Numerical Simulation of Dynamics and Heat Transfer Associated With a Single Bubble in Subcooled Boiling and in the Presence of Noncondensables

2011 ◽  
Vol 133 (4) ◽  
Author(s):  
Jinfeng Wu ◽  
Vijay K. Dhir
Keyword(s):  
Heat Transfer ◽  
Thermocapillary Convection ◽  
Bubble Dynamics ◽  
Bubble Diameter ◽  
Saturation Temperature ◽  
Subcooled Boiling ◽  
Bubble Liquid ◽  
Subcooled Liquid ◽  
Noncondensable Gases ◽  
Induced Flow

During phase change at the bubble-liquid interface, under subcooled boiling conditions, noncondensable gases dissolved in the liquid will be injected into the bubble along with vapor. Due to heat transfer into subcooled liquid, vapor will condense in the upper regions of the bubble while noncondensables will continue to accumulate. Subsequently, thermocapillary convection caused by nonuniform saturation temperature at the interface may occur. The aim of this work is to investigate the effects of noncondensables on heat transfer and bubble dynamics. The numerical results show that the effects of noncondensables on 5°C subcooled boiling of water are minor in terms of the equilibrium bubble diameter and overall Nusselt number. However, induced flow pattern around the bubble is altered, especially under reduced gravity conditions.

Numerical Simulations of Dynamics and Heat Transfer Associated With a Single Bubble in the Presence of Noncondensables

2007 ◽  
Author(s):  
Jinfeng Wu ◽  
Vijay K. Dhir
Keyword(s):  
Heat Transfer ◽  
Bubble Dynamics ◽  
Numerical Procedure ◽  
Saturation Temperature ◽  
Bubble Surface ◽  
Moving Mesh Method ◽  
Bubble Liquid ◽  
Noncondensable Gas ◽  
Noncondensable Gases ◽  
Level Set Function

Under subcooled boiling conditions, the liquid may contain dissolved noncondensabe gases. During phase change at the bubble-liquid interface, noncondensable gases will be injected into the bubble along with vapor. Due to heat transfer into sub-cooled liquid, vapor will condense in the upper regions of the bubble and the bubble interface is impermeable to noncondensables. As a result, noncondensabe gases will accumulate at the top of bubbles. This existing gradient of noncondensable concentration inside bubble determines the saturation temperature gradient around the bubble surface. The nonuniform saturation temperature may cause a difference in surface tension which would give rise to thermocapillary convection in the vicinity of the interface. So far, this description is merely a hypothesis. It is felt that much inspection is in vital demand to clarify the uncertainty as to the role of noncondensables throughout this process. In this study, air is taken as noncondensable gas, and the aim is to investigate the effects of noncondensable air on heat transfer and bubble dynamics. The results from a numerical procedure coupling level set function with moving mesh method show the evidence of effects of noncondensable air imposed on heat transfer and the induced flow pattern is presented as well.

Droplet and Bubble Dynamics in Saturated FC-72 Spray Cooling

2005 ◽  
Author(s):  
Ruey-Hung Chen ◽  
David S. Tan ◽  
Kuo-Chi Lin ◽  
Louis C. Chow ◽  
Alison R. Griffin ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Bubble Dynamics ◽  
Bubble Diameter ◽  
Spray Cooling ◽  
Transfer Enhancement ◽  
Secondary Nucleation ◽  
Bubble Density ◽  
Experimental Findings ◽  
Small Bubbles ◽  
Nucleation Bubble

Droplet and bubble dynamics and nucleate heat transfer in saturated FC-72 spray cooling were studied using a simulation model. Using the experimentally observed bubble growth rate, submodels were assumed based on physical reasoning for the number of secondary nuclei entrained by the impinging droplets, bubble puncturing by the impinging droplets, bubble merging and the spatial distribution of secondary nuclei. The predicted nucleate heat transfer was in agreement with experimental findings. Dynamic aspects of the droplets and bubbles, which had been difficult to observe experimentally, and their ability in enhancing nucleate heat transfer were then discussed based on the results of the simulation. These aspects include bubble merging, bubble puncturing by impinging droplets, secondary nucleation, bubble size distribution and bubble diameter at puncture. Simply increasing the number of secondary nuclei is not as effective in enhancing nucleate heat transfer as when it is also combined with increased bubble puncturing frequency by the impinging droplets. For heat transfer enhancement, it is desirable to have as many small bubbles and as high a bubble density as possible.

Calculation of Steam Volume Fraction in Subcooled Boiling

1968 ◽  
Vol 90 (1) ◽  
pp. 158-164 ◽  
Author(s):  
S. Zia Rouhani
Keyword(s):  
Heat Transfer ◽  
Relative Velocity ◽  
Single Phase ◽  
Volume Fraction ◽  
Subcooled Boiling ◽  
Vapor Generation ◽  
Subcooled Liquid ◽  
Limiting Value

An analysis of subcooled boiling is presented. It is assumed that heat is removed by vapor generation, heating of the liquid that replaces the detached bubbles, and to some extent by single-phase heat transfer. Two regions of subcooled boiling are considered and a criterion is provided for obtaining the limiting value of subcooling between the two regions. Condensation of vapor in the subcooled liquid is analyzed and the relative velocity of vapor with respect to the liquid is neglected in these regions. The theoretical arguments result in some equations for the calculation of steam volume fraction and true liquid subcooling.

Droplet and Bubble Dynamics in Saturated FC-72 Spray Cooling on a Smooth Surface

2008 ◽  
Vol 130 (10) ◽  
Author(s):  
Ruey-Hung Chen ◽  
David S. Tan ◽  
Kuo-Chi Lin ◽  
Louis C. Chow ◽  
Alison R. Griffin ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Bubble Dynamics ◽  
Cooling System ◽  
Bubble Diameter ◽  
Spray Cooling ◽  
Secondary Nucleation ◽  
Bubble Density ◽  
Experimental Findings ◽  
Small Bubbles ◽  
Nucleation Bubble

Droplet and bubble dynamics and nucleate heat transfer in saturated FC-72 spray cooling were studied using a simulation model. The spray cooling system simulated consists of three droplet fluxes impinging on a smooth heater, where secondary nuclei outnumber the surface nuclei. Using the experimentally observed bubble growth rate on a smooth diamond heater, submodels were assumed based on physical reasoning for the number of secondary nuclei entrained by the impinging droplets, bubble puncturing by the impinging droplets, bubble merging, and the spatial distribution of secondary nuclei. The predicted nucleate heat transfer was in agreement with experimental findings. Dynamic aspects of the droplets and bubbles, which had been difficult to observe experimentally, and their ability in enhancing nucleate heat transfer were then discussed based on the results of the simulation. These aspects include bubble merging, bubble puncturing by impinging droplets, secondary nucleation, bubble size distribution, and bubble diameter at puncture. Simply increasing the number of secondary nuclei is not as effective in enhancing nucleate heat transfer as when it is also combined with increased bubble puncturing frequency by the impinging droplets. For heat transfer enhancement, it is desirable to have as many small bubbles and as high a bubble density as possible.

NUMERICAL ANALYSIS OF CAVITATION SUSCEPTIBILITY FOR STEAM GENERATOR INTEGRAL PREHEATER TUBES

2014 ◽  
Vol 3 (01) ◽  
pp. 37-46 ◽  
Author(s):  
S. Laroche ◽  
L. Sun ◽  
J. Pietralik
Keyword(s):  
Heat Transfer ◽  
Numerical Analysis ◽  
Steam Generator ◽  
Cavitation Erosion ◽  
Saturation Temperature ◽  
Fluid Temperature ◽  
Baffle Plate ◽  
Subcooled Boiling ◽  
Local Flow ◽  
Flow And Heat Transfer

A new tube degradation mechanism was observed in a recirculating steam generator (SG) with an integral preheater tube at the clearance gap between the tube and the preheater baffle. The general pattern of the damage and material composition in the degraded region suggested that the degradation was cavitation erosion. Cavitation erosion occurs when vapour bubbles exist or form in the flowing liquid and then these bubbles collapse violently in the vicinity of a solid wall. The bubbles collapse when they contact water that is sufficiently subcooled, i.e., below the saturation temperature. In the clearance gap between the tube and the preheater baffle, secondary fluid flow exists due to the pressure difference across the baffle plate. Meanwhile, heat transfer occurs from the primary-side fluid to the secondary-side fluid within this clearance gap, driven by the primary-to-secondary temperature difference. Factors such as the tube position in the baffle hole and fouling may influence the local flow and heat transfer conditions and can cause subcooled boiling that results in cavitation. This paper presents a numerical analysis of flow and heat transfer phenomena to determine the factors contributing to cavitation erosion of tubes in the preheater of a recirculating SG. The analysis used the THIRST code for a 3-dimensional thermalhydraulic simulation of steam generator and the ANSYS Fluent® code for detailed calculations of flow and heat transfer in the clearance gaps. A detailed temperature distribution in the gap was obtained using this analysis to determine the regions where subcooled boiling could occur by comparing the local fluid temperature with its saturation temperature. The susceptibility to cavitation was found to increase with increased inclination (i.e., tilt) and eccentricity (i.e., off-centre) of the tube in the baffle plate gap, and increased fouling on baffle plate surfaces. This methodology could be applied to analyze the cavitation susceptibility for other preheater types with this “tube to baffle plate” gap, as these preheaters might have conditions where boiling followed by the rapid condensation of the steam bubbles are present.

Two-Phase Heat Transfer and Bubble Dynamics in a Microchannel Array

2008 ◽  
Author(s):  
T. P. Lagus ◽  
F. A. Kulacki
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Mass Flux ◽  
Bubble Dynamics ◽  
Bubble Diameter ◽  
Uniform Heat Flux ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Heat Transfer Coefficients ◽  
Microchannel Array

Heat transfer coefficients and bubble dynamics are reported for two-phase water flow in an array of 13 equally spaced microchannels over an area of 1 cm2. Each channel has Dh = 451 ± 3 8 μm, W/H = 0.8, and L/Dh = 22.2. Uniform heat flux is applied through the base, and wall temperatures are determined from thermocouple readings corrected for heat conduction effects. The upper surface is insulated and transparent. Single-phase heat transfer coefficients are obtained for 216 < Re < 2530 and 216 < G < 4100 kg/m2s and are in good agreement with comparable trends of existing correlations for developing flow and heat transfer, although a difference is seen due to the insulated upper surface. Two-phase experiments are run to determine overall heat transfer coefficients and bubble dynamics for a mass flux of 221 < G < 466 kg/sm2 and heat flux of 25 < q < 178 W/cm2. Heat transfer coefficients normalized with mass flux exhibit a trend comparable to that of available studies that use similar thermal boundary conditions. Two-phase flow visualization via shows expanding vapor slug flow as the primary flow regime, but bubbly flow and nucleation leading to elongated bubble flow are also observed. Analysis of bubble dynamics reveals a t1/3 dependence for bubble growth, and flow reversal is observed and quantified. Different speeds of the phase fronts are observed at the leading and trailing edges of elongated slugs once a bubble diameter equals the channel width. Bubble formation, growth, coalescence and detachment at the outlet of the array are characterized by the Weber number.

Numerical Solution on Spherical Vacuum Bubble Collapse Using MPS Method

2010 ◽  
Vol 132 (10) ◽  
Author(s):  
Wen xi Tian ◽  
Sui-zheng Qiu ◽  
Guang-hui Su ◽  
Yuki Ishiwatari ◽  
Yoshiaki Oka
Keyword(s):  
Cavitation Erosion ◽  
Bubble Dynamics ◽  
Pressure Pulse ◽  
Bubble Diameter ◽  
Bubble Collapse ◽  
Interfacial Velocity ◽  
Bubble Liquid ◽  
Mps Method ◽  
Good Consistency ◽  
Moving Particle

Single vacuum bubble collapse in subcooled water has been simulated using the moving particle semi-implicit (MPS) method in the present study. The liquid is described using moving particles, and the bubble-liquid interface was set to be the vacuum pressure boundary without interfacial heat mass transfer. The topological shape of the vacuum bubble is determined according to the location of interfacial particles. The time dependent bubble diameter, interfacial velocity, and bubble collapse time were obtained within a wide parametric range. Comparison with Rayleigh’s prediction indicates a good consistency, which validates the applicability and accuracy of the MPS method. The potential void-induced water hammer pressure pulse was also evaluated, which is instructive for the cavitation erosion study. The present paper discovers fundamental characteristics of vacuum bubble hydrodynamics, and it is also instructive for further applications of the MPS method to complicated bubble dynamics.

Experimental Study of Effect of Nucleation Site Size on Bubble Dynamics during Nucleate Pool Boiling Heat Transfer

2014 ◽  
Vol 592-594 ◽  
pp. 1596-1600 ◽  
Author(s):  
Abdul Najim ◽  
Anil R. Aacharya
Keyword(s):  
Heat Transfer ◽  
Boiling Heat Transfer ◽  
Bubble Dynamics ◽  
Bubble Diameter ◽  
Pool Boiling ◽  
Growth Period ◽  
Nucleation Site ◽  
Hypodermic Needle ◽  
Nucleate Pool Boiling ◽  
Pool Boiling Heat Transfer

In this paper, effect of nucleation site size on bubble dynamics during nucleate pool boiling heat transfer in saturated water is studied experimentally. Single bubble was generated using right angle tip of a hypodermic needle as a nucleation site. The hypodermic needles were used of inner diameters 0.413mm, 0.514mm, and 0.603 mm with a constant depth of 25mm. The bubble dynamics was studied using SONY Cyber-shot DSC-H100 camera operating at 30 frames per second at atmospheric pressure and at a wall superheat of 5K. The results show that, bubble diameter, bubble height and bubble volume increases with increase in diameter of nucleation site. The bubble growth period is found to be dependent on nucleation site size, and it decreases with increase in diameter of nucleation site. This happens because as volume of vapor bubble increases, buoyancy force starts dominates the capillary force and bubble detaches earlier. Effect of nucleation site size on bubble departure diameter and bubble release frequency is also discussed.

Mechanistic Prediction of Nucleate Boiling Heat Transfer–Achievable or a Hopeless Task?

2005 ◽  
Vol 128 (1) ◽  
pp. 1-12 ◽  
Author(s):  
Vijay K. Dhir
Keyword(s):  
Heat Transfer ◽  
Active Sites ◽  
Bubble Dynamics ◽  
Functional Dependence ◽  
Bubble Diameter ◽  
Nucleate Boiling ◽  
Complex Nature ◽  
The Past ◽  
Nucleation Sites ◽  
Nucleate Boiling Heat Transfer

Over the last half of the twentieth century, a number of purely empirical and mechanism-based correlations have been developed for pool nucleate boiling. Empirical correlations differ from each other substantially with respect to the functional dependence of heat flux on fluid and surface properties, including gravity. The mechanism-based correlations require knowledge of the number density of active sites, bubble diameter at departure, and bubble-release frequency. However, because of the complex nature of the subprocesses involved, it has not been possible to develop comprehensive models or correlations for these parameters. This, in turn, has led to the pessimistic view that mechanistic prediction of nucleate boiling is a hopeless task. However, there is an alternative to the past approaches—complete numerical simulation of the boiling process. Value of this approach for bubble dynamics and associated heat transfer is shown through excellent agreement of predictions with data obtained on microfabricated surfaces on which active nucleation sites can be controlled.

Numerical Solution on Spherical Vacuum Bubble Collapse Using MPS Method

2009 ◽  
Author(s):  
Wenxi Tian ◽  
Suizheng Qiu ◽  
Guanghui Su ◽  
Yoshiaki Oka
Keyword(s):  
Bubble Dynamics ◽  
Bubble Diameter ◽  
Liquid Pool ◽  
Bubble Collapse ◽  
Bubble Liquid ◽  
Mps Method ◽  
Noncondensable Gas ◽  
Cavitation Phenomenon ◽  
Rebound Phenomenon ◽  
Good Agreement

In this study, the vacuum bubble collapse in liquid pool has been simulated using MPS code. The liquid is described using moving particles and the bubble-liquid interface was set to be vacuum pressure boundary without interfacial heat mass transfer. The motion and location of interfacial particles can be competent in configurating the topological shape of vacuum bubble. The time dependent bubble diameter, interfacial velocity and bubble collapse time were obtained under wide parametric range. The comparison with Rayleigh’s prediction showed a good agreement which validates the applicability and accuracy on MPS method in solving present momentum problems. The potential void-induced water hammer pressure pulse was also evaluated which is instructive for cavitaion erosion study. The bubble collapse with noncondensable gas has also been simulated and the rebound phenomenon was successfully captured which is similar with vapor-filled cavitation phenomenon. The present study exhibits some fundamental characteristics of vacuum bubble hydrodynamics and it is also expected to be instructive for further applications of MPS method to in complicated bubble dynamics.

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