Effect Of Non-condensable Gas Research Articles

Effect of non-condensable gas on heat transfer in steam turbine condenser and modelling of ejector pump system by controlling the gas extraction rate through extraction tubes

The paper describes the impact of non-condensable gas (NCG) on heat transfer in a steam turbine condenser (STC) and modelling of the steam ejector pump system (SEPS) by controlling the gas extraction rate through extraction tubes. The ideal connection points for the NCG extraction from the STC are identified by analysing the impact of the NCG on the heat transfer and measuring the existing system at a thermal power plant in Slovenia. A simulation model is designed using the Matlab software and Simulink, Neural Net Work, Fuzzy Logic and Curve Fitting Toolboxes, to control gas extraction rate through extraction tubes of the gas pumped from the STC, thus optimising the operation of the steam ejector pump system (SEPS). The gas extraction rate from the STC is controlled in the extraction tubes by pumping only the NCG to the maximum extent. The SEPS is optimised by selecting a Laval nozzle of appropriate size to reduce the steam for the operation of the SEPS, whereby the amount of the extracted NCG is maintained. As the SEPS motive steam is produced in a boiler, the consumption of coal for the production of the SEPS motive steam is reduced as well as the greenhouse gas environmental pollution.

Assessment of improved Schnerr-Sauer model in cavitation simulation around a hydrofoil

To enhance the capability of Schnerr-Sauer model in simulating cavitating flows, in this study, we developed an improved Schnerr-Sauer model based on the Rayleigh-Plesset equation and homogeneous flow assumption. The model considers the effects of turbulent fluctuation and noncondensable gas. The unsteady cavitating flow over a two-dimensional Clark-Y hydrofoil was numerically investigated combined with the SST k-ω turbulence model, in which the turbulence eddy viscosity is corrected. We obtain the time-averaged lift and drag coefficients, the cavity shape evolution at cloud cavitation, and its x-velocity profiles from these calculations. Compared with available experimental data in the literature, the time-averaged lift and drag coefficients predicted from the improved Schnerr-Sauer model agree better with the experimental results than with those of the original. In addition, the modified model can accurately predict the characteristics of the time-averaged lift and drag coefficients during different cavitation conditions. Moreover, the improved model can better simulate the inception, growth, shedding, and collapse of cloud cavitation than the original model. The overall results prove the reliability and accuracy of the improved Schnerr-Sauer model in cavitating flow simulations over a hydrofoil.

Local heat transfer during reflux condensation at subatmospheric pressure and with and without non-condensable gases for power plant application

Reflux condensation heat transfer of steam–air flow has been studied experimentally and theoretically. Effect reflux and co-current flow configurations and flow pressure on condensation heat transfer are investigated. Particular attention was paid to phenomena occurring at the interface and produced by the high steam velocity when the system runs at very low pressure. A total of 200 data points were used to analyze the average condensation heat transfer. An analytical model based on diffusion layer theory, momentum balance and combination of heat and mass transfer, has been developed. A good accuracy was obtained between model predictions and measurements at low pressure. The heat transfer coefficient for the reflux condensation is lower than the co-current flows, because of a thicker condensate film. Comparison between experimental results and predictions shows that the wavy film and non-condensable gas effects are very pronounced for condensation at low pressure. A new equation of the Fwave factor is proposed.

Numerical study on cavitating flow due to a hydrofoil near a free surface

A numerical strategy is proposed for a viscous uniform flow past a 2-D partially cavitating hydrofoil placed at a finite depth from the free surface. The flow was modeled by the Reynolds-averaged Navier–Stokes (RANS) equations. A finite-volume method with the SIMPLE scheme and k-ε turbulence model were employed for computations. The “full cavitation model,” which included the effects of vaporization, noncondensible gases and compressibility, was incorporated in the computation of cavitating flow. The cavity shape and free surface were updated iteratively till a reasonable convergence was reached. As for the determination of the free surface, the VOF approach was adopted. The test cases show the accuracy and stability of our procedure to capture the cavitating flow near the free surface.

Modeling of Internal and Near-Nozzle Flow for a Gasoline Direct Injection Fuel Injector

A numerical study of two-phase flow inside the nozzle holes and the issuing spray jets for a multihole direct injection gasoline injector has been presented in this work. The injector geometry is representative of the Spray G nozzle, an eight-hole counterbore injector, from the engine combustion network (ECN). Simulations have been carried out for a fixed needle lift. The effects of turbulence, compressibility, and noncondensable gases have been considered in this work. Standard k–ε turbulence model has been used to model the turbulence. Homogeneous relaxation model (HRM) coupled with volume of fluid (VOF) approach has been utilized to capture the phase-change phenomena inside and outside the injector nozzle. Three different boundary conditions for the outlet domain have been imposed to examine nonflashing and evaporative, nonflashing and nonevaporative, and flashing conditions. Noticeable hole-to-hole variations have been observed in terms of mass flow rates for all the holes under all the operating conditions considered in this study. Inside the nozzle holes mild cavitationlike and in the near-nozzle region flash-boiling phenomena have been predicted when liquid fuel is subjected to superheated ambiance. Under favorable conditions, considerable flashing has been observed in the near-nozzle regions. An enormous volume is occupied by the gasoline vapor, formed by the flash boiling of superheated liquid fuel. Large outlet domain connecting the exits of the holes and the pressure outlet boundary appeared to be necessary leading to substantial computational cost. Volume-averaging instead of mass-averaging is observed to be more effective, especially for finer mesh resolutions.

Effect of non-condensable gas on thermal stratification and flow patterns in suppression pool

This work analyzes the effect of the non-condensable gas on the direct contact condensation in suppression pool with thermal stratification. Both the Particle Image Velocimetry (PIV) system and high speed camera are used for the experiments. The influences of the non-condensable gas on the thermal stratification, the condensation behavior, and the velocity field are obtained in detail through the experiments. What is more, the experimental quantitative results about the direct contact condensation of vapor mixing with the non-condensable gas in the suppression pool would be used as benchmarking for the CFD simulation of relevant phenomena.

CUPID 코드의 유체 물성치 변화를 고려한 자연대류 해석

Without electirc power to cool down the hot reactor core, passive systems utilizing natural circulation are becoming a big specialty of recent neculear systems after the severe accident in Fukusima. When we consider the natural circulation in a pool, thermal mixing phenomena may start from single phase circulation and can continue to two phase condition. Since the CUPID code, which has been developed for two-phase flow analysis, can deal with the phase transition phenomena, the CUPID would be pertinent to natural convection problems in single- and two-phase conditions. Thus, the CUPID should be validated against single- and two-phase natural circulation phenomena. For the first step of the validation process, this study is focused on the validation of single-phase natural circulation. Moreover, the CUPID code solves the fluid properties by the relationship to pressure and temperature from the steam table considering non-condensable gas effects, so that the effects from variable properties are included. Simple square thermal cavity problems are tested for laminar and turbulent conditions against numerical and experimental data. Throughout the investigation, it is found that the variable properties can affect the flow field in laminar condition, but the effect becomes weak in turbulence condition, and the CUPID code implementing steam table is capable of analyzing single phase natural circualtion phenomena.

Effect of non-condensable gas on the start-up of a gravity loop thermosyphon with gas–liquid separator

This study experimentally investigated the influence of non-condensable gas (NCG) on the start-up time of gravity loop thermosyphon (GLT) developed for regenerative building heating exchangers. A gas–liquid separator was added to the end of the condensate line in the GLT. Given characteristics of the NCG that accumulated in the gas–liquid separator, and the NCG is prevented from circulating in the loop, thereby effectively lowering the effect of NCG on heat exchange. The presence of NCG not only influenced the local condensation heat transfer of the condenser but also affected the start-up of the loop thermosyphon. Results of the experimental investigation revealed that the presence of NCG increased the start-up time of GLT. A higher NCG level corresponds to, a longer start-up time. In particular, the start-up time was 2.8 times more than that in the evacuation when amount of NCG was 30% in volume. The NCG–vapor blocks zone hinders the vapor transmission from the evaporator to the condenser in the vapor line between the evaporator and condenser, further causing a rapid increase in system pressure during start-up. Moreover, obvious pressure peak curve phenomena occurred in a number of conditions, such as heat load was greater than or equal 2.0kW and amount of NCG was less than or equal 30% in volume.

Effect of non-condensable gas on laminar film condensation of steam in horizontal minichannels with different cross-sectional shapes

In the present study, a 3-D numerical simulation of laminar film condensation of steam in the presence of non-condensable gas is performed in horizontal minichannels with six cross-sectional shapes based on the volume of fluid (VOF) method. Mixture of steam and oxygen enters the channel with uniform temperature, while the inlet volume fraction of oxygen increases from 0% to 3%. It is shown that the existence of non-condensable gas results in significant reduction in the mass transfer rate from vapor to liquid along the interface in the axial direction. And then the heat transfer coefficient of condensation with oxygen is demonstrated to decline sharply compared with that of the pure vapor condensation.

Operational Characteristics of the Oscillating Heat Pipe with Noncondensable Gas

In this study, the effects of noncondensable gas on the behavior of oscillating heat pipes were investigated. The oscillating heat pipe was made of capillary copper tube, and its turn number was 16. The working fluid used was ethanol, and argon gas was used as noncondensable gas. Experiments were conducted using four different noncondensable gas volume ratios. The temperature and inner pressure of the oscillating heat pipe were measured over a heat input range from 40 to 180 W. The results of this study suggest that the operating characteristics of the oscillating heat pipe were affected by noncondensable gas. In particular, the thermal resistance of the oscillating heat pipe increased with lower heat input as the amount of noncondensable gas increased. In addition, the thermal performance rapidly deteriorated with a large amount of noncondensable gas after local dryout. With higher heat input, the thermal resistance increased even with small noncondensable gas amounts.

An advanced CFD model to study the effect of non-condensable gas on cavitation in positive displacement pumps

AbstractAn advanced transient CFD model of a positive displacement reciprocating pump was created to study its behavior and performance in cavitating condition during the inlet stroke. The “full” cavitation model developed by Singhal et al. was utilized, and a sensitivity analysis test on two air mass fraction amounts (1.5 and 15 parts per million) was carried out to study the influence of the dissolved air content in water on the cavitation phenomenon. The model was equipped with user defined functions to introduce the liquid compressibility, which stabilizes the simulation, and to handle the two-way coupling between the pressure field and the inlet valve lift history. Estimation of the performance is also presented in both cases.

Pore Scale Experiments of Steam and Non-condensable Gaseous Additives Injection in a Fractured Micro Model System

Oil production mechanisms involving steam and non-condensable gaseous additives injection to fractured reservoirs are not fully understood. Visual pore scale experiments usually have been used and are very enlightening for this purpose. A series of experiments were performed to evaluate the effect of non-condensable gas as steam additives in production acceleration and recovery from fractured porous media. The experiments consist of injecting pure steam and mixtures of steam-air into a glass-etched micro model with fracture configuration. Compared to pure steam injection, non-condensable gaseous additives reduce oil recovery, although the difference is marginal in lower gas-steam ratio. Production acceleration was observed in steam injection with non-condensable gaseous additives. Some steam diversion from fracture to matrix system is observed, which can be attributed to emulsion generation in the steam-oil front. Fracture-wall non-uniformities seem to assist this diversion.

Numerical simulation of unsteady cavitating flows of pumpjet propulsor

In this study, an attempt has been made to study the cavitating flows of a pumpjet propulsor. A numerical study based on the unsteady Reynolds-averaged Navier–Stokes computational fluid dynamics method of homogeneous multiphase using structured grids and the shear stress transport (SST) k–ω turbulence model has been carried out. Considering the effects of non-condensable gas (NCG) on the cavitation performance, the Schnerr–Sauer cavitation model has been applied and improved by introducing the NCG. The numerical calculations of non-cavitating and cavitating flows for the marine propeller E779A are carried out with different advance ratios at several cavitation numbers to verify the numerical simulation method. Results show that the thrust, the torque, and the cavitation performance, such as the cavitation location and shape, are in good agreement with experimental data. Furthermore, numerical predictions for a pumpjet propulsor on an unmanned underwater vehicle are made with different non-cavitating and cavitating flow conditions. The numerical simulations accurately predict the propulsor efficiency changes and the cavitation inception and extension on the suction side of rotor blades. The circumferential distributions of velocity components in different regions along the axial direction have different characteristics. The pressure distributions around rotor and stator blades are reasonable and consistent with the cavitation phenomenon. Additionally, the existence of a tip vortex and tip clearance cavitation leads to a further loss in efficiency of cavitating flows.

ICONE23-2178 STUDY OF OVERALL HEAT TRANSFER COEFFICIENT FROM UPPER CRUST TO OVERLAYING WATER DURING MCCI

A model of the overall heat transfer between the molten core and the overlying coolant above crust during MCCI in severe accident is proposed and confirmed experimentally and analytically. The model assumes that the heat transferred from molten core to the overlaying water is proportional to the amount of water that reaches the molten core surface. The water flow to the molten core surface is assumes to be prevented by the CCFL in the porous crust. Thus, the steam flow and the non-condensable gas flow interact with the water flow. The present model describes the relationship between the overall heat transfer and the water flow, and furthermore, the CCFL effect on the water flow. The non-condensable gas effect on the overall heat transfer predicted by the present model agrees well with experiments. The effects of porosity and hole diameter on the amount of water, which reaches the molten core surface, has also been confirmed using RELAP5 code.

A231 加圧水型原子炉の加圧器スプレー配管における温度変動現象に及ぼす非凝縮性ガスの影響(OS2 保全・設備診断技術(5))

Steam-water two phase flow is present in normal operating condition in the horizontal part of the pressurizer spray pipe of PWR. High cycle fatigue crack generation is a concern under the conditions of such thermally laminar two phase flow, wherein temperature fluctuation under of steam-water interface is caused by internal gravity waves in thermal stratified flow. In this study the effect of non-condensable gas to the temperature fluctuation of thermal stratified flow was investigated by the experiments using visualization test section of rectangular pipe. As a result, temperature distribution and fluctuation were roughly divided into three patterns by the amount of the non-condensable gas.

Experimental and theoretical investigation on condensation inside a horizontal tube with noncondensable gas

An experimental and theoretical investigation on condensation from steam/air mixture was carried out in a horizontal tube with a large range of noncondensable gas fractions and inlet gas Reynolds number. A theoretical model is developed based on Liao’s modified diffusion layer theory including the roughness and suction effect. The model predictions were compared with experiment and literature data. The effect of noncondensable gas on overall heat transfer performance was studied. Moreover, the local parameters such as temperatures, gas concentrations and heat transfer coefficients were analyzed along the tube. The predicted values agree well with the experiment and literature data, showing the validation of theoretical model. The average heat transfer coefficient decreases with the increase of inlet noncondensable gas fraction and the decrease of inlet mass flux. The heat transfer rate increases with the increase of inlet pressure, while the heat transfer coefficient shows an opposite trend. The variation tendency of bulk temperature is consistent with that of bulk noncondensable gas fraction. For stratified flow, the heat transfer coefficients at the top part are higher than that at the bottom. But the difference is gradually closing especially at higher inlet noncondensable gas fractions due to the different distributions of thermal resistances. The heat flux decreases along the tube especially near the outlet. Meanwhile, increasing the inlet mass flux could significantly enhance the heat flux.

Effects of noncondensable gas and ultrasonic vibration on vapor bubble condensing and collapsing

Under the condition of high liquid subcooling, boiling is sometimes accompanied by the emission of microbubbles and the collapse of vapor film. This is termed as Microbubble Emission Boiling (MEB) by some researchers and realizes a better heat transfer performance with its heat flux even higher than CHF. In order to simulate the interaction between vapor bubble and cold bulk in a complex boiling, vapor bubbles were issued into a water tank from a circular injection tube with inner diameter of 2mm. In this work, the process of bubble condensing and collapsing in water with high liquid subcooling is focused and the effects of noncondensable gas and ultrasonic vibration on MEB are researched. Experimental results show that the condensation of vapor/noncondensable gas bubble presents different scenarios with the increase in initial mole fraction of noncondensable gas: collapse to many microbubbles suddenly (x0<2.5%); split up into several tiny bubbles (2.5%<x0<7.5%); keep infrangible (x0>7.5%). When an ultrasonic vibration is applied, the deformation and breakage of the vapor/noncondensable gas bubble become more furious and easier. Noncondensable gas could weaken the bubble condensation, reducing the inertial shock of the liquid on the bubble and making the bubble more stable. This can explain that the presence of noncondensable gas can inhibit the collapse of bubble and deteriorate the heat transfer performance consequently in MEB region. However, ultrasonic vibration will intensify the bubble condensation and enhance the inertial shock of liquid, which will enhance the instability of bubble surface. This, combined with the function of Bjerknes force, would lead the bubble to be more unstable to be broken up easily in the ultrasonic field. Hence, the occurrence of MEB for liquid with noncondensable gas may be intensified by the ultrasonic vibration.

Assessment of steam condensation model with the presence of non-condensable gas in a vertical tube using RELAP5 Mod 3.2 code and MIT exp. Data

The non-condensable gas effect is a primary concern in some passive systems used in advanced design concepts, such as the Passive Residual Heat Removal System (PRHRS) of AP1000, APR1400, AES-2006, the Passive Containment Cooling System (PCCS) of AP1000 design, and Isolation Condensation System (ICS) of ESBWR design. The accumulation of the non-condensable gas inside the condensing tubes can significantly reduce the level of heat transfer which affects the heat removal capacity in accident condition and impacts plant safety. The objective of the present work is to assess the analysis capability of two wall film condensation models of RELAP5/Mod3.2 with the presence of non-condensable gas in a vertical tube on condensation experiments performed at MIT, USA. The results of the simulations and experimental data show the similar tendencies that the heat transfer coefficients increase as the inlet steam-non condensable gas mixture flow rate increases, the inlet steam-non-condensable gas mass fraction decrease, and the inlet saturated steam temperature decrease

Analysis of experiments for the effect of noncondensable gases on steam condensation over a vertical tube external surface under low wall subcooling

Experimental investigations have been conducted to study the steam heat removal capacity with noncondensable gases (e.g. air, helium) under low wall subcooling over a vertical tube external surface. The effect of the wall subcooling on the steam condensation heat transfer coefficients has been researched by experiments when the pressure and the air mass fractions are stable. At the air/steam cases, condensation heat transfer coefficient has been obtained under the wall subcooling degree ranging from13 to 25°C, total pressure ranging from 0.4MPa to 0.6MPa and air mass fraction ranging from 0.07 to 0.52. Under the same pressure and noncondensable gases mass fraction, the effect of wall subcooling on condensation heat transfer coefficient with noncondensable gases is stronger than that with pure steam. The empirical correlation is developed for the heat transfer coefficient which covered all data points within 15%. Under air/helium/steam cases, the effect of helium (simulating hydrogen) on the heat transfer coefficient is investigated under the wall subcooling degree ranging from 18 to 27°C, total pressure ranging from 0.53MPa to 0.6MPa, steam mass fraction ranging from 0.6 to 0.92 and helium volume fraction in noncondensable gases keeping 0.3. None of the experimental conditions is found the helium stratification. The condensation heat transfer coefficient that got from steam/air/helium condition is about 20% lower than that got from air/steam cases.

Experimental study on condensation of steam/air mixture in a horizontal tube

The effect of noncondensable gas on condensation heat transfer inside horizontal tubes was investigated experimentally. Air was used as the noncondensable gas. The effects of inlet noncondensable gas mass fraction, inlet gas mixture mass flux and inlet pressure on overall heat transfer performance were analyzed. Moreover, local heat transfer performance was investigated by comparing centerline temperatures and local heat transfer coefficients. The results showed that the overall heat transfer coefficient decreased as inlet noncondensable gas fraction increased. Increasing inlet mass flux could enhance the heat transfer rate and overall heat transfer coefficient. Furthermore, the heat transfer rate showed an increasing trend, whereas the overall heat transfer coefficient decreased with increase of inlet pressure. The local heat transfer coefficient decreased along the condenser tube due to the decrease of gas mixture Reynolds number and the increase of liquid film thickness and local air fraction. For stratified flow, the local heat transfer coefficient at the top part was higher than that at the bottom owing to the asymmetrical liquid film. However, this gap gradually decreased along the tube, especially at higher inlet noncondensable gas fraction. Finally, two correlations respectively for stratified flow and annular flow regimes were developed, using the modified Froude number as the indicator of transition from stratified to annular flow.