Non-condensable Gas Concentration Research Articles

Applying isovolumic steam capsule as new thermal energy storage unit

In order to make up the inefficiencies of liquid–solid phase change material (PCM) such as low latent heat and low heat transfer rate, the possibility of adopting water steam as the phase change material is explored. Although great volume change occurs during the gas–liquid phase-changing, the specific latent heat is at least one order of magnitude larger than that of liquid–solid phase-changing. To minimize the adverse effect of the great volume change during vaporization or condensation, the steam can be accommodated inside sealed vessel with sturdy shell. In this study, an isovolumic steam capsule (ISC) was made by filling a cylinder with a small amount of liquid water and then heated and boiled to extinguish the non-condensable gas (NCG) before sealing it. Thermodynamic analysis shows the thermal energy contained in the isovolumic steam capsule per unit volume increases in approximately an exponential manner with the increase of temperature due to the evaporation of liquid, and can reach several times that of liquid–solid phase change material, demonstrating great potential as energy storage material. The heat transfer experiments show that the energy charging and discharging rates increase with the temperature difference. There exists thermodynamic non-equilibrium during heat transfer and the deviation from saturation enlarges with increasing temperature difference and non-condensable gas concentration. For both charging (vaporization) and discharging (condensation), a higher non-condensable gas concentration in the steam exhibits larger heat transfer rate in the beginning, but smaller heat transfer rate in the later stage. The mechanism of vaporization and condensation in the isovolumic steam capsule awaits to be further clarified.

Numerical analysis of pressure variation and gas load effects in the refrigeration system for household refrigerators

Insufficient air evacuation from a refrigeration system prior to refrigerant charging can lead to an increased non-condensable gas concentration, negatively impacting system performance. Despite its critical importance, literature on refrigeration system vacuuming procedures is notably lacking. This study developed numerical methods and constitutive models to assess gas load, validated against measured pressures using experimental setups. The model developed can be extended and applied to a wide range of vacuum systems. Examining the vacuuming process in a household refrigerator, a connected vacuum pump expedited the process, revealing higher pressures in the capillary tube and condenser outlet due to low flow conductance. The rate of pressure increase attributable to the gas load from outgassing and degassing remained below 0.6 %, deemed negligible during vacuum pump operation. A 24-hour simulation post-vacuum pump cessation showcased pressure equalization and subsequent rise due to outgassing and degassing, resulting in a 201 % increase in pressure within the compressor’s internal space connected to the process pipe. The pressure increase in the compressor attributable to outgassing amounted to 140 %, surpassing the 59 % from degassing. Notably, assuming a 3 μm crack in the process pipe led to a continuous increase in refrigerator system pressure over 24 h. Leakage significantly increases the amount of non-condensable gases inside the system, potentially leading to increased energy consumption and deterioration in system performance.

Microbubble oscillation on localized heat source affected by dissolved gases in water

Recently, we demonstrated that the local heating of degassed water can generate water vapor microbubbles and induce a rapid flow around the bubble. Although flow generation involves the self-excited oscillation of bubbles at a local heating point, the conditions under which the bubbles oscillate are not fully understood. In this study, the dependence of microbubble size and oscillation frequency on the concentration of non-condensable gases in water was investigated. A continuous-wave laser beam was focused on a β-FeSi2 thin film, and water was locally heated using the photothermal conversion properties of the film. The results showed that the lower the concentration of non-condensable gases dissolved in water, the smaller the bubble size and the higher the oscillation frequency. Furthermore, it was found that the bubbles oscillate when the amount of non-condensable gas absorbed by the bubbles, i.e., the bubble size, falls below a specific level. This study can provide a new understanding of the bubble oscillation mechanism and lead to the development of fluid control technology using bubbles.

Interfacial heat transfer with non-condensable gas in ASTEC V2.2: Application to severe accidents study during PWR cold shutdown states

In a diphasic flow, the presence of non-condensable gas has an important impact on interfacial heat transfer, especially at low global pressure. In severe accidents studies, such flow can be commonly encountered. For example, in pressurised water reactors, high concentration of non-condensable gas can be found in the reactor coolant system in case of late core reflooding with a high oxidation rate (high hydrogen concentration) or in case of accidents happening during the cold shutdown of the reactor, when the reactor coolant system has been partly drained (high air concentration). Such flows with non-condensable gas are challenging to compute for severe accident system codes. A new model is implemented in ASTEC v2.2 to improve the interfacial heat transfer calculation in presence of non-condensable gas. The model gives a more accurate estimation of the heat transfer by assuming that it is mainly driven by vapour diffusion in the gas phase. The new model is applied to study cold shutdown states for 1300 MWe pressurized water reactors. A complete calculation of the cooling, depressurisation and draining of the reactor can be successfully performed. In order to show ASTEC new capabilities, a first accident scenario with loss of the residual heat removal system is also presented.

Stress Corrosion Cracking in Metal Alloys Exposed to Geothermal Fluids with High Non-Condensable Gas Content

Geothermal energy production equipment operates under a host of corrosion conditions. Field corrosion testing of metals and alloys is a key part of plant design in most geothermal systems. This work focuses on field testing selected metal alloys in geothermal fluid containing a very high concentration of non-condensable gases (NCG) to evaluate the predisposition to stress corrosion cracking (SCC). SCC is caused by the simultaneous existence of stress and susceptible material in a corrosive environment, such as intermittent shut-down and discharge activities.U-bend coupons made from one standard API carbon steel and five different corrosion-resistant alloys were exposed for 95 days to almost dry steam with an enthalpy of 2745 kJ/kg at 307 °C and NCG content of 13.8% by weight.The analysis of the different coupons shows that L80 Type 1 carbon steel is the most susceptible to this corrosion damage. However, the risk of this occurring in tested well is likely low due to high temperatures and the scarcity of aqueous phase and chloride in the geothermal fluids.

Experimental Investigation of Bubble Oscillation and Leaping Driven by Thermocapillary Effects with Non-condensable Gas

Boiling phase-change plays a crucial role in heat transfer as it can dissipate higher heat fluxes than single phase. Bubble nucleation, growth, motion (oscillation or leaping), coalescence and departure, govern the boiling and the heat transfer performance on wires. Many factors affect the bubble mechanisms and interactions taking place, which include the nature of the fluid, experimental conditions, thermocapillary effects, etc. This work investigates the bubble oscillation and leaping phenomena caused by thermocapillary effects in the presence of oxygen and air as non-condensable gases during boiling on a platinum micro-wire. More in particular, the bubble oscillation performance is compared under various bulk temperatures and heat fluxes for two different non-condensable gases. It is observed that for a similar fluid bulk temperature, the lower the heat flux the longer the bubble displacement. Moreover, bubble oscillation phenomenon is influenced by the concentration of non-condensable gas dissolved in the liquid showing larger harmonic periods and shorter waiting times with decrease in the contact line pinning force by approximately 7–44% in the presence of air when compared to nitrogen. Last during oscillations, bubble leaping phenomenon was observed as a consequence of the interaction between the jet flows above the oscillating bubble.

A numerical study on film condensation of steam with non-condensable gas on a vertical plate

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.

An improved cavitation model with thermodynamic effect and multiple cavitation regimes

Mechanical feed pumps in organic Rankine cycle (ORC) power plants can suffer from cavitation to lose their normal feeding performance or even damage. Cavitation models for organic fluids in ORC systems are lacking presently. Hence, a new cavitation model with thermodynamic effect was proposed. Surface tension-controlled, inertia-controlled, intermediate and heat transfer-controlled cavitation regimes, and two key elements: vapour bubble growth rate and vapour bubble number density are included in the model. A known air or non-condensable gas concentration in the liquid was employed to determine cavitation nuclei number density. The model was coded in ANSYS CFX as user defined model and validated with cavitating flows of organic fluid R114 in a venturi, liquid nitrogen and liquid hydrogen on a tapered hydrofoil and warm water around a hydrofoil NACA 0015 in cavitation tunnels based on visualised cavity length. Two model constants, temperature depression, and minimal cavitation number were correlated to bulk liquid temperature, Reynolds number, and Jakob number. The temperature and pressure profiles of liquid nitrogen and hydrogen on hydrofoil surface were examined against the experimental data. The model was applied to simulate unsteady cavitating flows of organic fluid R245fa in a diaphragm pump. It was shown that the temperature depression and minimal cavitation number cannot be correlated to bulk liquid temperature, Reynolds number and Jakob number. Two model constants can be correlated fairly to Reynolds number. The model underestimates the thermodynamic effect by 43% for R114, 18.6% for liquid nitrogen and 32.6% for liquid hydrogen based on temperature depression. The predicted temperature and pressure profiles on hydrofoil surface agree with the experimental data for liquid nitrogen. The model can produce an expected curve of mean pump flow rate against net positive suction head available.

Modelling reinjection of two-phase non-condensable gases and water in geothermal wells

Steam production from high enthalpy geothermal systems is frequently accompanied by the emission of non-condensable gases (NCGs), initially dissolved in the liquid phase or mixed in the vapour phase at depth in the reservoir. Capturing and reinjecting geothermal gases (CO2, CH4, NH3, H2S, H2, …) together with condensed steam leads to a significant improvement of the environmental profile of geothermal power systems and helps with reservoir recharge and pressure support. Nowadays, there are several ongoing projects targeting the minimalization of the environmental impact of geothermal exploitation through reinjection of the NCGs. For low NCG content, the gases can be fully dissolved into the condensed water and reinjected. However, for a high concentration of NCGs, the dissolution is only partial, and a two-phase mixture needs to be reinjected to achieve this goal. We present here the numerical results for the reinjection process in two different geothermal sites and for two different injection scenarios, focusing on the case of two-phase (liquid–gas) flows. Three commercial software (UniSim®, PIPESIM, and OLGA) and one in-house developed code (GWellFM) were used, and their results were compared. The injection should always take place inside a liquid column in the well to avoid degassing and accumulation of the NCGs. When targeting high pressure reservoirs or when injecting high ratios of water to NCGs flow rates, mixing of the two phases should take place on the surface. Whereas for low pressure reservoirs or for high gas contents mixing must occur deep in the well through one or several mixing points to ensure either complete dissolution of the gas or the downward flow of a two-phase mixture with minimum compression on the surface. The uncertainties of two-phase downward flows and water/NCGs mixtures characterisations introduce additional complexities in the modelling of the reinjection process.

Analysis of water quality over non-condensable gases concentration on steam used for sterilization.

BackgroundNon-condensable gases (NCGs) are all gases that do not undergo liquefaction during the saturated steam sterilization process. During a sterilization cycle, the NCGs presence inside the chamber is one of the biggest threats to the sterilization process compromising process validation and product quality.MethodsIn this work, 170 testing of NCGs concentrations performed between September 2016 and August 2021 were carried out by Orionce Serviços de Metrologia Ltda (Barueri, SP, Brazil), according to EN285:2015 procedure. For steam generation, the types of water used were softened water (SW), one-step reverse osmosis (RO), purified water (PW), and water for injection (WFI). The data obtained were analyzed using Minitab® software, version 18.1, to identify a relationship between the water quality used for steam generation and the concentration of non-condensable gases determined into equipment qualification.FindingsFrom total tests performed, 109 tests passed, and 61 tests failed, representing 64.2% and 35.8%, respectively. A higher failure rate was observed in terms of concentration of non-condensable gases in systems that used purified water for steam generation (64.7%), followed by softened water (55.6%), one-step reverse osmosis (42.9%), and water for injection (7.6%).ConclusionSystem processes using WFI for steam generation showed better results for steam quality approvement, in terms of NCGs concentration, compared to softened, purified, or reverse osmosis water treatments in the concentration of non-condensable gases in steam used for sterilization processes of industrial utilities.

Co-existing boiling and condensation phase changes of a multicomponent fluid in a confined micro-space analysed by a modified LBM

In this study, we propose and validate a new phase change source term based on the Gong and Cheng's lattice Boltzmann (LB) model (Gong and Cheng, 2012) [1]. A modified phase transition LB model, combined with a multicomponent LB method, was applied to simulate co-existing boiling and condensation phenomena interesting a multicomponent fluid (i.e., water and non-condensable gas (NCG)) in a confined space. Additionally, we investigated and discussed numerically the effects of the NCG concentration on the heat and mass transfer performances during the phase change of multiphase and multicomponent fluids in a confined space. In particular, these effects were studied considering variable solid wettability and confined scale conditions.

Physical modeling of nitrogen slug operation in Xinjiang SAGD projects - Fundamental roles of NCG in SAGD process

Non-condensable gas (NCG) co-injection in mature Steam Assisted Gravity Drainage (SAGD) chamber had been widely implemented and significant amount of steam was saved. Encouraged by their performance, NCG SAGD was also tested in Xinjiang oilfield since 2012. Its strategy differed from others in that nitrogen slug was injected once per year since the early SAGD stage. However, its performance was quite mixed. A unique 2D model was used to mimic the field operation of SAGD and NCG SAGD. The general performance, temperature drop, pressure oscillation, gas fingering and gas coning were analyzed. It showed non-condensable feature of NCG lead to gas accumulation and pressure oscillation in NCG slug operation. Its partial pressure effect lowered down temperature, saving steam but reducing oil rate, potentially leading to gas coning issue. The main purge mechanism was gas solubility in water and oil which controlled the NCG concentration inside the steam chamber. NCG fingering was found to speed up vertical growth of steam chamber in the early SAGD stage. However, injecting NCG before chamber getting mature should be treated with caution. Lastly, NCG was recommended to inject through vertical well to the top of the formation.

Steam condenser for plants with carbon dioxide recovery

Power plants with CO2 utilization have been designed by Allam, Mateant, Turbocon, etc. One of the main problems of this plant is a condenser for steam-gas mixture with high concentration of non-condensable gas. The process of development of steam condenser for steam-gas mixture is described. Its design is based on the idea of maintaining a constant steam-gas mixture velocity along the steam condensation channel. The shape of the channel with constant SGM velocity is described. To research the heat-mass transfer of gas-team mixture the test plant with tubes crosscut by thermocouples is realized. In the process of testing, gas-steam mixture velocity, pressure and air concentration changed from 0% to 18%. The experimental results have been summarized in a dimensionless equation. The pressure drop and increase of air concentration contribute to the decrease of saturation temperature. The optimal velocity is reached when the surface area of the channel in the condenser is minimal. The optimal velocity is about 30 – 50 m/s. The research results are implemented in the experimental model of high-efficiency condenser. The heat transfer coefficient in this model is equal to about 4500 – 2700 W/(m2K) if air concentration at the inlet is 0–8 %. The designs of high-efficiency condenser for gas-steam turbine plant of 25 MW capacity and the condenser with vertical tubes have been presented.

Effect of non-condensable gas on a collapsing cavitation bubble near solid wall investigated by multicomponent thermal MRT-LBM* *Project supported by the National Natural Science Foundation of China (Grant Nos. 11874140 and 11574072), the State Key Laboratory of Acoustics, Chinese Academy of Sciences (Grant No. SKLA201913), the National Key Research and Development Program of China (Grant No. 2016YFC0401600), the Primary Research

A multicomponent thermal multi-relaxation-time (MRT) lattice Boltzmann method (LBM) is presented to study collapsing cavitation bubble. The simulation results satisfy Laplace law and the adiabatic law, and are consistent with the numerical solution of the Rayleigh–Plesset equation. To study the effects of the non-condensable gas inside bubble on collapsing cavitation bubble, a numerical model of single spherical bubble near a solid wall is established. The temperature and pressure evolution of the two-component two-phase flow are well captured. In addition, the collapse process of the cavitation bubble is discussed elaborately by setting the volume fractions of the gas and vapor to be the only variables. The results show that the non-condensable gas in the bubble significantly affects the pressure field, temperature field evolution, collapse velocity, and profile of the bubble. The distinction of the pressure and temperature on the wall after the second collapse becomes more obvious as the non-condensable gas concentration increases.

A 2D numerical study on the condensation characteristics of three non-azeotropic binary hydrocarbon vapor mixtures on a vertical plate

To improve the transportation efficiency and reduce the supply cost, the liquefaction becomes an important technology to store and transport the natural gas. During the liquefaction, the various components (e.g. propane, ethane, methane etc.) undergo fractional condensation phenomenon due to their different boiling points. This means that when one component condenses, others play a role of non-condensable gas (NCG). In order to reveal the influence mechanism of NCG on this condensation process, a numerical method was employed in this paper to study the condensation characteristics of three non-azeotropic binary hydrocarbon vapor mixtures, namely the propane/methane (80%–95%), ethane/methane (65%–85%) and methane/nitrogen (2%–13%) mixtures, on a vertical plate. The model was proposed based on the diffusion layer model, and the finite volume method was used to solve the governing equations. A user defined function was developed by cell iterative method to obtain the source terms in the condensation process. The numerical results show that the gas phase boundary layer formed by the NCG becomes the main resistance to the reduction of heat transfer coefficient. And for the above three mixtures, there is a negative correlation between the NCG concentration and the heat transfer coefficient. Meanwhile, the results show a good agreement with the experimental data, meaning that the proposed model is reliable. Three mixtures within same non-condensable mole fraction of 20% were also investigated, indicating that the mixtures with a higher binary hydrocarbon molecular ratio have a lower heat transfer coefficient. As a result, the presence of the lighter NCG contributes to a thicker boundary layer.

THE CONDENSATION OF WATER VAPOUR IN A MIXTURE CONTAINING A HIGH CONCENTRATION OF NON-CONDENSABLE GAS IN A VERTICAL TUBE

This paper deals with the condensation of water vapour possessing a content of noncondensable gas in vertical tubes. The condensation of pure steam on a vertical surface is introduced by the Nusselt condensation model. However, the condensation of water vapour in a mixture with non-condensable gas differs from pure vapour condensation and is a much more complex process. The differences for the condensation of water vapour in a mixture containing a high concentration were theoretically analysed and evaluated. In order to investigate these effects, an experimental stand was built. Experiments were carried out in regards to the case of pure steam condensation and the condensation of water vapour with a non-condensable gas mixture to evaluate the influence of the variable non-condensable gas content during the process. A non-condensable gas in a mixture with steam decreases the intensity of the condensation and the condensation heat transfer coefficient. A gradual reduction of the volume and partial pressure of steam in the mixture causes a decrease in the condensation temperature of steam, and the temperature difference between steam and cooling water. The increasing non-condensable gas concentration restrains the transportation of steam towards the tube wall and this has a significant effect on the decrease in the condensation rate.

Effect of non-condensable gas on the performance of steam-water ejector in a trigeneration system for hydrogen production: An experimental and numerical study

An ejector containing phase changing gas-liquid flow process acts as a popular and decisive device in multiple industrial applications, including the hydrogen production, electricity production, fuel cells, refrigeration, petroleum industry and desalination systems. However, non-condensable gas is inevitable for the usual operation of phase-changing gas-liquid ejector in the trigeneration or electrolyzer system for hydrogen production, and rarely research is concerned with this issue. In the present study, the effect of non-condensable gas contained in the condensable gas on the characteristics of gas-centered water ejector is presented, with steam, water and air acting as the gas, liquid and non-condensable gas, respectively. Experimentally, the flow rate of steam is controlled to be 1.45 g/s with an absolute pressure of 120 kPa, the air flow rate varies from 0 to 0.14 g/s, resulting in a non-condensable gas concentration ranging from 0 to 9%, and the resulted water flow rate at 100 kPa and 282.15 K changes from 34.7 to 37.3 g/s. Combined with the numerical methods, the performance of ejector expressed in ejected water flow rate was found to increase firstly with a small amount of non-condensable gas, and decrease when the non-condensable gas reaches a certain amount. In addition, the distributions of multiple local flow parameters including pressure, condensation rate and gas volume fraction, velocity and temperature inside the ejector were shown for different non-condensable concentration, by which the mechanism for the change of ejector performance under varying non-condensable concentration was demonstrated. These findings are initiative and insightful for the ejector design optimization in the trigeneration system for hydrogen production and the proposed numerical models can be utilized in analysis and design of steam ejector with non-condensable gas involved.

Theoretical Modeling of Vapor Condensation in the Presence of Noncondensable Gas on a Horizontal Tube

Abstract Double-boundary layer theory was adopted to investigate the distributions of the liquid film, gas film, heat transfer coefficient, and condensate mass fluxes around a horizontal tube for vapor condensation with noncondensable gases like steam–air and steam–CO2 mixtures under free convection. The investigation considered the effects of the noncondensable gas concentration, surface subcooling temperature, and pressure. The thicknesses of the liquid and gas films increase gradually along the wall from top to bottom, whereas the local heat transfer coefficient and the condensate mass flux decrease. The film thicknesses do not change significantly around the upper part of the tube but increase sharply around the lower part. The liquid film thicknesses, gas film thicknesses, condensate mass fluxes, and heat transfer coefficients of steam–air systems are compared with those of steam–CO2 systems. The condensate mass flux in the steam–air system is smaller than that of steam–CO2 system under the condition of the same surface subcooling and gas mass fraction because air has more moles of molecules in the mixture than CO2 and the steam more easily diffuses through CO2 than through air. The predicted average condensation heat transfer coefficients agree well with the available experimental data.

Hydrogeochemical similarities and differences between high temperature geothermal systems with similar geologic settings in the Büyük Menderes and Gediz Grabens of Turkey

The Büyük Menderes Graben (BMG) and the Gediz Graben (GG) are two major graben systems and they have important medium-high temperature geothermal systems, with suitable reservoir temperatures (e.g. 170–276 °C) for electricity production such as Kızıldere (Denizli city), Germencik, Salavatlı, Pamukören (Aydın city) in the BMG and Alaşehir (Manisa city) in the GG.These high temperature geothermal systems are located in a highly fractured zone because of the Aegean Extensional Zone effect. Although the main reservoir rocks retain similar compositions for each graben system, the geothermal fluids chemistry characterization can vary along the BMG and GG as a result of differing variables such as a paleo sea effect, the concentration of non-condensable gases (NCG), as well as mineral effects. The water chemistry results and δ18O-δD isotope values show remarkable differences within the Germencik and Kızıldere systems along the BMG, while the main reservoir rocks are of a similar composition. Chemical, isotope compositions and pH values of thermal waters in Alaşehir differ from those in the BMG geothermal systems.Results for δ13C isotopes indicate that the origin of the large amounts of CO2 is the marble in metamorphic rocks in the reservoirs in both graben systems. δ34S, δ34S- SO4 and δ18O-SO4 values indicate that the origin of SO4 indicates gypsum and also bacteria effect in the eastern part of the BMG, while different mechanisms such as; oxidation of sulfur, pH, temperature and possible buffer mineral effects on H2S dissolution to the west of the BMG and GG display a greater impact.

Lattice Boltzmann simulation of seawater boiling in the presence of non-condensable gas

In this study, three-dimensional (3D) boiling of seawater containing non-condensable gas (NCG) was simulated using the modified pseudopotential lattice Boltzmann model for multiphase multicomponent flow, and the effects of wettability and the NCG concentration on the heat flux between the heat source and its adjacent fluids, bubble departure period and diameter were analyzed. The simulation results show that, with an increase in the NCG concentration, the heat flux, bubble departure period and diameter decreased, while the effect of NCG on the bubble departure diameter and period plateaued as contact angle proceeded. Additionally, the boiling mechanisms of seawater containing NCG in a horizontal fissure were also analyzed. With an increase in the NCG concentration, the bubble departure diameter decreased while the bubble departure period increased. Furthermore, the influence was weakened with an increase in Re number.