Effect of Surface Wettability on Active Nucleation Site Density During Pool Boiling of Water on a Vertical Surface

1993 ◽  
Vol 115 (3) ◽  
pp. 659-669 ◽  
Author(s):  
C. H. Wang ◽  
V. K. Dhir
Keyword(s):  
Nearest Neighbor ◽  
Pool Boiling ◽  
Nucleate Boiling ◽  
Optical Microscope ◽  
Nucleation Site ◽  
Vertical Surface ◽  
Cumulative Number ◽  
Copper Surfaces ◽  
Average Value ◽  
Nucleation Sites

Pool boiling of saturated water at 1 atm pressure has been investigated. In the experiments, copper surfaces prepared by following a well-defined procedure were used. The cumulative number density of the cavities and their shapes were determined with an optical microscope. The surface had a mirror finish and had a surface Ra (centerline average) value of less than 0.02 μm. The wettability of the surface was changed by controlling the degree of oxidation of the surface. In the experiments with the primary surface, the wall heat flux and superheat were determined with the help of thermocouples embedded in the test block. The density, spatial distribution, local distribution, and nearest-neighbor distance distribution of active nucleation sites in partial and fully developed nucleate boiling were determined from still pictures.

Effects of Enhanced Surface Inclination on Pool Boiling of a Dielectric Fluid

2009 ◽  
Author(s):  
Liang-Han Chien ◽  
Shu-Che Lee
Keyword(s):  
Heat Flux ◽  
Orientation Angle ◽  
Nucleate Boiling ◽  
Vertical Surface ◽  
Dielectric Fluid ◽  
Test Surface ◽  
Nucleation Sites ◽  
Finned Surface ◽  
Surface Inclination ◽  
Enhanced Surface

The manuscript presents an experimental study of inclination and pin-finned surfaces on nucleate boiling in FC-72 of saturated 50°C. The orientation angle of test surface from horizontal plane was varied from 0° (upper surface) to 90° (vertical surface). The boiling surfaces include a plain surface, a straight surface (C-0.2-0.5) and a pin-finned surface (P-0.2-0.5), whose fin width, fin height, and fin gap are 0.2mm, 0.5mm and 0.2mm. The effect of the surface inclination angle is notable at the increasing heat flux tests, while no marked effect is observed at the decreasing heat flux tests. With 10K superheat, the straight fin surface(C-0.2-0.5) and pin-finned surface (P-0.2-0.5) enhanced the boiling performance by approximately 6.7 and 7.5 folds, respectively. The enhancement is attributed to the increased surface area, the increased nucleation sites and the proper fin and gap widths.

Suppression of Flow Boiling Nucleation

1997 ◽  
Vol 119 (3) ◽  
pp. 517-524 ◽  
Author(s):  
G. E. Thorncroft ◽  
J. F. Klausner ◽  
R. Mei
Keyword(s):  
Heat Transfer ◽  
Dimensionless Parameter ◽  
Two Phase Flow ◽  
Flow Boiling ◽  
Nucleate Boiling ◽  
Nucleation Site ◽  
Complete Suppression ◽  
Phase Flow ◽  
Two Phase ◽  
Nucleation Sites

A simple model is presented for estimating the ratio of the maximum to minimum cavity radius required for ebullition in two-phase flow with heat transfer. The resulting dimensionless parameter, rmax/rmin, is demonstrated to correlate flow boiling nucleation site density. As the convective heat transfer associated with bulk turbulence in two-phase flow is enhanced, rmax→rmin, and the probability of finding surface cavities whose radii lie between rmaxandrmin is reduced. Thus, active nucleation sites become deactivated. A vertical flow boiling facility was fabricated in which the nucleation suppression point can be measured. Experiments conducted for mass flux ranging from 183–315 kg/m2-s and inlet quality ranging from 0–0.151, along with data available from the literature, suggest that rmax/rmin is the leading order dimensionless parameter on which the complete suppression of nucleation sites depends. Although the suppression of nucleation sites also depends, to a certain extent, on the surface/fluid combination and heat flux, it is found that complete suppression occurs for rmax/rmin ranging from 40 to 120. This is proposed as a criterion to discriminate the purely convective regime from the nucleate boiling regime.

scholarly journals Numerical investigation of nucleate pool boiling heat transfer

2016 ◽  
Vol 20 (suppl. 5) ◽  
pp. 1301-1312
Author(s):  
Andrijana Stojanovic ◽  
Vladimir Stevanovic ◽  
Milan Petrovic ◽  
Dragoljub Zivkovic
Keyword(s):  
Heat Flux ◽  
Pool Boiling ◽  
Nucleation Site ◽  
Bubble Nucleation ◽  
Heated Wall ◽  
Wall Surface ◽  
Two Phase ◽  
Site Density ◽  
Nucleation Sites ◽  
Nucleation Site Density

Multidimensional numerical simulation of the atmospheric saturated pool boiling is performed. The applied modelling and numerical methods enable a full representation of the liquid and vapour two-phase mixture behaviour on the heated surface, with included prediction of the swell level and heated wall temperature field. In this way the integral behaviour of nucleate pool boiling is simulated. The micro conditions of bubble generation at the heated wall surface are modelled by the bubble nucleation site density, the liquid wetting contact angle and the bubble grow time. The bubble nucleation sites are randomly located within zones of equal size, where the number of zones equals the nucleation site density. The conjugate heat transfer from the heated wall to the liquid is taken into account in wetted heated wall areas around bubble nucleation sites. The boiling curve relation between the heat flux and the heated wall surface temperature in excess of the saturation temperature is predicted for the pool boiling conditions reported in the literature and a good agreement is achieved with experimentally measured data. The influence of the nucleation site density on the boiling curve characteristic is confirmed. In addition, the influence of the heat flux intensity on the spatial effects of vapour generation and two-phase flow are shown, such as the increase of the swell level position and the reduced wetting of the heated wall surface by the heat flux increase.

Theoretical and Experimental Analysis of Increasing Pressure During Pool-Boiling

2018 ◽  
Author(s):  
Smreeti Dahariya ◽  
Amy Rachel Betz
Keyword(s):  
Experimental Data ◽  
High Pressure ◽  
Bubble Dynamics ◽  
Pool Boiling ◽  
Nucleation Site ◽  
Copper Surface ◽  
System Pressure ◽  
Nucleation Sites ◽  
Wide Range ◽  
Fluid Properties

The thermo-fluid properties of water change at high pressure. The performance of high pressure pool boiling greater than 50 Psi has not been studied widely. The aim of this paper is to analyze the experimental data to describe the effect of increasing pressure during pool boiling. Hsu’s correlation was used to predict the active nucleation sites. The maximum and minimum radii of the active nucleation sites were determined as a function of heat flux or degree of wall superheats over a wide range of pressures. The bubble dynamics are discussed using the predicted values of fundamental boiling quantities such as bubble departure diameter, active nucleation site density and bubble release frequency. The thickness of the boundary layer was assumed to be 30 microns. Rohsenow’s and Forster’s correlations were used to predict the pool boiling curve for different pressures. The comparison was made with the experimental data for water of a plain copper surface of increasing pressure. The parametric trend provides fundamental insight and explains how the system pressure can maximize the boiling efficiency of new generation boilers.

Nucleate Pool Boiling on Ribbed Surfaces With Micro-Roughness at Low and Moderate Heat Flux

1999 ◽  
Vol 121 (2) ◽  
pp. 376-385 ◽  
Author(s):  
S.-S. Hsieh ◽  
C.-J. Weng ◽  
J.-J. Chiou
Keyword(s):  
Heat Flux ◽  
Pool Boiling ◽  
Nucleate Boiling ◽  
Nucleation Site ◽  
Nucleate Pool Boiling ◽  
Site Density ◽  
R 134A ◽  
Microlayer Evaporation ◽  
Two Parameters ◽  
Nucleation Site Density

Nucleate pool boiling correlation was developed for five different rib-type roughened tube geometries (including plain tube) with different rib angles of 30 deg, 45 deg, 60 deg, and 90 deg for both distilled water and R-134a as the working media. A scanning electron micrograph (SEM) examination was made for these horizontal roughened tubes. Bubble departure diameter, frequency of bubble emission, and the active nucleation site density with the influence of the rib angle for this type of roughened surface were obtained. Boiling heat flux incorporating natural convection, nucleate boiling, and microlayer evaporation mechanisms following Benjamin and Balakrishnan (1996) was predicted. Heat transfer correlation was also developed in terms of the degree superheat and active nucleation site density. The dependence for these two parameters was found in favorable agreement with that of previous study for smooth surfaces.

Enhancement of Saturation Boiling of PF-5060 on Microporous Surface

2011 ◽  
Author(s):  
Saeil Jeon ◽  
Byeongnam Jo ◽  
Debjyoti Banerjee
Keyword(s):  
Heat Flux ◽  
Silicon Wafer ◽  
Pool Boiling ◽  
Nucleate Boiling ◽  
Nucleation Site ◽  
Copper Surface ◽  
Porous Surface ◽  
Site Density ◽  
Porous Copper ◽  
Dry Out

Pool boiling experiments were conducted to investigate the saturation boiling of PF-5060 dielectric liquid on micro porous copper surface. The micro porous surface is deposited on a copper coated silicon wafer diced to a size of 40 mm × 68 mm. Reference experiments were performed using a bare silicon wafer of the same size. Experiments are also performed using deionized water that was degassed prior to the experiment. The experimental results show that there is ∼48% enhancement of heat flux in nucleate boiling regime on the micro porous copper surface, compared to that on a bare surface for pool boiling of PF-5060. The measurement uncertainty for heat flux in these experiments is estimated to be ∼15%. The enhanced surface area provided by the micro porous copper surface as well as the reduction in the magnitude of the Taylor instability wavelength on a copper surface, increase in the nucleation site density on the porous surface, capillary replenishment of the dry out regions and the increase in transient heat transfer from the porous surface — are postulated to be the enhancement mechanisms for the observed augmentation in heat flux values.

Temporal and Spatial Pattern of a Privet (Ligustrum vulgare) Invasion

2013 ◽  
Vol 6 (2) ◽  
pp. 310-319 ◽  
Author(s):  
Wanying Zhao ◽  
Charles Goebel ◽  
John Cardina
Keyword(s):  
Spatial Pattern ◽  
Spatial Data ◽  
Nearest Neighbor ◽  
Management Strategies ◽  
Age Distribution ◽  
Lag Phase ◽  
Suitable Habitat ◽  
Second Phase ◽  
Invasion History ◽  
Cumulative Number

AbstractPrivet has escaped from cultivation and is invading natural areas throughout eastern North America. Understanding the pattern of invasion over time could help us develop more efficient management strategies. We studied the invasion history and spatial distribution pattern of privet by mapping age and spatial data for established patches in a 132-ha (326 ac) forested natural area in northeast Ohio. We determined the age of 331 geo-referenced patches by counting annual rings, and mapped them with corresponding land habitat. Age distribution and cumulative number of privet patches over about 40 yr showed three phases of invasion. The initial 19-yr lag phase was characterized as a dispersed spatial pattern (based on nearest neighbor analysis), with patches located mostly at edges of different habitats and open places. In a second phase of about 15 yr, an average of 19 patches were initiated yearly, in a pattern that trended towards clustered. The final phase began around 2007, as the rate of new patch establishment declined, possibly because of saturation of the suitable habitat. Establishment of new patches was not associated with specific habitats. Aggregation of patches with similar ages increased after 1998 and became significantly clustered. Mapping of clusters of old and young patches identified invasion hot spots and barriers. Results affirmed that the best time for invasive control is during the lag phase. By monitoring edge habitats associated with early establishment, managers might detect and control early invaders and delay the onset of the expansion phase.

Experimental Investigation on Surface Particle Interactions During Pool Boiling of Nanofluids

2011 ◽  
Author(s):  
Harish Ganapathy ◽  
V. Emlin ◽  
Anant Narendra Parikh ◽  
V. Sajith
Keyword(s):  
Surface Roughness ◽  
Interaction Parameter ◽  
Surface Characterization ◽  
Pool Boiling ◽  
Particle Interaction ◽  
Nucleate Boiling ◽  
Optical Measurements ◽  
Sorption Layer ◽  
Surface Particle ◽  
Enhanced Boiling

The pool boiling characteristics of nanofluids is affected by the interaction between the nanoparticles and the heater surface which forms a sorption layer and this layer increases the surface wettability and thereby enhances the CHF. While deteriorated nucleate boiling has been attributed to the decreased activation of cavities due to the increased wettability, it fails to explain the enhanced performance observed by several researchers, which can be explained only by an increase in surface roughness and hence a direct increase in the number of cavities, thereby compensating for the increase in wettability. Attempts to characterize the roughness of heater surfaces have been restricted to magnified visualizations and intrusive probing. No non-intrusive tests have been reported on flat heaters, which are ideal to conduct surface analyses. The present work is aimed at conducting a non-intrusive experimental study to analyse the surface roughness modification due to the sorption layer on flat plate heaters. Experiments have been carried out using electro-stabilized aluminium oxide water based nanofluids of different concentrations with heaters having varying values of surface roughness. The burn-out heat flux was measured and the effect of sedimentation time was studied. The surface-particle interaction parameter (Ra/dp) was varied to capture the phenomena of plugging as well as splitting of nucleation sites. An experiment having a high value of the interaction parameter shows enhanced boiling performance and that with a value close to 1 shows deteriorated performance. Further it was seen that this behaviour is dependent on the particle concentration. Detailed surface characterization has been done using an optical measurements setup and atomic force microscopy. Boiling on nano-coated heaters has been investigated and presented as an effective solution to counter the disadvantageous transient boiling behavior of nanofluids.

Proton Induced Structuring of a Photostructurable Glass

2002 ◽  
Vol 739 ◽  
Author(s):  
Meg Abraham ◽  
Inmaculada Gomez-Morilla ◽  
Mike Marsh ◽  
Geoff Grime
Keyword(s):  
Three Dimensional ◽  
Particle Beam ◽  
Nucleation Site ◽  
Buried Structures ◽  
Corning Glass ◽  
Nucleation Sites ◽  
Initial Nucleation ◽  
Similar Product ◽  
Photon Process ◽  
Meta Silicate

ABSTRACTThe use of photons to create intricate three-dimensional and buried structures [1] in photo-structurable glass has been well demonstrated at several institutions [2]. In these instances the glass used whether it be Foturan™, made by the Schott Group or a similar product made by Corning Glass, forms a silver nucleation sites on exposure to intense UV laser light via a two-photon process. Subsequent annealing causes a localized crystal growth to form a meta-silicate phase which can be etched in dilute hydrofluoric acid at rates of 20 to 50 times that of the unprocessed glass. The same formulation of glass can be “exposed” using a particle beam to create the nucleation site. In the case of particle beam exposure, experiments have shown that the mechanisms that cause this initial nucleation and eventual stochiometric transformation, after annealing, depend largely on the beam energy.

Pool Boiling Heat Transfer in Aqueous Solutions of an Anionic Surfactant

2000 ◽  
Vol 122 (4) ◽  
pp. 708-715 ◽  
Author(s):  
V. M. Wasekar ◽  
R. M. Manglik
Keyword(s):  
Anionic Surfactant ◽  
Pure Water ◽  
Pool Boiling ◽  
Sodium Dodecyl ◽  
Dynamic Surface Tension ◽  
Nucleate Boiling ◽  
Optimum Level ◽  
Lauryl Sulfate ◽  
Dynamic Surface ◽  
Influence Of Temperature On

Saturated nucleate pool boiling of aqueous surfactant solutions on a horizontal cylindrical heater has been experimentally investigated. Sodium dodecyl or lauryl sulfate (SDS or SLS), an anionic surfactant, is employed. Boiling performance, relative to that for pure water, is found to be enhanced significantly by the presence of SDS, with an early onset of nucleate boiling. An optimum level of enhancement is observed in solutions at or near critical micelle concentration of the surfactant; the enhancement, however, decreases considerably in higher concentration solutions. The dynamic surface tension measurements indicate a substantial influence of temperature on the overall adsorption isotherm. The diffusion kinetics of surfactant molecules and micelles is, therefore, expected to be quite different at boiling temperature than at room temperature. This greatly modifies the boiling mechanism that is generally characterized by the formation of smaller-size bubbles with increased departure frequencies, and a decreased tendency to coalesce which causes considerable foaming. [S0022-1481(00)00704-0]

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