Contact Condensation Of Steam Jet Research Articles

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.

CFD Simulation on Pressure Profile for Direct Contact Condensation of Steam Jet in a Narrow Pipe

In the published experimental results, it has been observed that when high-speed steam spurt into the subcooled waterflow, the total pressure along the axial direction at trailing edge of the steam plume shows a pressure-lift. To reveal the mechanism behind this phenomenon, this study utilizes a particle model to investigate the pressure profile of steam jet condensation in subcooled water flow in a narrow pipe. A numerical model based on the Eulerian–Eulerian multiphase model has been developed to accurately simulate the characteristics of pressure profile along the axial direction. The model’s validity is established by comparing the steam plume shape and temperature profiles with the experimental data. By analyzing the total pressure profile of the axis and the contours of gas volume fraction, it is found that there exists a pressure-lift phenomenon at trailing edge of the steam plume. The dynamic pressure of the water also shows a pressure-lift at this position, so it can be inferred that the dynamic pressure of the water is the main factor of the total pressure-lift.

Entropy and exergy analysis of the steam jet condensation in crossflow of subcooled water

The direct contact condensation of steam jet in the liquid is an irreversible process with inevitable energy loss. In this paper, interaction between the subcooled water and gas-liquid two-phase boundary, and influence of thermal hydraulic parameters on the change of entropy and exergy are studied. Because of the crossflow of subcooled water, two-phase heat transfer occurs mainly in four regions of the plume cross-section. With increasing temperature, the growth rate of subcooled water entropy flow increases significantly, and the change in the dissipation ratio and damping ratio of kinetic energy is smoother. With the increase of steam mass flux, the entropy flow of the subcooled water reaches a peak at the end of the plume and the peak continuously increases, and the dissipation ratio of kinetic energy and the subcooled water entropy flow fluctuate more violently. Most energy dissipation occurs between the location of maximum jet velocity and the tail of steam jet.

Numerical Investigation on Unstable Direct Contact Condensation of Steam in Subcooled Water

Stable direct contact condensation of choked steam jets in subcooled water has been the focus of researchers during the last three decades. Comparatively fewer works were reported on unstable direct contact condensation of steam jets which typically occurs at low steam mass flux and low pool subcooling. The focus of this paper is on the study of unstable direct contact condensation of steam jets in subcooled water occurring at low steam mass flux using numerical techniques. A two-fluid modeling approach has been adopted with a thermal phase change model for capturing the condensation phenomena. The numerical results are compared with the available experimental data, and a reasonable agreement (average discrepancy was around 15% for overall heat transfer coefficients and 11% for average time periods) was observed. Attempts were made to understand the unstable nature of the steam jets under the simulated conditions. The effect of pool subcooling on plume shapes, heat transfer coefficients and pressure amplitudes were examined. Finally, semi-empirical models available in the literature were compared with the simulation data, and the results were analyzed. The outcome of the article will be useful in understanding the flow physics, and characterization and design recommendations for direct contact condensers operating in the unstable oscillatory regime.

Characteristics of interfacial oscillation caused by condensation of steam jet in subcooled water flow

An experimental study is conducted to investigate interfacial characteristics of direct contact condensation of steam jet in counter-current subcooled water flow in confined conditions. A customized visualization window and a high-speed camera are combined together to capture and record the dynamical interface behavior of the condensing jet. The transient interface behavior of the jet is analyzed and discussed quantitatively by utilizing digital image processing technology. With increase of steam mass flux, the bubbling and jetting regime appear successively at subsonic conditions and sonic or supersonic conditions, respectively. The transient radial interface position along all axial locations downstream of the jet is obtained quantitatively for these two typical condensation regimes. The probability distribution function and power spectrum density of the radial interface position along all axial locations of a certain jet follow almost the same principles in the time-frequency domain. Significant variations of the probability distribution function and power spectrum density between the bubbling and jetting regimes happen at transonic condition. With increase of axial distance away from the nozzle exit, the probability of the pinch-off events first rise and then drops in subsonic and sonic conditions. While the jet interface is very stable and no pinch-off events occur in supersonic condition.

Experimental investigation on interfacial oscillation of direct contact condensation of steam jet in water pipe flow

Interfacial oscillation associated with direct contact condensation of steam jet in water pipe flow is of high significance for industrial processes. In this paper, experimental study is conducted to reveal the mechanisms of the interfacial oscillation in steam jet condensation in subcooled water flow in a vertical pipe. The interfacial behavior of the jet plume is acquired by high speed camera, and the entire interface in both space and time simultaneously is quantitatively analyzed with digital image processing technology. Bubbling regime occurs at subsonic conditions, where an undulated bubble plume forms with one or more large bubbles falling off intermittently. Jetting regime happens at transonic or supersonic conditions, where a quasi-stable jet plume is observed with numerous uncondensed tiny bubbles continuously shedding off from the end of the jet plume. Distinct waveforms of the radial interface position in both space and time simultaneously are recognized for the two typical condensation regimes. The interfacial unsteadiness reaches a maximum near the sonic point and then drops in the supersonic region, which exhibits similar trend with pressure oscillation induced by condensing jet in a qualitative sense. The results confirm that the pressure oscillation is highly relevant to the motion of the jet interface and it should be induced by the interfacial oscillation. The spatial growth rate of the interface unsteadiness along the jet decreases steadily as steam mass flux increases from subsonic to sonic point and it almost does not vary in the supersonic region. The Kelvin-Helmholtz instability mechanism is more important near the nozzle exit, while in other region the Kelvin-Helmholtz instability is of the same importance as the Rayleigh-Taylor instability.

Experimental study of direct contact condensation of steam jet in water flow in a vertical pipe with square cross section

Direct contact condensation phenomenon (DCC) is widely used in applications which heat and mass transfer efficiently. In this study, several experiments are conducted to investigate the DCC of steam injected in water flow in a vertical square cross-section pipe. The characteristics of condensation, including steam plume shape and length, average heat transfer coefficient, and average Nusselt number, are studied. The dimensionless steam plume length and average heat transfer coefficient are found in the range of 0.5–5.1 and 0.716–3.131 MW/m2 K, respectively. Additionally, the influence of effective operating parameters, namely steam mass flux, water temperature, and water flow Reynolds number, on each condensation characteristic is investigated. Using a high-speed camera, three main regimes of steam plume (chugging, oscillatory, and stable jet) are observed. The distribution of these regimes versus flow effective parameters is presented in a three-dimensional condensation regime map. Finally, empirical correlations for a stable steam plume, which show a good agreement with measurements, are suggested to predict each characteristic of DCC of steam jet in water flow.

Experimental study on the direct contact condensation of steam jet in the passive safety injection tank

ABSTRACT The direct contact condensation and subsequent thermal mixing by the injected steam jet onto a quiescent coolant inside a tank were examined experimentally to simulate the phenomena in passive safety injection systems. Specifically, the influence of the steam injection velocity was studied. Even though the total flow rate of injected steam was unchanged, the pressure inside the tank increased quickly at the larger nozzle diameter. Additionally, at a larger nozzle diameter, the thickness of the thermal mixing zone decreased because the amount of direct contact condensation decreased. For the in-depth study on the role of the nozzle size for the thermal mixing, the particle image velocimetry method was used to understand the flow field of water inside the tank. The visualization results demonstrated the formation of a flow field in the coolant due to the expansion and contraction of the steam–air mixture boundary. Furthermore, the thermal mixing zone was found to be closely related to the penetration depth. Finally, a variety of penetration models were examined and compared against the experimental observation. The correlations based on the steam condensation approach under-predicted the penetration depth, whereas the approach that considers the momentum of non-condensable gas gave the reasonable prediction capability.

Mechanisms of pressure oscillation in steam jet condensation in water flow in a vertical pipe

Pressure oscillation associated with direct contact condensation of steam jet in water pipe flow is of high significance for industrial processes. In this paper, experimental study is conducted to reveal the mechanisms of the pressure oscillation in steam jet condensation in water flow in a vertical pipe. The interfacial characteristics of the jet plume are acquired by high speed camera, and the pressure oscillation due to condensing jet are captured by using high frequency pressure transducers. Four main types, including Chugging, Oscil-I, Oscil-II and Stable condensation regimes, are identified visually based on the interfacial behavior of the jet plume, and their distribution is described in a three-dimensional condensation regime diagram based on steam mass flux, water temperature, and Reynolds number of water flow. In the Chugging regime, the high-amplitude pressure oscillation appears at low frequency, and the unimodal PDF demonstrates that the pressure oscillation is only dominated by steam mass flux. In the Oscil-I regime, the pressure oscillation is approximately sinusoidal and its intensity is the highest among the four condensation regimes, whereas the intensity of the pressure oscillation remains at a low level and varies little in the Stable regime. In both the Oscil-I and Stable regimes, with increase of water temperature and Reynolds number of water, the unimodal PDF spreads out over a wider range, and finally the bimodal and symmetrical PDF appears for the Oscil-I regime. The statistical analysis shows that both the deviation and maximum of pressure signals could identify the four condensation regimes well, while both the skewness and kurtosis of pressure signals could easily distinguish the Chugging and Oscil-II regimes.

A physically based, one-dimensional three-fluid model for direct contact condensation of steam jets in flowing water

A simulation model for the direct contact condensation of steam jets in flowing water is presented. In contrast to previous empirical approaches, the model takes into account the underlying physical phenomena governing the condensation process. Condensation at the interface between the steam jet and the surrounding water is calculated according to the surface renewal theory. Entrainment of water into the steam jet is modeled based on the Kelvin–Helmholtz and Rayleigh–Taylor instability theories. The resulting steam-water two-phase flow is simulated based on a one-dimensional three-fluid model. An interfacial area transport equation is used to track changes of the interfacial area density due to droplet entrainment and steam condensation on droplets. The simulation results are in good qualitative agreement with published experimental data. In particular, the dependency of the steam jet length on the flow Reynolds number is properly reproduced. This corroborates our theory that the heat transfer coefficient at the interface of a condensing steam jet can be linked to the water flow rate via the interfacial friction factor.

Velocity field characteristics of the turbulent jet induced by direct contact condensation of steam jet in crossflow of water in a vertical pipe

Direct contact condensation of jets in fluid has been widely applied in many industrial applications owing to the low requirement of driving potential and high efficiency of heat and mass transfer. Here, experiments are carried out to investigate the velocity field characteristics of the turbulent jet induced by direct contact condensation of steam jet in crossflow of water in a vertical pipe. Visual equipment is specially invented to investigate the velocity field characteristics by using Particle Image Velocimetry (PIV) measurement technique. The high intensity laser light reflected by the pure steam region just outside the nozzle-exit brings out severe damage to the CCD camera. To solve this technical problem, a black plate is adopted to shield the pure steam region. According to the contours of the velocity fields and streamlines, the influences of jet momentum ratio, jet Reynolds number and water temperature on the jet flow field are explored. The jet centerline trajectory equations in exponential form are established based on the local maximum mean velocity. By introducing the jet Reynolds number and jet momentum ratio, the correlation for prediction of jet centerline trajectory equations is proposed, and the predicted results are within 30% of the experimental data. The reciprocal of the local maximum mean velocity and the half-width of the jet are proportional to the downstream coordinate along the jet velocity centerline trajectory. The scaled velocity field complies with the self-similarity principle.

Experimental study on the direct contact condensation of the steam jet in subcooled water flow in a rectangular channel: Flow patterns and flow field

Direct contact condensation (DCC) of steam jet in subcooled water flow in a channel was experimentally studied. The main inlet parameters, including steam mass flux, water mass flux and water temperature were tested in the ranges of 200–600kg/(m2s), 7–18×103kg/(m2s), 288–333K, respectively. Two unstable flow patterns and two stable flow patterns were observed via visualization window by a high speed camera. The flow patterns were determined by steam mass flux, water mass flux and water temperature, and the relationship between flow patterns and flow field parameters was discussed. The results indicated that whether pressure or temperature distributions on the bottom wall of channel could represent different flow patterns. And the position of pressure peak on the bottom wall could almost represent the condensation length. The upper wall pressure distributions were mainly dependent on steam and water mass flux; and the upper wall temperature distributions were affected by the three main inlet parameters. Moreover, the bottom wall pressure and temperature distributions of different unstable flow patterns had similar characteristics while those of stable flow patterns were affected by shock and expansion waves. The underlying cause of transition between different flow patterns under different inlet parameters was reflected and discussed based on pressure distributions.

A Physically Based, One-Dimensional Two-Fluid Model for Direct Contact Condensation of Steam Jets Submerged in Subcooled Water

A simulation model for the direct contact condensation of steam in subcooled water is presented that allows determination of major parameters of the process, such as the jet penetration length. Entrainment of water by the steam jet is modeled based on the Kelvin–Helmholtz and Rayleigh–Taylor instability theories. Primary atomization due to acceleration of interfacial waves and secondary atomization due to aerodynamic forces account for the initial size of entrained droplets. The resulting steam-water two-phase flow is simulated based on a one-dimensional two-fluid model. An interfacial area transport equation is used to track changes of the interfacial area density due to droplet entrainment and steam condensation. Interfacial heat and mass transfer rates during condensation are calculated using the two-resistance model. The resulting two-phase flow equations constitute a system of ordinary differential equations, which is solved by means of the explicit Runge–Kutta–Fehlberg algorithm. The simulation results are in good qualitative agreement with published experimental data over a wide range of pool temperatures and mass flow rates.

Direct contact condensation of steam jet in crossflow of water in a vertical pipe. Experimental investigation on condensation regime diagram and jet penetration length

The direct contact condensation of jets in fluid has been of great importance in many industrial applications. Experiments on condensing jets in initially stagnant fluid in pool have increased significantly in sophistication over the last few decades. For condensing jets in crossflow, however, the flow and geometry characteristics of the jet might be fundamentally different due to the complex convection effect induced by the crossflow. Here, experiments are performed to investigate direct contact condensation of steam jet in crossflow of water in a vertical pipe. The condensation regime diagram and jet penetration length are investigated visually by using high-speed camera and image processing methods. The condensation regime diagram mainly contains three kinds of condensation regime, i.e., chugging, condensation oscillation and stable condensation (i.e., stable conical shape, stable cylinder shape and stable expansion shape). The condensation regime is not only affected by steam mass flux and water temperature, but also affected significantly by Reynolds number of water flow. Therefore, condensation regime diagrams for different Reynolds number of water flow are developed. Both the regions of the chugging and condensation oscillation regimes expand slightly towards higher steam mass flux as Reynolds number of water flow increases. The dimensionless jet penetration length from experimental results is found to be in the range of 0.78–6.84. It increases with increase of steam mass flux and water temperature, but decreases with increase of Reynolds number of water flow. Empirical correlation is proposed for predicting the dimensionless jet penetration length depending on three dimensionless parameters, i.e., dimensionless steam mass flux, condensation driving potential and Reynolds number of water flow. The predicted results agree well with experiments and the discrepancies are within ±20%.

Experimental study on the direct contact condensation of steam jet in subcooled water flow in a rectangular mix chamber

Abstract An experimental study on the direct contact condensation (DCC) of steam jet in subcooled water flow in a rectangular mix chamber was conducted. A high-speed camera was employed to record the flow field of DCC in the visualized experimental rig, in which, the steam nozzle and water nozzle were both rectangular. The flow field was filmed when the steam mass flux, water mass flux and water temperature were in the range of 200–600 kg/m2 s, 6000–18000 kg/m2 s and 293–333 K, respectively. The results indicated that, the flow field of DCC in the rectangular mix chamber consisted of four regions, and they were steam region, interface, mixture layer and ambient water region. The interface between steam region and mixture layer was clearly observed. The flow pattern of DCC was performed as bubble flow, oscillatory jet, stable jet and divergent jet at various test conditions. The steam region dimensionless penetration length and average heat transfer coefficient of the stable jet were found to be in the range of 1.73–4.40 and 2.89–7.89 MW/m2 K, respectively. Furthermore, an analytical model was established and a correctional correlation was developed to predict the dimensionless penetration length. An empirical correlation was proposed to predict the average heat transfer coefficient.