Noncondensable Gas Mass Fraction Research Articles

Numerical Simulation on Two-Phase Ejector with Non-Condensable Gas

The two-phase ejector is a simple and compact pressure boosting device and widely used in ejector steam-generator water feeding systems and core emergency cooling systems. The direct contact condensation of water and steam is the key process of a two-phase ejector. Usually, the high-temperature and high-pressure steam will inevitably induce non-condensable gases. The existence of non-condensable gases will reduce the condensation heat transfer rate between steam and water, and harm the equipment. This study carried out 3D numerical simulations of a two-phase ejector based on an inhomogeneous multiphase model. The steam inlet pressure and the non-condensable gas mass fraction rang in 0.6–2.9 MPa and 1–10%, respectively. The heat and mass transfer characteristics were analyzed under different conditions. The results show that the heat transfer coefficient and plume penetration length increased with the steam inlet pressure. Non-condensable gas prevents direct contact condensation between the steam and water. The non-condensable gas mass fraction rises from 1% to 10%, the heat transfer between steam and water deteriorates, and leads to a lower heat transfer coefficient.

Experimental study on enhancement condensation heat transfer in tube by foam metal in presence of non-condensable gas

Condensation heat transfer in tube is widely applied in industrial production, and the heat transfer process is often weakened by non-condensable gas (NCG) in actual production. Enhancing condensation heat transfer is beneficial to improve production efficiency, which has always been a hot topic in current research. Foam metal material with large specific surface area and good thermal conductivity is an ideal material to enhance heat transfer. In order to study enhancement heat transfer effect and optimize structure of foam metal, this paper investigated condensation heat transfer in tube strengthened by foam metal in presence of NCG experimentally. Section shape of foam metal is annular, and the pores per inch (PPI) of foam metals is 10, 15, 20 respectively. The effects of PPI value, steam/air mixture mass flow, and NCG mass fraction on heat transfer coefficient (HTC) and flow resistance are studied. The results reveal the following: (1) Compared with smooth tube, the foam metal enhances heat transfer significantly, and HTC increases by 1.5-2.3 times. (2) At same steam/air mixture mass flow, 10PPI foam metal tube has the highest HTC compared to others. (3) With increase of NCG mass fraction and PPI value, pressure drop increases and the HTC decreases. Based on experimental data, pressure drop and HTC correlations are developed. This paper provides an important technical basis for foam metal material application in enhancement heat transfer area.

Experimental study on wet gas condensation heat transfer and flow resistance in horizontal intensified tube

The heat transfer and flow resistance characteristics of in-tube vapor condensation with high content non-condensable gas is significant for designing waste heat recovery devices of gas-fired boilers. In this paper, the forced convection condensation of wet gas in the horizontal tube is experimentally investigated with a non-condensable gas mass fraction of 83–95%. The condensation heat transfer coefficient, thermal resistance and pressure drop are compared between bare tube and two intensified tubes, i.e., the corrugated and spiral tube, under various Reynolds number, wall subcooling degree and inlet humidity. The results show that the in-tube condensation heat transfer coefficient increases with increasing Reynolds number and inlet humidity, but decreases with increasing wall subcooling degree. Compared with the bare tube, the heat transfer coefficient and pressure drop increase up to 47.13% and 16.00% respectively for the spiral tube, and 116.04% and 88.48% respectively for the corrugated tube. When combing the heat transfer and flow resistance factors, the maximum comprehensive performance coefficients are 1.71 and 1.44 for corrugated tube and spiral tube respectively. The superiority of corrugated tube in the wet gas condensation is benefit from effective breaking the non-condensable gas film and promoting the vapor diffusion on the interface.

GAS-LIQUID FILM DISTRIBUTION AND SEPARATION OF CONDENSATION FROM A DOWNWARD-FLOWING STEAM-NONCONDENSABLE GAS MIXTURE ONTO A HORIZONTAL TUBE AT SUBATMOSPHERIC PRESSURE

Based on the boundary layer, a mathematical model was established to investigate the thicknesses of liquid and gas films and the steam condensate distribution in the presence of noncondensable gas outside a horizontal tube at pressures lower than atmospheric pressure. The model accurately predicts the steam condensation heat transfer with noncondensable gas. The influences of the noncondensable gas mass fraction, pressure, velocity, and surface subcooling upon the condensation heat transfer, the thicknesses of liquid and gas films, and condensate distribution around the horizontal tube have been studied. The liquid film thickness rises as the surface subcooling raises but reduces with raising pressure and mass fraction of noncondensable gas. The gas film thickness rises with rising surface subcooling and noncondensable gas mass fraction, reducing as the pressure rises. The thicknesses of gas and liquid films and condensate distribution significantly affect the local heat transfer. The liquid film separation velocity reduces with raising pressure, surface subcooling, and mass fraction of noncondensable gas, which is most influenced by pressure.

Numerical simulation on the direct contact condensation in a steam-water two-phase ejector with non-condensable gas

The steam-water condensing ejector is widely used in many industrial fields and production processes. In the practical operation of ejectors in many systems such as nuclear reactors and underwater gas-ejection devices, the steam pressure is much higher than those in common direct heating systems or refrigeration systems. In addition, some non-condensable gas is inevitably mixed into steam jet. With the presence of non-condensable gas, the flow field and performance of ejector are significantly influenced by the changes in heat transfer characteristics. This paper presents a three-dimensional numerical simulation of the high-pressure steam-water condensing ejector with non-condensable gas based on inhomogeneous multiphase model. The steam inlet pressure, mass flow rate and non-condensable gas fraction are in the range of 0.70–2.40 MPa, 1019–3310 kg/(m2s) MPa and 0–0.05, respectively. The changes in steam plume shapes, distributions of thermal hydraulic parameters and pressure ratio are investigated under different boundary conditions. Numerical results show that the steam plume inside ejector transforms from ellipsoidal shape to divergent shape with the increase of steam inlet mass flow rate and the decrease of back pressure. The choking phenomenon in throat is found at divergent steam plume and the changes of flow field in diffuser do not spread upstream to the mixing chamber, so the thermal hydraulic parameters in mixing chamber and pressure ratio of ejector keep unchanged. In addition, the pressure ratio first increases from 1.08 to 2.34, then decreases to 1.99 with the increase of steam mass flux. As back pressure rises, the pressure ratio drops from 2.00 to 1.30 at low steam inlet mass flux; while first increasing linearly from 1.98 to 2.41 and then decreasing to 1.78 at high steam inlet mass flux. With the increase of non-condensable gas mass fraction, the pressure ratio slowly decreases from 1.48 to 1.39 at low steam mass flux while rapidly decreasing from 4.00 to 1.65 at high steam mass flux.

Condensation oscillation characteristic of steam with non-condensable gas through multi-hole sparger at low mass flux

To study oscillation characteristic of steam and non-condensable gas direct contact condensation through multi-hole sparger at low mass flux, a series of experiments of pure steam and mixture gas condensation have been carried out under the conditions of steam mass flux of 20–120kg/m2s, water temperature of 20–95 °C and mass fraction of non-condensable gas of 0–5%. The regime map of pure steam condensation through multi-hole sparger is divided into steam chugging, separated bubble, aggregated bubble and escaping aggregated bubble. The bubbles behavior of synchronization in the same hole columns and desynchronized excitation between different hole columns can be found. The coalescence effect of mixture bubbles increases with water temperature and non-condensable gas content increasing. Pressure oscillation intensity of pure steam condensation first increases and then decreases with water temperature increasing, and increases with steam mass flux increasing. Pressure oscillation intensity of mixture gas condensation decreases with water temperature and non-condensable gas content increasing, which is significantly weaker than that of pure steam condensation. The oscillation dominant frequency decreases with the rise of water temperature and non-condensable gas content. The correlations for oscillation intensity and dominant frequency respectively are developed in pure steam and mixture gas condensation at low mass flux.

Numerical analysis of two-stage vacuum ejector performance considering the influence of phase transition and non-condensable gases

Multi-effect distillation with thermal vapor compression system has not been able to penetrate the market because of the low coefficient of performance. The two-stage vacuum ejector is an effective vehicle to maintain system condensing temperature, discharge non-condensable gases and improve the system performance. Improving performance of two-stage vacuum ejector relies on the understanding of the fluid dynamic phenomena. Unfortunately, few studies paid attention to the effect of inner fluid phase transition and non-condensable gas mass fraction on the performance of vacuum ejector. Therefore, this paper contributes to proposing a Species transport and Phase transition model to investigate the two-stage vacuum ejector numerically considering the physical properties of non-condensable gases, thermodynamic transformation caused by condensation and evaporation with experimental validation. The results indicate that the entrainment performance of the ejector increases by about 14.95% when the non-condensable gases mass fraction increases from 0% to 100%. Meanwhile, with the consideration of heat and mass transfer in the phase change process, the mean error is 4.9%, which is much lower than single-phase model. Meanwhile, the internal fluid pressure, Mach number, shock waves and expansion degree can be largely influenced by the consideration of Species transport and Phase transition. The results of this paper proved that influence of non-condensable gases and phase transition cannot be ignored in the design and prediction of vacuum ejector and it can contribute to ejector optimization and enhancing the stability and efficiency of multi-effect distillation with thermal vapor compression system.

Experimental study on enhancement characteristics of steam/nitrogen condensation inside horizontal multi-start helical channels

Abstract The aim of this study was to reveal the internal mechanism of enhanced condensation heat transfer, by experimentally performing steam condensation with higher inlet velocity in the horizontal multi-start helical channels (HMSHCs), and investigating the influences of pressure of steam, mass flowrate of cooling water, and mass fraction of noncondensable (NC) gas on steam condensation performance. Taking steam condensation in horizontal circular condensation channel (HCCC) as a reference, the condensation heat transfer coefficients (CHTCs), the outlet condensate mass flowrates (CMFRs), and the total steam condensation pressure drops (SCPDs) were compared and discussed, respectively. The results indicated that NC gas had a strong inhibitory effect on steam condensation, and average condensation characteristics decreased with the increase in NC gas fraction for lower Rem. But for higher Rem, the gas–liquid interfacial shearing stress can likely weaken the negative effect of NC gas. In addition, increasing the cooling water flowrate can entirety promote steam condensation. The comparison results indicated that steam condensation performance of HMSHC is better than that of HCCC under same experimental conditions. For the specific experimental scope, the average CHTCs and the outlet CMFRs in HMSHC are approximately 2.35 and 1.25 times of that inside HCCC, respectively, while the overall SCPDs in HMSHC are about 1.16 times of that inside HCCC. After introducing the performance evaluation factor, the calculation results revealed that the performance evaluation factor h PEC {h}_{\text{PEC}} of the average CHTCs in HMSHC is approximately 2.02, and the performance evaluation factor m PEC {{m}}_{\text{PEC}} of the outlet CMFRs in HMSHC is approximately 1.08. The two evaluating values are reasonable.

The coupling process of steam condensation and falling film evaporation with non-condensable gas

For the steam condensation process inside a horizontal tube under small temperature difference, the operating parameters such as steam flow rate and temperature difference are narrowed in limited variation ranges to guarantee the high heat transfer performance. When the steam is mixed with non-condensable gas, the effective temperature difference shows more complexity compared with pure steam condensation. In this paper, the condensation process of the mixed steam in the tube cooled by the falling film evaporative seawater outside the tube is calculated with the steam mass flow rate of 2–9 kg/(m2·s), the evaporation temperature of the seawater of 50–70 °C, the total temperature difference of 2–4 °C and the inlet non-condensable gas (NCG) mass fraction of 1–4%. The mixed steam condensation heat transfer model combined with distributed parameter model is established and validated to couple the heat transfer on both sides of the tube. The local saturation temperature depression of the mixed steam condensation is divided into two factors, one caused by the flow resistance and the other caused by the non-condensable gas mass fraction. Both types of saturation temperature depression increase with the increase of the inlet non-condensable gas mass fraction. The mass flow rate and the temperature difference are found to have more significant impact on the total temperature depression on the saturation temperature. Besides, the saturation temperature is found to have no significant impact on the condensation heat transfer of the mixed steam. The mass flow rate corresponding to the maximum heat transfer of the heat transfer tube is presented.

Effect of light gas on condensation heat transfer of steam–air mixture and gas stratification

Condensation has been considered for various industrial applications. However, the characteristics of condensation heat transfer have not been fully elucidated. In this study, we identify the characteristics of condensation heat transfer deterioration due to light gas. We measure the condensation heat transfer coefficient by varying the mass fraction of noncondensable gas and the mole fraction of helium to noncondensable gas. We discuss parameters that can affect the condensation heat transfer coefficient, i.e., the gas density, diffusion coefficient, and mole fraction of helium. Gradual deterioration of condensation heat transfer coefficient by increasing mole fraction of helium to noncondensable gas is observed. Furthermore, conditions for helium stratification under condensation are identified. Models for predicting condensation heat transfer are evaluated by varying an effective diffusion coefficient model based on experimental data.

The Investigation on Heat Transfer Characteristics of Steam Condensation in Presence of Noncondensable Gas under Natural Convection

The NHR-200 reactor in China adopts the noncondensable gas self-stabilizing control and the noncondensable gas used for pressure stabilization control can weaken steam condensation heat transfer in the integrated steam-gas pressurizer. A condensation experimental system was established and the heat transfer characteristics of steam-nitrogen and steam-argon condensation under natural convection had been investigated. The pressure ranged from 0.516 to 5.10 MPa. The distributions of nitrogen and argon in the steam/gas mixture were obtained in the experiments, and the results showed that nitrogen and argon were evenly distributed in the steam under different pressure, respectively. The effects of heat transfer temperature difference had also been investigated and it is found that the total heat transfer coefficient difference had little influence on the total condensation heat transfer coefficient. However, the steam condensation heat transfer coefficient decreased with the increase of the degree of supercooling of the wall. The condensation heat transfer coefficient was reduced by approximately 0.11 kW/(m2·K) as the degree of supercooling of the wall changed from 14°C to 36°C. The condensation heat transfer coefficient also decreased with the mass/molar fraction of noncondensable gas increasing and a certain difference between the effect of the mass fraction of noncondensable gas and the effect of the molar fraction of noncondensable gas was discussed in this paper.

An improved model based on real gas state equation and fog formation for condensation heat and mass transfer

In order to predict the condensation heat transfer coefficient precisely, this work aimed at proposing a generalized model with a wide scope of parameters applicability, namely, we presented an improved model that can predict the condensation characteristics which based on heat and mass transfer analogy with consideration of gas compressibility factor, fog formation factor, film waviness factor, suction factor and eddy diffusion factor. The improved model is suitable for those conditions: low pressure condensation at plate-shape and curved-shape surface with natural/forced convection, high pressure condensation at curved shape surface with natural convection. The improved model shows good applicability with the scope of the pressure is up to 2 MPa and the non-condensable (NC) gas mass fraction up to 90%. Six experimental databases (including 436 data) were chosen to validate this model. More than 97% of the results predicted by the improved model were within ±30% bands.

Numerical simulation of dropwise condensation on rough structures in the presence of non-condensable gas using LBM

Dropwise condensation on rough surfaces enhanced with pillars in the presence of non-condensable gas (NCG) including the initial nucleation process is simulated using the multispecies multiphase lattice Boltzmann method, and the effect of mass fraction of NCG, the surface wettability, the bottom wall temperature and the geometrical parameter (the pillar height H) on condensation process are investigated. It's found that these four factors all have an effect on the nucleation position, waiting time, condensate behaviors, and the wetting state of the droplet. With higher values of NCG mass fraction, surface hydrophobicity, pillar height H, and lower bottom wall temperature, the nucleation occurs on top of the pillars and the waiting time before nucleation gets longer. It's also concluded that the wetting state of the droplet tends to be the Cassie state, and the average heat flux gets smaller with higher values of the former three parameters and lower bottom wall temperature.

Comparison of Heat Transfer Performance for Condensation in Corrugated Low Finned Tube and Smooth Tube with Air

The existence of air served as non-condensable gas makes it difficult to design effective titanium condenser in PTA plant. In this paper, the heat transfer characteristic for condensation inside corrugated low finned tube and smooth tube in presence of air was compared. The local heat transfer performance was studied by comparing bulk temperature and local heat transfer rate. The effect of non-condensable gas mass fraction on overall heat transfer performance was also analysed. The results indicated that both the bulk temperature and the local heat transfer rate decreased along the axial direction due to the reduction of steam partial pressure and temperature difference. The average heat transfer coefficient and total heat transfer rate decreased with the increase of inlet non-condensable gas mass fraction. And the corrugated low finned tube could reduce the impact of non-condensable gas by reducing the thickness of gas film and condensate film.

Effect of Surface Inclination on Filmwise Condensation Heat Transfer During Flow of Steam–Air Mixtures

Abstract Empirical/semi-empirical correlations are available in the literature to quantify the effect of several major parameters, like bulk pressure, non-condensable gas mass fraction, and wall subcooling, on condensation heat transfer coefficient (HTC). However, despite numerous applications of condensation on inclined flat plates, there is a lack of understanding of the effect of surface inclination on condensation heat transfer. Accordingly, a dedicated experimental program was undertaken to investigate the effect of surface inclination angle on filmwise steam condensation. Experiments were performed at different bulk pressures (1.7–4.2 bar absolute) and steam-air mass fractions (ranging from pure steam, i.e., 0% to 40% w/w air), with the steam-air mixture flowing over a flat test plate (Re range, 4200–4800). In each run, the inclination angle of the test surface was varied from −90 deg (condensation underneath the horizontal surface, facing downward) to +90 deg (condensation over the horizontal surface, facing upward) in increments of 15–20 deg (inclination angle θ measured from vertical). The results reveal an intriguing trend: for pure steam condensation, the HTCs decrease as the plate is inclined in either direction from the vertical, and the variation is nearly symmetric for both upward- and downward-facing configurations. On the other hand, for steam condensation in the presence of air, the HTCs decrease monotonically for upward-facing configurations, while they increase slightly (10–20%), and decrease subsequently (for θ < −70 deg) for downward-facing cases. Finally, the HTCs for inclined orientations are compared with the HTC in the standard vertical configuration to quantify the effect of inclination angle.

Combined Influence of Noncondensable Gas Mass Fraction and Mathematical Model on Cavitation Performance of Bearing

The presence of cavitation in the oil film seriously affects the bearing lubrication performance and bearing capacity. Now the research of this phenomenon mostly focuses on the model of Reynolds equation (R-E equation) or Navier-Stokes equation (N-S), the influence of the two computation models is less analyzed, and the effect of noncondensable gas (NCG) mass fraction on the bearing performance is seldom studied. In the manuscript, the cavitation mechanism is studied using the mixed model of three-dimensional N-S equation and Jakobsson-Floberg-Olsson (JFO) condition of two dimensional Reynolds equation, and the influence of rotational speed and NCG mass fraction on the cavitationoil film pressure, and bearing capacity was studied. The results show that the change trend of cavitation with the rotational speed is basically consistent for N-S equation and R-E equation. The bearing capacity calculated by N-S equation is greater than that calculated by R-E equation. The peak pressure and bearing capacity of film can be improved by increasing the NCG mass fraction of lubricant and rotational speed.

Numerical study on condensation of steam/air mixture inside corrugated low finned tubes

Corrugated low finned tubes are the specical spirally corrugated tubes, which can enhance the condensation heat transfer with and without noncondensable gas. In this paper, a numerical model on the basis of diffusion layer theory was established to investigate the local heat transfer characteristic inside corrugated low finned tubes. The local parameters contain bulk temperatures, gas mass fraction, heat transfer coefficient and heat flux. The results showed that the bulk temperatures decreased along the condenser tube but the noncondensable gas mass fraction displayed the opposite trend. The local heat transfer coefficient and heat flux decrease along the condenser tube especially near the outlet. Of the five enhanced tubes, #5 tube had the best overall heat transfer performance, but it also had the fastest rate of decline as condensation progressed, indicating that the rib was the main influence factor compared with pitch.

Experimental investigation on condensation heat transfer for bundle tube heat exchanger of the PCCS (Passive Containment Cooling System)

To provide a passive cooling system for the reactor containment, Passive Containment Cooling System (PCCS) was adopted in the design of i-POWER nuclear power plant. This study focused on validation tests for condensation heat transfer of the PCCS heat exchanger using the CLASSIC facility. The tests include investigation of the condensation heat transfer in prototypic single tube and bundle tubes. From the single tube experiments, condensation heat transfer model was proposed to reflect the PCCS heat exchanger tube geometry. Experimental results in the bundle tube show consistent trend compared to the proposed heat transfer model from the single tube test. The local condensation heat transfer coefficient of inside tubes was smaller than the average value due to a shadow effect by a larger mass fraction of non-condensable gas, so that design of the PCCS should take into account degradation of the condensation heat removal in the bundle geometry.

Hybrid Wettability-Induced Heat Transfer Enhancement for Condensation with NonCondensable Gas.

Heat transfer enhancement in dropwise condensation is widely investigated on a superhydrophobic surface with the advances in surface engineering, but the influence of a large amount of noncondensable gas (NCG) has not been clarified. In this work, the condensation heat transfer with a large amount of NCG is investigated by developing a multiphase lattice Boltzmann model for a multicomponent system. First, the condensation of a single droplet on a hydrophobic surface with NCG is simulated, demonstrating the capacity of the present model to capture the behaviors of different components during phase change and predict the significant influence of even a small fraction of the NCG on heat transfer. Then, solid surfaces with mixed wettability are built by introducing a fraction of hydrophilic parts to enhance heat transfer. It is found that there exists an optimized proportion which could maximize the condensation heat transfer efficiency corresponding to a specific mass fraction of NCG. Furthermore, the mechanism of this optimized proportion is revealed by examining the dynamic behaviors of condensation in a typical case, as a balance between a promotion of the nucleation rate and a put off of transition to filmwise condensation.

Condensation heat and mass transfer of steam with non-condensable gases outside a horizontal tube under free convection

The condensation heat and mass transfer of steam-He, steam-N2 and steam-CO2 mixtures on a horizontal tube under free convection was studied experimentally and theoretically. A model was developed to predict the total condensation heat transfer coefficient of these mixtures and the model considered the effects of suction, fog formation and the variation of the mixture density and molecular weight across the diffusion layer. The experiments were conducted to investigate the effects of noncondensable gas component, concentration and surface subcooling. The condensation heat transfer coefficients are significantly reduced due to the presence of noncondensable gases. The condensation heat transfer coefficient decreases slowly as the surface subcooling increases and the subcooling effect decreases with increasing noncondensable gas concentration. For a given noncondensable gas mole fraction and a given surface subcooling, the steam-He mixture has the highest measured condensation heat transfer coefficient, followed by the steam-N2 mixture and the steam-CO2 mixture has the lowest measured condensation heat transfer coefficient. But for a given noncondensable gas mass fraction and a given surface subcooling, the measured condensation heat transfer coefficient of the steam-He mixture is the lowest, followed by the steam-N2 mixture, CO2 mixture. The model predicts the relative errors of the total condensation heat transfer coefficients of these mixtures within ±30%. A condensation heat transfer correlation was developed based on the experimental data and the correlation achieved an uncertainty of less than 20%.