axis of the nozzle at 323 K tank water temperature. LNN decreases by increasing or decreasing the tank water temperature beyond 323 K. It is claimed that the heat transfer (HT) study at such a local scale has been conducted for the first time to the best of our knowledge, and it unfolds various crucial facts regarding steam-water interaction.

Analysis of cyclone separator solutions depending on spray ejector condenser conditions

The core design strategy for minimizing CO2 emissions in gas power plant entails combining a spray ejector condenser (SEC) and separator to accomplish steam condensation and CO2 purification. This innovative process involves direct-contact condensation of steam with CO2, facilitated by interaction with a subcooled water spray, along with a cyclone separator mechanism intended for generating pure CO2. The investigation of the SEC section, both experimentally and analytically, provides crucial insights into its operational dynamics. Given the susceptibility of cyclone efficiency to fluctuations in SEC conditions, this research endeavors to examine the impacts of CO2 volumetric flow rate and droplet break-up within the SEC on the separation efficacy of the cyclone separator. Additionally, the impact of cone size on the performance of the cyclone has been investigated. Here, a three-dimensional, transient, and turbulent cyclone separator is numerically simulated using Ansys Fluent 2021 R1. The Reynolds Stress Model is employed to simulate turbulent flow, while a mixture model is utilized to replicate swirl two-phase flow within the separators. The findings revealed that reductions in steam and CO2 flow rates were associated with a decrease in outlet temperature but an increase in SEC inlet temperature, leading to a rise in temperature difference and heat transfer rate. Furthermore, an augmentation in cyclone cone size (from 0.2 to 0.5 m) resulted in enhanced separation efficiency (from 77.30 % to 80.98 %) alongside an elevation in pressure drop (from 6.08 Pa to 10.91 Pa), suggesting a compromise between CO2 purification and energy consumption. Additionally, elevated CO2 flow rates induced a rise in pressure drop and separation efficiency, ultimately achieving maximum efficiency at a rate of 24 gs. Moreover, the exploration into droplet breakup manifesting in a boost in separation efficiency from 50.98 % to 100 % across droplet diameters ranging from 1 to 20 μm.

Theoretical study on pressure oscillation dominant frequency of bubbles submerged jet under rolling condition

Steam direct contact condensation is a highly efficient heat and mass transfer phenomenon, usually accompanied by strong mass, momentum and energy exchanges at the water-steam interface, which can rapidly realize cooling and pressure relief, but also accompanied by pressure oscillations. When the relevant equipment is used in offshore nuclear power plants and naval non-energetic systems, the additional inertial force field caused by ocean motion may cause greater harm to the safe operation of the relevant devices. Therefore, a theoretical study is conducted to investigate the effect of rolling motion on dominant frequency of steam submerged jets pressure oscillation with low mass fluxes. Firstly, based on bubble dynamics theory, a theoretical model of bubble condensation oscillations under rolling motion with low mass flux is established. Then, the mechanism of the rolling conditions on the dominant frequency of pressure oscillation is analyzed from the aspect of theoretical derivation. Finally, on the basis of the potential flow function theory and small perturbation theory, the predicted correlation of pressure oscillation dominant frequency under the rolling motion with low mass flux is derived, and compared with the numerical simulation results, the prediction deviation is within ±10%.

Experimental investigation on the effect of direct contact condensation regime on thermal stratification

Direct contact condensation affects the performance of a small modular reactor with pressure suppression system. Since the heat and mass transfer varies with the condensation regimes as well as steam-water interface shapes, the identification and classification of the condensation regimes are important. The experiment of steam direct contact condensation was carried out and the corresponding condensation regimes were studied. Specifically, the experiment was studied by injecting steam vertically into a wet well with subcooled water. The physical process of steam condensation phenomenon with varying undercooling degree of wet well was recorded by high-speed camera. According to the location of the steam-water interface and the shape of the steam bubble, the four condensation regimes were studied, namely chugging, external necking, spheroidal upward bubble and T-shaped upward bubble. Besides, it is found that thermal stratification occurs in the wet well at low steam mass flux, the influence of each condensation regime on the thermal stratification of wet well was studied. The experimental results show that the internal chugging and external necking cause a large downward circulation of subcooled water, which enhance the flow mixing around the discharge tube and the bottom of the wet well. Consequently, the thermal stratification phenomenon does not happen in those condensation regimes. However, the regimes like spheroidal upward bubble and T-shaped upward bubble cause the upward circulation of subcooled water in wet well, which cause the thermal stratification. The critical Richardson number (Ri) determines the condensation regimes. Furthermore, when the Ri is smaller than 1, the condensation regime is external necking. Besides, when the Ri is greater than 1, the condensation regimes are spheroidal upward bubble and T-shaped upward bubble.

Analysis of the Multiphase Flow With Condensation in the Two-Phase Ejector Condenser Using Computational Fluid Dynamics Modeling

Abstract The liquid-driven two-phase ejector condenser is the object of the numerical investigation. The spray-ejector condenser is one of the critical components of the developed gas power plant with negative CO2 emission. The task of the ejector is to entrain exhaust gas and condense steam contained in it. Computational fluid dynamics (CFD) modeling allows analyzing complex phenomena and predicting the influence of a wide range of operating parameters on the local structure of the multiphase flow with condensation. The geometrical model of the ejector was designed to provide efficient steam condensation and generate sub-pressure region at the gas inlet. The 2D, axisymmetric CFD model was created using simcenter star ccm+ software. The multiphase mixture model was used to take into account two-phase flow. Turbulent flow was computed using k–ω SST model. Direct contact condensation of steam was calculated using two different approaches: the Spalding/evaporation model and the thermally-driven boiling/condensation model. The influence of various gas inlet velocities and the presence of CO2 on the operation of the ejector condenser were investigated based on scalar fields and charts representing changes in the most important variables along the flow path. The condensation is the most intense in the suction chamber. The boiling/condensation model predicts lower suction pressure and higher condensation effectivity than Spalding/evaporation model. The CO2 considerably affects the pressure and temperature distributions and reduces the condensation rate.

Numerical study on dominant oscillation frequency of unstable steam jet under heaving condition

With its advanced efficiency in heat transfer, the steam direct contact condensation method is now extensively employed in many areas. The pressure oscillation characteristics of unstable steam jets under heaving conditions were investigated numerically in this study. The dominant oscillation frequency gradually rose with the decrease of the heaving period and the increase of the heaving amplitude. The dominant oscillation frequency under the heaving condition was higher than that under the static condition, with a maximum increase of 27.4%. The inertia and condensation dominated the evolution of steam bubbles at the necking stage under heaving conditions. With the decrease of the heaving period and the increase of heaving amplitude, the additional force induced by heaving movement increased, contributing to the condensation heat transfer enhancement. A dimensionless correlation predicting the dominant oscillation frequency at a low flow rate under heaving conditions was fitted, and the maximum error was within ±6.2%.

Influence of Noncondensable Gas–Dust Mixture on Direct Contact Condensation of Steam at Atmospheric Pressure

Abstract At the Department of Civil and Industrial Engineering (DICI) of the University of Pisa, an experimental research program, funded by International Thermonuclear Experimental Reactor (ITER) Organization, concerning steam direct condensation in a flux containing also noncondensable gas and dust, was carried out. This mixture of fluids and dust is injected into the ITER pressure suppression tanks during a loss of coolant accident (LOCA) in the Vacuum Vessel. The aim of the research program is to determine the steam condensation efficiency in such conditions. Experimental tests were performed injecting this mixture in a tank partially filled with water. Alumina was used to simulate the actual dust present in the ITER Vacuum Vessel. Mass flow rates, temperature, and pressure of the different fluids involved were recorded during the tests. The steam condensation into the subcooled water pool at a temperature ranging between 318 and 369 K was investigated to determine the condensation regimes occurring during the mixture injection. The values of the fraction of the energy absorbed by water, dust, and metallic structures of the heat losses and of the average heat transfer coefficient were determined considering pure steam, steam-dust and steam-air–dust injection. The average heat transfer coefficient, determined calculating the steam jet surfaces by means of image elaboration, was compared with empirical correlations.

Experimental investigation on thermal stratification characteristic of steam condensation through multi-hole sparger

Thermal stratification induced by steam direct contact condensation is experimentally investigated through a multi-hole sparger of horizontal injection with different steam mass flux, initial water temperature, and submergence depth. The exitance of chugging regime and oscillatory bubble regime causes the differences in flow patterns of pool water through multi-hole sparger. The four stages of temperature evolution, complete mixing, gradual stratification, stable stratification, and downward extension of the heated region stage, are found. Thermal stratification vanishes at water subcooling lower than 3℃. The influence of key factors on the thermal stratification and thermocline dynamic characteristic is discussed and analyzed. With steam mass flux increasing, the maximum temperature difference of pool water increases first and then decreases, and the inflection point of temperature growth increases. Besides, thermocline downward velocity increases with steam mass flux increasing resulting from the enhanced turbulence effect. Larger initial water temperature and smaller distance from sparger to pool bottom help to reduce the maximum temperature difference. The thermocline velocity increases with the initial water temperature rising due to the reduced density difference. Lower sparger position can effectively move down the thermocline position, and the thermocline velocity decreases resulting from the weakened turbulence motion. The initial water level has a limited effect on thermal stratification and thermocline velocity. In addition, the Richardson number, used to judge whether thermal stratification occurs, reaches the maximum at water temperature 65℃. The results are helpful to understand the mechanism of thermal stratification and provide an effective reference for the design of the suppression system.

RELAP5 validation for core makeup tank analysis based on separate effect tests

The RELAP5 code has been developed for best-estimate transient simulation of light water reactor coolant systems during accident and has been widely used in the field of nuclear thermal-hydraulics and safety analysis. The core make-up tank (CMT) is a crucial device of the passive core cooling system in the AP series pressurized water reactor nuclear power plants. Since the CMT not only provides full-pressure injection but also triggers auto depressurization system by its level signal during small-break loss of coolant accident. Therefore, it is necessary to carry out CMT separate effect tests to verify the feasibility and accuracy of RELAP5/MOD 3.4 to simulate CMT. The previous studies found that the lower version of the RELAP5 program has problems in simulating CMT, and the applicability of the latest RELAP5/MOD3.4 has not been evaluated. In this paper, a CMT separate effect test facility were presented and then RELAP5/MOD 3.4 was used to establish a CMT test bench model to evaluate the applicability, and obtain the general rules and methods of RELAP5/MOD 3.4 to simulate CMT. It’s found that RELAP5/MOD 3.4 can accurately simulate most of the CMT operating conditions. However, large uncertainty is expected in the simulation of delayed time and the flowrate of delayed drainage stage is not affected by the heat transfer coefficient of steam direct contact condensation. The simulation of delay time depends on experimental data and the CMT delayed drainage experiment cannot verify the accuracy of the RELAP5/MOD 3.4 direct contact condensation model.

Separate-effect drainage tests in a core make-up tank

Passive safety systems are widely used in the advanced nuclear reactors, such as AP1000 and CAP1400. As an important component in the passive safety system, the core make-up tank (CMT) plays a key role for the safety injection and the core decay heat removal. Although the structure of the CMT system is simple, it involves many thermal-hydraulic phenomena, most of which significantly impact the peak temperature of the fuel cladding and the liquid level of the core. Since the CMT not only provides full-pressure injection but also triggers the auto depressurization system by its liquid level signal during small-break loss of coolant accident (SBLOCA), its thermal hydraulic behaviors significantly affect the performance of the passive core cooling system (PXS). Therefore, separate effect tests are inevitable to verify the feasibility of CMT applied to passive safety and injection systems and to study its operating characteristics. In this work, a separate-effect CMT test facility was designed and constructed. Experiments were performed to investigate the CMT's thermal hydraulic characteristics under the effects of system pressure, steam condensation, and flow friction. The study found that the delay drainage phenomenon is the result of a pressure balance between the pipe line and the gravity head. Whether delayed drainage occurs depends on the degree of subcooling of the fluid at the top of the CMT. The flowrate is not affected by the heat transfer coefficient of steam direct contact condensation. The flow friction of the drainage pipeline has no effect on the delayed drainage process, but has a great influence on the gravity drainage process.

Effect of non-condensable gas in steam condensation at sub-atmospheric pressure condition

In the International Thermonuclear Experimental Reactor (ITER), a postulated Loss Of Coolant Accident (LOCA) in the Vacuum Vessel (VV) has to be managed with a pressure suppression system working at sub-atmospheric pressure. The operating conditions considerably differ from those experienced in the fission nuclear power plants such as BWR, since the ITER Tokamak works at very low pressure conditions and can withstand a maximum pressure of 0.15 MPa. For this reason, the pressure value must not exceed 10 kPa for a water temperature of 30 °C inside the Vapour Suppression Tanks (VSTs) that are the fundamental components of the Vacuum Vessel Pressure Suppression System (VVPSS). During a LOCA some non-condensable gases (mainly hydrogen and oxygen gases due to the water radiolysis or thermolysis) may be mixed in the steam and this could impair the condensation efficiency. In order to investigate the effects of non-condensable gas on DCC, we conducted a research program funded by ITER Organization at the laboratory of the University of Pisa: we designed and built a small-scale experimental rig to study the steam Direct Contact Condensation (DCC) with the presence of non-condensable gas and simulate the behaviour of a VST. Since DCC can occur with different characteristics, we ran 12 closed mode tests exploring all condensation regimes injecting a certain mass of air with the steam discharged in the subcooled water. The tests started at the saturation pressures corresponding to water temperatures ranging from 40 °C to 80 °C and ended when the free space volume reached the atmospheric pressure. From the analysis of the data acquired during the tests we observed that the condensation efficiency remained higher than 95%. We observed that despite this, the presence of a certain quantity of non-condensable gas has negative aspects on condensation: the condensation regime never reaches stability (the regimes quickly shift towards instability). Furthermore, the presence of air triggers a turbulence of the flow which interferes with the transfer of heat from the steam to the water. Not only the introduction of air into the flow increases linearly the pressure above the water head but its high temperature further contributes to the pressure increase. The air mixed with the flow also forms eddies that can trap the steam and transport it out of the water, preventing it from condensing. Apart from condensation, the most noticeable problem is the rapid increase in pressure inside the condensation tank.

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

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

Numerical study on dominant oscillation frequency of unstable steam jet under rolling condition

Steam direct contact condensation has been widely applied in many fields because of its high heat and mass transfer efficiency. However, this process may cause damage to related devices due to its pressure oscillation, especially under ocean condition. The axial and radial components of the additional force and buoyancy force were analyzed in this numerical study. Results indicated that the Coriolis force played a more important role than other forces. The effects of rolling period and rolling angle on the dominant oscillation frequency were investigated. Under rolling condition, as the rolling period decreased and the rolling angle increased, the dominant oscillation frequency of steam submerged jet increased because of the enhanced Coriolis force, which promoted the necking of the bubble. Moreover, a correlation was proposed to predict the dominant oscillation frequency of steam submerged jet under rolling condition. The maximum deviation was less than ± 9.5%.

Experimental investigation on the steam condensation dynamic characteristics at low steam mass flux

An experimental study has been performed to investigate the dynamic characteristics of steam direct contact condensation at low steam mass flux. Visible steam bubble parameters can be identified through the image processing algorithm. The maximum dimensionless diameter of steam bubble is calculated and the analysis model of identifying condensation regime is developed to predict transition boundaries of steam chugging and oscillatory bubble regimes. The pressure oscillation waveforms in pipe and in pool are distinguished. In chugging regime, the pressure pulse wave transforms to continuous wave in pool as water temperature increasing, however, in oscillatory bubble regime, continuous wave becomes pulse wave because of increased bubble pulsation volume. The oscillation frequencies are obtained from four different methods of bubble dynamic parameters, pressure pulse periods, pressure frequency spectrums in pipe and in pool to reveal the oscillation mechanism. The low-frequency component in chugging regime increases with water temperature increasing, while the intermediate-frequency component in chugging regime and the frequency in bubble regime decreases.

Experimental investigation on steam contact condensation in emergency makeup tank

The emergency makeup tank (EMT) is an important component of passive residual heat removal system (PRS) in Hualong Pressurized Reactor (HPR1000). However, the steam direct contact condensation (DCC) occurred in the EMT brings pressure and injection flow oscillation in station blackout scenarios, affecting the safety injection performance of EMT. Experimental facility was constructed to obtain the steam DCC characteristics under various initial and boundary conditions. The experimental phenomenon was observed and test data were obtained and analyzed. Three types of spargers were designed and installed to alleviate the pressure and flow rate oscillation in EMT. The test results reveal that spargers can significantly reduce the DCC duration and promote the water thermal stratification in EMT. The heat transfer coefficient of steam condensation substantially decreases after the spargers are installed. The steam flow rate and pressure oscillates vigorously at the early stage of the sparger-free experimental condition, and the oscillations are greatly reduced after the spargers are installed. In EMT drain experiment, the maximum steam flow rate and minimum pressure are reached simultaneously when the steam supply rate is balanced with the steam condensation rate. The drain of water begins at the start of the experiment while the liquid level in the EMT is not reduced due to the water supplement via rapid steam condensation. The EMT evacuation duration is significantly reduced when the spargers are installed, which could enhance the safety performance of passive safety system in accidental scenarios.

Plume Stability During Direct Contact Condensation of Steam in a Crossflow of Subcooled Water, at High Mass Flux and With a Small Nozzle Diameter

Abstract The stability of a steam plume during direct-contact condensation into a crossflow of subcooled water is investigated for mass fluxes that are higher (>600 kg/m2s) and a nozzle diameter (2.4 mm) that is smaller than typically seen in the literature. The transition from a stable steam plume to an unstable plume associated with the formation and collapse of steam bubbles is characterized by high-speed imaging and high-frequency pressure measurements. Four regimes are observed: stable, condensation oscillation, transition, and unstable. A regime map and spectral signatures of the different flow regimes are provided. Results are compared with correlations from the literature, which are typically derived for lower mass fluxes, larger nozzles, and injection into stagnant pools of water.

Experimental research on double-hole steam condensation effects and models under different diameters and pitch to diameter ratios conditions

The multi-hole steam Direct Contact Condensation (DCC) is of high efficiency in mass and heat transfer, which has been widely used in the engineering application, especially the advanced nuclear reactor power plant passive safety system. Most of the researches concerned on the single-hole steam DCC characteristics, whereas the multi-hole steam DCC heat transfer effects are influenced by a variety of mutual factors, and the micro mechanisms and models of which are still not very clear yet. In the present work, the double-hole steam condensation effects and models under different spraying diameters and pitch to diameter ratios (P/de) conditions are investigated based on the scaled IRWST & ADS experimental facility. The key parameters including the steam plumes, temperature distributions, penetration length, and heat transfer coefficients, etc. are analyzed. The experimental results show that both the P/de and de can impact the overall condensation behavior and the corresponding penetration length with variation range from -40% to 60% compared to the single-hole condensation cases, further influencing the double-hole steam DCC heat transfer effects. The revised double-hole steam condensation analytical models are proposed to depict the key condensation characteristics. Based on theoretical model and experimental results, the HTC calculation methods are developed to quantitatively estimate the double-hole condensation effects in the range of approximate 0.4-2.8MW/m2°C, which is in similar magnitude with the single-hole theoretical model. However, in overall, the double-hole HTC values are lower than the single-hole cases under the specific mutual influences between the adjacent plumes including overlapping, coalescences, and possible deflection with angles. The present theoretical and experimental work provide important references for the engineering multi-hole spargers design and modification.

Temperature and pressure oscillations induced by steam direct contact condensation in a T-junction with porous inner-structures

Steam direct contact condensation (SDCC) has been investigated experimentally with the steam mass flow rate in the range of 2 ~ 60 kg/h, the subcooled water flow rate in the field of 0.5 ~ 2 m3/h and the subcooled water temperature at 30 °C.in an empty T-junction and the T-junction with two porous inner-structures (made up by stainless steel ball with two different diameters). The effects of different porous inner-structures on temperature and pressure oscillations were investigated with different saturated steam mass flow rate and subcooled water flow rate. The results show that the porous inner-structures significantly reduces the temperature fluctuation near the branch pipe. Then, the positive peak value of pressure oscillation increases firstly and then decreases with the increase of porous inner-structures porosity. the intensity (RMS) of pressure oscillations were suppressed by filling the porous inner-structures. Besides, filling the porous inner-structures increases the viscous resistance and inertia resistance of the flow and enhances the intensity of turbulence. So the first dominant frequency increased significantly as the porosity of porous inner-structures decreased. Especially when the porosity ε = 0.318, the increase of the first dominant frequency is particularly evident and the maximum even reached 463 Hz.

Semi-batch and continuous production of Pickering emulsion via direct contact steam condensation.

We propose a versatile strategy for the production of highly stable water in oil Pickering emulsion by direct contact condensation of steam. In contrast to conventional methods that use mechanical energy for creating drops, the condensation of steam brought in contact with a non-aqueous colloidal dispersion is exploited to produce Pickering emulsions in two modes of operation, namely, semi-batch and continuous. As steam that comes in contact with oil condenses into water drops, the particles adsorb to the interface and thus arrest drop-drop coalescence. The adsorption of particles on the drop's surface imparts kinetic stability to the emulsions. The dependence of size of the emulsions as a function of parameters such as steam temperature, flow rate, particle type and particle concentration is investigated. We show that the tailoring of these parameters allows a precise control over droplet size distribution. The flexibility of continuous mode of operation makes it a potential technique for large scale production of emulsions suited for many applications.

Dynamic model to predict heat-induced protein denaturation and fouling in a Direct Contact Steam Condensation process

High heat treatment, using Direct Contact Condensation (DCC), is applied in the production of dairy products to ensure a high level of food safety. During this process a protein rich deposit layer can be formed causing fouling of the system resulting in a loss of effective production time and an increase in cleaning cycles. The dynamics of the heat treatment process is modelled, including the description of the pre-heating step with two laminar flow tubular heat-exchangers followed by a DCC. In this system the bulk reactions for whey proteins are modelled using unfolding, re-folding and aggregation kinetics. The formation of the deposit layer is described in the segment after the DCC using a flow averaged model incorporating diffusion of species through the mass boundary layer as well as adsorption to the wall and desorption from the wall. The desorption kinetics are key as the protein deposit layer releases from the wall once the wall friction increases due to the decreasing area available for throughflow. The model shows good agreement with experimental data and is capable of capturing the process dynamics, both for the heat exchanger and the DCC. The deposit layer formation model is in agreement with the trend observed in the experimental data but is not fully capturing the process dynamics.