Nucleate Boiling With High Gravity and Large Subcooling

1990 ◽  
Vol 112 (2) ◽  
pp. 451-457 ◽  
Author(s):  
M. E. Ulucakli ◽  
H. Merte
Keyword(s):  
Heat Flux ◽  
Heating Surface ◽  
Nucleate Boiling ◽  
Fluid Temperature ◽  
Heater Surface ◽  
Earth Gravity ◽  
Maximum Value ◽  
Wall Superheat ◽  
Nucleation Sites ◽  
Type Of Behavior

Measurements of the heater surface temperature are presented for pool boiling of distilled water in an accelerating system with various subcoolings and levels of heat flux. The ranges of the experimental variables are: heat flux between 0.19 MW/m2 and 1.5 MW/m2, accelerations normal to the flat heating surface from 1 to 100 times earth gravity, and liquid subcoolings between 0 K and 89 K. Increasing sub-cooling first produces an increase and then a decrease in wall superheat, with the eventual cessation of nucleate boiling for certain combinations of conditions. The increase in wall superheat is particularly enhanced at 10g, reaching a maximum value of 9 K at 1.05 MW/m2 with 60 K subcooling. This type of behavior is attributed to the interactions between the fluid temperature distribution in the immediate vicinity of the heater surface as it is influenced by natural convection, the activation of nucleation sites, and the influence of increased buoyancy on the heat transfer associated with each departing bubble.

Effects of Gap Geometry and Gravity on Boiling Around a Constrained Bubble in 2-Propanol/Water Mixtures

2006 ◽  
Vol 129 (2) ◽  
pp. 114-123
Author(s):  
Chen-li Sun ◽  
Van P. Carey
Keyword(s):  
Heat Flux ◽  
Heated Surface ◽  
Molar Fraction ◽  
Nucleate Boiling ◽  
Confined Space ◽  
Cold Surface ◽  
Boiling Regime ◽  
Wall Superheat ◽  
Boiling Process ◽  
Lower Heat

In this study, boiling experiments were conducted with 2-propanol/water mixtures in confined gap geometry under various levels of gravity. The temperature field created within the parallel plate gap resulted in evaporation over the portion of the vapor-liquid interface of the bubble near the heated surface, and condensation near the cold surface. Full boiling curves were obtained and two boiling regimes—nucleate boiling and pseudofilm boiling—and the transition condition, the critical heat flux (CHF), were identified. The observations indicated that the presence of the gap geometry pushed the nucleate boiling regime to a lower superheated temperature range, resulting in correspondingly lower heat flux. With further increases of wall superheat, the vapor generated by the boiling process was trapped in the gap to blanket the heated surface. This caused premature occurrence of CHF conditions and deterioration of heat transfer in the pseudo-film boiling regime. The influence of the confined space was particularly significant when greater Marangoni forces were present under reduced gravity conditions. The CHF value of x (molar fraction)=0.025, which corresponded to weaker Marangoni forces, was found to be greater than that of x=0.015 with a 6.4mm gap.

Near-Wall Microlayer Evaporation Analysis and Experimental Study of Nucleate Pool Boiling on Inclined Surfaces

1998 ◽  
Vol 120 (3) ◽  
pp. 641-653 ◽  
Author(s):  
G. F. Naterer ◽  
W. Hendradjit ◽  
K. J. Ahn ◽  
J. E. S. Venart
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heating Surface ◽  
Nucleate Boiling ◽  
Inclined Surfaces ◽  
Wide Range ◽  
Model Predictions ◽  
Microlayer Evaporation ◽  
Near Wall

Boiling heat transfer from inclined surfaces is examined and an analytical model of bubble growth and nucleate boiling is presented. The model predicts the average heat flux during nucleate boiling by considering alternating near-wall liquid and vapor periods. It expresses the heat flux in terms of the bubble departure diameter, frequency and duration of contact with the heating surface. Experiments were conducted over a wide range of upward and downward-facing surface orientations and the results were compared to model predictions. More active microlayer agitation and mixing along the surface as well as more frequent bubble sweeps along the heating surface provide the key reasons for more effective heat transfer with downward facing surfaces as compared to upward facing cases. Additional aspects of the role of surface inclination on boiling dynamics are quantified and discussed.

Boiling Heat Transfer and Critical Heat Flux Enhancement of Upward- and Downward-Facing Heater in Nanofluids

2013 ◽  
Vol 135 (7) ◽  
Author(s):  
Muhamad Zuhairi Sulaiman ◽  
Masahiro Takamura ◽  
Kazuki Nakahashi ◽  
Tomio Okawa
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Critical Heat Flux ◽  
Boiling Heat Transfer ◽  
Pool Boiling ◽  
Nucleate Boiling ◽  
Flux Enhancement ◽  
Optimum Configuration ◽  
Wall Superheat ◽  
Nucleate Boiling Heat Transfer

Boiling heat transfer (BHT) and critical heat flux (CHF) performance were experimentally studied for saturated pool boiling of water-based nanofluids. In present experimental works, copper heaters of 20 mm diameter with titanium-oxide (TiO2) nanocoated surface were produced in pool boiling of nanofluid. Experiments were performed in both upward and downward facing nanofluid coated heater surface. TiO2 nanoparticle was used with concentration ranging from 0.004 until 0.4 kg/m3 and boiling time of tb = 1, 3, 10, 20, 40, and 60 mins. Distilled water was used to observed BHT and CHF performance of different nanofluids boiling time and concentration configurations. Nucleate boiling heat transfer observed to deteriorate in upward facing heater, however; in contrast effect of enhancement for downward. Maximum enhancements of CHF for upward- and downward-facing heater are 2.1 and 1.9 times, respectively. Reduction of mean contact angle demonstrate enhancement on the critical heat flux for both upward-facing and downward-facing heater configuration. However, nucleate boiling heat transfer shows inconsistency in similar concentration with sequence of boiling time. For both downward- and upward-facing nanocoated heater's BHT and CHF, the optimum configuration denotes by C = 400 kg/m3 with tb = 1 min which shows the best increment of boiling curve trend with lowest wall superheat ΔT = 25 K and critical heat flux enhancement of 2.02 times.

Steady-State Subcooled Nucleate Boiling on a Downward-Facing Hemispherical Surface

1998 ◽  
Vol 120 (2) ◽  
pp. 365-370 ◽  
Author(s):  
K. H. Haddad ◽  
F. B. Cheung
Keyword(s):  
Heat Flux ◽  
Steady State ◽  
Heat Transport ◽  
Bubble Dynamics ◽  
Flow Direction ◽  
Heating Surface ◽  
Nucleate Boiling ◽  
High Heat ◽  
Bubble Nucleation ◽  
High Heat Flux

Steady-state nucleate boiling heat transfer experiments in saturated and subcooled water were conducted. The heating surface was a 0.305 m hemispherical aluminum vessel heated from the inside with water boiling on the outside. It was found that subcooling had very little effect on the nucleate boiling curve in the high heat flux regime where latent heat transport dominated. On the other hand, a relatively large effect of subcooling was observed in the low-heat-flux regime where sensible heat transport was important. Photographic records of the boiling phenomenon and the bubble dynamics indicated that in the high-heat-flux regime, boiling in the bottom center region of the vessel was cyclic in nature with a liquid heating phase, a bubble nucleation and growth phase, a bubble coalescence phase, and a large vapor mass ejection phase. At the same heat flux level, the size of the vapor masses was found to decrease from the bottom center toward the upper edge of the vessel, which was consistent with the increase observed in the critical heat flux in the flow direction along the curved heating surface.

On the Mechanism of Pool Boiling Critical Heat Flux Enhancement in Nanofluids

2010 ◽  
Vol 132 (6) ◽  
Author(s):  
Hyungdae Kim ◽  
Ho Seon Ahn ◽  
Moo Hwan Kim
Keyword(s):  
Heat Flux ◽  
Critical Heat Flux ◽  
Heated Surface ◽  
Pure Water ◽  
Pool Boiling ◽  
Nucleate Boiling ◽  
Titania Nanoparticles ◽  
Nanoparticle Layer ◽  
Wall Superheat ◽  
Dry Spot

The pool boiling characteristics of water-based nanofluids with alumina and titania nanoparticles of 0.01 vol % were investigated on a thermally heated disk heater at saturated temperature and atmospheric pressure. The results confirmed the findings of previous studies that nanofluids can significantly enhance the critical heat flux (CHF), resulting in a large increase in the wall superheat. It was found that some nanoparticles deposit on the heater surface during nucleate boiling, and the surface modification due to the deposition results in the same magnitude of CHF enhancement in pure water as for nanofluids. Subsequent to the boiling experiments, the interfacial properties of the heater surfaces were examined using dynamic wetting of an evaporating water droplet. As the surface temperature increased, the evaporating meniscus on the clean surface suddenly receded toward the liquid due to the evaporation recoil force on the liquid-vapor interface, but the nanoparticle-fouled surface exhibited stable wetting of the liquid meniscus even at a remarkably higher wall superheat. The heat flux gain attainable due to the improved wetting of the evaporating meniscus on the fouled surface showed good agreement with the CHF enhancement during nanofluid boiling. It is supposed that the nanoparticle layer increases the stability of the evaporating microlayer underneath a bubble growing on a heated surface and thus the irreversible growth of a hot/dry spot is inhibited even at a high wall superheat, resulting in the CHF enhancement observed when boiling nanofluids.

scholarly journals Interaction of the Nucleation Phenomena at Adjacent Sites in Nucleate Boiling

1983 ◽  
Vol 105 (1) ◽  
pp. 3-9 ◽  
Author(s):  
M. Sultan ◽  
R. L. Judd
Keyword(s):  
Active Sites ◽  
Heating Surface ◽  
Nucleate Boiling ◽  
Copper Surface ◽  
Nucleation Sites ◽  
Theoretical Predictions ◽  
Experimental Findings ◽  
Relationship Of ◽  
The Relationship ◽  
Different Levels

The present investigation is an original study in nucleate pool boiling heat transfer combining theory and experiment in which water boiling at atmospheric pressure on a single copper surface at two different levels of heat and different levels of subcooling was studied. Cross spectral analysis of the signals generated by the emission of bubbles at adjacent nucleation sites was used to determine the relationship of the time elapsed between the start of bubble growth at the two neighbouring active sites with the distance separating them. The experimental results obtained indicated that for the lower level of heat flux at three different levels of subcooling, the elapsed time and distance were directly related. Theoretical predictions of a temperature disturbance propagating through the heating surface in the radial direction gave good agreement with the experimental findings, suggesting that this is the mechanism responsible for the activation of the surrounding nucleation sites.

Some Possible Critical Conditions in Nucleate Boiling

1963 ◽  
Vol 85 (2) ◽  
pp. 89-99 ◽  
Author(s):  
Yan-Po Chang
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Boiling Heat Transfer ◽  
Maximum Rate ◽  
Unit Area ◽  
Heating Surface ◽  
Nucleate Boiling ◽  
Critical Conditions ◽  
Bubble Generation ◽  
Basic Ideas

The primary purpose of this paper is to introduce into boiling heat transfer certain basic ideas from which several critical conditions are derived. The heat transfer in nucleate boiling is considered as being limited by the maximum rate of bubble generation from a unit area of the heating surface. With certain simplified assumptions, an equation is obtained for the first critical heat flux of nucleate boiling with and without forced convection and subcooling.

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.

A New Correlation of Pool-Boiling Data Including the Effect of Heating Surface Characteristics

1969 ◽  
Vol 91 (2) ◽  
pp. 245-250 ◽  
Author(s):  
B. B. Mikic ◽  
W. M. Rohsenow
Keyword(s):  
Heat Transfer ◽  
Heating Surface ◽  
Surface Characteristics ◽  
Nucleate Boiling ◽  
Surface Characteristic ◽  
Organic Liquids ◽  
Cavity Size ◽  
New Correlation ◽  
Wall Superheat ◽  
Wide Range

The standard approach which relates heat transfer in nucleate boiling to heat transfer to the superheated layer averaged over the time between two successive departures of a bubble from a given site is extended in order to relate the heat flux to the wall superheat through the heating surface characteristic. It was found that the q/A versus ΔT relation depends on the cavity size distribution over the surface. For a known distribution of cavity size, the q/A versus ΔT relation may be predicted, or for unknown characteristics of the boiling surface it is sufficient to have boiling data at one pressure in order to predict the q/A versus ΔT relation of other pressure levels for the same surface and the same liquid. The latter was tried on a wide range of experimental data including water and three organic liquids with good results.

Nonlinear Aspects of High Heat Flux Nucleate Boiling Heat Transfer

1995 ◽  
Vol 117 (4) ◽  
pp. 981-989 ◽  
Author(s):  
P. Sadasivan ◽  
C. Unal ◽  
R. Nelson
Keyword(s):  
Heat Transfer ◽  
Chaotic Behavior ◽  
Period Doubling ◽  
Thermal Conditions ◽  
Nucleate Boiling ◽  
High Heat ◽  
Heat Transfer Process ◽  
High Heat Flux ◽  
Heater Surface ◽  
Nucleation Sites

This paper deals with potential nonlinear effects in nucleate boiling systems as a result of the behavior of individual nucleation sites on the heater surface. This requires detailed microscopic modeling of the surface. A computational model has been formulated for this purpose. The model addresses the three-dimensional transient conduction heat transfer process within the problem domain comprised of the macrolayer and heater. Hydrodynamic effects are represented through boundary conditions. Individual nucleation sites are activated or deactivated depending on the thermal conditions that prevail at the site. The model has been used to examine the behavior of sites on a realistic heater surface. The results indicate that significant spatial and temporal temperature variations can occur on the surface, and that thermal interactions among sites can result in some sites operating intermittently. Surface-averaged temperatures show nonlinear period-doubling behavior. A chaotic case was found. Qualitative comparisons are made to both local instantaneous temperature measurements and recent experiments that showed chaotic behavior. We believe that such nonlinear behavior is one of the reasons that mechanistic predictive capabilities for the boiling process have remained elusive.

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