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.

Pool Boiling in Saturated and Subcooled FC-72 Dielectric Fluid From a Porous Graphite Surface

2004 ◽  
Author(s):  
Mohamed S. El-Genk ◽  
Jack L. Parker
Keyword(s):  
Heat Flux ◽  
Pool Boiling ◽  
Nucleate Boiling ◽  
Heat Fluxes ◽  
Porous Coating ◽  
Dielectric Fluid ◽  
Subcooled Boiling ◽  
Porous Graphite ◽  
Rate Of Increase ◽  
Boiling Incipience

Experiments are conducted that investigated pool boiling of FC-72 liquid at saturation and 10, 20, and 30 K subcooling on porous graphite and smooth copper surfaces measuring 10 × 10 mm. The nucleate boiling heat flux, Critical Heat Flux (CHF), and surface superheats at boiling incipience are compared. Theses heat fluxes are also compared with those of other investigators for smooth copper and silicon, etched SiO2, surfaces and micro-porous coating. No temperature excursion at boiling incipience on the porous graphite that occurred at a surface superheats of < 1.0 K. Conversely, the temperature excursions of 24.0 K and 12.4–17.8 K are measured at incipient boiling in saturation and subcooled boiling on copper. Nucleate boiling heat fluxes on porous graphite are significantly higher and corresponding surface superheats are much smaller than on copper. CHF on porous graphite (27.3, 39.6, 49.0, and 57.1 W/cm2 in saturation and 10 K, 20 K, and 30 K subcooled boiling, respectively) are 61.5%–207% higher than those on copper (16.9, 19.5, 23.6, and 28.0 W/cm2, respectively). The surface superheats at CHF on the porous graphite of 11.5 K in saturation and 17–20 K in subcooled boiling are significantly lower that those on copper (25 K and 26–28 K, respectively). In addition, the rate of increase of CHF on porous graphite with increased subcooling is ~ 125% higher than that on copper.

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 Heater Material and Surface Orientation on Heat Transfer Coefficient and Critical Heat Flux of Nucleate Boiling

2017 ◽  
Author(s):  
Yong Mei ◽  
Yechen Zhu ◽  
Botao Zhang ◽  
Shengjie Gong ◽  
Hanyang Gu
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Boiling Heat Transfer ◽  
Orientation Angle ◽  
Nucleate Boiling ◽  
Copper Surface ◽  
Surface Orientation ◽  
Reactor Vessel

External reactor vessel cooling (ERVC) is the key technology for In-Vessel Retention (IVR) to ensure the safety of a nuclear power plant (NPP) under severe accident conditions. The thermal margin of nucleate boiling heat transfer on the reactor pressure vessel (RPV) lower head is important for ERVC and of wide concern to researchers. In such boiling heat transfer processes, the reactor vessel wall inclination effect on the heat transfer coefficient (HTC) and critical heat flux (CHF) should be considered. In this study, experiments were performed to investigate the effects of heater material and surface orientation on the HTC and CHF of nucleate boiling. Copper and stainless steel (SS) surfaces were used to perform boiling tests under atmosphere pressure. The orientation angle of both boiling surfaces were varied between 0° (upward) and 180° (downward). The experimental results show that the surface orientation effects on the HTC is slight for both the copper surface and the SS surface. In addition, the relationship of measured CHF values with the inclination angles was obtained and it shows that the CHF value changes little as the inclination angle increases from 0° to 120° but it decreases rapidly as the orientation angle increases towards 180° for both boiling surfaces. The material effect on CHF is also observed and the copper surface has higher CHF value than the SS surface. Based on the experimental data, a correlation for CHF prediction is developed which includes both the surface orientation effect and the heater material effect.

Saturation Boiling Critical Heat Flux of PF-5060 Dielectric Liquid on Microporous Copper Surfaces

2015 ◽  
Vol 137 (4) ◽  
Author(s):  
Mohamed S. El-Genk ◽  
Amir F. Ali
Keyword(s):  
Heat Flux ◽  
Critical Heat Flux ◽  
Inclination Angle ◽  
Nucleate Boiling ◽  
Dielectric Liquid ◽  
Copper Surfaces ◽  
Inclination Angles ◽  
Surface Inclination ◽  
Effect Of Surface ◽  
Good Agreement

Pool boiling experiments are performed to investigate potential enhancement of critical heat flux (CHF) of PF-5060 dielectric liquid on microporous copper (MPC) surfaces and the effect of surface inclination angle. The morphology and microstructure of the MPC surfaces change with thickness. The experiments tested seven 10 × 10 mm MPC surfaces with thicknesses from 80 to 230 μm at inclination angles of 0 deg (upward facing), 60 deg, 90 deg (vertical), 120 deg, 150 deg, 160 deg, 170 deg, and 180 deg (downward facing). CHF increases as the thickness of the surface increases and/or the inclination angle decreases. The values in the upward facing orientation are 36–59% higher than on smooth Cu. For all surfaces, CHF values in the downward facing orientation are approximately 28% of those in the upward facing orientation. A developed CHF correlation, similar to those of Zuber and Kutateladze, accounts for the effects of inclination angle and thickness of the MPC surfaces. It is in good agreement with experimental data to within ±8%. Still photographs of nucleate boiling on the MPC surfaces at different inclinations help the interpretation of the experimental results.

Optimization of Microporous Structures in Enhancing Pool Boiling Heat Transfer of Saturated R-123, FC-72 and Water

2007 ◽  
Author(s):  
Joo H. Kim ◽  
Madhav R. Kashinath ◽  
Sang M. Kwark ◽  
Seung M. You
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Boiling Heat Transfer ◽  
Pool Boiling ◽  
Nucleate Boiling ◽  
Particle Sizes ◽  
Microporous Coating ◽  
Nucleate Boiling Heat Transfer ◽  
Boiling Heat Transfer Coefficient ◽  
Enhanced Surface

The present research is an experimental study for the enhancement of boiling heat transfer using microporous coating techniques. The effects of different metal particle sizes in the coating compound for microporous coatings on pool boiling performance of refrigerants and water are investigated. All boiling tests were performed with 1×1cm2 test heaters in the horizontal, upward-facing orientation under increasing heat flux conditions at atmospheric pressure in saturated R-123, FC-72, and water. Results showed that the enhanced surface by microporous coating technique significantly augmented both nucleate boiling heat transfer coefficient and critical heat flux of FC-72 and R-123 over a plain surface. However, the enhancement of boiling performance for water was comparatively insignificant compared to the other liquids.

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.

Boiling Performance of Single-Layered Enhanced Structures

2005 ◽  
Vol 127 (7) ◽  
pp. 675-683 ◽  
Author(s):  
Camil-Daniel Ghiu ◽  
Yogendra K. Joshi
Keyword(s):  
Heat Flux ◽  
Atmospheric Pressure ◽  
Pool Boiling ◽  
Nucleate Boiling ◽  
Channel Width ◽  
Single Line ◽  
Power Curve ◽  
Boiling Regime ◽  
Curve Fit ◽  
Finned Surface

A study of pool boiling at atmospheric pressure from single-layered enhanced structures was conducted for a dielectric fluorocarbon liquid (PF 5060). The parameters investigated in this study were: (a) Heat flux (1-45W∕cm2); (b) width of the microchannels (65-105μm); and (c) microchannel pitch (0.2-0.7mm). The boiling performance of the enhanced structures was found to increase with the increase in channel width and decrease in channel pitch. A simple single line curve fit is provided as a practical way of predicting the data over the entire nucleate boiling regime. The exponent n in the single line power curve fit was found to be between 1 and 2. The modes of boiling from an enhanced structure proposed by previous researchers were unable to explain the boiling curves obtained in this study. The present data are explained in light of the contribution from the top finned surface of the enhanced structure.

A Painting Technique to Enhance Pool Boiling Heat Transfer in Saturated FC-72

1995 ◽  
Vol 117 (2) ◽  
pp. 387-393 ◽  
Author(s):  
J. P. O’Connor ◽  
S. M. You
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Boiling Heat Transfer ◽  
Pool Boiling ◽  
Nucleate Boiling ◽  
Reference Surface ◽  
Transfer Coefficients ◽  
Pool Boiling Heat Transfer ◽  
Heat Transfer Coefficients ◽  
Enhanced Surface

A benign method of generating a surface microstructure that provides pool boiling heat transfer enhancement is introduced. Pool boiling heat transfer results from an enhanced, horizontally oriented, rectangular surface immersed in saturated FC-72, indicate up to an 85 percent decrease in incipient superheat, a 70 to 80 percent reduction in nucleate boiling superheats, and a ∼ 109 percent increase in the critical heat flux (CHF = 30 W/cm2), beyond that of the nonpainted reference surface. For higher heat flux conditions (19 to 30 W/cm2), localized dryout results in increased wall superheats (8 to 48°C). The enhanced surface heat transfer coefficients are four times higher than those from the reference surface and similar to those from the Union Carbide High Flux surface. Photographs that identify differences in bubble size and departure characteristics between the painted and reference surfaces are presented.

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