Effect Of Non-condensable Gas Research Articles

Performances of the ITER Pressure Suppression System during unstable steam condensation regimes

Abstract The paper deals with the qualification of the main safety system of the nuclear fusion reactor ITER: the Vacuum Vessel Pressure Suppression System (VVPSS). This safety system manages the Loss of Coolant Accident (LOCA), that could occur in the Vacuum Vessel (VV), avoiding a significant increase of the internal pressure that could breach the primary confinement barrier. Steam condensation occurs at sub-atmospheric pressure. This condition is original respect the usual applications of steam direct condensation in nuclear fission reactors. An extensive experimental research program, funded by ITER Organization, on reduced scale experimental rigs (scale 1/22 and 1/10) have been carried out at the University of Pisa. Unstable condensation regimes occurred during some tests at about 500 g/s of steam mass flow rate (10 % of the maximum steam mass flow rate foreseen for the relevant accidental scenarios). In these conditions, high intensity vibrations of the whole experimental rig occurred. These events can be classified as ‘Chugging’ or Condensation Induced Water Hammer (CIWH). 
The performed tests have been analysed elaborating the images of the video-cameras located in the pool and comparing the steam jet shape with the acceleration values recorded by an accelerometer mounted on the sparger structure.
These elaborations permitted to evaluate the dynamic of bubble collapse, the volume of the developed external bubbles, the collapse frequency as function of thermal-hydraulic parameters. 
Moreover, the paper emphasizes the beneficial effects of non-condensable gases on the unstable condensation regimes. In fact, the non-condensable gas inhibits the occurrences of Water Hammer inside the sparger and eliminates the thermal stratification inside the water pool increasing the turbulence.

Determining the effect of non-condensable gas on a two-phase ammonia heat transfer loop of the satellite

It is advisable to design thermal management systems for high-power stationary satellites and specific ground applications using two-phase mechanically pumped loops with ammonia as the coolant. During prolonged operation in orbit, the accumulation of non-condensable gases can occur due to radiolysis and chemical reactions. The issues related to the effect of non-condensing gas on system parameters and performance have not yet received sufficient attention. The study of the distribution of non-condensable gas in the loop was performed by calculation-theoretical and experimental methods in a heat transfer loop with a Heat-Controlled Accumulator. Part of the gas accumulates in the steamgas zone of the Heat-Controlled Accumulator and affects the pressure value at a set temperature. The other gas is dissolved in liquid ammonia. This impacts the overheating of the cooled device when the heat load is switched on, the heat transfer intensity during boiling, and the cavitation reserve at the pump inlet. Accumulation of non-condensable gas up to ~0.075 mol nitrogen/kg ammonia, concentration of dissolved gas in the liquid up to ~5.3⋅10–4 mol/mol of the mixture does not significantly impact the parameters and performance of the system. But, if the aim is to precisely ensure the boiling temperature of the coolant or the cavitation reserve, the amount of necessary correction of the control parameters is up to 2.5 K. The results of the investigation can be used in the design of two-phase heat transfer loops for satellites and other applications, in particular, for the selection of the design and location of gas traps

Development of a simplified one-dimensional CDA bubble model

Sodium-cooled fast reactors (SFRs) have high safety with an extremely low probability of a core disruptive accident (CDA). However, from a defense-in-depth perspective, the CDA sequence is still worth studying. Severe accidents in SFRs, such as unprotected loss of flow, might lead to a CDA during which fuel and some fission products could be instantly released from a large CDA bubble through potential leak paths in the top shield structure. Therefore, a reasonable prediction of dynamic behavior of a large-scale bubble within the sodium pool is vital for accurately evaluating the migration of source terms. In this study, we propose a simplified one-dimensional CDA bubble model that can handle heat and mass transfer in two-phase multicomponent materials in different computational domains during the rising of bubbles through the sodium pool toward the cover-gas region. In this model, an entrainment model based on the Rayleigh–Taylor instability and Kelvin–Helmholtz instability was used to explain the coolant entrainment through the gas/liquid boundary and jet fragmentation. The model also addresses the mitigation effect of non-condensable gases on the condensation of fuel, steel and sodium vapor at bubble interface. We evaluated the model using a past experiment on the expansion of a two-phase, large bubble with high pressure in a stagnant liquid pool conducted by Purdue University in the late 1970 s using a 1/7-scale model of Clinch River Breeder Reactor. Good agreement with the experimental data demonstrates that the developed model can reasonably represent the essential characteristics of dynamic behavior of a large, high-pressure bubble with heat and mass transfer in two-phase multicomponent materials. This is valuable for evaluating the migration of the source terms, which will be carried out in future studies.

Liquid evaporation from nanochannel in the presence of non-condensable gas by direct simulation Monte Carlo

Liquid-vapor phase change in the form of evaporation and with the confinement of nanostructures is of vast importance in many engineering applications. The direct simulation Monte Carlo (DSMC) approach was employed to simulate the liquid evaporation from two-dimensional nanochannels in the presence of non-condensable (NC) gases. The thermodynamic properties of vapor and NC gas flow fields as well as the evaporation rate of liquid were calculated. Factors such as channel opening ratio, meniscus receding depth and the NC gas density were examined to reveal their impacts on the liquid evaporation rates. The results showed that the gas mixture flow field transforms to one-dimensional away from the channel exit. The overall vapor pressure drop can be divided into that across the liquid–vapor interface, that within the channel, outside the channel, as well as that caused by the binary diffusion. The effect of NC gas on the evaporation rate was found to be the most outstanding with pinned meniscus and with a wide channel opening, in which case the normalized evaporation rate drops to 0.43. Moreover, the Maxwell-Stefan equation could capture the evaporation data with modified diffusion lengths. For receded meniscus (250 nm deep) and small opening ratio (0.417), the effective diffusion length was as large as 1.6 times that in the one-dimensional case.

Numerical simulation on the effect of non-condensable gas on direct contact condensation of steam jet in a narrow pipe

A numerical model was developed to investigate the phenomenon of direct contact condensation involving steam-air jet in subcooled waterflow. This study encompassed a comprehensive exploration of the influence exerted by non-condensable gas from a multi-faceted perspective. These aspects included an examination of gas plume shape, distribution of air mass fraction, variation in axial thermodynamic parameters, the local heat transfer coefficient, and the local condensation rate. It was observed that the presence of non-condensable gas had the effect of extending the penetration length of the steam plume. Notably, the non-condensable gas was predominantly concentrated in proximity to the gas-liquid interface, a phenomenon that introduced hindrances to both heat and mass transfer processes. A detailed analysis of axial thermodynamic parameters further unveiled an intriguing trend. As the air content increased, the expansion of gas plume weakened, subsequently leading to a reduction in the condensation rate. This resulted in diminished pressure fluctuations in the two-phase mixing region. Moreover, the presence of non-condensable gas was shown to curtail the local heat transfer coefficient and the local condensation rate at the interface. This observation offered valuable insights into the underlying mechanisms responsible for the protraction of the gas plume.

Effect of non-condensable gas on the direct-contact condensation heat transfer of vapor in a convergent tube

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.

Effects of non-condensable gas on thermodynamic performance of transcritical organic Rankine cycle

The development and utilization of renewable energies and waste heat contribute to alleviating global issues of fossil energy shortage and environmental pollution, and energy consumption structure transition. Organic Rankine cycle (ORC), specifically transcritical ORC (tORC), garners significant attention for its potential in low-grade heat power generation. However, the existence of non-condensable gases (NCGs) caused by an incomplete vacuum process or organic fluid pyrolysis may have negative effects on system performance. Analyzing and quantifying the effects of different NCGs is of great significance for putting forward the relevant solution measures and helps improve the mechanism of pyrolysis products' influence. In this work, a novel thermodynamic model is proposed for tORC systems considering off-design performance to evaluate the effects of NCGs. Five different hydrocarbons including n-butane, n-pentane, i-pentane, cyclopentane, and n-hexane, are selected as working fluid candidates, while four NCGs are chosen as study objects including nitrogen, methane, ethane, and propylene. The established model realizes the function of analyzing and comparing the effects of different NCGs on thermodynamic performances of tORC systems. Results showed that the tORC system using cyclopentane had the best thermodynamic performances after the optimized design process. The case study indicated that an increase in the mass fraction of NCG caused the condensing pressure increase and system's thermodynamic performance degradation. Furthermore, larger variations were exhibited in the net power output when the design condensing temperature was higher. Finally, the comparative study showed that methane had the greatest negative effects on thermodynamic performances of tORC systems, especially for using n-butane.

Modeling liquid evaporation in nanopore and the effect of noncondensable gas

Modeling liquid evaporation in nanopore and the effect of noncondensable gas

Molecular dynamics simulation of effect of non-condensable gases on heat transfer of water molecule flow in nanochannels

With the development of higher performance and miniaturization of electronic components, the flow heat transfer of working fluids in nanochannels has received more attention. To elucidate this phenomenon, molecular dynamics simulations are used to simulate the behaviors of fluids within nanochannels at temperatures of 300 K, 325 K, and 350 K. Water serves as a flow medium, with argon substituted for any non-condensable gases. In the flow process, argon atoms aggregate into clusters that are characterized by high potential energy. As the temperature rises, the concomitant increases in the fluid’s potential energy, which leads to the gradual diminution or complete dissipation of these clusters. A minor presence of gas atoms can facilitate fluid movement; however, an excess of argon promotes the formation of larger gaseous clusters in the central region of the channel, thereby impeding fluid flow. Concurrently, the application of heat to the fluid appreciably diminishes the coefficient of flow resistance. The temperature of the fluid in the near-wall region exceeds that of the central area. In the clusters, the atoms exhibit heightened activity, leading to an increase in the average molecular kinetic energy and a concomitant rise in temperature. The inherent hydrogen-bonding structure of water enhances heat transfer within the nanochannels. Argon atoms exert an influence on the number of hydrogen bonds, and rising temperatures disrupts the hydrogen-bond network established by water molecules, ultimately leading to a decrease of the Nusselt number. This investigation offers insights into the heat transfer dynamics of water molecular flow within microchannels under the perturbation of non-condensable gases, thereby furnishing theoretical guidance for enhancing heat transfer within electronic devices.

Experimental investigation of non-condensable gas effects in a natural circulation system

Experimental investigation of non-condensable gas effects in a natural circulation system

LBM-PFM simulation of the effect of non-condensable gas on the directional crystallization of seawater

The present study employs the coupled Lattice Boltzmann Method-Phase Field Method (LBM-PFM) to investigate the impact of non-condensable gas bubbles on directional crystallization of seawater at the pore scale. Firstly, the LBM-PFM coupling model is proposed and experimentally validated. Subsequently, this model is applied to numerically simulate the two-phase (bubble -seawater) flow in directional crystallization. Additionally, the influence of factors such as bubble quantity, radius, and arrangement on ice crystal growth and the distribution, quantity, and area of internal brine pockets are discussed. The findings unequivocally demonstrate that the presence of non-condensable gas bubbles significantly enhances the rate of crystallization, resulting in a twofold increase in the area of freshwater ice. Bubbles with different radius, quantities, and spacing exert either promoting or inhibiting effects on the formation of brine pockets. Increasing bubble radius and quantity result in a larger area of freshwater ice crystals and a reduction in the quantity and area of brine pockets, ultimately resulting in an improved desalination efficiency. While changes in bubble spacing have a minimal impact on the generated ice crystal area, they significantly alter the distribution of brine pockets. Smaller spacing between bubbles leads to a lower number of brine pockets formed, thus inhibiting brine pocket generation.

A comprehensive investigation of non-condensable gas and condenser temperature effects on power plant ejector performance by considering condensation flow regime

Considering that the cycle of the steam power plant (Rankin) works with steam and water as working fluid in a closed cycle, the condenser will be one of the most important parts of this cycle, which has the task of changing the phase (condensation) of the turbine output steam and making it possible to transfer it to the beginning of the cycle. In addition to the working conditions of the cycle, such as the temperature and pressure of the turbine end, the performance of the condenser depends on the environmental conditions, such as the ambient temperature and the absence of non-condensable gases. In this paper, the effects of the condenser temperature and mass fraction (MF) of the air inside the condenser are investigated on the performance of the ejector (POE). It is shown that the effect of the condenser temperature on the POE is much higher than the effect of the air MF. With the increase of the condenser temperature and the air MF, the flow rate of the suction flow improves, and the entrainment ratio (ER) rises. With the temperature increment from 320 K to 340 K (without air in the condenser), ejector efficiency reduced by 61.16%, and exergy destruction enlarged by 12.13%. By incrementing the air MF from 0 to 0.35 at the temperature of 340 K, ejector efficiency, exergy destruction, and ER improve by 2.84%, 6.29%, and 3.88%, respectively.

Plasma-based identification of gases in a laser-induced cavitation bubble

This study presents a general methodology and an experimental approach to identify the gas components within laser-induced cavitation bubbles. A needle electrode inside the cavitation bubble, which introduces low electric energy into the bubble, produces a homogenous plasma discharge inside the vapor cavity. The primary bubble dynamics remain identical while the rebound bubble becomes about twice as large when a discharge is applied. The effect of non-condensable gases and the electric charge on bubble dynamics is explored theoretically, and the role of the electric charge is found to be significant. Optical emission spectroscopy reveals the evolution of emission lines from gases inside bubbles. H lines and OH lines are persistently observed in all cases, providing a dominant presence of water vapor. The results also confirm that the gases, which are initially present in the water rather than transported from the water, contribute to the optical emission characteristics with different dissolved gases.

Numerical study on the interfacial heat and mass transfer characteristics of bubble direct contact condensation with the effect of non-condensable gas

Bubble condensation is one of the fundamental issues in the direct contact condensation, which is also affected significantly by the existence of non-condensable gas. In this study, a further investigation is carried out on air-steam bubble condensation with the Proportion Integration Differentiation (PID) control model which adjusts the mass transfer coefficient of Lee model in each time step by comparing the parameters obtained in the simulation with the ones calculated based on the empirical correlations originated from the experiments. Furthermore, species transport equations are employed to obtain the local mass fractions of steam and air. The proposed simulation schema is verified by the existing experimental data.Results show that the air-steam bubble condensation can be divided into initial and stable stages. The mass transfer coefficient used in Lee model can be regarded as linear growth over time at each stage, but with different slopes. The non-condensable gas can weaken the heat and mass transfer of condensation, but stabilize the bubble deformation. The present study also reveals the influences of subcooling and initial bubble diameter on the air-steam bubble condensation, which is expected to be instructive for better understanding the effect of non-condensable gas on the interfacial characteristics of bubble condensation in subcooled water.

Experimental study of non-condensable gas effects on sonic limit of sodium heat pipe

Due to unexpected gas leakage and long-term operation, the non-condensable gas (NCG) inevitably exists in high-temperature alkali metal heat pipe. Previous studies have mainly focused on its influences on startup and steady state operation characteristics of heat pipes. However, few of them conducted experiments to study the effects of NCG on sonic limit, which usually occurs during heat pipe startup or during steady state operation when the heat transfer coefficient at condenser section is high. In present work, experimental and analytical studies are conducted to the explore the effects of NCG on sonic limit of sodium heat pipes. With the heating power ranging from 500 to 1400 W, the sonic limit of 1 m-long sodium heat pipes with artery wick and axial groove wick are obtained based on oil-cooling system, which can widely adjust the cooling capacity at condenser section. The amount of NCG in heat pipe is estimated by Heat Pipe Transient Analysis Code (HPTRAN) and verified by experimental data. It is found that the existence of NCG in heat pipe leads to the decrease of maximum heat transfer rate under sonic limit. The mechanism of NCG effects on sonic limit is discussed based on phenomenological analysis. By introducing the added back pressure, a modified model to predict sonic limit considering NCG effect is proposed and the comparison with experimental data shows good agreements.

The modeling of passive containment cooling system and sensitivity analysis using the SPRUCE code

Passive Containment Cooling Systems (PCCSs) have attracted wide attention to improve the inherent safety of nuclear power plants. This study summarizes a system analysis method of a closed-loop natural circulation of the PCCS via separately evaporation and condensation. A lumped-parameter model is built using SPRUCE, a code of system simulation of severe accidents, to investigate the natural circulation characteristics and heat-removal efficiency of the PCCS. The analysis of heat-removal capacity of the PCCS is carried out under typically thermal conditions of the containment, such as pressure from 0.28 to 0.4 MPa, and the results are validated by comparison with the experimental data obtained from a single-loop testing facility of the PCCS in full scale. The SPRUCE model agrees with the data, despite slightly underestimating the rate of condensation heat transfer. It conservatively satisfies the requirement of design capacity. To further verify the effectiveness of mitigation on containment overpressure, a representative scenario of LBLOCA (Large Break Loss of Coolant Accident) is implemented using the code. Meanwhile, the effects of non-condensable gas are also presented, as a reference for optimization of PCCS design.

Study on the liquid jet and shock wave produced by a near-wall cavitation bubble containing a small amount of non-condensable gas

The liquid jet and shock wave produced by a near-wall cavitation bubble are two major reasons resulting in material-wall damage. To better understand the destructive mechanism, the complete process of action of the multi-cycle cavitation bubble collapsing on the nearby wall with the effect of non-condensable gas under different stand-off distances was numerically investigated. For this purpose, a fully compressible solver is further developed with the implementation of a modified phase-change model. Validations were conducted by comparing the numerical results with the experimental data. Furthermore, the high-pressure zones on the wall induced by the shock wave and liquid jet are carefully analyzed. Numerical results reveal that the bubble behavior, shock wave propagation, and liquid jet types are highly associated with the stand-off distance. Finally, the potential material-wall damage is estimated by using the pressure impulse, and the relationship between the pressure impulse at the central point and the stand-off distance is quantitatively analyzed. It is found two pressure impulse peaks are at the central point.

Effect of non-condensable gas on submerged steam jet condensation in a narrow pipe

A visualization study was performed to investigate the effect of non-condensable gas on stable submerged steam jet condensation in water flow in a narrow pipe. The direct contact condensation (DCC) characteristics including jet plume shapes, dimensionless penetration length and average heat transfer coefficient were analyzed in a wide range of water flow subcooling, Reynolds number of water flow and steam–air mixture flow rates. As four different steam plume shapes for pure steam jet in subcooled water flow in a pipe were reported in the previous research, the effect of non-condensable gas on the four steam plume shapes was investigated by introducing a certain amount of air into steam. In the current study, the submerged steam–air mixture jet behavior was investigated through direct visualization techniques. The effect of non-condensable gas on jet plume shapes was recorded by using a high speed camera. The gas–liquid interface and the dimensionless penetration length was obtained by digital image processing method implemented by a MATLAB subroutine. Then the average heat transfer coefficient was calculated based on thermal equilibrium of gas–liquid interface. In the experiment, the gas mass flux at nozzle exit was within 320–780 kg/m2/s, with no more than 1 % non-condensable gas. The results indicated that the non-condensable gas plays an important role on the gas–liquid interface, jet penetration length and heat transfer coefficient. It was found that when 1 % non-condensable gas was mixed with steam jet, the dimensionless penetration length was extended by 16–70 %, and the average heat transfer coefficient decreased by 12–50 %. Based on the force-balance of jet plume, a new quantitative correlation for the steam–air mixture jet penetration length was proposed. The predicted jet penetration length agrees well with the experimental measured values.

Effect of turbulence modelling and non-condensable gas on cloud cavity dynamics

Turbulence modelling plays an important role in the prediction of unsteady and highly dynamic characteristics of cavitating flows. The models with turbulent viscosity modification as Density-Corrected Method (DCM) and Filter-Based Model (FBM), can deal with the dynamics of cavitating flows. Taking it into account, the application of these models to the cavitating flows of water with dissolved air (i.e. third phase) to predict the unsteady phenomena are worth to be analysed and compared. Due to poor self-oscillation characteristics of RNG k-epsilon model in modelling of the cavitating flow, in the present study, the DCM and FBM are implemented to perform the simulation of cavitating flow with consideration of dissolved air. Also, the numerical results are compared with the experimental data. The experiments are conducted in a rectangular test section equipped with Clark Y hydrofoil providing cavity visualisation, instantaneous pressure and vibration fluctuations. The simulations are carried out for different cavitation numbers with and without dissolved air. The Fast Fourier Transform and Continues Wavelet Transform are implemented to extract and compare the shedding frequency of experiments and numerical predictions. In addition, the influence of modification models on the cloud cavitation shedding evolution, dominant shedding frequency, vorticity, pressure, velocity profile, lift/drag coefficient is evaluated.

Synergetic Effect of Non-Condensable Gas and Steam Quality on the Production Capacity of Geothermal Wells and Geothermal Power Generation for Hot Dry Rock

This paper aims to fill the research gap on the effect of steam quality and non-condensable gas on heat-carrying fluid productivity, system performance and optimization. First, the effect of the temperature and quality of the heat-carrying fluid and non-condensable gas (NCG) content on the production parameters was evaluated. After that, three energy conversion systems which included a single flash (SF) system, an organic Rankine cycle (ORC) system and a single flash combined ORC (SFORC) system were constructed in this paper to utilize the heat-carrying two-phase flow with non-condensable gas. Finally, based on thermodynamic modeling, the effects of the temperature and quality of the heat-carrying fluid and non-condensable gas content on the performance and optimization of the three power conversion systems were investigated. The results show that single-phase heat-carrying fluids are more productive than two-phase heat-carrying fluids. NCG is always detrimental. The heat-carrying fluid temperature and quality are positively correlated with system efficiency and negatively correlated with the net power output. In the comparison of comprehensive performances, the SFORC system is the better, and the ORC system and the SF system are the worse. The optimal net power output of the SF system, the ORC system and the SFORC system is 4883 kW, 6557 kW and 7251 kW, respectively.