Condensation Of Vapor Bubbles Research Articles

Dynamics of vapor bubble condensation under directional ultrasonic actuation

Direct-contact condensation of vapor bubbles injected into a subcooled liquid is enhanced using ultrasonic O(1 MHz) acoustic actuation. In the absence of actuation, the surface tension-driven pinch-off process of the vapor bubble from the injection orifice induces a liquid spear that travels upward through the bubble and ruptures the top interface to form a toroidal bubble. Similarly, the acoustic actuator produces a narrow high-intensity acoustic beam that deforms the top interface of the vapor bubble via radiation pressure to form a liquid spear that travels downward though the bubble and ruptures the bottom interface to form a toroidal bubble. Comparisons between the growth and collapse of vapor bubbles in these two cases were performed using high-speed video imaging and particle image velocimetry. The results show that the actuated bubble collapsed about 35% faster than the unactuated bubble. The flow fields around the bubbles induced by the motion of the liquid spears are similar in both cases. By comparing vapor bubbles under different subcooling conditions with an unactuated, noncondensing air bubble, it was shown that condensation at the liquid–vapor interface strongly influences bubble collapse times and the velocity field surrounding each of the bubbles and that these effects increase as the level of subcooling increases.

Simulation of Single Vapor Bubble Condensation with Sharp Interface Mass Transfer Model

Pure numerical simulation of phase-change phenomena such as boiling and condensation is challenging, as there is no universal model to calculate the transferred mass in all configurations. Among the existing models, the sharp interface model (Fourier model) seems to be a promising solution. In this study, we investigate the limitation of this model via a comparison of the numerical results with the analytical solution and experimental data. Our study confirms the great importance of the initial thermal boundary layer prescription for a simulation of single bubble condensation. Additionally, we derive a semi-analytical correlation based on energy conservation to estimate the condensing bubble lifetime. This correlation declares that the initial diameter, subcooled temperature, and vapor thermophysical properties determine how long a bubble lasts. The simulations are carried out within the OpenFOAM framework using the VoF method to capture the interface between phases. Our investigation demonstrates that calculation of the curvature of interface with the Contour-Based Reconstruction (CBR) method can suppress the parasitic current up to one order.

Numerical investigation of vapor bubble condensation in subcooled quiescent water

The vapor bubble condensation process is numerically investigated via three-dimensional (3D) simulation using Volume of Fluid method (VoF). Two phase change models, i.e. Lee model and Tanasawa model, are implemented and assessed with experimental data. Since no mesh-independent results can be obtained with the Lee model, the Tanasawa model is adopted for the study of bubble condensation process. The single vapor bubble condensation in subcooled quiescent water is analyzed. Different influencing factors on bubble condensation, i.e. diameter size, subcooling and liquid properties, are studied. With the increase of the bubble diameter, the condensation rate increases due to increase of the shear stress between the vapor bubble and the cold bulk, resulting in the turbulence inside the bubble being more intensive and the thermal field around the bubble more unstable. High subcooling increases the mass flux across the interface, which brings about the interface instability on the bubble surface and bubble breakup is observed. The increase of the liquid viscosity restricts the bubble rising and deformation, which reduces the convective heat transfer and condensation rate. The occurrence of bubble central breakup due to the decrease of surface tension enlarges the effective condensation area and increases the condensation rate.

Nucleation and bubble evolution in subcooled liquid under pulse heating

The transient heating of liquid using a local heat source is widely used in practice including MEMS and laser medicine technologies. In particular the laser heating of liquid through the optical fiber has become a widespread method for obliteration of varicose veins (endovenous laser ablation, EVLA) and treatment of cysts of various localization. In this research there is proposed to use the electrically heated transparent microheater based on ITO film to simulate the laser-induced heating of the subcooled liquid through the optical fiber. The paper reports the experimental results on the nucleation and evolution of vapor bubbles in subcooled water induced by pulsed heating of the microheater. The experiments were performed at the initial liquid temperature of 27, 38, and 51°C, with heating power in the pulse of 3.6 - 41W and pulse duration of 100–2000 ms using high-speed visualization and infrared thermography. The boiling and convection onsets, the rates of growth and condensation of vapor bubbles, and their maximum sizes depending on the heating power and the liquid initial temperature were measured. The development of convection before the boiling onset was shown to significantly affect the nucleation and further evolution of bubbles. It was found that at the stage of bubbles condensation, the shape of the interfacial surface significantly deviates from the spherically symmetric one, and the maximum condensation rate is observed at some distance from the heated surface. Using infrared thermography and numerical simulation, the time dependences of the ITO microheater and sapphire surface temperature for various heating power and initial liquid temperatures were obtained. On the basis of the temperature dependences and experimentally measured times of boiling onset, the nucleation temperatures were determined.

Review on direct contact condensation of vapor bubbles in a subcooled liquid

Review on direct contact condensation of vapor bubbles in a subcooled liquid

An assessment and analysis of phase change models for the simulation of vapor bubble condensation

In this study, the assessment of five phase change models (Lee model, temperature recovery model, phase field model, heat flux balance model, and empirical correlation model) on the simulation of bubble condensation was investigated using the volume of fluid (VOF) method. The results show that the simulation accuracy of bubble condensation relates to the difference between the interfacial temperature and the saturation temperature. A comparison with the Stefan problem further reveals that the convection heat transfer near the vapor-liquid interface may prevent the convergence of the interfacial temperature to the saturation temperature. The quantitative expressions of interfacial temperature for different phase change models are derived and compared with the simulation results. Furthermore, a recommendation method for rough evaluation of the relaxation coefficient and mesh size in simulations of bubble condensation with the Lee model, phase field model and heat flux balance model is proposed.

Modelling the Optimal Schemes of Population Vaccination Using Epidemiological Data

Condensation upon direct contact of the phases can be divided into the following types: condensation of the steam stream in the volume of unheated liquid; condensation of vapor bubbles in liquid; condensation of steam by liquid droplets (dispersed liquid); vapor condensation on a jet of liquid.In visual experiments, the study of the process of condensation of the jet of steam in space was noted by the presence of a white emulsion at the collision of steam with liquid, due to the crushing of a jet of steam into small bubbles. The high intensity of the heat transfer process was explained by the sharp increase in the contact surface. When considering the structure of the flow taking into account the two-phase region, it can be noted that there is a smooth conical surface of the separation between the phases and the formation of dispersed bubbles and droplets in the flow. This allows to determine the dependence of the geometry of the contact zone of the phases on the temperature head.An increase in the surface area of the contact phase can be achieved by dispersing one of the contacting phases. Existing liquid spraying machines have significant energy costs as a result of doing some work to overcome the surface tension that causes the liquid to reduce the free surface.So the heat transfer between a liquid drop and a saturated vapor is determined by the heat distribution along the drop radius. The vapor condenses on the surface of the liquid droplet, and the released heat condensation must be discharged inside the droplet. According to the equation of thermal conductivity under the relevant conditions of the problem under consideration, the intensity of condensation is determined by the rate of heat runoff per drop. Studies of heat exchange on dispersed jets of liquid have proven high intensity of the process.Condensation on a jet of liquid is used in many industrial devices (deaerators, condensers of mixing type, jet heaters).Theoretical and experimental studies of this type of condensation are scarce. Studies of heat exchange during condensation of a dispersed steam stream on a swirling stream of water are absent at all. The results of the experiments of heat exchange at the contact condensation of steam on jets of water, consisting of a continuous section and a section that falls into drops, are represented by the criterion equation. Recent studies are related to the development of a mathematical model for the calculation of jet condensation and analysis of past developments with its application.

Modeling aspects of vapor bubble condensation in subcooled liquid using the VOF approach

ABSTRACTDirect contact condensation of a vapor bubble during subcooled boiling flow scenario has diverse applications in many fields such as thermal, chemical, and nuclear energies. The present work aims at the exploration of the underlying physics of single vapor bubble condensation in subcooled water following the volume of fluid method approach using ANSYS FLUENT 14.5. This work emphasizes on the modeling of the mass transfer rate using interfacial jump conditions for investigating the effect of various parametric conditions on the collapse phenomenon. A comparative study is also performed between the interface jump approach and the models based on the proposed empirical correlations to assess the condensation heat transfer (in terms of the collapse rate and Nusselt number) and bubble shape. The mass transfer model based on the interfacial jump condition is found to be the more realistic among all models for capturing the collapse rate as well as its shape.

Numerical simulation of bubble condensation using CF-VOF

In present study, subcooled boiling is simulated using color function volume of fluid (CF-VOF) method. For this purpose, energy equation and Tanasawa mass transfer model accompanied with some suitable source terms are implemented in OpenFOAM solver (interFoam). The surface tension between vapor–liquid phases is considered using continuous surface force (CSF) method. In order to reduce spurious current near interface, a smoothing filter is applied to improve curvature calculation. The variation of saturation temperature in vapor bubble with local pressure is considered with Clausius–Clapeyron relation. The numerical model is validated with one-dimensional Stefan problem.The shape and life time history of single vapor bubble condensation are verified with existing experimental data. Computational study shows bubble life time is nearly proportional with bubble size and it is prolonged at bubble swarm motion. The present study reveals some fundamental characteristics of single and multiple vapor bubble condensation and is expected to be instructive for further applications.

Effect of liquid subcooling on acoustic characteristics during the condensation process of vapor bubbles in a subcooled pool

Sound characteristics of direct contact condensation of vapor bubbles in a subcooled pool were investigated experimentally with a hydrophone and a high-speed video camera. Three different condensation modes were observed, which were referred to as shape oscillation regime, transition regime and capillary wave regime in the paper. Time domain analysis indicated that the acoustic signals were boosted in their maximum amplitude with increase in subcooling, while their standard and average absolute deviations shifted to decrease after reaching a peak value. In addition, two different waveforms were found, possible sources of which were split-up and collapse of bubbles, respectively. From the amplitude spectra obtained by FFT, the first dominant frequency was found at frequency of 150–300Hz for all condensation regimes, whereas some peaks in high frequency region were observed only for the capillary wave regime. The first dominant frequency was the result of the periodic variation in the vapor bubble volume, and the peaks in high frequency region were due to the high-frequency oscillation of water in pressure caused by sudden bubble collapse. The frequency of first peak was considered to be resulted from the periodic bubble collapse or split-up and thus was close to the bubble collapse frequency obtained from snapshots of bubble condensation. Moreover, according to results of short-time Fourier transform (STFT), the time intervals in which a certain process of bubble condensing occurred could be well known.

Enhanced vapor bubble condensation and collapse with ultrasonic vibration

Investigation was carried out concerning the effects of ultrasonic field on the condensation and collapse of vapor bubbles in a quiescent subcooled pool. Experimental results showed that the vapor bubbles were split gradually at liquid subcooling of 15–30K, while were collapsed into many tiny bubbles when subcooling was higher than 40K. Once the ultrasonic vibration was applied, capillary waves would arise on the bubble surface, and the threshold of liquid subcooling for collapsing the bubble was diminished to 20–26K. Further, the presence of capillary wave increased the contacting area of the bubble with the cold bulk, and disturbs the thermal boundary layer in the vicinity of the vapor–liquid interface, resulting in the enhancement of condensation process. Therefore, the inertial shock of liquid on the vapor bubble was much stronger than that without ultrasonic vibration at the same liquid subcooling. This would also accelerate the instability of the bubble surface in turn. Based on the experimental data at liquid subcooling of 15–60K, empirical correlations were given to predict the condensation heat transfer of vapor bubbles with and without ultrasonic, with deviations within ±30%.

Feature of acoustic sound signals involved in vapor bubble condensation and its application in identification of condensation regimes

Experiments were carried out on the sound pressure oscillations condensation regime map, and bubble collapse frequency during the direct contact condensation of vapor with the aid of an acoustic hydrophone and a high-speed video camera. The injection rate of vapor and liquid subcooling in the experiments were 0.19–3.73m3/h and of 10–70K, respectively. Four different condensation regimes were identified according to features presented on the bubble surface and whether and when the bubble collapse occurred. The state-of-the-art signal processing methods (statistical, spectral, fractal and discrete wavelet transform analyses) were applied to processing the detected acoustic signals. The results showed that only the kurtosis and DWT in the four methods could distinguish the different regimes well. Furthermore, the spectral and fractal analyses showed that strongly persistent behavior in the signals corresponded to the dominant frequency in the range of 120–400Hz might be arisen from the periodic variation in the vapor bubble volume. While that corresponded to peaks with frequency higher than 7000Hz in transition and capillary wave regimes were probably the high-frequency oscillation in pressure induced by sudden bubble collapse. Contrarily, the first peak in 0–200Hz caused by the periodic bubble break-up or split-up was high anti-persistent. DWT analysis showed that the sound pressure oscillation introduced by bubble collapse was similar to that by bubble split-up for all condensation regimes, whereas at very high frequency two different types of oscillations arose. Furthermore, the bubble collapse frequency increased with increase in liquid subcooling and vapor injection rate, and could be obtained from the spectral and Hurst analyses of the signals indirectly.

A wave equation model for retrograde media with a bubble structure

A nonlinear wave equation is obtained for liquid-vapor mixtures with regard to arbitrary change of equilibrium sound speed in a mixture with growth and condensation of vapor bubbles, which has a limit transition to a wave equation for pure liquid at full collapse of vapor cavities. A particular case of a collapsing wave equation (CWE) of retrograde media is considered, e.g., liquid-vapor media with low vaporization heat and low dissipation, observed near the critical liquid-vapor point, where the main effect is variable sound speed. Based on the CWE numerical solutions it is shown that in such liquid-vapor media, one can observe previously unknown nonlinear wave structures with depression waves.

Disintegration of flows of superheated liquid films and jets

This paper represents results on investigating the dynamics of boiling and disintegration of superheated liquid films and jets. The first part deals with experimental study of boiling liquid outflow through short cylindrical and slit channels. Evolution of disintegration of a hot water jet flow is observed both at low and moderate superheating and at high and limit superheating, and also for vaporization mechanisms corresponding to these superheatings. Peculiarities of disintegration of jets through slit and cylindrical channels are noticed. Results on measuring the reactive thrust of the jet through a slit channel under different geometrical conditions behind the channel outlet are represented. The 1/f fluctuations in transient regimes of superheated liquid boiling and in transient regimes of behavior of the jet shape are found. The second part of this article represents results on experimental investigation of nonsteady heat transfer and dynamics of the development of crisis phenomena at boiling of a falling subcooled liquid film in the conditions of stepwise heat release. The experimental data were obtained using synchronized high-speed infrared thermography and video. It is shown that with growth and condensation of vapor bubbles, on the liquid film interface appear large-amplitude waves that lead to considerably increasing local intensity of heat transfer. New data on the boiling incipience temperature in a subcooled liquid film, depending on the heat flux density, are obtained. It is found that the development of boiling crisis is a result of appearance of local dry patches and their subsequent growth by the mechanism of longitudinal thermal conductivity in the heat transfer wall as the equilibrium heat flux density is exceeded.

Numerical investigation of vapor bubble condensation characteristics of subcooled flow boiling in vertical rectangular channel

Abstract In this study, the behavior of condensing single vapor bubble in subcooled boiling flow within two different vertical rectangular channels has been numerically investigated by using the VOF (Volume Of Fluid) multiphase flow model. The mass and energy transfer model of bubble condensing process induced by the interfacial heat transfer was proposed to describe the interfacial transportation between the two phases. The results of VOF simulations show a good agreements with previous experimental data in the bubble size variation and lifetime. The bubble lifetime is almost proportional to bubble initial size and be prolonged at increasing system pressure. With the increasing of the subcooling, the bubble lifetime reduces significantly, and the effect of mass flux could be negligible. When the bubble size increased, the bubble shape tends to be changed in a large channel. The VOF simulation results of deformation have good agreement with those of Kamei’ experiment and the results of MPS (Moving Particle Semi-implicit) simulation in a larger channel. Furthermore, the initial bubble size, subcooling of liquid and system pressure play an important role to influence the bubble deformation behaviors significantly. The bubble could be deformed sharper with the increasing subcooling and initial diameter, or could breakup when the subcooling and the initial diameter reach a certain value at the last bubble stage. Nevertheless, the trends of bubble deformation will be weakening with the increasing system pressure.

Heat transfer in subcooled jet impingement boiling at high wall temperatures

An analytical approach for heat transfer modelling of jet impingement boiling is presented. High heat fluxes with values larger than 10 MW/m 2 can be observed in the stagnation region of an impinging jet on a red hot steel plate with wall temperatures normally being associated with film boiling. However, sufficiently high degrees of subcooling and jet velocity prevent the formation of a vapor film, even if the wall superheat is large. Heat transfer is governed by turbulent diffusion caused by the rapid growth and condensation of vapor bubbles. Due to the high population of bubbles at high heat fluxes it has to be assumed that a laminar sublayer cannot exist in the immediate vicinity of a red hot heating surface. A mechanistic model is proposed which is based on the assumption that due to bubble growth and collapse the maximum turbulence intensity is located at the wall/liquid interface and that eddy diffusivity decreases with increasing wall distance.

Application of the holographic interferometry in transport phenomena studies

This article provides an overview of all the experimental research studies in the field of heat and mass transfer by means of the holographic interferometry which were performed under the supervision of Professor Franz Mayinger during his professorship. The principle objective of this paper is to contribute to the knowledge base of the heat and mass transfer processes in various fields as well as to illustrate the capabilities of the holographic interferometry. Investigations of the heat transfer pattern in grooved channels and in various geometries of compact heat exchangers, drying processes of a dispersed, water-based varnish on paper, mixed convection in bent ducts, the growth and condensation of vapor bubbles in subcooled boiling and the simultaneous heat and mass transfer are presented. The results of all these studies demonstrate the successful application of the holographic interferometry and Professor Mayinger's highly valuable contribution in this area.

Thermal energy storage characteristics of a latent heat storage vessel packed with surface cross-linked, form-stabilized, high-density polyethylene pellets by boiling phenomenon

This paper deals with an experimental investigation of latent thermal energy storage characteristics of surface cross-linked form-stabilized high-density polyethylene pellets as a phase change material (PCM), using pool boiling and condensation of an ethylene glycol–water solution. The polyethylene pellets and the heat transfer medium of ethylene glycol were mixed and poured into a cylindrical heat storage vessel. The heat transfer into the polyethylene pellets was mainly enhanced by the condensation of vapor bubbles of the ethylene glycol–water solution, which was heated by an electric heater set at the bottom of the vessel. The effects of heat input; amounts of PCM and ethylene glycol–water solution; and heater surface temperature on the heat storage characteristics were all investigated. As a result, a nondimensional correlation equation of the completion time of the heat storage process was derived as a function of nondimensional parameters. © 1999 Scripta Technica, Heat Trans Asian Res, 28(8): 649–663, 1999

Thermal energy storage characteristics of a latent heat storage vessel packed with surface cross‐linked, form‐stabilized, high‐density polyethylene pellets by boiling phenomenon

This paper deals with an experimental investigation of latent thermal energy storage characteristics of surface cross-linked form-stabilized high-density polyethylene pellets as a phase change material (PCM), using pool boiling and condensation of an ethylene glycol–water solution. The polyethylene pellets and the heat transfer medium of ethylene glycol were mixed and poured into a cylindrical heat storage vessel. The heat transfer into the polyethylene pellets was mainly enhanced by the condensation of vapor bubbles of the ethylene glycol–water solution, which was heated by an electric heater set at the bottom of the vessel. The effects of heat input; amounts of PCM and ethylene glycol–water solution; and heater surface temperature on the heat storage characteristics were all investigated. As a result, a nondimensional correlation equation of the completion time of the heat storage process was derived as a function of nondimensional parameters. © 1999 Scripta Technica, Heat Trans Asian Res, 28(8): 649–663, 1999

Mechanism of vapor bubble condensation in a vapor-water mixture under impact

The mechanism and the cause of vapor bubble condensation in a vapor-water stream are analyzed. The causes (inertia of the liquid and heat transfer) actively contributing to condensation are examined. Experimental data are presented on the collapse of vapor bubbles in boiling water under impact.